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Sarohia, V.

Publications and source records attributed to Sarohia, V..

At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1983

Atomization and combustion performance of antimisting kerosene and jet fuel

Combustion performance of antimisting kerosene (AMK) containing FM-9 polymer was investigated at various levels of degradation (restoration of AMK for normal use in a gas turbine engine). To establish the relationship of degradation and atomization to performance in an aircraft gas turbine combustor, sprays formed by the nozzle of a JT8-D combustor with Jet A and AMK at 1 atmosphere (atm) (14.1 lb/square in absolute) pressure and 22 C at several degradation levels were analyzed. A new spray characterization technique based on digital image analysis of high resolution, wide field spray images formed under pulsed ruby laser sheet illumination was developed. Combustion tests were performed for these fuels in a JT8-D single can combustor facility to measure combustion efficiency and the lean extinction limit. Correlation of combustion performance under simulated engine operating conditions with nozzle spray Sauter mean diameter (SMD) measured at 1 atm and 22 C were observed. Fuel spray SMD and hence the combustion efficiency are strongly influenced by fuel degradation level. Use of even the most highly degraded AMK tested (filter ratio = 1.2) resulted in an increase in fuel consumption of 0.08% to 0.20% at engine cruise conditions.

Fleeter, R.↗
NASA NTRS1983

Antimisting fuel breakup and flammability

The breakup behavior and flammability of antimisting turbine fuels subjected to aerodynamic shear are investigated. Fuels tested were Jet A containing 0.3% FM-9 polymer at various levels of degradation ranging from virgin AMK to neat Jet A. The misting behavior of the fuels was quantified by droplet size distribution measurements. A technique based on high resolution laser photography and digital image processing of photographic records for rapid determination of droplet size distribution was developed. The flammability of flowing droplet-air mixtures was quantified by direct measurements of temperature rise in a flame established in the wake of a continuous ignition source. The temperature rise measurements were correlated with droplet size measurements. The flame anchoring phenomenon associated with the breakup of a liquid fuel in the wake of bluff body was shown to be important in the context of a survivable crash scenario. A pass/fail criterion for flammability testing of antimisting fuels, based on this flame-anchoring phenomenon, was proposed. The role of various ignition sources and their intensity in ignition and post-ignition behavior of antimisting fuels was also investigated.

Parikh, P.↗
NASA NTRS1983

Influence of liquid water and water vapor on antimisting kerosene (AMK)

Experiments have been performed to evaluate the compatibility of liquid water and water vapor with antimisting kerosenes (AMK) containing polymer additive FM-9 developed by Imperial Chemical Industries. This effort consists of the determination of water solubility in AMK, influence of water on restoration (degradation) of AMK, and effect of water on standard AMK quality control methods. The principal conclusions of this investigation are: (1) the uptake of water in AMK critically depends upon the degree of agitation and can be as high as 1300 ppm at 20 C, (2) more than 250 to 300 ppm of water in AMK causes an insoluble second phase to form. The amount of this second phase depends on fuel temperature, agitation, degree of restoration (degradation) and the water content of the fuel, (3) laboratory scale experiments indicate precipitate formation when water vapor comes in contact with cold fuel surfaces at a much lower level of water (125 to 150 ppm), (4) precipitate formation is very pronounced in these experiments where humid air is percolated through a cold fuel (-20 C), (5) laboratory tests further indicate that water droplet settling time is markedly reduced in AMK as compared to jet A, (6) limited low temperature testing down to -30 C under laboratory conditions indicates the formation of stable, transparent gels.

Yavrouian, A. H.↗
NASA NTRS1983

Entrainment and mixing in thrust augmenting ejectors

An experimental investigation of two-dimensional thrust augmenting ejector flows has been conducted. Measurements of the shroud surface pressure distribution, mean velocity, turbulent intensities and Reynolds stresses were made in two shroud geometries at various primary nozzle pressure ratios. The effects of shroud geometry and primary nozzle pressure ratio on the shroud surface pressure distribution, mean flow field and turbulent field were determined. From these measurements the evolution of mixing within the shroud of the primary flow and entrained fluid was obtained. The relationship between the mean flow field, the turbulent field and the shroud surface pressure distribution is discussed.

