Pub Date : 2021-01-01DOI: 10.1299/JFST.2021JFST0013
Mehdi Badri Ghomizad, Hosnieh Kor, K. Fukagata
Based on the Moving Least Square (MLS) approximation, we propose a sharp interface direct-forcing immersed boundary method for incompressible fluid flows with fixed and moving boundaries. Since the domain of definition for the interpolation is highly flexible and the MLS approximation provides an accurate reconstructed approximation of the solution, the proposed method serves the precision and versatility required for a numerical framework to study the fluid-structure interaction problems. To alleviate the inherent spurious numerical oscillation that occurs in the calculated forces on moving boundary embedded objects, we use a two step predictor-corrector method in which the direct forcing terms are calculated after the predictor step and imposed on the whole solid domain as well as at the immediate vicinity of the solid boundary inside the fluid domain. To represent the arbitrary geometries, we adopt a signed distance function representation of the rigid body and an interpolation strategy to considerably reduce the computational cost of the re-initialization of the distance function at every time step. The potential capability of the method is demonstrated for both fixed and moving boundary problems. We also solve a sedimentation of a single cylinder to demonstrate the ability of the present method in solving fluid-structure interaction problems. These numerical experiments show that the proposed moving least square immersed boundary method can handle relatively complex moving problems while enjoying a versatile interpolation strategy and keeping the boundary conditions sharp with remarkable accuracy.
{"title":"A sharp interface direct-forcing immersed boundary method using the moving least square approximation","authors":"Mehdi Badri Ghomizad, Hosnieh Kor, K. Fukagata","doi":"10.1299/JFST.2021JFST0013","DOIUrl":"https://doi.org/10.1299/JFST.2021JFST0013","url":null,"abstract":"Based on the Moving Least Square (MLS) approximation, we propose a sharp interface direct-forcing immersed boundary method for incompressible fluid flows with fixed and moving boundaries. Since the domain of definition for the interpolation is highly flexible and the MLS approximation provides an accurate reconstructed approximation of the solution, the proposed method serves the precision and versatility required for a numerical framework to study the fluid-structure interaction problems. To alleviate the inherent spurious numerical oscillation that occurs in the calculated forces on moving boundary embedded objects, we use a two step predictor-corrector method in which the direct forcing terms are calculated after the predictor step and imposed on the whole solid domain as well as at the immediate vicinity of the solid boundary inside the fluid domain. To represent the arbitrary geometries, we adopt a signed distance function representation of the rigid body and an interpolation strategy to considerably reduce the computational cost of the re-initialization of the distance function at every time step. The potential capability of the method is demonstrated for both fixed and moving boundary problems. We also solve a sedimentation of a single cylinder to demonstrate the ability of the present method in solving fluid-structure interaction problems. These numerical experiments show that the proposed moving least square immersed boundary method can handle relatively complex moving problems while enjoying a versatile interpolation strategy and keeping the boundary conditions sharp with remarkable accuracy.","PeriodicalId":44704,"journal":{"name":"Journal of Fluid Science and Technology","volume":null,"pages":null},"PeriodicalIF":0.8,"publicationDate":"2021-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"66306042","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2021-01-01DOI: 10.1299/jfst.2021jfst0018
Kovid Bhatt, Y. Tsuji
{"title":"Identification of vortex structures in flow fields using tomographic PIV method","authors":"Kovid Bhatt, Y. Tsuji","doi":"10.1299/jfst.2021jfst0018","DOIUrl":"https://doi.org/10.1299/jfst.2021jfst0018","url":null,"abstract":"","PeriodicalId":44704,"journal":{"name":"Journal of Fluid Science and Technology","volume":null,"pages":null},"PeriodicalIF":0.8,"publicationDate":"2021-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"66306310","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2021-01-01DOI: 10.1299/jfst.2021jfst0006
K. Shimoyama, Yoshio Sato, J. Onodera, Jun Liu
A heating ventilation and air conditioning (HVAC) unit is an essential unit to adjust temperature for passenger’s comfortability in an automotive cabin. For efficient and reliable design and development of the HVAC unit, the interior thermal flow needs to be simulated and the performance needs to be evaluated with low cost and high fidelity. Hence, this paper develops measurement-based strategies for high-fidelity thermo-fluid dynamics simulation of an HVAC heat exchanger. These strategies tune up the parameters of a porous media model in the governing equations, which model the interaction between the heat exchanger and the surrounding thermal flow field and are conventionally fixed to certain constants, by functionalization or data assimilation with actual measurement data. The present results show that both strategies are able to reduce discrepancies between the simulation and the actual measurements, and improve fidelity to simulate the temperature field without sacrificing the simulation cost very much. Especially, the data assimilation strategy is more effective to yield more accurate simulation results only with the measurement data while the functionalization strategy needs to derive theoretical correlations. It demonstrates that data assimilation is helpful to assist reliable and efficient design and development of an HVAC unit regardless of designer’s professional skills or knowledge.
