Wind Tunnel Testing: Setup and Procedures

MAE 5930, Rocket Systems Design Wind Tunnel Types Closed Circuit Tunnel (P0 )tunnel ! pambient

MAE 5930, Rocket Systems Design 2 Wind Tunnel Types (2)

Our Tunnel is an “Open Circuit” Tunnel

(P0 )tunnel ! pambient

MAE 5930, Rocket Systems Design 3 About Wind Tunnel Testing Key issues • Maintaining \, 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 4 Laminar and Turbulent Boundary Layers

• Laminar • Turbulent

MAE 5930, Rocket Systems Design 5 Laminar and Turbulent Boundary Layers (2)

• Location of transition point strongly a function of Reynolds number

Laminar

flow

Transitional

Turbulent

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

MAE 5930, Rocket Systems Design 6 Comparison of Reynolds Number and

Mach Number

Mach number is a measure of the rao of the fluid Kinec energy to the fluid internal energy (direct moon To random thermal moon of gas molecules) -- Fundamental Parameter of --

$ V 2 ' V $ 2 ' %& 2 () M = = & ) " c % ! "(! # 1)( e

Reynold’s number is a measure of the rao of the Ineral Forces acng on the fluid -- to -- the Viscous Forces Acng on the fluid -- Fundamental Parameter of Viscous Flow --

!VL L !V 2 Inertial & Forces Re = = 2 # % µ " $ wall Viscous & Forces

MAE 5930, Rocket Systems Design 7 About Wind Tunnel Testing (2)

V! !" #V" # L flight (Re ) flight = µ" L flight

(Re ) ! (Re )wind flight tunnel Vtest

!test "Vtest " Lmodel (Re )wind = tunnel µtest Lmodel

MAE 5930, Rocket Systems Design 8 About Wind Tunnel Testing (3)

Trip Strip along leading edge of a wind tunnel model

MAE 5930, Rocket Systems Design 9 Types of Drag

Skin Fricon Strongly Effected by Boundary Layer state

W.H. Mason, Virginia Tech MAE 5930, Rocket Systems Design 10 Empirical Skin Friction Correlations

“Smooth Flat Plate with No Pressure Gradient” “Schoenherr Plot”

Re~10,000,000

Effect of Compressibility

Re~500,000

MAE 5930, Rocket Systems Design 11 Wind Tunnel Blockage Effects

Atest = Ai ! Amodel m AV ! = !i i i

Ai

Ai Vtest ! #Vi Ai " Amodel

MAE 5930, Rocket Systems Design 12 Wind Tunnel Blockage Effects (2) NASA Ames Blockage Criterion for Low Speed, Subsonic Flow

4

Assumes Airspeed correcons for Flow expansion around model

(CD )measured (CD )corrected = 2 ( " % + * 1 $ Amodel ' - *1+ ! - 4 $ Atest ' Herriot, John G.: Blockage Corrections for Three-Dimensional-Flow Closed-Throat Wind * # sec tion & - Tunnels, with Consideration of the Effect of Compressibility. NACA TR 990, 1950 ) ,

MAE 5930, Rocket Systems Design 13 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

(CD )corrected =

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

MAE 5930, Rocket Systems Design 14 Wind Tunnel Instrumentation

MAE 5930, Rocket Systems Design 15 Wind Tunnel Instrumentation (2)

MAE 5930, Rocket Systems Design 16 Wind Tunnel Instrumentation (3)

MAE 5930, Rocket Systems Design 17 Wind Tunnel Instrumentation (4)

MAE 5930, Rocket Systems Design 18 Survey Results

MAE 5930, Rocket Systems Design 19 Questions??

MAE 5930, Rocket Systems Design 20