Ali Khavari - Academia.edu (original) (raw)
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Università degli Studi di Firenze (University of Florence)
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Papers by Ali Khavari
Research Square (Research Square), Nov 8, 2022
For high-aspect-ratio turbine blades, profile loss is dominant and its reduction is important for... more For high-aspect-ratio turbine blades, profile loss is dominant and its reduction is important for improving performance. In this paper, a two-stage low-pressure turbine (power turbine) is optimized in two steps: cycle optimization and aerodynamic optimization. In the cycle optimization step, the thermodynamic boundary condition of the turbine is modified. In the second step, which is the main focus of this study, the aerodynamic improvement of a turbine using a two-dimensional optimization technique is performed. The Genetic Algorithm (GA) is used in the optimization process to identify variables that satisfy a defined objective function which is subject to some constraints. The Artificial Neutral Network (ANN) is introduced to correlate variables with the defined objective functions and constraints. Maximum velocity and its location on the blade surface determine transition location and diffusion factor which directly affect total pressure losses. Therefore, in the optimization process, maximum velocity and its location are controlled and defined as objective functions. Profile shape at any given radius is represented with the camber-thickness method. The flow solver used for the aerodynamic analysis of profiles is the cascade analysis code MISES. After improving the performance of vanes and blades' 2D sections, to be confident for performance enhancement of final power turbine ANSYS CFX is used. Finally, the aerodynamic characteristics of the power turbine using optimized geometries are discussed and compared to the original one. The results demonstrate a 1.19 percent improvement in power turbine efficiency at the same pressure ratio.
Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy, May 5, 2022
Propulsion and Power Research
The current article presents conceptual, preliminary and detailed aero-thermal redesign of a typi... more The current article presents conceptual, preliminary and detailed aero-thermal redesign of a typical high pressure turbine nozzle guide vane (HPNGV). Design targets are lower coolant consumption, reduced manufacturing costs and improved durability. These goals are sought by 25% reduction in vane count number and lower number of airfoils per segment. Design challenges such as higher airfoil loading, associate aerodynamic losses and higher thermal loads are discussed. In order to maximize coolant flow reduction and avoid higher aerodynamic losses, airfoil Mach distribution is carefully controlled. There has been an effort to limit design changes so that the proven design features of the original vane are used as much as possible. Accordingly, the same cooling concept is used with minor modifications of the internal structures in order to achieve desired coolant flow and internal heat transfer distribution. Platforms of the new design are quite similar to the original one except for cooling holes and application of thermal barrier coating (TBC). Detailed aerodynamics/heat transfer simulations reveals that the reduced trailing edge (T.E.) blockage and skin friction dominated the negative effect of increased secondary losses. As a result the reduced design performs acceptable in terms of total pressure loss, improving stage efficiency for a wide range of varying
Research Square (Research Square), Nov 8, 2022
For high-aspect-ratio turbine blades, profile loss is dominant and its reduction is important for... more For high-aspect-ratio turbine blades, profile loss is dominant and its reduction is important for improving performance. In this paper, a two-stage low-pressure turbine (power turbine) is optimized in two steps: cycle optimization and aerodynamic optimization. In the cycle optimization step, the thermodynamic boundary condition of the turbine is modified. In the second step, which is the main focus of this study, the aerodynamic improvement of a turbine using a two-dimensional optimization technique is performed. The Genetic Algorithm (GA) is used in the optimization process to identify variables that satisfy a defined objective function which is subject to some constraints. The Artificial Neutral Network (ANN) is introduced to correlate variables with the defined objective functions and constraints. Maximum velocity and its location on the blade surface determine transition location and diffusion factor which directly affect total pressure losses. Therefore, in the optimization process, maximum velocity and its location are controlled and defined as objective functions. Profile shape at any given radius is represented with the camber-thickness method. The flow solver used for the aerodynamic analysis of profiles is the cascade analysis code MISES. After improving the performance of vanes and blades' 2D sections, to be confident for performance enhancement of final power turbine ANSYS CFX is used. Finally, the aerodynamic characteristics of the power turbine using optimized geometries are discussed and compared to the original one. The results demonstrate a 1.19 percent improvement in power turbine efficiency at the same pressure ratio.
Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy, May 5, 2022
Propulsion and Power Research
The current article presents conceptual, preliminary and detailed aero-thermal redesign of a typi... more The current article presents conceptual, preliminary and detailed aero-thermal redesign of a typical high pressure turbine nozzle guide vane (HPNGV). Design targets are lower coolant consumption, reduced manufacturing costs and improved durability. These goals are sought by 25% reduction in vane count number and lower number of airfoils per segment. Design challenges such as higher airfoil loading, associate aerodynamic losses and higher thermal loads are discussed. In order to maximize coolant flow reduction and avoid higher aerodynamic losses, airfoil Mach distribution is carefully controlled. There has been an effort to limit design changes so that the proven design features of the original vane are used as much as possible. Accordingly, the same cooling concept is used with minor modifications of the internal structures in order to achieve desired coolant flow and internal heat transfer distribution. Platforms of the new design are quite similar to the original one except for cooling holes and application of thermal barrier coating (TBC). Detailed aerodynamics/heat transfer simulations reveals that the reduced trailing edge (T.E.) blockage and skin friction dominated the negative effect of increased secondary losses. As a result the reduced design performs acceptable in terms of total pressure loss, improving stage efficiency for a wide range of varying