{"title":"Measurement-based strategies for high-fidelity thermo-fluid dynamics simulation of an automotive heat exchanger","authors":"K. Shimoyama, Yoshio Sato, J. Onodera, Jun Liu","doi":"10.1299/jfst.2021jfst0006","DOIUrl":"https://doi.org/10.1299/jfst.2021jfst0006","url":null,"abstract":"A heating ventilation and air conditioning (HVAC) unit is an essential unit to adjust temperature for passenger’s comfortability in an automotive cabin. For efficient and reliable design and development of the HVAC unit, the interior thermal flow needs to be simulated and the performance needs to be evaluated with low cost and high fidelity. Hence, this paper develops measurement-based strategies for high-fidelity thermo-fluid dynamics simulation of an HVAC heat exchanger. These strategies tune up the parameters of a porous media model in the governing equations, which model the interaction between the heat exchanger and the surrounding thermal flow field and are conventionally fixed to certain constants, by functionalization or data assimilation with actual measurement data. The present results show that both strategies are able to reduce discrepancies between the simulation and the actual measurements, and improve fidelity to simulate the temperature field without sacrificing the simulation cost very much. Especially, the data assimilation strategy is more effective to yield more accurate simulation results only with the measurement data while the functionalization strategy needs to derive theoretical correlations. It demonstrates that data assimilation is helpful to assist reliable and efficient design and development of an HVAC unit regardless of designer’s professional skills or knowledge.","PeriodicalId":44704,"journal":{"name":"Journal of Fluid Science and Technology","volume":null,"pages":null},"PeriodicalIF":0.8,"publicationDate":"2021-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"66305799","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2021-01-01DOI: 10.1299/jfst.2021jfst0017
T. Bamba, T. Fukui, K. Morinishi
{"title":"Numerical study on the effects of aspect ratio of two types of fin folds on the propulsion performance by fish larvae’s swimming simulation","authors":"T. Bamba, T. Fukui, K. Morinishi","doi":"10.1299/jfst.2021jfst0017","DOIUrl":"https://doi.org/10.1299/jfst.2021jfst0017","url":null,"abstract":"","PeriodicalId":44704,"journal":{"name":"Journal of Fluid Science and Technology","volume":null,"pages":null},"PeriodicalIF":0.8,"publicationDate":"2021-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"66306292","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2021-01-01DOI: 10.1299/jfst.2021jfst0019
T. Nakazawa
This paper presents a shape optimazation method for transient Non-Newtonian fluid which is playing important roles of calculating blood flow, oil flow and so on. So far, the author constructed a shape optimization problem for suppressing transient Newtonian fluid by using Snapshot POD, and extends it toward to Non-Newtonian fluid, here. For such the suggested shape optimization, the eigenvalue in Snapshot POD is defined as a cost function, where the constraint functions are the Oldroyd-B model, and an eigenvalue equation of Snapshot POD. For numerical calculations, a two–dimensional cavity flow with a disk-shaped isolated body is adopted for an initial domain. To descritize the Oldroyd-B model spatially, Galerkin Method (GM) and Hybridized Discontinuous Galerkin Method (HDGM) are used to compare numerical accuracies. As a result, it is considered that HDGM is able to obtain better solutions than GM during numerical validations. Finally, eigenvalues of Snapshot POD are compared in the initial and optimal domains obtained by HDGM.
