Investigations of Heat Transfer and Fluid Flow in the Pocket Region of a Gas Turbine Engine and Cooling of a Turbine Blade

Abstract: In the present work, heat transfer within gas turbine applications are investigated bothexperimentally and numerically. The main content concerns heat transfer and fluidflow over the pocket region and cooling of a turbine blade.A pocket cavity is generated at the junction part of the low pressure turbine (LPT) andthe outlet guide vane (OGV) in the rear part of a gas turbine engine. The heat transferdistribution and fluid flow over the pocket cavity have significant effects on theincoming flow of the OGV placed downstream. These pocket cavities are built withdifferent radii to find out improved heat transfer distributions and flow patterns. Theeffects of a pocket cavity on heat transfer and flow characteristics on the endwall witha symmetric vane are also investigated. The relative location between the pocketcavity and the symmetric vane is varied. In addition, the effect of incoming flowattack angle of the pocket cavity upstream of an OGV is investigated numerically.Liquid Crystal Thermography (LCT) is employed to measure the heat transfer of thetested surfaces. The results show that the smaller fillet radius provides a higher heattransfer peak value with a stronger recirculating flow inside the pocket cavity. When apocket cavity is placed upstream of the symmetric vane, the high heat transfer areasaround the symmetric vane are decreased. The attack angles of the incoming flow overthe pocket cavity affect the forming of horseshoe vortices in leading edge of the vaneand then affect the heat transfer distribution.Rib turbulators are widely employed in internal cooling passages of a turbine blade.Firstly, truncated ribs with various truncation types and arrangements are considered.Secondly, perforated ribs with differently shaped penetration holes and perforationratios are investigated. LCT is employed to measure surface temperature and deriveheat transfer coefficients over the ribbed surfaces in the tested channels. The turbulentflow details are presented by numerical calculations with an established turbulencemodel, i.e., the k-ω SST model. From the results, the truncated ribs can reduce thepressure loss penalty without reducing the heat transfer enhancement. By changing theconfigurations to staggered arrangements, the heat transfer can be further enhancedassociated with a moderate pressure drop. By using perforated ribs, the low heattransfer regions downstream of the rib rows are greatly improved.Endwall film cooling is a significant cooling method to protect the endwall regionwhere the flow structures are complex due to horseshoe vortices and generatedsecondary flows. This study firstly concentrates on film cooling holes arrangedupstream of the leading edge of a turbine vane. Several arrangements are designedaiming at improving the coolant coverage. Based on the calculated results, the filmcooling holes upstream the leading edge have cooling effects on both the vanesurfaces and the endwall. A case with two rows of compound angle holes in staggeredarrangement shows relatively high overall averaged cooling effectiveness independentof the blowing ratios. Then full-scale endwall film cooling is also investigated in thisstudy. The film holes arrangements are designed based on the pressure coefficientdistribution, streamline distribution and heat transfer distribution on the endwall. Withcompound angle holes, the design based on the pressure distribution forces the flowsto the suction side, which creates benefits for cooling the vane surfaces. The designbased on the streamline distribution has more uniform coolant coverage on theendwall. The design based on the heat transfer distributions has relatively largecoolant coverage and is effective in removing the high temperature region.Keywords: pocket cavity, symmetric vane, Liquid Crystal Thermography, truncatedribs, staggered arrangement, perforated ribs, secondary flows, endwall film cooling,leading edge, turbine vane, coolant coverage