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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 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
NASA NTRS1976

Numerical simulation of small perturbation transonic flows

The results of a systematic study of small perturbation transonic flows are presented. Both the flow over thin airfoils and the flow over wedges were investigated. Various numerical schemes were employed in the study. The prime goal of the research was to determine the efficiency of various numerical procedures by accurately evaluating the wave drag, both by computing the pressure integral around the body and by integrating the momentum loss across the shock. Numerical errors involved in the computations that affect the accuracy of drag evaluations were analyzed. The factors that effect numerical stability and the rate of convergence of the iterative schemes were also systematically studied.

Seebass, A. R.↗
NASA NTRS1981

Transonic flow computations in cascades using finite element method

Analysis of transonic flow through a cascade of airfoils is investigated using the finite element method. Development of a computational grid suitable for complex flow structures and different types of boundary conditions is presented. An efficient pseudo-time integration scheme is developed for the solution of equations. Modeling of the shock and the convergence characteristics of the developed scheme are discussed. Numerical results include a 45 deg staggered cascade of NACA 0012 airfoils with inlet flow Mach number of 0.8 and angles of attack 1, 0, and 1 deg.

Akay, H. U.↗
NASA NTRS1985

Unsteady transonic flows - Introduction, current trends, applications

The computational treatment of unsteady transonic flows is discussed, reviewing the historical development and current techniques. The fundamental physical principles are outlined; the governing equations are introduced; three-dimensional linearized and two-dimensional linear-perturbation theories in frequency domain are described in detail; and consideration is given to frequency-domain FEMs and time-domain finite-difference and integral-equation methods. Extensive graphs and diagrams are included.

Yates, E. C., Jr.↗
NASA NTRS1991

Transonic Flows About A Fighter Airplane

Report describes computational study of transonic flows about airplane having shape similar to F-16A fighter. Navier-Stokes calculations simulate complicated flow fields and interactions.

Reznick, Steve↗
NASA NTRS1993

Analyzing Transonic Flow Over A Wing And Fuselage

TAWFIVE computer program calculates transonic flow over transport-type wing and fuselage. Combines multigrid acceleration technique in iterative solution of potential equation with use of integral-form boundary-layer equations to provide software tool computationally efficient, yet accurate enough for use in design. Simplifies solution process by breaking problem into loosely coupled set of modified equations. Inviscid-flow method, using standard inviscid-flow equations, valid in "outer" region away from wing, whereas boundary-layer equations valid in thin region near solid surface of wing. Written in FORTRAN 77.

Melson, N. Duane↗
NASA NTRS1983

Calculation of unsteady small disturbance transonic flow at arbitrary reduced frequency using an extended integral equation method.

A novel analytical-numerical method for calculating unsteady small disturbance transonic flow over airfoils has been developed. The method uses an extended integral equation technique, based on both the velocity potential and the acceleration potential, to predict unsteady aerodynamic loading on airfoils oscillating in subcritical transonic free stream conditions. The formulation is an extension of the work of Sivaneri and Harris (1980) for steady, non-lifting flows and utilizes the linear theory of Landahl (1961) for decoupling of steady and unsteady components. The analytical-numerical procedure involves several intnegrating schemes and applies to general frequencies of oscillations. The technique is illustrated by computing the transonic flow about parabolic arc airfoils. Specific unsteady results for reduced frequencies based on semi-chord of 0.01, 0.1, 0.3, 0.4 and 0.6 are given. Comparison of results with those obtained by an ADI finite difference scheme is made.

Lamah, C. A.↗
NASA NTRS1988

Calculations of transonic flows with shocks using Newton's method and direct solver. II - Solution of Euler equations

Transonic flows with shocks are simulated using steady Euler equations and by simultaneously solving the resulting nonlinear algebraic equations using Newton's method. At each iteration, a direct solver computes the corrections and the process is repeated until convergence is achieved. The corrections and errors are reduced quadratically with the present method, allowing solutions of machine accuracy to be obtained in a few steps. Nonunique inviscid solutions and nonunique solutions of the Navier Stokes equations for quasi-one-dimensional flows in nozzles are presented. Calculations are also presented for steady two-dimensional inviscid flows around a cylinder in the transonic regime.

Hafez, M.↗
NASA NTRS1974

Numerical simulation of high Reynolds number transonic flows

A code has been developed for simulating high Reynolds number transonic flow fields of arbitrary configuration. An explicit finite-difference method with time splitting is used to solve the time-dependent equations for compressible turbulent flow. A nonorthogonal computational mesh of arbitrary configuration facilitates the description of the flow field. The code is applied to simulate the flow over an 18 percent thick circular-arc biconvex airfoil at zero angle of attack and free-stream Mach number of 0.775. A simple mixing-length model is used to describe the turbulence and chord Reynolds numbers of 1, 2, 4, and 10 million are considered. The solution describes in sufficient detail both the shock-induced and trailing-edge separation regions, and provides the profile and friction drag.

