aerospace engineering aerodynamics lab exercises

7/25/2019 Aerospace Engineering Aerodynamics Lab Exercises

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Department of Aerospace Engineering

AER 504 AERODYNAMICS

LABORATORY MANUAL

September, 2013

P. Walsh

J. Karpynczyk


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1

Table of Contents

Table of Contents

Laboratory Instructions ..2

General Safety Rules and Regulations ...4

Nomenclature 6

Lab # 1

Wind Tunnel and Airfoil Drag Analysis (room KHE-33) ..7

Lab # 2

Pressure Distribution on the NACA 0015 (room KHE-33).13

Lab # 3Effect of Flaps and Slats (room KHE-33) .19

Appendix A: Manometers ..........37

Appendix B: Pitot-Static Tubes....26

Appendix C: Guidelines for Lab Report Writing .28

Appendix D: Calculation of Forces on Airfoils ....33

Appendix E: Lab report grading template .. 36


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2

Laboratory Instructions

(i) ALL students must attend the laboratory in order to receive credit. Lab reports are

to be done in pairs. Students are responsible for performing an equitable share ofthe lab report preparation.

(ii) Lab reports are to be prepared with any standard word processor. Hand written labs

will NOT be accepted.

(iii) Guidelines for writing lab reports are given in Appendix C, but as a minimum each

report should contain the following sections:

Title Page

Obtain at: www.ryerson.ca/aerospace/undergraduate/coverassignmentsheet/

Lab report grading table, obtain from Blackboard, AER 504 siteMain Body of Report

Abstract Short Introduction Description of the data analysis, theory, and procedures (not for CFD labs) Results and Discussion Brief Conclusion References (if necessary)

Appendix

Graphs of results (if applicable)

A sample calculation Raw experimental data

(iv) The main body of the report must be concise, with no more than four pages (in 12

point font). Lab reports exceeding this length will be penalized 10% per extra page.The technical writing in the lab reports is therefore expected to be of high quality

and low quantity.

(v) No restriction is placed on the length of the Appendix. Graphs contained within thereport must have a title, labeled axes, and a legend if more than one set of data is

presented on one plot. Electronically generated plots are expected.

(vi) Sample calculations and raw experimental data should be placed in the reportAppendix and must be presented neatly and be clearly labeled. Figures must be

numbered, have a descriptive caption, and be reference in the text of the report.

(vii) Lab reports are given a grade out of 10, with individual points given for technical

content, formatting, presentation, spelling and grammar. The grading template is

given in Appendix E.


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(viii) Material and figures taken from external sources must be clearly referenced.

(ix) Be aware that partial or complete plagiarism will result in a grade of 0 for allparties concerned and will result in further disciplinary action up to a grade

of F in the course.

(x) Lab reports must use the standard cover page obtained from the departmental

website given in point (iii) above. All students responsible for the report must sign

the cover page in the designated space. Digital signatures are NOT acceptable.Students not signing the report will not receive a grade for the lab.

(xi) Lab reports are due 1 week after the lab is conducted. Reports submitted late will

be penalized 10% per day. Labs are to be placed in the Instructors box across fromoffice (ENG 149) before 3:00 pm on the due date.


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4

Department of Aerospace Engineering

GENERAL SAFETY RULES ANDREGULATIONS FOR

LABORATORIES ANDRESEARCH AREAS

The following safety rules and regulations are to be followed in all Aerospace Engineering laboratories and research facilities. These

rules and regulations are to insure that all personnel working in these laboratories and research areas are protected, and that a safe

working environment is maintained.

1.Horseplay is hazardous and will not be tolerated.

2. No student may work alone in the laboratory at any time, except to prepare operating procedures for equipment or data write-

up/reduction/simulations.

3. Required personal protective equipment (PPE) will be provided by the Department for use whenever specified by the Faculty,

Engineering Support or Teaching Assistant, .i.e., hearing protection, face shields, dust masks, gloves, etc.

4. Contact lenses will not be worn in the laboratory when vapours or fumes are present.

5. Safety glasses with side shields and plastic lenses will be required when operating targeted class experiments as outlined in the

experimental procedures. Splash goggles or face shields will also be provided and worn also, for those experiments which have been

identified as a requirement.

6. Each student must know where the location of the First Aid box, emergency equipment, eye wash station is, if required in the

laboratories, shops, and storage areas.

7. All Faculty, Engineering Support and Teaching Assistants must know how to use the emergency equipment and have the knowledge

to take action when an accident has occurred, .i.e., emergency telephone number, location, emergency response services.

8. All Faculty, Engineering Support and Teaching Assistants, and Research Assistants, must be familiar with all elements of fire safety

alarm, evacuation and assembly, fire containment and suppression, rescue.

9. Ungrounded wiring and two-wire extension cords are prohibited. Worn or frayed extension cords or those with broken connections

or exposed wiring must not be used. All electrical devices must be grounded before they are turned on.

10. All Faculty, Engineering Support and Teaching Assistants, and Research Assistants, must be familiar with an approved emergency

shutdown procedure before initiating any experiment.

11. There will be NO deviation from approved equipment operating procedures.

12. All laboratory aisles and exits must remain clear and unblocked.

13. No student may sniff, breathe, or inhale any gas or vapour used or produced in any experiment.

14. All containers must be labeled as to the content, composition, and appropriate hazard warning: flammable, explosive, toxic, etc.

15. The instructions on all warning signs must be read and obeyed in all laboratories and research facilities.

16. All liquid and solid waste must be segregated for disposal according to Faculty, Engineering Support or Teaching Assistant

instructions. All acidic and alkaline waste should be neutralized prior to disposal. NOTE: NO organic waste material is to be poured

down the sink or floor drains. These wastes should be property placed in designed waste disposal containers, labeled and stored in the

departments flammable storage cabinet which is ventilated and secured.

