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At least 1,081 records · Page 60
All sourcesNASA NTRSDOE OSTI
NASA NTRS1973

Experiments in free shear flows: Status and needs for the future

Experiments in free turbulent flows are recommended with the primary concern placed on classical flows in order to augment understanding and for model building. Five classes of experiments dealing with classical free turbulent flows are outlined and proposed as being of particular significance for the near future. These classes include the following: (1) Experiments clarifying the effect of density variation owing to use of different gases, with and without the additional effect of density variation due to high Mach number or other effects; (2) experiments clarifying the role and importance of various parameters which determine the behavior of the near field as well as the condictions under which any of these parameters can be neglected; (3) experiments determining the cumulative effect of initial conditions in terms of distance to fully established flow; (4) experiments for cases where two layers of distinctly different initial turbulence structure flow side by side at the same mean speed; and (5) experiment using contemporary experimental techniques to study structure in free turbulent shear flows in order to compliment and support contemporary work on boundary layers.

Kline, S. J.↗
NASA NTRS1973

Study of exothermic processes in shock ignited gases by the use of laser shear interferometry.

The paper reports on the measurements of maximum exothermic power pulses attainable from a given chemical system. Experimental tests involved the use of a shock tube technique whereby the exothermic process of combustion was controlled by reflected shock so that it occurred under virtually inviscid flow conditions, the data having been obtained at a resolution commensurate with the actual rate of chemical reaction. Experimental observations were made by means of a novel method of laser shear interferometry. Chemical systems treated in this manner comprised of mixtures of stoichiometric hydrogen-oxygen with 80 and 90% argon, while the measurements covered the full permissible range of initial thermodynamic conditions.

Meyer, J. W.↗
NASA NTRS1973

Mean flow and turbulence measurements in a Mach 5 shear layer.

Hot-wire study of turbulent mixing in the near field of a Mach 5 jet with extension of the results into the hypersonic range. Mean and fluctuating measurement data are given for the free shear layer of the 10.6-cm diameter jet which was contained in a 61-by-61 cm vacuum chamber and exhausted into a diffuser 44 cm downstream of the jet exit. An auxiliary air supply was used to equalize the static pressures in the chamber and the nozzle. The nozzle wall boundary layer was turbulent at the jet exit, providing measurement data at higher Reynolds numbers, which are also included.

Morrisette, E. L.↗
NASA NTRS1973

Linear viscous stability theory for stably stratified shear flow - A review.

In this paper the linear viscous stability theory for stably stratified parallel shear flow is reviewed and some new results are presented. Attention is focused on recent work on unbounded flows with emphasis placed on results which demonstrate apparent destabilizing effects of diffusivity which lie beyond the scope of inviscid theory. In particular it is shown that self-excited disturbances may exist with phase speeds lying outside the range of basic flow speed and that with strong thermal diffusivity, instability may occur even though the local Richardson number exceeds 0.25 throughout the flow.

Gage, K. S.↗
NASA NTRS1973

Aerodynamic noise emission from turbulent shear layers.

The Phillips (1960) convected wave equation is employed in this paper to study aerodynamic noise emission processes in subsonic and supersonic shear layers. The wave equation in three spatial dimensions is first reduced to an ordinary differential equation by Fourier transformation and then solved via the WKBJ method. Three typical solutions are required for discussions in this paper. The current results are different from the classical conclusions. The effects of refraction, convection, Mach-number dependence and temperature dependence of turbulent noise emission are analyzed in the light of solutions to the Phillips equation.

Pao, S. P.↗
NASA NTRS1973

Free vibration of arches flexible in shear.

An analysis reported by Veletsos et al. (1972) concerning the free vibrational characteristics of circular arches vibrating in their own planes is considered. The analysis was based on a theory which neglects the effects of rotatory inertia and shearing deformation. A supplementary investigation is conducted to assess the effects of the previously neglected factors and to identify the conditions under which these effects are of practical significance or may be neglected. A simple approximate procedure is developed for estimating the natural frequencies of arches, giving due consideration to the effects of the previously neglected factors.

Austin, W. J.↗
NASA NTRS1973

Effect of shear on duct wall impedance.

The solution to the equation governing the propagation of sound in a uniform shear layer is expressed in terms of parabolic cylinder functions. This result is used to develop a closed-form solution for acoustic wall impedance which accounts for both the duct liner and the presence of a boundary layer in the duct. The effective wall impedance can then be used as the boundary condition for the much simpler problem of sound propagation in uniform flow.

Goldstein, M.↗
NASA NTRS1973

Acoustic propagation in ducts with varying cross sections and sheared mean flow.

An analysis is presented of the wave propagation and attenuation in two-dimensional ducts with slowly varying cross sections which carry sheared mean flow. A uniformly valid asymptotic expansion of the acoustic waves is obtained in terms of the maximum slope of the wall by using the method of multiple scales. The result is a first-order differential equation describing the amplitude variation with the axial distance. This equation is used to evaluate the effects of variations of the duct cross section and growing boundary layers on the different acoustic modes.

