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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 793 records · Page 44
All sourcesNASA NTRSDOE OSTI
NASA NTRS1977

Forward speed effects on blown flap noise

The effects of forward speed on the noise of under-the-wing (externally blown flaps, EBF) and over-the-wing (upper surface blown, USB) blown flap configurations were measured in wind tunnel model tests with cold jets. The results are presented without correction for the effects (e.g., signal convection, shear layer refraction) associated with flight simulation in a wind tunnel or free jet facility. Noise decreases were generally observed at microphones forward of the wing. The reductions were larger at the low frequencies (below peak SPL) than at the high (above peak SPL). Noise increases of 10 dB or more were observed at the aft microphones, especially in the high frequency range.

Pennock, A. P.↗
NASA NTRS1977

Neutrally stable atmospheric flow over a two-dimensional rectangular block

The phenomena of atmospheric flow over a two dimensional surface obstruction such as a building modeled as a rectangular block are analyzed by an approach using the Navier-Stokes equations with a two equation model of turbulence. The partial differential equations for the vorticity, stream function, turbulence kinetic energy, and turbulence length scale are solved by a finite difference technique. The predicted results are in agreement with the limited experimental data available. Current computed results show that the separation bubble originates from the upper front corner of the block and extends approximately 11.5 block heights behind the block. The decay of the mean velocity along the wake center line coincides almost perfectly with the experimental data. The vertical profiles of the mean velocity defect are also in reasonable agreement with wind tunnel results. Velocity profiles in the mixing region are shown to agree with the error function profile typically found in the shear layer. Details of the behavior of the turbulence kinetic energy and the turbulence length scale are also discussed.

Shieh, C. F.↗
NASA NTRS1977

A possible explanation of the mechanism of formation of the equatorial jet on the surface of Jupiter

Formation of the equatorial jet of the Jovian surface was explained as a consequence of the Taylor-Proudman theorem. The asymptotic theory of motion of low viscosity fluids in a rotating spherical shear layer was included. The model shows the straited structure of the Jovian surface as the outflow of convective cells having the shape of axisymmetric rolls extended along the axis of rotation in the meridional direction. Depth of the layer was found to be of the order of 1000 kilometers.

Yavorskaya, I. M.↗
NASA NTRS1978

Laser velocimeter survey about a NACA 0012 wing at low angles of attack

An investigation was conducted in the Langley V/STOL tunnel with a laser velocimeter to obtain measurements of airflow velocities about a wing at low angles of attack. The applicability of the laser velocimeter technique for this purpose in the V/STOL tunnel was demonstrated in this investigation with measurement precision bias calculated at -1.33 percent to 0.91 percent and a random uncertainty calculated at + or - 0.47 percent. Free stream measurements were obtained with this device and compared with velocity calculations from pitot static probe data taken near the laser velocimeter measurement location. The two measurements were in agreement to within 1 percent. Velocity measurement results about the centerline at 0.6 degrees angle of attack were typically those expected. At 4.75 degrees, the velocity measurements indicated that a short laminar separation bubble existed near the leading edge with an oscillating shear layer.

Hoad, D. R.↗
NASA NTRS1978

Noise characteristics of upper surface blown configurations: Summary

A systematic experimental program was conducted to develop a data base for the noise and related flow characteristics of upper surface blown configurations. The effect of various geometric and flow parameters was investigated experimentally. The dominant noise was identified from the measured flow and noise characteristics to be generated downstream of the trailing edge. The possibilities of noise reduction techniques were explored. An upper surface blown (USB) noise prediction program was developed to calculate noise levels at any point and noise contours (footprints). Using this noise prediction program and a cruise performance data base, aircraft design studies were conducted to integrate low noise and good performance characteristics. A theory was developed for the noise from the highly sheared layer of a trailing edge wake. Theoretical results compare favorably with the measured noise of the USB model.

Reddy, N. N.↗
NASA NTRS1978

Noise characteristics of upper surface blown configurations: Analytical Studies

Noise and flow results of upper surface blown configurations were analyzed. The dominant noise source mechanisms were identified from experimental data. From far-field noise data for various geometric and operational parameters, an empirical noise prediction program was developed and evaluated by comparing predicted results with experimental data from other tests. USB aircraft compatibility studies were conducted using the described noise prediction and a cruise performance data base. A final design aircraft was selected and theory was developed for the noise from the trailing edge wake assuming it as a highly sheared layer.

