Prediction of Resonance Frequencies for Ventilated Wall Wind Tunnels,
NATIONAL AERONAUTICAL ESTABLISHMENT OTTAWA (ONTARIO)
Pagination or Media Count:
Based on the reflection and refraction of plane acoustic waves at an interface between the moving stream and the stagnant plenum air, a simple theory is developed for ventilated walls. The intensity and frequency of resonance are determined from the modulus and the argument of the wall reflection coefficient respectively. In contrast to the eigenvalue method, the present technique is capable of predicting partial resonance, occuring in perforated walls and also in slotted walls at Mach numbers below 0.618, for which the resonant waves are partly reflected and partly transmitted at the wall. The reverse transmission of waves from the plenum into the test section is found to be inconsistent with the postulated resonance condition and is therefore not considered.