chp 4 hypersonics 4

8/17/2019 Chp 4 Hypersonics 4

http://slidepdf.com/reader/full/chp-4-hypersonics-4 1/15

Hypersonic Educational Initiative

Viscous Interactions

4.1 Leading-Edge Interactions

4.2 High-Altitude Vehicle Aerodynamics Scaling

4.3 Shock-Boundary Layer Interactions;

Shock-Shock Interactions




Leading-Edge Interactions

or Viscous Interactions

• Consider a flat plate in a hypersonic stream

• Boundary layer displaces the flow:

– Shock wave forms

– Pressure rise compresses the BL, introduces an

axial pressure gradient

– Changes growth of BL, which affects shock

• Use theory to determine scaling of this effect

Shock Wave

Boundary Layer Displacement, !*

M >> 1




Leading-Edge Interactions

or Viscous Interactions

• CFD solutions:

Adiabatic Wall

M = 6, Re = 284,000 based on plate length

Cold Wall: Tw/Te=2





• Use approximate variation of pressure with flow

turning angle to derive variation of displacement

thickness with M and Re

Adiabatic Wall Cold Wall

Strong

Weak





• Comparison of theory with CFD:





Viscous Interactions:

Vehicle Scaling

• Aerodynamic coefficients scale differently:

• Viscous interactions tend to increase drag, but not

change lift much

– L/D should scale with

– CD should increase with

– Effect is larger for vehicles with large wetted area

• Approach free-molecular limit at very low density

(large )




Viscous Interactions:

Vehicle Scaling

From Anderson (1989) and Stollery (1972)





• Edney classified shock interactions into 6 types:




Shock-Shock Interactions:

Example

Mach 14.2, ReD=4000 Flow on a Cylinder with a 10o Shock Generator




Shock-Shock Interactions:

Example

• Huge increase in surface pressure and heat flux

Surface Pressure and Heat Flux Relative to Undisturbed Flow

Note compression of BL





• Huge localized pressure and heating augmentation

– Jet compresses boundary layer

– In reality, jet is unsteady

– Augmentation for turbulent flow, reacting gas is

difficult (impossible) to compute.

• Strength decreases with cylinder sweep

– Limited experiments in this area: Berry and Nowak

• S-SI must be avoided or designed around

– Bow shock – wing-leading edge interaction




Shock-Boundary Layer

Interactions

• Shock impinges on a boundary layer

CFD of a 2D Shock-Boundary Layer Interaction

Compression of BL

Separation





Interactions

• CFD of a 2-D Laminar Mach 6 SW-BL Interaction





Interactions

• SBLI also cause high localized pressure & heating

• SBLI also occur on compression corners:

– If laminar, separation is large; shear layer

transitions at all but lowest Re

– Turbulent separation is much smaller, unsteady?

• Tend to be a much larger issue inside engines

• Difficult (impossible) to accurately compute high

Mach number turbulent interactions

chp 4 hypersonics 4

Documents