Pub Date : 2021-11-26DOI: 10.1080/10618562.2022.2042272
Kuangxu Chen, C. Liang
When the high-order Spectral Difference (SD) method is used to discretize ideal magnetohydrodynamic (MHD) equations, it is challenging to satisfy the divergence-free constraint for the magnetic field over long time integration. To ensure that the discrete equals to zero exactly and globally, the SD method is integrated with an unstaggered Constrained Transport approach (SDCT) by replacing the magnetic field with the curl of the magnetic potential at every time step. The SDCT method stores the variables for the hydrodynamics and the magnetic field at the same set of solution points, which avoids designing 2D Riemann solvers and preserves the compactness of the stencil for spatial discretization. Moreover, the additional computational cost is less than 1/8 of that without the constrained transport. Meanwhile, the SDCT method is found to have excellent convergence in test cases with and without shocks.
{"title":"A Divergence-Free High-Order Spectral Difference Method with Constrained Transport for Ideal Compressible Magnetohydrodynamics","authors":"Kuangxu Chen, C. Liang","doi":"10.1080/10618562.2022.2042272","DOIUrl":"https://doi.org/10.1080/10618562.2022.2042272","url":null,"abstract":"When the high-order Spectral Difference (SD) method is used to discretize ideal magnetohydrodynamic (MHD) equations, it is challenging to satisfy the divergence-free constraint for the magnetic field over long time integration. To ensure that the discrete equals to zero exactly and globally, the SD method is integrated with an unstaggered Constrained Transport approach (SDCT) by replacing the magnetic field with the curl of the magnetic potential at every time step. The SDCT method stores the variables for the hydrodynamics and the magnetic field at the same set of solution points, which avoids designing 2D Riemann solvers and preserves the compactness of the stencil for spatial discretization. Moreover, the additional computational cost is less than 1/8 of that without the constrained transport. Meanwhile, the SDCT method is found to have excellent convergence in test cases with and without shocks.","PeriodicalId":56288,"journal":{"name":"International Journal of Computational Fluid Dynamics","volume":"11 1","pages":"826 - 849"},"PeriodicalIF":1.3,"publicationDate":"2021-11-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"77256945","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2021-11-26DOI: 10.1080/10618562.2021.2009468
Alexis Picard, N. Lelong, O. Jamond, V. Faucher, C. Tenaud
This article deals with fast transient dynamics of compressible flows in which local flow details matter. An overlapping grid Chimera method is proposed in a finite volume framework. Euler's equations are considered, as well as explicit time integration with a second-order discretisation in time and space. The method is intended to improve the accuracy of a large scale calculation by adding a local grid containing important flow details that alter the flow within the global grid. This paper evaluates the impact of the Chimera exchange on flow dynamics crossing the overlapping grid interface. With a second-order interpolated solution inside the receiving cells, the method does not alter the order of convergence of the global model. It produces numerical solutions with better quality when using a finer local model compared to a single grid computation, providing significant gains in terms of CPU time and memory usage.
{"title":"A Finite Volume Chimera Method for Fast Transient Dynamics in Compressible Flow Problems","authors":"Alexis Picard, N. Lelong, O. Jamond, V. Faucher, C. Tenaud","doi":"10.1080/10618562.2021.2009468","DOIUrl":"https://doi.org/10.1080/10618562.2021.2009468","url":null,"abstract":"This article deals with fast transient dynamics of compressible flows in which local flow details matter. An overlapping grid Chimera method is proposed in a finite volume framework. Euler's equations are considered, as well as explicit time integration with a second-order discretisation in time and space. The method is intended to improve the accuracy of a large scale calculation by adding a local grid containing important flow details that alter the flow within the global grid. This paper evaluates the impact of the Chimera exchange on flow dynamics crossing the overlapping grid interface. With a second-order interpolated solution inside the receiving cells, the method does not alter the order of convergence of the global model. It produces numerical solutions with better quality when using a finer local model compared to a single grid computation, providing significant gains in terms of CPU time and memory usage.","PeriodicalId":56288,"journal":{"name":"International Journal of Computational Fluid Dynamics","volume":"45 1","pages":"799 - 825"},"PeriodicalIF":1.3,"publicationDate":"2021-11-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"83046432","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2021-10-21DOI: 10.1080/10618562.2021.1989421
F. Duchaine, Mehdi Cizeron, N. Odier, J. Dombard, S. Marchall, Nicolas-Yoan François, T. Poinsot
This work focuses on the development of a simulation strategy able to quantify risks of airborne virus contagion in many scenarios found in enclosed domains by using high-fidelity fluid dynamics simulation to predict the trajectories and distribution of virus-loaded respiratory droplets over long times. Large-Eddy simulation is used to predict the turbulent flow fields in a city bus for different operating conditions of the Air Conditioning system. The time-averaged velocity distributions and associated turbulent kinetic energy are shown to be drastically dependent on the studied operating conditions. Lagrangian tracking of respiratory droplets is then used over long times on statically converged Eulerian flow fields to investigate their turbulent dispersion depending on the emitter position in the bus. Importance of air conditioning conditions on respiratory droplet trajectories and concentration in the configuration is illustrated indicating that air treatment devices play a crucial role in the mitigation solution of airborne virus propagation.
