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At least 73 records · Page 4

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NASA NTRS1975

Analysis of liquid-metal-jet impingement cooling in a corner region and for a row of jets

A conformal mapping method was used to analyze liquid-metal-jet impingement heat transfer. The jet flow region and energy equation are transformed to correspond to uniform flow in a parallel plate channel with nonuniform heat addition along a portion of one wall. The exact solution for the wall-temperature distribution was obtained in the transformed channel, and the results are mapped back into the physical plane. Two geometries are analyzed. One is for a single slot jet directed either into an interior corner formed by two flat plates, or over the external sides of the corner; the flat plates are uniformly heated, and the corner can have various included angles. The heat-transfer coefficient at the stagnation point at the apex of the plates is obtained as a function of the corner angle, and temperature distributions are calculated along the heated walls. The second geometry is an infinite row of uniformly spaced parallel slot jets impinging normally against a uniformly heated plate. The heat-transfer behavior is obtained as a function of the spacing between the jets. Results are given for several jet Peclet numbers from 5 to 50.

Siegel, R.↗

NASA NTRS1978

A comparison of the noise produced by a small jet on a moving vehicle with that in a free jet

A 2.54 cm (1.00 in.) nozzle supplied with nitrogen was mounted above an automobile and driven over an asphalt roadway past stationary microphones in an attempt to quantify the effects of the vehicle motion on jet mixing noise. The nozzle was then tested in the Langley anechoic noise facility with a large free jet simulating the relative motion. The results are compared for these two methods of investigating forward speed effects on jet mixing noise. The vehicle results indicate a noise with forward speed throughout the Doppler-shifted static spectrum. This decrease across the entire frequency range was also apparent in the free-jet results. The similarity of the results indicates that the effects of flight on jet mixing noise can be predicted by simulation of forward speed with a free jet. Overall sound pressure levels were found to decrease with forward speed at all observation angles for both methods of testing.

Norum, T. D.↗

NASA NTRS1982

Into Mesh Lubrication of Spur Gears with Arbitrary Offset Oil Jet. I: For Jet Velocity Less than or Equal to Gear Velocity

An analysis was conducted for into mesh oil jet lubrication with an arbitrary offset and inclination angle from the pitch point for the case where the oil jet velocity is equal to or less than pitch line velocity. The analysis includes the case for the oil jet offset from the pitch point in the direction of the pinion and where the oil jet is inclined to intersect the common pitch point. Equations were developed for the minimum oil jet velocity required to impinge on the pinion or gear and the optimum oil jet velocity to obtain the maximum impingement depth.

Akin, L. S.↗

NASA NTRS1983

Into mesh lubrication of spur gears with arbitrary offset oil jet. I - For jet velocity less than or equal to gear velocity

Akin, L. S.↗

NASA NTRS1957

Far Noise Field of Air Jets and Jet Engines

An experimental investigation was conducted to study and compare the acoustic radiation of air jets and jet engines. A number of different nozzle-exit shapes were studied with air jets to determine the effect of exit shape on noise generation. Circular, square, rectangular, and elliptical convergent nozzles and convergent-divergent and plug nozzles were investigated. The spectral distributions of the sound power for the engine and the air jet were in good agreement for the case where the engine data were not greatly affected by reflection or jet interference effects. Such power spectra for a subsonic or slightly choked engine or air jet show that the peaks of the spectra occur at a Strouhal number of 0.3.

Callaghan, Edmund E↗

NASA NTRS2015

On the Comparison of the Long Penetration Mode (LPM) Supersonic Counterflowing Jet to the Supersonic Screech Jet

The authors provide a brief overview of the classic tonal screech noise problem created by underexpanded supersonic jets, briefly describing the fluid dynamic-acoustics feedback mechanism that has been long established as the basis for this well-known aeroacoustics problem. This is followed by a description of the Long Penetration Mode (LPM) supersonic underexpanded counterflowing jet phenomenon which has been demonstrated in several wind tunnel tests and modeled in several computational fluid dynamics (CFD) simulations. The authors provide evidence from test and CFD analysis of LPM that indicates that acoustics feedback and fluid interaction seen in LPM are analogous to the aeroacoustics interactions seen in screech jets. Finally, the authors propose applying certain methodologies to LPM which have been developed and successfully demonstrated in the study of screech jets and mechanically induced excitation in fluid oscillators for decades. The authors conclude that the large body of work done on jet screech, other aeroacoustic phenomena, and fluid oscillators can have direct application to the study and applications of LPM counterflowing supersonic cold flow jets.

