Search NASA⌕ Search

SEARCH · Search NASA

Results for “Conductance decay”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 199 records · Page 11
All sourcesNASA NTRSDOE OSTI
NASA NTRS2000

Separation Control at Flight Reynolds Numbers: Lessons Learned and Future Directions

Active separation control, using periodic excitation, was studied experimentally at high Reynolds numbers. The effects of compressibility, mild sweep, location of excitation slot and steady momentum transfer on the efficacy of the method were identified. Tests conducted at chord Reynolds numbers as high as 40 x 10(exp 6) demonstrated that active control using oscillatory flow excitation can effectively delay flow separation from, and reattach separated flow to aerodynamic surfaces at flight conditions. The effective frequencies generate one to four vortices over the controlled region at all times, regardless of the Reynolds number. The vortices are initially amplified by the separated shear-layer, and after initiating reattachment, the strength of the vortices decay as they are convected downstream. Large amplitude, low frequency vortices break down to smaller ones upon introduction at the excitation slot. The effects of steady mass transfer were compared to those of periodic excitation. It was found that steady blowing is significantly inferior to periodic excitation in terms of performance benefits and that the response to steady blowing is abrupt, and therefore undesirable from a control point of view. Steady suction and periodic excitation are comparable in effectiveness and both exhibit a gradual response to changes in the magnitude of the control input. The combination of weak steady suction and periodic excitation is extremely effective while the addition of steady blowing could be detrimental. Compressibility effects are weak as long as separation is not caused by a shock-wave/boundary-layer interaction. The undesirable effects of the shock-induced separation could be alleviated by the introduction of periodic excitation upstream of the shock wave, inside the region of supersonic flow. The effects of mild sweep were also studied and periodic excitation was found to be very effective in reattaching three-dimensional separated flow. Scaling laws that correlate 2D and 3D controlled flows were tested and verified. Several performance benefits could be gained by applying the method to existing configurations, but it is expected that the full potential of the method can only be realized through the design of new configurations. A comprehensive, fully turbulent, database was generated in order to guide the development, and enable validation, of candidate unsteady CFD design tools.

Pack, LaTunia G.↗
NASA NTRS1996

Comparison of Hover/Ground-Effect Characteristics for a Joint Strike Fighter Configuration

Hover and ground-effect tests were conducted with the Lockheed-Martin Large Scale Powered Model (LSPM) during June-November 1995 at the NASA Ames Research Center's Outdoor Aerodynamics Research Facility (OARF). This was done in support of the Joint Strike Fighter (JSF) Program being lead by the Department of Defense. The program was previously metered to as the Joint Advanced Strike Technology (JAST) Program. The tests at the OARF included: engine thrust calibrations out of ground effect, measurements of individual nozzle jet pressure decay characteristics, and jet-induced hover force and moment measurements in and out of ground effect. The engine calibrations provide data correlating propulsion system throttle and nozzle settings to thrust forces and moments for the bare fuselage with the wings, canards, and tails removed. This provides propulsive forces and moments while minimizing any of the effects due to the presence of the airframe. The engine calibrations were used later to determine thrust for hover testing at the OARF and for transition testing which took place in the NASA Ames 80 by 120 foot Wind Tunnel. The jet decay characteristics reflect the jet entrainment properties and are related to the aircraft suckdown characteristics. The JSF program provided the opportunity to obtain model scale effects using two models; one at small scale and one at large scale. Examples of data from these tests will be presented out of ground effect which will demonstrate the effect of scale. For one JSF configuration, two small-scale models and one large-scale model were tested and obtained different values for the lift loss out of ground effect. These differences were examined and are found to be largely dependent on the jet efflux characteristics. The jet-induced hover forces and moments are presented in and out of ground effect. For the hover testing the model is methodically built up from the bare fuselage, to include the wings, canards, and vertical tails, to determine the effects of each. Other components such as weapons bay doors, landing gear doors, and other lift improvement devices and their effect on the jet-induced forces and moments are examined.

