Differential Stress Modelling of Turbulent Flows in Model Reciprocatin G Engines

Lea, C J; Watkins, A P
February 1997
Proceedings of the Institution of Mechanical Engineers -- Part D;1997, Vol. 211 Issue 1, p59
Academic Journal
A study is made here of the application of a differential stress model (DSM) of turbulence to flows in two model reciprocating engines. For the first time this study includes compressive effects. An assessment between DSM and k--ℇ results is made comparing with laser Doppler anemometry experimental data of the mean flow and turbulence intensity levels during intake and compression strokes. A well-established two-dimensional finite-volume computer code is employed. Two discretization schemes are used, namely the HYBRID scheme and the QUICK scheme. The latter is found to be essential if different iation is to be made between the turbulence models. During the intake stroke the DSM results are, in general, similar to the k--ℇ results in comparison to the experimental data, except for the turbulence levels, which the DSM seriously underpredicts. This is in contrast to a parallel set of calculations of steady in-flow, which showed significant gains from using the DSM, particularly at the turbulence field level. The increased number of grid lines employed in those calculations contribute to this apparent difference between steady and unsteady flows, but cycle-to-cycle variations are more likely to be the primary cause, resulting in too high levels of turbulence intensity being measured. However, during the compression stroke the DSM returns vastly superior results to the k--ℇ model at both the mean flow and turbulence intensity levels. This is because the DSM generates an anisotropic shear stress field during the early stages of compression that suppress es the main vortical structure, in line with the experimental data.


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