{"title":"Shape optimization problem for transient Non-Newtonian fluid in hybridized discontinuous Galerkin method","authors":"T. Nakazawa","doi":"10.1299/jfst.2021jfst0019","DOIUrl":"https://doi.org/10.1299/jfst.2021jfst0019","url":null,"abstract":"This paper presents a shape optimazation method for transient Non-Newtonian fluid which is playing important roles of calculating blood flow, oil flow and so on. So far, the author constructed a shape optimization problem for suppressing transient Newtonian fluid by using Snapshot POD, and extends it toward to Non-Newtonian fluid, here. For such the suggested shape optimization, the eigenvalue in Snapshot POD is defined as a cost function, where the constraint functions are the Oldroyd-B model, and an eigenvalue equation of Snapshot POD. For numerical calculations, a two–dimensional cavity flow with a disk-shaped isolated body is adopted for an initial domain. To descritize the Oldroyd-B model spatially, Galerkin Method (GM) and Hybridized Discontinuous Galerkin Method (HDGM) are used to compare numerical accuracies. As a result, it is considered that HDGM is able to obtain better solutions than GM during numerical validations. Finally, eigenvalues of Snapshot POD are compared in the initial and optimal domains obtained by HDGM.","PeriodicalId":44704,"journal":{"name":"Journal of Fluid Science and Technology","volume":null,"pages":null},"PeriodicalIF":0.8,"publicationDate":"2021-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"66306388","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2021-01-01DOI: 10.1299/jfst.2021jfst0020
Naoki Okamura, T. Fukui, M. Kawaguchi, K. Morinishi
Einstein’s viscosity formula is sometimes strongly limited for viscosity estimation of suspensions; that is, it is only applicable for low-concentration suspensions in which hydrodynamic interactions are sufficiently negligible. In particular, hydrodynamic interactions between particles (cylinders in two dimensions) should be taken into consideration when finite-size particles are suspended. Therefore, change in the microstructure, i.e., spatial arrangement of particles in the flow field, is important for understanding mechanism of suspension rheology. In order to provide better practical applications for viscosity estimation instead of Einstein’s formula, we investigated the influence of each cylinder’s contribution on the total effective viscosity of a suspension with finite-size cylinders considering the microstructure, especially in terms of cylinder-wall and cylinder-cylinder distances. Two-dimensional pressure-driven flow simulations were performed using the regularized lattice Boltzmann method and a two-way coupling scheme. The rigid circular cylinders suspended in a Newtonian fluid were assumed to be neutrally buoyant and non-Brownian. As a result, we found that both distances between cylinders and cylinder-wall are significant for viscosity estimation. In addition, the effective viscosity can be estimated accurately when the confinement is sufficiently low ( C ≈ 0.04). It can be stated that the microstructure of the suspension is one of the promising factors to estimate and control suspension rheology.
{"title":"Influence of each cylinder’s contribution on the total effective viscosity of a two-dimensional suspension by a two-way coupling scheme","authors":"Naoki Okamura, T. Fukui, M. Kawaguchi, K. Morinishi","doi":"10.1299/jfst.2021jfst0020","DOIUrl":"https://doi.org/10.1299/jfst.2021jfst0020","url":null,"abstract":"Einstein’s viscosity formula is sometimes strongly limited for viscosity estimation of suspensions; that is, it is only applicable for low-concentration suspensions in which hydrodynamic interactions are sufficiently negligible. In particular, hydrodynamic interactions between particles (cylinders in two dimensions) should be taken into consideration when finite-size particles are suspended. Therefore, change in the microstructure, i.e., spatial arrangement of particles in the flow field, is important for understanding mechanism of suspension rheology. In order to provide better practical applications for viscosity estimation instead of Einstein’s formula, we investigated the influence of each cylinder’s contribution on the total effective viscosity of a suspension with finite-size cylinders considering the microstructure, especially in terms of cylinder-wall and cylinder-cylinder distances. Two-dimensional pressure-driven flow simulations were performed using the regularized lattice Boltzmann method and a two-way coupling scheme. The rigid circular cylinders suspended in a Newtonian fluid were assumed to be neutrally buoyant and non-Brownian. As a result, we found that both distances between cylinders and cylinder-wall are significant for viscosity estimation. In addition, the effective viscosity can be estimated accurately when the confinement is sufficiently low ( C ≈ 0.04). It can be stated that the microstructure of the suspension is one of the promising factors to estimate and control suspension rheology.","PeriodicalId":44704,"journal":{"name":"Journal of Fluid Science and Technology","volume":null,"pages":null},"PeriodicalIF":0.8,"publicationDate":"2021-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"66305945","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2021-01-01DOI: 10.1299/jfst.2021jfst0002
T. Nakazawa, T. Misaka, C. Poignard
This paper presents an optimal design obtained as a shape optimization problem in a domain with a singular point. For shape optimization, the eigenvalue in Snapshot Proper Orthogonal Decomposition (Snapshot POD) is defined as a cost function. The main problems are a Non-stationary Navier–Stokes problem and eigenvalue problem of Snapshot POD. An objective functional is described using Lagrange multipliers and finite element method. Twodimensional open cavity flow is adopted for an initial domain, where the domain includes a singular point. In this paper, two kinds of sensitivities assuming velocity vector in H1 and H2 are used. Using H1 gradient method for domain deformation, all triangles over a mesh are deformed as the cost function decreases. Finally, eigenvalues of Snapshot POD are compared in the initial and optimal domains.