Hange, Craig↗
NASA NTRS1998

Continuing Studies of Planetary Atmospheres Associated with Experiments on the Galileo Jupiter Probe and Infrared Observations of Venus

The results of the nephelometer experiment conducted aboard the Probe of the Galileo mission to Jupiter are presented. The tenuous clouds and sparse particulate matter in the relatively particle-free 5-micron "hot spot" region of the Probe's descent were documented from about 0.46 bars to about 12 bars. Three regions of apparent coherent structure were noted, in addition to many indications of extremely small particle concentrations along the descent path. From the first valid measurement at about 0.46 bars down to about 0.55 bars a feeble decaying lower portion of a cloud, corresponding with the predicted ammonia particle cloud, was encountered. A denser, but still very modest, particle structure was present in the pressure regime extending from about 0.76 to a distinctive base at 1.34 bars, and is compatible with the expected ammonium hydrosulfide cloud. No massive water cloud was encountered, although below the second structure, a small, vertically thin layer at about 1.65 bars may be detached from the cloud above, but may also be water condensation, compatible with reported measurements of water abundance from other Galileo Mission experiments. A third small signal region, extending from about 1.9 to 4.5 bars, exhibited quite weak but still distinctive structure, and, although the identification of the light scatterers in this region is uncertain, may also be a water cloud perhaps associated with lateral atmospheric motion and/or reduced to a small mass density by atmospheric subsidence or other explanations. Rough descriptions of the particle size distributions and cloud properties in these regions have been derived, although they may be imprecise because of the small signals and experimental difficulties. These descriptions document the small number densities of particles, the moderate particle sizes, generally in the slightly submicron to few micron range, and the resulting small optical depths, mass densities due to particles, column particle number loading and column mass loading in the atmosphere encountered by the Galileo Probe during its descent.

Ragent, Boris↗
NASA NTRS1998

Continuing Studies of Planetary Atmospheres Associated With Experiments on the Galileo Jupiter Probe and Infrared Observations of Venus

The results of the nephelometer experiment conducted aboard the Probe of the Galileo mission to Jupiter are presented. The tenuous clouds and sparse particulate matter in the relatively particle-free 5-micron "hot spot" region of the Probe's descent were documented from about 0.46 bars to about 12 bars. Three regions of apparent coherent structure were noted, in addition to many indications of extremely small particle concentrations along the descent path. From the first valid measurement at about 0.46 bars down to about 0.55 bars a feeble decaying lower portion of a cloud, corresponding with the predicted ammonia particle cloud, was encountered. A denser, but still very modest, particle structure was present in the pressure regime extending from about 0.76 to a distinctive base at 1.34 bars, and is compatible with the expected ammonium hydrosulfide cloud. No massive water cloud was encountered, although below the second structure, a small, vertically thin layer at about 1.65 bars may be detached from the cloud above, but may also be water condensation, compatible with reported measurements of water abundance from other Galileo Mission experiments. A third small signal region, extending from about 1.9 to 4.5 bars, exhibited quite weak but still distinctive structure, and, although the identification of the light scatterers in this region is uncertain, may also be a water cloud perhaps associated with lateral atmospheric motion and/or reduced to a small mass density by atmospheric subsidence or other explanations. Rough descriptions of the particle size distributions and cloud properties in these regions have been derived, although they may be imprecise because of the small signals and experimental difficulties. These descriptions document the small number densities of particles, the moderate particle sizes, generally in the slightly submicron to few micron range, and the resulting small optical depths, mass densities due to particles, column particle number loading and column mass loading in the atmosphere encountered by the Galileo Probe during its descent.

Goodman,Jindra↗
NASA NTRS1999

Digging for Fossils in the Hertzsprung Gap

Objective was to conduct deep (approx. 250 ks) pointings on two EUV sources, the early-F giant beta Cas and the mid-G giant mu Velorum; to obtain spectra in the range 70-300 A and to record Deep Survey light curves over the extensive duration of each observation. We have analyzed the DS lightcurve and the SW spectrum, breaking the latter lip into time slices corresponding to key phases of the observation: pre-flare, flare rise, and two segments of the flare decay.

Ayres, Thomas R.↗
NASA NTRS2004

Saturn's Rings, the Yarkovsky Effects, and the Ring of Fire

Saturn's icy ring particles, with their low thermal conductivity, are almost ideal for the operation of the Yarkovsky effects. The dimensions of Saturn's A and B rings may be determined by a near balancing of the seasonal Yarkovsky effect with the Yarkovsky- Schach effect. The two effects, which are photon thrust due to temperature gradients, may confine the A and B rings to within their observed dimensions. The C ring may be sparsely populated with icy particles because Yarkovsky drag has pulled them into Saturn, leaving the more slowly orbitally decaying rocky particles. Icy ring particles ejected from the B ring and passing through the C ring, as well as some of the slower rocky particles, should fall on Saturn's equator, where they may create a luminous "Ring of Fire" around Saturn's equator. This predicted Ring of Fire may be visible to Cassini's camera. Curiously, the speed of outwards Yarkovsky orbital evolution appears to peak near the Cassini Division. The connection between the two is not clear. D. Nesvorny has speculated that the resonance at the outer edge of the B ring may impede particles from evolving via Yarkovsky across the Division. If supply from the B ring is largely cut off, then Yarkovsky may push icy particles outward, away from the inner edge of the A ring, leaving only the rocky ones in the Division. The above scenarios depend delicately on the properties of the icy particles.

