Transition fixing for hypersonic flow

Present wind-tunnel f a c i l i t i e s lack the capability t o duplicate the Reynolds number associated with the hypersonic-cruise vehicle.overcoming t h i s problem, a t t e n t i o n i s being given t o a r t i f i c i a l promotion of t r a n s i t i o n by means of surface roughness.A t lower speeds, boundary-layer roughness has been used successfully.However, a t hypersonic speeds, the required roughness height i s so large t h a t the method raises many questions.This paper considers these questions and examines the overall problems associated with boundary-layer "trips" t o produce turbulence a t hypersonic conditions. As a means ofThe data indicate that the required roughness heights a r e so large t h a t For example, an engineer can success-whether t r i p s should be used i n hypersonic wind-tunnel t e s t s depends upon the particular purpose of any experiment.f u l l y use t r i p s t o study the heat t r a n s f e r associated with an a i r c r a f t component or t o produce turbulent f l o w i n front of an i n l e t or control t h a t otherwise m i g h t be t r a n s i t i o n a l or laminar.cannot be used when an accurate value of the t o t a l drag of a configuration i s required because of the large pressure drag associated with the roughness elements.With additional study, the drag associated with the roughness elements could probably be determined accurately.The vortex shedding that occurs i n the l e e side of d e l t a wings a t moderate angles of attack places further l i m it a t i o n s on the use of t r i p s f o r wind-tunnel simulations of hypersoriic cruise vehicles.For any t e s t , care must be taken t o dimension the t r i p s properly.However, a t the present time, t r i p s