A new, molecular Rayleigh-scattering-based flow diagnostic developed at the NASA Glenn Research Center has been used for the first time to measure the power spectrum of both gas density and radial velocity components in the plumes of... more
A new, molecular Rayleigh-scattering-based flow diagnostic developed at the NASA Glenn Research Center has been used for the first time to measure the power spectrum of both gas density and radial velocity components in the plumes of high-speed jets. The objective of the work is to develop an unseeded, nonintrusive dynamic measurement technique for studying turbulent flows in NASA test facilities. This technique provides aerothermodynamic data not previously obtainable. It is particularly important for supersonic flows, where hot wire and pitot probes are difficult to use and disturb the flow under study. The effort is part of the nonintrusive instrumentation development program supporting propulsion research at the NASA Glenn Research Center. In particular, this work is measuring fluctuations in flow velocity, density, and temperature for jet noise studies. These data are valuable to researchers studying the correlation of flow fluctuations with far-field noise. One of the main obj...
Research Interests:
Research Interests:
Scattering of coherent light as it propagates parallel to a shock wave, formed in front of a bluff cylindrical body placed in a supersonic stream, is studied experimentally and numerically. Two incident optical fields are considered.... more
Scattering of coherent light as it propagates parallel to a shock wave, formed in front of a bluff cylindrical body placed in a supersonic stream, is studied experimentally and numerically. Two incident optical fields are considered. First, a large diameter collimated beam is allowed to pass through the shock containing flow. The light intensity distribution in the resultant shadowgraph image, measured by a low light CCD camera, shows well-defined fringes upstream and downstream of the shadow cast by the shock. In the second situation, a narrow laser beam is brought to a grazing incidence on the shock and the scattered light, which appears as a diverging sheet from the point of interaction, is visualized and measured on a screen placed normal to the laser path. Experiments are conducted on shocks formed at various free-stream Mach numbers, M, and total pressures, P0. It is found that the widths of the shock shadows in a shadowgraph image become independent of M and P0 when plotted a...
Research Interests:
Research Interests:
Research Interests:
Many supersonic military aircraft and some of the modern civilian aircraft (such as the Boeing 777) produce shock-associated noise. This noise is generated from the jet engine plume when the engine nozzle is operated beyond the subsonic... more
Many supersonic military aircraft and some of the modern civilian aircraft (such as the Boeing 777) produce shock-associated noise. This noise is generated from the jet engine plume when the engine nozzle is operated beyond the subsonic operation limit to gain additional thrust. At these underexpanded conditions, a series of shock waves appear in the plume. The turbulent vortices present in the jet interact with the shock waves and produce the additional shock-associated noise. Screech belongs to this noise category, where sound is generated in single or multiple pure tones. The high dynamic load associated with screech can damage the tailplane. One purpose of this study at the NASA Glenn Research Center at Lewis Field was to provide an accurate data base for validating various computational fluid dynamics (CFD) codes. These codes will be used to predict the frequency and amplitude of screech tones. A second purpose was to advance the fundamental physical understanding of how shock-...
Research Interests:
Typically, a limited number of dynamic pressure sensors is employed to determine the unsteady aerodynamic forces on large, slender aerospace structures. This paper describes a robust calculation pr...
Research Interests:
A numerical investigation of unsteady transitional flow over an oscillating NACA 0012 airfoil at a Reynolds number of 44,000 and reduced frequency of 0.2 is carried out and the results are compared with experimental data. The... more
A numerical investigation of unsteady transitional flow over an oscillating NACA 0012 airfoil at a Reynolds number of 44,000 and reduced frequency of 0.2 is carried out and the results are compared with experimental data. The Navier-Stokes equations defined on arbitrary Lagrangian-Eulerian coordinates are solved by a time-accurate finite volume method that incorporates an incremental pressure equation for the conservation of mass. The transitional turbulence field is described by multiple-time-scale turbulence equations. The numerical method successfully predicts the large dynamic stall vortex (DSV) and the trailing edge vortex (TEV) that are periodically generated by the oscillating airfoil. The numerical results show that the transition from laminar to turbulent state and relaminarization occur widely in time and in space. The calculated streaklines and the ensemble-averaged velocity profiles are in good agreement with the measured data.
