Effect of Squealer Geometry on Tip Flow and Heat Transfer for a Turbine Blade in a Low Speed Cascade

摘要

A detailed investigation on the effect of squealer geometries on the blade tip leakage flow and associated heat transfer is presented for a scaled up high pressure turbine blade in a low-speed wind tunnel facility. The linear cascade is made of four blades with the two corner blades acting as guides. The tip profile of a first stage rotor blade is used to fabricate the two-dimensional blade. The wind tunnel accommodates an 116° turn for the blade cascade. The mainstream Reynolds number based on the axial chord length based on cascade exit velocity is 4.83 X 10~5. An upstream wake effect is simulated with a spoked wheel wake generator placed upstream of the cascade. A turbulence grid placed even farther upstream generates a free-stream turbulence of 4.8%. The center blade has a tip clearance gap of 1.56% with respect to the blade span. Static pressure measurements are obtained on the blade surface and the shroud. Results show that the presence of the squealer alters the tip gap flow field significantly and produces lower overall heat transfer coefficients. The effects of different squealer arrangements are basically to study the effect of squealer rim placement on tip leakage flow and associated heat transfer. Detailed heat transfer measurements are obtained using a steady state liquid crystal technique. The effect of periodic unsteady wake effect is also investigated by varying the wake Strouhal number from 0-0.4. Results show that suction side squealers may be favorable in terms of overall reduction in heat transfer coefficients over the tip surface. However, the presence of a full squealer is most beneficial in terms of reducing overall heat load on the tip surface. There is reasonable effect of wake induced periodicity on tip heat transfer.