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At least 793 records · Page 44
All sourcesNASA NTRSDOE OSTI
NASA NTRS2021

Raman Temperature and Density Measurements in Supersonic Jets

Prediction of flow-field properties in supersonic jets using computational fluid dynamics (CFD) code predictions has become routine; however, obtaining accurate solutions becomes more challenging when there is a significant temperature difference between the jet core and the ambient air and/or compressibility effects are significant. Benchmark sets of flow field property data are required in order to assess current CFD capabilities and develop better modeling approaches for these turbulent flow fields where accurate calculation of temperatures and turbulent heat flux is important. Particle Image Velocimetry (PIV), spontaneous rotational Raman scattering (SRS) spectroscopy and Background Oriented Schlieren (BOS) have been previously used to acquire measurements of the mean and root mean square (rms) velocities, the mean and rms gas temperatures and density gradients in subsonic jet flows and film cooling flows. In this work, the ability to measure density is added to the list of measurands available using the acquired Raman spectra. The suite of measurement techniques are now applied to supersonic jet flows. The computation of the local gas pressure in the potential core of an over-expanded jet is demonstrated using the Raman measured gas temperature and density. Additionally, a unique density feature in temperature matched, perfectly expanded jet flow shear layers identified using BOS was verified using the Raman measurement technique. These non-intrusive flow measurements are compared against RANS predictions of the supersonic jet flow properties as a means of assessing their prediction accuracy.

Raman Spectroscopy↗
NASA NTRS2014

Jet-Surface Interaction Test: Flow Measurements Results

Modern aircraft design often puts the engine exhaust in close proximity to the airframe surfaces. Aircraft noise prediction tools must continue to develop in order to meet the challenges these aircraft present. The Jet-Surface Interaction Tests have been conducted to provide a comprehensive quality set of experimental data suitable for development and validation of these exhaust noise prediction methods. Flow measurements have been acquired using streamwise and cross-stream particle image velocimetry (PIV) and fluctuating surface pressure data acquired using flush mounted pressure transducers near the surface trailing edge. These data combined with previously reported far-field and phased array noise measurements represent the first step toward the experimental data base. These flow data are particularly applicable to development of noise prediction methods which rely on computational fluid dynamics to uncover the flow physics. A representative sample of the large flow data set acquired is presented here to show how a surface near a jet affects the turbulent kinetic energy in the plume, the spatial relationship between the jet plume and surface needed to generate surface trailing-edge noise, and differences between heated and unheated jet flows with respect to surfaces.

Flow↗
NASA NTRS1979

A computational model for three-dimensional incompressible wall jets with large cross flow

A computational model for the flow field of three dimensional incompressible wall jets prototypic of thrust augmenting ejectors with large cross flow is presented. The formulation employs boundary layer equations in an orthogonal curvilinear coordinate system. Simulation of laminar as well as turbulen wall jets is reported. Quantification of jet spreading, jet growth, nominal separation, and jet shrink effects due to corss flow are discussed.

Murphy, W. D.↗
NASA NTRS1972

Temperature and velocity field of the two-dimensional transverse hot-air jet in a freestream flow.

Experimental investigation of the low subsonic, two-dimensional transverse hot-air jet. In the study jet-to-freestream angles of 90, 120, 135, and 150 deg and jet-to-freestream velocity ratios of 5, 10, and 20 were investigated. In the tests the jet velocity and temperature fields were measured using a temperature-compensated hot-wire anemometer. Photographs of the flowfield were also made. The tests results are compared with the available data and analysis. Results indicate a relatively minor deflection of the freestream by the jet and the presence of a large separated flow region behind the jet.

Tatom, J. W.↗
NASA NTRS1983

Interaction of multiple supersonic jets with a transonic flow field

The influence of multiple high pressure, supersonic, radial or tangential jets, that are injected from the circumference of the base plane of an axisymmetric body, on its longitudinal aerodynamic coefficients in transonic flow is studied experimentally. The interaction of the jets with the body flow field increases the pressures on the forebody, thus altering its lift and static stability characteristics. It is shown that, within the range of parameters studied. This interaction has a stabilizing effect on the body. The contribution to lift and stability is significant at small angles of attack and decreases nonlinearly at higher angles when the crossflow mechanism becomes dominant.

Seginer, A.↗
NASA NTRS1948

Investigation of the Penetration on an Air Jet Directed Perpendicularly to an Air Stream

An experimental investigation was conducted to determine the penetration of a circular air Jet directed perpendicularly to an air stream as a function of Jet density, Jet velocity, air-stream density, air-stream velocity, Jet diameter, and distance downstream from the Jet. The penetration was determined for nearly constant values of air-stream density at two tunnel velocities, four Jet diameters, four positions downstream of the Jet, and for a large range of Jet velocities and densities. An equation for the penetration was obtained in terms of the Jet diameter, the distance downstream from the jet, and the ratios of Jet and air-stream velocities and densities.