{"title":"High-performance CFD for Respiratory Droplet Turbulent Dispersion in a Ventilated City Bus","authors":"F. Duchaine, Mehdi Cizeron, N. Odier, J. Dombard, S. Marchall, Nicolas-Yoan François, T. Poinsot","doi":"10.1080/10618562.2021.1989421","DOIUrl":"https://doi.org/10.1080/10618562.2021.1989421","url":null,"abstract":"This work focuses on the development of a simulation strategy able to quantify risks of airborne virus contagion in many scenarios found in enclosed domains by using high-fidelity fluid dynamics simulation to predict the trajectories and distribution of virus-loaded respiratory droplets over long times. Large-Eddy simulation is used to predict the turbulent flow fields in a city bus for different operating conditions of the Air Conditioning system. The time-averaged velocity distributions and associated turbulent kinetic energy are shown to be drastically dependent on the studied operating conditions. Lagrangian tracking of respiratory droplets is then used over long times on statically converged Eulerian flow fields to investigate their turbulent dispersion depending on the emitter position in the bus. Importance of air conditioning conditions on respiratory droplet trajectories and concentration in the configuration is illustrated indicating that air treatment devices play a crucial role in the mitigation solution of airborne virus propagation.","PeriodicalId":56288,"journal":{"name":"International Journal of Computational Fluid Dynamics","volume":"36 1","pages":"758 - 777"},"PeriodicalIF":1.3,"publicationDate":"2021-10-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"83035653","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2021-10-21DOI: 10.1080/10618562.2022.2042903
T. Saad
The Covid-19 outbreak has caused significant human and economic loss across the world. While rules-ofthumb for social distancing and masking are thought to be effective measures at inhibiting the spread of the virus, the science behind them is still in its infancy and is often limited to quiescent air conditions. Because airborne diseases such as Covid-19 are transported primarily via aerosolized respiratory droplets, fluid dynamics plays a fundamental role in its spread and, subsequently, mitigation. This is where CFD can play a critical role in understanding how Covid-19 and other airborne diseases spread. With the powerful insight that CFD can provide, simple and effective engineering controls can be implemented therefore reducing the burden of compliance with other measures such as masking, social distancing, and vaccination. CFD has been used in the past to study the spread of airborne diseases in close quarters such as school buses, hospital wards, schools, and other crowded venues. Most of the existing work, however, was limited to low order RANS-type models due to technological limitations. With our modern computational power, it seems natural to seek advanced CFD calculations for Covid-19 and airborne disease transmission. More importantly, therewas little technology exchange between those studying the science of viral transmission and engineering fluid mechanics, in part because CFD was not very popular or was considered as an interesting gadget at best. Recent advances in computational science, however, and their impact on health sciences has created a newfound trust in tools such as CFD to study the spread of airborne disease. There is no better time to capitalise on that opportunity than the present. CFD for airborne transmission has two major components: modelling respiratory disease sources (e.g. mouth) and subsequently tracking their motion with the air. In general, it is not possible to do bothwith very high-fidelity because the former requires DNSlevel calculations while the latter can generally be well managed with LES or RANSmodels. In addition, CFD applied to understanding respiratory sources must at some point rely on observational data of particle size distributions and their properties at the source. On the other hand, if sources are properlymodelled, those can be effectively input to the CFD model to capture their bulk motion with the air. The objective of this special issue is to bring-in world experts in CFD and fluid mechanics to contribute to the scientific understanding of the spread of Covid-19 using advanced computational techniques. The list of contributors was carefully curated from active CFD practitioners and pioneers who were among the first to apply their expertise to study the spread of Covid-19 in close quarters. Contributions to this special issue include high-fidelity calculations of respiratory droplet transport accounting for deposition, evaporation, and transmission, within an LES framework. In additio