17. Good housekeeping must be practiced in all teaching and research laboratories, shops, and storage areas.

Campus Security Dial: 5001/5040

Emergency Dial: 80

Jerry Karpynczyk, Safety Officer: 6420


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18. Eating, drinking, use of any tobacco products, gum chewing or application of makeup are strictly prohibited in the laboratories,

shops, and storage areas.

19. Only chemicals may be placed in the Chemicals Only refrigerator. Only food items may be placed in the Food Only refrigerator

Ice from any refrigerator is not be used for human consumption or to cool any food or drink.

20. Glassware breakage must be disposed in the cardboard boxes marked Glass Disposal. Any glassware breakage and malfunctioning

instruments or equipment must be reported to the Faculty, Engineering Support or Teaching Assistant present.

21. All injuries, accidents, and near misses must be reported to the Faculty, Engineering Support or Teaching Assistant. The Accident

Report must be completed as soon as possible after the event by the Faculty, Engineering Support or Teaching Assistant and reported

to the Departmental Safety Officer immediately. Any person involved in an accident must be sent or escorted to the University Health

Centre. All accidents are to be REPORTED.

22. All chemical spills are to be reported to the Faculty, Engineering Support or Teaching Assistant, whose direction must be followed

for containment and cleanup. Faculty, Engineering Support or Teaching Assistant will follow the prescribed instructions for cleanup

and decontamination of the spill area. The Departmental Safety Officer must be notified when a major spill has been reported.

23. All students and Faculty, Engineering Support or Teaching Assistant must wash their hands before leaving targeted laboratories,

research facilities or shops.

24. No tools, supplies, or any other items may be tossed from one person to another.

25. Compressed gas cylinders must be secured at all times. Proper safety procedures must be followed when moving compressed gas

cylinders. Cylinders not in use must be capped.

26. Only gauges that are marked Use no oil are for Oxygen cylinders. Do not use an oiled gauge for any oxidizing or reactiv e gas.

27. Students are never to play with compressed gas hoses or lines or point their discharges at any person.

28. Do not use adapters or try to modify any gas regulator or connection.

29. There will be no open flames or heating elements used when volatile chemicals are exposed to the air.

30. Any toxic chemicals will be only be exposed to the air in a properly ventilated Fume Hood. Flammable chemicals will be exposed

to the air only under a properly ventilated hood or in an area which is adequately ventilated.

31. Personal items brought into the laboratory or research facility must be limited to those things necessary for the experiment and safe

operation of the equipment in the laboratories and research facilities.

32. General laboratory coats, safety footwear are not provided by the Department of Aerospace Engineering, although some targeted

laboratories and research areas will be supported by a reasonable stock of protective clothing and accessories, i.e., gloves, welding

aprons, dust masks, face shields, safety glasses, etc.

33. Equipment that has been deemed unsafe must be tagged and locked out of service by the Technical Officer in charge of the laboratory

or research facility. The Departmental Safety Officer must be notified of the equipment lockout IMMEDIATELY!

34. In June 1987 both the Federal & Ontario Governments passed legislation to implement the workplace hazardous material

information system or WHMIS across Canada. WHMIS was designed to give workers the right-to-know about hazardous material towhich they are exposed to on the job. Any person who is required to handle any hazardous material covered by this act should first read

the label and the products material safety data sheet (MSDS). No student is to handle any hazardous materials unless supervi sed by a

Faculty, Engineering Support or Teaching Assistant. The laboratory Technical Officer, Faculty, Engineering Support or Teaching

Assistant is responsible for ensuring that any hazardous materials are stored safely using WHMIS recommended methods and storage

procedures. All MSDS must be displayed and stored in a readily accessible place known to all users in the workplace and laboratory

35. All the foregoing rules and regulations are in addition to the Occupational Health and Safety Act, 1987.

36. Casual visitors to the laboratory and research areas are to be discouraged and must have permission from the Faculty, Engineering

Support or Teaching Assistant to enter. All visitors must adhere to the safety guidelines and is the responsibility of the visitor.

37. Only the Safety Officer may make changes to these policies upon confirmation of the Safety Committee and approval of the

Department Chair.


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Nomenclature

Ai Area of surface i

A Axial force on an airfoil, chordwise direction

C Dimensionless force/moment/location coefficientc Airfoil chord length

D Drag force on an airfoil, opposite to flight direction

ds, ds Incremental surface area vector, incremental lengthi Index variable

L Lift force on an airfoil, normal to flight direction

LE, TE Leading edge, trailing edge

M,m Moment acting on airfoil (Nm)

n

Unit vector normal to a surface

N Normal force on an airfoil, perpendicular to the chord

p Static pressure

R Resultant force on an airfoil, vector sum of L,Dor A,Nr, Polar spatial coordinatest

Unit vector tangent to a surface

u,v Velocity components in thex,y cartesian directions respectively

V Velocity vectorx,y Cartesian spatial coordinates

xcp, xac location of center of pressure, aerodynamic center (from the LE)

Angle of attack Doublet strength Stream function Air density


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7

Lab # 1

Wind Tunnel and Airfoil Drag Analysis


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Wind Tunnel and Airfoil Drag Analysis 8

Wind Tunnel and Airfoil Drag Analysis

Purpose

The objective of this lab is to familiarize the student with some of thecharacteristics of wind tunnel operation. In particular, the student will determine the

velocity coefficient, the mean velocity and the theoretical velocity of the test section.This experiment will also acquaint the student drag prediction using the velocity profile

downstream of a NACA 0015 airfoil.

