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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 991 records · Page 55
All sourcesNASA NTRSDOE OSTI
NASA NTRS1983

Experimental investigation of a two-dimensional shock-turbulent boundary layer interaction with bleed

The two-dimensional interaction of an oblique shock wave with a turbulent boundary layer that included the effect of bleed was examined experimentally using a shock generator mounted across a supersonic wind tunnel. The studies were performed at Mach numbers 2.5 and 2.0 and unit Reynolds number of approximately 2.0 x 10 to the 7th/meter. The study includes surface oil flow visualization, wall static pressure distributions and boundary layer pitot pressure profiles. In addition, the variation of the local bleed rates were measured. The results show the effect of the bleed on the boundary layer as well as the effect of the flow conditions on the local bleed rate.

Hingst, W. R.↗
NASA NTRS1983

Lateral-directional stability investigation of the space shuttle orbiter at Mach 6

Lateral-directional aerodynamic data and oil-flow visualization results are pesented from four tests (conducted in two facilities using three models) which were designed to verify the hypersonic aerodynamics of the Space Shuttle orbiter at M=6. Comparisons of measured lateral-directional stability data and oil-flow results between the tests show excellent agreement, especially considering the nonuniform, unpredictable flow which occurs in the vicinity of the vertical tail. Results ere shown to be sensitive to Reynolds number with the higher Reynolds number cases producing more stable values and also showing good agreement with flight values. The results also show that the effects of Reynolds number, angle of attack, and angle of sideslip on the lateral-directional stability of future entry configuration should be carefully assessed for non-linearities.

Calloway, R. L.↗
NASA NTRS1986

Aspects of the equilibrium puff in transitional pipe flow

In the transitional pipe flow-visualization studies presently undertaken to investigate the self-sustenance mechanism of a turbulent equilibrium puff, the upstream laminar fluid continuously enters the relatively more slowly moving turbulent puff around the pipe center. The passage of this high speed laminar plug flow past the slower fluid residing near the wall at the upstream interface leads to the shedding of a train of three-dimensional, wake-like vortices near the wall. The prominent feature of the decay region is a series of longitudinal vortices that appear to be undergoing stretching.

Bandyopadhyay, P. R.↗
NASA NTRS1991

The vortex interaction in a propeller/stator flow field

The vortex interaction encounered in the flow field of a propeller and a stator has been investigated using smoke flow visualization. A stator at angle of attack was used to generate a line vortex which interacted with the helical vortex filaments generated by a propeller. Changes in the relative vortex strengths and vortex rotational directions yielded several distinct vortex structures. Axial flow in the vortex cores is determined to influence the development of the vortex interaction.

Johnston, R. T.↗
NASA NTRS2003

Pore Formation and Mobility Investigation (PFMI): Description and Initial Analysis of Experiments Conducted Aboard the International Space Station

Flow Visualization experiments on the controlled melting and solidification of succinonitrile were conducted in the glovebox facility of the International Space Station (ISS). The experimental samples were prepared on ground by filling glass tubes, 1 cm 1D and approximately 30 cm in length, with pure succinonitrile (SCN) under 450 millibar of nitrogen. Porosity in the samples arose from natural shrinkage, and in some cases by direct insertion of nitrogen bubbles, during solidification of the liquid SCN. The samples were processed in the Pore Formation and Mobility Investigation (PFMI) apparatus that is placed in the glovebox facility (GBX) aboard the ISS. Experimental processing parameters of temperature gradient and translation speed, as well as camera settings, were remotely monitored and manipulated from the ground Telescience Center (TSC) at the Marshall Space Flight Center. During the experiments, the sample is first subjected to a unidirectional melt back, generally at 10 microns per second, with a constant temperature gradient ahead of the melting interface. The temperatures in the sample are monitored by six in situ thermocouples. Real time visualization of the controlled directional melt back shows bubbles of different sizes initiating at the melt interface and, upon dislodging from the melting solid, migrating at different speeds into the temperature field ahead of them, before coming to rest. The thermocapillary flow field set up in the melt, ahead of the interface, is dramatic in the context of the large bubbles, and plays a major role in dislodging the bubble. A preliminary analysis of the observed bubble formation and mobility during melt back and its implication to future microgravity experiments is presented and discussed.