{"title":"Special Issue: CFD and Covid-19","authors":"T. Saad","doi":"10.1080/10618562.2022.2042903","DOIUrl":"https://doi.org/10.1080/10618562.2022.2042903","url":null,"abstract":"The Covid-19 outbreak has caused significant human and economic loss across the world. While rules-ofthumb for social distancing and masking are thought to be effective measures at inhibiting the spread of the virus, the science behind them is still in its infancy and is often limited to quiescent air conditions. Because airborne diseases such as Covid-19 are transported primarily via aerosolized respiratory droplets, fluid dynamics plays a fundamental role in its spread and, subsequently, mitigation. This is where CFD can play a critical role in understanding how Covid-19 and other airborne diseases spread. With the powerful insight that CFD can provide, simple and effective engineering controls can be implemented therefore reducing the burden of compliance with other measures such as masking, social distancing, and vaccination. CFD has been used in the past to study the spread of airborne diseases in close quarters such as school buses, hospital wards, schools, and other crowded venues. Most of the existing work, however, was limited to low order RANS-type models due to technological limitations. With our modern computational power, it seems natural to seek advanced CFD calculations for Covid-19 and airborne disease transmission. More importantly, therewas little technology exchange between those studying the science of viral transmission and engineering fluid mechanics, in part because CFD was not very popular or was considered as an interesting gadget at best. Recent advances in computational science, however, and their impact on health sciences has created a newfound trust in tools such as CFD to study the spread of airborne disease. There is no better time to capitalise on that opportunity than the present. CFD for airborne transmission has two major components: modelling respiratory disease sources (e.g. mouth) and subsequently tracking their motion with the air. In general, it is not possible to do bothwith very high-fidelity because the former requires DNSlevel calculations while the latter can generally be well managed with LES or RANSmodels. In addition, CFD applied to understanding respiratory sources must at some point rely on observational data of particle size distributions and their properties at the source. On the other hand, if sources are properlymodelled, those can be effectively input to the CFD model to capture their bulk motion with the air. The objective of this special issue is to bring-in world experts in CFD and fluid mechanics to contribute to the scientific understanding of the spread of Covid-19 using advanced computational techniques. The list of contributors was carefully curated from active CFD practitioners and pioneers who were among the first to apply their expertise to study the spread of Covid-19 in close quarters. Contributions to this special issue include high-fidelity calculations of respiratory droplet transport accounting for deposition, evaporation, and transmission, within an LES framework. In additio","PeriodicalId":56288,"journal":{"name":"International Journal of Computational Fluid Dynamics","volume":"17 1","pages":"707 - 707"},"PeriodicalIF":1.3,"publicationDate":"2021-10-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"84326847","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2021-10-05DOI: 10.1080/10618562.2022.2057479
Rohit Singhal, S. Ravichandran, Sourabh S. Diwan
The COVID-19 pandemic has inspired several studies on the fluid dynamics of respiratory events. Here, we propose a computational approach in which respiratory droplets are coarse-grained into an Eulerian liquid field advected by the fluid streamlines. A direct numerical simulation is carried out for a moist cough using a closure model for space-time dependence of the evaporation time scale. Stokes-number estimates are provided, for the initial droplet size of 10 μm, which are found to be ≪1, thereby justifying the neglect of droplet inertia, over the duration of the simulation. Several important features of the moist-cough flow reported in the literature using Lagrangian tracking methods have been accurately captured using our scheme. Some new results are presented, including the evaporation time for a ‘mild’ cough, a saturation-temperature diagram and a favourable correlation between the vorticity and liquid fields. The present approach can be extended for studying the long-range transmission of virus-laden droplets.
