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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
All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

An embedded mesh procedure for leading-edge vortex flows

A cell-vertex scheme is outlined for solving the flow about a delta wing with M (sub infinity) is greater than 1. Embedded regions of mesh refinement allow solutions to be obtained which have much higher resolution than those achieved to date. Effects of mesh refinement and artificial viscosity on the solutions are studied, to determine at what point leading-edge vortex solutions are grid-converged. A macroscale and a microscale for the size of the vortex are defined, and it is shown that the macroscale (which includes the wing surface properties) is converged on a moderately refined grid, while the microscale is very sensitive to grid spacing. The level of numerical diffusion in the core of the vortex is found to be substantial. Comparisons with the experiment are made for two cases which have transonic cross-flow velocities.

Powell, Kenneth G.↗
NASA NTRS1985

Assessment of preliminary prediction techniques for wing leading-edge vortex flows at supersonic speeds

A theoretical investigation of the aerodynamics of sharp leading-edge delta wings at supersonic speeds has been conducted. The primary objective of this was to determine the applicability of existing theoretical methods to predict wing leading-edge separated-flow characteristics at conditions conductive to high-lift supersonic flight. Predicted results from two modified linear-theory methods (LTSTAR and VORCAM) are compared with experimental data. Comparison of the two methods for uncambered wings revealed that the LTSTAR code is in much better agreement with experimentally measured vortex strength, vortex position, and total lifting characteristics than the VORCAM code. Selected analysis was also performed with an Euler code, SWINT. The results of this study indicated that the SWINT code was not well suited to the analysis of wings with separated flow at high lift and low supersonic speeds.

Wood, R. M.↗
NASA NTRS1985

Computation of transonic vortex flows past delta wings Integral equation approach

The steady full-potential equation is written in the form of Poisson's equation, and the solution of the velocity field is expressed in terms of an integral equation. The solution consists of a surface integral of vorticity distribution on the wing and its free-vortex sheets and a volume integral of source distribution within a volume around the wing and its free-vortex sheets. The solution is obtained through successive iteration cycles. The source distribution is computed by using a mixed finite-difference scheme of the Murman-Cole type. The method is applied to delta wings. Numerical examples show that a conical shock is captured on the suction side of the wing. It is attached to the lower surface of the leading-edge vortex but does not necessarily reach to the wing surface.

Kandil, O. A.↗
NASA NTRS1984

Assessment of preliminary prediction techniques for wing leading-edge vortex flows at supersonic speeds

The applicability of existing theoretical models for predicting wing leading edge separated flow characteristics for high-lift supersonic flight was examined with regard to previous experimental force, pressure and flow visualization data. Correlations of data on uncambered delta wings revealed that the upper surface normal force and minimum pressure coefficients decreased nonlinearly with increasing angles of attack. The attainable vacuum pressure decreased with increasing Mach number, while the lower surface normal force increased nonlinearly with increasing speed. The LISTAR and VORCAM linear theory aerodynamic codes generated predictions for comparison with the data. LISTAR displayed better agreement with measured vortex strength and position and lifting characteristics than did VORCAM. The Euler code SWINT was ill-suited to calculating wing performance in separated flows at high lift and low supersonic speeds.

Wood, R. M.↗
NASA NTRS1988

Computational technique for compressible vortex flows using the integral equation solution

The steady full-potential equation is written in the form of Poisson's equation, and the solution for the velocity field is expressed in terms of an integral equation. The integral solution consists of two surface integrals and one volume integral. The solution is obtained through successive iteration cycles. Each cycle of iteration consists of two sub-cycles, an inner cycle for wake relaxation and an out cycle for the strength of the source distribution integrals representing the flow compressibility. The density gradients in the source distribution is computed by using a type-differencing scheme of the Murman-Cole type. The method is applied to delta wings and the numerical examples show that a curved shock is captured on the wing suction side beneath the leading edge vortex sheet. Recently, a modified version of the scheme was applied to rectangular wings. In this modified scheme, the surface integral terms were computed by using a bilinear distribution of vorticity on triangular vortex panels which represent the wing and its wake. The results were compared with the available experimental data and they are in good agreement.

Kandil, Osama A.↗
NASA NTRS1972

Wind tunnel test data for wing trailing vortex flow survey

Data are presented on velocity measurements made with hot wire anemometers in the wake of a model of the CV-990 aircraft and a rectangular wing in the NASA-Ames 2.14x3.05 meter (7- by 10-foot) wind tunnels. Variables included angle of attack, tunnel speed and axial distance up to 12 chord lengths downstream from the wing trailing edge. Effects of deflecting trailing edge flaps and small spoiler panels are shown.

Chigier, N. A.↗
NASA NTRS1977

Performance of high-area-ratio annular dump diffuser using suction-stabilized-vortex flow control

A short annular dump diffuser having a geometry conductive to formation of suction stabilized toroidal vortices in the region of abrupt area change was tested. The overall diffuser area ratio was 4.0 and the length to inlet height ratio was 2.0. Performance data were obtained at near ambient temperature and pressure for inlet Mach numbers of 0.18 and 0.30 with suction rates ranging from 0 to 18 percent of total inlet mass flowrate. Results show that the exit velocity profile could be readily biased toward either wall by adjustment of inner and outer wall suction rates. Symmetric exit velocity profiles were inherently unstable with a tendency to revert to a hub or tip bias. Diffuser effectiveness was increased from about 38 percent without suction to over 85 percent at a total suction rate of 10 to 12 percent. At the same time diffuser total pressure loss was reduced from 3.1 percent to 1.1 percent at an inlet Mach number of 0.3.

Juhasz, A. J.↗
NASA NTRS1978

Noise calculation on the basis of vortex flow models

Flow-modeling technique yields relatively simple method for calculating sound radiation involving planar, cylindrical, or spherical surfaces. Model employs potential flow theory with action of viscosity on flowfield described in terms of point vortices. Surface presence in flow is analyzed, using classical image method; sound is calculated through sound generation theory reformulation.

Hardin, J. C.↗
NASA NTRS1978

Performance characteristics of two annular dump diffusers using suction-stabilized vortex flow control

Test results are described for two abrupt area change annular diffusers with provisions for maintaining suction stabilized toroidal vortices at the area discontinuity. Both diffusers had an overall area ratio of 4.0 with the prediffuser area ratio being 1.18 for diffuser A and 1.4 for diffuser B. Performance was evaluated at near atmospheric pressure and temperature for a range of inlet Mach numbers from 0.18 to 0.41 and suction rates from 0 to 18%. Static pressure recovery improved significantly as the suction rate was increased to approximately 11%. Results obtained with diffuser A were superior to that obtained with diffuser B. Flat radial profiles of exit velocity were not obtained since the flow showed preferential hub or tip attachment at moderate suction rates. At high suction rates the diffuser exit flow became circumferentially nonuniform and unstable.

Juhasz, A. J.↗
NASA NTRS1978

Measurements of unsteady vortex flow fields

A combined surface hot film and laser velocimeter measurement technique, used to obtain new information on the mean, constant phase-averaged and turbulent structure of time-dependent flow fields, is described. Data obtained in a cylinder wake are presented, and its structure in both the Eulerian and Lagrangian frames is discussed. Turbulence data obtained by conventional and conditional averaging of the velocity fluctuations are also presented. These data provide details of the small- and large-scale contributions to the total turbulent field.

Owen, F. K.↗