pinecone/core-2020-05-10-deduplication huggingface dataset:
On the relative impact of subgrid-scale modelling and conjugate heat transfer in LES of hot jets in cross-ﬂow over cold plates\ud

This work describes numerical simulations of a hot jet in cross-ﬂow with applications to anti-ice systems of aircraft engine nacelles. Numerical results are compared with experimental measurements obtained at ONERA to evaluate the performances of LES in this industrial context. The combination of complex geometries requiring unstructured meshes and high Reynolds number does not allow the resolution of boundary layers so that wall models must be employed. In this framework, the relative inﬂuence of subgrid-scale modelling and conjugate heat transfer in LESs of aerothermal ﬂows is evaluated. After a general overview of the transverse jet simulation results, a LES coupled with a heat transfer solver in the walls is used to show\ud
that thermal boundary conditions at the wall have more inﬂuence on the results than subgrid scale models.\ud
Coupling ﬂuid ﬂow and heat transfer in solids simulations is the only method to specify their respective thermal boundary conditions. \u
An efficient discontinuous Galerkin method for aeroacoustic propagation

An efficient discontinuous Galerkin formulation is applied to the solution of the linearized Euler equations and the acoustic perturbation equations for the simulation of aeroacoustic propagation in two-dimensional and axisymmetric problems, with triangular and quadrilateral elements. To improve computational efficiency, a new strategy of variable interpolation order is proposed in addition to a quadrature-free approach and parallel implementation. Moreover, an accurate wall boundary condition is formulated on the basis of the solution of the Riemann problem for a reflective wall. Time discretization is based on a low dissipation formulation of a fourth-order, low storage Runge-Kutta scheme. Along the far-field boundaries a perfectly matched layer boundary condition is used. For the far-field computations, the integral formulation of Ffowcs Williams and Hawkings is coupled with the near-field solver. The efficiency and accuracy of the proposed variable order formulation is assessed for realistic geometries, namely sound propagation around a high-lift airfoil and the Munt problem
Kriging-based optimization applied to flow control

International audienceThe automatic optimization of flow control devices is a delicate issue, due to the drastic computational time related to unsteady high-fidelity flow analyses and the possible multimodality of the objective function. Thus, we experiment in this article the use of kriging-based algorithms to optimize flow control parameters, since these methods have shown their efficiency for global optimization at moderate cost. Navier-Stokes simulations, carried out for different control parameters, are used to build iteratively a kriging model. At each step, a statistical analysis is performed to enrich the model with new simulation results by exploring the most promising areas, until optimal flow control parameters are found. This approach is validated and demonstrated on two problems, including comparisons with similar studies: the control of the flow around an oscillatory rotating cylinder and the reduction of the intensity of a shock wave for a transonic airfoil by adding a bump to the airfoil profile
High-order implicit time integration for unsteady incompressible flows

The spatial discretization of unsteady incompressible Navier–Stokes equations is stated as a system of differential\ud
algebraic equations, corresponding to the conservation of momentum equation plus the constraint due\ud
to the incompressibility condition. Asymptotic stability of Runge–Kutta and Rosenbrock methods applied\ud
to the solution of the resulting index-2 differential algebraic equations system is analyzed. A critical comparison\ud
of Rosenbrock, semi-implicit, and fully implicit Runge–Kutta methods is performed in terms of\ud
order of convergence and stability. Numerical examples, considering a discontinuous Galerkin formulation\ud
with piecewise solenoidal approximation, demonstrate the applicability of the approaches and compare their\ud
performance with classical methods for incompressible flows.Peer ReviewedPostprint (published version
A moving mesh algorithm for aero-thermo-mechanical modelling in turbomachinery

This paper describes the development of a mesh deformation method used for aero-thermo-mechanical coupling of turbo-engine components. The method is based on the nonlinear solution of an elastic medium analogy, solved using finite element discretisation and modified to let the boundary nodes be free to slide over the deflected surfaces. This sliding technique relies on a B-spline reconstruction of the moving boundary and increases the robustness of the method in situations where the boundary deflection field presents significant gradients or large relative motion between two distinct boundaries. The performance of the method is illustrated with the application to an interstage cavity of a turbine assembly, subjected to the deformations computed by a coupled thermo-mechanical analysis of the engine component
On pressure boundary conditions for thermoconvective problems

Solving numerically hydrodynamical problems of incompressible fluids raises
the question of handling first order derivatives (those of pressure) in a
closed container and determining its boundary conditions. We research several
pressure boundary conditions for the primitive variables formulation of
thermoconvective problems. In particular we study the Marangoni instability of
an infinite fluid layer and we show that the numerical results with a Chebyshev
collocation method are highly correspondent to the exact ones. These ideas have
been applied to linear stability analysis of the B\'enard-Marangoni (BM)
problem in cylindrical geometry and the results obtained have been very
accurate.Comment: 16 pages, Latex, 1 figure. Some typos corrected. To appear in Int. J.
  for Numerical Methods in Fluid
Local moving least square-one-dimensional integrated radial basis function networks technique for incompressible viscous flows

