In this work, a numerical study has been performed to simulate the heat transfer and fluid flow in a transonic high-pressure turbine stator vane passage. Four turbulence models (the Spalart-Allmaras model, the low-Reynolds-number realizable k-e model, the shear-stress transport (SST) k-ω model and the v2-f model) are used in order to assess the capability of the models to predict the heat transfer and pressure distributions. The simulations are performed using the FLUENT commercial software package, but also two other codes, the in-house code VolSol and the commercial code CFX are used for comparison with FLUENT results. The results of the three-dimensional simulations are compared with experimental heat transfer and aerodynamic results available for the so-called MT1 turbine stage. It is observed that the predictions of the vane pressure field agree well with experimental data, and that the pressure distribution along the profile is not strongly affected by choice of turbulence model. It is also shown that the v2-f model yields the best agreement with the measurements. None of the tested models are able to predict transition correctly. Copyright © 2006 by ASME. (Less)

In this work, a numerical study has been performed to simulate the unsteady fluid flow and heat transfer in a transonic high-pressure turbine stage. The main objective of this study is to understand the unsteady flow field and heat transfer in a single transonic turbine stage using an unsteady structured Navier-Stokes solver. For the time accurate computation, a fully implicit time discretization, dual-time stepping, is performed. The results of the CFD simulations are compared with experimental heat transfer and aerodynamic results available for the so-called MT1 turbine stage. The predicted heat transfer and static pressure distributions show reasonable agreement with experimental data. In particular, the results show significant fluctuations in heat transfer and pressure at mid-span on the rotor blade, and that the rotor has a limited influence on the heat transfer to the NGV at mid span. Copyright (Less)

In the present work, a numerical study has been performed to simulate the effect of free-stream turbulence, length scale and variations in rotational speed of the rotor on heat transfer and fluid flow for a transonic high-pressure turbine stage with tip clearance. The stator and rotor rows interact via a mixing plane, which allows the stage to be computed in a steady manner. The focus is on turbine aerodynamics and heat transfer behavior at the mid-span location, and at the rotor tip and casing region. The results of the fully 3D CFD simulations are compared with experimental results available for the so-called MT1 turbine stage. The predicted heat transfer and static pressure distributions show reasonable agreement with the experimental data. In general, the local Nusselt number increases, at the same turbulence length scale, as the turbulence intensity increases, and the location of the suction side boundary layer transition moves upstream towards the blade leading edge. Comparison of the different length scales at the same turbulence intensity shows that the stagnation heat transfer was significantly increased as the length scale increased. However, the length scale evidenced no significant effects on blade tip or rotor casing heat transfer. Also, the results presented in this paper show that the rotational speed in addition to the turbulence intensity and length scale has an important contribution to the turbine blade aerodynamics and heat transfer. Copyright (Less)

With the attempts to achieve higher thermal efficiency, turbine blades are exposed to very high temperature gases and may undergo severe thermal stress and fatigue. Thus, in order to develop optimal cooling strategies and reduce the heat transfer it is important to obtain a good understanding of both the complex flow field and the heat transfer characteristics in turbine rotor/stator hot-gas passages. The flow field in a high pressure gas turbine is very complex. It is strongly three-dimensional, unsteady, viscous, with several types of secondary flows and vortices (passage vortex, leakage flow, horseshoe vortex, etc.). Transitional flow and high turbulence intensity result in additional complexities. The most significant contribution to the unsteadiness of the flow field is the relative motion of the blade rows. The understanding of such complex flow fields and heat transfer characteristics is necessary to improve the blade design and prediction in terms of efficiency as well as the evaluation of mechanical and thermal fatigue. This thesis aims to investigate the convective flow and heat transfer processes in turbine rotor/stator hot-gas passages. The focus is on turbine aerodynamics and heat transfer behaviour at the mid-span location, and at the rotor tip and casing region. The heat transfer and fluid flow has been numerically simulated by CFD (Computational Fluid Dynamics) methods for turbulent and compressible flow conditions. A commercial finite volume based Navier-Stokes solver FLUENT was extended to multi-block and parallel computations, with implementation of some turbulence models. Grid and scheme independence has been verified, and a few general guidelines about the numerics are summarized. In this study numerical simulations of heat transfer and fluid flow have been performed using different turbulent models (the Spalart-Allmaras model, the standard high Re k-? model, the low Re k-? model, the low Re k-? (SST) model and model). Firstly, the study was focused on the different turbulence models in order to assess the capability of the models to correctly predict the blade heat transfer. Secondly, the effect of different tip clearances on the blade tip and casing, the effect of free-stream turbulence, length scale and variations in rotational speed of the rotor on heat transfer and fluid flow was studied. Also, in this work, a numerical study has been performed to simulate the unsteady fluid flow and heat transfer in a transonic high-pressure turbine stage. The predicted heat transfer and static pressure distributions show reasonable agreement with the experimental data. In general, it is shown that the model yield the best agreement with measurements. It was also observed that the tip clearance has a significant influence on the local tip heat transfer coefficient distribution. Comparison of the different length scales at the same turbulence intensity showed that the stagnation heat transfer was significantly increased as the length scale increased. However, the inlet length scale showed no significant effect on the blade tip or rotor casing heat transfer. Also, the results presented in this thesis show that the rotational speed in addition to the turbulence intensity and length scale have an important contribution to the turbine blade aerodynamics and heat transfer. (Less)

Abstract in Undetermined A numerical study has been performed to simulate the tip leakage flow and heat transfer on the first stage of a high-pressure turbine, which represents a modern gas turbine blade geometry. The low Re k-ω (SST) model is used to model the turbulence. Calculations are performed for both a flat and a squealer blade tip for three different tip gap clearances. The computations were carried out using a single blade with periodic conditions imposed along the boundaries in the circumferential (pitch) direction. The predicted tip heat transfer and static pressure distributions show reasonable agreement with experimental data. It was also observed that the tip clearance has a significant influence on local tip heat transfer coefficient distribution. The flat tip blade provides a higher overall heat transfer coefficient than the squealer tip blade. (Less)