Preamble

The purpose of an aeronautical wind tunnel is to obtain aerodynamic

measurements on scaled models of actual flight vehicles. If the size of the model and theconditions inside the test section are precisely known, then the forces and flow

characteristics on and about the model can be directly related to those on the actual flightvehicle. Therefore, it is critical to know the air properties accurately, and to be confident

that these properties remain uniform and constant throughout the test section.Early measurements of lift and drag on airfoils did not use sophisticated forces

balances and transducers that are in common use today. Yet reliable force measurements

of numerous airfoils were available as early as the 1920s. If the airfoil is made tocompletely span the tunnel, airfoil end effects can be eliminated and the problem is

simplified to an application of two-dimensional theory. The two-dimensional momentum

equation indicates that the forces on an airfoil inside the wind tunnel can be directly

related to the velocity profiles in the air stream and the pressures on the tunnel walls. Thislab will determine the drag force on the airfoil at various angles of attach through

integration of the downstream velocity profile.

Theory

Consider a segment of wind tunnel, with two separate test sections denoted as

1 and 2 (shown in Figure 1). The cross-sectional areas for each section are defined asA1

andA2, while the velocities are V1and V2, and the air densities are1and2. If no mass is

lost between the two sections then by mass conservation;

(1)

If the flow is incompressible ( as will be the case for this lab ), the density of the air willbe constant throughout the wind tunnel segment and;

(2)

If it is also assumed that there are no losses caused by the viscosity of the air (inviscid),

then by Bernoullis equation;

222111 AVAV

2211 AVAV


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(3)

Equations 1 and 2 can be solved to find the theoretical velocity V2that any section;

This velocity is theoretical only since assumptions were made concerning

compressibility and viscous effects. This value is easy to obtain from pressure taps in the

tunnel wall, but it is approximate only. A pitot-static tube can be used to find the actual

velocity at any point in the flow V2act. With this value a velocity coefficient Cvcan becomputed;

If this coefficient remains constant as the velocity in the wind tunnel is varied, it can beused as a correction factor to find the actual velocity from the theoretical,

The steady-state integral momentum equation of fluid dynamics relates the flux of

momentum through the boundary of a control volume to the forces applied to its surface.

Consider an airfoil inside the wind tunnel that completely spans the test section. A

control volume ( bounded with a dashed line ) can be drawn parallel to the upper anlower surfaces and vertically upstream and downstream of the airfoil, as shown in figure

1.2. If theses boundaries are drawn to coincide with the x and y coordinate directions, the

computation of lift and drag can be further simplified. The airfoil is not within the control

volume but its surface forms another boundary of the control volume allowing the surfaceforces to appear in the momentum equations.

2

1

2

212

1

/)(2

AA

ppV th

th

actv V

V

C2

2

thvact VCV

22

18 in.

45o

48 in.

4.75 in.Inlet cross-section

Outlet cross-section

Figure 1.1: Dimensions of the cross-sections at the pressure taps.

2

22

2

112

1

2

1VpVp


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The surface forces acting on the control volume are a result of air pressure and the

reaction from the airfoil itself denoted as R.

R-dSpForcesSurface The integration is carried out over the entire outer surface of the control volume. The netforce acting on the airfoil R, is a result of surface shear stress and pressure. The reaction

Ris negative in the integral momentum equation since the force applied to the controlvolume is each in magnitude and opposite in direction to the force exerted on the airfoilby the flow of air, consistent with Newtons third law, as demonstrated in figure 1.3.

Figure 1.2: Outline of the control volume inside the small subsonic wind tunnel,

not including the airfoil.

Figure 1.3: Force exerted on the airfoil by the flow of air and the opposing

reaction on the control volume, by Newtons third law

The steady-state integral momentum equation can be written:

R-dSdS)VV p( or

dS.dS)VVR p(


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The drag force can be isolated by considering the horizontal component of this equation

only:

xx dS)V dSu(RDrag p Since the control volume boundaries were selected to coincide with the Cartesiancoordinate axis, only the inflow and outflow planes need be considered when evaluating

the integral. For low subsonic flight speeds, the pressure and density at these planes willbe nearly uniform and equal. Therefore, the pressure integral can be dropped for thecalculation of the drag force.

t

b

io

t

b

o

t

b

i dyuudyudyu )(u(RDrag2222 dS)Vx

Here, the two-dimensional nature of the flow and the alignment of the boundaries withthe coordinate axis have reduced the equation further. Note that the vector dSis an

outward normal to the local control volume surface with a magnitude equal to an

incremental surface area. With the assumption that the inflow velocity is uniform and the

density constant, the equation can be further simplified.

Experimental Equipment

Small subsonic wind tunnel Handheld pitot-static tube Inclined manometer Manometer rake with 1 cm intervals

Procedure

1.

Ensure that the wind tunnel discharge area is clear of objects that could becomeairborne when the tunnel is started ( paper, rags, binders, people etc. ) and make sure

that the students are well behind the floor safety strip. Set the baffle at the wind

tunnel inlet to the fully open position (5/5) and start the wind tunnel. Record the wind

tunnel manometer reading (inclined manometer attached to the two pressure tapslocated at the two areas). This will provide the theoretical velocity. The actual

velocity is determined from the manometer attached to the handheld pitot-static tube

mounted ahead of the airfoil at the test section, record this value also. Be sure torecord the air temperature in the room. See Appendices A and B for analysis.

2. Close the baffle at the wind tunnel inlet to the 4/5 position and repeat the

measurements. Do the same for the 3/5, 2/5, and 1/5 positions.

3.

Calculate V2act, V2th and Cvfor each wind tunnel setting. The appendix section onpitot-static tubes may be of assistance.

4. With the wind tunnel off and the manometer rake in place record the zero reading on

the rake pitot tubes. Set the angle of attack to 10 degrees and open the baffle fully.Start the tunnel and record all of the pitot tube values of the rake. Be sure to record

the air temperature in the room and the inclination of the manometer. Record the

value of uIusing the tunnel manometer. Do the same procedure for angles of attack

of 15 and 20 degrees.