Grugel, R. N.↗
NASA NTRS2003

Bubble Formation and Transport during Microgravity Materials Processing: Model Experiments on the International Space Station

Flow Visualization experiments on the controlled melting and solidification of succinonitrile were conducted in the glovebox facility of the International Space Station (ISS). The experimental samples were prepared on ground by filling glass tubes, 1 cm ID and approximately 30 cm in length, with pure succinonitrile (SCN) under 450 millibar of nitrogen. Porosity in the samples arose from natural shrinkage, and in some cases by direct insertion of nitrogen bubbles, during solidification of the liquid SCN. The samples were processed in the Pore Formation and Mobility Investigation (PFMI) apparatus that is placed in the glovebox facility (GBX) aboard the ISS. Experimental processing parameters of temperature gradient and translation speed, as well as camera settings, were remotely monitored and manipulated from the ground Telescience Center (TSC) at the Marshall Space Flight Center. During the experiments, the sample is first subjected to a unidirectional melt back, generally at 10 microns per second, with a constant temperature gradient ahead of the melting interface. The temperatures in the sample are monitored by six in situ thermocouples. Real time visualization of the controlled directional melt back shows bubbles of different sizes initiating at the melt interface and, upon dislodging from the melting solid, migrating at different speeds into the temperature field ahead of them, before coming to rest. The thermocapillary flow field set up in the melt, ahead of the interface, is dramatic in the context of the large bubbles, and plays a major role in dislodging the bubble. A preliminary analysis of the observed bubble formation and mobility during melt back and its implication to future microgravity experiments is presented and discussed.

Grugel, R. N.↗
NASA NTRS2003

Bubble Formation and Transport during Microgravity Materials Processing: Model Experiments on the International Space Station

Flow Visualization experiments on the controlled melting and solidification of succinonitrile were conducted in the glovebox facility of the International Space Station (ISS). The experimental samples were prepared on ground by filling glass tubes, 1 cm ID and approximately 30 cm in length, with pure succinonitrile (SCN) under 450 millibar of nitrogen. Porosity in the samples arose from natural shrinkage, and in some cases by direct insertion of nitrogen bubbles, during solidification of the liquid SCN. The samples were processed in the Pore Formation and Mobility Investigation (PFMI) apparatus that is placed in the glovebox facility (GBX) aboard the ISS. Experimental processing parameters of temperature gradient and translation speed, as well as camera settings, were remotely monitored and manipulated from the ground Telescience Center (TSC) at the Marshall Space Flight Center. During the experiments, the sample is first subjected to a unidirectional melt back, generally at 10 microns per second, with a constant temperature gradient ahead of the melting interface. The temperatures in the sample are monitored by six in situ thermocouples. Real time visualization of the controlled directional melt back shows bubbles of different sizes initiating at the melt interface and, upon dislodging from the melting solid, migrating at different speeds into the temperature field ahead of them, before coming to rest. The thermocapillary flow field set up in the melt, ahead of the interface, is dramatic in the context of the large bubbles, and plays a major role in dislodging the bubble. A preliminary analysis of the observed bubble formation and mobility during melt back and its implication to future microgravity experiments is presented and discussed.

Grugel, R. N.↗
NASA NTRS2003

Bubble Formation and Transport during Microgravity Materials Processing: Model Experiments on the Space Station

Flow Visualization experiments on the controlled melting and solidification of succinonitrile were conducted in the glovebox facility of the International Space Station (ISS). The experimental samples were prepared on ground by filling glass tubes, 1 cm ID and approximately 30 cm in length, with pure succinonitrile (SCN) under 450 millibar of nitrogen. Porosity in the samples arose from natural shrinkage, and in some cases by direct insertion of nitrogen bubbles, during solidification of the liquid SCN. The samples were processed in the Pore Formation and Mobility Investigation (PFMI) apparatus that is placed in the glovebox facility (GBX) aboard the ISS. Experimental processing parameters of temperature gradient and translation speed, as well as camera settings, were remotely monitored and manipulated from the ground Telescience Center (TSC) at the Marshall Space Flight Center. During the experiments, the sample is first subjected to a unidirectional melt back, generally at 10 microns per second, with a constant temperature gradient ahead of the melting interface. The temperatures in the sample are monitored by six in situ thermocouples. Real time visualization of the controlled directional melt back shows bubbles of different sizes initiating at the melt interface and, upon dislodging from the melting solid, migrating at different speeds into the temperature field ahead of them, before coming to rest. The thermocapillary flow field set up in the melt, ahead of the interface, is dramatic in the context of the large bubbles, and plays a major role in dislodging the bubble. A preliminary analysis of the observed bubble formation and mobility during melt back and its implication to future microgravity experiments is presented and discussed.

