Hybrid physical-AI based system modeling and simulation approach demonstrated on an automotive fuel cell

This paper presents an approach on how to train a Neural Network model based on a detailed physical Modelica model. The necessary steps to generate training data from simulation will be explained as well as the generation process of a surrogate model. It will be shown, how the surrogate will be re-integrated into the Modelica system model. A benchmark based on accuracy and simulation performance will be performed. The tools used are Modelon Impact, an online modeling and simulation platform, the TensorFlow/Keras toolbox in a Jupyter Notebook which provides a Python-based interface for generating Neural Networks, and the Modelica Neural Network Library that provides functions for constructing Neural Networks within Modelica. The approach is demonstrated on an automotive fuel cell model which is part of an overall vehicle system model. One possible application is to train the neural network via repeated simulations and then to reuse it as an embedded software component for efficiently estimating fuel use and range for various driving cycles and ambient conditions

Corrigendum to Numerical assessment of fan blades screen effect on fan/OGV interaction tonal noise [Journal of Sound and Vibration, 481 September 2020 115428]

[Abstract:] The authors apologise for any inconvenience.The authors acknowledge the financial support from Safran Aircraft Engines. Xesús Nogueira and Luis Ramírez acknowledge the support given by FEDER funds of the European Union, Grants #DPI2015- 68431-R of the Ministerio de Economía y Competitividad and #RTI2018-093366-B-I00 of the Ministerio de Ciencia, Innovación y Universidades of the Spanish Government, and by the Consellería de Cultura, Educación e Ordenación Universitaria of the Xunta de Galicia (program Axudas para potenciación de grupos de investigación do Sistema Universitario de Galicia 2018, grant #ED431C 2018/41)

A very fast high-order flux reconstruction for Finite Volume schemes for Computational Aeroacoustics

Financiado para publicación en acceso aberto: Universidade da Coruña/CISUG[Abstract:] Given the small wavelengths and wide range of frequencies of the acoustic waves involved in Aeroacoustics problems, the use of very accurate, low-dissipative numerical schemes is the only valid option to accurately capture these phenomena. However, as the order of the scheme increases, the computational time also increases. In this work, we propose a new high-order flux reconstruction in the framework of finite volume (FV) schemes for linear problems. In particular, it is applied to solve the Linearized Euler Equations, which are widely used in the field of Computational Aeroacoustics. This new reconstruction is very efficient and well suited in the context of very high-order FV schemes, where the computation of high-order flux integrals are needed at cell edges/faces. Different benchmark test cases are carried out to analyze the accuracy and the efficiency of the proposed flux reconstruction. The proposed methodology preserves the accuracy while the computational time relatively reduces drastically as the order increases.L. Ramírez and X. Nogueira acknowledge the support provided by the [Grant PID2021-125447OB-I00] funded by MCIN/AEI/ 10.13039/501100011033 and by “ERDF A way of making Europe”, and the funds by [Grant TED2021-129805B-I00] funded by MCIN/AEI/ 10.13039/501100011033 and by the “European Union NextGenerationEU/PRTR”. They also acknowledge the funding provided by the Xunta de Galicia (Grant #ED431C 2022/06).Xunta de Galicia; ED431C 2022/0

A naturally anti-diffusive compressible two phases Kapila model with boundedness preservation coupled to a high order finite volume solver

This paper presents a two phases flow model combined with a high order finite volume solver on unstructured mesh. The solver is highly conservative and preserves the sharpness of the interface without any reconstruction. Special care has been taken for boundedness preservation, as a high order scheme does not guaranty the boundedness of the volume fraction. The efficiency of the method is demonstrated with two numerical experiments: the simple advection test and the interaction between the shock and a bubble. Although experiments have been carried out with fine mesh, it is also demonstrated that the method allows satisfactory results to be obtained with coarse mesh

Performance assessment of a standard radial turbine as turbo expander for an adapted solar concentration ORC

Organic Rankine cycles are one of the available solutions for converting low grade heat source into electrical power. However the development of plants tends to be very expansive due to the specific design of the expander. Usually, the input parameters for designing an ORC plant are the temperature and power of the heat and cold sources. They lead to the selection of a working fluid, pressures and temperatures. The expander is then designed based on the required operating parameters. Using standard turbine easily available on the market and with well known performances would allow to reduce the development and manufacturing cost. However, the ORC would have to be adapted to make the expander work in its best conditions. For a solar concentrated heat source, the temperature and power can be adapted by adjusting the concentration factor and the total area of the collector. In this paper, a given gas turbine is considered to be used as the expander of the ORC. Knowing the turbine's performances with air, the optimal operating parameters (pressure, temperature, flow rate and rotational speed) of the ORC with different fluids are sought based on similitude rules. The adaptation aims to maintain the same density evolution, inlet speed triangle and inlet Mach number with the working fluid as with air. The performance maps of the turbine are then computed with CFD simulations and showed a maximum isentropic efficiency close to the one with air, about 78%

Multiphase smoothed particle hydrodynamics approach for modeling soil–water interactions

