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At least 559 records · Page 31

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NASA NTRS1988

An experimental study of rotor-vortex interactions

A scheme for investigating general blade/vortex interactions (BVIs) has been used to obtain an unusual body of data. The scheme involves locating a vortex generator upstream of a nonlifting rotor so that the vortex interacts with the rotor at any desired forward azimuth. Parallel BVIs produced by this external vortex generator are shown to be nearly identical to those produced by the rotor alone operating in a normal descent mode. The test delineates various generic features of parallel and oblique BVIs. However, the dominant feature is the leading-edge pressure pulse. The effects of blade/vortex angle, and proximity (including head-on interactions) on this pulse are discussed. The effect of Mach number on the leading edge pressure variation is shown to be small even for supercritical interactions.

Caradonna, F. X.↗

NASA NTRS1987

Aerodynamic interaction between vortical wakes and lifting two-dimensional bodies

Unsteady rotor wake interactions with the empenage, tail boom, and other aerodynamic surfaces of a helicopter have a significant influence on its aerodynamic performance, the ride quality, and amount of vibration. A numerical method for computing the aerodynamic interaction between an interacting vortex wake and the viscous flow about arbitrary two-dimensional bodies has been developed to address this helicopter problem. The method solves for the flow field velocities on a body-fitted computational mesh using finite-difference techniques. The interaction of a rotor wake with the flow about a 4:1 elliptic cylinder at 45-deg incidence was calculated for a Reynolds number of 3000.

Stremel, Paul M.↗

NASA NTRS1988

Three-dimensional unsteady transonic viscous-inviscid interaction using the Euler and boundary-layer equations

The objective of this study is the development of a numerical technique which can provide three-dimensional, time-accurate, compressible, turbulent flow solutions in a practical and relatively economical way. The approach taken is that of the method of viscous-inviscid interaction. The Euler equations are assumed to govern the outer inviscid portion of the flow, and the viscous layer close to the solid wall is described by a set of integral boundary-layer equations. The viscous solutions are obtained in a direct fashion with a weighted-average phase error scheme. The method of equivalent sources is used for viscous-inviscid coupling. Steady-state and unsteady computations for an AGARD airfoil and a wing show that satisfactory engineering solutions can be obtained for attached, high Reynolds number flows using this method. Quasi-unsteady interactions are shown to produce similar results to those provided by true-unsteady interactions. Considerable computer resources can be saved for some cases by using quasi-unsteady interactions.

Whitfield, David L.↗

NASA NTRS1988

The nonlinear interaction of Tollmien-Schlichting waves and Taylor-Goertler vortices in curved channel flows

The development of Tollmien-Schlichting waves (TSWs) and Taylor-Goertler vortices (TGVs) in fully developed viscous curved-channel flows is investigated analytically, with a focus on their nonlinear interactions. Two types of interactions are identified, depending on the amplitude of the initial disturbances. In the low-amplitude type, two TSWs and one TGV interact, and the scaled amplitudes go to infinity on a finite time scale; in the higher-amplitude type, which can also occur in a straight channel, the same singularity occurs if the angle between the TSW wavefront and the TGV is greater than 41.6 deg, but the breakdown is exponential and takes an infinite time if the angle is smaller. The implications of these findings for external flow problems such as the design of laminar-flow wings are indicated. It is concluded that longitudinal vortices like those observed in the initial stages of the transition to turbulence can be produced unless the present interaction mechanism is destroyed by boundary-layer growth.

Hall, P.↗

NASA NTRS1988

Vehicle environment interactions - An overview

The advent of Space Shuttle Orbital operations utilizing science and technology payloads has led to a renewal of interest of vehicle-environmental interactions in low earth orbit. The first science payload on STS-3 showed an interaction on the surface of the Orbiter which, although it had been detected earlier on unmanned spacecraft, quickened interest in the possible impact of this phenomena on future missions. Subsequent flights have yielded data on a wide variety of interaction phenomena resulting from the large size of the Orbiter and its outgassing characteristics. These drivers have given rise to modifications in the neutral gas and plasma environments of the Space Shuttle Orbiter. The physics of the interactions result in the generation of disturbed wave fields, optical emissions and particle distributions in the vicinity of the Orbiter. In this overview, the present observations, suggested interpretations and open questions will be addressed.

Raitt, W. J.↗

NASA NTRS1988

PIPS: A Procedure for Interactive Pyramid Segmentation

The Procedure for Interactive Pyramid Segementation was designed to identify regions of spatially connected and spectrally homogeneous pixels in multispectral image data, and to allow these regions to be interactively manipulated without the use of processing parameters. The objective is to provide the user with the capability to easily extract and identify regions corresponding to target objects of interest. The approach is to segment a multispectral image into a set of regions and to allow the analyst to interactively refine the segmentation by direct manipulation. The user can elect to: interactively display maps of the spatial distribution of regions for any designated image subset; display the statistics of a given region; and label, merge, or split regions.