Research Interests: Engineering, Physics, Mechanics, Turbulence, Oscillations, and 4 moreLaminar Flow, Vortex, Airfoil, and Naca Airfoil
Research Interests:
Recent advancements in a molecular Rayleigh scattering based diagnostic technique allowed for simultaneous measurement of velocity and density fluctuations with high sampling rates. The technique was used to investigate unheated high... more
Recent advancements in a molecular Rayleigh scattering based diagnostic technique allowed for simultaneous measurement of velocity and density fluctuations with high sampling rates. The technique was used to investigate unheated high subsonic and supersonic fully expanded free jets in the Mach number range from 0.8 to 1.8. The difference between the Favre-averaged and the Reynolds-averaged axial velocity and axial component of the turbulent kinetic energy is found to be small. On average, estimates based on Morkovin’s strong Reynolds analogy are found to underpredict turbulent density fluctuations.
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Unsteady aerodynamic forces on large, slender aerospace structures are established in wind-tunnel tests that employ a limited number of dynamic pressure sensors and use a correlation-based approach...
Research Interests:
A detailed survey of pressure fluctuations was conducted on a replica of the generic, “hammerhead” shaped space vehicle tested more than half century ago by Coe and Nute (1962). A large number of current and past space vehicles follow... more
A detailed survey of pressure fluctuations was conducted on a replica of the generic, “hammerhead” shaped space vehicle tested more than half century ago by Coe and Nute (1962). A large number of current and past space vehicles follow this general hammerhead configuration. The present test was conducted in the 11-by-11 ft Transonic Wind Tunnel of NASA Ames Research Center over the critical transonic Mach number range of 0.6 ≤ M ≤ 1.2 where typical vehicles encounter very high levels of surface pressure fluctuations during ascent through the atmosphere. Out of the many different types of instrumentations used for this test, data from the dynamic pressure sensors are presented in this paper. In addition, shadowgraph flow visualizations, and a qualitative measure of turbulent fluctuations, estimated from high-speed photography, are also presented. The data set provided a clear insight into the local high level of fluctuations from the formation of the transonic shocks on the payload fa...
Research Interests: Physics and Aeroacoustics
Time histories of pressure fluctuations on a generic, “hammerhead” launch vehicle model were measured using unsteady pressure-sensitive paint over a Mach number range of 0.6≤M≤1.2. The calibration ...
Research Interests:
A 70 microphone, 10×10 ft, microphone phased array was built for use in the harsh environment of rocket launches. The array was set up at NASA Wallops launch pad 0A during a static-test firing of Orbital Sciences’ Antares engines and... more
A 70 microphone, 10×10 ft, microphone phased array was built for use in the harsh environment of rocket launches. The array was set up at NASA Wallops launch pad 0A during a static-test firing of Orbital Sciences’ Antares engines and again during the first launch of the Antares vehicle. It was placed 400 ft away from the pad and was hoisted on a scissor lift 40 ft above ground. The data sets provided unprecedented insight into rocket noise sources. The duct exit was found to be the primary source during the static-test firing; the large amount of water injected beneath the nozzle exit and inside the plume duct quenched all other sources. The maps of the noise sources during launch were found to be time dependent. As the engines came to full power and became louder, the primary source switched from the duct inlet to the duct exit. Further elevation of the vehicle caused spilling of the hot plume, resulting in a distributed noise map covering most of the pad. As the entire plume emerged from the duct, and ...
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
ABSTRACT
Research Interests:
The primary objective of this investigation is to determine experimentally the sources of jet mixing noise. In the present study, four different approaches are used. It is reasonable to assume that the characteristics of the noise sources... more
The primary objective of this investigation is to determine experimentally the sources of jet mixing noise. In the present study, four different approaches are used. It is reasonable to assume that the characteristics of the noise sources are imprinted on their radiation fields. Under this assumption, it becomes possible to analyse the characteristics of the far-field sound and then infer back to the characteristics of the sources. The first approach is to make use of the spectral and directional information measured by a single microphone in the far field. A detailed analysis of a large collection of far-field noise data has been carried out. The purpose is to identify special characteristics that can be linked directly to those of the sources. The second approach is to measure the coherence of the sound field using two microphones. The autocorrelations and cross-correlations of these measurements offer not only valuable information on the spatial structure of the noise field in th...