{"title":"Shape optimization for suppressing coherent structure of two-dimensional open cavity flow","authors":"T. Nakazawa, T. Misaka, C. Poignard","doi":"10.1299/jfst.2021jfst0002","DOIUrl":"https://doi.org/10.1299/jfst.2021jfst0002","url":null,"abstract":"This paper presents an optimal design obtained as a shape optimization problem in a domain with a singular point. For shape optimization, the eigenvalue in Snapshot Proper Orthogonal Decomposition (Snapshot POD) is defined as a cost function. The main problems are a Non-stationary Navier–Stokes problem and eigenvalue problem of Snapshot POD. An objective functional is described using Lagrange multipliers and finite element method. Twodimensional open cavity flow is adopted for an initial domain, where the domain includes a singular point. In this paper, two kinds of sensitivities assuming velocity vector in H1 and H2 are used. Using H1 gradient method for domain deformation, all triangles over a mesh are deformed as the cost function decreases. Finally, eigenvalues of Snapshot POD are compared in the initial and optimal domains.","PeriodicalId":44704,"journal":{"name":"Journal of Fluid Science and Technology","volume":null,"pages":null},"PeriodicalIF":0.8,"publicationDate":"2021-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"66305497","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2021-01-01DOI: 10.1299/JFST.2021JFST0014
Mehdi Badri Ghomizad, Hosnieh Kor, K. Fukagata
We develop a versatile and accurate structured adaptive mesh refinement (S-AMR) strategy with a moving least square sharp-direct forcing immersed boundary method (IBM) for incompressible fluid-structure interaction (FSI) simulations. The computational grid consists of several nested blocks in different refinement levels. While blocks with the coarsest grid cover the entire computational domain, the computational domain is locally refined at the location of solid boundary (moving or fixed) by bisecting selected blocks in every coordinate direction. The grid topology and data structure is managed by an extended version of Afivo toolkit (Teunissen and Ebert, 2018), where a novel technique is introduced for conservative data transfer between the coarser and the finer blocks, particularly in velocity transformation for which the mass conservation plays a crucial role. In the present study, the continuity and Navier-Stokes equations for incompressible flows are spatially discretized with a second order central finite difference method using a collocated arrangement and are time-integrated using a semi-implicit second order fractional step method, although the proposed S-AMR strategy can be used with different discretization schemes. An IBM using a moving least square approach is utilized to impose boundary conditions. To handle FSI problems, all the governing equations for the dynamics of fluid and structure are simultaneously advanced in time by a predictorcorrector strategy. Several test cases of increasing complexity are solved in order to demonstrate the robustness and accuracy of the proposed method as well as its capability in simulation-driven mesh adaptivity.
