Documents published in Scipedia

• Effect of graphite-particle morphology on thermomechanical performance of compacted graphite iron: Numerical modelling

  M. Cao, E. Palkanoglou, K. Baxevanakis, V. Silberschmidt

  eccomas2022.

  
  

  Abstract

  Compacted graphite iron (CGI) is used in numerous applications, e.g., in the automotive industry, in tools and pipes, thanks to its excellent thermomechanical properties. Despite its extensive industrial use, its fracture at the microscale was not thoroughly investigated. Interfacial debonding is the main mechanism of fracture of CGI at the microscale and is based on the deformational incompatibility between graphite and the surrounding matrix. To study this decohesion, a two-dimensional micromechanical model of elliptical inclusions embedded in a metallic matrix is generated. An elastoplastic response is assumed for both constituents, and cohesive finite elements are applied to the graphite-matrix interface to simulate decohesion. A parametric analysis of interfacial features such as thickness and stiffness is performed to identify the effect of these parameters on debonding. The obtained results provide insights into the thermomechanical behaviour of CGI at the microscale and enable more effective modelling of this engineering alloy.

  Abstract
  Compacted graphite iron (CGI) is used in numerous applications, e.g., in the automotive industry, in tools and pipes, thanks to its excellent thermomechanical properties. [...]

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• An efficient strategy of parcel modeling for polydispersed multiphase turbulent flows

  L. Bahramian, J. Muela, C. Oliet, C. Pérez-Segarra, F. Trias

  eccomas2022.

  
  

  Abstract

  A three-dimensional particle-laden two-phase turbulent flow by employing the Eulerian-Lagrangian method using multiphase Particle-In-Cell model is implemented to analyze the effects of parcel modeling. In order to achieve an optimal trade-off between accuracy and computational cost, a hybrid approach is proposed. This approach is a combination of two typical models: the volume fixed model, in which each parcel has the same volume, and the number fixed model, in which each parcel has the same number of particles. This approach is studied for the particle-laden turbulent flow benchmark case of Boreé et al. [1], with a mass loading of 22%, by using large eddy simulation through a two-way coupling between continuous and polydispersed phases.

  Abstract
  A three-dimensional particle-laden two-phase turbulent flow by employing the Eulerian-Lagrangian method using multiphase Particle-In-Cell model is implemented to analyze the [...]

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• A numerical analysis of CO2 storage by adsorption using ZIF-8

  G. Fonseca da Silva, L. Rodrigues Capello Silva, M. Oliveira Pelic, B. Galelli Chieregatti, J. de Sá Brasil Lima

  eccomas2022.

  
  

  Abstract

  In 21st century, the reduction of CO2 concentration in the atmosphere is one of the most challenges of the humanity, specifically in the engineering. To start a possibility solution proposal, this work consisted in an analysis of carbon dioxide storage, using adsorption by ZIF8, a material that belongs to a class called Zeolitic Imidazolate Frameworks, which have high porosity, high thermal resistance and chemical stability. The main contribution of this work is to verify which parameters are relevant in the CO2 storage capacity by adsorption. To archive this goal, the study was made through computational simulations using the open source FreeFem++ software, inputting a specified quantity of pure CO2, entering in an 1,82 liter tank filled by the adsorbent until its internal pressure reached 1,0 MPa. First, the isothermal curve was validated with the literature, and after adjusting the parameters of adsorption model, called Dubinin Astakov (D-A). The simulations were performed, varying CO2 inlet flow, the tank’s aspect ratio with the values of 1; 1,9; 3; 5 and 7, and the external wall’s heat transfer coefficient with values of 5, 700 and 1000 W/m²K. Each simulation generated at each step the tank’s average and maximum temperatures, internal pressure, and the carbon dioxide adsorption density. All the simulations started with a standard temperature of 300 K and pressure of 100 kPa. Temperature and adsorption density distributions were generated to analyze in which part of the tank the adsorption is higher. The results showed that the regions where the temperatures are higher, the adsorption is lower, and in the end of the simulation, the simulations with the lower average temperatures had the higher adsorption density. The highest values of adsorption density were obtained with higher surface areas under the influence of forced convection, rather than natural convection, and with lower CO2 inlet flow. The highest adsorption density reached was 15,67 %, in a simulation with 50% of the tank’s volume per minute as CO2 inlet flow rate, aspect ratio of 7,0; and 700 W/m²K heat transfer coefficient. The average temperature obtained in the end of this simulation was 326,20 K and it took 3644 seconds for the tank to achieve the internal pressure of 1,0 MPa.