This paper presents a local moving least square-one-dimensional integrated radial basis function networks
method for solving incompressible viscous flow problems using stream function-vorticity formulation. In this method, the partition of unity method is employed as a framework to incorporate the moving least square and one-dimensional integrated radial basis function networks techniques. The major advantages of the proposed method include the following: (i) a banded sparse system matrix which helps reduce the computational cost; (ii) the Kronecker-ı property of the constructed shape function which helps impose the essential boundary condition in an exact manner; and (iii) high accuracy and fast convergence rate owing to the use of integration instead of conventional differentiation to construct the local radial basis function approximations. Several examples including two-dimensional (2D) Poisson problems, lid-driven cavity flow and flow past a circular cylinder are considered, and the present results are compared with the exact solutions
and numerical results from other methods in the literature to demonstrate the attractiveness of the proposed method.
Numerical simulation of orbitally shaken viscous fluids with free surface

Orbitally shaken bioreactors are an emerging alternative to stirred-tank bioreactors for large-scale mam- malian cell culture, but their fluid dynamics is still not well defined. Among the theoretical and practical issues that remain to be resolved, the characterization of the liquid free surface during orbital shaking remains a major challenge because it is an essential aspect of gas transfer and mixing in these reactors. To simulate the fluid behavior and the free surface shape, we developed a numerical method based on the finite element framework. We found that the large density ratio between the liquid and the gas phases induced unphysical results for the free surface shape. We therefore devised a new pressure correction scheme to deal with large density ratios. The simulations operated with this new scheme gave values of wave amplitude similar to the ones mea- sured experimentally. These simulations were used to calculate the shear stress and to study the mixing principle in orbitally shaken bioreactorsPeer ReviewedPostprint (author’s final draft
Unified semi-analytical wall boundary conditions for inviscid, laminar or turbulent flows in the meshless SPH method

International audienceWall boundary conditions in smoothed particle hydrodynamics (SPH) is a key issue to perform accurate simulations. We propose here a new approach based on a renormalising factor for writing all boundary terms. This factor depends on the local shape of a wall and on the position of a particle relative to the wall, which is described by segments (in two-dimensions), instead of the cumbersome fictitious or ghost particles used in most existing SPH models. By solving a dynamic equation for the renormalising factor, we significantly improve traditional wall treatment in SPH, for pressure forces, wall friction and turbulent conditions. The new model is demonstrated for cases including hydrostatic conditions for still water in a tank of complex geometry and a dam break over triangular bed profile with sharp angle where significant improved behaviour is obtained in comparison with the conventional boundary techniques. The latter case is also compared with a finite volume and volume-of-fluid scheme. The performance of the model for a two-dimensional laminar flow in a channel is demonstrated where the profiles of velocity are in agreement with the theoretical ones, demonstrating that the derived wall shear stress balances the pressure gradient. Finally, the performance of the model is demonstrated for flow in a schematic fish pass where both the velocity field and turbulent viscosity fields are satisfactorily reproduced compared with mesh-based codes
Finite volume methods for unidirectional dispersive wave models

25 pages, 12 figures, 51 references. Other authors papers can be downloaded at http://www.lama.univ-savoie.fr/~dutykh/International audienceWe extend the framework of the finite volume method to dispersive unidirectional water wave propagation in one space dimension. In particular we consider a KdV-BBM type equation. Explicit and IMEX Runge-Kutta type methods are used for time discretizations. The fully discrete schemes are validated by direct comparisons to analytic solutions. Invariants conservation properties are also studied. Main applications include important nonlinear phenomena such as dispersive shock wave formation, solitary waves and their various interactions
One-dimensional shock-capturing for high-order discontinuous Galerkin methods

Discontinuous Galerkin methods have emerged in recent years as an alternative for nonlinear conservation equations. In particular, their inherent structure (a numerical flux based on a suitable approximate Riemann solver introduces some stabilization) suggests that they are specially adapted to capture shocks. However, numerical fluxes are not sufficient to stabilize the solution in the presence of shocks. Thus, slope limiter methods, which are extensions of finite volume methods, have been proposed. These techniques require, in practice, mesh adaption to localize the shock structure. This is is more obvious for large elements typical of high-order approximations. Here, a new approach based on the introduction of artificial diffusion into the original equations is presented. The order is not systematically decreased to one in the presence of the shock, large high-order elements can be used, and several linear and nonlinear tests demonstrate the efficiency of the proposed methodology.Peer ReviewedPostprint (published version
A formally second order cell centered scheme for convection-diffusion equations on unstructured non-conforming grids

