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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 163 records · Page 9
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NASA NTRS1976

Transonic solutions of the Euler equations by the finite volume method

An investigation is conducted of the time-accurate convergence of representative transonic flows to a steady state under given constraints of time-accuracy. Factored explicit and implicit difference operators are used to accelerate the calculations. Attention is given to flow at a Mach number of 1.35 past a circular cylinder and supersonic flow past a NACA 0012 airfoil for three different Mach numbers. Questions of transonic wave behavior are considered along with the equations of motion and the characteristics of the mesh network.

Rizzi, A.↗
NASA NTRS1977

A finite volume method for transonic potential flow calculations

It is proposed to solve the exact transonic potential flow equation on a mesh constructed from small volume elements, which can be conveniently packed around any reasonably smooth configuration. The calculation is performed on two sets of interlocking cells. The velocity and density are calculated in the primary cells, and a flux balance is then established in the secondary cells. The scheme is desymmetrized by the addition of artificial viscosity in the supersonic zone. Some results are included for a swept wing and a wing-cylinder combination.

Jameson, A.↗
NASA NTRS1977

Numerical calculation of transonic flow past a swept wing by a finite volume method

The utility of numerical methods for predicting transonic flows over wings and bodies is well established. The computer program FLO22, based on a method presented earlier, has actually been widely used to calculate the aerodynamic performance of wings of transport aircraft. Provided that a correction is made for the displacement effect of the viscous boundary layer, this code has been found to give predictions which are accurate enough to serve as a useful design guide. The main disadvantages of the scheme used in FLO22 are the use of nonconservative difference formulas, which result in a failure to satisfy conservation of mass across shock waves, and the difficulty of finding suitable transformations of coordinates to permit the treatment of more complex geometric configurations. The method described here is an attempt to overcome these shortcomings, while retaining the successful features of the previous method. The basic idea is to use a discrete approximation which directly represents a balance of the mass flow through small volume elements. This leads to a relatively simple treatment of the potential flow equation in conservation form.

Jameson, A.↗
NASA NTRS1978

A finite volume method for calculating transonic potential flow around wings from the pressure minimum integral

Analysis of the pressure minimum integral in the calculation of three-dimensional potential flow around wings makes it possible to use non-rectangular mesh networks for distributing the three-dimensional potential into discrete points. The method is comparatively easily expanded to the treatment of realistic airplane configurations. Shock-pressure affected pressure distributions on any wings are determined with accuracy using this method.

Eberle, A.↗
NASA NTRS1985

A comparison of finite volume flux vector splittings for the Euler equations

A comparison is made between the computational results of the Steger-Warming (1981) and van Leer (1982) flux splitting methods, which have been applied in generalized coordinates to quasi-one-dimensional transonic flow in a nozzle and two-dimensional subsonic, transonic, and supersonic flow over airfoils. The latter splitting method leads to higher convergence rates and a sharper representation of shocks in the transition region. The second-order accurate, one-sided-difference model is extended to a third-order, upwind-biased model with only small additional computational effort.

Anderson, W. K.↗
NASA NTRS1985

A finite volume method for the calculation of compressible chemically reacting flows

Several efficient pseudo time techniques have been developed for calculating steady state chemically reacting flows. The techniques include the implicit treatment of the chemical source term, point implicit multiple grid accelerator and a constant CFL condition. It turns out that these methods can be viewed as ways of rescaling the equations in time such that all chemical and convective phenomena evolve at comparable pseudo time scales. Consequently the number of iterations needed to solve reacting problems is approximately the same as for non-reacting problems. The techniques are demonstrated for a simple dissociation model and a nontrivial H2 - Air combustion model.

Bussing, T. R. A.↗
NASA NTRS1987

Conservative finite volume solutions of a linear hyperbolic transport equation in two and three dimensions using multiple grids

The feasibility of the multiple grid technique is investigated by solving linear hyperbolic equations for simple two- and three-dimensional cases. The results are compared with exact solutions and those obtained from the single grid calculations. It is demonstrated that the technique works reasonably well when two grid systems contain grid cells of comparative sizes. The study indicates that use of the multiple grid does not introduce any significant error and that it can be used to attack more complex problems.

Tiwari, Surendra N.↗
NASA NTRS1989

A time accurate finite volume method for propulsion chamber flows

An implicit three-dimensional time-accurate method for propulsion chamber flows is proposed which uses line Gauss-Seidel relaxation and multiple axial sweeps for the convergence of each time step. The general time-integration algorithm employed includes such schemes as the Euler implicit method. The results of spatial and temporal accuracy tests reveal that Roe's (1981) flux difference splitting provides excellent tracking of acoustic wave speeds. In comparison with other methods, no low mean flow Mach number convergence limitation or Courant number stabilization restriction is observed.

Beddini, R. A.↗
NASA NTRS1992

Aspects of Unstructured Grids and Finite-Volume Solvers for the Euler and Navier-Stokes Equations

One of the major achievements in engineering science has been the development of computer algorithms for solving nonlinear differential equations such as the Navier-Stokes equations. In the past, limited computer resources have motivated the development of efficient numerical schemes in computational fluid dynamics (CFD) utilizing structured meshes. The use of structured meshes greatly simplifies the implementation of CFD algorithms on conventional computers. Unstructured grids on the other hand offer an alternative to modeling complex geometries. Unstructured meshes have irregular connectivity and usually contain combinations of triangles, quadrilaterals, tetrahedra, and hexahedra. The generation and use of unstructured grids poses new challenges in CFD. The purpose of this note is to present recent developments in the unstructured grid generation and flow solution technology.

Barth, Timothy J.↗