Computers & Fluids最新文献

{"title":"Energy-consistent discretization of viscous dissipation with application to natural convection flow","authors":"B. Sanderse ,&nbsp;F.X. Trias","doi":"10.1016/j.compfluid.2024.106473","DOIUrl":"10.1016/j.compfluid.2024.106473","url":null,"abstract":"<div><div>A new energy-consistent discretization of the viscous dissipation function in incompressible flows is proposed. It is <em>implied</em> by choosing a discretization of the diffusive terms and a discretization of the local kinetic energy equation and by requiring that continuous identities like the product rule are mimicked discretely. The proposed viscous dissipation function has a quadratic, strictly dissipative form, for both simplified (constant viscosity) stress tensors and general stress tensors. The proposed expression is not only useful in evaluating energy budgets in turbulent flows, but also in natural convection flows, where it appears in the internal energy equation and is responsible for viscous heating. The viscous dissipation function is such that a <em>consistent total energy balance</em> is obtained: the ‘implied’ presence as sink in the kinetic energy equation is exactly balanced by explicitly adding it as source term in the internal energy equation.</div><div>Numerical experiments of Rayleigh–Bénard convection (RBC) and Rayleigh–Taylor instabilities confirm that with the proposed dissipation function, the energy exchange between kinetic and internal energy is exactly preserved. The experiments show furthermore that viscous dissipation does not affect the critical Rayleigh number at which instabilities form, but it does significantly impact the development of instabilities once they occur. Consequently, the value of the Nusselt number on the cold plate becomes larger than on the hot plate, with the difference increasing with increasing Gebhart number. Finally, 3D simulations of turbulent RBC show that energy balances are exactly satisfied even for very coarse grids. Therefore, the proposed discretization also forms an excellent starting point for testing sub-grid scale models and is a useful tool to assess energy budgets in any turbulence simulation, with or without the presence of natural convection.</div></div>","PeriodicalId":287,"journal":{"name":"Computers & Fluids","volume":"286 ","pages":"Article 106473"},"PeriodicalIF":2.5,"publicationDate":"2024-11-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142658458","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Gas-kinetic unified algorithm for aerodynamics covering various flow regimes by computable modeling of Boltzmann equation","authors":"Zhi-Hui Li ,&nbsp;Yong-Dong Liang ,&nbsp;Ao-Ping Peng ,&nbsp;Jun-Lin Wu ,&nbsp;Hao-Gong Wei","doi":"10.1016/j.compfluid.2024.106472","DOIUrl":"10.1016/j.compfluid.2024.106472","url":null,"abstract":"<div><div>The gas-kinetic unified algorithm (GKUA), to solve the modeling of the Boltzmann equation, has been developed to study the aerothermodynamics problems with the effects of wall activation energy covering various flow regimes. The unified velocity distribution function equation could be accordingly presented on the basis of the Boltzmann–Shakhov model. To remove the dependence of the distribution function on velocity space, the conservational discrete velocity ordinate method has been developed for hypervelocity flows. The gas-kinetic finite difference scheme is constructed to directly solve the discrete velocity distribution functions by the operator splitting technique. The discrete velocity numerical integration method with the Gauss-type weight function has been developed to evaluate the macroscopic flow variables. Specially, to model the real physical process between gas molecules and the surface, the Maxwell-type gas-surface interaction model has been presented by the MD (molecular dynamic) simulation to obtain the energy adaptability coefficient. The multi-processing domain decomposition strategy and parallel implementation of high parallel efficiency and expansibility designed for the gas-kinetic numerical method is presented with good load balance and data communication efficiency. To validate the accuracy and feasibility of the present algorithm, the supersonic flows past two-dimensional circular cylinder are simulated covering various flow regimes. The results are in good agreement with the related theoretical, DSMC (Direct Simulation Monte Carlo), N–S (Navier–Stokes), and experimental data. The hypersonic reentry flows with the effects of wall activation energy around the Tianzhou-5 cargo spacecraft are simulated by the present GKUA and the massive parallel strategy. It has been confirmed that the present algorithm from the gas-kinetic point of view probably provides a promising approach to resolve the hypersonic aerothermodynamic problems with the complete spectrum of flow regimes during the re-entry and disintegration of the large-scale spacecraft.