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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 1,009 records · Page 56
All sourcesNASA NTRSDOE OSTI
NASA NTRS1980

Aerodynamic response of an airfoil with thickness to a longitudinal and transverse periodic gust

The unsteady lift of an airfoil with thickness subject to a two-dimensional periodic gust is analyzed using the recent theory of Goldstein and Atassi. It is found that to properly account for the coupling between the steady potential flow and the unsteady vortical flow, one has to consider the contribution of order alpha-squared (when alpha is steady state disturbance) to the potential flowfield. A closed form analytical formula is then derived for the lift function. The results show strong dependence on the wave members of the gust.

Hamad, G.↗
NASA NTRS1980

A perturbation solution for transverse pressure-sensitive combustion instability in an annulus

A method for analysis of combustion instability in rocket motors based on a combination of the Galerkin method and the two-variable (or multiple-scales) perturbation method is developed. The method is illustrated by applying it to the problem of pressure-sensitive combustion instability in a liquid-fuel annular combustion chamber. To the order of approximation inherent in the method it is found that the complete linear stability analysis and most of the nonlinear stability analysis can be carried out in closed form. The results thus obtained are used to clarify several aspects of the interpretation of numerical solutions obtained by previous investigators.

Googerdy, A.↗
NASA NTRS1981

Electron microscopical and histochemical studies on the transverse striated muscles of birds after prolonged hypokinesis

Studies of the gastrocnemius muscle were carried out in 4 month old cockerels of the laying hybrid after hypokinesis lasting 15 and 30 days. It was found that restricted movement resulted in dystrophic changes of myotibrils, enlargement of the sarcoplasmic reticulum and oedem of interfibrillar spaces. Histochemical studies revealed focuses of increased activity of non-specific esterase, decreased activity of dehydrogenase of lactic acid and a positive reaction of acid phosphatase.

Belak, M.↗
NASA NTRS1982

Transverse velocity measurement

Carbon dioxide (CO2) laser Doppler lidar systems are employed in the remote measurement of wind velocities. The cross velocity component is measured utilizing an appropriate detector array configuration. This allows determination of the three dimensional characteristics of the wind with conventional Doppler lidar systems.

Source record↗
NASA NTRS1983

On the stability of the unsteady boundary layer on a cylinder oscillating transversely in a viscous fluid

The stability of the two-dimensional flow induced by the tranverse oscillation of a cylinder in a viscous fluid is investigated in both the linear and weakly nonlinear regime. The major assumption that is made to simplify the problem is that the oscillation frequency is large in which case an unsteady boundary layer is set up on the cylinder. Results are given for cylinders of elliptic cross section and it is found that for any given eccentricity the most dangerous configuration is when the cylinder oscillates parallel to its minor axis. Some discussion of nonlinear effects is also given and for the circular cylinder it is shown that the steady streaming boundary layer of the basic flow is significantly altered by the instability.

Hall, P.↗
NASA NTRS1984

An analytical model for the vorticity associated with a transverse jet

A two dimensional model is developed for a turbulent jet injected normally into a uniform crossflow, in which particular emphasis is placed on the contra-rotating vortex pair associated with the jet. By approximating the forces acting on each of the viscous vortices, equations governing the vortex spacing and downstream jet velocity are evolved. No empirical information is incorporated into this model. A description of the variation in total vortex strength is utilized in which vorticity generated by the jet's impulse dominates the farfield. Numerical solution of the governing equations yields results for the vortex trajectory, half spacing, varying circulation, and viscous core size that correlate quite well with experimental data and asymptotic relations. Based on these findings, we conclude that vortex separation and other important characteristics of the jet cross-section are two dimensional and viscous in nature. Hence it becomes possible to predict, on purely theoretical grounds, the behavior of the vortex pair and of the jet itself.

Karagozian, A. R.↗
NASA NTRS1984

Electromagnetic induction by finite wavenumber source fields in 2-D lateral heterogeneities - The transverse electric mode

Electromagnetic induction in a laterally homogeneous earth is analyzed in terms of a source field with finite dimensions. Attention is focused on a time-varying two-dimensional current source directed parallel to the strike of a two-dimensional anomalous structure within the earth, i.e., the E-parallel mode. The spatially harmonic source field is expressed as discontinuities in the magnetic (or electric) field of the current in the source. The model is applied to describing the magnetic gradients across megatectonic features, and may be used to predict the magnetic fields encountered by a satellite orbiting above the ionosphere.

Hermance, J. F.↗
NASA NTRS1983

Clearance flow-generated transverse forces at the rotors of thermal turbomachines

Self-excited rotor whirl represents a serious hazard in the operation of turbomachines. The reported investigation has, therefore, the objective to measure the lateral forces acting on the rotor and to determine the characteristic pressure distribution in the rotor clearance area. A description is presented of an approach for calculating the leakage flow in the case of an eccentric rotor position on the basis of empirical loss coefficients. The results are reported of an experimental investigation with a turbine stage, taking into account a variation of the clearance characteristics. The pressure data measured are consistent with the theoretical considerations.

Urlichs, K.↗
NASA NTRS1985

A three-dimensional turbulent boundary layer undergoing transverse strain and streamwise pressure gradient

Results from an experimental investigation designed to provide data on both mean and turbulence quantities in the axisymmetric, swirling boundary layer (with and without pressure gradient) flowing over a stationary cylinder downstreams of a spinning cylindrical section are presented. The pressure gradient was introduced into the flow field by a 25.4 mm-high, forward-facing, circular step mounted on the stationary cylinder, the step height being nearly equal to the thickness of the approaching boundary layer. All the measurements were made at a nominal upstream reference Reynolds number of 2.4 x 10 to the 6th power/m (corresponding to an upstream reference velocity of 36 to 37 m/sec) with the rotation of the spinner set to make its peripheral speed equal the reference velocity. The data reported included measurements of surface pressure and the mean surface shear-stress vector taken with a miniature, directional, surface-fence gage. These measurements were supplemented by oil-flow visualization studies of the stationary cylinder. The data indicates that the streamwise pressure gradient controls the development of the streamwise component of wall shear, but leaves the peripheral component of wall shear practically unaffected.

