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Application of LDV to Investigation of Turbulent Scparation-Reattachment Flow in a Curved-Wall Diffuser

A 2-D laser velocimeter was employed to study the turbulent separation-reattachment flow field in a 2-D diffuser which is a lower curved wall and upper flat plate. There is a parallel channel connected with the exit of the diffuser. In the inlet of the diffuser, the Reynolds number is 5,000 based on the momentum thickness and the inlet velocity is 25.2 m/s. Mean velocity and Reynolds stresses were measured from upstream of the separation to the downstream of the reattachment. The minimum distance from the surface is 0.3 mm. The significant factors were that after TD, within the reversing flow, there exists the second extreme of u and minus of -ιΓν. Normal stresses and cross-stream pressure gradient are important immediately in the separating flow and associated with strong streamline curvature. The maximum of the displacement thickness curvature K * , ^ corresponds to the intermittency transitory detachment. Several velocity profiles and Cebeci & Smith algebraic eddy-viscosity are compared with the experiment. A new approximate correction of the effect of normal stress is supposed and could be in agreement with the experiment before the transitory detachment.