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Results

1. With the results obtained in procedure 3, plot V2actvs. V2thand Cvvs. V2act.

Determine if the velocity coefficient can be used as a correction factor for the

theoretical velocity.2. Compute the drag force on the airfoil at the three attack angles considered bynumerically integrating the velocity profile. Note that the integral between a pitot

tube atjand an adjacent one atj+1 can be approximated as:

1

1

2

1

22

1

222 )()(2

1)(

j

j

jjijjojjio yyuuuudyuu

Note

a) Density is assumed constant and that uiis constant for allj.

b) This approximation must be repeated between all pitot tubes and summed in orderto estimate total drag.

c) The pitot tubes do not measure velocity at the wall. You will need to extrapolate a

uovalue at the wall from nearby internal values.d) Values of uowill be nearly constant at the wall but will not be the same as ui.

3.

Given that the airfoil has a chord length of 15.24 cm, calculate the drag coefficientper unit span of the three attack angles. Compare to results you find in literature.

Questions

1.

How could you improve the measurements of drag using the wake rake?

2. Is the assumption of uo,max> ui a valid one? Explain.

Reference

Rae, W.H., Pope, A., Low-Speed Wind Tunnel Testing 2ndEd., John Wiley, 1984.

ui uo,max

uo,min

Initial

ProfileWakeProfile

ui uo,max


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13

Lab # 2

Pressure Distribution on the NACA 0015


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Pressure Distribution in the NACA 0015 14

Pressure Distribution on the NACA 0015

Purpose

The purpose of this lab is to investigate the surface static pressure on a NACA 0015

airfoil at various flight speeds and angles of attack. The lift, drag, and pitching momentfound from the surface pressures are used to define the NACA 0015s performance.

Theory

Figure 2.1: Airfoil conventions

Conventions used in this lab are defined in the figure above. The x,y coordinate axis is

aligned with the airfoil as shown. Here,Nis the normal force,Athe axial force,Rthe

resultant force,LandDthe lift and drag respectively. The normal (n) and tangent (t)vectors to the airfoil surface are defined as:

Here, is the angle between a line tangent to the airfoil surface and the positive x axis, orthe angle between a normal line from the surface and the positive y axis (measured

positive in the clockwise direction). To obtain the proper orientation, note that

-180o< < +180o.

Figure 2.2: Surface vector orientation conventionThe contribution to the total resultant force from a small region on the airfoil surface of

length dsis a sum of normal pressure (p) and tangential shear forces ():

dstdsnpRd

V

N

LR

D

A

Y

XUpper Surface

Lower SurfaceX=c

X=0

TrailingEdge (TE)

Leading

Edge (LE)

n

t

+

X

=0ds

Airfoil

surface

+

Y

jin

)cos()sin( jit

)sin()cos(


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Since the shear stress is assumed small (in this case), it is ignored. The total force due to

pressure is formed by integration around the entire surface of the airfoil:

The axial and normal force components are

The integration above is carried out in a closed loop in the clockwise direction about theairfoil, consistent with Aerospace convention. To avoid confusion with the class text, the

integration will instead be conducted from leading to trailing edge, on upper and lower

surfaces.It is convenient to place the pressures in terms of pressure coefficient since the pressure

difference obtained by the manometers is essentially , (see Appendix A)

The normal force coefficient CN(per unit airfoil length), can be found from;

The subscripts UandLrefer to the upper surface and lower surface respectively and cis

the chord length. This integration is easily done since the airfoil is symmetric and thesegments are the same on both surfaces. It should also be noted that the coefficients in

this lab are computed on a per unit length of airfoil basis since only a two-dimensional

pressure profile is used. The axial force coefficient (per unit length):

The lift and drag coefficients are found from:

The pitching moment coefficient at the leading edge caused by the normal force is:

Caused by the axial force:

dsjipdsnpR ))cos()sin((

dspRdspR NA ))(cos())(sin(

pdxRpdyR NA

2

2

1

V

ppCP

1

02

)(

2

1 c

xdCC

cV

NC

LU PPN

1

02

)(

2

1 cxd

xyC

xyC

cV

AC lPu

PA lU

1

022

)(

2

1 cxdcxCCcV

M

C LUN

N PP

LE

M

)cos()sin()sin()cos( ANDANL

CCCCCC

pp


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The Total moment about the leading edge ( per unit length of wing ) is:

Procedure

1. Holding the symmetrical airfoil by its supports, center the model horizontally at the

mouth of the subsonic wind tunnel.

2. Clamp the model with 4 C clamps that are available.

3. Loosen the brass incidence set screw, and gently set the trailing edge (TE) of themodel to zero degrees angle of attack.

4. Hook-up all 21 static pressure lines in numerical order to the multi tube manometer

and incline the manometer to 30

degrees.5. Ensure that the wind tunnel discharge area is clear of objects that could become

airborne when the device is started (paper, rags, binders, people etc. ) and make sure

that students are well behind the floor safety strip. Set the baffle at the wind tunnel

inlet to the fully open position (5/5) and start the wind tunnel. Observe the pressuredistribution pattern on the multi tube manometer. The pressure distribution for a

symmetric airfoil at zero degrees angle of attack should be symmetric as shown in

figure 2.3 below.

Figure 2.3: Pressure tap readings at zero degrees angle of attack

6. Adjust the airfoil to obtain a symmetric pressure distribution by SLOWLY and

GENTLY adjusting the attack angle until the above symmetric pattern is obtained.7. The airfoil model is now calibrated for zero degrees angle of attack. Record this

value.