Reddy, N. N.↗
NASA NTRS1978

Computation of three-dimensional nozzle-exhaust flow fields with the GIM code

A methodology is introduced for constructing numerical analogs of the partial differential equations of continuum mechanics. A general formulation is provided which permits classical finite element and many of the finite difference methods to be derived directly. The approach, termed the General Interpolants Method (GIM), can combined the best features of finite element and finite difference methods. A quasi-variational procedure is used to formulate the element equations, to introduce boundary conditions into the method and to provide a natural assembly sequence. A derivation is given in terms of general interpolation functions from this procedure. Example computations for transonic and supersonic flows in two and three dimensions are given to illustrate the utility of GIM. A three-dimensional nozzle-exhaust flow field is solved including interaction with the freestream and a coupled treatment of the shear layer. Potential applications of the GIM code to a variety of computational fluid dynamics problems is then discussed in terms of existing capability or by extension of the methodology.

Spradley, L. W.↗
NASA NTRS1978

Symmetrical and asymmetrical separations about a yawed cone

Three dimensional flow separations about a circular cone were investigated in the Mach number range 0.6 - 1.8. The cone was tested in the Ames 1.8 by 1.8 m wind tunnel at Reynolds numbers based on the cone length from 4,500,000 to 13,500,000 under nominally zero heat transfer conditions. Results indicate that: (1) the lee-side separated flow develops from initially symmetrically disposed and near-conical separation lines at angle of incidence/cone semiangle equal to approximately 1, with the free shear layers eventually rolling up into tightly coiled vortices at all Mach numbers; (2) the onset of asymmetry of the lee-side separated flow about the mean pitch plane is sensitive to Mach number, Reynolds number, and the nose bluntness; and (3) as the Mach number is increased beyond 1.8, the critical angle of incidence for the onset of asymmetry increases until at about M = 2.75 there is no longer any significant side force development.

Peake, D. J.↗
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.↗
NASA NTRS1977

NO-NO2 measurements in a methane-fueled swirl-stabilized combustor

Exhaust plane measurements of NO and NO2 emissions from a methane-fueled swirl-stabilized combustor are reported. Samples were obtained by water-cooled probes and analyzed by chemiluminescent and UV absorption techniques. The combustor consists of two confined concentric jets having swirl. The inner jet flows premixed fuel and air, the outer jet is air. Variable outer jet swirl allows operation with jets swirling either in the same or opposite directions (co- or counter-swirl), and the combustion is stabilized by the resulting recirculation zone formed on the combustor centerline. Swirl conditions strongly affect the NOx emissions because of the influence of swirl on the combustion process. In the co-swirl conditions, the inner flow reaches high temperatures, and the correspondingly high NOx emissions are primarily NO. Under counter-swirl conditions much lower values of total NO are found, and these emissions are almost entirely NO2. In this case vigorous mixing in the inter-jet shear layer leads to severe flame quenching and lower temperatures. Formation of NO2 is associated with quenching processes in the combustor and is thought to be formed via NO oxidation by HO2 free radicals.

Oven, M. J.↗
NASA NTRS1978

Sound production in a moving stream

Jet noise is modeled by particle-attached quadrupoles convected with the velocity of the actual fluid but positioned near a hypothetical instability-free vortex sheet. The strength of each quadrupole is Lighthill's stress tensor per unit mass. The work of Mani (1976) has shown that this type of model agrees well with experiment, and the present work establishes some of the equivalent sources needed for an exact analogy. The instability waves of the shear layer, as they grow into turbulence, are heard as sound that builds up as a precursor of the main turbulence-driven field. The circular compact jet is examined in some detail, and it is found that when the jet is very light it can provide a waveguide in which the effects of source activity persist for some time but eventually leak out as sound. This interaction greatly distorts the free field characteristics of the turbulent sources, so that Reynolds-stress-induced waves have an intensity that scales with the fourth power of jet velocity.

Dowling, A. P.↗
NASA NTRS1978

The free jet as a simulator of forward velocity effects on jet noise

A thorough theoretical and experimental study of the effects of the free-jet shear layer on the transmission of sound from a model jet placed within the free jet to the far-field receiver located outside the free-jet flow was conducted. The validity and accuracy of the free-jet flight simulation technique for forward velocity effects on jet noise was evaluated. Transformation charts and a systematic computational procedure for converting measurements from a free-jet simulation to the corresponding results from a wind-tunnel simulation, and, finally, to the flight case were provided. The effects of simulated forward flight on jet mixing noise, internal noise and shock-associated noise from model-scale unheated and heated jets were established experimentally in a free-jet facility. It was illustrated that the existing anomalies between full-scale flight data and model-scale flight simulation data projected to the flight case, could well be due to the contamination of flight data by engine internal noise.

