Abstract

LEWIS, K. L.  and  VON BACKSTROM, T. W.. The experimental optimization of an annular dump diffuser. R&D j. (Matieland, Online) [online]. 1991, vol.7, pp.7-15. ISSN 2309-8988.

Dump diffuser performance is influenced by dump gap, flow split and prediffuser geometry. Maximum static pressure recovery is normally obtained at a flow split different from the ratio of the outer to inner annulus area. To ensure that the optimal flow split occurs at the design value the prediffuser can be canted so as to bias the flow towards one of the annuli. An extensive experimental program was undertaken to define the optimum prediffuser geometry for a predefined diffuser/combustor combination with a fully developed turbulent profile at inlet. Variables included dump gap and prediffuser cant angle, area ratio and length. A 3% improvement in diffuser effectiveness and a 5% reduction in loss was obtained by canting the prediffuser such that the optimal flow split coincided with the design value. A symmetrical distribution around the combustor dome was obtained at this condition. It was found that the prediffuser area ratio could be reduced to below the overall area ratio without significantly affecting the overall performance. Skewing the velocity profile towards the inner and outer walls affected the overall performance of the diffuser configurations but did not change the optimum prediffuser geometry. Decreasing the prediffuser length to below that indicated by the Cp* line but retaining the same mean cant angle and area ratio influenced the overall performance detrimentally; skewing the inlet profile tended to exacerbate this further.

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