</div></div>","PeriodicalId":287,"journal":{"name":"Computers & Fluids","volume":"287 ","pages":"Article 106472"},"PeriodicalIF":2.5,"publicationDate":"2024-11-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142703302","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"The numerical analysis of complete and partial electrocoalescence in the droplet-layer system employing the sharp interface technique for multiphase-medium simulation","authors":"Grigorii Yagodin,&nbsp;Ilia Elagin,&nbsp;Sergei Vasilkov,&nbsp;Vladimir Chirkov","doi":"10.1016/j.compfluid.2024.106478","DOIUrl":"10.1016/j.compfluid.2024.106478","url":null,"abstract":"<div><div>In this paper, the coalescence of a drop of water suspended in oil with a layer of water under the influence of a constant electric field is numerically investigated. Unlike most existing studies, the calculations are based on the application of the arbitrary Lagrangian-Eulerian method (ALEM), also called the moving mesh method, which belongs to the class of methods for modeling two-phase liquids with a sharp interface. Using this approach made it possible to avoid a false \"escape\" of the surface charge from the interface, which often occurs when using methods involving a diffuse interface. Despite the fact that ALEM does not allow describing topology changes by default, a numerical model was implemented in which the calculation is divided into three parts: the convergence of the drop and the layer before the moment of touch; the manual construction of the bridge at the moment of touch; the union of the drop and the layer. The developed model allowed us to obtain three possible modes of this process: complete coalescence, partial coalescence and a mode of stretching which has not practically been considered yet. The dependence of the volume of the separated secondary droplet on the size of the initial droplet and the average intensity of the applied electric field is obtained. The model showed good quantitative agreement with experimental studies. It has been shown that generally, the spots where the bridge and the neck are formed in case of partial coalescence do not coincide. A map of coalescence modes was obtained, i.e., the dependence of the transition threshold from coalescence to partial coalescence and from partial coalescence to stretching regime in a wide range of radii of initial droplets and electric field strengths. It has been shown that there is a maximum field strength at which droplets of any size merge with the layer. This map makes it possible to predict the coalescence regime in electrocoalescer. The proposed modeling technique can be used to calculate electrocoalescence modes at various values of the main parameters, which will help to optimize electrocoalescers at the design stage.</div></div>","PeriodicalId":287,"journal":{"name":"Computers & Fluids","volume":"286 ","pages":"Article 106478"},"PeriodicalIF":2.5,"publicationDate":"2024-11-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142657996","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Numerical investigation on the end effects of the flow past a finite rotating circular cylinder with two free ends","authors":"Qiliang Liu,&nbsp;Shuguang Gong,&nbsp;Haishan Lu,&nbsp;Guilan Xie,&nbsp;Zhijian Zuo","doi":"10.1016/j.compfluid.2024.106475","DOIUrl":"10.1016/j.compfluid.2024.106475","url":null,"abstract":"<div><div>This paper studies the impact of the aspect ratio and free end shape on the end effects in the flow past a rotating circular cylinder with two flat, radiused, hemispherical, and conical ends, using the large eddy simulation method at a Reynolds number of <span><math><mrow><mn>4.6</mn><mo>×</mo><msup><mrow><mn>10</mn></mrow><mn>4</mn></msup></mrow></math></span>. The aspect ratio in the range of 6–30 and the rotation rate in the range of 0–3, are investigated. The results show that the mean drag coefficient initially decreases slightly before rapidly increasing with the rotation rate, with a critical rotation rate that rises from 1 to 1.5 as the aspect ratio increases from 6 to 30. In contrast, the mean lift coefficient increases with both the rotation rate and the aspect ratio. When the rotation rate increases and the aspect ratio decreases, the differences between the aerodynamic coefficients of the four end shapes become more pronounced. The flat end results in the highest mean drag and lift coefficients, while the hemispherical end yields the lowest ones. In addition, when the rotation rate increases, the alternate shedding vortices shift to the opposite side. They even disappear and increase the elongated streamwise vortices. Due to the combined impacts of the rotation and end effects, large-scale tip vortices are formed, significantly altering the wake structure. The intense rotation effect results in expanding the strong influence region of the end effects and shrinking (or even removing) the weak influence region.</div></div>","PeriodicalId":287,"journal":{"name":"Computers & Fluids","volume":"285 ","pages":"Article 106475"},"PeriodicalIF":2.5,"publicationDate":"2024-11-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142657442","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"On correctly evaluating orders of truncation error for node-centered edge-based schemes","authors":"Cosimo Tarsia Morisco,&nbsp;Hiroaki Nishikawa","doi":"10.1016/j.compfluid.2024.106470","DOIUrl":"10.1016/j.compfluid.2024.106470","url":null,"abstract":"<div><div>In this short note, we present a simple analysis to show that an observed order of truncation error on a regular grid can change, if not correctly evaluated, depending on the choice of the norm and also on the discretization scheme. For a second-order scheme, it can be first order, second order, or anywhere in between. Using the node-centered edge-based discretization as an example, we provide a guide on how to evaluate the order of truncation error correctly: one should evaluate it separately for a set of nodes, where the residual stencil is symmetric and the same at every node, and the rest of nodes.