Bernal, L.↗
NASA NTRS1982

Application of digital image analysis techniques to antimisting fuel spray characterization

Pulsed ruby laser sheet illumination of the spray is used for the initial recording of data on very-high-resolution photographic film. The digitization of mosaic elements is effected with a vidicon and video digitizer whose output is stored in computer RAM memory for processing. Highly nonspherical elements and a broad range of drop diameters (8-2000 microns) resulting from the unusual rheological properties of the fuel-additive system are accommodated by the device configuration and algorithms. It is found that the generation of two-dimensional images by means of scattered light also eliminates errors resulting from variations in the index of refraction and from the submicron scattering sites that are often present within the modified fuel. No a priori information on the drop size distribution or on the system response to various drop sizes is required.

Fleeter, R.↗
NASA NTRS1982

Antimisting kerosene atomization and flammability

Various parameters found to affect the flammability of antimisting kerosene (Jet A + polymer additive) are investigated. Digital image processing was integrated into a technique for measurement of fuel spray characteristics. This technique was developed to avoid many of the error sources inherent to other spray assessment techniques and was applied to the study of engine fuel nozzle atomization performance with Jet A and antimisting fuel. Aircraft accident fuel spill and ignition dynamics were modeled in a steady state simulator allowing flammability to be measured as a function of airspeed, fuel flow rate, fuel jet Reynolds number and polymer concentration. The digital imaging technique was employed to measure spray characteristics in this simulation and these results were related to flammability test results. Scaling relationships were investigated through correlation of experimental results with characteristic dimensions spanning more than two orders of magnitude.

Fleeter, R.↗
NASA NTRS1981

Experimental and analytical investigation of a fluidic power generator

A combined experimental and analytical investigation was performed to understand the various fluid processes associated with the conversion of flow energy into electric power in a fluidic generator. Experiments were performed under flight-simulated laboratory conditions and results were compared with those obtained in the free-flight conditions. It is concluded that the mean mass flow critically controlled the output of the fluidic generator. Cross-correlation of the outputs of transducer data indicate the presence of a standing wave in the tube; the mechanism of oscillation is an acoustic resonance tube phenomenon. A linearized model was constructed coupling the flow behavior of the jet, the jet-layer, the tube, the cavity, and the holes of the fluidic generator. The analytical results also show that the mode of the fluidic power generator is an acoustical resonance phenomenon with the frequency of operation given by f approx = a/4L, where f is the frequency of jet swallowing, a is the average speed of sound in the tube, and L is the length of the tube. Analytical results further indicated that oscillations in the fluidic generator are always damped and consequently there is a forcing of the system in operation.

Sarohia, V.↗
NASA NTRS1981

Flight effects on supersonic convergent-divergent nozzle jet noise

The influence of forward flight on the noise generation from convergent-divergent (C-D) nozzle flows was determined experimentally. The experiments were performed in an anechoic chamber using a 2.03 cm diameter C-D nozzle with a design Mach number of 1.4 in a 25 cm diameter free jet flow. Far-field noise measurements and spectral analyses were carried out and visualization of the jet shock structure was made by a spark shadowgraph technique. Jet noise from supersonic C-D nozzle flows under forward flight was found to depend critically on the flight velocity and nozzle pressure ratio. Noise reduction up to 20 dB was observed in the rearward quadrant under flight; excess noise in the forward quadrant under flight resulted from relatively high frequency noise sources in the jet flow field. Screech tones, observed from overexpanded C-D nozzle flows, were suppressed during the simulated flight flow.

Wat, J.↗
NASA NTRS1981

Noise radiated from inverted velocity profile jets under simulated flight

Measurements were made of the noise radiated by an inverted profile coannular jet. The measurements were made inside an anechoic chamber and forward flight was simulated with an open jet surrounding a coannular nozzle. The diameters of the center and the annular nozzles were 1.27 cm and 2.03 cm, respectively. The open jet wind tunnel was 17.1 cm in diameter and could be operated at speeds up to 150 m/sec. Noise measurements were made in the acoustic far field at several spherical angles ranging from 20 deg to 120 deg relative to the jet axis. Flow through the center jet decreased the noise radiated by the annular jet. The addition of forward velocity further decreased the noise, and the two noise reductions seem to be additive. Measurements of the mean velocity profile demonstrate that forward flight reduced the growth rate of the high speed annular jet, and that center flow reduced the rate of merging of the annular jet.

Petersen, R. A.↗
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.↗
NASA NTRS1981

Fundamental studies of antimisting fuels

Research is currently being undertaken to determine the various physical characteristics of antimisting fuel. It is an endeavor to prevent post-crash fuel mist fires. The following studies were done: (1) drop and jet breakup studies using an image processing technique, (2) flammability of fuel mist under simulated plane crash conditions; (3) skin friction measurements; (4) determination of the tensile viscosity of non-Newtonian antimisting fuel as a function of the extensional rate; and (5) water compatibility measurements. The results indicate that the mechanism which prevents antimisting fuel breakup is related to the time-dependent tensile viscosity of antimisting fuel under stress. Drag reduction phenomenon was also observed at Reynolds numbers higher than 20,000. Uptake of water by the antimisting fuel is higher than that for the neat fuel. In addition, its rate of absorption depends on the concurrent degree of agitation.