Wharton, S. W.↗

NASA NTRS1988

Rotating hot-wire investigation of the vortex responsible for blade-vortex interaction noise

This distribution of the circumferential velocity of the vortex responsible for blade-vortex interaction noise was measured using a rotating hot-wire rake synchronously meshed with a model helicopter rotor at the blade passage frequency. Simultaneous far-field acoustic data and blade differential pressure measurements were obtained. Results show that the shape of the measured far-field acoustic blade-vortex interaction signature depends on the blade-vortex interaction geometry. The experimental results are compared with the Widnall-Wolf model for blade-vortex interaction noise.

Fontana, Richard Remo↗

NASA NTRS1988

The role of radiation-dynamics interaction in regional numerical weather prediction

The role of radiation-dynamics interaction in regional numerical weather prediction of severe storm environment and mesoscale convective systems over the United States is researched. Based upon the earlier numerical model simulation experiments, it is believed that such interaction can have a profound impact on the dynamics and thermodynamics of regional weather systems. The research will be carried out using real-data model forecast experiments performed on the Cray-X/MP computer. The forecasting system to be used is a comprehensive mesoscale prediction system which includes analysis and initialization, the dynamic model, and the post-forecast diagnosis codes. The model physics are currently undergoing many improvements in parameterizing radiation processes in the model atmosphere. The forecast experiments in conjunction with in-depth model verification and diagnosis are aimed at a quantitative understanding of the interaction between atmospheric radiation and regional dynamical processes in mesoscale models as well as in nature. Thus, significant advances in regional numerical weather prediction can be made. Results shall also provide valuable information for observational designs in the area of remote sensing techniques to study the characteristics of air-land thermal interaction and moist processes under various atmospheric conditions.

Chang, Chia-Bo↗

NASA NTRS1988

Wave/current interaction model

The wave-current interaction for the application to remote sensing data via numerical simulations and data comparison is modelled. Using the field data of surface current shear, wind condition and ambient wave spectrum, the numerical simulations of directional wave spectrum evolution were used to interpret and to compare with the aircraft data from Radar Ocean Wave Spectrometer (ROWS) and Surface Contour Radar (SCR) across the front during Frontal Air Sea Interaction Experiment (FASINEX). The wave-ice interaction was inspired by the observation of large amplitude waves hundreds of kms inside the ice pack in the Weddell Sea, resulting in breakup of the ice pack. The developed analysis of processes includes the refraction of waves at the pack edge, the effects of pack compression on wave propagation, wave train stability and buckling stability in the ice pack. Sources of pack compression and interaction between wave momentum and pack compression are investigated. Viscous camping of propagating waves in the marginal ice zone are also studied. The analysis suggests an explanation for the change in wave dispersion observed from the ship and the sequence of processes that cause ice pack breakup, pressure ridge formation and the formation of open bands of water.

Liu, A. K.↗

NASA NTRS1989

Interaction of a vortex and a premixed flame

The interaction of a vortex structure and a premixed flame is studied. The presence of pressure gradients in the vortex and density gradients in the flame result in a complicated interaction. This interaction has been examined when the flame and vortex are fully coupled and in two special cases where they are decoupled: a frozen flame case and a frozen vortex case. In the frozen flame case the main effect of the flame on the vortex is through the barocline torque term. This has been modeled for high Damkoehler numbers. In the frozen vortex case the main effect, at moderate Damkoehler numbers, is to convect the flame around the vortex. At low Damkoehler numbers, depending on the length scales, pockets of unburned gas can form or the flame structure can be significantly changed. The two frozen cases provide a basis for understanding the full interaction.

Ferziger, Joel H.↗

NASA NTRS1989

Interaction dynamics of multiple mobile robots with simple navigation strategies

The global dynamic behavior of multiple interacting autonomous mobile robots with simple navigation strategies is studied. Here, the effective spatial domain of each robot is taken to be a closed ball about its mass center. It is assumed that each robot has a specified cone of visibility such that interaction with other robots takes place only when they enter its visibility cone. Based on a particle model for the robots, various simple homing and collision-avoidance navigation strategies are derived. Then, an analysis of the dynamical behavior of the interacting robots in unbounded spatial domains is made. The article concludes with the results of computer simulations studies of two or more interacting robots.

Wang, P. K. C.↗

NASA NTRS1989

A theoretical formulation of wave-vortex interactions

A unified theoretical formulation for wave-vortex interaction, designated the '(omega, Pi) framework,' is presented. Based on the orthogonal decomposition of fluid dynamic interactions, the formulation can be used to study a variety of problems, including the interaction of a longitudinal (acoustic) wave and/or transverse (vortical) wave with a main vortex flow. Moreover, the formulation permits a unified treatment of wave-vortex interaction at various approximate levels, where the normal 'piston' process and tangential 'rubbing' process can be approximated dfferently.

