An Experimental Study of the Receptivity of a Compressible Laminar Boundary Layer and the Effects on Stability and Receptivity of 2-D and 3-D Pressure Gradients

Techniques have been developed to provide, for the first time, pure tone acoustic forcing with a wave packet having a particular wave vector and at instability wave frequencies for a supersonic boundary layer. Receptivity to this pure tone forcing has been studied, initially with continuous forcing...

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Bibliographic Details
Main Author: Brown, Garry L
Format: Report
Language:English
Subjects:
ACOUSTIC FORCING
COMPRESSIBLE FLOW
COMPUTATIONAL FLUID DYNAMICS
DISTURBANCES
Fluid Mechanics
FREE STREAM
LAMINAR BOUNDARY LAYER
PRESSURE GRADIENTS
RESPONSE
STABILITY
SUPERSONIC FLOW
THREE DIMENSIONAL
TONE FORCING
TRANSITIONS
TWO DIMENSIONAL
WAVE PACKETS
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Summary:Techniques have been developed to provide, for the first time, pure tone acoustic forcing with a wave packet having a particular wave vector and at instability wave frequencies for a supersonic boundary layer. Receptivity to this pure tone forcing has been studied, initially with continuous forcing and now with well defined wave packets. In the latter case precise measurements can now be made of the detailed response to the free-stream disturbance. The wave velocity and wave vector in the free-stream have been determined consistently. A preliminary finding from the wave packet experiments is that the boundary layer response is broadly in two parts; one which is a local forced response in phase with the free-stream forcing and the other which, at downstream locations, has larger amplitude, is growing with downstream distance and has a significant time delay compared with the first forced response. The explanation for this second wave packet and its relation to the first is not yet clear and is the present subject of detailed investigation. Once the data and an understanding are obtained with the present U + a wave forcing attention will be focused on U - a waves. It was found in 1, that the stream-wise wavelengths of the instability waves and the acoustic U - a free-stream fluctuations were closely matched and it was speculated that this played an important role in receptivity.