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    A genetic algorithm based multi-objective optimization of squealer tip geometry in axial flow turbines: A constant tip gap approach
    (2020) Maral, Hıdır; Şenel, Cem Berk; Deveci, Kaan; Alpman, Emre; Kavurmacıoğlu, Levent Ali; Camci, Cengiz
    Tip clearance is a crucial aspect of turbomachines in terms of aerodynamic and thermal performance. A gap between the blade tip surface and the stationary casing must be maintained to allow the relative motion of the blade. The leakage flow through the tip gap measurably reduces turbine performance and causes high thermal loads near the blade tip region. Several studies focused on the tip leakage flow to clarify the flow-physics in the past. The “squealer” design is one of the most common designs to reduce the adverse effects of tip leakage flow. In this paper, a genetic-algorithm-based optimization approach was applied to the conventional squealer tip design to enhance aerothermal performance. A multi-objective optimization method integrated with a meta-model was utilized to determine the optimum squealer geometry. Squealer height and width represent the design parameters which are aimed to be optimized. The objective functions for the genetic-algorithm-based optimization are the total pressure loss coefficient and Nusselt number calculated over the blade tip surface. The initial database is then enlarged iteratively using a coarse-to-fine approach to improve the prediction capability of the meta-models used. The procedure ends once the prediction errors are smaller than a prescribed level. This study indicates that squealer height and width have complex effects on the aerothermal performance, and optimization study allows to determine the optimum squealer dimensions.
  • [ X ]
    Öğe
    Aerothermal optimizaiton of squealer geometry in axial flow turbines using genetic algorithm
    (2018) Deveci, Kaan; Maral, Hıdır; Şenel, Cem Berk; Alpman, Emre; Kavurmacıoğlu, Levent Ali
    In turbomachines, a tip gap is required in order to allow the relative motion of the blade and to prevent the blade tip surface from rubbing. This gap which lay out between the blade tip surface and the casing, results in fluid leakage due to the pressure difference between the pressure side and the suction side of the blade. The tip leakage flow causes almost one third of the aerodynamic loss and unsteady thermal loads over the blade tip. Previous experimental and numerical studies revealed that the squealer blade tip arrangements are one of the effective solutions in increasing the aerothermal performance of the axial flow turbines. In this paper the tip leakage flow is examined and optimized with the squealer geometry as a means to control those losses related with the tip clearance. The squealer height and width have been selected as design parameters and the corresponding computational domain was obtained parametrically. Numerical experiments with such parametrically generated multizone structured grid topologies paved the way for the aerothermal optimization of the high pressure turbine blade tip region. Flow within the linear cascade model has been numerically simulated by solving Reynolds Averaged Navier-Stokes (RANS) equations in order to produce a database. For the numerical validation a well-known test case, Durham cascade is investigated in end wall profiling studies has been used. Sixteen different squealer tip geometries have been modeled parametrically and their performance have been compared in terms of both aerodynamic loss and convective heat transfer coefficient at blade tip. Also, these two values have been introduced as objective functions in the optimization studies. A state of the art multi-objective optimization algorithm, NSGA-II, coupled with an Artificial Neural Network is used to obtain the optimized squealer blade tip geometries for reduced aerodynamic loss and minimum heat transfer coefficient. Optimization results are verified using CFD.
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    Öğe
    Electrical layout optimization of onshore wind farms based on a two-stage approach
    (Ieee-Inst Electrical Electronics Engineers Inc, 2020) Deveci, Kaan; Barutçu, Burak; Alpman, Emre; Tascıkaraoğlu, Akın; Erdinç, Ozan
    Electrical layouts have a significant impact on the investment cost and electrical losses of wind farms, and therefore, layouts should be optimized for reducing their share in the project budgets. In this study, a two-stage method for electrical layout optimization is given. In the first stage, the total trenching length between wind turbines and substation is minimized and in the second stage, the cabling process is performed. The contribution of this article with respect to earlier studies is twofold: First, a new theory for cabling is given and it has shown that determination of the best type of electrical cable is a priori. The suggested cabling theory reduces the complexity of the electrical layout problem since the cable related variables and constraints are avoided. Second, a new bi-objective problem is defined which allows parallel cabling over the previously defined paths. The cabling problem defined aims to minimize the net present cost of the electrical losses and initial investment costs over a known path. Moreover, a novel 3D methodology is introduced for calculating the total length of cables and trenching over the surface of the ground more accurately. All theoretical work is applied on a real onshore wind farm.