The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Bje Bert Blocken - One of the best experts on this subject based on the ideXlab platform.
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computational evaluation of pedestrian wind comfort and wind safety around a high rise building in an urban area
2014Co-Authors: W Wendy D Janssen, Bje Bert Blocken, Taj Twan Van HooffAbstract:Pedestrian wind comfort is analyzed for a new shopping street area in Eindhoven city center. Wind nuisance is especially perceived around a tower of 105 m high, at an intersection of two streets. The Dutch wind nuisance standard NEN 8100 combined with CFD (Computational Fluid Dynamics) simulations is used to assess the pedestrian wind comfort. Special care is given to the Grid Generation and comparison of the CFD simulations with on-site wind speed measurements. The effectiveness of a series of incremental remedial measures is analyzed. A large canopy is shown to be successful in bringing the wind comfort to an acceptable level.
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coupled urban wind flow and indoor natural ventilation modelling on a high resolution Grid a case study for the amsterdam arena stadium
Environmental Modelling and Software, 2010Co-Authors: T Van Hooff, Bje Bert BlockenAbstract:Wind flow in urban environments is an important factor governing the dispersion of heat and pollutants from streets, squares and buildings. This paper presents a coupled CFD modelling approach for urban wind flow and indoor natural ventilation. A specific procedure is used to efficiently and simultaneously generate the geometry and the high-resolution body-fitted Grid for both the outdoor and indoor environment. This procedure allows modelling complex geometries with full control over Grid quality and Grid resolution, contrary to standard semi-automatic unstructured Grid Generation procedures. It also provides a way to easily implement various changes in the model geometry and Grid for parametric studies. As a case study, a parametric analysis of natural ventilation is performed for the geometrically complex Amsterdam ArenA stadium in the Netherlands. The turbulent wind flow and temperature distribution around and inside the stadium are solved with the 3D steady Reynolds-averaged Navier-Stokes equations. Special attention is given to CFD solution verification and validation. It is shown that small geometrical modifications can increase the ventilation rate by up to 43%. The coupled modelling approach and Grid Generation procedure presented in this paper can be used similarly for future studies of wind flow and related processes in complex urban environments.
Ahmed Kovacevic - One of the best experts on this subject based on the ideXlab platform.
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numerical study of customised mesh for twin screw vacuum pumps
Designs, 2019Co-Authors: Ahmed Kovacevic, Matthew Read, Naushee AshaAbstract:The market for dry vacuum pumps is expected to increase in the coming years. Improving the efficiency of these machines requires comprehensive understanding of the flow dynamics within the working chambers. For this purpose, Computational Fluid Dynamics (CFD) is used as it offers better insight of the working process of a screw machine. In this study, a twin-screw vacuum pump with a large helix angle was analysed. This is a challenging case for CFD due to the limitations of Grid Generation in the transverse plane on the mesh quality. Two types of transverse meshes were generated using the software SCORGTM: casing to rotor non-conformal mesh and casing to rotor conformal mesh. The quality of the mesh in terms of aspect ratio and orthogonality were compared. The casing to rotor conformal mesh was used with ANSYS Fluent in order to obtain performance characteristics of the vacuum pump with the moderate helix angle of 62° such as the mass flow rate, rotor torque, and indicated power. The performance prediction results were satisfactory but the Grid quality was relatively low with orthogonality reaching 40° and aspect ratio over 250 in some cases. As the helix angle increases the quality of mesh decreases. This paper presents the new development of a Grid Generation algorithm which uses the normal rack to map the fluid domain in the normal plane instead of the transverse plane. This new mesh Generation method is expected to better align the computational Grid with the main and leakage flows in order to significantly improve Grid quality and reduce the numerical diffusion in case of screw machines with large helix angles.
