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At least 127 records · Page 7

Comparison between design and installed acoustic characteristics of NASA Lewis 9- by 15-foot low-speed wind tunnel acoustic treatment

The test section of the NASA Lewis 9- by 15-Foot Low-Speed Wind Tunnel was acoustically treated to allow the measurement of sound under simulated free-field conditions. The treatment was designed for high sound absorption at frequencies above 250 Hz and for withstanding the environmental conditions in the test section. In order to achieve the design requirements, a fibrous, bulk-absorber material was packed into removable panel sections. Each section was divided into two equal-depth layers packed with material to different bulk densities. The lower density was next to the facing of the treatment. The facing consisted of a perforated plate and screening material layered together. Sample tests for normal-incidence acoustic absorption were also conducted in an impedance tube to provide data to aid in the treatment design. Tests with no airflow, involving the measurement of the absorptive properties of the treatment installed in the 9- by 15-foot wind tunnel test section, combined the use of time-delay spectrometry with a previously established free-field measurement method. This new application of time-delay spectrometry enabled these free-field measurements to be made in nonanechoic conditions. The results showed that the installed acoustic treatment had absorption coefficients greater than 0.95 over the frequency range 250 Hz to 4 kHz. The measurements in the wind tunnel were in good agreement with both the analytical prediction and the impedance tube test data.

Dahl, Milo D.↗

TPSAS-NF1676L-32577-DND

The ground testing of hypersonic vehicles requires the replication of the flow conditions at high speed and altitude. To produce these flow conditions, stored compressed air is expanded through a convergent-divergent nozzle to produce the required pressures and speed. However, the expansion process also cools the air, and so to match the flight temperatures, some form of heating needs to be employed. Vitiated heating is a common method, where the air is heated by burning fuel in the low speed side of the nozzle, and then oxygen is added to bring the level of O2 up to match that of standard air. The resulting flow no longer has the same composition as standard air, (except for the oxygen level), but rather contains combustion products, often referred to as vitiates as part of the mixture. The presence of these vitiates in the flow effects the wind tunnel test conditions. For example, the specific heat and molecular density are changed, the kinetics of combustion are altered and the flow features in the test article are altered. In this talk, the effects of the vitiates on the testing conditions and on the performance of test articles is described. Specific examples include the effects of molecular density on the flow, how combustion processes are altered by the presence of vitiates and how condensation of vitiates can alter the test conditions. In addition, the effect of the less common vitiates produced by arc-heated tunnels are mentioned, such as NO, non-thermal equilibrium and the presence of copper solids in the flow. Finally some thoughts on how large an effect these vitiates have on the test results are presented.

Andrew T Norris↗

Investigation of Unsteady Pressure-Sensitive Paint (uPSP) and a Dynamic Loads Balance to Predict Launch Vehicle Buffet Environments

This NESC assessment examined the accuracy of estimating buffet loads on in-line launch vehicles without booster attachments using sparse unsteady pressure measurements. The buffet loads computed using sparse sensor data were compared with estimates derived using measurements with much higher spatial resolution. The current method for estimating launch vehicle buffet loads is through wind tunnel testing of models with approximately 400 unsteady pressure transducers. Even with this relatively large number of sensors, the coverage can be insufficient to provide reliable integrated unsteady loads on vehicles. In general, sparse sensor spacing requires the use of coherence-length-based corrections in the azimuthal and axial directions to integrate the unsteady pressures and obtain reasonable estimates of the buffet loads. Coherence corrections have been used to estimate buffet loads for a variety of launch vehicles with the assumption methodology results in reasonably conservative loads. For the Space Launch System (SLS), the first estimates of buffet loads exceeded the limits of the vehicle structure, so additional tests with higher sensor density were conducted to better define the buffet loads and possibly avoid expensive modifications to the vehicle design. Without the additional tests and improvements to the coherence-length analysis methods, there would have been significant impacts to the vehicle weight, cost, and schedule. If the load estimates turn out to be too low, there is significant risk of structural failure of the vehicle. This assessment used a combination of unsteady pressure-sensitive paint (uPSP), unsteady pressure transducers, and a dynamic force and moment balance to investigate the integration schemes used with limited unsteady pressure data by comparing them with direct integration of extremely dense fluctuating pressure measurements. An outfall of the assessment was to evaluate the potential of using the emerging uPSP technique in a production test environment for future launch vehicles. The results show that modifications to the current technique can improve the accuracy of buffet estimates. More importantly, the uPSP worked remarkably well and, with improvements to the frequency response, sensitivity, and productivity, will provide an enhanced method for measuring wind tunnel buffet forcing functions (BFFs).