Datum

1 2 3 4 5 .. 11 .. 20 21

1

022

2

1 c

xd

c

y

x

yC

c

y

x

yC

cV

MC

L

lP

U

UP

LE

M lU

A

A

NALE MMM CCC


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8. At this zero angle of attack and with the wind tunnel inlet baffle fully open, record the

wind tunnel manometer and all 21 static pressure tap readings on the multi tube

manometer inclined at 30 degrees. Record the level at the remaining stations, this isthe datum Patm. All pressures will be calculated from this datum.

9. Repeat the procedure at 10, 12o, 14, 16, and 18degrees angle of attack. Note that

the green fluid is water and that a pressure higher than atmospheric will push the levelin a tube BELOW the datum level. In your calculations, the value ofP-Pdatumshouldyield a positive value at the stagnation point.

Report

1. Compute the corrected tunnel velocity for each attack angle using the correction

coefficient found in lab 1. Using a spreadsheet, convert all pressure tap readings to

pressure coefficient values. Average the readings at taps 1 and 21 to get a value for

the trailing edge.

2.

Calculate the normal, axial, and moment coefficients for each angle of attack usingthe same spreadsheet and an appropriate approximation. Then compute CL, CD, CM,and Ccp for each angle. Note the appendix on the next page provides numerical

approximations.

3. Plot CL, CD, and Ccpvs. angles of attack.

4. Plot CLvs. CMfor all angles of attack. Find the aerodynamic center (as a percentageof chord) by computing the inverse slope of this line.

5. Discuss the characteristics of the NACA 0015 in terms of its lift/drag behavior. What

was the stall angle of this airfoil? How does this compare with other values found inliterature? Is the aerodynamic center where it was expected?

Table 2.1: Coordinates of the pressure taps and numbering scheme on the NACA 0015Taps 11 10,12 9,13 8,14 7,15 6,16 5,17 4,18 3,19 2,20 1,21 T.E.

X (cm) 0 0.3048 0.9144 1.524 3.048 4.572 6.096 7.620 9.144 10.668 12.192 15.240

Y (cm) 0 0.5182 0.7010 0.9144 1.0973 1.1582 1.1277 1.0058 0.8534 0.7010 0.4877 0

Figure 2.4: Pressure tap locations on the NACA 0015 airfoil.

X

Y 12

2120

3456

117

8

19181716

14 15


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Appendix:Numerical Approximations

Figure 2.5: New tap order for upper/lower integration

In order to numerically integrate the surface pressures in a manner consistent with the

class text, the taps need to be renumbered according to Figure 2.5 above. The iindex

refers to the upper surface whilejthe lower. Both i=1, andj=1 are the leading edgepressure tap. The pressure at the trailing edge can be taken as the average of pressure

values at taps 1 and 21. By averaging these two taps to get a trailing edge value, you are

essentially creating another node, which must be included in any calculation. Remember,

point i+1is adjacent to ibut closer to the trailing edge along the airfoil surface.Numerical formulas are given below.

c

Ll

PUU

PM dxyx

yCy

x

yC

cC

lUA

0

2

1

m

j

jjjjjPjP

n

i

iiiiiPiP yyyyCCyyyyCC

c 111)1()(

1

11)1()(2

4

1

c

PPM xdxCC

cC

LUN

0

2 )(

1

m

j

jjjjjPjP

n

i

iiiiiPiP xxxxCCxxxxCCc 1

11)1()(

1

11)1()(24

1

n

i

iiiPiP

m

j

jjjPjP

c

PPN xxCCxxCCc

dxCCc

CLU

1

1)1()(

1

1)1()(

0 2

1)(

1

c

lP

uPA dx

x

yC

x

yC

cC

lU

0

)(1

m

j

jjjPjP

n

i

iiiPiP yyCCyyCCc 1

1)1()(

1

1)1()(2

1

X

Y i=1110

j=1110

987i=6

15i=4

987j=6

j=4 5


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20

Lab # 3

Effect of Flaps and Slats


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Airfoil Design Using CFD 21

Effect of Flaps and Slats

Purpose

The purpose of this lab experiment is to familiarize the student with the effects of high

lift devices such as flaps and slats. The student should gain an understanding of therelative effects of each device on the lift, drag, and stall angle of the wing.

Preamble

Flaps and slats effect the airflow over the airfoil in different ways, and thus effect the

performance of a wing in a dissimilar fashion. Flaps tend to change the effective camberof the airfoil while slats tend to stabilize the flow over the top surface of the airfoil. These

two effects will change both the stall angle and the lift produced at a given attack angle.

In this lab, the influence of each control surface will be investigated.

Apparatus

Symmetric airfoil with slat and flat components: chord=15.0 cm, span=35.5 cm Small sub-sonic wind tunnel Pyramidal strain gage balance

Data signal amplifier and analysis software

Procedure

1. Install the airfoil on the test stand in the wind tunnel. The slat and flap should be in

the retracted position. The windows should cover the test section when the tunnel is

in operation. Be careful not to bump or place any weight on the strain gage balance.

2. Turn on the data acquisition system located under the table by the side of the wind

tunnel. Then turn on the computer. Once the computer is up, double click the wind

tunnel data acquisition icon.

3. Before data can be taken, the lift, drag, and moment gages must be zeroed. Click on

the tare button just underneath each of the five gages. Figure 3.1 below shows theappearance of the data acquisition display.

4. Ensure that the wind tunnel discharge area is clear of objects that could become

airborne when the tunnel is started ( paper, rags, binders, people etc. ) and make surethat students are well behind the floor safety strip. Set the baffle at the wind tunnel

inlet to the fully open position (5/5) and start the wind tunnel.

5. Turn on the tunnel again and observing the lift parameter. You may need to

aerodynamically reset the symmetrical wing for zero angle of attack (zero lift at zero

angle of attack) With zero degrees angle of attack indicated on the test stand, adjust

the orientation of the stand with the knob just underneath the model holder. Adjust


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the orientation until zero lift is produced. This is the true zero degree angle

orientation. Tare all gages.