Deiwert, G. S.↗
NASA NTRS1977

Calculation of transonic flow over supercritical airfoil sections

Two numerical methods for calculating the transonic flow, including viscous effects over lifting airfoil sections and experimental data are compared for turbulent flow over a supercritical airfoil. In addition, results for a NACA 64A010 airfoil at nonzero angle of attack are compared to demonstrate the applicability of the numerical methods to classical, lifting airfoils. One numerical method is a solution to the time-averaged Navier-Stokes equations throughout the entire flow field. The other is a hybrid method that combines inviscid, boundary-layer, and Navier-Stokes equations in appropriate regions of the flow field. Both methods adequately predict the surface pressures and flow field about the 64A010 airfoil at M = 0.8 and alpha = 2 deg when an appropriate turbulence model is used. The methods are not as successful for the supercritical airfoil.

Rose, W. C.↗
NASA NTRS1978

Solution of transonic flows by an integro-differential equation method

Solutions of steady transonic flow past a two-dimensional airfoil are obtained from a singular integro-differential equation which involves a tangential derivative of the perturbation velocity potential. Subcritical flows are solved by taking central differences everywhere. For supercritical flows with shocks, central differences are taken in subsonic flow regions and backward differences in supersonic flow regions. The method is applied to a nonlifting parabolic-arc airfoil and to a lifting NACA 0012 airfoil. Results compare favorably with those of finite-difference schemes.

Ogana, W.↗
NASA NTRS1979

On turbulence modeling for unsteady transonic flows

A detailed examination of the turbulent field in an unsteady transonic flow undergoing shock-induced separation is conducted. Ensemble-averaged mean and fluctuating velocities, obtained from conditionally sampled laser velocimeter data, are described and analyzed to assess the applicability of modeling concepts usually employed in steady-flow problems. Some comparisons with computations employing the Reynolds averaged Navier-Stokes equations with a mixing length turbulence model are then presented to illustrate the status of current predictive capabilities. The results appear to imply that turbulence models developed for steady flows apply and that the model need not reflect all the fine details of the turbulent structure but rather account in an approximate way for the production and destruction of the turbulence.

Marvin, J. G.↗
NASA NTRS1981

Numerical simulation of transonic flows in diffusers

Numerical simulations were made of two-dimensional transonic flows in diffusers, including flow separation induced by a shock or adverse pressure gradient. The mass-averaged, time-dependent, compressible Navier-Stokes equations, simplified by the thin-layer approximation, were solved using MacCormack's hybrid method. The eddy-viscosity formulation was described by the Wilcox-Rubesin's two-equation, k-omega model. Detailed comparison of the computed results with measurements showed good agreement in all cases, including one with massive separation induced by a strong shock. The computation correctly predicted the details of a distinct lambda shock pattern, closely duplicating the configuration observed experimentally in spark-schlieren photographs.

Liou, M.-S.↗
NASA NTRS1983

Use of CYBER 203 and CYBER 205 computers for three-dimensional transonic flow calculations

Experiences are discussed for modifying two three-dimensional transonic flow computer programs (FLO 22 and FLO 27) for use on the CDC CYBER 203 computer system. Both programs were originally written for use on serial machines. Several methods were attempted to optimize the execution of the two programs on the vector machine: leaving the program in a scalar form (i.e., serial computation) with compiler software used to optimize and vectorize the program, vectorizing parts of the existing algorithm in the program, and incorporating a vectorizable algorithm (ZEBRA I or ZEBRA II) in the program. Comparison runs of the programs were made on CDC CYBER 175. CYBER 203, and two pipe CDC CYBER 205 computer systems.

Melson, N. D.↗
NASA NTRS1985

Computations of unsteady transonic flows

During the last eight years, the subject of computational unsteady transonic aerodynamics has undergone a period of rapid growth. A brief survey of some of the fundamental advances during this period is provided, and some of the research done at NASA Ames Research Center is described in detail. The small-distance potential equation is considered, taking into account features of the unsteady transonic flow, the governing equation, the pressure coefficient, the wake condition, the airfoil tangency condition, the downstream boundary condition, the alternating direction implicit (ADI) algorithm, a grid system, boundary conditions, an airfoil with oscillating trailing edge flap, three types of shock-wave motion, and an example of a simple aeroelastic problem. A description is given of an implicit algorithm for the unsteady full potential equation in conservation form.

Goorjian, P. M.↗
NASA NTRS1990

Comparison Of Calculations Of Viscous Transonic Flow

Report presents compendium of results of numerical simulations of viscous transonic flows about airfoils. Results appear in narrative, tabular, and graphical form to facilitate comparisons with each other and with measured data.

Holst, Terry L.↗
NASA NTRS1991

Euler calculations of unsteady transonic flow in cascades

In the present paper, Euler calculations of unsteady transonic flow in cascades are presented. A finite volume scheme is used to discretize the equations, which are implemented on a blade-fitted deformable mesh. The space-discretized equations are integrated forward in time using a multistage Runge-Kutta scheme. Adaptive dissipation terms of the type proposed by Jameson and Baker are added to capture shocks and to suppress nonphysical oscillations. Phase-shifted boundary conditions are used to reduce the computational domain to a single reference passage. No assumptions of small amplitudes or small flow deflections are made. Thus, the present code makes it possible to carry out aeroelastic calculations for cases where the shock strengths and oscillation amplitudes exceed the inherent limitations of potential flow codes.

Bendiksen, Oddvar O.↗