Schuster, David M.↗

SOFIA 2 model telescope wind tunnel test report

This document outlines the tests performed to make aerodynamic force and torque measurements on the SOFIA wind tunnel model telescope. These tests were performed during the SOFIA 2 wind tunnel test in the 14 ft wind tunnel during the months of June through August 1994. The test was designed to measure the dynamic cross elevation moment acting on the SOFIA model telescope due to aerodynamic loading. The measurements were taken with the telescope mounted in an open cavity in the tail section of the SOFIA model 747. The purpose of the test was to obtain an estimate of the full scale aerodynamic disturbance spectrum, by scaling up the wind tunnel results (taking into account differences in sail area, air density, cavity dimension, etc.). An estimate of the full scale cross elevation moment spectrum was needed to help determine the impact this disturbance would have on the telescope positioning system requirements. A model of the telescope structure, made of a light weight composite material, was mounted in the open cavity of the SOFIA wind tunnel model. This model was mounted via a force balance to the cavity bulkhead. Despite efforts to use a 'stiff' balance, and a lightweight model, the balance/telescope system had a very low resonant frequency (37 Hz) compared to the desired measurement bandwidth (1000 Hz). Due to this mechanical resonance of the balance/telescope system, the balance alone could not provide an accurate measure of applied aerodynamic force at the high frequencies desired. A method of measurement was developed that incorporated accelerometers in addition to the balance signal, to calculate the aerodynamic force.

Keas, Paul↗

Unsteady PSP in the NASA Transonic Dynamics Tunnel

For the first time, unsteady pressure sensitive paint (uPSP) has been applied in the NASA Langley Transonic Dynamics Tunnel. Obtaining global surface pressure measurements using the uPSP technique required the development of a new paint formulation for use in the low oxygen heavy gas atmosphere, as well as environmental enclosures to protect sensitive electro-optical components from the high temperature, low pressure environment present during tunnel operation. A high-speed datalink connecting the wind tunnel to Langley’s local high performance compute resource was also established for this test to enable near real time processing of the large datasets that were obtained throughout the campaign. A high-speed lifetime measurement technique was also utilized to yield steady state surface pressures at each condition using the same equipment that was used to provide unsteady measurements. Important metrics such as pressure time histories and power spectral density are compared against traditional unsteady pressure point measurements, and more advanced data products such as dynamic mode decomposition are also explored to provide insight into the underlying flow phenomena.

Daniel T. Reese↗

Velocities of windblown particles in saltation: Venus, Earth, and Mars

Particle velocities were determined in environmental wind tunnels capable of simulating aeolian processes on Earth, Mars, and Venus. Comparisons of results for Earth, Mars, and Venus reveal some remarkable differences. Most particles achieve speeds nearly equal to freestream wind speed on Venus, but seldom achieve half the wind speed on Mars; Earth cases are of intermediate values. This is attributed to the differences in atmospheric density and to the threshold wind speeds among the three planetary environments. Particles are more easily moved in the dense venusian atmosphere than on Mars; consequently, threshold speeds are very low, and for the range of wind speeds in which most movement is presumed to occur (just above threshold speeds), the grains need not be moving very fast to achieve 100% of the wind speed. Conversely, particles on Mars must accelerate very rapidly to achieve the speed of the high winds required for threshold, and despite the fact that saltation path lengths are long on Mars, most grains fall to the surface before achieving even 50 to 60% of freestream wind speed.

Greeley, R.↗

Burnett solutions along the stagnation line of a cooled cylinder in low-density hypersonic flows

The Burnett equations in the cylindrical coordinate system have been applied to the hypersonic flow over a cylinder in low density environments. Through a local similarity transformation, the Burnett equations are degenerated into nonlinear third-order ordinary differential equations which are only valid along the stagnation line. These equations are solved by the multi-staged Runge-Kutta integration technique. Steady state solutions are asymptotically reached by the time-marching procedure. A newly-developed computer code is used to solve both the Navier-Stokes and the Burnett equations within the shock layer. The computed heat transfer coefficients are consistent with wind-tunnel and STS flight data. Comparisons with the DSMC solutions and the Boltzmann solutions show that the Burnett equations are more appropriate as the governing equations than the Navier-Stokes equations in the transitional flow regime.