JETS↗
NASA NTRS1947

Three-Component Force and Mass-Flow Measurement on a Jet Nacelle

The present report contains three-component forces and mass-flow measurements on a jet nacelle at small inlet-velocity ratios v(sub A)/v(sub o) < 1. The mass-flow measurement on two cross sections of the nacelle demonstrate the local-velocity distribution with varying flow and angle of attack.

Ilgmann, G.↗
NASA NTRS1984

Dilution Jets in Accelerated Cross Flows

Results of flow visualization experiments and measurements of the temperature field produced by a single jet and a row of dilution jets issued into a reverse flow combustor are presented. The flow in such combustors is typified by transverse and longitudinal acceleration during the passage through its bending section. The flow visualization experiments were designed to examine the separate effects of longitudinal and transverse acceleration on the jet trajectory and spreading rate. A model describing a dense single jet in a lighter accelerating cross flow is developed. The model is based on integral conservation equations, including the pressure terms appropriate to accelerating flows. It uses a modified entrainment correlation obtained from previous experiments of a jet in a cross stream. The flow visualization results are compared with the model calculations in terms of trajectories and spreading rates. Each experiment is typified by a set of three parameters: momentum ratio, density ratio, and the densimetric Froude number. When injection velocities are large or densities are small, the Froude number becomes very large and hence, unimportant. Therefore, the Froude number is generally significant in describing liquid experiments but is unimportant for the gas experiments in the combustor. Agreement between test and calculated results is encouraging but tends to become poorer with increasing momentum ratio. The temperature measurements are presented primarily in the form of consecutive normalized temperature profiles. Some interpolated isothermal contours are also shown. The single jet trajectories are consistently found to be swept towards the inner wall of the bend, whether injection is from the outer or the inner wall. This behavior is explained by a drifting effect which consists of a transverse velocity component across the combustor due to the developing nature of the flow along it. Plots of lateral temperature distributions of the jet indicate that under longitudinal acceleration conditions the thermal spreading of the jet may be completely suppressed. Comparison between combustor experimental results and model calculations shows poor agreement due to the drifting effect which is not taken into consideration in the model calculations. The row of jets experiments are characterized by two additional parameters: spacing ratio and confinement parameter. The results are shown in the form of consecutive normalized temperature profiles. The confinement parameter appears to become increasingly important with decreasing spacing ratio, in particular when its effect is enhanced by the drifting phenomenon and associated pressure field. A tightly spaced row of jets injected from the inner wall, prior to the bend, is surprisingly kept attached to the inner wall in spite of the strong turning. A similar attachment for a jet injected from the outer wall is not observed.

Lipshitz, Abraham↗
NASA NTRS1984

Dilution jets in accelerated cross flows

Results of flow visualization experiments and measurements of the temperature field produced by a single jet and a row of dilution jets issued into a reverse flow combustor are presented. The flow in such combustors is typified by transverse and longitudinal acceleration during the passage through its bending section. The flow visualization experiments are designed to examine the separate effects of longitudinal and transverse acceleration on the jet trajectory and spreading rate. A model describing a dense single jet in a lighter accelerating cross flow is developed. The model is based on integral conservation equations, including the pressure terms appropriate to accelerating flows. It uses a modified entrainment correlation obtained from previous experiments of a jet in a cross stream. The flow visualization results are compared with the model calculations in terms of trajectories and spreading rates. Each experiment is typified by a set of three parameters: momentum ratio, density ratio and the densimetric Froude number.

Lipshitz, A.↗
NASA NTRS1990

Experimental studies of shock wave/wall jet interaction in hypersonic flow

The interaction between a planar shock wave and a wall jet produced by slot cooling in turbulent hypersonic flow was experimentally studied. Detailed distributions of heat transfer and pressure are obtained in the incident shock/wall jet interaction region for a series of shock strengths and impingement positions for two nozzle heights. The major result is that the cooling film could be readily dispersed by relatively weak incident shocks such that the peak heating in the recompression region was not significantly reduced by even the largest levels of film cooling. Regions of boundary layer separation were induced in the film cooling layer, the size of which first increased and then decreased with increasing film cooling. The size of the separated regions and magnitude of the recompression heating were not strongly influenced by the thickness of the cooling film or point of shock impingement relative to the exit plane of the nozzles.

Holden, Michael S.↗
NASA NTRS1978

Propagation of sound through a sheared flow

Sound generated in a moving fluid must propagate through a shear layer in order to be measured by a fixed instrument. These propagation effects were evaluated for noise sources typically associated with single and co-flowing subsonic jets and for subcritical flow over airfoils in such jets. The techniques for describing acoustic propagation fall into two categories: geometric acoustics and wave acoustics. Geometric acoustics is most convenient and accurate for high frequency sound. In the frequency range of interest to the present study (greater than 150 Hz), the geometric acoustics approach was determined to be most useful and practical.

Woolley, J. P.↗