Author : Akash Hiremath 1
Date of Publication :10th May 2017
Abstract: To increase thermal efficiency, advanced gas turbine is designed to operate at increasingly higher temperature. Since the gas temperature exceed the allowable material temperature, cooling techniques of turbine components are increasingly important. Film cooling is a standard method applied to turbine blades and vanes, whereby cold air is injected from small holes which forms a thin layer over walls and protects the wall from high temperature gases. This study describes thermal analysis of film cooled High Pressure Turbine (HPT) blade platform for an Aero Gas Turbine engine using FEM analysis; platform is exposed to combustor exit gas temperature of 1700K and the coolant air at 800K temperature. During this work the coefficient of discharge (Cd) and film effectiveness (ɛ) of film cooling holes is estimated from CFD analysis. Film cooling adiabatic effectiveness estimation is done using Fluent commercial code, Version 14.5. For the Flat plate film cooling model three different RANS turbulence models are studied I. Realizable k-ɛ turbulence model with enhanced wall treatment. II. Standard k-ω turbulence model. III. SST K-ω turbulence model. With the cooling hole inclined at Ɵ the study is performed at density ratio 1.6 with the mainstream and coolant temperatures at298k and 188K respectively and for two different blowing ratios 0.5 and 1. Centreline adiabatic effectiveness and spanwise adiabatic effectiveness is extracted from the different models and compared with the experimental results. The predicted effectiveness and experimental data are in good agreement. The CFD prediction over predicts the effectiveness. Good quality hexa-mesh is created using ICEM CFD multi-blocking method. HPT blade top and bottom platforms is meshed using Tri elements in HYPERMESH and thermal analysis is performed in ANSYS APDL.The calculated adiabatic wall effectiveness is used to calculate the adiabatic wall temperature for both platforms. Isentropic mass flow, coefficient of discharge and blowing ratio through each film hole is determined. Convective HTC (Heat Transfer Coefficient) within the film hole, on the coolant side and along mainstream gas side is calculated based on geometric and flow parameters. Platform metal temperatures are estimated by considering the film cooling effect only and also the effect of impingement cooling combined with film cooling is considered.
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