{"title":"Direct Numerical Simulation of a Moist Cough Flow using Eulerian Approximation for Liquid Droplets","authors":"Rohit Singhal, S. Ravichandran, Sourabh S. Diwan","doi":"10.1080/10618562.2022.2057479","DOIUrl":"https://doi.org/10.1080/10618562.2022.2057479","url":null,"abstract":"The COVID-19 pandemic has inspired several studies on the fluid dynamics of respiratory events. Here, we propose a computational approach in which respiratory droplets are coarse-grained into an Eulerian liquid field advected by the fluid streamlines. A direct numerical simulation is carried out for a moist cough using a closure model for space-time dependence of the evaporation time scale. Stokes-number estimates are provided, for the initial droplet size of 10 μm, which are found to be ≪1, thereby justifying the neglect of droplet inertia, over the duration of the simulation. Several important features of the moist-cough flow reported in the literature using Lagrangian tracking methods have been accurately captured using our scheme. Some new results are presented, including the evaporation time for a ‘mild’ cough, a saturation-temperature diagram and a favourable correlation between the vorticity and liquid fields. The present approach can be extended for studying the long-range transmission of virus-laden droplets.","PeriodicalId":56288,"journal":{"name":"International Journal of Computational Fluid Dynamics","volume":"12 1","pages":"778 - 797"},"PeriodicalIF":1.3,"publicationDate":"2021-10-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"83861190","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2021-09-14DOI: 10.1080/10618562.2021.2016720
M. Schouler, Y. Prévereaud, L. Mieussens
Recent work on the Intermediate eXperimental Vehicle (IXV) re-entry simulation in hypersonic rarefied regime highlighted several numerical and experimental key aspects for a satisfactory reconstruction of its aerothermodynamic flight data. Indeed, among the investigated sources of discrepancies, the atmospheric model uncertainty on the density estimation appeared as one of the major sources of error for the heat flux calculation. The initial investigation was based on the NRLMSISE-00 model of 2000 which was recently updated in the NRLMSIS 2.0 version of 2020. This last version incorporates major formulation changes and new measurements yielding significantly smaller densities for altitudes below 100 km. The present work therefore focuses on the impact of improving our knowledge of the atmospheric environment to reduce the error related to the numerical reconstruction of the heat flux.
{"title":"Atmospheric Model Effect on Flight Data Reconstruction: Application to the Early Phase of the IXV Reentry","authors":"M. Schouler, Y. Prévereaud, L. Mieussens","doi":"10.1080/10618562.2021.2016720","DOIUrl":"https://doi.org/10.1080/10618562.2021.2016720","url":null,"abstract":"Recent work on the Intermediate eXperimental Vehicle (IXV) re-entry simulation in hypersonic rarefied regime highlighted several numerical and experimental key aspects for a satisfactory reconstruction of its aerothermodynamic flight data. Indeed, among the investigated sources of discrepancies, the atmospheric model uncertainty on the density estimation appeared as one of the major sources of error for the heat flux calculation. The initial investigation was based on the NRLMSISE-00 model of 2000 which was recently updated in the NRLMSIS 2.0 version of 2020. This last version incorporates major formulation changes and new measurements yielding significantly smaller densities for altitudes below 100 km. The present work therefore focuses on the impact of improving our knowledge of the atmospheric environment to reduce the error related to the numerical reconstruction of the heat flux.","PeriodicalId":56288,"journal":{"name":"International Journal of Computational Fluid Dynamics","volume":"1 1","pages":"594 - 609"},"PeriodicalIF":1.3,"publicationDate":"2021-09-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"88321658","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2021-09-14DOI: 10.1080/10618562.2022.2026339
Jorge Alberto García Pérez, Kojiro Suzuki
This paper introduces a new plasma-surface interaction simulation program called Solar Corona – Spacecraft Interaction (SCSI). The program's main focus is to keep modularity and generality in its implementation. For this purpose, SCSI was programmed with an object-oriented approach, composed of a set of numerical methods organised in classes and a main file that connects them in order for the simulation to run. The program also contains a system of embedded meshes. These meshes run almost independently and allow the user to execute different numerical methods in different regions of the domain. The program is tested by simulating the interaction of a satellite with the solar wind at a distance of 8.5 R from the surface of the Sun. Results exhibited good agreement between SCSI and previous codes and demonstrated the capability of the program to capture the main physical phenomena present in plasma-surface systems.
