slide 1 announcements/opportunities next year’s aircraft design class: –we will (again) have a...
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Aerospace andOcean Engineering slide 1
Announcements/Opportunities
• Next year’s Aircraft Design class:
– We will (again) have a joint team with ME to build and fly a morphing airplane
– Send me email: whmason@vt.edu to apply
– We will have 4 AEs on this team
• Undergraduate research:
- lots of opportunities to help the design class software and do student AIAA papers, see me if you are interested.
Aerospace andOcean Engineering slide 2
AOE 3054AOE 3054Aerospace and Ocean Aerospace and Ocean
EngineeringEngineeringInstrumentation and LaboratoryInstrumentation and Laboratory
A Lectureon
Aerodynamic Testing
W.H. Mason
Aerospace andOcean Engineering slide 3
Overview
• Where you test
• Why you test
• How you test
• Some specifics for your lab
Aerospace andOcean Engineering slide 4
The NTF at NASA Langley
Hampton, VA
Performance: M = 0.2 to 1.20PT = 1 to 9 atmTT = 77° to 350° Kelvin
Feb. 1982
Aerospace andOcean Engineering slide 5
The Full Scale Tunnel at NASA Ames
80x120 FootTest Section
40x80 FootTest Section
Aviation Week & Space Technology, Dec. 7, 1987
Aerospace andOcean Engineering slide 6
Information Sources
• Lot's of introductory material on
Aero Test in the manual: read it!
• The standard reference book:
Barlow, Rae and Pope,
Low Speed Wind Tunnel Testing
Aerospace andOcean Engineering slide 7
Wind Tunnel Testing is Expensive
Preparation and planning are required to get into any tunnel:
• Make pre-test estimates
• Prepare a pre-test report including a Run Schedule
Aerospace andOcean Engineering slide 8
So Will the Computer Eliminate the WT?
Cost,Flowtime
Number of Simulations
10 100 1,000 10,000
E.N. Tinoco, (Boeing) “The Impact of CFD in Aircraft Design,”Canadian Aeronautics and Space Journal, Sept., 1998, pp. 132-144
Aerospace andOcean Engineering slide 9
Key Items
• Safety, accidents can happen
• Pretest Planning - the key to success
• Model Design
• The Run schedule
• Typical Tests:
- force and moment
both performance, stability, and control
- pressure distributions
- flow diagnostics
on and off surface flow visualization
Aerospace andOcean Engineering slide 10
Test Hours, F-16 WT Test
0 500 1000 1500 2000
general arrangementwing planform,camber
LE & TE flapsstrake developmentcontrol deflections
storesstore loads
pressure loadsinlet
flutterstore separation
spin/stallspillage and nozzle
miscellaneous
Aerospace andOcean Engineering slide 11
Research Fighter Configuration (RFC)Visualization with a Tuft Grid
Small Model in Grumman Tunnel
Aerospace andOcean Engineering slide 12
Another Way To Do Flow Diagnostics
Kurt Chankaya, Grumman (now Lockheed)
Aerospace andOcean Engineering slide 13
Typical way to put tufts on the wing
From Pope and Harper’s text, taken in the Wichita State tunnel
Aerospace andOcean Engineering slide 14
Oil Flows for Surface Visualization 1
SC3 Wing, M = 1.62, = 8° (nominally attached)
Aerospace andOcean Engineering slide 15
Oil Flows for Surface Visualization 2
SC3 Wing, M = 1.62, = 12° (TE flow separation)
Aerospace andOcean Engineering slide 16
Laser Light Sheet example
Aviation Week & Space Technology, July 29, 1985
Light Sheet from an argon laser, the flow is seeded with an standard smoke generator.
Northrop IR & D example of vortex flow over a delta wing configuration.
Exhibited at the 36th Paris air show.
Aerospace andOcean Engineering slide 17
Model Fabrication:
• Accuracy important!
- drag, under all conditions
- low speed near max lift
- transonic cruise condition
Aerospace andOcean Engineering slide 18
WT model with high LE accuracy Req’ts. Supercritical Conical Camber (SC3)
Wing, developed using CFD. The leading edge contour accuracy is critical.
