Response of a Vibrating Plate in a Fluid 



was Intended to simulate the clamped edge condition. The panel 

 formed most of one wall of a rigid cavity measuring 14X8X6.6 

 inches. The other surface of the panel was exposed to the flow field. 

 The pressure differential across the panel was variable. The experi- 

 ment was conducted at two pressure differentials, viz. 0.06 and 

 14 psi; the latter corresponds to the actual differential between wind 

 tunnel pressure and local ambient. 



The side wall of the tunnel was modified to accommodate 

 two identical, rigid, steel plates, which supported the necessary- 

 instrumentation. One plate contained an array of holes in which 

 pressure transducers were mounted. The pressure transducers 

 were mounted on the center-line of the tunnel in the streamwiise 

 direction at the same locations where the mean static pressure 

 measurements were made. Two types of pressure transducers 

 were used; one, the conventional lead zlrconate tltanate type made 

 by Atlantic Research, the other a capacitance type made by Photocon 

 Corporation with sensitive diameters of 0.06 Inch and 0.09 Inch 

 respectively. Correction due to finite size transducers was made 

 adopting the Corcos [ 1963] approach. The panel displacement was 

 measured with Photocon capacitance, displacement transducers 

 mounted on brackets which could slide along a bar and could be set 

 precisely by means of a screw mechanism. 



The output of both pressure transducers and dlsplacennent 

 transducer were recorded on Ampex FR-1800H 14- channel tape, 

 recorded In the FM mode. Four channels were used for simultane- 

 ously recording data for correlation measurements. The mcixlmum 

 dynamic range was obtained by splitting each data channel into two 

 tape tracks through phase matched filters to separate the lower and 

 higher frequencies. 



b) The Wall Pressure Field 



Measurements Indicated that the flow field In front of the 

 shock closely approximated the properties of equilibrium of an adl- 

 abatlc flat-plate boundary layer [ Maestrello 1968] . The flow In 

 front of the shock has the following characteristics: Mach number 

 Me =3,03, free stream velocity Ue = 2,100 ft/sec, total tempera- 

 ture Tf = 567° R, boundary layer thickness 6 = 1,3 7 Inch, bound- 

 ary layer displacement thickness 6* = 0.445 Inch, momentum thick- 

 ness = 0,083 Inch, Reynolds number R = Ue6/U = 4.87 X 10°, skin 

 friction coefficient Cf = 1.27 X 10 , and ■C^R^=39.8 Coles param- 

 eter [ Coles 1964] . 



The pressure ratio across the shock Is a well defined function 

 of Mach number, for a 1 5° half- cone angle, the pressure ratio Is 

 approxlnnately 8.5. Experimental results show, however, that this 

 ratio Is considerably smaller (Ap = 2.3). It Is postulated that inter- 

 action with an expansion wave originating at the base of the wedge is 

 responsible for lowering the pressure differential and producing an 



479 