Sarohia, V.↗
NASA NTRS1980

Influence of antimisting polymer on aviation fuel breakup

Experiments have been performed to determine the influence of a moving airstream on jet and drop breakup of fuel containing small concentrations of antimisting polymers. This study was motivated by the needs to inhibit the ignition of fuel during a survivable aircraft crash landing. High speed motion pictures of initial deformation rates and instant pictures of initial deformation rates and instant pictures of the drop breakup suggest that the enormous resistance to the sudden deformation of fuel containing antimisting polymer is related to the development of high tensile viscosity, even though the shear viscosity is not markedly affected. Study of a pendant drop fiber was undertaken to determine this tensile viscosity of antimisting fuel as a function of temperature and of polymer concentration.

Sarohia, V.↗
NASA NTRS1979

Experimental investigation of flow and heating in a resonance tube

Experiments have been performed to determine the basic mechanism of heating in resonance tubes of square section with constant area excited by underexpanded jet flows. The jet flow between the nozzle exit and the tube inlet plays a key role in the performance of a resonance tube. A detailed and systematic investigation of the unsteady complex shock structure in this part of the flow region has led to a better understanding of the fundamental mechanisms associated with the gas heating in such tubes. A study of the effects of tube location in relation to free-jet shock location (without the presence of the resonance tube) has shed further light on the underlying mechanism of sustained oscillations of the flow in a resonance tube.

Sarohia, V.↗
NASA NTRS1979

Large-scale turbulent structures in jets and in flows over cavities and their relationship to entrainment and mixing

Large scale structures in jets and in flows over cavities were investigated experimentally to determine their role in entrainment, mixing, and noise production. The presence of these structures resulted in growth of the shear layer and entrainment. Merging of adjacent large scale structures caused the near field pressure signal in excited flows. It is believed that both the entrained fluid as well as its eventual mixing with the jet flow can be controlled by introducing pulsation in the jet flow at a frequency for which the flow is most unstable.

Sarohia, V.↗
NASA NTRS1979

Flight effects on subsonic jet noise

Experimental results obtained by a combination of fluid mechanics and radiated noise measurements associated with subsonic jets over a range of simulated flight speeds between 25 m/s and 110 m/s indicate that noise reduction in flight is predominantly a result of the reduced noise producing volume. These results do not support the generally accepted notion that noise reduction from jets in motion results primarily from the reduced strength of the noise producing eddies. These eddies, in flight, have previously been assumed to scale with the relative velocity V(J)-Vo where V(J) is the mean nozzle exit velocity and Vo is the flight velocity.

Sarohia, V.↗
NASA NTRS1979

Effect of density on noise radiation from subsonic inverted velocity profile jets

In this study, experiments were performed to investigate the influence of jet density in the generation of noise from inverted velocity profile subsonic jets. Such jets consist of low-speed gas flow in the center and a higher-speed annular flow. A combination of helium, nitrogen, and argon gases at various flow velocities were expanded through center and through annular convergent nozzles to obtain the desired density effects. Shadowgraphs of the jet flow were obtained, and mean velocity profiles and radiated noise were measured. The results clearly show that a difference in density between the inner and outer flows is an important factor in the development of the jet flow and in the production of jet noise.

Sarohia, V.↗
NASA NTRS1979

Excess noise from supersonic underexpanded jets in flight. I

A combination of flow visualization and measurement of both the near and far-field radiated noise of supersonic underexpanded jets under simulated flight conditions has led to the identification of a mechanism of excess jet noise production. It was observed that large lateral oscillations were imparted to the entire jet by the complex interaction of the outer flow with the jet. These jet oscillations appeared to develop almost abruptly into large oscillations becoming fully developed at about 6 to 10 diameters downstream of the nozzle exit at a location where the jet became subsonic. This lateral jet motion was observed to be planar and was accompanied by the production of weak shock waves. These weak shock waves existed in 'localized' circumferential regions outside the jet, e.g., quadrants or portions thereof and traveled upstream. It was determined that the measured excess noise was produced by these weak shock waves. Neither the jet oscillations nor the excess noise existed when there was no outer flow around the supersonic underexpanded jet.

Sarohia, V.↗