Farr, Rebecca A.↗

NASA NTRS2015

On the Comparison of the Long Penetration Mode (LPM) Supersonic Counterflowing Jet to the Supersonic Screech Jet

Classic tonal screech noise created by under-expanded supersonic jets; Long Penetration Mode (LPM) supersonic phenomenon -Under-expanded counter-flowing jet in supersonic free stream -Demonstrated in several wind tunnel tests -Modeled in several computational fluid dynamics (CFD) simulations; Discussion of LPM acoustics feedback and fluid interactions -Analogous to the aero-acoustics interactions seen in screech jets; Lessons Learned: Applying certain methodologies to LPM -Developed and successfully demonstrated in the study of screech jets -Discussion of mechanically induced excitation in fluid oscillators in general; Conclusions -Large body of work done on jet screech, other aero-acoustic phenomenacan have direct application to the study and applications of LPM cold flow jets

Farr, Rebecca A.↗

NASA NTRS1973

Preliminary results for a large angle oblique jet impingement and flow and for the effect of initial conditions on the near field of an axisymmetric jet

The structure of an axisymmetric jet in the near field is discussed for jet noise and for jet impingment schemes for STOL aircraft. It is inferred from previous studies, and the inference is supported by analysis, that the scale and intensity of the turbulence structure at the jet exit plane are the important boundary conditions which effect the development of the flow in the near field. The techniques to study these effects while maintaining a uniform mean flow and the results which document the range of the initial conditions are presented. The large angle, oblique jet impingment condition is of interest in terms of the jet/flap interaction. Detailed turbulence data can be obtained with the specially constructed facility. The development of the flow and instrumentation system and initial data from the new facility are presented.

Foss, J. F.↗

NASA NTRS1977

Experimental results of large-scale structures in jet flows and their relation to jet noise production

Experiments have been performed to determine the role of large-scale turbulent structures in the production of jet noise. Axisymmetric turbulent jet flows at ambient stagnation temperature have been observed with the aid of flow visualization techniques. Jet Mach numbers at the nozzle exit ranged between 0.1 and 0.9, and the Reynolds number, based on nozzle exit diameter, was approximately 10 to the 6th. Large organized turbulent structures existed as far downstream of the nozzle exit as 7 diameters. High-speed schlieren motion pictures synchronized with near-field pressure measurements of an excited jet indicated that strong instantaneous peaks in the pressure signal occurred whenever a merging process between two large-scale organized structures occurred. This pressure pulse propagated at a speed which was somewhat larger than the velocity of the jet at the nozzle exit.

Sarohia, V.↗

NASA NTRS1978

Investigation of impingement region and wall jets formed by the interaction of high aspect ratio lift jets and a ground plane

Flow characteristics of impinging jets emanating from rectangular exit area converging nozzles of exit area aspect ratio four, six, and eight were investigated. Azimuthal distributions of wall jet radial momentum flux in the ground plane were strongly directional and sensitive to rectangular nozzle exit area aspect ratio, jet impingement angle, and height above ground, H/D. Effects of jet exit velocity profile nonuniformities were also investigated. Data from the single nozzle rectangular jet impringement investigations were incorporated into an existing VTOL aircraft ground flow field computer program. It is suggested that this program together with the Douglas Neumann program modified for V/STOL applications may be used for the analysis and prediction of flow fields and resulting forces and moments on multijet V/STOL aircraft hovering in ground effect.

