Resonance frequencies of ventilated wind tunnels

Abstract

Experiments suggest that the theory widely used to predict the transverse resonance frequencies in slotted tunnels is in error in the Mach number range from 0 to 0.5. One reason for the error is that the theory is based on an unrepresentative wall boundary condition. Moreover, the theory implies that the plenum chamber surrounding the working section is large, whereas the plenum chamber depth is generally less than twice the tunnel height. An improved theory is developed, which shows that the resonance frequencies of ventilated tunnels are influenced by the depth of the plenum chamber for Mach numbers up to about M - 0.6. Although the theory is approximate, it agrees well with experiments for slotted and perforated walls (with both normal and 60o inclined holes). The results are consistent with other experiments which show that plenum chamber design can influence the flow unsteadiness within the working section of a ventilated tunnel.