Rubincam, David↗
NASA NTRS2016

Characterization of Three-Stream Jet Flow Fields

Flow-field measurements were conducted on single-, dual- and three-stream jets using two-component and stereo Particle Image Velocimetry (PIV). The flow-field measurements complimented previous acoustic measurements. The exhaust system consisted of externally-plugged, externally-mixed, convergent nozzles. The study used bypass-to-core area ratios equal to 1.0 and 2.5 and tertiary-to-core area ratios equal to 0.6 and 1.0. Axisymmetric and offset tertiary nozzles were investigated for heated and unheated high-subsonic conditions. Centerline velocity decay rates for the single-, dual- and three-stream axisymmetric jets compared well when axial distance was normalized by an equivalent diameter based on the nozzle system total exit area. The tertiary stream had a greater impact on the mean axial velocity for the small bypass-to-core area ratio nozzles than for large bypass-to-core area ratio nozzles. Normalized turbulence intensities were similar for the single-, dual-, and three-stream unheated jets due to the small difference (10%) in the core and bypass velocities for the dual-stream jets and the low tertiary velocity (50% of the core stream) for the three-stream jets. For heated jet conditions where the bypass velocity was 65% of the core velocity, additional regions of high turbulence intensity occurred near the plug tip which were not present for the unheated jets. Offsetting the tertiary stream moved the peak turbulence intensity levels upstream relative to those for all axisymmetric jets investigated.

Noise↗
NASA NTRS2016

Characterization of Three-Stream Jet Flow Fields

Flow-field measurements were conducted on single-, dual- and three-stream jets using two-component and stereo Particle Image Velocimetry (PIV). The flow-field measurements complimented previous acoustic measurements. The exhaust system consisted of externally-plugged, externally-mixed, convergent nozzles. The study used bypass-to-core area ratios equal to 1.0 and 2.5 and tertiary-to-core area ratios equal to 0.6 and 1.0. Axisymmetric and offset tertiary nozzles were investigated for heated and unheated high-subsonic conditions. Centerline velocity decay rates for the single-, dual- and three-stream axisymmetric jets compared well when axial distance was normalized by an equivalent diameter based on the nozzle system total exit area. The tertiary stream had a greater impact on the mean axial velocity for the small bypass-to-core area ratio nozzles than for large bypass-to-core area ratio nozzles. Normalized turbulence intensities were similar for the single-, dual-, and three-stream unheated jets due to the small difference (10 percent) in the core and bypass velocities for the dual-stream jets and the low tertiary velocity (50 percent of the core stream) for the three-stream jets. For heated jet conditions where the bypass velocity was 65 percent of the core velocity, additional regions of high turbulence intensity occurred near the plug tip which were not present for the unheated jets. Offsetting the tertiary stream moved the peak turbulence intensity levels upstream relative to those for all axisymmetric jets investigated.

Noise↗
NASA NTRS1973

Nuclear safety considerations for the design of a shuttle launched 500 to 2000 watt isotope Brayton power system.

An extensive study was conducted to evaluate the safety requirements for the design of a heat source assembly for use in a shuttle launched, isotope Brayton electric power system for the 500-W(e) to 2 kWe range. The assembly is a self-contained package which supplies heat to a power conversion system. A typical mission profile for a shuttle launched, earth orbital mission was assumed. Critical mission accidents were identified and evaluated to determine their impact upon the design of the Heat Source Assembly. Earth-orbital decay reentry analyses were performed to demonstrate survivability of the heat source. Safety design requirements were developed to ensure survivability under credible accident conditions including loss of the power conversion system in orbit.