{"title":"A structured adaptive mesh refinement strategy with a sharp interface direct-forcing immersed boundary method for moving boundary problems","authors":"Mehdi Badri Ghomizad, Hosnieh Kor, K. Fukagata","doi":"10.1299/JFST.2021JFST0014","DOIUrl":"https://doi.org/10.1299/JFST.2021JFST0014","url":null,"abstract":"We develop a versatile and accurate structured adaptive mesh refinement (S-AMR) strategy with a moving least square sharp-direct forcing immersed boundary method (IBM) for incompressible fluid-structure interaction (FSI) simulations. The computational grid consists of several nested blocks in different refinement levels. While blocks with the coarsest grid cover the entire computational domain, the computational domain is locally refined at the location of solid boundary (moving or fixed) by bisecting selected blocks in every coordinate direction. The grid topology and data structure is managed by an extended version of Afivo toolkit (Teunissen and Ebert, 2018), where a novel technique is introduced for conservative data transfer between the coarser and the finer blocks, particularly in velocity transformation for which the mass conservation plays a crucial role. In the present study, the continuity and Navier-Stokes equations for incompressible flows are spatially discretized with a second order central finite difference method using a collocated arrangement and are time-integrated using a semi-implicit second order fractional step method, although the proposed S-AMR strategy can be used with different discretization schemes. An IBM using a moving least square approach is utilized to impose boundary conditions. To handle FSI problems, all the governing equations for the dynamics of fluid and structure are simultaneously advanced in time by a predictorcorrector strategy. Several test cases of increasing complexity are solved in order to demonstrate the robustness and accuracy of the proposed method as well as its capability in simulation-driven mesh adaptivity.","PeriodicalId":44704,"journal":{"name":"Journal of Fluid Science and Technology","volume":null,"pages":null},"PeriodicalIF":0.8,"publicationDate":"2021-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"66306124","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2021-01-01DOI: 10.1299/JFST.2021JFST0011
Mikimasa Kawaguchi, G. Nitta, K. Mimura, K. Nishida, Masanobu Koutoku, Ryo Yamamoto, A. Nakashima, Y. Ogata
efficiency. Both methods increase the heat Abstract In general, technical methods for improving the thermal efficiency of an engine increase the heat load on peripheral components. Recently, a piston cooling gallery equipped with a flow path has been developed. The engine oil is supplied an oil jet from the nozzle, which is placed under the piston to the piston gallery entrance hall. The nozzle of the oil jet is curved to minimize its size, and the jet interface between ambient air and oil fluctuates near the nozzle exit owing to the shape. Few studies have investigated the behavior of oil jets ejecting from curved pipes. We therefore investigated the flow in two nozzles having a basic bend of 90° with radii of curvature of 15 and 60 mm. Our results clarify the effect of internal flow on the ejecting oil jet behavior. Silicone oil was used as the working fluid. The kinematic viscosity of the silicone oil at 298 K was similar to that of engine oil at 353 K. The behavior of the oil jet was investigated by visualization using background light. A light-emitting-diode displacement meter was installed to measure the jet width. We found that the width of the oil jet increased on the downstream side with large fluctuation of the interface under the condition of a small radius of curvature and large Reynolds number. Furthermore, we time-synchronously measured flow in the nozzle, two-dimensional two-component time-resolved particle image velocimetry, and visualization of the jet. The Reynolds number was set from 1000 to 3000, which is close to that of the engine oil jet. The oil flow velocity in the nozzle fluctuated in the radial direction. The fluctuation became strong under the condition of a small radius and large Reynolds number. The fluctuation propagation speed calculated from the correlation coefficient was as high as the flow speed itself. Furthermore, the jet interface fluctuation speed in the flow direction was as high as the fluctuation propagation speed in the nozzle. Our results demonstrate that the cause of the interface fluctuation is the fluctuation propagation of flow in the nozzle.
{"title":"Effect of flow in the circular 90-degree curved nozzles on ejecting oil jet behavior","authors":"Mikimasa Kawaguchi, G. Nitta, K. Mimura, K. Nishida, Masanobu Koutoku, Ryo Yamamoto, A. Nakashima, Y. Ogata","doi":"10.1299/JFST.2021JFST0011","DOIUrl":"https://doi.org/10.1299/JFST.2021JFST0011","url":null,"abstract":"efficiency. Both methods increase the heat Abstract In general, technical methods for improving the thermal efficiency of an engine increase the heat load on peripheral components. Recently, a piston cooling gallery equipped with a flow path has been developed. The engine oil is supplied an oil jet from the nozzle, which is placed under the piston to the piston gallery entrance hall. The nozzle of the oil jet is curved to minimize its size, and the jet interface between ambient air and oil fluctuates near the nozzle exit owing to the shape. Few studies have investigated the behavior of oil jets ejecting from curved pipes. We therefore investigated the flow in two nozzles