6. With the baffle fully open, read the lift, drag, and moment. Increase the angle of

attack in two degree increments up to and including 20 degrees while recording all

parameters. When complete, reduce the angle of attack back to zero. Turn off thetunnel.

7. Fully deploy the slat on the model without removing it from the test stand. Repeat

procedure 6.

8. Set the flap on the model with the provided tool to 45 degrees flap angle. Repeat

procedure 6.

9. Retract slat on the model while leaving the flap in place. Repeat procedure 6.

10.

Shut down the wind tunnel, the computer, and the data acquisition system in thatorder.

Report

1. Create three plots: CLvs. , CDvs. , and CMle/CLvs. . On each plot, put the resultsof the four test cases.

2. Compute the center of pressurexcpand the aerodynamic centerxacfor each case.

Discussion

In your report, discuss:

1. The airfoil performance with the high lift devices compared to the baseline case.

2. The changes in the lift and drag curves with the flap and slat.

3. The influence of these devices on stall angle. What configuration would you

recommend in take-off? In landing?

4. How do these devices change the center of pressure and aerodynamic center?


24/37


Figure 3.1:Display of the data acquisition system window.


25/37

Appendix A: Manometers 24

Appendix A: Manometers

Manometers are simple devices that are used extensively in this course to provide

accurate pressure measurements. It is essential for the students to have a good

understanding of the fundamental principles involved. Any fluid mechanics text will havea discussion of manometry under the topic of hydrostatics. To assist the student a verybrief discussion is provided here.

In a fluid at rest, the pressure at any point will vary according to:

Here, is the specific weight of the fluid, which is a product of its density and the

gravitational constant g, = g. The coordinatez, decreases in the direction opposite tothe direction of gravity. In other words,zgrows in magnitude with increasing height.

Integration of this expression yields an expression relating the pressure at some pointzto

the pressure at the datumpowhere z = 0,

Note that in this reference frame z will be a negative value, which means that pressure

will increase with depth. A more intuitive reference frame measures depth in a positive

sense, with hbeing the depth of the fluid,

This simple relation allows an analysis of hydrostatic systems. Consider the manometer

below;

The pressure at A can be related to the pressure at B by following a path from A to B

through the fluid and accounting for the changes in pressure with variations in fluidproperties and height.

zz

p

zpzpo

)(

hpp o

BADatum

h = 01

2

3

h1

h2


26/37

Appendix A: Manometers 25

If the fluids have very different specific weights, the fluid with the smaller specificweight can usually be ignored with very little loss of accuracy. For instance, in the above

problem, if 1and 3were both air ( = 11.4 N/m

3

) and fluid 2 was water,2= 9810 N/m3, the effects of the air can be ignored to produce,

It should be emphasized that the depths included in these expressions are vertical depths.

An inclined manometer can be considered if vertical depths are obtained after conversionof the inclined depthLvia h =Lsin(). Where, is the angle from the horizontal of the

inclined tube.

BA phhhhp 2312211 )(

)( 122 hhpp AB


27/37

Appendix B: Pitot-Static Tubes 26

Appendix B: Pitot-Static Tubes

A pitot-static tube determines the velocity of an incompressble flow bycomparing the the total pressure of the fluid to its static pressure. The static pressure is

what an observer would measure if they were moving with the flow, in other words, in

static relation ( P1). The total pressure is a sum of the static pressure and the dynamic

pressure which is measured when the fluid is brought to rest ( P2). By Bernoullisequation:

(1)

Therefore;

(2)

The pressure difference is measured by an inclined manometer, which can measure slightpressure differences with reasonable accuracy. The manometer fluid is often coloured

water, but other fluids such as mercury can be used if the pressure differences are large.

Whatever the fluid, its specific gravity ( SG ) must be known. Specific gravity is definedas;

Hydrostatic relations give the pressure at the bottom of a column of fluid with vertical

height hand specific gravity SGas;

L

P2,V2= 0 P

1 P1 , V1

P2 P1Datum

CatOH

fluid

O

SG4

2

2

2

112

1PVP

)(2 121

PPV


28/37

Appendix B: Pitot-Static Tubes 27

Here,gis the gravitational constant ( g = 9.81 m/s2) andH2Ois 1000 kg/m3. This

relation provides a means of determining the pressure differenceP2P1in equation 2.With the inclined manometer shown in the figure, the vertical height of the column offluid is;

Where,Lis the inclined length of the fluid column and the angle of incline of the

column with the horizontal. Caution is advised with the calculation of the vertical height

h, some fixed inclined manometers measureLwith the slope already included. Thismeans that the scale on the manometer readsLsin() and not justL.

Combining these relations the air velocity can be found from;

Note that the specific gravity of the manometer fluid is denoted as SGf, and the density

of the air in the wind tunnel isair.

hgSGp OH 2

)sin( Lh

air

OHf LgSGV

)sin(22

1


29/37

Appendix C: Guidelines for Lab Report Writing 28

Appendix C: Guidelines for Lab Report Writing

The exact format of a lab report is as varied as the number of institutions that

require them. For this reason, lab reports in this course will conform to the universally

accepted format of a formal academic paper. The format of which contains most of the

structure of a lab report from any other university but with additional elements. Theintent of using such a rigid structure is to give each student experience in writing formal

reports, something they will be required to do at some point in their engineering careers.As a consequence, the structure, format, grammar and spelling are all considered when

determining a grade for an individual lab report. To assist students in preparing their

reports, a set of guidelines covering content and style is given in this appendix.

Writing StyleFormal academic papers in engineering are almost exclusively written in third person

sometimes called passive voice. In first person, the writer tends to present his or her pointof view from a personal prospective, using the terms I and We frequently. While in

third person, a writer refrains from giving written text the appearance of a personalopinion. This style of writing is used in academic works since it does not readily convey

any bias towards the subject matter on the part of the writer. It is more conducive toallowing the reader to form an objective opinion on the subject. It should be noted that

this entire lab manual is written in third person. Examples of each;

First person: When I switched on the power to the wind tunnel I realized the model had

not been secured since it flew out the back and hit the wall.

