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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 325 records · Page 18
All sourcesNASA NTRSDOE OSTI
NASA NTRS1980

Acoustic oscillation phenomena in low-velocity steady flow with heating

Thermally driven acoustic oscillations in low-velocity mean flows are investigated. A criterion is developed for marginal stability with respect to a fluid temperature increase; a cylindrical geometry is chosen for flow in a constant-area tube where any circumferential variation is neglected. The range of parameters of concern is limited to conditions resembling cryogenic storage designs proposed for long-term space missions; helium was chosen as the fluid in order to allow comparison with zero flow rate results in half-open tubes.

Liburdy, J. A.↗
NASA NTRS1993

Interactive-Boundary-Layer Computations For Oscillating Airfoil

Interactive-boundary-layer method developed for computations of steady flow, extended under assumption of quasi-steady flow, to computations of evolution of two-dimensional flow about oscillating airfoil under light-dynamic-stall conditions. Represents advance toward ability to compute unsteady flows at even greater angles of attack with solutions of equations normally used for description of boundary-layer flows on airfoils prior to stall. Important in practical studies of flow on blades of helicopter rotors, axial compressors, and turbines.

Carr, L. W.↗
NASA NTRS1987

Unsteady aerodynamics of an oscillating cascade in a compressible flow field

Fundamental experiments were performed in the NASA Lewis Transonic Oscillating Cascade Facility to investigate and quantify the unsteady aerodynamics of a cascade of biconvex airfoils executing torsion-mode oscillations at realistic reduced frequencies. Flush-mounted, high-response miniature pressure transducers were used to measure the unsteady airfoil surface pressures. The pressures were measured for three interblade phase angles at two inlet Mach numbers, 0.65 and 0.80, and two incidence angles, 0 and 7 deg. The time-variant pressures were analyzed by means of discrete Fourier transform techniques, and these unique data were then compared with predictions from a linearized unsteady cascade model. The experimental results indicate that the interblade phase angle had a major effect on the chordwise distributions of the airfoil surface unsteady pressure, and that reduced frequency, incidence angle, and Mach number had a somewhat less significant effect.

Buffum, Daniel H.↗
NASA NTRS1988

The unsteady aerodynamics of an oscillating cascade in a compressible flow field

Fundamental experiments were performed in the NASA Lewis Transonic Oscillating Cascade Facility to investigate and quantify the unsteady aerodynamics of a cascade of biconvex airfoils executing torsion-mode oscillations at realistic reduced frequencies. Flush-mounted, high-response miniature pressure transducers were used to measure the unsteady airfoil surface pressures. The pressures were measured for three interblade phase angles at two inlet Mach numbers, 0.65 and 0.80, and two incidence angles, 0 and 7 deg. The time-variant pressures were analyzed by means of discrete Fourier transform techniques, and these unique data were then compared with predictions from a linearized unsteady cascade model. The experimental results indicate that the interblade phase angle had a major effect on the chordwise distributions of the airfoil surface unsteady pressure, and that reduced frequency, incidence angle, and Mach number had a somewhat less significant effect.

Buffum, Daniel H.↗
NASA NTRS1977

A simplified theory of oscillating airfoils in transonic flow - Review and extension

Significant old and new results are presented to show to what extent a simplified theory for transonic flow may be used. Solutions are obtained by classical techniques and compared with experiment. Results are given for two-dimensional, steady and unsteady flow and three-dimensional, steady flow. The effects of flow separation and improvements in Bernoulli's equations and the surface boundary condition are also briefly discussed.

Dowell, E. H.↗
NASA NTRS1980

Flow measurements in a model swirl combustor

Flow measurements in a model combustor composed of two confined coaxial swirling jets under noncombusting conditions are presented. Mean flow results are obtained for five different flow conditions to determine the effect of outer swirl on the recirculation zone (which is used for flame stabilization under combustion conditions). As the outer swirl magnitude is first decreased from maximum counter-swirl to zero and then increased to give co-swirl conditions, the size and the reverse flow velocity in the recirculation zone diminish. Detailed time mean and fluctuating flow measurements are obtained for a co-swirl and a counter-swirl condition with a directional pitot probe and hot-wire anenometry. For these two cases, recirculation zone occurs only with counter-swirl, near the exit of the inner jet. The recirculation zone is in the form of a one celled toroidal vortex having very low swirl velocity. Axial development of fluctuation levels, energy dissipation rates and turbulence length scales are described for the two flow conditions. Spectral analysis reveals periodic oscillations in both flows. The oscillations originate from the inner jet and up to 4 harmonics are observed. The fundamental frequencies are comparable to the rotational frequencies of the inner jets at the exit which are approximately under solid body rotation. The significance of the present results for the combustion process is discussed.

Vu, B. T.↗
NASA NTRS1980

A simplified theory of oscillating aerofoils in transonic flow - Review and extension

A simplified theory of the dynamic motion of aerofoils of finite thickness in transonic flow is presented which excludes the effect of shock waves on the aerofoil itself and, thus, is restricted to free stream Mach numbers equal to unity or above. Numerical examples are analyzed for two-dimensional steady and unsteady (including transient) aerofoil motion and three-dimensional steady and unsteady flow over delta wings. The effects of flow separation and improvements in Bernoulli's equation and the surface boundary condition are briefly discussed.

Dowell, E. H.↗
NASA NTRS1989

Low speed wind tunnel investigation of the flow about delta wing, oscillating in pitch to very high angle of attack

Six-component airload histories were obtained for models of aspect ratio 1, 1.5, and 2. Examples are given from data obtained over a range of 'reduced frequency' parameters from 0.01 to 0.08. They include the unsteady response of the leading-edge vortices, as evidenced both by the time-dependent airloads and motion pictures of smoke released from the leading edge and illuminated by a thin sheet of laser light.

Jarrah, Mohammad-Ameen M.↗
NASA NTRS1991

Laser velocimetry measurements of oscillating airfoil dynamic stall flow field

Ensemble-averaged two-component velocity measurements over an airfoil experiencing oscillatory dynamic stall under compressibility conditions were obtained. The measurements show the formation of a separation bubble over the airfoil that persists till angles of attack close to when the dynamic stall vortex forms and convects. The fluid attains mean velocities as large as 1.6 times the free stream velocity with instantaneous values of 1.8 times the free stream velocity. The airfoil motion induces these large velocities in regions that are far removed from the surface.

Chandrasekhara, M. S.↗