Kotansky, D. R.↗

NASA NTRS1985

Jets in air-jet family

The A-jet families on Chacaltaya emulsion chamber experiments were analyzed by the study of jets which are reconstructed by a grouping procedure. It is demonstrated that large-E sub J R sub J events are characterized by small number of jets and two-jet like asymmetric shape, binocular events and the other type. This type has a larger number of jets and more symmetrical shape in the P sub t plane.

Navia, C. E.↗

NASA NTRS1985

Exotic interactions among C-jets and Pb-jets

The C-jets and Pb-jets were surveyed on the part of Chacaltaya emulsion chamber No.19 amounting to an exposure of 28.8 sq m yr. It is shown that the adopted events make up an unbiased sample of C-jets for sigma sub E gamma TeV. Mini-Centauro interaction gives the most natural explanation for the eight pinaught-less C-jets with three or more constituent shower core. Out of the eight double-cored pinaught-less events, three are found to have visible invariant masses 1.8 GeV/c. Three Pb-jets-lower are composed of double cores whose respective visible transverse momenta are greater than 0.5 GeV/c, suggesting that they are of Geminion origin or chiron origin. The energies of the parent particles are estimated to be 100 to 200 TeV for all three kinds of events. The implications of this energy estimate and the frequency of observed exotic events are discussed.

Source record↗

NASA NTRS1985

Numerical simulations of a transverse indirect circulation and low-level jet in the exit region of an upper-level jet

A numerical study was performed of a severe weather event (tornado) which occurred on May 10, 1973 in the Ohio region. The situation was modeled with a primitive equation mesoscale dynamic formulation. Account was taken of precipitation, the planetary boundary layer parameters as bulk quantities, the vertical pressure gradient, and lateral boundary conditions based on radiosonde data. Two 12-hr simulations, adiabatic and nondivergent, respectively, were analyzed for relationships between upper and lower level jets. In the adiabatic formulation, a transverse circulation with a low level jet formed at the exit region of the upper level jet. The nondivergent situation led to similar, but weaker, phenomena. Both forms suggest that indirect circulation in the exit zone of an upper level jet is strongly influenced by the initial structure of the jet.

Brill, K. F.↗

NASA NTRS1985

Heat transfer characteristics within an array of impinging jets. Effects of crossflow temperature relative to jet temperature

Spanwise average heat fluxes, resolved in the streamwise direction to one stream-wise hole spacing were measured for two-dimensional arrays of circular air jets impinging on a heat transfer surface parallel to the jet orifice plate. The jet flow, after impingement, was constrained to exit in a single direction along the channel formed by the jet orifice plate and heat transfer surface. The crossflow originated from the jets following impingement and an initial crossflow was present that approached the array through an upstream extension of the channel. The regional average heat fluxes are considered as a function of parameters associated with corresponding individual spanwise rows within the array. A linear superposition model was employed to formulate appropriate governing parameters for the individual row domain. The effects of flow history upstream of an individual row domain are also considered. The results are formulated in terms of individual spanwise row parameters. A corresponding set of streamwise resolved heat transfer characteristics formulated in terms of flow and geometric parameters characterizing the overall arrays is described.

Florschuetz, L. W.↗

NASA NTRS1991

On the estimation of jet-induced fountain lift and additional suckdown in hover for two-jet configurations

Currently available methods for estimating the net suckdown induced on jet V/STOL aircraft hovering in ground effect are based on a correlation of available force data and are, therefore, limited to configurations similar to those in the data base. Experience with some of these configurations has shown that both the fountain lift and additional suckdown are overestimated but these effects cancel each other for configurations within the data base. For other configurations, these effects may not cancel and the net suckdown could be grossly overestimated or underestimated. Also, present methods do not include the prediction of the pitching moments associated with the suckdown induced in ground effect. An attempt to develop a more logically based method for estimating the fountain lift and suckdown based on the jet-induced pressures is initiated. The analysis is based primarily on the data from a related family of three two-jet configurations (all using the same jet spacing) and limited data from two other two-jet configurations. The current status of the method, which includes expressions for estimating the maximum pressure induced in the fountain regions, and the sizes of the fountain and suckdown regions is presented. Correlating factors are developed to be used with these areas and pressures to estimate the fountain lift, the suckdown, and the related pitching moment increments.