Hebbar, S. K.↗
NASA NTRS1985

Equatorial trapped plasmasphere ion distributions and transverse stochastic acceleration

Observations by the DE 1 and SCATHA satellites have revealed ion distribution functions in the equatorial plasmasphere which are sharply peaked at 90 deg pitch angle. The pitch angle anisotropy increases with increasing energy for the observed distributions. Also observed by SCATHA and earlier spacecraft are cyclotron harmonic emissions which are closely confined to the plasmasphere equator. It is demonstrated here that the observed highly anisotropic ion distribution at thermal energies can be explained, as the consequence of the nonlinear evolution of an initially Maxwellian distribution with a characteristic plasmasphere thermal plasma temperature by stochastic acceleration, using the observed levels of wave turbulence.

Curtis, S. A.↗
NASA NTRS1985

Effects of transverse shearing on cylindrical bending, vibration, and buckling of laminated plates

The displacements for cylindrical bending and stretching of laminated and thick plates are expressed through-the-thickness by a few algebraic terms and a complete set of trigonometric terms. Only a few terms of this series are needed to get sufficiently accurate results for laminated and thick plates. Equations of equilibrium based on a sufficient number of terms of this series for displacements are determined using variational theorems from three-dimensional elasticity. Several examples are worked out. The displacements and stresses are obtained for simply supported isotropic and layered beams with a rectangular cross section and a sinusoidal lateral load distribution. These results are compared to an exact elasticity solution. Results for several approximations are obtained for a simply supported and a clamped beam with a rectangular cross section loaded at the center and results are compared to experimental results. Results are also obtained for isotropic and layered beams with a rectangular cross section for several approximations for the lowest natural frequency and buckling load.

Stein, M.↗
NASA NTRS1985

Phase averaged transverse vorticity measurements in an excited, two-dimensional mixing layer

Experiments were run to characterize the global vorticity distribution in an excited plane mixing layer. A reciprocating piston excited the mixing layer at a 0.0053 intensity, a Strouhal number of 0.97, and a 15 Hz frequency. An X-wire anemometer and a pitot tube furnished data in the 13 m/sec free stream velocity flow. Deep depressions were observed in the velocity contours on the high-speed side of the mixing layer, while primary vortex growth occurred on the low-speed side. The cores of the vortices moved at highly differentiated velocities. Phase plots were also generated to show tearing and fusing of the vortex contours.

Disimile, P. J.↗
NASA NTRS1985

Failure mechanisms of laminates transversely loaded by bolt push-through

Stiffened composite panels proposed for fuselage and wing design utilize a variety of stiffener-to-skin attachment concepts including mechanical fasteners. The attachment concept is an important factor influencing the panel's strength and can govern its performance following local damage. Mechanical fasteners can be an effective method for preventing stiffener-skin separation. One potential failure mode for bolted panels occurs when the bolts pull through the stiffener attachment flange or skin. The resulting loss of support by the skin to the stiffener and by the stiffener to the skin can result in local buckling and subsequent panel collapse. The characteristic failure modes associated with bolt push-through failure are described and the results of a parametric study of the effects that different material systems, boundary conditions, and laminates have on the forces and displacements required to cause damage and bolt pushthrough failure are presented.

Waters, W. A., Jr.↗
NASA NTRS1985

An experimental investigation of the transverse pressure gradient associated with curved free jets in the proximity of solid boundaries

An experiment has been performed to determine the mass flow and thrust augmentation associated with the flow of a two-dimensional incompressible jet issued parallel to an adjacent offset wall. A theoretical analysis based on a linear static pressure profile across the jet exit reveals that thrust augmentation is possible only for a wall offset of less than one half of the nozzle exit width. Mass flow augmentation measurements are in reasonable agreement with the proposed theory. Augmented mass flow of over three percent is observed directly, while thrust augmentation in excess of three percent is predicted when measured values of the pressure difference across the exiting jet are supplied to the theory. Measurements of the separation cavity length are presented which complement those given by previous investigators by extending the range to small values of the ratio of the wall offset to the slot height. For large offset ratios it is found that the cavity length approaches 1.25 times the wall offset distance. The initial radius of curvature of the jet centerline is found to be substantially greater than the mean radius of curvature over the cavity length, thereby indicating that the trajectory of the jet does not follow the arc of a circle as has been previously assumed.

Lund, T. S.↗
NASA NTRS1986

A laser-induced-fluorescence visualization study of transverse, sonic fuel injection in a nonreacting supersonic combustor

The present paper reports work which has been conducted in the first phase of a research program which is to provide a data base of spatially-resolved measurements in nonreacting supersonic combustors. In the measurements, a nonintrusive diagnostic technique based on the utilization of laser-induced fluorescence (LIF) is employed. The reported work had the objective to conduct LIF visualization studies of the injection of a simulated fuel into a Mach 2.07 airstream for comparison with corresponding numerical calculations. Attention is given to injection from a single orifice into a constant-area duct, injection from a single orifice behind a rearward-facing step, and injection from staged orifices behind a rearward-facing step.

Mcdaniel, J. C.↗