Note the arc of the wingalong the trailing edge,a sort of “gull shape”
Aerospace andOcean Engineering slide 21
Simulation Issues
• Fundamental: Mach number and Reynolds number
- Match Mach, do your best on Reynolds, leads to:
- transition fixing
• Test issues:
- wall interference, flow angularity, nonuniformity
• Adjustment from model scale to full scale
Aerospace andOcean Engineering slide 22
Tunnel/Mounting Interference
Tunnel and Balance Centerline
Dmeas
Dtrue
LmeasLtrue
Walls restrict airflow around model
Flow angularity causes causes true forces to be
in a direction different than the reference
upV Exposed strut senses addtional drag
on external balance
Aerospace andOcean Engineering slide 28
The Virginia Tech Stability Tunnel
• A high quality flowfield- uniform mean flow- low turbulence level- low flow angularity
• came from NASA in 1958• 6'x6' test section, 24 ' long• 600 hp motor/14' fan• 275 fps max speed
Aerospace andOcean Engineering slide 30
Velocity Variation in the Test Section
0.96
0.98
1.00
1.02
1.04
-2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0
V/Vref, U = 125 fps, Z = 0 ftV/Vref, U = 125 fps, Z = 0.5 ftV/Vref, U = 200 fps, Z = 0.0 ftV/Vref, U = 200 fps, Z = 0.5 ft
Virginia Tech Stability Wind TunnelMean Flow Calibration Characteristics
V/Vref
VPI Aero-161, Dec. 1987
y, ft
Aerospace andOcean Engineering slide 31
Upwash Variation in the Test Section
-1.50°
-1.00°
-0.50°
0.00°
0.50°
1.00°
1.50°
-2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0
Alpha, U = 125 fps, Z = 0 ftAlpha, U = 125 fps, Z = 0.5 ftAlpha, U = 200 fps, Z = 0.0 ftAlpha, U = 200 fps, Z = 0.5 ft
Virginia Tech Stability Wind TunnelMean Flow Calibration Characteristics
, y ft
-161, . 1987VPI Aero Dec
Aerospace andOcean Engineering slide 32
Sidewash Variation in the Test Section
-2.00°
-1.50°
-1.00°
-0.50°
0.00°
0.50°
1.00°
-2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0
Beta, U = 125 fps, Z = 0 ftBeta, U = 125 fps, Z = 0.5 ftBeta, U = 200 fps, Z = 0.0 ftBeta, U = 200 fps, Z = 0.5 ft
Virginia Tech Stability Wind TunnelMean Flow Calibration Characteristics
β
, y ft
-161, . 1987VPI Aero Dec
Aerospace andOcean Engineering slide 33
Use a Strain Gage Force Balanceto Measure Loads
Tension change in wire changes resistance
You used one before?
• Assume that the balance is adequatelycalibrated - we will not check it this year
Aerospace andOcean Engineering slide 34
Strain Gages
strain gage element simple strain gage balance
true force balance circuit for balance
1 2
3 4
5 Volts
OutputVoltage
Load
StrainGages
1
2
l1
M
M
2
1
Δl
l2
1 2Δl
D =M M-
Load (D)
3
4
1
2
M = D l
M = D l
M - M = D(l - l )
= D Δl
1
1 12
2
2
1
2
x
x
Aerospace andOcean Engineering slide 35
Mechanics for this lab:
• two weeks
• 1st week - get ready
- check out tunnel, make pretest estimates
• 2nd week: test!
- run the model
Aerospace andOcean Engineering slide 36
The Tests!
New this year: we have 2 possibilities:
1. The “standard” rectangular wing
2. The Pelikan Tail (from a senior design project)
Your choice!
Aerospace andOcean Engineering slide 37
Objective:
Use Experimental techniques to find aero characteristics of:1. A rectangular, unswept wing
• with and w/o transition stripsor
2. A novel tail concept almost used on the Boeing JSF, and subsequently adopted by our senior UCAV-N team
Aerospace andOcean Engineering slide 38
The Rectangular Wing Model
6.0 "
Wing Mounting Holes
Trailing Edge
34.0 "
3.667"
(.98" between holes)
The airfoil: originally a Clark Y, recently modified (thickened) to strengthen the model - How does this change the test estimates?
Aerospace andOcean Engineering slide 39
Rectangular Wing Model Airfoil Section
-0.05
0.00
0.05
0.10
0.15
0.20
-0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2
CLARK Y Airfoil for Aero Lab TestTheoretical Coordinates and Coordinates after Wing reinforcement
y/c uppery/c lowery/c measured
y/c
x/c
Not to scale
Aerospace andOcean Engineering slide 40
Expected Lift Coefficient Variation: Rectangular Wing Model
-0.50
0.00
0.50
1.00
1.50
2.00
2.50
-15° -10° -5° 0° 5° 10° 15° 20° 25°
CL
, .deg
,Estimate( )Inviscid Theory
Clark Y Airfoil = 5.6 AR Rectangular Wing
NACA data = 1.0 10Re x6
,VPI data = .3 10Re x6
Aerospace andOcean Engineering slide 41
Expected Pitching Moment: Rectangular Wing Model
-0.50
0.00
0.50
1.00
1.50
2.00
2.50
-0.15-0.10-0.05-0.000.05
CL
CmCm
Clark Y AirfoilAR = 5.6 Rectangular Wing
NACA data,Re = 1.0x106
Aerospace andOcean Engineering slide 42
Expected Drag Coefficient Variation: Rectangular Wing Model
-0.30
-0.00
0.30
0.60
0.90
1.20
1.50
0.00 0.05 0.10 0.15 0.20
CL
CD
NACA Data, Clark Y airfoil, rectangular wing, AR = 5.6, Re = 1x10 6
Theoretical 100%Suction Polar, e = .98
Theoretical 0% Suction Polar
Wind tunnel test data
Note: Theoretical polars shifted to match experimental zero lift drag
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