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
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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??
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