Wu, J. Z.↗

NASA NTRS1989

Nonlinear a Tollmien-Schlichting/vortex interaction in boundary layers

The nonlinear reaction between two oblique three-dimensional Tollmien-Schlichting (TS) waves and their induced streamwise-vortex flow is considered theoretically for an incompressible boundary layer. The same theory applies to the destabilization of an incident vortex motion by subharmonic TS waves, followed by interaction. The scales and flow structure involved are addressed for high Reynolds numbers. The nonlinear interaction is powerful, starting at quite low amplitudes with a triple-deck structure for the TS waves but a large-scale structure for the induced vortex, after which strong nonlinear amplification occurs. This includes nonparallel-flow effects. The nonlinear interaction is governed by a partial differential system for the vortex flow coupled with an ordinary-differential one for the TS pressure. The solution properties found sometimes produce a breakup within a finite distance and sometimes further downstream, depending on the input amplitudes upstream and on the wave angles, and that then leads to the second stages of interaction associated with higher amplitudes, the main second stages giving either long-scale phenomena significantly affected by nonparallelism or shorter quasi-parallel ones governed by the full nonlinear triple-deck response.

Hall, P.↗

NASA NTRS1989

The interaction of supernovae with circumstellar bubbles

This paper examines the interaction of a massive star supernova with the shell created by the fast wind from a blue supergiant, either in the main-sequence phase or in a late evolutionary phase. Making a number of idealizations, the general features of shell interaction are described by semianalytical solutions. The expected properties of the supernova and its environment are discussed, and the hydrodynamics of the interaction is described. It is found that, typically, the shock traversal occurs before the energy transfer is significant. Applications of the model to observed objects are considered, with special attention given to the interaction of SN 1987A with its circumstellar shell, which is expected to occur within decades.

Chevalier, Roger A.↗

NASA NTRS1989

Techniques for optimizing human-machine information transfer related to real-time interactive display systems

In recent years the needs of ground-based researcher-analysts to access real-time engineering data in the form of processed information has expanded rapidly. Fortunately, the capacity to deliver that information has also expanded. The development of advanced display systems is essential to the success of a research test activity. Those developed at the National Aeronautics and Space Administration (NASA), Western Aeronautical Test Range (WATR), range from simple alphanumerics to interactive mapping and graphics. These unique display systems are designed not only to meet basic information display requirements of the user, but also to take advantage of techniques for optimizing information display. Future ground-based display systems will rely heavily not only on new technologies, but also on interaction with the human user and the associated productivity with that interaction. The psychological abilities and limitations of the user will become even more important in defining the difference between a usable and a useful display system. This paper reviews the requirements for development of real-time displays; the psychological aspects of design such as the layout, color selection, real-time response rate, and interactivity of displays; and an analysis of some existing WATR displays.

Granaas, Michael M.↗

NASA NTRS1989

On strongly nonlinear vortex/wave interactions in boundary-layer transition

The interactions between longitudinal vortices and accompanying waves considered are strongly nonlinear, in the sense that the mean-flow profile throughout the boundary layer is completely altered from its original undisturbed state. Nonlinear interactions between vortex flow and Tollmien-Schlichting waves are addressed first, and some analytical and computational properties are described. These include the possibility in the spatial-development case of a finite-distance break-up, inducing a singularity in the displacement thickness. Second, vortex/Rayleigh wave nonlinear interactions are considered for the compressible boundary-layer, along with certain special cases of interest and some possible solution properties. Both types, vortex/Tollmien-Schlichting and vortex/Rayleigh, are short-scale/long-scale interactions and they have potential applications to many flows at high Reynolds numbers. The strongly nonlinear nature is believed to make them very relevant to fully fledged transition to turbulence.

Hall, Philip↗

NASA NTRS1990

Flow separation in shock wave boundary layer interactions at hypersonic speeds

An assessment is presented for the experimental data on separated flow in shock wave turbulent boundary layer interactions at hypersonic and supersonic speeds. The data base consists mainly of two dimensional and axisymmetric interactions in compression corners or cylinder-flares, and externally generated oblique shock interactions with boundary layers over flat plates or cylindrical surfaces. The conditions leading to flow separation and the subsequent changes in the flow empirical correlations for incipient separation are reviewed. The effects of the Mach number, Reynolds number, surface cooling and the methods of detecting separation are discussed. The pertinent experimental data for the separated flow characteristics in separated turbulent boundary layer shock interaction are also presented and discussed.

Hamed, A.↗

NASA NTRS1990

Swept shock/boundary layer interaction experiments in support of CFD code validation

Research on the topic of shock wave/turbulent boundary layer interaction was carried out. Skin friction and surface pressure measurements in fin-induced, swept interactions were conducted, and heat transfer measurements in the same flows are planned. The skin friction data for a strong interaction case (Mach 4, fin-angles equal 16 and 20 degrees) were obtained, and their comparison with computational results was published. Surface pressure data for weak-to-strong fin interactions were also obtained.

Settles, G. S.↗