Garate, J. A.↗
NASA NTRS1986

Experiments in software reliability - Life-critical applications

The paper discusses four reliability data gathering experiments which were conducted using a small sample of programs for two problems having ultrareliability requirements, n-version programming for fault detection, and repetitive run modeling for failure and fault rate estimation. The experimental results agree with those of Nagel and Skrivan in that the program error rates suggest an approximate log-linear pattern and the individual faults occurred with significantly different error rates. Additional analysis of the experimental data raises new questions concerning the phenomenon of interacting faults. This phenomenon may provide one explanation for software reliability decay. The fourth experiment underscored the difficulty in distinguishing between observations of deficiencies in the design of the algorithm and observations of software faults for real-time process control software. These experiments are a part of a program of serial experiments being pursued by the System Validation Methods of NASA-Langley Research Center to find a means of credibly performing reliability evaluations of flight control software.

Dunham, J. R.↗
NASA NTRS1992

Acoustical evaluation of the NASA Lewis 9 by 15 foot low speed wind tunnel

The test section of the NASA Lewis 9- by 15-Foot Low Speed Wind Tunnel was acoustically treated to allow the measurement of acoustic sources located within the tunnel test section under simulated free field conditions. The treatment was designed for high sound absorption at frequencies above 250 Hz and to withstand tunnel airflow velocities up to 0.2 Mach. Evaluation tests with no tunnel airflow were conducted in the test section to assess the performance of the installed treatment. This performance would not be significantly affected by low speed airflow. Time delay spectrometry tests showed that interference ripples in the incident signal resulting from reflections occurring within the test section average from 1.7 dB to 3.2 dB wide over a 500 to 5150 Hz frequency range. Late reflections, from upstream and downstream of the test section, were found to be insignificant at the microphone measuring points. For acoustic sources with low directivity characteristics, decay with distance measurements in the test section showed that incident free field behavior can be measured on average with an accuracy of +/- 1.5 dB or better at source frequencies from 400 Hz to 10 kHz. The free field variations are typically much smaller with an omnidirectional source.

Dahl, Milo D.↗
NASA NTRS1993

Control of jet noise

This reports describes experiments conducted at the High-Speed Jet Facility at the University of Southern California on supersonic jets. The goal of the study was to develop methods for controlling the noise emitted from supersonic jets by passive and/or active means. Work by Seiner et al (1991) indicates that eddy Mach wave radiation is the dominant noise source in a heated high speed jet. Eddy Mach radiation is caused by turbulent eddies traveling at supersonic speed in the shear layer of the jet. The convection velocity of the eddies decays with increasing distance from the nozzle exit due to the mixing of the jet stream with the ambient fluid. Once the convection speed reaches subsonic velocities, eddy Mach wave radiation ceases. To control noise, a rapid decay of the convection velocity is desired. This may be accomplished by enhanced mixing in the jet. In this study, small aspect ratio rectangular jet nozzles were tested. A flapping mode was noticed in the jets. By amplifying screech components of the jets and destabilizing the jet columns with a collar device, the flapping mode was excited. The result was a rapid decay of the jet velocity. A reduction in eddy Mach radiation in rectangular supersonic jets may be achieved with this device.

Schreck, Stefan↗
NASA NTRS2007

Iapetus' Geophysics: Rotation Rate, Shape, and Equatorial Ridge

Iapetus has preserved evidence that constrains the modeling of its geophysical history from the time of its accretion until now. The evidence is (a) its present 79.33-day rotation or spin rate, (b) its shape that corresponds to the equilibrium figure for a hydrostatic body rotating with a period of approximately 16 h, and (c) its high, equatorial ridge, which is unique in the Solar System. This paper reports the results of an investigation into the coupling between Iapetus' thermal and orbital evolution for a wide range of conditions including the spatial distributions with time of composition, porosity, short-lived radioactive isotopes (SLRI), and temperature. The thermal model uses conductive heat transfer with temperature-dependent conductivity. Only models with a thick lithosphere and an interior viscosity in the range of about the water ice melting point can explain the observed shape. Short-lived radioactive isotopes provide the heat needed to decrease porosity in Iapetus? early history. This increases thermal conductivity and allows the development of the strong lithosphere that is required to preserve the 16-h rotational shape and the high vertical relief of the topography. Long-lived radioactive isotopes and SLRI raise internal temperatures high enough that significant tidal dissipation can start, and despin Iapetus to synchronous rotation. This occurred several hundred million years after Iapetus formed. The models also constrain the time when Iapetus formed because the successful models are critically dependent upon having just the right amount of heat added by SLRI decay in this early period. The amount of heat available from short-lived radioactivity is not a free parameter but is fixed by the time when Iapetus accreted, by the canonical concentration of Al-26, and, to a lesser extent, by the concentration of Fe-60. The needed amount of heat is available only if Iapetus accreted between 2.5 and 5.0Myr after the formation of the calcium aluminum inclusions as found in meteorites. Models with these features allow us to explain Iapetus? present synchronous rotation, its fossil 16-h shape, and the context within which the equatorial ridge arose.

