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MAE 5930, Rocket Systems Design MAE 5930, Rocket Systems Design
Wind Tunnel Testing: Setup and Procedures
MAE 5930, Rocket Systems Design
Wind Tunnel Types
2
Closed Circuit Tunnel P0( )tunnel ! pambient
MAE 5930, Rocket Systems Design
Wind Tunnel Types (2)
3
Our Tunnel is an “Open Circuit” Tunnel
P0( )tunnel ! pambient
MAE 5930, Rocket Systems Design
About Wind Tunnel Testing
4
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)
8
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)
9
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
15
MAE 5930, Rocket Systems Design
Wind Tunnel Instrumentation (2)
16
MAE 5930, Rocket Systems Design
Wind Tunnel Instrumentation (3)
17
MAE 5930, Rocket Systems Design
Wind Tunnel Instrumentation (4)
18
MAE 5930, Rocket Systems Design
Wake Survey Results
19
MAE 5930, Rocket Systems Design 20
Questions??
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