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At least 271 records · Page 15
All sourcesNASA NTRSDOE OSTI
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 NTRS1974

Measurements in a large angle oblique jet impingement flow

Velocity and surface pressure measurements, in the flow field of an obliquely impinging jet, and their interpretation as regards the governing mechanics and the aerodynamic noise generation characteristics of such a flow are reported. A computer controlled probe positioning mechanism allowed the measurement of the velocity magnitude and direction in the plane parallel to the plate. The mean velocity and Reynolds stress components were recorded. Measures of the terms in the momentum equation reveal the character of the pressure gradients in the neighborhood of the stagnation point. The effects of the stagnation streamline location on the vorticity field and the vortex sound considerations are discussed in relationship to the aerodynamic noise generation effects of this flow.

Foss, J. F.↗
NASA NTRS1978

Measurements in a large angle oblique jet impingement flow

The flow field associated with the oblique impingement of an axisymmetric jet was investigated in the externally blown flap configuration for the STOL aircraft. The passive and active spreading characteristics of the shallow angle (a greater than or = approximately to 15 degrees) oblique impingement flow, the role of the initially azimuthal vorticity field, and the stagnation point region were studied, and compared to the large ( a = 45 degres) oblique jet impingement flow. A description of the characteristics of the large angle impingement flow is presented: A flow field near the plate as showing two distinct patterns, one near the location of the maximum surface pressure, and another about the geometric intersection of the jet axis with the plate; and turbulence in the region above the plate which is greater than the one accounted for by the convection of turbulence energy by the mean motion.

Foss, J. F.↗
NASA NTRS1960

Low-Speed Investigation of a Full-Span Internal-Flow Jet-Augmented Flap on a High-Wing Model with a 35 deg Swept Wing of Aspect Ratio 7.0

An investigation of a full-span 17-percent-chord internal-flow jet-augmented flap on an aspect-ratio-7.0 wing with 35 deg of sweepback has been made in the Langley 300-MPH 7- by 10-foot tunnel. Blowing over the conventional elevator and blowing down from a nose jet were investigated as a means of trimming the large diving moments at the high momentum and high lift coefficients. The results of the investigation showed that the model with the horizontal tail 0.928 mean aerodynamic chord above the wing-chord plane was stable to the maximum lift coefficient. The large diving-moment coefficients could be trimmed either with a downward blowing nose jet or by blowing over the elevator. Neither the downward blowing nose jet nor blowing over the elevator greatly affected the static longitudinal stability of the model. Trimmed lift coefficients up to 8.8 with blowing over the elevator and up to 11.4 with blowing down at the nose were obtained when the flap was deflected 70 deg and the total momentum coefficients were 3.26 and 4.69.

Turner, Thomas R.↗
NASA NTRS1985

Tone excited jets. III - Flow measurements

This paper describes the effects of upstream excitation on the flow characteristics of tone-excited jet under static as well as simulated forward velocity conditions. The data presented include axial and radial distributions of mean velocities and turbulence intensities as functions of excitation conditions. Results for both unheated and heated jets are presented. The measured distributions of pressures associated with the large-scale turbulence are also presented for some test conditions.

Lepicovsky, J.↗
NASA NTRS1975

Developments in the large angle oblique jet impingement flow investigation

Single-wire (hot-wire) measurements are presented of the mean velocity and turbulence quantities near the impact plate for a 45-degree impingement flow responsible for acoustic noise production. These results are summarized along with the conclusions which shaped the subsequent direction of the study of large angle oblique jet impingement flow. The development of a unique signal processing circuit for finding the instantaneous transverse vorticity from an array of four hot-wires is discussed.

