Maestrelto and Linden 



the action of discontinuities like tear stoppers, etc. , have little 

 effect on altering sound pressure level, since the sound radiation by 

 the panel is in the form of Mach wave radiation. 



The experiment described in this paper indicates that some 

 simplifications in the model can be made, viz. (i) that there is no 

 significant interaction between the plate and the aerodynamic forces 

 on the plate; and (2) that the panel displacement is small in compari- 

 son to its thickness so that thin plate theory may be used. The plate 

 is, however, acoustically coupled to the external flow field and the 

 internal cavity. 



Lyamshev [ 1968] has solved a similar problem for a com- 

 plex structure. Dowell [ 1969] computed the transient, non-linear 

 response of a simply supported plate coupled to an external flow 

 field and a cavity. Dzygadlo [ 1967] presented a linear analysis 

 allowing mutual interaction between the plate and the external flow. 

 Fahy and Pretlove [ 1967] have computed a first order approximation 

 to the acoustic coupling of a flexible duct wall to the flow field through 

 the duct. Maidajiek [ 1966] considers an infinite, orthotropic plate 

 coupled acoustically to an external flow field. Numerous other in- 

 vestigations have been reported on acoustically coupled structures 

 with varying degrees of approximation, Irgens and Brand [ 1968] , 

 White and Cottis [ 1968] , Strawderman [ 1967] , Creighton [ 1970] , 

 Ffowcs- Williams [ 1966] , Crighton and Ffowcs- Williams [ 1969] , 

 Dolgova [ 1969] , Feit [ 1966] , Lapin [ 1967] , Pal'tov and Pupyrev 

 [1967] . 



II. MEASUREMENTS 



a) The Experimental Arrangement 



The flow investigated was the sidewall boundary layer of the 

 Jet Propulsion Laboratory 20- inch supersonic wind tunnel; the shock 

 was induced by a 30° wedge mounted outside the boundary layer, 

 off-center and on the same side that the measurements were made. 

 This was done to offset the position of the reflected shock from the 

 opposite wall. The position of the shock was determined by observing 

 the displacement of a line of tufts , and by a static pressure survey. 

 For zero pressure gradient, detail of flow field and panel response 

 has been previously reported by Maestrello [ 1968] . 



The experiment was arranged to performi three basic measure- 

 ments: mean velocity profile ahead of the shock with static pressure 

 distribution across the shock, wall pressure fluctuations and measure- 

 ment of displacement response of a simple panel structure. The 

 titanium test panel measure 12X6 X0.0 62 inches and was brazed 

 on all four sides of a 3/4 inch X 3/4 inch titanium fram.e. The brazing 



■if, 



TI-6AL-4V Titanium alloy containing 6% aluminum, 4% vanadium, 

 90% titanium. 



478 



