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Development of a Turbulence Model for Numerical Simulation of Film Cooling flow with Heat Transfer over a Turbine Rotating Blade

Mir Emad, Mohsen | 2025

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 58211 (45)
  4. University: Sharif University of Technology
  5. Department: Aerospace Engineering
  6. Advisor(s): Mazaheri, Karim; Darbandi, Masoud
  7. Abstract:
  8. This research aims to develop an improved model for turbulent heat flux and increase the accuracy of numerical simulation of flow with heat transfer in turbine blade film cooling, especially in rotating blades. The necessity of this research stems from the high importance of blade cooling in increasing the efficiency of gas turbines and the sensitivity of blade life to temperature; such that a 30-degree Celsius error in predicting blade temperature can halve its lifespan. Turbulent heat flux, caused by velocity and temperature fluctuations, plays a key role in film cooling heat transfer. Conventional methods and commercial software often model this characteristic in a simplified manner, leading to significant errors in highly turbulent and anisotropic flows. Accurate modeling of turbulent heat flux is key to achieving more accurate flow field predictions in these problems. In real turbine blades, rotation effects also significantly affect film cooling and cannot be ignored. The proposed model in this research is an explicit algebraic model that considers the effects of anisotropy and non-equilibrium, the difference in turbulence time scales of the hydrodynamic and thermal fields, and, most importantly, the effects of blade rotation. The proposed model is obtained by introducing new terms into the turbulent heat flux transport equation to account for rotation effects, then performing algebraic calculations to obtain the algebraic form, and also introducing a new damping coefficient. Among the innovations of this thesis, we can mention the development of an improved explicit algebraic model for turbulent heat flux with the mentioned features and examining its performance first a-priori in basic stationary and rotating channel flow problems, and then various film cooling problems (flat plate, leading edge, and stationary and rotating turbine blade), as well as examining and comparing existing turbulent heat flux models in turbine blade film cooling. The results of the a-priori study show that the developed models in predicting turbulent heat flux in a stationary channel and a rotating channel (at different rotation numbers) perform up to 53.7% better than the base model (without rotation effects) and up to 25.1% better than other existing algebraic models. The results of evaluating the performance of these models in practical film cooling problems, including flat plate film cooling, blade leading edge, and C3X blade, show that the new models, especially in regions with non-equilibrium hydrodynamic and thermal characteristics, show a 37.9% improvement for the flat plate problem and a 51.1% improvement for the leading edge problem compared to previous simulations in predicting film cooling effectiveness and perform better than the previous model and other anisotropic RANS models. Also, evaluating the performance of the developed model in simulating rotating turbine blade film cooling shows that considering rotation effects in the turbulent heat flux model improves the results by up to 40.6% compared to other similar models and up to 71.6% compared to simulations without a turbulent heat flux model. Also, examining the performance of various turbulent heat flux models alongside various Reynolds Stress Model (RSM) turbulence models in flat plate film cooling indicates that choosing a suitable RSM model is very important in the final simulation results. Also, a case study of the effect of anti-vortex hole blockage on film cooling performance using the developed model shows that side holes (if not blocked) can reduce the negative effect of the main hole blockage
  9. Keywords:
  10. Film Cooling ; Turbine Blades ; Turbulent Heat Flux ; Gas Turbine Blades ; Blade Rotation ; Numerical Flow Simulation

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