5,341 research outputs found
Computational fluid dynamics
An overview of computational fluid dynamics (CFD) activities at the Langley Research Center is given. The role of supercomputers in CFD research, algorithm development, multigrid approaches to computational fluid flows, aerodynamics computer programs, computational grid generation, turbulence research, and studies of rarefied gas flows are among the topics that are briefly surveyed
On the plane wave Riemann Problem in Fluid Dynamics
The paper contains a stability analysis of the plane-wave Riemann problem for
the two-dimensional hyperbolic conservation laws for an ideal compressible gas.
It is proved that the contact discontinuity in the plane-wave Riemann problem
is unstable under perturbations. The implications for Godunovs method are
discussed and it is shown that numerical post shock noise can set of a contact
instability. A relation to carbuncle instabilities is established.Comment: 27 pages, 1 figur
Arbitrary-Lagrangian-Eulerian discontinuous Galerkin schemes with a posteriori subcell finite volume limiting on moving unstructured meshes
We present a new family of high order accurate fully discrete one-step
Discontinuous Galerkin (DG) finite element schemes on moving unstructured
meshes for the solution of nonlinear hyperbolic PDE in multiple space
dimensions, which may also include parabolic terms in order to model
dissipative transport processes. High order piecewise polynomials are adopted
to represent the discrete solution at each time level and within each spatial
control volume of the computational grid, while high order of accuracy in time
is achieved by the ADER approach. In our algorithm the spatial mesh
configuration can be defined in two different ways: either by an isoparametric
approach that generates curved control volumes, or by a piecewise linear
decomposition of each spatial control volume into simplex sub-elements. Our
numerical method belongs to the category of direct
Arbitrary-Lagrangian-Eulerian (ALE) schemes, where a space-time conservation
formulation of the governing PDE system is considered and which already takes
into account the new grid geometry directly during the computation of the
numerical fluxes. Our new Lagrangian-type DG scheme adopts the novel a
posteriori sub-cell finite volume limiter method, in which the validity of the
candidate solution produced in each cell by an unlimited ADER-DG scheme is
verified against a set of physical and numerical detection criteria. Those
cells which do not satisfy all of the above criteria are flagged as troubled
cells and are recomputed with a second order TVD finite volume scheme. The
numerical convergence rates of the new ALE ADER-DG schemes are studied up to
fourth order in space and time and several test problems are simulated.
Finally, an application inspired by Inertial Confinement Fusion (ICF) type
flows is considered by solving the Euler equations and the PDE of viscous and
resistive magnetohydrodynamics (VRMHD).Comment: 39 pages, 21 figure
Applied aerodynamics: Challenges and expectations
Aerospace is the leading positive contributor to this country's balance of trade, derived largely from the sale of U.S. commercial aircraft around the world. This powerfully favorable economic situation is being threatened in two ways: (1) the U.S. portion of the commercial transport market is decreasing, even though the worldwide market is projected to increase substantially; and (2) expenditures are decreasing for military aircraft, which often serve as proving grounds for advanced aircraft technology. To retain a major share of the world market for commercial aircraft and continue to provide military aircraft with unsurpassed performance, the U.S. aerospace industry faces many technological challenges. The field of applied aerodynamics is necessarily a major contributor to efforts aimed at meeting these technological challenges. A number of emerging research results that will provide new opportunities for applied aerodynamicists are discussed. Some of these have great potential for maintaining the high value of contributions from applied aerodynamics in the relatively near future. Over time, however, the value of these contributions will diminish greatly unless substantial investments continue to be made in basic and applied research efforts. The focus: to increase understanding of fluid dynamic phenomena, identify new aerodynamic concepts, and provide validated advanced technology for future aircraft
Regularity of weak solutions of the compressible isentropic Navier-Stokes equation
Regularity and uniqueness of weak solution of the compressible isentropic
Navier-Stokes equations is proven for small time in dimension under
periodic boundary conditions. In this paper, the initial density is not
required to have a positive lower bound and the pressure law is assumed to
satisfy a condition that reduces to when and
. In a second part we prove a condition of blow-up in
slightly subcritical initial data when . We finish by
proving that weak solutions in \T^{N} turn out to be smooth as long as the
density remains bounded in L^{\infty}(L^{(N+1+\e)\gamma}) with \e>0
arbitrary small
Long-Time Behavior of a Point Mass in a One-Dimensional Viscous Compressible Fluid and Pointwise Estimates of Solutions
We consider the motion of a point mass in a one-dimensional viscous
compressible barotropic fluid. The fluid--point mass system is governed by the
barotropic compressible Navier--Stokes equations and Newton's equation of
motion. Our main result concerns the long-time behavior of the fluid and the
point mass, and it gives pointwise convergence estimates of the volume ratio
and the velocity of the fluid to their equilibrium values. As a corollary, it
is shown that the velocity of the point mass satisfies a decay estimate
--- a faster decay compared to known for the
motion of a point mass in the viscous Burgers fluid~[J.~L.~V{\'{a}}zquez and
E.~Zuazua, Comm. Partial Differential Equations \textbf{28} (2003),
1705--1738]. The rate is essentially related to the compressibility and
the nonlinearity. As a consequence, it follows that the point mass is convected
only a finite distance as opposed to the viscous Burgers case. The main tool
used in the proof is the pointwise estimates of Green's function. It turns out
that the understanding of the time-decay properties of the transmitted and
reflected waves at the point mass is essential for the proof.Comment: Ver. 4: Although the logic of the proof is unchanged, some notations
have been changed and several typos are corrected. The abstract and the
introduction have been modified and some remarks are adde
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