Liaw, G. S.↗

Shock-Wave/Boundary-Layer Interactions in Hypersonic Low Density Flows

Results of numerical simulations of Mach 10 air flow over a hollow cylinder-flare and a double-cone are presented where viscous effects are significant. The flow phenomena include shock-shock and shock- boundary-layer interactions with accompanying flow separation, recirculation, and reattachment. The purpose of this study is to promote an understanding of the fundamental gas dynamics resulting from such complex interactions and to clarify the requirements for meaningful simulations of such flows when using the direct simulation Monte Carlo (DSMC) method. Particular emphasis is placed on the sensitivity of computed results to grid resolution. Comparisons of the DSMC results for the hollow cylinder-flare (30 deg.) configuration are made with the results of experimental measurements conducted in the ONERA RSCh wind tunnel for heating, pressure, and the extent of separation. Agreement between computations and measurements for various quantities is good except that for pressure. For the same flow conditions, the double- cone geometry (25 deg.- 65 deg.) produces much stronger interactions, and these interactions are investigated numerically using both DSMC and Navier-Stokes codes. For the double-cone computations, a two orders of magnitude variation in free-stream density (with Reynolds numbers from 247 to 24,7 19) is investigated using both computational methods. For this range of flow conditions, the computational results are in qualitative agreement for the extent of separation with the DSMC method always predicting a smaller separation region. Results from the Navier-Stokes calculations suggest that the flow for the highest density double-cone case may be unsteady; however, the DSMC solution does not show evidence of unsteadiness.

Moss, James N.↗

Slow ions in plasma wind tunnels

One of the limitations of simulation experiments for the study of interaction between a satellite and its space environment is the background of slow ions in the plasma chamber. These ions appear to be created by charge exchange between the beam ions and residual neutral gas and may affect measurements of the current and potential in the wake. Results are presented for a plasma wind tunnel experiment to study the effect of slow ions on both the ion and electron current distribution and the electron temperature in the wake of a body in a streaming plasma. It is shown that the effect of slow ions for beam ion density not exceeding 3 is not significant for measurements of ion current variations in the wake zone. This is not the case when studies are aimed at the quantitative examination of electron current and temperature variations in the near wake zone. In these instances, the measurements of electron properties in the wake should be done at very low system pressures or over a range of system pressures in order to ascertain the influence of slow ions.

Oran, W. A.↗

Acoustic and aerodynamic performance investigation of inverted velocity profile coannular plug nozzles

The results of model scale parametric static and wind tunnel aerodynamic performance tests on unsuppressed coannular plug nozzle configurations with inverted velocity profile are discussed. The nozzle configurations are high-radius-ratio coannular plug nozzles applicable to dual-stream exhaust systems typical of a variable cycle engine for Advanced Supersonic Transport application. In all, seven acoustic models and eight aerodynamic performance models were tested. The nozzle geometric variables included outer stream radius ratio, inner stream to outer stream ratio, and inner stream plug shape. When compared to a conical nozzle at the same specific thrust, the results of the static acoustic tests with the coannular nozzles showed noise reductions of up to 7 PNdB. Extensive data analysis showed that the overall acoustic results can be well correlated using the mixed stream velocity and the mixed stream density. Results also showed that suppression levels are geometry and flow regulation dependent with the outer stream radius ratio, inner stream-to-outer stream velocity ratio and inner stream velocity ratio and inner stream plug shape, as the primary suppression parameters. In addition, high-radius ratio coannular plug nozzles were found to yield shock associated noise level reductions relative to a conical nozzle. The wind tunnel aerodynamic tests showed that static and simulated flight thrust coefficient at typical takeoff conditions are quite good - up to 0.98 at static conditions and 0.974 at a takeoff Mach number of 0.36. At low inner stream flow conditions significant thrust loss was observed. Using an inner stream conical plug resulted in 1% to 2% higher performance levels than nozzle geometries using a bent inner plug.

Knott, P. R.↗

Fuselage-drag tests in the variable-density wind tunnel: streamline bodies of revolution, fineness ratio of 5

Results are presented of the drag tests of six bodies of revolution with systematically varying shapes and with a fineness ratio of 5. The forms were derived from source-sink distributions, and formulas are presented for the calculation of the pressure distribution of the forms. The tests were made in the N.A.C.A. variable-density tunnel over a range of values of Reynolds number from about 1,500,000 to 25,000,000. The results show that the bodies with the sharper noses and tails have the lowest drag coefficients, even when the drag coefficients are based on the two-thirds power of the volume. The data shows the most important single characteristic of the body form to be the tail angle, which must be fine to obtain low drag.