</div></div>","PeriodicalId":287,"journal":{"name":"Computers & Fluids","volume":"285 ","pages":"Article 106470"},"PeriodicalIF":2.5,"publicationDate":"2024-11-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142657443","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Non-inertial computational framework for long-distance shock-driven object dynamics","authors":"Dagao Wang ,&nbsp;Guilai Han ,&nbsp;Meikuan Liu ,&nbsp;Zongxian Li","doi":"10.1016/j.compfluid.2024.106474","DOIUrl":"10.1016/j.compfluid.2024.106474","url":null,"abstract":"<div><div>In the realm of dynamic separation problems, the motion of a body triggered by shock interactions is a common phenomenon. This is particularly important in terms of the safe separation of two-stage-to-orbit vehicles, where the motion must remain stable despite long-distance disturbances from shock waves. The flow field in these cases is complex, marked by interactions between hypersonic shock waves and a moving boundary. This leads to significant unsteady effects due to the body's translation and rotation over extended distances. Existing simulation techniques fall short in rapidly and accurately predicting the aerodynamic force and thermal properties for these problems, largely due to the overwhelming computational demands that result from oversize computational domains and the necessity of grid deformation. This paper presents a novel non-deforming grid method to address these challenges. The central concept is to anchor the reference frame to the moving object itself and to approach the problem from a non-inertial frame perspective. This accounts for the motion of the object solely via the inertial source term, circumventing the complexities of mesh manipulation typically required to link flow and motion equations. The moving shock boundary is designed to be closely compatible with selected shock-captured schemes, which reduces non-physical oscillations compared to the traditional method of direct assembly with theoretical shock relations. Other boundary conditions and the solution process are also refined to specifically target the unsteady, shock-dominated flow. These modifications significantly alleviate the computational burden. The effectiveness of the proposed method is demonstrated through several test cases. To showcase the method's practical application, a scenario is simulated wherein an ellipse is dislodged from a wedge by an incident shock wave, covering a long distance. These tests confirm the method's feasibility in aerospace engineering problems.</div></div>","PeriodicalId":287,"journal":{"name":"Computers & Fluids","volume":"286 ","pages":"Article 106474"},"PeriodicalIF":2.5,"publicationDate":"2024-11-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142658460","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Reduced data-driven turbulence closure for capturing long-term statistics","authors":"Rik Hoekstra ,&nbsp;Daan Crommelin ,&nbsp;Wouter Edeling","doi":"10.1016/j.compfluid.2024.106469","DOIUrl":"10.1016/j.compfluid.2024.106469","url":null,"abstract":"<div><div>We introduce a simple, stochastic, <em>a-posteriori</em>, turbulence closure model based on a reduced subgrid scale term. This subgrid scale term is tailor-made to capture the statistics of a small set of spatially-integrated quantities of interest (QoIs), with only one unresolved scalar time series per QoI. In contrast to other data-driven surrogates the dimension of the “learning problem” is reduced from an evolving field to one scalar time series per QoI. We use an <em>a-posteriori</em>, nudging approach to find the distribution of the scalar series over time. This approach has the advantage of taking the interaction between the solver and the surrogate into account. A stochastic surrogate parametrization is obtained by random sampling from the found distribution for the scalar time series. We compare the new method to an <em>a-priori</em> trained convolutional neural network on two-dimensional forced turbulence. Evaluating the new method is computationally much cheaper and gives similar long-term statistics.</div></div>","PeriodicalId":287,"journal":{"name":"Computers & Fluids","volume":"285 ","pages":"Article 106469"},"PeriodicalIF":2.5,"publicationDate":"2024-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142593109","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"On an explicit method for pre-estimate flux for incompressible flow simulation","authors":"Shumian Zhao ,&nbsp;Bernhard Stoevesandt ,&nbsp;Joachim Peinke","doi":"10.1016/j.compfluid.2024.106458","DOIUrl":"10.1016/j.compfluid.2024.106458","url":null,"abstract":"<div><div>For incompressible Computational Fluid Dynamics (CFD) problems, the finite volume method (FVM) often uses explicit velocity flux to linearise the convection term. This makes the convergence sensitive to the initial velocity field. The pre-estimation of the initial field is a common strategy to stabilise and/or speed up the solving process. A common technique is to pre-solve a potential flow problem. Here we present an alternative method to pre-estimate the initial flow field for incompressible flow problems. The method will be based on explicit cell-wise flux balancing combined with face shear corrections. This distinguishes it from a typical potential flow pre-estimation where no viscous effects are considered. We will also demonstrate the effectiveness of the method in terms of increasing the convergence speed of CFD simulations on the popular open source platform OpenFOAM in both 2d and 3d scenarios.