Optimization methodology assessment for the inlet

Authors: Galván Sergio Rubio Carlos Jesús Pacheco Solorio Gildardo Carbajal Georgina

Publish Date: 2012/12/05

Volume: 55, Issue: 4, Pages: 729-749

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Abstract

Computational Fluids Dynamics CFD tools guide engineers and designers to estimate the performance of new designs However a CFD analysis can be very timeconsuming depending mainly on the grid size and domain complexity Thus this paper aims to describe the tools used to evaluate and compare the performance of different 3D draft tube models for reducing the timeeffort needed in an optimization procedure The results presented here are the second part of an overall research to establish a global optimization methodology to improve the performance of an hydraulic draft tube through the inlet velocity profile Previously three steps of optimization methodology to minimize the energy losses were studied the inlet velocity profile parameterization the numerical optimization setup and the objective function validation In the latter step a global optimization method called Multi Island Genetic Algorithm MIGA was considered which requires a large number of iterations before producing a reliable result This step is able to identify an efficient inlet velocity profile to minimize the energy losses through the draft tube model However each iteration is expensive in terms of computational time due to the need for 3D Navier–Stokes NS computations to evaluate each profile’s fitness Thus in this work the methodology attempts to accelerate the optimization process with accurate results In order to achieve the goal the grid size of the 3D draft tube model was minimized resulting in a much lower computational cost Specifically the draft tube calculations were performed on a sequence of five different grids each having approximately twice the number of elements compared to the previous The measurements of the sensitivity of the draft tube performance quantities to the change of the inlet velocity parameters during the process showed that in spite of the numerical difference between its performance the results have the same tendency Consequently the 3D draft tube numerical model with a minimal grid size is reliable and left record of its capabilities for being integrated in the optimization process

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