MAE 5930, Rocket Systems Design MAE 5930, Rocket Systems Design

Wind Tunnel Testing: Setup and Procedures

MAE 5930, Rocket Systems Design

Wind Tunnel Types

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Closed Circuit Tunnel P0( )tunnel ! pambient

MAE 5930, Rocket Systems Design

Wind Tunnel Types (2)

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Our Tunnel is an “Open Circuit” Tunnel

P0( )tunnel ! pambient

MAE 5930, Rocket Systems Design

About Wind Tunnel Testing

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Key issues •  Maintaining Reynolds number \, Mach number similarity •  Accounting for possible flow non-uniformities in the wind tunnel •  Wind Tunnel Blockage •  Effects of the model support system. •  Leaks and Losses •  Open or Closed Circuit Tunnel

Turbulent or Laminar Flow? •  In most cases the full scale flight conditions will produce turbulent flow. •  In wind tunnels, low Reynolds number will result in a significant amount of

laminar flow. •  To achieve a boundary layer similar flight Reynolds number, the boundary layer

is often "tripped" to force transition to turbulent flow.

MAE 5930, Rocket Systems Design

Laminar and Turbulent Boundary Layers

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• Laminar • Turbulent

MAE 5930, Rocket Systems Design 6  

Laminar and Turbulent Boundary Layers (2) • Location of transition point strongly a function of Reynolds number

Laminar

Transitional

Turbulent

• Laminar --> orderly • Turbulent --> chaotic

flow

MAE 5930, Rocket Systems Design 7  

Comparison of Reynolds Number and Mach Number

Reynold’s  number  is  a  measure  of  the  ra:o  of  the    Iner:al  Forces  ac:ng  on  the  fluid  -­‐-­‐  to  -­‐-­‐  the  Viscous    Forces  Ac:ng  on  the  fluid    -­‐-­‐  Fundamental  Parameter  of  Viscous  Flow  -­‐-­‐  

Mach  number  is  a  measure  of  the  ra:o  of  the  fluid  Kine:c  energy  to  the  fluid  internal  energy  (direct  mo:on  To  random  thermal  mo:on  of  gas  molecules)    -­‐-­‐  Fundamental  Parameter  of  Compressible  Flow  -­‐-­‐  

M =Vc=

2! " ! #1( )

$

%&'

()"

V 2

2$%&

'()

e

Re =!VLµ

= 2 L"#!V 2

$wall%Inertial & ForcesViscous & Forces

MAE 5930, Rocket Systems Design

About Wind Tunnel Testing (2)

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V!

Vtest

Lflight

Lmodel

Re( ) flight =!" #V" # Lflight

µ"

Re( )windtunnel

=!test "Vtest " Lmodel

µtest

Re( ) flight ! Re( )windtunnel

MAE 5930, Rocket Systems Design

About Wind Tunnel Testing (3)

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Trip Strip along leading edge of a wind tunnel model airfoil

MAE 5930, Rocket Systems Design 10  

Types of Drag

W.H.  Mason,  Virginia  Tech "

Skin  Fric)on  Strongly  Effected  by  Boundary  Layer  state  

MAE 5930, Rocket Systems Design 11  

Empirical Skin Friction Correlations

“Smooth  Flat  Plate  with  No  Pressure  Gradient”  

Re~500,000  

“Schoenherr  Plot”  

Re~10,000,000  

Effect  of    Compressibility  

MAE 5930, Rocket Systems Design 12  

Wind Tunnel Blockage Effects

!m = !iAiVi

Ai

Atest = Ai ! Amodel

Vtest !Ai

Ai " Amodel#Vi

MAE 5930, Rocket Systems Design 13  

Wind Tunnel Blockage Effects (2) NASA Ames Blockage Criterion for Low Speed, Subsonic Flow

Herriot, John G.: Blockage Corrections for Three-Dimensional-Flow Closed-Throat Wind Tunnels, with Consideration of the Effect of Compressibility. NACA TR 990, 1950

4

Assumes  Airspeed  correc:ons  for  Flow  expansion  around  model  

CD( )corrected =CD( )measured

1+ 14! AmodelAtestsec tion

"

#

$$

%

&

''

(

)

***

+

,

---

2

MAE 5930, Rocket Systems Design 14  

Wind Tunnel Blockage Effects (3)

Example, 10% Model Blockage, Measured Airspeed 50 m/sec

Actual airspeed at Model Maximum cross section … 55 m/sec

Measured Drag Coefficient = 0.4 … Corrected drag Coefficient

Herriot, John G.: Blockage Corrections for Three-Dimensional-Flow Closed-Throat Wind Tunnels, with Consideration of the Effect of Compressibility. NACA TR 990, 1950

CD( )corrected =

MAE 5930, Rocket Systems Design

Wind Tunnel Instrumentation

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MAE 5930, Rocket Systems Design

Wind Tunnel Instrumentation (2)

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MAE 5930, Rocket Systems Design

Wind Tunnel Instrumentation (3)

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MAE 5930, Rocket Systems Design

Wind Tunnel Instrumentation (4)

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MAE 5930, Rocket Systems Design

Wake Survey Results

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MAE 5930, Rocket Systems Design 20

Questions??