Unsteady supersonic inlet cascade aerodynamics—a schlieren study

Abstract

The fundamental mechanism of many aerodynamic-vibration problem areas currently being investigated with regard to the development of advanced fan and compressor components is directly related to unsteady cascade aerodynamic phenomena. Such problem areas include: discrete frequency noise generation; forced vibration phenomena due to wakes from upstream obstructions, inlet distortion, or turbulence; and self-excited vibrations, in particular, supersonic inlet torsional flutter. This paper describes the flow visualization of a unique unsteady supersonic inlet two-dimensional cascade experiment wherein five flattened double-wedge-shaped airfoils are cantilevered and mounted in a mirrored sidewall. This mirrored sidewall serves as a tunnel wall as well as a reflective surface in the double-pass schlieren system, thereby providing flow visualization. The cascade was tuned to and excited at a torsional frequency of approximately 100 Hz. Over a Mach number range of 1.4–1.67, the cascade was excited, the excitation stopped, and the resulting dynamic stability observed and recorded. High-speed color schlieren movies (5000 frames per second) of the unsteady cascade phenomena including the effect of interblade vibratory phasing angle and shock wave-airfoil interaction were made and are presented. [This work was supported, in part, by the Power Program, Office of Naval Research, under Contract N00014-72-C-0351.]