Documents published in Scipedia

• A mixed midelity conceptual design process for Boundary Layer Ingestion concepts

  O. Atinault, M. Méheut, S. Defoort

  eccomas2022.

  
  

  Abstract

  Boundary Layer Ingestion (BLI) is a promising concept that helps improving aircraft aeropropulsive performance. However, it remains difficult to bring together OAD (Overall Aircraft Design) process and high-fidelity tools due to the time of response of complex disciplinary tools. ONERA has thus developed a mixed fidelity approach inside its in-house OAD platform. The purpose is to mix conventional and robust OAD methods with high levels of fidelity from disciplinary tools such as CFD (Computational Fluid Dynamics), FEM (Finite Element Model) or CAA (Computational Aero Acoustics). This paper focuses on the integration of rapid CFD tools inside the OAD process, in order to assess BLI benefits. The resulting process is validated against reference and experimental cases when available, or high-fidelity RANS data elsewhere. The paper intends to present the tools and their validation process. These modules are applied to the common inlet concept, which aims at ingesting00% of the fuselage boundary layer. The results demonstrate the potential gain on the Power Saving Coefficient (up to 3% obtained with the L2 BLI module without resizing loop) but with non-negligible fan losses (up to 1.5%).

  Abstract
  Boundary Layer Ingestion (BLI) is a promising concept that helps improving aircraft aeropropulsive performance. However, it remains difficult to bring together OAD (Overall [...]

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• Shape Optimisation of Turbomachinery Components

  B. Semlitsch, A. Huscava

  eccomas2022.

  
  

  Abstract

  Low-order models are the first choice to find the initial design of turbomachinery components screening many configurations. The final optimisation of the three-dimensional geometry is crucial for the best performance. Because of the ability to accurately predict the performance of turbomachinery, fluid dynamic simulations became a powerful tool [10]. However, parameter studies for shape optimisation relying on fluid dynamic simulations are computationally expensive and might fail to reveal the optimal geometry. Gradient-based optimisation approaches allow a significant reduction of simulations and hence, determine the optimum efficiency. The adjoint method finds the optimisation gradient by calculating the derivatives of the state variables with respect to the design objective without the need for finite differences [6]. Thus, the adjoint optimisation is especially efficient for problems with many degrees of freedom and few design objectives, e.g. increasing efficiency. The application of the adjoint method for shape optimisation is demonstrated on the example of a centrifugal compressor impeller. The shape of the rotor blades is optimised, and the impact of different objection functions, i.e. reducing the required moment or increasing the achieved pressure ratio, and optimisation constraints, i.e. retaining the operating point or keeping an area ratio, is analysed. The results demonstrate that the compressor performance can be significantly improved using the adjoint method. However, the challenge is to obtain not only an optimised shape for operating points but also for the entire operating map. The final shapes, obtained for different operating points, are compared.

  Abstract
  Low-order models are the first choice to find the initial design of turbomachinery components screening many configurations. The final optimisation of the three-dimensional [...]

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• Hemodynamics in healthy and pathological thoracic aorta: integration of in-vivo data in CFD simulations and in in-vitro experiments

  A. Mariotti, E. Vignali, E. Gasparotti, P. Marchese, M. Morello, M. Salvetti, S. Celi

  eccomas2022.

  
  

  Abstract

  A comparison between the results of the CFD simulations and the in-vitro experiments carried out on a circulatory mock loop is presented. Both approaches integrate in-vivo measurements obtained from a patient-specific clinical data set. Three thoracic-aorta geometries are analyzed: a healthy aorta, an aneurysmatic aorta, and a coarctated aorta. The healthy geometry is obtained from Magnetic Resonance Imaging (MRI) acquisitions, together with the patient-specific flow-rate waveform, whereas the diseased ones are derived from the former geometry by locally morphing the vessel's wall. The open-source code Simvascular is used for simulations. The in-vitro results are measured in a fully controlled and sensorized circulatory mock loop for 3D-printed aortic models. Differently from in-vivo acquisitions, the experimental set-up eliminates some of the uncontrollable uncertainties that characterize MRI data. Indeed, perfect control of the flow rate and full knowledge of the wall model characteristics (rigid walls in the present case) is allowed in experiments and, thus, clear indications can be obtained to validate and improve the accuracy of numerical models. The numerical and experimental results are in good agreements for the three analyzed geometries and the flow-rate conditions. In-vivo data from the healthy case are in a satisfactory agreement with numerical/in-vitro results, and they can be ascribed to possible differences between MRI and numerical/in-vitro set-ups. The velocity fields obtained through CFD are consistent with the echographic results in in-vitro experiments, showing the same flow patterns in healthy and pathological cases.

