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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 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
NASA NTRS1996

Effects of Coupled Rolling and Pitching Oscillations on Transonic Shock-Induced Vortex-Breakdown Flow of a Delta Wing

Unsteady, transonic vortex-breakdown flow over a 65 deg. sharp edged, cropped-delta wing of zero thickness undergoing forced coupled pitching and rolling oscillations is investigated computationally. The initial condition of the flow is characterized by a transverse terminating shock which induces of the leading edge vortex cores to breakdown. The computational investigation uses the time-accurate solution of the laminar, unsteady, compressible, full Navier-Stokes equations with the implicit, upwind, Roe flux-difference splitting, finite-volume scheme. The main focus is to analyze the effects of coupled motion on the wing response and vortex-breakdown flow by varying oscillation frequency and phase angle while keeping the maximum pitch and roll amplitude equal.

Kandil, Osama A.↗
NASA NTRS2024

Prediction of Concentrated Vortex Aerodynamics: Current CFD Capability Survey

Concentrated vortex flows contribute to the aerodynamic performance of aircraft at elevated load conditions. For military interests, the vortex flows are exploited at maneuver conditions of combat aircraft and missiles. For transport interests, the vortex flows are exploited at takeoff and landing conditions as well as at select transonic conditions. Aircraft applications of these vortex flows are reviewed with a historical perspective followed by a discussion of the underlying physics of a concentrated vortex flow. A hierarchy of computational fluid dynamics simulation technology is then presented followed by findings from a capability survey for predicting concentrated vortex flows with computational fluid dynamics. Results are focused on military and civil aircraft; only limited results are included for missiles. Opportunities for predictive capability advancement are then reported with comments related to digital transformation interests. A hierarchical approach that merges a physics-based perspective of the concentrated vortex flows with a systems engineering viewpoint of the air vehicle is also used to frame much of the discussion.

vortex flow↗
NASA NTRS1983

Vortex flap flow reattachment line and subsonic longitudinal aerodynamic data on 50 deg to 74 deg Delta wings on common fuselage

Positions of the primary vortex flow reattachment line and longitudinal aerodynamic data were obtained at Mach number 0.3 for a systematic series of vortex flaps on delta wing body configurations with leading edge sweeps of 50, 58, 66, and 74 deg. The investigation was performed to study the parametric effects of wing sweep, vortex flap geometry and deflection, canards, and trailing edge flaps on the location of the primary vortex reattachment line relative to the flap hinge line. The vortex reattachment line was located via surface oil flow photographs taken at selected angles of attack. Force and moment measurements were taken over an angle of attack range of -1 deg to 22 deg at zero sideslip angle for many configurations to further establish the data base and to assess the aforementioned parametric effects on longitudinal aerodynamics. Both the flow reattachment and aerodynamic data are presented.

Frink, N. T.↗
NASA NTRS1989

Improved Flow-Controlling Vortex Generator

Symmetrical tangential streams control flow of radial primary streams. Vortex generator uses small secondary stream of fluid to control normally-larger primary stream. Improved version of vortex generator described in "Variable Control Port for Fluidic Control Device," (NPO-16603). Secondary, or control, flows entering tangentially through diametrically opposite ports set up swirling motion restraining primary flow. Pressure of secondary fluid in relation to primary fluid controlling factor. Like valve, vortex generator varies rate of flow of primary fluid from maximum value down to zero. When properly designed, requires low pressure differential between primary and secondary streams and expends relatively small amount of secondary fluid.

