A State-of-the-Art Report on Aeroacoustic Testing in Conventional Wind Tunnels

Abstract

The increasing attention given to aerodynamically generated noise brings into focus the need for quality experimental research in this area. To meet this need, several specialized anechoic wind tunnels have been constructed. In many cases, however, it is desirable to use conventional wind tunnels. Two basic problems are inherent in conventional facilities; high background noise and strong frequency-dependent reverberation effects. This paper reviews the known acoustic characteristics of several existing tunnels and presents new data obtained in a conventional 7 × 10 wind tunnel and a smaller 4 × 5 wind tunnel, which is convertible from a closed-jet to an open-jet mode with an anechoic test section. The data from the smaller tunnel serve as a guideline for evaluating design techniques involving a closed-jet and sandwich-wall construction. Model scaling parameters and data reduction techniques are also considered. It is concluded that existing conventional wind tunnels can be utilized for aeroacoustic measurements. The overall technique, however, will require a careful balance of acoustic treatment, selection of proper model scaling, experimental technique, and data reduction schemes. Several suggestions are offered that are pertinent to a relatively large, low-speed wind tunnel facility.