Research Interests:
The flow field of an airfoil oscillated periodically over a reduced frequency range, 0 ≤ k ≤ 1.6, is studied experimentally at chord Reynolds numbers of Rc = 22000 and 44000. For most of the data, the NACA0012 airfoil is pitched... more
The flow field of an airfoil oscillated periodically over a reduced frequency range, 0 ≤ k ≤ 1.6, is studied experimentally at chord Reynolds numbers of Rc = 22000 and 44000. For most of the data, the NACA0012 airfoil is pitched sinusoidally about one quarter chord between angles of attack α of 5° and 25°. The cyclic variation of the near wake flow field is documented through flow visualization and phase-averaged vorticity measurements. In addition to the familiar dynamic stall vortex (DSV), an intense vortex of opposite sign is observed to originate from the trailing edge just when the DSV is shed. The two together take the shape of the cross-section of a large ‘mushroom’ while being convected away from the airfoil. The phase delay in the shedding of the DSV with increasing k, as observed by previous researchers, is documented for the full range of k. It is observed that the sum of the absolute values of all vorticity convected into the wake over a cycle is nearly constant and is i...
Research Interests:
Low-frequency noise sources in heated single-stream jets were identified by cross-correlating turbulent density fluctuations ρ′ with the far-field sound pressure fluctuations p′. The turbulent density fluctuations were measured by a... more
Low-frequency noise sources in heated single-stream jets were identified by cross-correlating turbulent density fluctuations ρ′ with the far-field sound pressure fluctuations p′. The turbulent density fluctuations were measured by a molecular Rayleigh-scattering technique. For a fixed jet velocity Uj, the normalized correlation coefficient 〈ρ′; p′〉/(ρ′rmsp′rms is found to increase progressively with an increase in the plume temperature (subscript rms stands for root-mean-square). The result indicates an improvement of the noise radiation efficiency with heating. Directly measured noise spectra from fixed velocity jets with increasing temperature ratio show confusing trends. However, if such spectra are normalized by theplume density, then a consistent trend of increasing noise level with increased plume temperature emerges. The increased noise is the most prominent at the low-frequency end, consistent with the correlation data. The effect of increasing jet velocity keeping the plume...
Research Interests:
The air density fluctuations in the plumes of fully expanded, unheated free jets were investigated experimentally using a Rayleigh-scattering-based technique. The point measuring technique used a continuous-wave laser, fibre-optic... more
The air density fluctuations in the plumes of fully expanded, unheated free jets were investigated experimentally using a Rayleigh-scattering-based technique. The point measuring technique used a continuous-wave laser, fibre-optic transmission and photon counting electronics. The radial and centreline profiles of time-averaged density and root-mean-square density fluctuation provided a comparative description of jet growth. To measure density fluctuation spectra a two-photomultiplier-tube (PMT) technique was used. Cross-correlation between the two PMT signals significantly reduced the electronic shot noise contribution. The density fluctuation spectra were found to be remarkably similar for all Mach number jets. A detailed survey in fully expanded Mach 0.95, 1.4 and 1.8 jets further confirmed that the distribution of various Strouhal frequency fluctuations remained similar, except for a spatial stretching with increased Mach number. In spite of this similarity in flow fluctuations t...
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Noise sources in high-speed jets were identified by directly correlating flow density fluctuation (cause) to far-field sound pressure fluctuation (effect). The experimental study was performed in a nozzle facility at the NASA Glenn... more
Noise sources in high-speed jets were identified by directly correlating flow density fluctuation (cause) to far-field sound pressure fluctuation (effect). The experimental study was performed in a nozzle facility at the NASA Glenn Research Center in support of NASA s initiative to reduce the noise emitted by commercial airplanes. Previous efforts to use this correlation method have failed because the tools for measuring jet turbulence were intrusive. In the present experiment, a molecular Rayleigh-scattering technique was used that depended on laser light scattering by gas molecules in air. The technique allowed accurate measurement of air density fluctuations from different points in the plume. The study was conducted in shock-free, unheated jets of Mach numbers 0.95, 1.4, and 1.8. The turbulent motion, as evident from density fluctuation spectra was remarkably similar in all three jets, whereas the noise sources were significantly different. The correlation study was conducted by...