Foss, J. F.↗
NASA NTRS1977

Finite element analysis of aeroacoustic jet-flap flows

A computational analysis was performed on the steady, turbulent aerodynamic flowfields associated with a jet-blown flap. For regions devoid of flow separation, a parabolic approximation to the governing time-averaged Navier-Stokes equations was applied. Numerical results are presented for the symmetry plane flow of a slot-nozzle planar jet flap geometry, including prediction of flowfield evolution within the secondary mixing region immediately downstream of the trailing edge. Using a two equation turbulence kinetic energy closure model, rapid generation and decay of large spatial gradients in mean and correlated fluctuating velocity components within the immediate wake region were predicted. Modifications to the turbulent flow structure, as induced by porous surface treatment of the flap, were evaluated. The recirculating flow within a representative discrete slot in the surface was evaluated, using the two dimensional, time-averaged Navier-Stokes equations.

Baker, A. J.↗
NASA NTRS1992

Investigation of a co-flowing buoyant jet - Experiments on the effect of Reynolds number and Richardson number

The behavior of a vertical jet of helium issuing into a co-flow of air at a fixed exit velocity ratio of 2 was investigated experimentally over a wide range of governing parameters with emphasis on flow structure and the scaling properties of the natural frequency of the jet. The experiments were conducted in a variable-pressure facility, which made it possible to vary the Reynolds number and the Richardson number independently. At all the experimental conditions studied, the flow exhibits a strong self-excited periodicity. A buoyancy Strouhal number is defined and used to correlate frequency data from the approximately seventy different Reynolds and Richardson numbers studied. The buoyancy Strouhal number is found to be nearly independent of Reynolds number and Richardson number for Richardson numbers greater than one.

Subbarao, E. R.↗
NASA NTRS1996

Computational study of a contoured plug-nozzle as a supersonic jet noise suppressor

The report summarizes a computational jet noise study of an ideal contoured plug-nozzle (CPN). The gasdynamics of the jet flows have been predicted using the CFD code, NPARC with k-epsilon turbulence model; these data are then used as inputs to perform the noise computations based on the modified version of General Electric MGB code. The study covers a range of operating pressure ratio, 2.0 less than xi less than 5.0 (shockless flow at design pressure ratio, xi(d) = 3.62). The agreement of the computational aeroacoustics results with the available experimental data may be considered to be favorable. The computational results indicate consistent noise reduction effectiveness of the CPN at all operating pressure ratios. At the design pressure ratio (shockless), the codes predict overall sound pressure levels within +3.O dB of the experimental data. But at the off-design pressure ratios (flaws with shocks), the agreement is rather mixed. The theory overpredicts the OASPL's at all pressure ratios except at lower angles to the jet axis in overexpanded mode (xi less than xi(d)), the deviations being within 4.5 dB. The mechanism of shock formations in the CPN jet flows is noted to be basically different from those in the convergent-divergent nozzle jet flows.

Khavaran, A.↗
NASA NTRS1992

Numerical simulation of jet noise

Jet noise and jet-induced structural loads have become key issues in the design of commercial and military aircraft. Computational Fluid Dynamics (CFD) can be of use in predicting the underlying jet shear-layer instabilities and, in conjunction with classical acoustic theory, jet noise. The computational issues involved in the resolution of high Reynolds number unsteady jet flows are addressed in this paper. Once these jet flows can be accurately resolved, it should be possible to use acoustic theory to extract, for example, the far-field jet noise. An assessment of future work and computational resources required for directly computing far-field jet noise is also presented.

Van Dalsem, W. R.↗
NASA NTRS1992

Acoustic analysis using numerical solutions of the Navier-Stokes equations

Numerical solutions of the time-dependent compressible Navier-Stokes equations are employed to analyze the unsteady features of jet flows which contribute to jet noise. The turbulent-mass flux spectra are examined in detail in the numerical analysis, and MacCormack's explicit finite difference algorithm is used to solve the governing equations. The computational grid is based on an axisymmetric jet with simple exponential stretching used to optimize the resolution of critical unsteady flow features. The time-varying numerical data are analyzed, and the time averages of the velocity and turbulence-intensity profiles are shown to agree with experimental data. Grid refinement and longer run times improved the prediction of the experimental mass-flux spectra. The numerical procedure can be extended to 3D jet-flow configurations to study the related 3D unsteady flow features.