In this work, a weakly compressible smoothed particle hydrodynamics (WCSPH) multiphase model is developed. The model is able to deal with soil-water interactions coupled in a strong and natural form. A Regularized Bingham Plastic constitutive law including a pressure-dependent Mohr-Coulomb yield criterion (RBPMC-αμ) is proposed to model fluids, soils and their interaction. Since the proposed rheology model is pressure-sensitive, we propose a multiphase diffusive term to reduce the spurious pressure resulting from the weakly compressible flow hypothesis. Several numerical benchmarks are investigated to assess the robustness and accuracy of the proposed multiphase SPH model

Numerical assessment of fan blades screen effect on fan/OGV interaction tonal noise

This work deals with sound generation and transmission in a fan stage. The study is done on a subsonic Fan stage and interaction noise between the fan wakes and the Outlet Guide Vanes (OGV) is considered. For this purpose, the Linearized Euler Equations (LEE) are solved with a steady axisymmetric flow. The acoustic sources are modelled by a scattering approach. Numerical simulations are carried out in an unwrapped cylindrical layer using a high-order finite volume solver. In order to explicitly take into account the moving fan blades into the propagation medium, a high-resolution sliding mesh technique is used. The simulation results, which highlight the screen effect of moving fan blades on fan/OGV interaction tones, are consistent with analytical literature.Xesús Nogueira and Luis Ramírez acknowledge the support given by FEDER funds of the European Union, Grants #DPI2015- 68431-R of the Ministerio de Economía y Competitividad and #RTI2018-093366-B-I00 of the Ministerio de Ciencia, Innovación y Universidades of the Spanish Government, and by the Consellería de Cultura, Educación e Ordenación Universitaria of the Xunta de Galicia (program Axudas para potenciación de grupos de investigación do Sistema Universitario de Galicia 2018, grant #ED431C 2018/41)

High-order preserving sliding-mesh techniques for Turbomachinery

Ce travail porte sur le développement de maillages glissants pour le calcul d'écoulements/d'ondes acoustiques en présence de configuration avec rotor/stator. Deux familles de techniques de transmission de l'information d'un maillage à l'autre sont proposées. Afin de s'adapter aux applications industrielles et leurs géométries complexes, ces méthodes ont été proposé pour les maillages non-structurés. Basés sur l'approximation des moindres carrés mobiles, ces techniques s'adaptent naturellement à une discrétisation de type volumes finis d'ordre élevé. Dans cette communication nous montrons, à l'aide du cas test du pulse acoustique, les propriétés de précision et de conservation de ces méthodes numériques ainsi que leur domaine de stabilité

Numerical Investigations of Flows and Heat Transfer in Turbine Disk Cavities

In gas turbines, the stator wells play a key role in the efficiency of the turbomachine. The research for performance gains requires a good understanding and an accurate modeling of the flows and heat transfers occurring in these areas. Within the framework of the European program main annulus gas path interaction (MAGPI) WP1, a two-stage axial turbine test rig provided an experimental database used to validate the computational fluid dynamics (CFD) models. The aim of this study is to setup a numerical methodology using the CFD solver ANSYSFluent to accurately predict the conjugate heat transfer in the stator well area. The validation of the methodology relies on thorough comparison of the results with the MAGPI WP1 experimental temperature/pressure measurements. A geometry with axial cooling injection through lock plate slot was chosen. A Reynolds-averaged Navier–Stokes (RANS) three-dimensional sectorized CFD model of the turbine with conjugate heat transfer was used. It includes main gas path, cavities with labyrinths, disks rotor, the casing, and the nozzle guide vanes (NGV). Mixing planes are placed between the static and rotating frames. Different influences (mesh, turbulence model, thermal boundary conditions, radial labyrinths clearances) were studied and compared with experimental data. As a baseline, the first calculations were performed with a cooling flowrate chosen so that hot gas ingresses from the main stream into the stator well cavity. Good agreements between predicted and measured temperatures/pressures were observed, especially in the vicinity of the stator well. Discrepancies were spotted at the first rotor hub endwall and at the upstream wheelspace and will be discussed. Two other cooling configurations were conducted, one with cooling air exiting from the disk rim cavity to the main gas path and the other with the lowest cooling flowrate and so the highest ingress. Finally, the turbine performance under nonadiabatic conditions has been evaluated with an appropriate efficiency definition

Smoothed Particle Hydrodynamics: A consistent model for interfacial multiphase fluid flow simulations

In this work, a consistent Smoothed Particle Hydrodynamics (SPH) model to deal with interfacial multiphase fluid flows simulation is proposed. A modification to the Continuum Stress Surface formulation (CSS) [1] to enhance the stability near the fluid interface is developed in the framework of the SPH method. A non-conservative first-order consistency operator is used to compute the divergence of stress surface tensor. This formulation benefits of all the advantages of the one proposed by Adami et al. [2] and, in addition, it can be applied to more than two phases fluid flow simulations. Moreover, the generalized wall boundary conditions [3] are modified in order to be well adapted to multiphase fluid flows with different density and viscosity. In order to allow the application of this technique to wall-bounded multiphase flows, a modification of generalized wall boundary conditions is presented here for using the SPH method. In this work we also present a particle redistribution strategy as an extension of the damping technique presented in [3] to smooth the initial transient phase of gravitational multiphase fluid flow simulations. Several computational tests are investigated to show the accuracy, convergence and applicability of the proposed SPH interfacial multiphase model