Collins, Earl R., Jr.↗
NASA NTRS1992

Computation of vortex wake flows and control of their effects on trailing wings

The near-vortex-wake flow of a large aspect-ratio rectangular wing is accurately computed by using the thin-layer and full Navier-Stokes (NS) equations. The chordwise section of the wing is a NACA-0012 airfoil and its tip is round. The computations have been carried out on a fine C-O grid using an implicit, upwind, flux-difference splitting, finite-volume scheme. The thin-layer NS results have been obtained with and without flux limiters, and the full NS results have been obtained without flux limiters. Flow transition from laminar to turbulent is mimicked by turning-on the Baldwin-Lomax algebraic model at an experimentally prescribed chord-station location of 0.05. Comparison of computed results and experimental data shows that the full NS results give the best resolution of the near-vortex-wake flow. Next, the strength of the wing-tip vortex has been reduced substantially without reducing the lift coefficient by using flow-injection from a slot along a portion of the wing tip. The flow injection is directed in the wing plane at 45 deg with the wing-tip chord.

Wong, Tin-Chee↗
NASA NTRS1985

A three-dimensional viscous flow analysis for the helicopter tip vortex generation problem

The tip vortex flow field occurring in the vicinity of the tip region of a a helicopter rotor blade is a very complicated three-dimensional, viscous flow phenomenon. The details of the flow in the tip region can have a major effect in determining the generated rotor noise and can significantly affect the performance and dynamic loading of the rotor blade. The three-dimensional viscous subsonic tip vortex generation processes is investigated by a numerical procedure which allows spatial forward-marching integration, utilizing flow approximations from the velocity-decomposition approach of Briley and McDonald. The approach has been applied to compute the laminar and turbulent tip vortex flows for a constant thickness slab airfoil with a square tip, a constant thickness slab airfoil with a half round tip and a NACA 0012 airfoil with a half round tip. The basic mechanism of the tip vortex generation process as well as the prediction of vortex appearance, strength and secondary flow shown by the calculations are in qualitative agreement with experimental results.

Lin, S. J.↗
NASA NTRS1986

A three-dimensional viscous flow analysis for the helicopter tip vortex generation process about square and round tipped blades

The tip vortex flow field occurring in the vicinity of the tip region of a helicopter rotor blade is a very complicated three-dimensional, viscous flow phenomenon. The details of the flow in the tip region can have a major effect in determining the generated rotor noise and can significantly effect the performance and dynamic loading of the rotor blade. The three-dimensional viscous subsonic tip vortex generation processes is investigated by a numerical procedure which allows spatial forward-marching integration, utilizing flow approximations from the velocity-decomposition approach of Briley and McDonald. The approach has been applied to compute the laminar and turbulent tip vortex flows for a constant thickness slab airfoil with a square tip, a constant thickness slab airfoil with a half round tip and a NACA 0012 airfoil with a half round tip. The basic mechanism of the tip vortex generation process as well as the prediction of vortex appearance, strength and secondary flow shown by the calculations are in qualitative agreement with experimental results.

Lin, S.-J.↗
NASA NTRS1984

Two dimensional blade-vortex interaction flow visualization study

Blade-vortex interaction occurs when a rotor blade encounters the tip vortex from a previous rotor blade. To obtain details of the close encounter process, the results from a flow visualization study of an airfoil representing a rotor blade in the wake of an oscillating airfoil serving as a vortex generator are described. A distinguishing feature of this study is that the vortex filament is oriented parallel to the blade span, orthogonal to the test section free stream velocity. This orientation simulates the case of two-dimensional blade-vortex interaction, which is known to produce the most impulsive and most intensive BVI noise. Photographic data are examined to deduce qualitative and quantitative details of the close encounter interaction process with emphasis on structural changes in the vortex filament and its trajectory.

Booth, E. R., Jr.↗
NASA NTRS1993

Prediction and control of vortex-dominated and vortex-wake flows

This progress report documents the accomplishments achieved in the period from December 1, 1992 until November 30, 1993. These accomplishments include publications, national and international presentations, NASA presentations, and the research group supported under this grant. Topics covered by documents incorporated into this progress report include: active control of asymmetric conical flow using spinning and rotary oscillation; supersonic vortex breakdown over a delta wing in transonic flow; shock-vortex interaction over a 65-degree delta wing in transonic flow; three dimensional supersonic vortex breakdown; numerical simulation and physical aspects of supersonic vortex breakdown; and prediction of asymmetric vortical flows around slender bodies using Navier-Stokes equations.

