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At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1993

Shock-vortex interaction over a 65-degree delta wing in transonic flow

Transonic flow over a 65-deg swept-back, sharp-edged, cropped delta wing is investigated computationally using the time-accurate solution of the unsteady, compressible, full Navier-Stokes equations with an implicit, upwind, flux-difference splitting, finite-volume scheme. Coarse and fine O-H grids are used to obtain the solution. The grid consists of 125 x 85 x 84 points in the wrap-around, normal, and axial directions, respectively. The results are presented for an angle of attack of 20 deg Mach number of 0.85 and Reynolds number of 3.23 x 10 exp 6. With the fine grid, the results show that a system of shocks has been captured over the upper wing surface and that the leading-edge vortex core experiences an unsteady supersonic vortex breakdown after passing through a spanwise shock near the wing trailing edge. The computed results at a certain time are in good agreement with the experimental data. Topological aspects of the vortex breakdown flowfield are also presented and discussed.

Kandil, Osama A.↗
NASA NTRS1981

Transonic flow studies

Major emphasis was on the design of shock free airfoils with applications to general aviation. Unsteady flow, transonic flow, and shock wave formation were examined.

Seebass, A. R.↗
NASA NTRS1988

A Study of Flow Separation in Transonic Flow Using Inviscid and Viscous Computational Fluid Dynamics (CFD) Schemes

A comparison of flow separation in transonic flows is made using various computational schemes which solve the Euler and the Navier-Stokes equations of fluid mechanics. The flows examined are computed using several simple two-dimensional configurations including a backward facing step and a bump in a channel. Comparison of the results obtained using shock fitting and flux vector splitting methods are presented and the results obtained using the Euler codes are compared to results on the same configurations using a code which solves the Navier-Stokes equations.

Rhodes, J. A.↗
NASA NTRS1988

A new look at wind tunnel flow quality for transonic flows

The implementation of several transonic hot wire anemometry techniques for obtaining fluctuating data related to wind tunnel flow quality has been evaluated. An overview of the theoretical considerations, calibration techniques, and related assumptions are discussed for the data presented from the LaRC 8' Transonic Pressure Tunnel. The impact of incorrect assumptions related to hot wire sensitivities are highlighted. Velocity, density, total temperature, and mass flow results from three-element, two-element, and single-element probes are presented in rms and spectral formats. Based on these comparisons, great caution should be used when relying on flow quality information obtained utilizing hot wire techniques other than the three-element technique.

Jones, Gregory S.↗
NASA NTRS1977

A Green's function formulation for a nonlinear potential flow solution applicable to transonic flow

Routine determination of inviscid subsonic flow fields about wing-body-tail configurations employing a Green's function approach for numerical solution of the perturbation velocity potential equation is successfully extended into the high subsonic subcritical flow regime and into the shock-free supersonic flow regime. A modified Green's function formulation, valid throughout a range of Mach numbers including transonic, that takes an explicit accounting of the intrinsic nonlinearity in the parent governing partial differential equations is developed. Some considerations pertinent to flow field predictions in the transonic flow regime are discussed.

Baker, A. J.↗
NASA NTRS1979

Laser velocimetry and holographic interferometry measurements in transonic flows

Measurements of the transonic flow about a two-dimensional airfoil have been made with holographic interferometry and laser velocimetry. Quantitative data obtained with the interferometer are compared to the laser velocimeter and surface pressure measurements to evaluate the accuracy of the technique. Good agreement in the results confirmed the two-dimensionality of the flow and the potential of the interferometer in making unsteady transonic flow measurements in the future.

Bachalo, W. D.↗
NASA NTRS1989

Design optimization of axisymmetric bodies in nonuniform transonic flow

An inviscid transonic code capable of designing an axisymmetric body in a uniform or nonuniform flow was developed. The design was achieved by direct optimiation by coupling an analysis code with an optimizer. Design examples were provided for axisymmetric bodies with fineness ratios of 8.33 and 5 at different Mach numbers. It was shown that by reducing the nose radius and increasing the afterbody thickness of initial shapes obtained from symmetric NACA four-digit airfoil contours, wave drag could be reduced by 29 percent for a body of fineness ratio 8.33 in a nonuniform transonic flow of M = 0.98 to 0.995. The reduction was 41 percent for a body of fineness ratio 5 in a uniform transonic flow of M = 0.925 and 65 percent for the same body but in a nonuniform transonic flow of M = 0.90 to 0.95.

Lan, C. Edward↗
NASA NTRS1981

Inviscid transonic flow over axisymmetric bodies

Axisymmetric transonic flow is of interest not only because of its practical application to missile and launch vehicle aerodynamics but also because of its relation, in terms of area rule, to fully three dimensional flow. RAXBOD computer program analyzes steady, inviscid, irrotational, transonic flow over axisymmetric bodies in free air. RAXBOD uses finite-difference relaxation method to solve numerically exact formulation of disturbance velocity potential with exact surface boundary conditions. Agreement with available experimental results has been good in cases where viscous effects and wind-tunnel wall interference are not important.