having a basic bend of 90° with radii of curvature of 15 and 60 mm. Our results clarify the effect of internal flow on the ejecting oil jet behavior. Silicone oil was used as the working fluid. The kinematic viscosity of the silicone oil at 298 K was similar to that of engine oil at 353 K. The behavior of the oil jet was investigated by visualization using background light. A light-emitting-diode displacement meter was installed to measure the jet width. We found that the width of the oil jet increased on the downstream side with large fluctuation of the interface under the condition of a small radius of curvature and large Reynolds number. Furthermore, we time-synchronously measured flow in the nozzle, two-dimensional two-component time-resolved particle image velocimetry, and visualization of the jet. The Reynolds number was set from 1000 to 3000, which is close to that of the engine oil jet. The oil flow velocity in the nozzle fluctuated in the radial direction. The fluctuation became strong under the condition of a small radius and large Reynolds number. The fluctuation propagation speed calculated from the correlation coefficient was as high as the flow speed itself. Furthermore, the jet interface fluctuation speed in the flow direction was as high as the fluctuation propagation speed in the nozzle. Our results demonstrate that the cause of the interface fluctuation is the fluctuation propagation of flow in the nozzle.","PeriodicalId":44704,"journal":{"name":"Journal of Fluid Science and Technology","volume":null,"pages":null},"PeriodicalIF":0.8,"publicationDate":"2021-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"66306215","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2021-01-01DOI: 10.1299/jfst.2021jfst0007
H. Yao, T. Nambu, Y. Mizobuchi
A combustion simulation software tool, “HINOCA”, has been developed for automotive engine analysis. HINOCA is based on fully compressible Navier-Stokes equations, which are Reynolds-averaged (RANS) or spatially-filtered (LES), and employs the Cartesian grid and immersed boundary (IB) methods to reduce the mesh generation cost. In the present paper, focusing on flow simulations using k-ε models, a robust and reliable IB method coupled with wall functions is proposed. One major aspect of the method is that different IB cell information is employed for inviscid and viscous flux evaluations at fluid-IB cell interfaces. To improve the evaluation of wall shear stress, the shear stresses on the boundaries of an IB cell are transformed into a body force acting on the adjacent fluid cell. The computational method for ε-equation and the source terms of the k-equation near IB cells are modified so that the development of the turbulent boundary layer on a flat plate is well reproduced. The effects of these modifications are validated by the 2D Zero Pressure Gradient Flat Plate problem. To improve the mass conservation property of the IB method, multiple geometric parameters are defined for IB cells; that is, different image point information is immersed on IB cell centers for evaluating the inviscid flux on each cell interface. Evaluation with the Steady State Flow Bench problem shows that the proposed method drastically improves the mass conservation property of simulations and is able with a coarse mesh to reproduce flow structures obtained by LES with a much finer mesh.
{"title":"An immersed boundary method for practical simulations of high-Reynolds number flows by k-ε RANS models","authors":"H. Yao, T. Nambu, Y. Mizobuchi","doi":"10.1299/jfst.2021jfst0007","DOIUrl":"https://doi.org/10.1299/jfst.2021jfst0007","url":null,"abstract":"A combustion simulation software tool, “HINOCA”, has been developed for automotive engine analysis. HINOCA is based on fully compressible Navier-Stokes equations, which are Reynolds-averaged (RANS) or spatially-filtered (LES), and employs the Cartesian grid and immersed boundary (IB) methods to reduce the mesh generation cost. In the present paper, focusing on flow simulations using k-ε models, a robust and reliable IB method coupled with wall functions is proposed. One major aspect of the method is that different IB cell information is employed for inviscid and viscous flux evaluations at fluid-IB cell interfaces. To improve the evaluation of wall shear stress, the shear stresses on the boundaries of an IB cell are transformed into a body force acting on the adjacent fluid cell. The computational method for ε-equation and the source terms of the k-equation near IB cells are modified so that the development of the turbulent boundary layer on a flat plate is well reproduced. The effects of these modifications are validated by the 2D Zero Pressure Gradient Flat Plate problem. To improve the mass conservation property of the IB method, multiple geometric parameters are defined for IB cells; that is, different image point information is immersed on IB cell centers for evaluating the inviscid flux on each cell interface. Evaluation with the Steady State Flow Bench problem shows that the proposed method drastically improves the mass conservation property of simulations and is able with a coarse mesh to reproduce flow structures obtained by LES with a much finer mesh.","PeriodicalId":44704,"journal":{"name":"Journal of Fluid Science and Technology","volume":null,"pages":null},"PeriodicalIF":0.8,"publicationDate":"2021-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"66305885","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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