Periodic forcing of a shock train in Mach 2.0 flow

Abstract

High-speed schlieren movies and pressure measurements are collected to analyze the response of a shock train due to downstream forcing. The shock train is generated in a Mach 2.0 ducted flow and controlled by a downstream butterfly valve. Cyclic opening and closing of the valve (at rates up to 10 Hz) leads to oscillations in back pressure measured at the end of the duct. Subsequently, the shock train oscillates between two locations in the duct, traveling at speeds up to 3.5 m/s. Different cases with varied forcing frequency and magnitude of back pressure change are studied. For each case we evaluate the response of the back pressure and shock location by quantifying the magnitude of change, rise time, delay time, and maximum rate of change. Some of the key results include: 1) there is a linear relationship between the magnitude of the shock displacement and the back pressure change that is independent of the forcing parameters; 2) the leading shock in the shock train responds to forcing ≈6 ms after the back pressure starts to change indicating an upstream propagating disturbance; 3) the rise time of the back pressure and leading shock location are approximately the same.

Backpressure propagation mode and balance property in a rectangular duct

“…The result indicated that the analytical method predicts the flow characteristics and structure well. Hunt et al 14 investigated experimentally the response of shock train to downstream backpressure forcing through the schlieren and pressure measurement techniques. They found that the oscillatory motion of shock train and the subsequent backpressure oscillation at the end of duct are formed by the cyclic opening and closing of the throttling valve.…”