Effects of Blade Leading Edge Fillet on Near Wall Pressure and Heat Transfer in a Linear Turbine Cascade

Abstract

Thermal stresses and failure of components in the gas turbine passages are common due to exposure of the passage walls to extremely hot combustion gasses. In addition, the gas turbine engine efficiency suffers due to secondary flows and passage vortex formations in turbine passages. Investigations are being conducted to reduce the thermal stresses and secondary flows in the turbine passages with endwall modifications and film cooling. The present investigation employs two types of fillets at the junction of blade leading edge and endwall in a low speed linear blade cascade to control the effects of passage vortex. Blade and endwall static pressure, axial vorticity and air temperature near endwall, and Nusselt numbers on endwall and blade wall are measured and presented in the cascade passage with and without the leading edge fillets. A constant Reynolds number of 233,000 based on the blade chord and the inlet velocity is employed for the measurements. The blade profile is obtained from the hub-side of first stage blade in the GE-E3 gas turbine and scaled 10 times in the present cascade. One of the two fillet shapes has a linear profile from the blade to endwall (Filet 1), and the other has a parabolic profile (Fillet 2) from the blade to endwall. Fillets are employed only at the blade leading edge at the bottom endwall. Results on axial vorticity and air temperature indicate that the fillets weaken passage vortex and reduce heat transfer from the endwall. This occurs as the pitchwise endwall pressure difference from the pressure side to the suction side is reduced near the filleted region. However, the distributions of wall static pressure coefficients and Nusselt numbers along the blade surface are about the same with and without the fillets and indicate no effects from the fillets on the blade surface. The blade-loadings are thus unaffected and require no design modifications with the fillets. The endwall Nusselt number distributions show lower values for the fillets than for the baseline (without fillets) which also indicate reduced heat transfer to or from the endwall. The results of the present investigations thus can be applied in designing the blade passages where the secondary flow effects are passively controlled and endwall thermal stresses are reduced.