Abbott, Ira H↗

Experimental evaluation of compliant surfaces at low speeds

An experimental study was devised to determine the profile drag on a subsonic wind tunnel model partially covered with various compliant surface materials. The model consisted of a large section of constant thickness bounded fore and aft by symmetric airfoil fairings. A flat rigid plate, the control surface, could be exchanged for four contiguous complaint panels. The flexible media generally consisted of thin polyvinylchloride membranes stretched to various tensions over trapped fluid cavities of air, water, or polyethelene oxide solution, or over dry or flooded open-celled polyurethane foams. On the basis of very accurate direct-force cell measurements, all configurations were found to yield profile drags equal to or slightly higher than that obtained for the conventional rigid surface case. The results indicate that the potential for practical drag-reducing applications will be limited to either high-density or high-speed flows where more sensible pressure perturbations occur.

Mcalister, K. W.↗

Turbulent Skin Friction at High Mach Numbers and Reynolds Numbers

For a number of years now, experimenters have been making measurements of skin friction. Formerly, the main interest was at low Mach numbers; later, measurements were made at supersonic Mach numbers. However, almost all of these measurements were over a limited range of Reynolds numbers. On the other hand, these measurements fairly well determined the effects of Mach number and heat transfer on skin friction. The purpose of this paper is to give the results of skin-friction measurements in turbulent boundary layers at high Mach numbers and high Reynolds numbers where data have not previously existed. The equipment used was expressly designed to provide these conditions. As is well known, it is difficult to obtain high Mach numbers and high Reynolds numbers simultaneously with air in a wind tunnel. In order to avoid condensation, it is necessary to heat the air, with a resulting loss in density and Reynolds number. It is desirable, then, to use a gas that does not condense at high Mach numbers. This suggested helium, which was used as a working fluid in some of the tests. At high Mach numbers in a given wind tunnel, higher Reynolds numbers can be obtained with helium than with air, principally because no heating of the helium is required. The different ratios of specific heats also contribute to the increase. In using helium as a working fluid, it is, of course, necessary to determine the equivalence of air and helium in the turbulent boundary layer.

Matting, Fred W.↗

Environmental dynamics at orbital altitudes

The influence of real satellite aerodynamics on the determination of upper atmospheric density was investigated. A method of analysis of satellite drag data is presented which includes the effect of satellite lift and the variation in aerodynamic properties around the orbit. The studies indicate that satellite lift may be responsible for the observed orbit precession rather than a super rotation of the upper atmosphere. The influence of simplifying assumptions concerning the aerodynamics of objects in falling sphere analysis were evaluated and an improved method of analysis was developed. Wind tunnel data was used to develop more accurate drag coefficient relationships for studying altitudes between 80 and 120 Km. The improved drag coefficient relationships revealed a considerable error in previous falling sphere drag interpretation. These data were reanalyzed using the more accurate relationships. Theoretical investigations of the drag coefficient in the very low speed ratio region were also conducted.

