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A Study of Acoustic Disturbances and Means of Suppression in Ventilated Transonic Wind Tunnel Walls

The use of ventilated test section valle is the standard practice 
for establishing flows near Mach 1.0 In vind tunnels. Guidelines for 
choosing the configuration of the ventilated test section walls and the 
relative aerodynamic performance of various configurations are discussed 
in Ref. l. However, most Of the configurations produce intense aero— 
dynamic noise in the test section, e.g., Refs. 2 through 6, In some 
cases exceeding 152 db (Ref. 0.0002 dynes/cm2) 
the free—stream dynaic pressure of the flow. 
section n11g vere found to be the predninant 
dynamic noise. 
There is growing concern that aerodynamic noise found In transonic 
vind tunnels can have potentially deleterious effects on test data. Two 
Investigations vh1ch have shovn effects to exist are the boundary—layer 
transition data correlation in Ref. 7 and the buffet and vibration data 
studies In Ref. 8. 
With this In mind, the reduction of aerodynamic noise in transonic 
tunnels has been an ob3ective of experimental research at AEDC for 
several years. of the results of this research has been the ' 'splitter 
modification for perforated walls (Ref. 9). This "splitter 
plate" modification iB a proposed device for suppressing edgetones {n 
perforated walls which have 60—deg Inclined holes such as the test 
section walls in the Arnold Engineering Development Center (ADC) 
transonic wind tunnels.

A recently developed technique giving effective suppression of 
edgetones in variable—porosity perforated walls having 60—deg inclined 
holes 18 vire acreen overlay. The screen overlay vas In 
the Space Flight Center 14—1n. Transonic Wind Tunnel and 
Is described {n Ref. 12. Both the "ep11eter plate" and the vire screen 
overlay noise suppression schemes have been used vith success on 
experimental vall samples In the ONERA 6— by 6—ft tunnel at bdane, 
France, vhleh algo has 60—deg Inclined—hole, variable—porosity valls 
(see. Ref. 13).