Third person: When the wind tunnel was activated the model flew out the back strikingthe wall, leading to the conclusion that it had not been secured.

First person: My analysis of the data leads me to conclude that the stall angle of theNACA 0004 airfoil is 11 degrees.

Third person: The analysis of the data indicates that the stall angle of the NACA 0004airfoil is 11 degrees.

Writing Precision

Since your lab report is considered a formal scientific work, the language used to conveyinformation should be exacting, leaving no possibility for ambiguity or misinterpretation.

Examples:

vague: somewhat noticeable was relatively small ..

.. it looked good ..

better: fluctuated by +/- 3 cm ..

.. produced a CLof 1.2 ..

.. was 5% less than published NACA results for the same airfoil


30/37


Title PageThe title of the lab report should be concise, with no more than 10 words. It should give

the reader exact information about the subject of the work only. It should not contain anyinformation about the results or the conclusions. It should also contain the following:

Names and student numbers of all authors and contributors

The date and time the lab was performedThe section numbers of all authorsThe names of the TA and course professor

AbstractThe abstract is a summary of the entire report and should be written last. Usually, an

abstract should be between 100 and 200 words in length and is placed at the beginning of

the report. The function of an abstract is to give a reader a general overview of the report.

The reader can then decide to read further if he or she is interested. The abstract shouldbe concise and provide specific details of the work and the results. A good abstract will

answer the following questions:

1)

What was done in the lab or experiment?2)

How was the lab or experiment performed?

3) What was found?

4) What was concluded?

Introduction

You cannot assume that your reader has an in-depth knowledge of the subject area of the

report. You must then lead the reader from a point of general knowledge of the topic tothe point of specific knowledge necessary to benefit from reading the remainder of the

report. Questions that should be answered are:

1) What has been done in this area in the past?

To answer this, the author must develop a historical prospective based on citedworks that are listed in the References section. Accepted facts and knowledge

gaps in the subject area should be mentioned.

2) What is the significance of the results?After the literature review given in the last step, it should be easy to place the

present report in it historical prospective. Give an indication of where the results

of the report fit in and how it contributes to the body of knowledge of the subjectarea.

3) Why was this specific study performed?

You should present the specific hypothesis and experimental design being

investigated.

Data Analysis, theoretical Background and Procedures

In longer reports based on broad investigations it is sometimes necessary to give the

reader an overview of the subject through a development of its theory. A mathematicaldevelopment, if applicable, is appropriate along with a discussion of the assumptions and

limitations of the theory.


31/37


If the procedures in the experiment are complex or highly detailed then a listing of all the

steps used in its performance should be listed. The objective of this section is to provide

sufficient detail on the equipment and the method such that the experiment can berepeated to confirm its results. However, the author should be wary of providing to much

detail to the point of overwhelming the reader. Technical drawings and specifications of

the equipment should be provided or referenced. This section should answer:1) What apparatus was used?Provide detailed engineering drawings with dimensions and a written description.

2) What instruments and sensors were used?

List the individual components an sensors used in the apparatus with theirspecifications.

3) What conditions were required?

List experimental mediums such as water, air, oil, etc. Also provide their

conditions such as temperature, pressure, contamination ( humidity for air ).

Results and Discussion

The Results and Discussion sections are usually combined but can be made separate ifcircumstances warrant. This section provides all of the key findings. Sample data

calculations can be provided here or left to the appendix. All presented data should be in

graphical or tabular form unless the amount of data produced is very small. All tables

plots that appear in this section must be numbered and be accompanied by a descriptivecaption of one or two sentences in length. If a table or a plot appears in this section it

must be discuss somewhere in the text. If you have nothing to say about a figure, it

should not be included in this section. All plots must be easy to read with labeled axis anda title. All tables must have a title and labeled columns and rows to make interpretation

easier.

What you present in this section and how you interpret the results is the most importantpart of the report. This is the section where you show understanding and knowledge of

the subject area beyond simple performance of the experiment. Discuss the relationships

and trends that you see in the data and how this relates to achieving the objective of theinvestigation. A few examples:

example figure caption: Figure 3:Plot showing the relation between the lift coefficientand the angle of attack for the NACA 0012 airfoil.

example discussion: Figure three provides a plot of the lift coefficient (CL) as a function

of the angle of attack () for the NACA 0012 airfoil. Clearly, the liftcoefficient increases steadily as the angle of attack is increased. Thisindicates that this airfoil will generate higher lift at a given airspeed

by simply increasing attack angle. The rapid decrease in CLseen in

the figure once the angle of attack passes 16 degrees is consistentwith known lift behavior past the stall angle.

Questions that may help you to write a better discussion:


32/37


1) What do the results indicate clearly?

2) What trends do you see in the results?3) How do these trends change as various parameters are varied?

4) How accurate are the results and how could you estimate the accuracy?

5)

What are the significance of the results?6) Are there any ambiguities in the data?7) How do the results compare to know or related values?

8) How do the results relate to the theory?

ConclusionThe conclusion is usually short but concise. It will accomplish the following tasks:

1) Restate known facts or trends presented in the Results and Discussion section.2) Justify each fact or trend. This is most often done with quantitative data obtained

from the Results and Discussion section. Do not use the conclusion to present new

data or to further discussion. The only data quoted in the conclusion are from theResults and Discussion section.

3) Indicate any weaknesses or limitations of the experimental design. The Conclusion

can also be used to suggest further research and to discuss the implications of your

findings.