Karr, G. R.↗

Large Solar-Rejection Filter

NASA utilized Image Intensified Video Cameras for ATV data acquisition from a jet flying at 12.8 km. Afterwards the video was digitized and then analyzed with a modified commercial software package, Image Systems Trackeye. Astrometric results were limited by saturation, plate scale, and imposed linear plate solution based on field reference stars. Time-dependent fragment angular trajectories, velocities, accelerations, and luminosities were derived in each video segment. It was evident that individual fragments behave differently. Photometric accuracy was insufficient to confidently assess correlations between luminosity and fragment spatial behavior (velocity, deceleration). Use of high resolution digital video cameras in future should remedy this shortcoming. A scenically accurate description of matter interpreted as a substance made up of corpuscular constituents was established during the course of the 19th century. In this description, atoms--the building blocks of the matter--form molecules. The properties of the molecules were described by chemistry or thermodynamics depending on what characteristics of the matter were investigated. In both theories, the molecules can dissociate to atoms when the kinetic energies of the atoms exceed the strength of the chemical bonds. The number of atoms is always preserved in a closed system. This is not true, however, when the matter takes up much higher energies at relativistic scales. New particles can be produced at the expense of the kinetic energy. The number of particles is no longer preserved. There are other conserved quantities, however, these quantities, the charge, baryon number, lepton number, are associated with particles that are considered elementary today. The properties and behavior of these elementary particles is the subject of Particle Physics or High Energy Physics. Practice Page: A crewmember touching a positively charged surface was thought to be galvanically isolated from the vehicle ground analogous to a bird on a high voltage power wire. Recent analysis confirms that positive floating potentials, ionospheric currents to the EVA suit, can be hazardous. The analysis is wrong in that the ionospheric plasma itself can close the circuit. Parametric analysis of very low voltage exposures (2 to 15 volts) could cause pain and/or involuntary muscle tetani or spinal cord shock. NASA worked with the Naval Health Research Center Detachment Directed Energy Bioeffects Laboratory to examine the affects electrical hazards could have on extravehicular activity using two models. The results of the two computational models were combined to predict areas of the body in which neurons of different diameters would be excited. They predicted that physiologically active current could be conducted across the crew member causing catastrophic hazards. Future work to analyze additional current paths was proposed. The FUSE spectrum of BB Dor, observed in a high state, is modeled with an accretion disk with a very low inclination (possibly lower than 10 degrees). Assuming an average WD mass of 0.8 solar mass leads to a distance of the order of approximately 650pc, consistent with the extremely low galactic reddening in its direction, and a mass accretion rate of 10 (exp -9) solar mass a year. The spectrum presents some broad and deep silicon and sulfur absorption lines, indicating that these elements are over-abundant: silicon is 3 times solar, and sulfur is 20 times solar. The FUSE spectrum of BB Dor, observed in a high state, is modeled with an accretion disk with a very low inclination (possibly lower than 10 degrees). Assuming an average WD mass of 0.8 solar mass leads to a distance of the order of approximately 650pc, consistent with the extremely low galactic reddening in its direction, and a mass accretion rate of 10 (exp -9) solar mass a year. The spectrum presents some broad and deep silicon and sulfur absorption lines, indicating that these elements are over-abundant: silicon is times solar, and sulfur is 20 times solar. From its previously observed optical emission lines, P831-57 (WD 0334 6400 or Ret 1 in A Catalog and Atlas of Cataclysmic Variables: Living Edition) has been suspected to contain an accretion disk associated with a companion star in orbit around a subdwarf star with a temperature T is greater than 21,000K. P831-57 has therefore been classified as a nova-like. However, our present observations show it to be a DA + dMe binary. The analysis of its Far Ultraviolet Spectroscopic Explorer (FUSE) spectrum (continuum and lines) reveal an average mass white dwarf (Log(g) approximately equals 7.8 plus or minus 0.1)with a temperature T approximately equals 37,000 plus or minus 500K, an extremely low projected rotational velocity, and a distance of about 115 plus or minus 5pc. The photosphere contains C, N, Si, and S (at about 1% of solar abundances). The dMe star is seen as a flux excess in near-infrared photometry and appears to show occasional flaring of about one magnitude as seen in the Harvard plates. There is no evidence of periodic variability in the spectroscopic or photometric data. We find no evidence of a an accretion disk, instead we find evidence of wind accretion as the stellar carbon abundance (N(C)/N(H) = 2.5 x 10 (exp -6) is about ten times larger than predicted by radiative levitation for such a gravity and temperature. The power needs and solutions for the space exploration and lunar mobility program are discussed. Long term missions in space and on the lunar surface require high energy batteries. Rechargeable batteries for mobility systems and portable utility pallet are needed for successful exploration missions. Nanomaterial usage increases the energy density of the cells apart from increasing the power density. The symptoms and threats from acute mountain sickness (AMS) are discussed. The underlying assumptions concerning spacecraft atmosphere mean there is a potential risk to astronauts. The baseline worst case scenario is about 25% based on direct ascent to 8.0 psia with 32% O2. The practical mitigation approach is a staged depressurization scheme. Due to the uncertainty about potential AMS risk the flight surgeon should prepare, focused research should proceed, and current analytical efforts should continue. This slide presentation reviews the threat astronauts face from acute mountain sickness (AMS). The incidence of AMS is highly variable and the risk to astronauts is unclear. However, the potential risk is higher than current EAAs suggest and precautions should be implemented. Due to the uncertain nature of the risk flight surgeons should prepare, and focused research should proceed. Quasiparticle tunneling can be understood at low temperatures using a non-equilibrium kinetic theory. Low-temperature tunneling can be suppressed using existing techniques: island-lead gap engineering, lead cooling with SIN junctions, and quasiparticle traps. The slide presentation reviews the science goals and mission planning for the proposed Jupiter System Observer (JSO). The spacecraft would accommodate 9 instruments making the instrument payload more capable than any previously flown to Jupiter. The would-be mission includes study programs for Jupiter's satellites, interior, magnetosphere and atmosphere. The power needs and solutions for the space exploration and lunar mobility program are discussed. Long term missions in space and on the lunar surface require high energy batteries. Rechargeable batteries for mobility systems and portable utility pallet are needed for successful exploration missions. Nanomaterial usage increases the energy density of the cells apart from increasing the power density. This slide presentation reviews the power requirements for the space exploration and the lunar surface mobility programs. It includes information about the specifications for high energy batteries and the power requirements for lunar rovers,