Nayfeh, A. H.↗
NASA NTRS1972

Shockwave determination of the shear velocity at very high pressures

A shock wave experiment is described for confirming changes in density, from seismic interpretation, for determining the properties of planet interiors. The experiment focuses on the problem of measurements in a pressure region, where the shear velocity tends to vanish, or become very small. Pressure-sensitive lattice stability, and the equations for an atomic model of the NaCl lattice are discussed along with the particle velocity shock technique.

Anderson, O. L.↗
NASA NTRS1973

Algebraically growing waves in ducts with sheared mean flow

Standing or traveling waves which vary algebraically with the axial distance in uniform ducts with sheared mean velocity profiles are investigated. The results show that such waves are not possible for ducts with uniform cross sections and fully developed mean flows.

Nayfeh, A. H.↗
NASA NTRS1974

Pahranagat Shear System, Lincoln County, Nevada

The author has identified the following significant results. A structural model which relates strike-slip deformation to Basin Range extensional tectonics was formulated on the basis of analysis and interpreatation of ERTS-1 MSS imagery over southern Lincoln County, Nevada. Study of published geologic data and field reconnaissance of key areas has been conducted to support the ERTS-1 data interpretation. The structural model suggests that a left-lateral strike-slip fault zone, called the Pahranagat Shear System, formed as a transform fault separating two areas of east-west structural extension.

Liggett, M. A.↗
NASA NTRS1974

Shear-stress intensity factors for elastic sheets with cover plates

Shear stress intensity factors are calculated for three problems concerning inextensible cover plates either bonded to or embedded in an elastic sheet which is under uniaxial tension. The stress intensity factors are small when the ratio of sheet thickness to cover plate length is small and, as the ratio increase, rapidly approach their asymptotic values for infinite sheet thickness. In the problem of the embedded cover plate, the stress intensity factor also depends on the Poisson's ratio of the sheet material. The dependence on Poisson's ratio, however, is significant only when the ratio of sheet thickness to cover plate length is small. Some possible implications of the present results for debonding of reinforced sheets under cyclic loading are briefly discussed.

Fichter, W. B.↗
NASA NTRS1973

Deformation and burst of a liquid droplet freely suspended in a linear shear field

A theoretical method is presented for predicting the deformation and the conditions for breakup of a liquid droplet freely suspended in a general linear shear field. This is achieved by expanding the solution to the creeping-flow equations in powers of the deformation parameter epsilon and using linear stability theory to determine the onset of bursting. When compared with numerical solutions and with the available experimental data, the theoretical results are generally found to be of acceptable accuracy although, in some cases, the agreement is only qualitative.

Barthes-Biesel, D.↗
NASA NTRS1973

Compressional and shear wave velocities in granular materials to 2.5 kilobars

The velocities of seismic compressional waves and, for the first time, shear wave velocities in silica sand, volcanic ash, and basalt powder were determined under hydrostatic confining pressures to 2.5 kb. Simultaneously, the porosity of these materials was obtained as a function of confining pressure. The presented results have important implications for the self-compaction hypothesis that has been postulated to explain the lunar near-surface seismic velocity variation.

Talwani, P.↗
NASA NTRS1974

Transmission of sound through annular ducts of varying cross sections and sheared mean flow

An asymptotic solution is presented for the transmission and attenuation of acoustic waves in an annular duct of slowly varying cross section which carries a sheared mean flow. The analysis also takes into account the growth of the boundary layer as well as any slow variations in the acoustic liner properties. The problem is reduced to the solution of a first-order ordinary differential equation for the amplitude. The analysis is used to estimate the effects of the variations of the duct cross section and boundary layer growth on the different acoustic modes.

Nayfeh, A. H.↗
NASA NTRS1974

Algebraically growing waves in ducts with sheared mean flow

Analysis of the behavior of standing and traveling acoustic waves in a smooth duct with a fluid flow having a sheared mean velocity profile, when the waves grow algebraically as they travel along the duct axis. It is shown that standing waves growing algebraically with the axial distance cannot exist in a smooth duct when the duct wall have a finite resistance. The existence of traveling waves subject to the same law of growth is also dismissed under realistic flow conditions.

Nayfeh, A. H.↗
NASA NTRS1974

Antiplane shear crack terminating at and going through a bimaterial interface

The antiplane shear problem of two bonded elastic half-planes containing a crack perpendicular to the interface is considered. The cases of a semiinfinite crack terminating at the interface, a finite crack away from and terminating at the interface, two cracks one on each side of the interface, and a finite crack crossing the interface are separately investigated. The nature of the stress singularity for the crack terminating at and going through the interface is studied, and it is shown that at the irregular point on the interface, for the former the power of singularity is not -1/2 and for the latter the stresses are bounded. For a material pair of aluminum-epoxy some numerical results giving the stress intensity factors, the density functions, and the crack opening displacements are presented.

Erdogan, F.↗