Design and Construction of a Mach 2 Wind Tunnel For Cavity Acoustics Research

Abstract

Cavity flow is encountered in many practical applications of ground and air vehicles operating at high speed. Examples include airflow past open windows, sunroofs, and wheel-wells of automobiles as well as landing gear and weapon bays of aircraft. Cavity flow becomes a design consideration at high-speeds hence research in the area of supersonic cavity acoustics is more motivated by military applications. In a typical cavity, the compressible shear layer separating from the front end of a cavity impinges on the rear wall and initiates a sequence of events consisting of intense edge tones, high decibel acoustics and resonance that leads to fluid-structure coupling, unsteady loads, and structural vibrations. Furthermore, the trajectories of the weapons released from an internal weapon bay become unpredictable resulting in the released store hitting the carrier. A Mach 2 wind tunnel was designed using the method of characteristics with a viscous approximation to conduct research is the area of cavity flow acoustics. Unique features of the supersonic wind tunnel include a modular design for quick changes in cavity configuration and optical access from all sides for qualitative and quantitative design techniques including multiple plane schlieren/shadowgraphy, anemometry, particle image velocimetry and high speed photography. The designed nozzle blocks and windows were machined on a CNC machine of the AE machine shop and assembled in the aerodynamics lab. Pressure signal histories and schlieren images suggest that the wind tunnel operated at designed values.