  Abstract
  A comparison between the results of the CFD simulations and the in-vitro experiments carried out on a circulatory mock loop is presented. Both approaches integrate in-vivo [...]

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• Effect of Laser Beam Scattering in SPH-Simulation of Deep Penetration Laser Beam Welding

  D. Sollich, F. Fetzer, P. Eberhard

  eccomas2022.

  
  

  Abstract

  The effect of laser beam scattering on capillary stability and melt dynamics is investigated simulatively for deep penetration laser beam welding. The mesh-free Lagrangian Smoothed Particle Hydrodynamics (SPH) method is coupled with a ray-tracing scheme. The SPH model covers fluid and thermodynamics, including temperature-dependent surface tension, recoil pressure, heat conduction, and phase transitions. The ray tracer models the laser-material interaction by tracking the propagation of light rays within the capillary according to the laws of geometrical optics, and taking into account multiple reflections and scattering. Surface scattering due to surface roughness, and volume scattering due to condensed droplets or local changes of the complex refractive index in the vapor plume are evaluated separately. For surface scattering, the reflections at the material surface are divided into a specular part and a diffuse part with randomly reflected rays. For volume scattering, the Henyey-Greenstein model is used to specify the angular distribution of the scattered light ray. The effect of scattering is examined for laser beam welding of aluminum and titanium. The results show that volume scattering has a stabilizing effect on the capillary for the highly reflective material aluminum, while the effect of surface scattering is small for both materials.

  Abstract
  The effect of laser beam scattering on capillary stability and melt dynamics is investigated simulatively for deep penetration laser beam welding. The mesh-free Lagrangian [...]

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• Dirichlet boundary control of a steady multiscale fluid-structure interaction system

  G. Barbi, A. Chierici, V. Giovacchini, L. Manes, S. Manservisi, L. Sirotti

  eccomas2022.

  
  

  Abstract

  This work aims to extend the techniques used for the optimal control of the NavierStokes systems to control a steady multi-scale FSI system. In particular, we consider a multiscale fluid-structure interaction problem where the structure obeys a membrane model derived from the Koiter shell equations. With this approach, the thickness of the solid wall can be neglected, with a meaningful reduction of the computational cost of the numerical problem. The fluid-structure simulation is then reduced to the fluid equations on a moving mesh together with a Robin boundary condition imposed on the moving solid surface. The inverse problem is formulated to control the velocity on a boundary to obtain a desired displacement of the solid membrane. For this purpose, we use an optimization method that relies on the Lagrange multiplier formalism to obtain the first-order necessary conditions for optimality. The arising optimality system is discretized in a finite element framework and solved with an iterative steepest descent algorithm, used to reduce the computational cost of the numerical simulations.

  Abstract
  This work aims to extend the techniques used for the optimal control of the NavierStokes systems to control a steady multi-scale FSI system. In particular, we consider a multiscale [...]

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• A posteriori MOOD limiting approach for multicomponent flows on unstructured meshes

  P. Tsoutsanis, P. Farmakis

  eccomas2022.

  
  

  Abstract

  A relaxed, high-order, Multidimensional Optimal Order Detection (MOOD) framework is extended to the simulation of compressible multicomponent flows on unstructured meshes in the open-source unstructured compressible flow solver UCNS3D. The class of diffuse interface methods (DIM) is employed with a five-equation model. The high-order CWENO spatial discretisation is selected due to its low computational cost and improved non-oscillatory behaviour compared to the original WENO variants. The relaxed MOOD enhancement of the CWENO method has been necessary to further improve the robustness of the CWENO method. A series of challenging compressible multicomponent flow problems have been implemented in UCNS3D, including shock wave interaction with a water droplet and shock-induced collapse of bubbles arrays. Such problems are generally very stiff due to the strong gradients present, and it has been possible to tackle them using the extended MOOD-CWENO numerical framework.