geophysics↗
NASA NTRS1994

A Numerical Investigation of Turbulent Flow in Noncircular Ducts

Since turbulent duct flows play an important role in engineering, continuous efforts to investigate this problem have been made. Until recently, these investigations were limited mostly to experiments and various semi-analytic methods. Owing to the improvement of turbulence modeling, the prevailing method of prediction is now mainly numerical. The majority of these studies deals, however, with turbulent flows in circular or square ducts and only limited information is available for straight noncircular ducts. In view of this situation, we propose to conduct a numerical investigation of turbulent flow in a class of ducts, whose cross sections vary from a circle to a near square. Turbulent flow in a noncircular duct is characterized by the presence of secondary flow for which a more refined turbulence model than the k-epsilon equations is required. In order to show that the calculated results are credible, various modes of verification were used to examine the results for a selected configuration, including an accuracy check by a scaling law and observing the decay of secondary flow as the cross section changes from a noncircular shape to a circle. After this was done, computations were performed for other configurations and with different Reynolds numbers from which wall shear stresses and friction factors are plotted.

Kao, Hsiao C.↗
NASA NTRS2001

Numerical Simulations of Precipitation Processes, Microphysics, and Microwave Radiative Properties of flood Producing Storms in Mediterranean & Adriatic Basins

A comprehensive understanding of the meteorological and microphysical nature of Mediterranean storms requires a combination of in situ data analysis, radar data analysis, and satellite data analysis, effectively integrated with numerical modeling studies at various scales. An important aspect of understanding microphysical controls of severe storms, is first understanding the meteorological controls under which a storm has evolved, and then using that information to help characterize the dominant microphysical processes. For hazardous Mediterranean storms, highlighted by the October 5-6, 1998 Friuli flood event in northern Italy, a comprehensive microphysical interpretation requires an understanding of the multiple phases of storm evolution. This involves intense convective development, Sratiform decay, orographic lifting, and sloped frontal lifting processes, as well as the associated vertical motions and thermodynamical instabilities governing physical processes that effect details of the size distributions and fall rates of the various types of hydrometeors found within the storm environment. This talk overviews the microphysical elements of a severe Mediterranean storm in such a context, investigated with the aid of TRMM satellite and other remote sensing measurements, but guided by a nonhydrostatic mesoscale model simulation of the Friuli flood event. The data analysis for this paper was conducted by my research groups at the Global Hydrology and Climate Center in Huntsville, AL and Florida State University in Tallahassee, and in collaboration with Dr. Alberto Mugnai's research group at the Institute of Atmospheric Physics in Rome. The numerical modeling was conducted by Professor Oreg Tripoli and Ms. Giulia Panegrossi at the University of Wisconsin in Madison, using Professor Tripoli's nonhydrostatic modeling system (NMS). This is a scalable, fully nested mesoscale model capable of resolving nonhydrostatic circulations from regional scale down to cloud scale and below.

Smith, Eric A.↗
NASA NTRS2023

Delayed Development of Cool Plasmas in X-Ray Flares from the Young Sun-like Star κ1 Ceti

The Neutron star Interior Composition Explorer (NICER) X-ray observatory observed two powerful X-ray flares equivalent to superflares from the nearby young solar-like star κ 1 Ceti in 2019. NICER follows each flare from the onset through the early decay, collecting over 30 counts s −1 near the peak, enabling a detailed spectral variation study of the flare rise. The flare in September varies quickly in ∼800 s, while the flare in December has a few times longer timescale. In both flares, the hard-band (2–4 keV) light curves show typical stellar X-ray flare variations with a rapid rise and slow decay, while the soft X-ray light curves, especially of the September flare, have prolonged flat peaks. The time-resolved spectra require two temperature plasma components at kT ∼0.3–1 and ∼2–4 keV. Both components vary similarly, but the cool component lags by ∼200 s with a four to six times smaller emission measure (EM) compared to the hot component. A comparison with hydrodynamic flare loop simulations indicates that the cool component originates from X-ray plasma near the magnetic loop footpoints that mainly cools via thermal conduction. The time lag represents the travel time of the evaporated gas through the entire flare loop. The cool component has a several times smaller EM than its simulated counterpart, suggesting a suppression of conductive cooling, possibly by the expansion of the loop cross-sectional area or turbulent fluctuations. The cool component's time lag and EM ratio provide important constraints on the flare loop geometry.