{"title":"Development of Object-oriented PIC Code for Simulation of Plasma Flow Around a Satellite in Solar Corona","authors":"Jorge Alberto García Pérez, Kojiro Suzuki","doi":"10.1080/10618562.2022.2026339","DOIUrl":"https://doi.org/10.1080/10618562.2022.2026339","url":null,"abstract":"This paper introduces a new plasma-surface interaction simulation program called Solar Corona – Spacecraft Interaction (SCSI). The program's main focus is to keep modularity and generality in its implementation. For this purpose, SCSI was programmed with an object-oriented approach, composed of a set of numerical methods organised in classes and a main file that connects them in order for the simulation to run. The program also contains a system of embedded meshes. These meshes run almost independently and allow the user to execute different numerical methods in different regions of the domain. The program is tested by simulating the interaction of a satellite with the solar wind at a distance of 8.5 R from the surface of the Sun. Results exhibited good agreement between SCSI and previous codes and demonstrated the capability of the program to capture the main physical phenomena present in plasma-surface systems.","PeriodicalId":56288,"journal":{"name":"International Journal of Computational Fluid Dynamics","volume":"46 1","pages":"685 - 706"},"PeriodicalIF":1.3,"publicationDate":"2021-09-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"84982137","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2021-09-14DOI: 10.1080/10618562.2022.2047666
F. Giroux, J. McDonald
The use of moment-closure methods to predict continuum and moderately rarefied flow offers many modelling and numerical advantages over traditional methods. The maximum-entropy family of moment closures offers models described by hyperbolic systems of equations. In particular, the twenty-one moment model of the maximum-entropy hierarchy offers a hyperbolic treatment of viscous flows exhibiting heat transfer. This model has the ability to provide accurate solutions where the Navier–Stokes equations lose physical validity. Furthermore, its first-order hyperbolic nature offers the potential for improved numerical accuracy as well as a decreased sensitivity to mesh quality. Unfortunately, the distribution function associated with the 21 moment model is an exponential of a fourth-order polynomial. Such a function cannot be integrated in closed form, resulting in unobtainable closing fluxes. This work presents an approximation to the closing fluxes that respects the maximum-entropy philosophy as closely as possible. The proposed approximation is able to provide shock predictions in good agreement with the Boltzmann equation and surpassing the prediction of the Navier–Stokes equations. A dispersion analysis as well as an investigation of the hyperbolicity of the model is also shown.
{"title":"An Approximation for the Twenty-One-Moment Maximum-Entropy Model of Rarefied Gas Dynamics","authors":"F. Giroux, J. McDonald","doi":"10.1080/10618562.2022.2047666","DOIUrl":"https://doi.org/10.1080/10618562.2022.2047666","url":null,"abstract":"The use of moment-closure methods to predict continuum and moderately rarefied flow offers many modelling and numerical advantages over traditional methods. The maximum-entropy family of moment closures offers models described by hyperbolic systems of equations. In particular, the twenty-one moment model of the maximum-entropy hierarchy offers a hyperbolic treatment of viscous flows exhibiting heat transfer. This model has the ability to provide accurate solutions where the Navier–Stokes equations lose physical validity. Furthermore, its first-order hyperbolic nature offers the potential for improved numerical accuracy as well as a decreased sensitivity to mesh quality. Unfortunately, the distribution function associated with the 21 moment model is an exponential of a fourth-order polynomial. Such a function cannot be integrated in closed form, resulting in unobtainable closing fluxes. This work presents an approximation to the closing fluxes that respects the maximum-entropy philosophy as closely as possible. The proposed approximation is able to provide shock predictions in good agreement with the Boltzmann equation and surpassing the prediction of the Navier–Stokes equations. A dispersion analysis as well as an investigation of the hyperbolicity of the model is also shown.","PeriodicalId":56288,"journal":{"name":"International Journal of Computational Fluid Dynamics","volume":"70 1","pages":"632 - 652"},"PeriodicalIF":1.3,"publicationDate":"2021-09-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"76947005","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2021-09-14DOI: 10.1080/10618562.2021.2050478
R. Myong, K. Xu
Rarefied gas flows are present in a wide range of scientific and technological problems, such as hypersonic vehicles flying at very high altitudes, propulsion systems of spacecraft navigating in space, and vacuum devices operating on the ground. To continue engagement in the rarefied gas dynamics (RGD) community and bring together researchers, the ‘Pre-RGD32 Online Workshop on Recent Hot Topics in Rarefied Gas Dynamics’ was held during July 7-10th, 2021. This special issue presents a selection of papers from the workshop, highlighting works of innovative CFD research and developments of a fundamental or applied nature, and their applications to the field of rarefied gas dynamics.