Kuhn, Richard E.↗

NASA NTRS1962

Jet Interference Effects on a Model of a Single-Engine Four Jet V/STOL Airplane at Mach Numbers from 0.60 to 1.00

An investigation was conducted in the Langley 16-foot transonic tunnel to determine the interference from four exhaust jets on the aerodynamic characteristics of a model of a V/STOL airplane. The single- engine four-jet turbofan power plant of the airplane was simulated by inducing tunnel airflow through two large side inlets and injecting the decomposition products of hydrogen peroxide into the internal flow. The heated gas mixture was exhausted through four nozzles located on the sides of the fuselage under the wing, two near the wing leading edge and two forward of the trailing edge; the nozzles were deflected downward 1.5 deg and outward 5.0 deg to simulate cruise conditions. The wing of the model was a clipped delta with leading-edge sweep of 40 deg, aspect ratio of 3.06, taper ratio of 0.218, thickness-chord ratio of 0.09 at the root and 0.07 at the tip, and 10 deg negative dihedral. Aerodynamic and longitudinal stability coefficients were obtained for the model with the tail removed, and for horizontal-tail incidences of 0 deg and -5 deg. Data were obtained at Mach numbers from 0.60 to 1.00, angles of attack from 0 deg to 12 deg, and with jet total-pressure ratios up to 3.1. Jet operation generally caused a decrease in lift, an increase in pitching-moment coefficient, and a decrease in longitudinal stability at subsonic speeds. The jet interference effects on drag were detrimental at a Mach number of 0.60 and favorable at higher speeds for cruising-flight attitudes.

Schmeer, James W.↗

NASA NTRS2003

Synthetic Jets in Cross-flow: Jets From Orifices of Different Geometry - Part 2

The flow fields of synthetic jets in a cross-flow from orifices of different geometry are investigated. The geometries include a straight, a tapered, a pitched and a cluster of nine orifices, all having the same cross-sectional area through which the perturbation is discharged into the cross-flow. The strength of the jet from the tapered orifice in comparison to that from the straight one is found to be only slightly enhanced. The flow field from the cluster of orifices, when viewed a few equivalent diameters downstream, is similar to that from the single orifice. However, the penetration is somewhat lower in the former case due to the increased mixing of the distributed jets with the cross-flow. The penetration for the pitched configuration is the lowest, as expected. The jet trajectories for the straight and pitched orifices are well represented by correlation equations available for steady jets-in-cross-flow. Distributions of streamwise velocity, vorticity as well as turbulence intensity are documented for various cases. In addition, distributions of phase-averaged velocity and vorticity for the cylindrical and the clustered orifices are presented providing an insight into the flow dynamics.

Milanovic, Ivana M.↗

NASA NTRS2020

User's Guide for GAA_JET_FV (v1): A Jet Noise Prediction Code Based on the Generalized Acoustic Analogy

This document is a user’s guide for the jet noise prediction code GAA_JET_FV, which can be used to make predictions of turbulent mixing noise in high-speed free jets (ie. in the absence of any solid surfaces) of arbitrary cross section. The code requires a Reynolds-averaged Navier-Stokes (RANS) solution for the mean flow and turbulence as input. A script is provided in the code package which can be used to interpolate structured or unstructured RANS solutions onto a structured grid suitable for the noise calculations. Output file formats for two commonly used RANS solvers are currently supported by this script. The document describes how the code can be obtained and installed on a user’s system. A simple test case is provided that can be run with minimal user knowledge of the code details. General instructions for running the interpolation script and the main code are given along with descriptions of the input and output data files and individual code modules. Several additional test cases are provided which allow the user to exercise additional features of the code. This document is Version 1, Revision 0 of the User’s Guide, which contains examples of round and non-axisymmetric unheated jet test cases. Future versions are planned which will include additional functionality for the code and more complex test cases.

Jet Noise↗