Research Interests:
Research Interests:
A molecular Rayleigh-scattering-based air-density measurement system was built in a large nozzle-and-engine-component test facility for surveying supersonic plumes from jet-engine exhaust. A molecular Rayleigh-scattering-based air-density... more
A molecular Rayleigh-scattering-based air-density measurement system was built in a large nozzle-and-engine-component test facility for surveying supersonic plumes from jet-engine exhaust. A molecular Rayleigh-scattering-based air-density measurement system was built in a large nozzle-and-enginecomponent test facility for surveying supersonic plumes from jet-engine exhaust
Research Interests:
Spectra of air density fluctuations in the thermal boundary layers over a heated flat plate were measured using a molecular Rayleigh scattering setup. A 12 inch X 9 inch size flat plate was heated over a range of temperatures 0°C ≤ ΔT ≤... more
Spectra of air density fluctuations in the thermal boundary layers over a heated flat plate were measured using a molecular Rayleigh scattering setup. A 12 inch X 9 inch size flat plate was heated over a range of temperatures 0°C ≤ ΔT ≤ 170°C using electrical strip heaters. The heated plate was placed in a low-speed wind tunnel in a range of free-stream velocity of 20 ft/s ≤ U0 ≤ 90 ft/s. At first, care was taken to avoid laminar separation bubble at the plate leading edge. The thermal and velocity boundary layers at different streamwise locations were measured using a hot film probe operated in constant current and constant temperature modes. The temperature distribution on the plate was measured by an infra-red camera. In spite of a relatively high level of free-stream turbulent fluctuations, the relatively low plate Reynolds number 1.2e5 ≤ Re ≤ 5.3e5 ensured laminar flow at unheated condition. Progressively increased heating was found to expedite transition to turbulence. To setu...
Nonintrusive optical point-wise measurement techniques utilizing the principles of molecular Rayleigh scattering have been developed at the NASA Glenn Research Center to obtain time-averaged information about gas velocity, density,... more
Nonintrusive optical point-wise measurement techniques utilizing the principles of molecular Rayleigh scattering have been developed at the NASA Glenn Research Center to obtain time-averaged information about gas velocity, density, temperature, and turbulence, or dynamic information about gas velocity and density in unseeded flows. These techniques enable measurements that are necessary for validating computational fluid dynamics (CFD) and computational aeroacoustic (CAA) codes. Dynamic measurements allow the calculation of power spectra for the various flow properties. This type of information is currently being used in jet noise studies, correlating sound pressure fluctuations with velocity and density fluctuations to determine noise sources in jets. These nonintrusive techniques are particularly useful in supersonic flows, where seeding the flow with particles is not an option, and where the environment is too harsh for hot-wire measurements.
Research Interests:
Screech tones from supersonic jets are known to be nozzle exit and a pressure anti-node downstream. In suppressed or augmented by appropriate positioning contrast, minimum screech developed when the of an upstream reflector. The purpose... more
Screech tones from supersonic jets are known to be nozzle exit and a pressure anti-node downstream. In suppressed or augmented by appropriate positioning contrast, minimum screech developed when the of an upstream reflector. The purpose of our paper positions of the node and anti-node were reversed, is to account for this remarkable property by A further implication arises from the fact that the experimentally investigating how a reflector alters the node or anti-node was not at the nozzle exit: pressure field surrounding a jet. Our results from a coupling between acoustic and instability waves may rectangular jet indicate that the nearfield consists of not occur right at the nozzle exit, but in a small both standing and travelling waves. Surprisingly, it region downstream of the nozzle exit. Finally, we was the standing and not the travelling (feedback) believe that our results are of significance for wave that directly determined the fate of screech. understanding screech, and for devising strategies to Maximum screech was obtained when the standing minimize fatigue failure of aircraft components, wave exhibited a pressure node upstream of the ^Member AIAA, Senior Member AIAA, Copyright © 1997 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.
