City Research Online

Abstract

It is well known that unsteady combustion can generate temperature fluctuations (also known as entropy waves or “hot/cold spots”). These entropy waves remain silent when advected by a non-accelerated mean flow, but generate additional sound (or "noise/acoustics") when accelerated. The mean flow can be accelerated, for instance, by a nozzle or a sudden cross-sectional area change, i.e. a hole. Several analytical models that predict entropy noise in nozzles exist for a wide range of parameters. However, these models, which are often based on inviscid and one-dimensional assumptions, are believed to be inadequate for holes. Several mechanisms may need to be considered when entropy waves interact with holes, e.g. flow separation, vortex shedding, multi-dimensional effects or non-isentropicity. In the present work, we study the effect of the entropy profile (mainly affected by f low separation) on the generation of entropy noise. To this end, an analytical model based on a strict acoustic analogy formulation of the problem is developed. Subsequently, an analytical solution is obtained by using the Green’s function method.

Publication Type:	Conference or Workshop Item (Paper)
Publisher Keywords:	Entropy noise, Hole acoustics, Flow contraction, Flow expansion
Subjects:	T Technology > TL Motor vehicles. Aeronautics. Astronautics
Departments:	School of Science & Technology > Engineering

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