Roberts, William↗

Assessment of Buffet Forcing Function Development Process Using Unsteady Pressure Sensitive Paint

A wind tunnel test was conducted at the Ames Unitary Plan Wind Tunnel to characterize the transonic buffet environment of a generic launch vehicle forebody. The test examined a highly instrumented version of the Coe and Nute Model 11 test article first tested in the 1960s. One of the measurement techniques used during this test was unsteady pressure sensitive paint (uPSP) developed at the Arnold Engineering Development Complex. This optical measurement technique measured fluctuating pressures at over 300,000 locations on the surface of the model. The high spatial density of these measurements provided an opportunity to examine in depth the assumptions underpinning the development of buffet forcing functions (BFFs) used in the development of the Space Launch System vehicle. The comparison of discrete-measurement-based BFFs to BFFs developed by continuous surface pressure integration indicates that the current BFF development approach under predicts low frequency content of the BFFs while over predicting high frequency content. Coherence-based adjustments employed to reduce over prediction in the surface integration of discrete pressure measurements contribute to the inaccuracy of the BFFs and their implementation should be reevaluated.

Sekula, Martin K.↗

Response of aerospace structures to reentry aerodynamic excitation

A bibliography on aerodynamic excitation and associated structural response is presented. Very little applicable data under actual reentry conditions was found, but many wind tunnel tests and some in-flight data were. Aerodynamic excitation and proposed space shuttle configurations and reentry trajectories were studied. Attached turbulent boundary layer, separated turbulent boundary layer, and base pressure fluctuations are the region of aerodynamic excitation most applicable to exterior panels of space shuttle-type vehicles; prediction techniques are presented for these environments. Methods for predicting the response of panel structures to acoustic excitation were investigated. A normal mode approach was developed for the low frequency response and a statistical energy approach was utilized for the high frequency response. A finite element model was made of a thermal protective system test panel. Computer programs were used to determine the natural frequencies and mode shapes of the panel and to calculate the response of the panel to a reverberant acoustic field. Power spectral densities of response displacement and acceleration are presented.

Carlin, D., Jr.↗

Microspheres for laser velocimetry in high temperature wind tunnel

The introduction of non-intrusive measurement techniques in wind tunnel experimentation has been a turning point in error free data acquisition. Laser velocimetry has been progressively implemented and utilized in various wind tunnels; e.g. subsonic, transonic, and supersonic. The success of the laser velocimeter technique is based on an accurate measurement of scattered light by seeding particles introduced into the flow stream in the wind tunnel. Therefore, application of appropriate seeding particles will affect, to a large extent the acquired data. The seeding material used depends on the type of experiment being run. Among the seeding material for subsonic tunnel are kerosene, Kaolin, and polystyrene. Polystyrene is known to be the best because of being solid particles, having high index of refraction, capable of being made both spherical and monodisperse. However for high temperature wind tunnel testing seeding material must have an additional characteristic that is high melting point. Typically metal oxide powders such as Al2O3 with melting point 3660 F are used. The metal oxides are, however polydispersed, have a high density, and a tendency to form large agglomerate that does not closely follow the flow velocity. The addition of flame phase silica to metal oxide helps to break up the agglomerates, yet still results in a narrow band of polydispersed seeding. The less desirable utility of metal oxide in high temperature wind tunnels necessitates the search for a better alternative particle seeding which this paper addresses. The Laser Velocimetry (LV) characteristic of polystyrene makes it a prime candidate as a base material in achieving the high temperature particle seeding inexpensively. While polystyrene monodisperse seeding particle reported has been successful in a subsonic wind tunnel, it lacks the high melting point and thus is not practically usable in a high temperature wind tunnel. It is well known that rise in melting point of polystyrene can be achieved by a cross-linking technique. Since polystyrene already possesses all the desired characteristics for LV, to circumvent the low melting point, a cross-linking technique was investigated.

Ghorieshi, Anthony↗