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algebraic Generation of single domain computational Grid for twin screw machines part i implementation
Advances in Engineering Software, 2017Co-Authors: Sham Rane, Ahmed KovacevicAbstract:New algebraic algorithm for deforming Grid Generation of twin screw machines developed.Regularized distribution achieved by control function and a reference blocking structure.Independent Grid refinement in interlobe region achieved for better accuracy in the leakage gaps.Non-conformal interface between two rotor domains eliminated, thereby producing a single domain.New Grid adaptable with multiple CFD flow solvers and capable of solving multiphase models. Special attention is required for Generation of computational Grids in highly deforming working chambers of twin screw machines for 3D CFD calculations. Two approaches for customised Grid Generation are practically available. The first is an algebraic Grid Generation and the second is a differential decomposition method. This paper reports on new developments in the algebraic approach that has the advantages associated with both algebraic and differential methods. Two control functions are introduced for regularisation of the initial algebraic distribution. One is based on an analytical control function in transformed coordinate system while the other uses background blocking structure in order to guide the initial algebraic distribution towards a single computational mesh. This paper presents implementation and Grid characteristics of these new functions. Developed Grids have been tested and results from flow calculations on a dry air compressor have been validated in part II of the paper [29].It was possible to achieve two distinct characteristics desirable in a twin screw rotor domain mesh. Firstly, it is possible to independently control Grid refinement in the interlobe region thereby providing better accuracy in representation of the leakage gaps. Secondly and most importantly, it is possible now to eliminate the non-conformal interface between the two rotor domains thereby producing a single domain structured Grid for the rotors, while still maintaining the fully hexahedral cell topology. An improvement in the global orthogonality of the cells was achieved. Despite of a decrement in the Face warp quality, aspect ratio of cells retained similar scale.
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analytical Grid Generation for accurate representation of clearances in cfd for screw machines
IOP Conference Series: Materials Science and Engineering, 2015Co-Authors: Sham Rane, Ahmed Kovacevic, Nikola StosicAbstract:One of the major factors affecting the performance prediction of twin screw compressors by use of computational fluid dynamics (CFD) is the accuracy with which the leakage gaps are captured by the discretization methods. The accuracy of mapping leakage flows can be improved by increasing the number of Grid points on the profile. However, this method faces limitations when it comes to the complex deforming domains of a twin screw compressor because the computational time increases tremendously. In order to address this problem, an analytical Grid distribution procedure is formulated that can independently refine the region of high importance for leakage flows in the interlobe space. This paper describes the procedure of analytical Grid Generation with the refined mesh in the interlobe area and presents a test case to show the influence of the mesh refinement in that area on the performance prediction. It is shown that by using this method, the flow domains in the vicinity of the interlobe gap and the blowhole area are refined which improves accuracy of leakage flow predictions.
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screw compressors three dimensional computational fluid dynamics and solid fluid interaction
2007Co-Authors: Ahmed Kovacevic, Nikola Stosic, Ian K SmithAbstract:Computational Fluid Dynamics in Screw Machines.- Grid Generation of Screw Machine Geometry.- Applications.- Conclusions.
Z U A Warsi - One of the best experts on this subject based on the ideXlab platform.
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numerical mapping of arbitrary domains using spectral methods
Journal of Computational Physics, 1993Co-Authors: G P Koomullil, Z U A WarsiAbstract:Abstract In order to maintain spectral accuracy, the Grids on which a physical problem is to be solved must also be obtained by spectrally accurate techniques. The purpose of this paper is to describe a method of solving the quasilinear elliptic Grid Generation equations by spectral techniques both in Euclidean ( E 2 ) and Riemannian ( R 2 ) spaces. A parametric continuation method is used to generate Grids in completely arbitrary domains.
Michiko Kuroda - One of the best experts on this subject based on the ideXlab platform.
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numerical analysis of the electromagnetic wave scattering from a moving dielectric body by overset Grid Generation method
Asia-Pacific Conference on Applied Electromagnetics, 2012Co-Authors: Shafrida Sahrani, Michiko KurodaAbstract:This paper presents an alternative approach for the analysis of EM field with moving boundaries by FDTD method combined with Overset Grid Generation method, considering Lorentz transformation for the higher velocity cases. This approach has been previously proposed for the case of moving/rotating body with empty Grids. Here, the approach is expanded to a moving dielectric body that moves linearly towards and against to the incident wave. The scattering of the EM fields when the incident wave hits the dielectric moving body with high velocity are analyzed. The numerical results are compared with the theoretical results and achieved good agreements between both results. This numerical approach may have numerous situations to which it can be applied. This may be involved with the design of the high-frequency devices such as microactuator, commutator and the others.
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over set Grid Generation method coupled with fdtd method while considering the doppler effect
Ieej Transactions on Fundamentals and Materials, 2009Co-Authors: Hiroshi Iwamatsu, Michiko KurodaAbstract:Over set Grid Generation method coupled with FDTD method is proposed for the analysis of the moving boundary problems while considering the Doppler Effect. As a bench mark, the received wave at the observation point is calculated when the observation point moves and compared with the theoretical results. Good agreements were obtained.