  Abstract
  In 21st century, the reduction of CO2 concentration in the atmosphere is one of the most challenges of the humanity, specifically in the engineering. To start a possibility [...]

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• A multigrid immersed boundary method for the CFD solver Horses3D

  S. Colombo, E. Ferrer, E. Valero

  eccomas2022.

  
  

  Abstract

  This work describes the implementation of the Immersed Boundary Method (IBM) in a high order discontinuous Galerkin framework for the CFD solver Horses3D [1]. High order schemes are very attractive due to their low numerical dissipation, their capability of providing high-accurate solutions and higher efficiency for a given level of accuracy with respect to low order schemes. However, the generation of high order meshes needed by these schemes is still a bottleneck since it requires a large amount of time. IBM tries to tackle the problem by preserving the high order beneficial properties while avoiding the generation of complex meshes.

  Abstract
  This work describes the implementation of the Immersed Boundary Method (IBM) in a high order discontinuous Galerkin framework for the CFD solver Horses3D [1]. High order schemes [...]

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• On highly scalable 2-level-parallel unstructured CFD

  J. Jaegerskuepper, D. Vollmer

  eccomas2022.

  
  

  Abstract

  Exascale HPC systems are just about to become available. Such enormous simulation capabilities from the hardware perspective, however, require software that can effectively make efficient use of this massively parallel hardware. For the domain-decomposition based algorithms generally used for CFD, it has become apparent that running one MPI process, i.e. one domain, per CPU core is no longer apt when there are hundreds of cores available per cluster node. There are just too many processes per node that need to communicate with other remote processes. Message aggregation is thus a key aspect of highly scalable parallel codes. A 2-level parallelization featuring a shared-memory level in addition to the MPI process level seems a promising solution. The CODA (CFD for ONERA, DLR, Airbus) software for high-fidelity compressible-flow simulations of industrial configurations implements such a 2-level domaindecomposition hybrid-parallel approach. The processing of unstructured meshes is particularly challenging with respect to load balancing and non-linear data access. For maximum parallel scalability, CODA's parallelization not only features overlapping communication with computation on the process level, but also a dedicated Single Program (on) Multiple Data (SPMD) programming model for the shared-memory level. Here, the design principles of this parallelization concept are outlined, followed by details concerning its implementation in the Flucs infrastructure (FLIS), which has become part of CODA. Moreover, results of scalability studies with CODA are presented, which impressively demonstrate the extreme scalability realized with this parallelization approach. The studies were performed on two distinct HPC clusters, one based on Intel's Xeon Scalable Processor, the other one based on AMD's EPYC.

  Abstract
  Exascale HPC systems are just about to become available. Such enormous simulation capabilities from the hardware perspective, however, require software that can effectively [...]

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• EXPLICIT AND IMPLICIT LARGE EDDY SIMULATION FOR A NACA0012 USING A HIGH ORDER DISCONTINUOUS GALERKIN SOLVER

  O. Marino, E. Ferrer, E. Valero, J. Errasti

  eccomas2022.

  
  

  Abstract

  We perform Large Eddy Simulation on a 3D NACA0012 airfoil using a high order discontiuous Galerkin spectral element solver at moderate Reynolds numbers, Re = 1.0 · 105. The aim is to compare the results of classic explicit Sub Grid Scale models, e.g. the WALE and VREMAN models, with the ones get by using implicit LES, where no explicit SGS is used, but we use stabilising split-form energy-stable formulations, with two-point Pirozzoli and KennedyGruber fluxes. We compare general qualitative variables such as the Q-criteria as well as local quantitative variables, as boundary layer velocity profiles. We show that both methods achive similar predictions for the integrated global variables, but differences can be appreciated in the local velocity profiles.

  Abstract
  We perform Large Eddy Simulation on a 3D NACA0012 airfoil using a high order discontiuous Galerkin spectral element solver at moderate Reynolds numbers, Re = 1.0 · [...]

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• Free response of a gravitational liquid sheet by means of three-dimensional Volume-of-Fluid simulations

  A. Della Pia, L. Grande, A. Colanera, M. Chiatto, L. Luca

  eccomas2022.

  
  

  Abstract
  The volume-of-fluid (VOF) method is employed to simulate the dynamics of gravitational liquid sheets (curtains) issuing into an initially quiescent gaseous environment.