main sequence stars↗
NASA NTRS1992

Analysis of rotationally symmetric arrays of apertures on conducting spherical surfaces

Rotationally symmetric arrays of circular waveguide fed apertures on conducting spherical surfaces have been analyzed. Representation of the outside electromagnetic fields in terms of spherical transmission line modes permit the array analysis to be viewed as a spherical waveguide junction discontinuity problem. The apertures, in general, carry dual polarized circular waveguide TE11 modes. Two independent formulations - the unit cell method and the eigenexcitation method that take rotational symmetry into account - are developed and are checked against each other numerically for computational accuracy. These two formulations are analytically linked as discrete Fourier series pairs. It is seen that mutual coupling along the array decays more rapidly when the polarization of excitation is perpendicular to the array plane than when it is parallel to it. This analysis has been applied in the performance analysis of the Dome Lens phased array radar antenna.

Bondyopadhyay, Probir K.↗
NASA NTRS1999

Attenuation of Gas Turbulence by a Nearly Stationary Dispersion of Fine Particles

Turbulence attenuation by greater than a factor of two has been observed in many practical gas flows carrying volume fractions as small as 0.01% of dispersed particles. Particles which cause such attenuation usually are smaller than the smallest scales of the turbulence and have time constants 5 to 10 times greater than the time scale of a typical turbulent eddy. That is, strongly attenuating particles usually have Stokes numbers in the range of 5 to 10, indicating that they do not respond to the turbulent fluctuations, but instead just fall through the flow responding only to the mean flow. There are two mechanisms by which free falling particles may attenuate turbulence. First, the unresponsive particles act as a drag on the turbulent eddies, passing energy from the turbulent eddies to the small scale wakes of the particles where it is quickly dissipated by viscosity. The second mechanism is more complicated. Particles falling under gravity convert gravitational potential energy to turbulent velocity fluctuations. If the particles are large, this mechanism increases the overall turbulence level. However, with moderate size particles, the small scale turbulence generated apparently distorts the turbulent eddies leading to more rapid dissipation. Unfortunately, this conclusion is supported only by circumstantial evidence to date. The objectives of the experiment are to use microgravity to separate the two mechanisms. A region of nearly-isotropic decaying turbulence with zero mean flow will be formed in a box in the microgravity environment. Different sets of particles with Stokes numbers in the range of 2 to 20 will be dispersed in the flow. With zero gravity and no mean fluid velocity the particles will have zero mean velocity. With the large Stokes numbers, the fluctuating velocities will also be small. Therefore, the only attenuation mechanism will be the direct action of the particles on the turbulence. Control experiments will also be done in which the particles fall through the measurement volume. Measurements will be acquired using a high resolution image velocimetry (PIV) system being developed specifically for work in particle-laden flows. The measurements will include the decay of the turbulence kinetic energy under various particle loadings. The spatial spectra of the turbulence will also be measured. In a second set of experiments, the interaction of a single eddy with a collection of nearly stationary particles will be examined. The eddy will be a vortex ring emitted by a jet pulse through an orifice. The distortion of the vortex under the influence of the particles will be examined to gain a better understanding of how fine particles can cause such large reductions in turbulence levels. This experiment could not be conducted in terrestrial gravity because the high particle velocities would overwhelm the relatively low speed motion of the vortex ring. This experimental program is just getting underway. The initial challenge is to build a closed facility containing reasonably homogeneous and isotropic turbulence with zero mean velocity. Our approach is to use a set of synthetic jets mounted on the periphery of a transparent plexiglass box to create the turbulence. A synthetic jet is a plenum chamber with an orifice open to the volume of interest. The volume of the chamber fluctuates periodically so alternately a jet is ejected from the volume or flow is drawn back in as a sink. The asymmetry of this situation results in a net transport of momentum and kinetic energy into the volume of interest. The present apparatus includes eight synthetic jets each powered independently by a six inch loudspeaker. The synthetic jets discharge through ejector tubes to increase the scale of the turbulence. Construction of the apparatus is now complete and preliminary flow visualization studies have been conducted. The PIV system is also under development. A compact dual-pulse YAG laser has been acquired as the light source and special software is under development to allow simultaneous measurements of both the particle phase and the fluid phase (marked by fine tracers).

Paris, A. D.↗