</div></div>","PeriodicalId":287,"journal":{"name":"Computers & Fluids","volume":"285 ","pages":"Article 106458"},"PeriodicalIF":2.5,"publicationDate":"2024-10-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142586291","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Modal and nonmodal global instabilities of rotating incompressible axisymmetric boundary layer","authors":"Ramesh Bhoraniya ,&nbsp;Mayank Thummar ,&nbsp;Zahir Hussain","doi":"10.1016/j.compfluid.2024.106459","DOIUrl":"10.1016/j.compfluid.2024.106459","url":null,"abstract":"<div><div>This study discusses the modal and non-modal global instabilities of the boundary layer produced on a rotating circular cylinder. An investigation was conducted on a flow of in-compressible fluid over a rotating cylinder of fixed length. The rotation effect of a cylinder generates pressure gradient and centrifugal force radially. The Reynolds number (Re) and rotation rate (S) were calculated using the cylinder’s radius. The Spectral collocation approach discretizes the 3D stability equations in cylindrical polar coordinates, resulting in an initial value problem. Computations were performed for azimuthal wave numbers, N = 0, 1, 2, and 3, Re = 2600, 5200, and 20800, and S = 0.0, 0.5, 1.0, and 2.0. The transient energy growth (<span><math><mrow><mi>G</mi><mrow><mo>(</mo><mi>t</mi><mo>)</mo></mrow></mrow></math></span>) and optimal disturbances were computed by appropriately superimposing the global modes. The perturbation structure that maximizes <span><math><mrow><mi>G</mi><mrow><mo>(</mo><mi>t</mi><mo>)</mo></mrow></mrow></math></span> has been analyzed. The S enhances the optimal value of <span><math><mrow><mi>G</mi><mrow><mo>(</mo><mi>t</mi><mo>)</mo></mrow></mrow></math></span> for a specific Re and N. The highest <span><math><mrow><mi>G</mi><mrow><mo>(</mo><mi>t</mi><mo>)</mo></mrow></mrow></math></span> was observed for helical mode <span><math><mrow><mi>N</mi><mo>=</mo><mn>1</mn></mrow></math></span> at low Re and for axisymmetric mode <span><math><mrow><mi>N</mi><mo>=</mo><mn>0</mn></mrow></math></span> at higher Re. The disturbances’ spatial structure has been elongated in the shear direction and has grown and intensity as <span><math><mi>S</mi></math></span> and <span><math><mrow><mi>R</mi><mi>e</mi></mrow></math></span> have increased. The perturbation structures are qualitatively distinct for <span><math><mrow><mi>N</mi><mo>=</mo><mn>0</mn></mrow></math></span> and <span><math><mrow><mi>N</mi><mo>=</mo><mn>1</mn></mrow></math></span>. The energy budget components have been notably impacted by the alterations in the base-flow caused by the influence of <span><math><mi>S</mi></math></span>.</div></div>","PeriodicalId":287,"journal":{"name":"Computers & Fluids","volume":"285 ","pages":"Article 106459"},"PeriodicalIF":2.5,"publicationDate":"2024-10-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142554876","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"A high-order local correlation based transition model for transonic airfoil flows","authors":"Matthias Plath ,&nbsp;Florent Renac ,&nbsp;Olivier Marquet ,&nbsp;Christian Tenaud","doi":"10.1016/j.compfluid.2024.106461","DOIUrl":"10.1016/j.compfluid.2024.106461","url":null,"abstract":"<div><div>Accurate transition modeling is a key ingredient towards the all-time goal of improved aerodynamic performance in the aircraft industry. While several different approaches exist to model transition, local correlation based transition models (LCTM) are one of the most versatile strategies. Many versions of LCTM were proposed in the context of lower order finite volume discretizations, but so far only a few transition models have been brought to higher-order numerical schemes. The present work represents a first attempt of including a one equation LCTM into the high-order discontinuous Galkerin (DG) framework. Several modifications are accessed to improve the model’s robustness and tailor it for transonic airfoil flows. Validation is conducted for a series of test cases, starting with zero pressure gradient flat plates, progressing through high Reynolds number airfoil flows, and concluding with a complex unsteady transonic buffet scenario. All results are compared against experiments and previous numerical references.</div></div>","PeriodicalId":287,"journal":{"name":"Computers & Fluids","volume":"285 ","pages":"Article 106461"},"PeriodicalIF":2.5,"publicationDate":"2024-10-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142578239","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}