Kandil, Osama↗
NASA NTRS1985

Vortex-dominated flow with viscous core structure

Recent theoretical studies of vortex-dominated flows are reviewed with special emphasis on those for which the viscous core structures play an important role. The problems to be described are: The interaction and merging of two-dimensional vortices and of curved vortex filaments, the roll-up and decay of trailing far wakes, and the initiation of vortex breakdown. The analysis utilizes finite-difference solutions of the Navier-Stokes equations complemented by asymptotic expansion techniques.

Liu, C. H.↗
NASA NTRS1992

Influence of airfoil geometry on delta wing leading-edge vortices and vortex-induced aerodynamics at supersonic speeds

An assessment of the influence of airfoil geometry on delta wing leading edge vortex flow and vortex induced aerodynamics at supersonic speeds is discussed. A series of delta wing wind tunnel models were tested over a Mach number range from 1.7 to 2.0. The model geometric variables included leading edge sweep and airfoil shape. Surface pressure data, vapor screen, and oil flow photograph data were taken to evaluate the complex structure of the vortices and shocks on the family of wings tested. The data show that airfoil shape has a significant impact on the wing upper surface flow structure and pressure distribution, but has a minimal impact on the integrated upper surface pressure increments.

Wood, Richard M.↗
NASA NTRS1986

Vortical dissipation in two-dimensional shear flows

An exact expression is derived for the viscous dissipation function of a real homogeneous and isotropic fluid, which has terms associated with the square of vorticity, wave radiation, and dilatation. The implications of the principle of maximal dissipation rate, are explored by means of this equation for a parallel channel flow and a cylindrical vortex flow. The consequences of a condition of maximum dissipation rate on the growth of disturbances in an unsteady, laminar shear layer are apparently consistent with predictions and observations of maximum growth rate of vortical disturbances. Finally, estimates of the magnitudes of several dissipative components of an unsteady vortex flow are obtained from measurements of a periodic wall jet.

Horne, W. Clifton↗
NASA NTRS1986

Finite-volume and integral-equation techniques for transonic and supersonic vortex-dominated flows

Two computational techniques are developed to calculate the compressible vortex-dominated flows. The first technique is a finite-volume Euler Solver which uses four-Stage Runge-Kutta time stepping with second- and fourth-order dissipation terms. The technique is applied to supersonic conical and three-dimensional flows about sharp- and round-edged delta wings. Attached and separated-flow solutions have been obtained depending on the values of damping coefficients. The second technique is an integral-equation solver of the full potential equation which uses a volume-integral term in addition to the classical surface-integral terms. The technique is applied to transonic three-dimensional flows about sharp-edged delta wings. A hybrid technique which combines the finite-volume and the integral-equation solvers is also presented.

Kandil, O. A.↗
NASA NTRS1991

Unsteady vortex-dominated flow around wings with oscillating leading-edge flaps

Unsteady vortex-dominated flow around delta wings with oscillating leading-edge flaps represents an important classs of problems for supermaneuverability and flow control of advanced aircraft. The problem is solved using time accurate integration of the unsteady, compressible, thin-layer Navier-Stokes equations in conjunction with the unsteady, linearized, Navier-displacement equations. Starting with an initial configuration of the wing and its flaps, the Navier-Stokes equations are solved on an initial structured grid for the steady flow. The forced oscillation of the flaps is then applied, and the problem is solved accurately in time. The Navier-displacement equations are solved for the grid deformation and the Navier-Stokes equations are solved for the flowfield. Symmetric and anti-symmetric flaps oscillations are presented to study the effect of the flaps oscillation on the leading-edge vortical flow.

Kandil, Osama A.↗