Jet pipe reflections - Influence of geometrical and flow exit conditions

Abstract

In this paper, we study the influence of the exit conditions on the acoustic reflections at a jet pipe opening. For the flow exit conditions, the model of Munt assuming a vortex sheet at the exit of a semi-infinite jet pipe is improved by considering more general coupling conditions. We focus on modelling the acoustic properties at the shear layer in general and the stability properties in particular. Experimental methods are used for studying primarily the geometric exit conditions. Both theoretical and experimental results are presented and discussed. Numerical results related to the theory show that the thickness of the shear layer causes an expected increase in the magnitude of the reflection coefficient compared to the original infinitely thin shear layer in the Munt model. The experimental results, on the other hand, show that there are additional effects due to the presence of thick walls at the exit of the straight pipes used in the experiments. These effects are observed to be more dominant than the effects due to the shape of the edges. Based on the discussions, further theoretical and experimental investigations are proposed. © 2010 by the American Institute of Aeronautics and Astronautics, Inc. © 2018 Elsevier B.V., All rights reserved.