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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 343 records · Page 19
All sourcesNASA NTRSDOE OSTI
NASA NTRS1984

Flight characteristics of a manned, low-speed, controlled deep stall vehicle

A successful manned, low-speed, controlled deep stall flight research program was conducted at NASA Ames Research Center's Dryden Flight Research Facility. Piloting techniques were established that enabled the pilot to attain and stabilize on an angle of attack in the 30 to 72 deg range. A flight-determined aerodynamic data base was established for angles of attack as high as 72 deg. Poor lateral-directional flying qualities were encountered at angles of attack above 60 deg. Insight into the high angle-of-attack, lateral-directional dynamics was gained through a basic root-locus analysis.

Sim, A. G.↗
NASA NTRS1984

Synthesized airfoil data method for prediction of dynamic stall and unsteady airloads

The synthesized unsteady airfoil data method, which accurately describes the unsteady aerodynamic characteristics of stalled airfoils in the time domain, is expanded and improved. Nine sets of unsteady drag data are synthesized, providing a basis for the successful expansion of the method to include the computation of unsteady pressure drag of airfoils and rotor blades. An improved prediction model for airfoil flow reattachment is incorporated into the method. Application of the model results in a better correlation of analytic predictions with measured full-scale helicopter blade loads and stress data. The results show that it is feasible to generalize the empirical parameters embedded in the method over a range of angles of attack, Mach number, airfoil shape, and sweep angle.

Gangwani, S. T.↗
NASA NTRS1985

Simulator study of the stall departure characteristics of a light general aviation airplane with and without a wing-leading-edge modification

A six-degree-of-freedom nonlinear simulation was developed for a two-place, single-engine, low-wing general aviation airplane for the stall and initial departure regions of flight. Two configurations, one with and one without an outboard wing-leading-edge modification, were modeled. The math models developed are presented simulation predictions and flight-test data for validation purposes and simulation results for the two configurations for various maneuvers and power settings are compared to show the beneficial influence of adding the wing-leading-edge modification.

Riley, D. R.↗
NASA NTRS1986

A new, improved method for separating turbulent boundary layer for aerodynamic performance prediction of trailing edge stall airfoils

A method based on integral techniques is presented to determine the turbulent separation location and separation pressure for trailing edge stall airfoils exhibiting extensive separated flow regions during prestall and poststall conditions. The method and experimental laser velocimetry data in the turbulence amplification region are used to establish a relationship between fluctuating velocity components and mean velocity in the boundary layer. The method is demonstrated for symmetrical, cambered, conventional and supercritical airfoils in the 5-to-21-percent thickness ratio range, and over a Reynolds number range of 2 to 22 million. Good agreement with experimental data is found, and the method is used in conjunction with the NASA Multi-Component Airfoil Computer Program to predict maximum L/D ratios and maximum section/lift coefficients.

Goradia, S.↗
NASA NTRS1986

Deep stall characteristics of MU-300

The deep stall characteristics of the MU-300 Diamond aircraft are described. The MU-300 obtained type certification from the FAA in 1981, and from Canada, West Germany, and England in 1983. The aircraft has achieved a high angle of attack. The aerodynamic design, structural dimensions, and flight tests of the MU-300 are described.

Hanai, T.↗
NASA NTRS1987

Subsychronous vibration of multistage centrifugal compressors forced by rotating stall

A multistage centrifugal compressor, in natural gas re-injection service on an offshore petroleum production platform, experienced subsynchronous vibrations which caused excessive bearing wear. Field performance testing correlated the subsynchronous amplitude with the discharge flow coefficient, demonstrating the excitation to be aerodynamic. Adding two impellers allowed an increase in the diffuser flow angle (with respect to tangential) to meet the diffuser stability criteria based on factory and field tests correlated using the theory of Senoo (for rotating stall in a vaneless diffuser). This modification eliminated all significant subsynchronous vibrations in field service, thus confirming the correctness of the solution. Other possible sources of aerodynamically induced vibrations were considered, but the judgment that those are unlikely has been confirmed by subsequent experience with other similar compressors.

Fulton, J. W.↗
NASA NTRS1986

Unsteady separation characteristics of airfoils operating under dynamic stall conditions

Unsteady viscous/inviscid interaction phenomena are investigated for airfoils operating under dynamic stall conditions, using coupling procedures between a time-dependent inviscid panel method and two-dimensional unsteady boundary layer codes. Two strategies are pursued: a coupling of the inviscid panel method with the boundary layer code, and a strong coupling of the inviscid panel method with the boundary layer code. Attention is given to the main features of the unsteady time-marching panel method and boundary layer codes, as well as to numerical stability and the phenomenon of unsteady separation.

Geissler, Wolfgang↗
NASA NTRS1988

Application of Navier-Stokes analysis to stall flutter

A solution procedure was developed to investigate the two-dimensional, one- or two-dimensional flutter characteristics of arbitrary airfoils. This procedure requires a simultaneous integration in time of the solid and fluid equations of motion. The fluid equations of motion are the unsteady compressible Navier-Stokes equations, solved in a body-fitted moving coordinate system using an approximate factorization scheme. The solid equations of motion are integrated in time using an Euler implicit scheme. Flutter is said to occur if small disturbances imposed on the airfoil attitude lead to divergent oscillatory motions at subsequent times. The flutter characteristics of airfoils in subsonic speed at high angles of attack and airfoils in high subsonic and transonic speeds at low angles of attack are investigated. The stall flutter characteristics are also predicted using the same procedure.

