Flow Separation Prevention on a Turbine Blade in Cascade at Low Reynolds Number

摘要

The problem of flow separation from a low pressure turbine blade was investigated. The operating conditions under which the separation occurred were documented through measurement of surface pressure coefficients, boundary layer velocity and turbulence profiles, total pressure loss coefficient and wake velocity momentum deficit. Three different means for reducing the losses associated with the flow separation were also investigated. A boundary layer trip, dimples, and V-grooves were studied as passive means requiring no additional energy to reduce the separation losses. The boundary layer trip was only successful for an inlet and axial chord Reynolds number of 50k with a reduction in loss coefficient of 58.2%. Three sets of dimples were tested with the placement of each at axial chord locations of 50%, 55%, and 65%. The dimples provided reductions in the loss coefficient for Reynolds numbers of 50k, 100k, and 200k ranging from 5.1% (Re = 100k, freestream turbulence level of 4%) to 51. 7% (Re = 50k, freestream turbulence level of 4%). Two sets of V-grooves were tested with axial chord start locations of 55% and 60%. The V-grooves provided smaller reductions in loss coefficient than the dimples. Boundary layer profiles, total pressure loss coefficients, and wake velocity momentum deficits are presented for the three passive modifications.