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• A level-set model for two-phase flow with variable surface tension: Thermocapillary and surfactants

  N. Balcazar-Arciniega, J. Rigola, A. Oliva

  eccomas2022.

  
  

  Abstract

  An unstructured conservative level-set method for two-phase flow with variable surface tension is introduced. Surface tension is a function of temperature or surfactant concentration on the interface. Consequently, the called Marangoni stresses induced by temperature gradients or surfactant concentration gradients on the interface lead to a coupling of momentum transport equation with thermal energy transport equation or interface surfactant transport equation. The finite-volume method discretizes transport equations on 3D collocated unstructured meshes. The unstructured conservative level-set method is employed for interface capturing, whereas the multiple marker approach avoids the numerical coalescence of fluid particles. The fractional-step projection method solves the pressure-velocity coupling. Unstructured flux-limiters are proposed to discretize the convective term of transport equations. A central difference scheme discretizes diffusive terms. Gradients are evaluated by the weighted least-squares method. Verifications and validations are reported.

  Abstract
  An unstructured conservative level-set method for two-phase flow with variable surface tension is introduced. Surface tension is a function of temperature or surfactant concentration [...]

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• Comparison of different entropy stabilization techniques for discontinuous Galerkin spectral element methods

  J. Markert, G. Gassner

  eccomas2022.

  
  

  Abstract

  We review and compare two techniques to get entropy stability for nodal Discontinuous Galerkin Spectral Element Methods (DG) in compressible flows. One technique is based on entropy split-forms, e.g., [8, 15, 5] and one is based on a direct algebraic correction [1]. We have implemented the Flux Differencing methodology for both, Legendre-Gauss-Lobatto (Lobatto) and Legendre-Gauss (Gauss) based spectral element basis functions. While the Lobatto operators belong to the class of diagonal norm summation-by-parts (SBP) operators, the Gauss operators belong to the generalized class of SBP operators, where it is not necessary that the boundary nodes are included. To reach entropy stability, respectively guaranteed entropy dissipation, a key ingredient is an entropy conserving numerical flux function. With this ingredient, only the volume integral term of the DG method has to be modified accordingly. We have also implemented an alternative technique, which is in general applicable for a wide range of discretizations. Abgrall [R. Abgrall, A general framework to construct schemes satisfying additional conservation relations. Application to entropy conservative and entropy dissipative schemes. Journal of Computational Physics, vol 372, 2018] introduced an algebraic correction term that retains conservation of the primary quantities and is furthermore constructed such, that an entropy (in-) equality can be shown. The second technique is at first sight a simpler alternative to the split-form based approach. Hence, questions regarding its advantages and disadvantages naturally come up.

  Abstract
  We review and compare two techniques to get entropy stability for nodal Discontinuous Galerkin Spectral Element Methods (DG) in compressible flows. One technique is based [...]

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• A Machine Learning based Expert System for Optimizing CFD Solver Parameters

  L. El Zaatari, T. Leicht, S. Langer, P. Bekemeyer, S. Görtz

  eccomas2022.

  
  

  Abstract

  Computational Fluid Dynamics is a viable tool in the field of aerodynamics enabling to reduce time, effort and budget required for experimental testing. Although powerful and established for various years, it remains a complex tool calling for experienced users to ensure consistent high-quality results. This complexity primarily stems from the underlying model, namely the Navier-Stokes equations typically combined with a set of equations resolving the effects of turbulence. Additionally, to obtain accurate high-fidelity result appropriate meshes are required. As a consequence, a substantial number of parameters needs to be selected carefully and the quality of a result often highly depends on individual knowledge and experience of a user. Hence, a strong desire exists to reduce the number of input parameters without causing a loss of accuracy and efficiency. Such reduction of parameters might be viewed as a prerequisite to CFD as a tool in process chains for multidisciplinary applications where typically no user interaction is possible. In this article we propose a machine-learned Expert System for CFD to provide guidance for users in selecting optimal or at least near optimal parameter combinations. The proposed Expert System is divided into two macro steps, the surrogate model and a genetic algorithm to determine from the surrogate model the parameters. Numerical examples are presented to demonstrate the approach.

  Abstract
  Computational Fluid Dynamics is a viable tool in the field of aerodynamics enabling to reduce time, effort and budget required for experimental testing. Although powerful [...]

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