The screech noise generation process from supersonic underexpanded jets, issuing from a sonic nozzle at pressure ratios of 2.4 and 3.3 (fully expanded Mach number, Mj=1.19 and 1.42), was investigated experimentally. The extremely detailed... more
The screech noise generation process from supersonic underexpanded jets, issuing from a sonic nozzle at pressure ratios of 2.4 and 3.3 (fully expanded Mach number, Mj=1.19 and 1.42), was investigated experimentally. The extremely detailed data provide a fresh, new look at the screech generation mechanism. Spark schlieren visualization at different phases of the screech cycle clearly shows the convection of the organized turbulent structures over a train of shock waves. The potential pressure field (hydrodynamic fluctuations) associated with the organized structures is fairly intense and extends outside the shear layer. The time evolution of the near-field pressure fluctuations was obtained from phase-averaged microphone measurements. Phase-matched combined views of schlieren photographs and pressure fluctuations show the sound generation process. The individual compression and rarefaction parts of the sound waves are found to be generated from similar hydrodynamic fluctuations. A pa...
Research Interests:
The periodic oscillation of the shock waves in screeching, underexpanded, supersonic jets, issuing from a choked, axisymmetric, nozzle at fully expanded Mach numbers (Mj) of 1.19 and 1.42, is studied experimentally and analytically. The... more
The periodic oscillation of the shock waves in screeching, underexpanded, supersonic jets, issuing from a choked, axisymmetric, nozzle at fully expanded Mach numbers (Mj) of 1.19 and 1.42, is studied experimentally and analytically. The experimental part uses schlieren photography and a new shock detection technique which depends on a recently observed phenomenon of laser light scattering by shock waves. A narrow laser beam is traversed from point to point in the flow field and the appearance of the scattered light is sensed by a photomultiplier tube (PMT). The time-averaged and phase-averaged statistics of the PMT data provide significant insight into the shock motion. It is found that the shocks move the most in the jet core and the least in the shear layer. This is opposite to the intuitive expectation of a larger-amplitude shock motion in the shear layer where organized vortices interact with the shock. The mode of shock motion is the same as that of the emitted screech tone. Th...
Research Interests:
J. Panda Ohio Aerospace Institute, Brook Park, Ohio KBMQ Zaman and RG Seasholtz Glenn Research Center, Cleveland, Ohio Measurement of Initial Conditions at ... KBMQ Zaman and RG Seasholtz Glenn Research Center, Cleveland, Ohio Measurement... more
J. Panda Ohio Aerospace Institute, Brook Park, Ohio KBMQ Zaman and RG Seasholtz Glenn Research Center, Cleveland, Ohio Measurement of Initial Conditions at ... KBMQ Zaman and RG Seasholtz Glenn Research Center, Cleveland, Ohio Measurement of Initial Conditions at ...
Measurements of balloon loudness and pressure signatures are presented for a variety of balloon shapes. The loudness and recordings were made 3.2 meters from the popped balloons. The balloons were of 3 types: round, long, and extremely... more
Measurements of balloon loudness and pressure signatures are presented for a variety of balloon shapes. The loudness and recordings were made 3.2 meters from the popped balloons. The balloons were of 3 types: round, long, and extremely long (the same type that is used to make balloon animals), filled with 3 gases, and inflated to multiple sizes. The data indicates that all 3 types of latex balloons share similar peak frequencies and acoustic signatures in spite of differences in shape and diameter or length when inflated. The data also shows a correlation of loudness to the ratio of specific heats of the gas and inflated diameter of the balloons. The data does not support some of the common hypotheses of balloon popping noise generation. It appears that the sound is generated by the vibration of the balloon surface and the ruptured edge of the latex. This explanation is consistent with the current acoustic measurements and shadowgraph videos, and the hypothesis of Patynen, et al.
Research Interests:
Near-plume fluctuating pressures were measured during five static burns of a two-stage solid rocket motor. An array of 11 water-cooled dynamic pressure sensors was used for the near-field survey, and a condenser microphone was used to... more
Near-plume fluctuating pressures were measured during five static burns of a two-stage solid rocket motor. An array of 11 water-cooled dynamic pressure sensors was used for the near-field survey, and a condenser microphone was used to monitor the far-field acoustic fluctuations. During the initial high-thrust phase of the burn, the plume was nearly ideally expanded, while in the following low-thrust phase, it was highly over-expanded and showed the presence of clear shock patterns. This paper presents time histories and spectra measured for the two thrust conditions. Spectra from very close to the plume show high levels of low-frequency fluctuations which are known to produce significant vibro-acoustic response of the spacecraft structures. The far-field microphone signal was dominated by mixing noise with little evidence of contribution from shock-associated noise, even for the over-expanded condition. The work was performed in support of an effort to improve predictions of the aco...