Scott, James N.↗
NASA NTRS1990

Navier-Stokes simulation of transonic afterbody flows with jet exhaust

Three-dimensional Navier-Stokes simulations have been made for the transonic flow past a nonaxisymmetric nozzle typical of those advocated for advanced fighter airplanes. Jet exhaust simulation is evaluated as are the Baldwin-Lomax (1978) and Goldberg (1986) turbulence models. Solutions are presented for Mach numbers of 0.80 and 0.94 at 0-deg angle of attack and a Reynolds number of 20 x 10 to the 6th. The numerical results are compared to wind-tunnel data. They show that including the jet exhaust in the calculations gives the most accurate solution near the nozzle exit. Also, the two turbulence models predict considerably different flow fields.

Compton, William B., III↗
NASA NTRS1990

Numerical study of twin-jet impingement upwash flow

Two horizontally spaced jets impinging normally on a flat surface create a fountain upwash flow due to the collision of the radially flowing wall jets. This fountain flow is of importance to the dynamics and propulsion of STOVL aircraft. The fountain flow influences the lift forces on the aircraft and the ingestion of hot gases and debris by the engine inlet. In this paper, a multigrid based finite-difference numerical procedure has been applied to solve the equations governing this three-dimensional flow. The standard k-epsilon turbulence model has been used. Comparisons with experimental data reveal that while the mean velocities are predicted with reasonable accuracy, the turbulent kinetic energies are seriously in error. The reasons for this discrepancy could be the intense unsteadiness and large-scale structures of the flow in the near-wall region, which cannot be captured well by any Reynolds-averaged turbulence model.

Pegues, W. J.↗
NASA NTRS2009

Broadband Shock Noise in Internally-Mixed Dual-Stream Jets

Broadband shock noise (BBSN) has been studied in some detail in single-flow jets and recently in dual-stream jets with separate flow exhaust systems. Shock noise is of great concern in these latter cases because of the noise created for the aircraft cabin by the underexpanded nozzle flow at cruise. Another case where shock noise is of concern is in the case of future supersonic aircraft that are expected to have bypass ratios small enough to justify internally mixed exhaust systems, and whose mission will push cycles to the point of imperfectly expanded flows. Dual-stream jets with internally mixed plume have some simplifying aspects relative to the separate flow jets, having a single shock structure given by the common nozzle pressure. This is used to separate the contribution of the turbulent shear layer to the broadband shock noise. Shock structure is held constant while the geometry and strength of the inner and merged shear layers are varying by changing splitter area ratio and core stream temperature. Flow and noise measurements are presented which document the efforts at separating the contribution of the inner shear layer to the broadband shock noise.

Bridges, James E.↗
NASA NTRS1972

Analysis of the Injection of a Heated, Turbulent Jet into a Moving Mainstream, with Emphasis on a Thermal Discharge in a Waterway

An experimental and theoretical investigation was undertaken to study the trajectory and growth of thermal effluents having a range of discharge velocities and temperatures. The discharge of a turbulent effluent into a waterway was mathematically modeled as a submerged jet injection process by using an integral method which accounts for natural fluid mechanisms such as turbulence, entrainment, buoyancy, and heat transfer. The analytical results are supported by experimental data and demonstrate the usefulness of the theory for estimating the location and size of the effluent with respect to the discharge point. The capability of predicting jet flow properties, as well as two- and three-dimensional jet paths, was enhanced by obtaining the jet cross-sectional area during the solution of the conservation equations. Realistic estimates of temperature in the effluent were acquired by accounting for heat losses in the jet flow due to forced convection and to entrainment of free-stream fluid into the jet.

Campbell, J. F.↗