Title: An experimental study of the transient flow over a backward-facing step
Abstract: The phase averaged behavior of the velocity field behind a backward facing step during pulsatile flow was measured using laser velocimetry. Results showed a periodic growth and shrinkage of the recirculation zone downstream of the step in response to inlet mass flow pulsations at frequencies of 0-10 Hz. This behavior was shown to deviate from a quasi-steady representation of the flow. The magnitude of the reaction to inlet flow transients is governed by the levels of acceleration applied to the inlet flow. Tnfrnrinpfinn The flow over a backward-facing step is a simple, separated, reattaching flow. The flow is inherently unsteady, due to the presence of vortices of various sizes. Many studies have investigated the dynamics of this flow under steady boundary conditions. However, the assumption of steady, invariant boundary conditions is an unrealistic ideality in some applications. Transients are common in most engineering devices. Most machinery does not operate in a steadystate for any length of time. In the reacting flow in a jet engine, the air flow and fuel flow being delivered to the combustor change drastically over a period of a few seconds during takeoff. In a gas turbine, other phenomena, such as axial flow compressor stall and compressor surge, can also cause rapid changes in the air flow to the combustor. As shown in Figure 1, axial compressor surge can deliver large-amplitude, lowfrequency (typically ~10 Hz) oscillations in the air flow rate, as indicated by the large variations in compressor pressure ratio. An important part of any continuous combustion process is flame stabilizatioa Without it, combustion cannot sustain itself. Stabilization is governed in terms of both chemical and fluid mechanic time scales. For the sake of simplicity, this discussion will focus on premixed combustion phenomena, rather than the more complex phenomena involved in non premixed systems. 103
Publication Year: 1996
Publication Date: 1996-01-15
Language: en
Type: article
Indexed In: ['crossref']
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Cited By Count: 9
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