Grugel, R. N.↗
NASA NTRS2007

Use of Plasma Actuators as a Moving-Wake Generator

The work documented in this report tests the concept of using plasma actuators as a simple and easy way to generate a simulated moving-wake and the disturbances associated with it in turbines. This wake is caused by the blades of the upstream stages of the turbine. Two types of devices, one constructed of arrays of NACA 0018 airfoils, and the one constructed of flat plates were studied. The airfoils or plates were equipped with surface mounted dielectric barrier discharge (DBD) plasma actuators, which were used to generate flow disturbances resembling moving-wakes. CTA hot-wire anemometry and flow visualization using a smoke-wire were used to investigate the wake independence at various spacings and downstream locations. The flat plates were found to produce better results than the airfoils in creating large velocity fluctuations in the free-stream flow. Different dielectric materials, plasma actuator locations, leading edge contours, angles of attack and plate spacings were investigated, some with positive results. The magnitudes of the velocity fluctuations were found to be comparable to existing mechanical moving-wake generators, thus proving the feasibility of using plasma actuators as a moving-wake generator.

Corke, Thomas C.↗
NASA NTRS2008

Fluorescence Imaging Study of Impinging Underexpanded Jets

An experiment was designed to create a simplified simulation of the flow through a hole in the surface of a hypersonic aerospace vehicle and the subsequent impingement of the flow on internal structures. In addition to planar laser-induced fluorescence (PLIF) flow visualization, pressure measurements were recorded on the surface of an impingement target. The PLIF images themselves provide quantitative spatial information about structure of the impinging jets. The images also help in the interpretation of impingement surface pressure profiles by highlighting the flow structures corresponding to distinctive features of these pressure profiles. The shape of the pressure distribution along the impingement surface was found to be double-peaked in cases with a sufficiently high jet-exit-to-ambient pressure ratio so as to have a Mach disk, as well as in cases where a flow feature called a recirculation bubble formed at the impingement surface. The formation of a recirculation bubble was in turn found to depend very sensitively upon the jet-exit-to-ambient pressure ratio. The pressure measured at the surface was typically less than half the nozzle plenum pressure at low jet pressure ratios and decreased with increasing jet pressure ratios. Angled impingement cases showed that impingement at a 60deg angle resulted in up to a factor of three increase in maximum pressure at the plate compared to normal incidence.

Inman, Jennifer A.↗
NASA NTRS1981

Analytical and experimental study of flow phenomena in noncavitating rocket pump inducers

The flow processes in rocket pump inducers are summarized. The experimental investigations were carried out with air as the test medium. The major characteristics features of the rocket pump inducers are low flow coefficient (0.05 to 0.2) large stagger angle (70 deg to 85 deg) and high solidity blades of little or no camber. The investigations are concerned with the effect of viscosity not the effects of cavitation. Flow visualization, conventional and hot wire probe measurement inside and at the exit of the blade passage, were the analytical methods used. The experiment was carried out using four three and two bladed inducers with cambered blades. Both the passage and the exit flow were measured. The basic research and boundary layer investigation was carried out using a helical flat plate (of some dimensions as the inducer blades tested), and flat plate helical inducer (four bladed). Detailed mean and turbulence flow field inside the passage as well as the exit of the rotor were derived from these measurement. The boundary layer, endwall, and other passage data reveal extremely complex nature of the flow, with major effects of viscosity present across the entire passage. Several analyses were carried out to predict the flow field in inducers. These included an approximate analysis, the shear pumping analysis, and a numerical solution of exact viscous equations with approximate modeling for the viscous terms.

Lakshminarayana, B.↗
NASA NTRS1989

Vortex control for tail buffet alleviation on a twin-tail fighter configuration

Two aerodynamic concepts proposed for alleviating high-alpha tail buffet characteristics of a LEX (Leading Edge Extension) vortex dominated twin-tail fighter configuration were explored in low-speed tunnel tests on generic models via flow visualizations, 6-component balance measurements and monitoring of tail dynamics. Passive dorsal-fin extensions of the vertical tails, and an active LEX arrangement with up-deflected edge sections were evaluated as independent means of re-structuring the adverse vortical flow environment in the tail region. Each of these techniques successfully reduced the buffet as measured by the root-mean-square of tail accelerometer output, particularly at post-stall angles of attack when the baseline configuration was characterized by high buffet intensity. Used in combination, the two concepts indicated significant tail buffet relief with relatively minor impact on the high-alpha configuration aerodynamics.

Rao, Dhanvada M.↗
NASA NTRS1991

Experimental study of an independently deflected wingtip mounted on a semispan wing

The results of a subsonic wind tunnel test of a semispan wing with an independently deflected tip surface are presented and analyzed. The tip surface was deflected about the quarter chord of the rectangular wing and accounted for 17 percent of the wing semispan. The test was conducted to measure the loads on the tip surface and to investigate the nature of aerodynamic interference effects between the wing and the deflected tip. Results are presented for two swept tip surfaces of similar planform but different airfoil distributions. The report contains plots of tip lift, drag, and pitching moment for various Reynolds numbers and tip deflection angles with respect to the inboard wing. Oil flow visualization photographs for a typical Reynolds number are also included. Important aerodynamic parameters such as lift and pitching moment slopes and tip aerodynamic center location are tabulated. A discussion is presented on the relationship between tip experimental data acquired in a steady flow and the prediction of unsteady tip motion at fixed wing angles of attack.

