Search results for "compressible"
showing 9 items of 29 documents
A numerical study of postshock oscillations in slowly moving shock waves
2003
Abstract Godunov-type methods and other shock capturing schemes can display pathological behavior in certain flow situations. This paper discusses the numerical anomaly associated to slowly moving shocks. We present a series of numerical experiments that illustrate the formation and propagation of this pathology, and allows us to establish some conclusions and question some previous conjectures for the source of the numerical noise. A simple diagnosis on an explicit Steger-Warming scheme shows that some intermediate states in the first time steps deviate from the true direction and contaminate the flow structure. A remedy is presented in the form of a new flux split method with an entropy i…
High-order simulation scheme for active particles driven by stress boundary conditions
2020
Abstract We study the dynamics and interactions of elliptic active particles in a two dimensional solvent. The particles are self-propelled through prescribing a fluid stress at one half of the fluid-particle boundary. The fluid is treated explicitly solving the Stokes equation through a discontinuous Galerkin scheme, which allows to simulate strictly incompressible fluids. We present numerical results for a single particle and give an outlook on how to treat suspensions of interacting active particles.
Two-Dimensional Boundary Layer Equations: High Resolution Capturing Methods
1993
In this paper we apply the piecewise hyperbolic and parabolic essentially non-oscillatory (ENO) capturing schemes (see [2] and [4]) to approximate the solution to the boundary layer equations for two-dimensional incompressible flow. We have tested several numerical examples analyzing their resolutive power and efficiency with respect to small values of the kinematic viscosity of the flow.
Localized forms of the LBB condition and a posteriori estimates for incompressible media problems
2018
The inf–sup (or LBB) condition plays a crucial role in analysis of viscous flow problems and other problems related to incompressible media. In this paper, we deduce localized forms of this condition that contain a collection of local constants associated with subdomains instead of one global constant for the whole domain. Localized forms of the LBB inequality imply estimates of the distance to the set of divergence free fields. We use them and deduce fully computable bounds of the distance between approximate and exact solutions of boundary value problems arising in the theory of viscous incompressible fluids. The estimates are valid for approximations, which satisfy the incompressibility …
Equilibrium real gas computations using Marquina's scheme
2003
Marquina's approximate Riemann solver for the compressible Euler equations for gas dynamics is generalized to an arbitrary equilibrium equation of state. Applications of this solver to some test problems in one and two space dimensions show the desired accuracy and robustness
The lift computation for an oscillating flat plate in incompressible potential flow
1994
The initial aim of this work was the estimation of the lift acting on a flat plate performing small oscillations in a plane uniform stream by means of a simplified model based on one or at the most two lumped vortices, and the assessment of its results by comparison to those that were exact. The model was found to work well up to a reduced frequency of about 1 or 2, above which the results diverged from those that were correct. In order to improve the model, its behaviour at very high frequencies was then investigated, discovering: (i) that if the number of lumped vortices is greater than one the possibility to impose all boundary conditions is subject to certain geometrical constraints; (i…
A flux-split algorithm applied to conservative models for multicomponent compressible flows
2003
In this paper we consider a conservative extension of the Euler equations for gas dynamics to describe a two-component compressible flow in Cartesian coordinates. It is well known that classical shock-capturing schemes applied to conservative models are oscillatory near the interface between the two gases. Several authors have addressed this problem proposing either a primitive consistent algorithm [J. Comput. Phys. 112 (1994) 31] or Lagrangian ingredients (Ghost Fluid Method by Fedkiw et al. [J. Comput. Phys. 152 (1999) 452] and [J. Comput. Phys. 169 (2001) 594]). We solve directly this conservative model by a flux-split algorithm, due to the first author (see [J. Comput. Phys. 125 (1996) …
Hybrid equilibrium element with high-order stress fields for accurate elastic dynamic analysis
2021
In the present article the two-dimensional hybrid equilibrium element formulation is initially developed, with quadratic, cubic, and quartic stress fields, for static analysis of compressible and quasi-incompressible elastic solids in the variational framework of the minimum complementary energy principle. Thereafter, the high-order hybrid equilibrium formulation is developed for dynamic analysis of elastic solids in the variational framework of the Toupin principle, which is the complementary form of the Hamilton principle. The Newmark time integration scheme is introduced for discretization of the stress fields in the time domain and dynamic analysis of both the compressible solid and qua…
Analysis of fluid flow through porous media based on x-ray micro-tomographic reconstructions
2010
This thesis deals with creeping fluid flow through fibrous porous materials. Permeability through a porous medium is a measure of the ability of the material to transmit fluids. For testing and demonstration purposes the permeability values of a few fibrous heterogeneous materials, namely synthetic non-woven felt, wet pressing felt, cardboard, newsprint and hardwood paper, were measured experimentally. Reconstructions of the same materials under similar compression states were captured by x-ray micro-tomography. The actual microscopic pore structure thus obtained was utilised in the numerical lattice-Boltzmann analysis for solving the fluid flow permeability of the materials. Agreement betw…