{"title":"Special Issue on Recent Hot Topics in Rarefied Gas Dynamics","authors":"R. Myong, K. Xu","doi":"10.1080/10618562.2021.2050478","DOIUrl":"https://doi.org/10.1080/10618562.2021.2050478","url":null,"abstract":"Rarefied gas flows are present in a wide range of scientific and technological problems, such as hypersonic vehicles flying at very high altitudes, propulsion systems of spacecraft navigating in space, and vacuum devices operating on the ground. To continue engagement in the rarefied gas dynamics (RGD) community and bring together researchers, the ‘Pre-RGD32 Online Workshop on Recent Hot Topics in Rarefied Gas Dynamics’ was held during July 7-10th, 2021. This special issue presents a selection of papers from the workshop, highlighting works of innovative CFD research and developments of a fundamental or applied nature, and their applications to the field of rarefied gas dynamics.","PeriodicalId":56288,"journal":{"name":"International Journal of Computational Fluid Dynamics","volume":"39 1","pages":"563 - 565"},"PeriodicalIF":1.3,"publicationDate":"2021-09-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"76933468","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2021-09-14DOI: 10.1080/10618562.2021.2023737
Yajun Zhu, Chengwen Zhong, K. Xu
The Boltzmann equation is the fundamental governing equation in rarefied gas dynamics. Due to the complexity of Boltzmann collision term, operator splitting treatment is commonly adopted, where the Boltzmann equation is split into a convection equation for particles' free transport and an ordinary differential equation for particles' collision. However, this split treatment will introduce numerical error proportional to the time step, which may contaminate the physical solution in the near continuum regime. Therefore, for a multiscale kinetic method, the asymptotic preserving property to obtain the Navier–Stokes–Fourier (NSF) solution in the hydrodynamic limit is very important. In this paper, we analyse the effective relaxation time from different evolution processes of several kinetic schemes and investigate their capabilities to recover the NSF solution. The general requirement on a splitting kinetic method for the NSF solution has been presented. Numerical validation has been carried out, which shows good agreement with the theoretical analysis.
{"title":"Numerical Transport Process of Splitting Kinetic Schemes in the Navier–Stokes–Fourier Limit","authors":"Yajun Zhu, Chengwen Zhong, K. Xu","doi":"10.1080/10618562.2021.2023737","DOIUrl":"https://doi.org/10.1080/10618562.2021.2023737","url":null,"abstract":"The Boltzmann equation is the fundamental governing equation in rarefied gas dynamics. Due to the complexity of Boltzmann collision term, operator splitting treatment is commonly adopted, where the Boltzmann equation is split into a convection equation for particles' free transport and an ordinary differential equation for particles' collision. However, this split treatment will introduce numerical error proportional to the time step, which may contaminate the physical solution in the near continuum regime. Therefore, for a multiscale kinetic method, the asymptotic preserving property to obtain the Navier–Stokes–Fourier (NSF) solution in the hydrodynamic limit is very important. In this paper, we analyse the effective relaxation time from different evolution processes of several kinetic schemes and investigate their capabilities to recover the NSF solution. The general requirement on a splitting kinetic method for the NSF solution has been presented. Numerical validation has been carried out, which shows good agreement with the theoretical analysis.","PeriodicalId":56288,"journal":{"name":"International Journal of Computational Fluid Dynamics","volume":"54 1","pages":"653 - 665"},"PeriodicalIF":1.3,"publicationDate":"2021-09-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"72797979","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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