South, J. C., Jr.↗
NASA NTRS1989

Asymptotic methods for internal transonic flows

For many internal transonic flows of practical interest, some of the relevant nondimensional parameters typically are small enough that a perturbation scheme can be expected to give a useful level of numerical accuracy. A variety of steady and unsteady transonic channel and cascade flows is studied with the help of systematic perturbation methods which take advantage of this fact. Asymptotic representations are constructed for small changes in channel cross-section area, small flow deflection angles, small differences between the flow velocity and the sound speed, small amplitudes of imposed oscillations, and small reduced frequencies. Inside a channel the flow is nearly one-dimensional except in thin regions immediately downstream of a shock wave, at the channel entrance and exit, and near the channel throat. A study of two-dimensional cascade flow is extended to include a description of three-dimensional compressor-rotor flow which leads to analytical results except in thin edge regions which require numerical solution. For unsteady flow the qualitative nature of the shock-wave motion in a channel depends strongly on the orders of magnitude of the frequency and amplitude of impressed wall oscillations or fluctuations in back pressure. One example of supersonic flow is considered, for a channel with length large compared to its width, including the effect of separation bubbles and the possibility of self-sustained oscillations. The effect of viscosity on a weak shock wave in a channel is discussed.

Adamson, T. C., Jr.↗
NASA NTRS1983

Monotone implicit algorithms for the small-disturbance and full potential equations applied to transonic flows

Numerical calculations of transonic flows by potential equations typically use algorithms that change the method of calculation for regions of subsonic and supersonic flow. In this paper, implicit approximate-factorization algorithms are modified to use the monotonic switch in the type of finite-differencing that was developed by Godunov for the Euler equations. Calculations of flows over airfoils by these algorithms are compared with calculations by other methods that are in common usage. For the small-disturbance potential equation, comparisons are made with the Murman-Cole method and the monotone method of Engquist and Osher for both steady and unsteady flows. For the full potential equation, comparisons are made with the methods of Jameson and of Holst and Ballhaus for steady flows. The comparisons show that the monotone methods are more stable. For steady flows, solutions are obtained for cases where the Murman-Cole switch requires a time step over ten times smaller in order for the calculations to remain stable. These improvements are achieved with no increase in computer storage and only minor modifications in current codes.

Goorjian, P. M.↗
NASA NTRS1985

Solution of viscous transonic flow over wings

Since the calculations of plane steady transonic flows conducted by Murman and Cole (1971), steady progress has been made with respect to the computation of inviscid transonic flows. It has been found that it is inadequate to consider practical wing design at transonic speeds without considering the effects of viscosity and turbulence. The present study has the objective to develop a zonal method for viscous transonic flow over three-dimensional (3-D) wings. The employed approach follows closely the viscous/inviscid interaction techniques discussed by Melnik et al. (1983) for viscous flow about airfoils. Attention is given to inviscid flow equations and boundary conditions, the solution of 3-D boundary layer and wake, an iterative solution to viscid-inviscid interaction analysis, and results obtained for a transonic cruise wing of transport type.

Chow, R. R.↗
NASA NTRS1975

Strong interaction associated with transonic flow past boattailed afterbodies

The problem of transonic flow past boattails was studied with the aid of numerical relaxative schemes. Preliminary calculations were restricted to a particular model configuration which had been tested in an experimental program. It was found that the full potential equation must be considered in the study. The final results agreed very well with the experimental data. The investigation illustrates the strong interaction character of the transonic flow past a boattailed afterbody.

Chow, W. L.↗
NASA NTRS1977

On the prediction of viscous phenomena in transonic flows

An algorithm developed by MacCormack (1971) and applied to transonic flows by Deiwert (1974) is used in the reported investigation. The investigation is concerned with flows of aerodynamic interest. However, many of the concepts apply equally to flows in turbomachinery. Turbulent transonic flows are considered, taking into account a biconvex circular arc and a shockless lifting airfoil. A simple algebraic eddy viscosity model is used for the description of the turbulent transport process.

Deiwert, G. S.↗
NASA NTRS1990

Predictions Of Drag In Viscous Transonic Flow

NASA technical memorandum summarizes results of computations of viscous, transonic flow reported at Viscous Transonic Airfoil Workshop. Results reexamined and analyzed with special emphasis on drag. Compared with each other and with data from experiments. Test cases include attached and separated transonic flows about NACA 0012 airfoil.

Holst, Terry L.↗
NASA NTRS1978

Lifting line theory for transonic flow

Lifting line theory is applied to describe the flow about a lifting wing at transonic speeds. The method extends that of Van Dyke (1975), in which lifting line theory is viewed as a singular perturbation problem, to transonic flows. Inner and outer expansions as the aspect ratio approaches infinity of the transonic small disturbance equations are found. It is shown that the solutions match asymptotically. A boundary value problem is formulated which describes the first aspect ratio correction to the two dimensional cross sectional transonic flow. The theory is especially applicable to wings of similar cross-sections.

Cook, L. P.↗
NASA NTRS1983

Numerical computation of transonic flow governed by the full-potential equation

Numerical solution techniques for solving transonic flow fields governed by the full potential equation are discussed. In a general sense relaxation schemes suitable for the numerical solution of elliptic partial differential equations are presented and discussed with emphasis on transonic flow applications. The presentation can be divided into two general categories: An introductory treatment of the basic concepts associated with the numerical solution of elliptic partial differential equations and a more advanced treatment of current procedures used to solve the full potential equation for transonic flow fields. The introductory material is presented for completeness and includes a brief introduction (Chapter 1), governing equations (Chapter 2), classical relaxation schemes (Chapter 3), and early concepts regarding transonic full potential equation algorithms (Chapter 4).

Holst, T. L.↗