International audienceWe propose, in this paper, a finite volume scheme to compute the solution of the convection-diffusion equation on unstructured and possibly non-conforming grids. The diffusive fluxes are approximated using the recently published SUSHI scheme in its cell centred version, that reaches a second-order spatial convergence rate for the Laplace equation on any unstructured two-dimensional/three-dimensional grids. As in the MUSCL method, the numerical convective fluxes are built with a prediction-limitation process, which ensures that the discrete maximum principle is satisfied for pure convection problems. The limitation does not involve any geometrical reconstruction, thus allowing the use of completely general grids, in any space dimension
Assessment of coupling conditions in water way intersections.

We present a numerical assessment of coupling conditions in T-junction for water flow in open canals. The mathematical model is based on the well-established shallow water equations for open channel flows. In the present work, the emphasis is given to the description of coupling conditions at canal-to-canal intersections. The accurate prediction of these coupling conditions is essential in order to achieve good performance and reliable numerical simulations of water canals in networks. There exist several theoretical results for coupling conditions in a reduced geometry. The purpose of our work is to numerically verify these conditions for different water flow regimes. More precisely, we consider a local zooming of the T-junction resulting in a two-dimensional flow problem at the canals intersection. A high-order non-oscillatory method is used for solving the governing two-dimensional equations, and the water flow solutions are space-averaged over the junction areas. The obtained are thereafter, used for verification and comparison with the theoretical results. Verifications are conducted for two types of junctions, namely the 1-to-2 and 2-to-1 situations
SWASHES: a compilation of Shallow Water Analytic Solutions for Hydraulic and Environmental Studies

40 pages There are some errors in the published version. This is a corrected version.International audienceNumerous codes are being developed to solve Shallow Water equations. Because there are used in hydraulic and environmental studies, their capability to simulate properly flow dynamics is critical to guarantee infrastructure and human safety. While validating these codes is an important issue, code validations are currently restricted because analytic solutions to the Shallow Water equations are rare and have been published on an individual basis over a period of more than five decades. This article aims at making analytic solutions to the Shallow Water equations easily available to code developers and users. It compiles a significant number of analytic solutions to the Shallow Water equations that are currently scattered through the literature of various scientific disciplines. The analytic solutions are described in a unified formalism to make a consistent set of test cases. These analytic solutions encompass a wide variety of flow conditions (supercritical, subcritical, shock, etc.), in 1 or 2 space dimensions, with or without rain and soil friction, for transitory flow or steady state. The corresponding source codes are made available to the community (http://www.univ-orleans.fr/mapmo/soft/SWASHES), so that users of Shallow Water-based models can easily find an adaptable benchmark library to validate their numerical methods
An unstructured finite-volume method for coupled models of suspended sediment and bed load transport in shallow-water flows.

The aim of this work is to develop a well-balanced finite-volume method for the accurate numerical solution of the equations governing suspended sediment and bed load transport in two-dimensional shallow-water flows. The modelling system consists of three coupled model components: (i) the shallow-water equations for the hydrodynamical model; (ii) a transport equation for the dispersion of suspended sediments; and (iii) an Exner equation for the morphodynamics. These coupled models form a hyperbolic system of conservation laws with source terms. The proposed finite-volume method consists of a predictor stage for the discretization of gradient terms and a corrector stage for the treatment of source terms. The gradient fluxes are discretized using a modified Roe's scheme using the sign of the Jacobian matrix in the coupled system. A well-balanced discretization is used for the treatment of source terms. In this paper, we also employ an adaptive procedure in the finite-volume method by monitoring the concentration of suspended sediments in the computational domain during its transport process. The method uses unstructured meshes and incorporates upwinded numerical fluxes and slope limiters to provide sharp resolution of steep sediment concentrations and bed load gradients that may form in the approximate solutions. Details are given on the implementation of the method, and numerical results are presented for two idealized test cases, which demonstrate the accuracy and robustness of the method and its applicability in predicting dam-break flows over erodible sediment beds. The method is also applied to a sediment transport problem in the Nador lagoon
Hybridizable discontinuous Galerkin p-adaptivity for wave propagation problems