Wu, J. C.↗
NASA NTRS1988

Fluid mechanics of dynamic stall. I - Unsteady flow concepts

Advanced military aircraft 'supermaneuverability' requirements entail the sustained operation of airfoils at stalled flow conditions. The present work addresses the effects of separated flow on vehicle dynamics; an analytic method is presented which employs static experimental data to predict the separated flow effect on incompressible unsteady aerodynamics. The key parameters in the analytic relationship between steady and nonsteady aerodynamics are the time-lag before a change of flow conditions can affect the separation-induced aerodynamic loads, the accelerated flow effect, and the moving wall effect.

Ericsson, L. E.↗
NASA NTRS1988

Fluid mechanics of dynamic stall. II - Prediction of full scale characteristics

Analytical extrapolations are made from experimental subscale dynamics to predict full scale characteristics of dynamic stall. The method proceeds by establishing analytic relationships between dynamic and static aerodynamic characteristics induced by viscous flow effects. The method is then validated by predicting dynamic test results on the basis of corresponding static test data obtained at the same subscale flow conditions, and the effect of Reynolds number on the static aerodynamic characteristics are determined from subscale to full scale flow conditions.

Ericsson, L. E.↗
NASA NTRS1990

Effect of acoustic excitation on stalled flows over an airfoil

The effect of acoustic excitation on post-stalled flows over an airfoil, i.e., flows that are fully separated from near the leading edge, is investigated. The excitation results in a tendency towards reattachment, which is accompanied by an increased lift and reduced drag, although the flow may still remain fully separated. It is found that with increasing excitation amplitude, the effect becomes more pronounced but shifts to a Strouhal number which is much lower than that expected from linear, inviscid instability of the separated shear layer.

Zaman, K. B. M. Q.↗
NASA NTRS1991

Observations of dynamic stall phenomena using liquid crystal coatings

Novel, shear stress-sensitive/temperature-insensitive liquid crystal coatings have been applied to the surface of an oscillating airfoil in order to ascertain the unsteady fluid physics associated with the dynamic-stall process. Surface microtufts and laser sheet/smoke-particle flow visualization were used to compare the liquid-crystal results. Boundary-layer transition and turbulent separation locations were measured as a function of geometric angle of attack. The results obtained are compared with Eppler (1980) aerodynamic design code predictions.

Reda, Daniel C.↗
NASA NTRS1991

Oscillating airfoil velocity field during large amplitude dynamic stall

The leading edge flowfield of an airfoil executing a sinusoidal oscillatory motion and experiencing dynamic stall under compressibility conditions has been studied using a two component LDV system. Phase averaged mean velocity measurements and some flow quantities derived from it are presented and discussed. The results indicate extremely large accelerations of the flow are present around the leading edge with mean velocity values 60 percent higher than and instantaneous velocities as large as 1.75 times the free stream velocity. The velocity profiles at certain locations over the airfoil resemble that of a wake.

Chandrasekhara, M. S.↗
NASA NTRS1993

Visualizing Dynamic-Stall Airflows

Wind-tunnel apparatus facilitates experiments on airfoils undergoing dynamic stall. Possible to visualize flow on oscillating airfoils nonintrusively. In new apparatus, mounting structure also viewing window: airfoil pin-mounted between two optical-quality glass windows. Windows oscillated simultaneously, giving unobstructed view of complex flow around pitching airfoil.

Carr, L.↗
NASA NTRS1993

Active control of wing rock of a delta wing at post-stall using tangential leading edge blowing

Post-stall roll control utilizing tangential leading edge blowing is demonstrated in a wind tunnel on a delta wing model that exhibited wing rock. The dampening effect of symmetric blowing alone on wing rock is found to be effective up to a certain maximum amount of blowing. A moderate amount of symmetric blowing was shown to be effective in linearizing the asymmetric blowing static rolling moment responses.

Wong, G. S.↗
NASA NTRS1957

Effect of Interstage Bleed on Rotating Stall and Blade Vibration in a 13-stage Axial-flow Compressor in a Turbojet Engine

The compressor case of a 13-stage axial-flow compressor was modified to incorporate air-bleed systems over the fifth and tenth rotor stages. Rotating stall-exited rotor-blade vibrations were measured in the first and second stages at 60 and 68 percent of rated speed, respectively. Either the fifth- or the tenth-stage bleeds satisfactorily eliminated the peak vibratory stresses.

Calvert, Howard F↗
NASA NTRS1944

Effects of Small Angles of Sweep and Moderate Amounts of Dihedral on Stalling and Lateral Characteristics of a Wing-Fuselage Combination Equipped with Partial- and Full-Span Double Slotted Flaps

Tests of a wing-fuselage combinations incorporating NACA 65-series airfoil sections were conducted in the NACA 19-foot pressure tunnel. The investigation included the tests with flaps neutral and with partial- and full-span double slotted flaps deflected to determine the effects of (1) variations of wing sweep between -4 degrees and 8 degrees on stalling and lateral stability and control characteristics and (2) variations of dihedral between 0 degree and 6.75 degrees on lateral stability characteristics.

Teplitz, Jerome↗