Ahuja, K. K.↗
NASA NTRS1979

Attenuation of sound in a low Mach number nozzle flow

The energy conversion mechanisms which govern the emission of low frequency sound from an axisymmetric jet pipe of arbitrary nozzle contraction ratio in the case of low Mach number nozzle flow are discussed. The energy of the incident sound which flows through the nozzle is used to maintain two distinct characteristic disturbances in the exterior fluid. First, there is the emitted radiation which has the directivity equivalent to that of a monopole-dipole combination. Second, essentially incompressible vortex waves are induced on the jet by vortex shedding from the lip of the nozzle and may involve the excitation of instability modes. Two linearized analytical models are examined to determine the partition of the emitted energy between the radiation field and the vortex waves. One of these is an exact linear theory in which the jet boundary is treated as a vortex sheet. The second model assumes that the width of the mean shear layer of the jet cannot be neglected. The results are discussed with reference to recent nozzle attenuation measurements.

Howe, M. S.↗
NASA NTRS1979

Space shuttle orbiter trimmed center-of-gravity extension study. Volume 3: Impact of retrofits for center-of-gravity extension on orbiter thermal-protection system

Heat transfer studies were conducted at Mach 10.3 on space shuttle orbiter models with the S-2 fillet and C-4 canard retrofit moldlines which were generated in aerodynamic and system design studies to increase the allowable c.g. range of the orbiter. Areas of orbiter most strongly affected were the sides where a shear layer which separated along the wing leading edge impinged. Analytical studies of the heating effect on the thermal-protection system were made which indicated that scar weight on the orbiter sides due to allowances for retrofits of the S-2 fillet and C-4 canard is small (less than about 90 kg (200 lbs) in comparison to the total weight of the retrofit).

Dunavant, J. C.↗
NASA NTRS1979

Fluid dynamic problems associated with air-breathing propulsive systems

A brief account of research activities on problems related to air-breathing propulsion is made in this final report for the step funded research grant NASA NGL 14-005-140. Problems include the aircraft ejector-nozzle propulsive system, nonconstant pressure jet mixing process, recompression and reattachment of turbulent free shear layer, supersonic turbulent base pressure, low speed separated flows, transonic boattail flow with and without small angle of attack, transonic base pressures, Mach reflection of shocks, and numerical solution of potential equation through hodograph transformation.

Chow, W. L.↗
NASA NTRS1979

Supersonic burning in separated flow regions

Activities reported include: (1) the construction of a thermocouple with a protective coating or sheath for obtaining reliable temperature measurements of gases in the base region; (2) the construction of a multiposition back step plate for trough tests for step sizes 0.63 cm and 0.25 cm; and (3) flow pattern studies with the 6.35 cm trough to determine the complex flow resulting when a shear layer reattaches in a corner. Reliable ignition and stable burning were achieved at Mach = 2 for the 0.63 cm trough. Photographs of side wall oil streaks for M=2 flow, and some static and pitot pressure results at M = 3 are included.

Zumwalt, G. W.↗
NASA NTRS1979

Effect of grazing flow on the acoustic impedance of Helmholtz resonators consisting of single and clustered orifices

A semiempirical fluid mechanical model is derived for the acoustic behavior of thin-walled single orifice Helmholtz resonators in a grazing flow environment. The incident and cavity sound fields are connected in terms of an orifice discharge coefficient whose values are determined experimentally using the two-microphone method. Measurements show that at high grazing flow speeds, acoustical resistance is almost linearly proportional to the grazing flow speed and almost independent of incident sound pressure. The corresponding values of reactance are much smaller and tend towards zero. For thicker-walled orifice plates, resistance and reactance were observed to be less sensitive to grazing flow as the ratio of plate thickness to orifice diameter increased. Loud tones were observed to radiate from a single orifice Helmholtz resonator due to interaction between the grazing flow shear layer and the resonator cavity. Measurements showed that the tones radiated at a Strouhal number equal to 0.26. The effects of grazing flow on the impedance of Helmholtz resonators consisting of clusters of orifices was also studied. In general, both resistance and reaction were found to be virtually independent of orifice relative spacing and number. These findings are valid with and without grazing flow.

Hersch, A. S.↗