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Results for “Vortex flows”

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 847 records · Page 47
All sourcesNASA NTRSDOE OSTI
NASA NTRS1972

Lee-surface vortex effects over configurations in hypersonic flow.

The role of vortices in producing intense localized hea ting to the leeward regions of a variety of configurations is shown and discussed. From experimental results, flow-field models are proposed which account for the interaction of the vortex and the upper surface boundary layer; correlation of the heating is then possible for planar delta wings. Guidelines derived from these studies are offered which reduce the vortex-induced heating by appropriate shaping of configurations such as the space shuttle. Reynolds number is shown to exert a large influence on the magnitude and location of the induced heating.

Whitehead, A. H., Jr.↗
NASA NTRS1976

Implicit finite-difference procedures for the computation of vortex wakes

Implicit finite-difference procedures for the primitive form of the incompressible Navier-Stokes and the compressible Euler equations are used to compute vortex wake flows. The partial differential equations in strong conservation-law form are transformed to cluster grid points in regions with large changes in vorticity. In addition to clustering, fourth-order accurate, spatial difference operators are used to help resolve the flow-field gradients. The use of implicit time-differencing permits large time steps to be taken since temporal variations are typically small. Computational efficiency is achieved by approximate factorization. Both two-dimensional and preliminary three-dimensional calculations are described and qualitatively compared with existing experimental data.

Steger, J. L.↗
NASA NTRS1977

The effect of blade sweep on propeller performance

The advanced propeller developed for high Mach number cruise incorporates swept blades to reduce compressibility losses. In order to evaluate the induced flow-field vortex lattice methods are applied to a swept propeller blade. The blade is modeled by a radial distribution of helical horseshoe vortices with a single swept bound vortex at the quarter chord and the control point at the three-quarter chord of each radial section. The results of numerical calculations show that the power coefficient decreases as the blade is swept and the power loading distribution shifts inboard.

Sullivan, J. P.↗
NASA NTRS1979

Computational simulation of corotational vortex merger using 0, 1, and 2 equation turbulence models

A computational study has been conducted to gain a better understanding of the role of turbulence in the merger of corotating vortices and in the decay of a single vortex. The flow field is simulated by using an inviscid flow model and zero-, one-, and two-equation turbulent-flow models. An implicit finite-difference procedure is employed to integrate the unsteady, two-dimensional, incompressible flow equations in a cross-plane. In the zero- and one-equation models, a spatially varying mixing-length model that simulates the streamline curvature effect is used to define an eddy viscosity. The computational merging distance criterion is in good agreement with the experimental one. In the case of the two-equation model, the turbulent kinetic energy and a modified rate of dissipation equation incorporating a curvature correction term are solved. A comparative study of the computational results corresponding to the various flow models and the available experimental data is presented.

Raj, P.↗
NASA NTRS1984

Laser velocimeter measurements of dynamic stall

Laser velocimeter measurements were made during the study of a two-dimensional NACA 0012 airfoil undergoing conditions of dynamic stall. The measurements, which were obtained in the Ames 2 foot wind tunnel at reduced frequencies of 0.12 and 1.2, show significant flow field hysteresis around the static stall angle. Comparisons were also made with dual-plate interferograms and good agreement was found for the attached flow cases. For separated flow, characteristic vortex shedding caused poor agreement and significantly increased the measured Reynolds shear stresses.

Owen, F. K.↗
NASA NTRS1987

Numerical solution of the Navier-Stokes equations with emphasis on rotorcraft applications

Recent advances in CFD are surveyed, with a focus on the applicability of codes based on the Navier-Stokes (NS) equations to helicopter aerodynamics. The developmental history of two- and three-dimensional NS codes is recalled; the formulations employed by codes of increasing complexity are outlined; and previous reviews are noted. Particular attention is given to Reynolds-averaged NS methods and their use in analyzing subsonic, transonic, and vortex-dominated flows. Typical numerical results are compared with experimental data in diagrams and graphs, and a number of outstanding problems are considered.

Holst, Terry L.↗
NASA NTRS1988

Prediction of unsteady loads on maneuvering delta wings using time-accurate Euler schemes

Three-dimensional steady and unsteady vortex-dominated flows around sharp-edged delta wings are considered in this paper. The problem is formulated by using the unsteady conservative Euler equations for the flow relative motion with respect to a moving frame of reference. An implicit approximately-factored finite volume scheme is used to solve the resulting equations on a three-dimensional computational grid which is generated by using a modified Joukowski transformation in cross-flow planes at the grid chord stations. The scheme is applied to a delta wing undergoing pitching oscillation around a large angle of attack. The initial conditions correspond to a steady flow around a delta wing of aspect ratio of one, freestream Mach number of 0.3 and mean angle of attack of 20.5. The steady flow results are compared with those of an explicit computational scheme and the experimental data, and they are in good agreement.

Kandil, Osama A.↗