References

A list of publications cited in the report is provided in the Reference section. The formatof this section can vary from one publication to the next but the function is the same in

all. For example, at some point in the text a published work is referenced:

. convective flow was studied extensively by Le Peutrec and Lauriat [2].

In the Reference section a citing with the following format will appear:

[2] Le Peutrec, Y., Lauriat, G., Effects of Heat Transfer at the Side Walls on Natural

Convection CavitiesJournal of Heat Transfer, Vol 112, pp. 370-378, 1990.

The number to the left indicates the order in which it appears in the text. For example, the

first work referenced will have number [1], the second [2], and so on. If you need to refer

back to a work previously referenced, you can use the number previously assigned.

another example:

. foundations for numerical turbulence modeling were developed at Imperial

College in London, UK (Launder, B.E., Spalding, D.B.,1972). .

In the Reference section:

Launder, B.E., Spalding, D.B. (1972) Lectures in Mathematical Models of Turbulence,

Academic Press, London, England.


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AppendicesThe appendices contain all raw experimental data ( in tables ), sample calculations,

superfluous plots and drawings. Again, all plots should have a caption and all tablesshould have a title. Data for separate sections of the work should be contained in different

appendices. For example, if several airfoil shapes are studied, the data pertaining to each

airfoil would warrant its own appendix section. At some point in the text of the report theinformation contained in the appendix should be referenced:

further results on the performance characteristics of the NACA 0012 is provided in

Appendix C.


34/37

Appendix E: Calculation of Forces on Airfoils 33

Appendix D: Calculation of Forces on Airfoils

Figure D.1: Airfoil conventions

This Appendix is intended for students not satisfied with the method of calculation for

airfoil forces used in the class text. Presented is a more mathematical method ofdetermining the same result. In the end, a set of compact formulas requiring integration

about a closed loop (the airfoil surface) will be created. The aerospace sign convention on

moments is used only in the calculation on the moments about the leading edge. Theclassic mathematical convention of defining moments as positive counter-clockwise in a

right handed system is used to derive normal and tangential vectors. The geometries used

in this appendix are defined in the figure above, D.1 and below D.2. The x,y coordinate

axis is aligned with the airfoil as shown. Here,Nis the normal force,Athe axial force,Rthe resultant force,LandDthe lift and drag respectively. The normal outward (n) and

tangent (t) vectors to the airfoil surface are defined as:

Here, is the angle between a line normal to the airfoil surface and the positive x axis (measured positive in the counter-clockwise direction, see figure D.2). Note that the

integration is conducted counter-clockwise meaning that dx=xi+1xi, which accounts

for some of the negative signs in the expressions above. To obtain the proper orientation,note that 0o< < +360o.

Figure D.2: Surface vector orientation convention

V

N

LR

D

A

Y

XUpper Surface

Lower SurfaceX=c

X=0

Trailing

Edge (TE)

Leading

Edge (LE)

n

t

X

=0

ds

Airfoil

surface+

Y

dy

dx

+

i+1

i

22

dydxds

jdxidydsjin

1

)sin()cos( jdyidxdsjit

1

)cos()sin(


35/37

Appendix D: Calculation of Forces on Airfoils 34

The contribution to the total resultant force from a small region on the airfoil surface of

length dsis a sum of normal pressure (p) and tangential shear forces ():

The total force is formed by integration around the entire surface of the airfoil in a

counter-clockwise direction:

The axial and normal force components are

It is convenient to place these forces in terms of non-dimensional coefficients since the

pressure difference obtained by the manometers is essentially , (see AppendixA)

The normal force coefficient CN(per unit airfoil length), can be found from;

The axial force coefficient is found with a similar expression. The lift and drag

coefficients are found from the angle of attack :

The Total moment about the leading edge ( per unit length of wing ) is:

The shear stress term in these expressions is difficult to determine experimentally. Sincepressure force is easier, it will be the only term used in the subsequent discussion. Theforce and moment terms due to pressure can be written in numerical form based on the

analytical equations, as shown below. Note, integration is done counter-clockwise. For

example, an element of arc length dshas the component dx=xi+1xi, where the node

i+1, is further counter-clockwise on the airfoil surface than node i, as in figure D.2. The

integration is a closed loop, which means node i=1 and i=n+1 are the same node.

dstdsnpRd

dsjijipdstnpR )cos()sin())sin()cos((

dspRdspR NA )cos()sin()sin()cos(

dypdxRdxpdyR NA

22

2

1

2

1

VC

V

ppC fP

c

ydC

c

xdC

cV

RC fp

NN

2

2

1

)cos()sin()sin()cos( ANDANL

CCCCCC

NLEALELE MMM

CCC,,

xdypdxMydxpdyM NLEALE ,,

pp


36/37

Appendix D: Calculation of Forces on Airfoils 35

n

i

iiiiiPiPpM yyyyCCc

ydyCc

CA

1

11)1()(22 4

111

n

i

iiiiiPiPpM xxxxCCc

xdxCc

CN

1

11)1()(22 4

111

n

i

iiiPiPPN xxCC

cdxC

cC

1

1)1()(2

111

n

i

iiiPiPPA yyCCc

dyCc

C1

1)1()(2

111


37/37

Appendix E: Lab report grade template 36

Appendix E: Lab Report Grading Template

AER 504: Aerodynamics, Laboratory Report Evaluation

Student Name(s):Lab Number: Section Number: TA:

Component: Excellent Good Satisfactory NeedsImprovement

Grade

Technical writing (/2)Grammar, spelling

/2

Clear, concise, legible

Logical train of thought

Proper use of citations/references

Report content and formatting (/2)Required formatting

/2

Organization of content

Figures, tables, equations captioned/numbered

Quality of figures

Data and calculations (/3)Observations and data

/3Calculations and/or resultsQuestions and conclusions (/3)Discussion points and questions

/3Conclusions

Overall: /10Comments:

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