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comparative study of over set Grid Generation method and body fitted Grid Generation method with moving boundaries
IEEE Antennas and Propagation Society International Symposium, 2008Co-Authors: Hidetoshi Iwamatsu, R Fukumoto, M Ishihara, Michiko KurodaAbstract:In this paper, the received wave at the observation point is calculated when observation point moves. It can be shown that the frequency of the received wave is shifted. To verify the over set Grid Generation method, numerical results are compared with the body fitted Grid Generation method and the theoretical results. Good agreements are obtained in these three results. The over set Grid Generation technique is easier to use for the moving boundary problems. We believe that these numerical techniques will have great promises for the analysis of the moving boundary problems in electromagnetic field.
Sham Rane - One of the best experts on this subject based on the ideXlab platform.
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algebraic Generation of single domain computational Grid for twin screw machines part i implementation
Advances in Engineering Software, 2017Co-Authors: Sham Rane, Ahmed KovacevicAbstract:New algebraic algorithm for deforming Grid Generation of twin screw machines developed.Regularized distribution achieved by control function and a reference blocking structure.Independent Grid refinement in interlobe region achieved for better accuracy in the leakage gaps.Non-conformal interface between two rotor domains eliminated, thereby producing a single domain.New Grid adaptable with multiple CFD flow solvers and capable of solving multiphase models. Special attention is required for Generation of computational Grids in highly deforming working chambers of twin screw machines for 3D CFD calculations. Two approaches for customised Grid Generation are practically available. The first is an algebraic Grid Generation and the second is a differential decomposition method. This paper reports on new developments in the algebraic approach that has the advantages associated with both algebraic and differential methods. Two control functions are introduced for regularisation of the initial algebraic distribution. One is based on an analytical control function in transformed coordinate system while the other uses background blocking structure in order to guide the initial algebraic distribution towards a single computational mesh. This paper presents implementation and Grid characteristics of these new functions. Developed Grids have been tested and results from flow calculations on a dry air compressor have been validated in part II of the paper [29].It was possible to achieve two distinct characteristics desirable in a twin screw rotor domain mesh. Firstly, it is possible to independently control Grid refinement in the interlobe region thereby providing better accuracy in representation of the leakage gaps. Secondly and most importantly, it is possible now to eliminate the non-conformal interface between the two rotor domains thereby producing a single domain structured Grid for the rotors, while still maintaining the fully hexahedral cell topology. An improvement in the global orthogonality of the cells was achieved. Despite of a decrement in the Face warp quality, aspect ratio of cells retained similar scale.
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analytical Grid Generation for accurate representation of clearances in cfd for screw machines
IOP Conference Series: Materials Science and Engineering, 2015Co-Authors: Sham Rane, Ahmed Kovacevic, Nikola StosicAbstract:One of the major factors affecting the performance prediction of twin screw compressors by use of computational fluid dynamics (CFD) is the accuracy with which the leakage gaps are captured by the discretization methods. The accuracy of mapping leakage flows can be improved by increasing the number of Grid points on the profile. However, this method faces limitations when it comes to the complex deforming domains of a twin screw compressor because the computational time increases tremendously. In order to address this problem, an analytical Grid distribution procedure is formulated that can independently refine the region of high importance for leakage flows in the interlobe space. This paper describes the procedure of analytical Grid Generation with the refined mesh in the interlobe area and presents a test case to show the influence of the mesh refinement in that area on the performance prediction. It is shown that by using this method, the flow domains in the vicinity of the interlobe gap and the blowhole area are refined which improves accuracy of leakage flow predictions.
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Deforming Grid Generation and CFD analysis of variable geometry screw compressors
Computers & Fluids, 2014Co-Authors: Sham Rane, Asja Kovacevic, Nikola Stosic, Madhulika KethidiAbstract:The most common type of twin screw machines are twin screw compressors. These normally contain rotors of uniform pitch and profile along the rotor length. However, in some cases such as in twin screw vacuum pumps with very large pressure ratios, the variable pitch rotors are often used to improve efficiency. The limited use of rotors with variable pitch and/or section profile is mainly due to manufacturing constraints. In order to analyse the performance of such machines by means of Computational Fluid Dynamics (CFD), it is necessary to produce a numerical mesh capable of calculating 3D transient fluid flows within their working domains. An algebraic Grid Generation algorithm applicable to unstructured Grid, Finite Volume Method (FVM) for variable pitch and variable profile screw machines is described in this paper. The Grid Generation technique has been evaluated for an oil free air compressor with “N” profile rotors of 3/5 lobe configuration. The performance was obtained by calculations with commercial CFD code. The Grid Generation procedure provides mesh of the required quality and results from CFD calculations are presented to compare performance of constant pitch rotors, variable pitch rotors and variable profile rotors. The variable pitch and variable profile rotors achieve steeper internal pressure rise and a larger discharge area for the same pressure ratio. Variable pitch rotors achieve reduced sealing line length in high pressure domains.