  Abstract
  A relaxed, high-order, Multidimensional Optimal Order Detection (MOOD) framework is extended to the simulation of compressible multicomponent flows on unstructured meshes [...]

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• Non-reflecting boundary condtions on unstructured grids

  H. Kersken, C. Frey

  eccomas2022.

  
  

  Abstract

  Non-reflecting boundary condition at interfaces for flow simulations in turbomachinery using the method laid out by Giles [1] and Saxer [2] require averages or Fourier decomposition of the flow solution using stations of constant radius at the interface. On structured grids the grid generation process can easily enforce grids having element centers with this property while on unstructured grids this is rarely achievable. We describe an approach which works on an auxiliary mesh with a band structure created from the surface mesh at interfaces and study the influence of the prescribed distribution of the bands on the solution. The effectiveness of the approach is demonstrated by applying it to the simulation of a compressor stage and comparing the results with results obtained by using the existing approach for creating bands and a simulation on a structured grid.

  Abstract
  Non-reflecting boundary condition at interfaces for flow simulations in turbomachinery using the method laid out by Giles [1] and Saxer [2] require averages or Fourier decomposition [...]

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• Numerical methods for diffuse interface multifluid models

  C. Le Touze, N. Rutard

  eccomas2022.

  
  

  Abstract

  We describe some numerical methods developed in ONERA's Cedre platform to solve diffuse interface multifluid models with a view to realistic industrial applications. These methods are illustrated on test cases such as a shock-droplet interaction case.

  Abstract
  We describe some numerical methods developed in ONERA's Cedre platform to solve diffuse interface multifluid models with a view to realistic industrial applications. These [...]

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• Numerical Investigation of Oleo-Pneumatic Shock Absorber: A Multifidelity Approach

  A. Sheikh Al-Shabab, B. Grenko, D. Vitlaris, P. Tsoutsanis, A. Antoniadis, M. Skote

  eccomas2022.

  
  

  Abstract

  A representative shock absorber geometry is developed based on the general guidelines available in the literature, and it is validated against experimental measurements from a drop test. Simulations are conducted using a multi-fidelity approach ranging from unsteady scale resolving three-dimensional simulations to dynamic system models. High fidelity simulations provide a detailed insight into the flow physics inside the shock absorber, as well as help calibrate and validate lower fidelity methods, under conditions for which no experimental measurements are available to achieve that purpose. On the other hand, lower fidelity methods are used to efficiently scan the design space and test the dependency of the shock absorber performance on the various design parameters, in addition to identifying parameter combinations that would be of interest to investigate using a high-fidelity approach.

  Abstract
  A representative shock absorber geometry is developed based on the general guidelines available in the literature, and it is validated against experimental measurements from [...]

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• High-order, high-fidelity simulation of unsteady shock-wave/boundary layer interaction using flux reconstruction

  N. Goffart, B. Tartinville, K. Puri, C. Hirsch, S. Pirozzoli

  eccomas2022.

  
  

  Abstract

  In this work, a high-order implicit large-eddy simulation of an oblique shockwave/boundary layer interaction at Mach 2.3 is performed. The high-order solver is based on the flux reconstruction method, allowing an arbitrary order of accuracy. A particular attention is paid to the shock-capturing technique which consists in a combination of a Laplacian artificial viscosity with the Ducros sensor. The ability of such a solver to accurately predict the flow features is assessed on both steady and unsteady fields. In particular, the typical lowfrequency motion of the reflected shock is reproduced. The shock-capturing methodology is proven to be efficient at resolving the shocks without damping the turbulence in the boundary layer. The results obtained give confidence in this solver to study in more details the shockwave/boundary layer interaction phenomenon and future work is focused on the analysis of the oscillatory turbulent field in the interaction region.

  Abstract
  In this work, a high-order implicit large-eddy simulation of an oblique shockwave/boundary layer interaction at Mach 2.3 is performed. The high-order solver is based on the [...]

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