Browsing by Author "Akay, Hasan U."
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Conference Object Citation Count: 0Effects Of Chamber Pressure Variation On Pollutant Formation In Cryogenic Combustion(Ieee, 2021) Akay, Hasan Umur; Akay, Hasan U.; Automotive EngineeringLiquid rocket engines have played a major role in enabling the pursuit of space exploration. Cryogenic propellants have simplified the storage in liquid rocket engines with higher densities and lower pressures. One of the main driving forces in today's engine research is the reduction of pollutants while keeping the fuel consumption as low as possible. In this study cryogenic combustion has been simulated using the `Steady Laminar Flamelet' approach. Pollutant concentrations have been evaluated at different chamber pressures. It has been shown that combustion at higher chamber pressures results in less pollutant formation.Article Citation Count: 6Flows around moving bodies using a dynamic unstructured overset-grid method(Taylor & Francis Ltd, 2010) Akay, Hasan Umur; Akay, Hasan U.; Ecer, Akin; Payli, Resat U.; Automotive EngineeringIn this article, a computational fluid dynamics algorithm is presented for simulations of complex unsteady flows around rigid moving bodies using an unstructured overset-grid method. For this purpose, a highly automated, three-dimensional, tetrahedral, unstructured overset-grid method is developed with one-cell-width overlapping zone in order to model the arbitrary geometries for steady and unsteady flow simulations. A method has been described to obtain the inter-grid boundaries of the one-cell-wide overlapping zone shared by a background grid and a minor grid. In the overset-grid methodology, vector intersection algorithm and bounding box techniques have been utilised. The mesh refinement and overset-scheme conservation studies proved the accuracy and efficiency of the method developed here. The applications of the developed algorithms were also performed through simulations that included complex internal flows around a flow-control butterfly valve as well as flows in an internal combustion engine with a moving piston. Lastly, validations with experimental data were conducted for both steady and unsteady flows around rigid bodies with relative motions.Article Citation Count: 2A new strategy for solving store separation problems using OpenFOAM(Sage Publications Ltd, 2022) Akay, Hasan Umur; Akay, Hasan U.; Bicer, Baris; Automotive EngineeringThe ability of OpenFOAM to solve the problem of a store separating from an air vehicle (store separation problem) has been evaluated using a dynamic mesh (Overset/Chimera) technique for an industry-class (transonic and generic) benchmark test case. The major limitations of the standard libraries have been determined. To tackle these challenges, a new strategy has been proposed and implemented using only open-source libraries and tools. The strategy combines porting, modifying, and adapting an overset library from the OpenFOAM fork platform (foam-extend) to the standard OpenFOAM platform (ESI). Furthermore, in order to overcome the well-known weakness of the standard OpenFOAM compressible solvers, the newly adapted overset library was integrated with an open-source, density-based, and coupled solver (HiSA), which uses the OpenFOAM technology. Additionally, a force restrained model was developed to consider the externally applied forces on the store by the store ejectors. The accuracy of the developed strategy has been compared with wind tunnel tests and the solutions of two well-known commercial codes, showing good agreements with them. While the study has focused on simulations with inviscid Euler equations (typical of the test case considered here), the viscosity effect on the solution has also been studied with Navier-Stokes equations and compared with other results in the literature, showing minor differences. To the best of the authors' knowledge, this is the first work which studies and validates the store separation problem in transonic regime with OpenFOAM.Article Citation Count: 0Numerical investigation of store separation from cavity problems at high speeds(Sage Publications Ltd, 2023) Akay, Hasan Umur; Akay, Hasan U.; Automotive EngineeringIn this work, the ability of open-source CFD tools to conduct store separation simulations from cavities is evaluated and validated using a generic test case from the literature. Firstly, the ability and accuracy of these tools for solving cavity flows at high speeds are evaluated. Secondly, their competence in predicting the trajectory of a generic store from a generic deep cavity is checked. Finally, and in order to reduce the associated computational costs, a release-time dependability factor from the recent literature is studied and evaluated. The obtained results using the selected open-source CFD tools matched quite well with the wind tunnel results. Furthermore, the results show that predicting the release-time dependability using a quantified index/factor can be a potential remedy for reducing the computational cost for this type of CFD simulations.Article Citation Count: 18Three-dimensional structural topology optimization of aerial vehicles under aerodynamic loads(Pergamon-elsevier Science Ltd, 2014) Akay, Hasan Umur; Akay, Hasan U.; Sehitoglu, Onur T.; Automotive EngineeringA previously developed density distribution-based structural topology optimization algorithm coupled with a Computational Fluid Dynamics (CFD) solver for aerodynamic force predictions is extended to solve large-scale problems to reveal inner structural details of a wing wholly rather than some specific regions. Resorting to an iterative conjugate gradient algorithm for the solution of the structural equilibrium equations needed at each step of the topology optimizations allowed the solution of larger size problems, which could not be handled previously with a direct equation solver. Both the topology optimization and CFD codes are parallelized to obtain faster solutions. Because of the complexity of the computed aerodynamic loads, a case study involving optimization of the inner structure of the wing of an unmanned aerial vehicle (UAV) led to topologies, which could not be obtained by intuition alone. Post-processing features specifically tailored for visualizing computed topologies proved to be good design tools in the hands of designers for identifying complex structural components. (C) 2013 Elsevier Ltd. All rights reserved.