On flow structure in an oscillating-triangular-jet nozzle: Conditionally-averaged wall pressure

Abstract

A jet flow from a triangular-inlet orifice can be made to oscillate or “precess” by partially confining it with a short cylindrical chamber. However, for a narrow range of chamber lengths, the jet is deflected but does not oscillate. Earlier flow-visualisation experiments with this stationary-deflected triangular jet (SDTJ) have revealed a complex flow pattern inside the chamber. The aim of this study is to discover by conditional averaging if there is a similar flow pattern in the fully oscillating jet flow. A backward-facing pressure probe placed in the reattaching flow region of the chamber surface is used as a detector of jet-flow oscillation. With the signal from this detector and simultaneous wall-pressure measurements, we have obtained conditionally-averaged pressure distributions on the wall of the oscillating-triangular-jet (OTJ) nozzle. The OTJ surface pressure distributions have the same features as the time averaged SDTJ surface-pressure distribution, and so the inferred OTJ surface-flow topology has the same features as the SDTJ. However, for the OTJ, the chamber is twice as long, and the conditionally-averaged pressure distribution is much more asymmetrical about a mirror plane drawn through the axis of the nozzle and the detector probe. We conclude that the net radial force due to the asymmetric pressure distribution is large enough to produce significant deflection of the OTJ flow in directions normal to the chamber axis.