Experimental Investigation of the Flow Through Axisymmetric Expansions

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Abstract
This study examines the flow field in three axisymmetric expansions having diffuser half-angles of 14, 18, and 90 deg, respectively. Velocity measurements were performed at a Reynolds number of Re = 1.56 × 104 using a single component LDA operated in forward scatter. The test facility was refractive index matched, allowing measurement of the velocities U , V , W , u2 , v2 , w2 , uv and uw upstream of, and throughout the entire recirculation region. The results indicate that the diffuser geometry influences the separated shear layer appreciably over the entire length of the diffuser section. The production of turbulence immediately after separation is much higher in the case of the 14 and 18 deg diffuser compared to the 90 deg expansion, leading to higher diffusion rates in the separated shear layer, and hence earlier reattachment of the shear layer.

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