A p-adaptive hybridizable discontinuous Galerkin method for the solution of wave problems is presented in a challenging engineering problem. Moreover, its performance is compared with a high-order continuous Galerkin. The hybridization technique allows to reduce the coupled degrees of freedom to only those on the mesh element boundaries, whereas the particular choice of the numerical fluxes opens the path to a superconvergent postprocessed solution. This superconvergent postprocessed solution is used to construct a simple and inexpensive error estimator. The error estimator is employed to obtain solutions with the prescribed accuracy in the area (or areas) of interest and also drives a proposed iterative mesh adaptation procedure. The proposed method is applied to a nonhomogeneous scattering problem in an unbounded domain. This is a challenging problem because, on the one hand, for high frequencies, numerical difficulties are an important issue because of the loss of the ellipticity and the oscillatory behavior of the solution. And on the other hand, it is applied to real harbor agitation problems. That is, the mild slope equation in frequency domain (Helmholtz equation with nonconstant coefficients) is solved on real geometries with the corresponding perfectly matched layer to damp the diffracted waves. The performance of the method is studied on two practical examples. The adaptive hybridizable discontinuous Galerkin method exhibits better efficiency compared with a high-order continuous Galerkin method using static condensation of the interior nodes.Peer ReviewedPostprint (author’s final draft
A meshless finite point method for three-dimensional analysis of compressible flow problems involving moving boundaries and adaptivity

This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving.A finite point method for solving compressible flow problems involving moving boundaries and adaptivity is presented. The numerical methodology is based on an upwind-biased discretization of the Euler equations, written in arbitrary Lagrangian–Eulerian form and integrated in time by means of a dual-time steeping technique. In order to exploit the meshless potential of the method, a domain deformation approach based on the spring network analogy is implemented, and h-adaptivity is also employed in the computations. Typical movable boundary problems in transonic flow regime are solved to assess the performance of the proposed technique. In addition, an application to a fluid–structure interaction problem involving static aeroelasticity illustrates the capability of the method to deal with practical engineering analyses. The computational cost and multi-core performance of the proposed technique is also discussed through the examples provided.Peer ReviewedPostprint (author's final draft
Stability of a Crank-Nicolson Pressure Correction Scheme Based on Staggered Discretizations

International audienceIn the context of Large Eddy Simulation of turbulent flows, the control of kinetic energy seems to be an essential requirement for the numerical scheme. Designing such an algorithm, ie as less dissipative as possible while being simple, for the resolution of variable density Navier-Stokes equations is the aim of the present work.The developed numerical scheme, based on a pressure correction technique, uses a Crank-Nicolson time discretization and a staggered space discretization relying on the Rannacher-Turek finite element. For the inertia term in the momentum balance equation, we propose a finite volume discretization, for which we derive a discrete analogue of the continuous kinetic energy local conservation identity. Contrary to what was obtained for the backward Euler discretization, the dissipation defect term associated to the Crank-Nicolson scheme is second order in time. This behaviour is evidenced by numerical simulations
A Petrov-Galerkin method for flows in cavities: enclosure of aspect ratio 8

A Petrov-Galerkin method for computations of fully enclosed flows is developed. It makes use of divergence-free basis functions which also satisfy the boundary conditions for the velocity field. This allows the elimination of the unknown pressure. The computational procedure reduces to the solution of a system of nonlinear first order ordinary\ud
differential equations for the spectral expansion coefficients. We illustrate the effectiveness and accuracy of the method by solving the problem of the two-dimensional thermoconvective flow in a rectangular cavity of aspect ratio 8 at Rayleigh number 3.4 x 10^5
A Modular, Operator Splitting Scheme for Fluid-Structure Interaction
  Problems with Thick Structures

We present an operator-splitting scheme for fluid-structure interaction (FSI)
problems in hemodynamics, where the thickness of the structural wall is
comparable to the radius of the cylindrical fluid domain. The equations of
linear elasticity are used to model the structure, while the Navier-Stokes
equations for an incompressible viscous fluid are used to model the fluid. The
operator splitting scheme, based on Lie splitting, separates the elastodynamics
structure problem, from a fluid problem in which structure inertia is included
to achieve unconditional stability. We prove energy estimates associated with
unconditional stability of this modular scheme for the full nonlinear FSI
problem defined on a moving domain, without requiring any sub-iterations within
time steps. Two numerical examples are presented, showing excellent agreement
with the results of monolithic schemes. First-order convergence in time is
shown numerically. Modularity, unconditional stability without temporal
sub-iterations, and simple implementation are the features that make this
operator-splitting scheme particularly appealing for multi-physics problems
involving fluid-structure interaction.Comment: International Journal for Numerical Methods in Fluid
A linear solver based on algebraic multigrid and defect correction for the solution of adjoint RANS equations

A new solution approach for discrete adjoint Reynolds-averaged Navier–Stokes equations is suggested. The approach is based on a combination of algebraic multigrid and defect correction. The efficient interplay of these two methods results in a fast and robust solution technique. Algebraic multigrid deals very well with unstructured grids, and defect correction completes it in such a way that a required second-order accuracy of the solution is achieved. The performance of the suggested solution approach is demonstrated on a number of representative benchmarks