Martin, D. M.↗
NASA NTRS1981

Modification in drag of turbulent boundary layers resulting from manipulation of large-scale structures

The effects of placing a parallel-plate turbulence manipulator in a boundary layer are documented through flow visualization and hot wire measurements. The boundary layer manipulator was designed to manage the large scale structures of turbulence leading to a reduction in surface drag. The differences in the turbulent structure of the boundary layer are summarized to demonstrate differences in various flow properties. The manipulator inhibited the intermittent large scale structure of the turbulent boundary layer for at least 70 boundary layer thicknesses downstream. With the removal of the large scale, the streamwise turbulence intensity levels near the wall were reduced. The downstream distribution of the skin friction was also altered by the introduction of the manipulator.

Corke, T. C.↗
NASA NTRS1981

Organized motion in turbulent flow

A review of organized motion in turbulent flow indicates that the transport properties of most shear flows are dominated by large-scale vortex nonrandom motions. The mean velocity profile of a turbulent boundary layer consists of a viscous sublayer, buffer layer, and a logarithmic outer layer; an empirical formula of Coles (1956) applies to various pressure gradients. The boundary layer coherent structure was isolated by the correlation methods of Townsend (1956) and flow visualization by direct observations of complex unsteady turbulent motions. The near-wall studies of Willmart and Wooldridge (1962) used the space-time correlation for pressure fluctuations at the wall under a thick turbulent boundary layer; finally, organized motion in free shear flows and transition-control of mixing demonstrated that the Reynolds number invariance of turbulence shows wide scatter.

Cantwell, B. J.↗
NASA NTRS1992

An experimental study of oscillatory thermocapillary convection in cylindrical containers

An experimental study of oscillatory thermocapillary in small cylindrical containers with a heating wire placed along the center axis is performed by investigating the flow structures and temperature distributions under various conditions. To supplement the flow visualization the surface is scanned using an infrared imager. Here, 2 cS viscosity (Pr = 27) silicone oil is used as the test fluid. It is observed that beyond a certain temperature difference between the container wall and the heating wire, a distinctive unsteady flow pattern appears. This unsteady phenomenon is identified as oscillatory thermocapillary. After the onset of oscillations the flow structure becomes nonaxisymmetric and wave motion is observed at the free surface. It is shown that the critical temperature difference is independent of container dimensions if the aspect ratio is fixed.

Kamotani, Y.↗
NASA NTRS1995

Delta wing vortex manipulation using pulsed and steady blowing during ramp pitching

The effectiveness of steady and pulsed blowing as a method of controlling delta wing vortices during ramp pitching has been investigated in flow visualization experiments conducted in a water tunnel. The recessed angled spanwise blowing technique was utilized for vortex manipulation. This technique was implemented on a beveled 60 delta wing using a pair of blowing ports located beneath the vortex core at 40% chord. The flow was injected primarily in the spanwise direction but was also composed of a component normal to the wing surface. The location of vortex burst was measured as a function of blowing intensity and pulsing frequency under static conditions, and the optimum blowing case was applied at three different wing pitching rates. Experimental results have shown that, when the burst location is upstream of the blowing port, pulsed blowing delays vortex breakdown in static and dynamic cases. Dynamic tests verified the existence of a hysteresis effect and demonstrated the improvements offered by pulsed blowing over both steady blowing and no-blowing scenarios. The application of blowing, at the optimum pulsing frequency, made the vortex breakdown location comparable in static and ramp pitch-up conditions.

Moreira, J.↗
NASA NTRS1981

Entrainment and thrust augmentation in pulsatile ejector flows

This study comprised direct thrust measurements, flow visualization by use of a spark shadowgraph technique, and mean and fluctuating velocity measurements with a pitot tube and linearized constant temperature hot-wire anemometry respectively. A gain in thrust of as much as 10 to 15% was observed for the pulsatile ejector flow as compared to the steady flow configuration. From the velocity profile measurements, it is concluded that this enhanced augmentation for pulsatile flow as compared to a nonpulsatile one was accomplished by a corresponding increased entrainment by the primary jet flow. It is also concluded that the augmentation and total entrainment by a constant area ejector critically depends upon the inlet geometry of the ejector. Experiments were performed to evaluate the influence of primary jet to ejector area ratio, ejector length, and presence of a diffuser on pulsatile ejector performance.

Sarohia, V.↗