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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 397 records · Page 22
All sourcesNASA NTRSDOE OSTI
NASA NTRS1977

Vortices induced in a stagnation region by wakes - Their incipient formation and effects on heat transfer from cylinders

Horseshoe-like vortices, induced by wakes in the stagnation region of bluff bodies, are proposed as an efficient mechanism for augmentation of convective heat transfer. The vortex 'flow module' induced by single or multiple wakes, which had not been observed previously, was first documented and the resulting flow field was studied using various visualization techniques and hot-wire anemometry. In an attempt to understand the driving force behind this flow module, the conditions at which incipient formation of the vortices occurs were investigated. Existence of such a threshold is essential and was hitherto an open question in analytical studies of stability of flow in stagnation region. Finally, effects of the flow module on heat transfer from a cylinder were measured.

Nagib, H. M.↗
NASA NTRS1977

Measurements in the turbulent boundary layer with slot injection of helium

Hot-wire anemometry and digital techniques are used to develop time series for the streamwise and transverse velocity components and for the mass fraction of helium in the low-speed turbulent boundary layer of air involving the slot injection of helium. Profiles are developed at several streamwise stations. In the present contribution the data are presented principally in terms of conventional, unconditioned averages. It is found that the mean velocity and concentration profiles develop in the downstream direction in the expected fashion but that the intensities of the velocity, concentration, and density fluctuations increase sharply downstream of the slot and peak in the region where the mixing region from the splitter plate impinges on the wall. Close to the wall where the helium concentration is relatively high counterfluxes of helium are found.

Larue, J. C.↗
NASA NTRS1977

Active control of spacecraft charging on ATS-5 and ATS-6

Effects on spacecraft ground potential of active emission of charged particles are being investigated through experiments using the ATS-5 and ATS-6 spacecraft. Each spacecraft is equipped with ion engine neutralizers which emit low energy charged particles. Despite great differences in design between the two spacecraft, they attain similar potentials in similar environments. Therefore, effects on spacecraft potential of neutralizer operations can be used to compare the effects of operating the two different neutralizers (hot wire filament and plasma bridge). The neutralizers on both spacecraft were operated in eclipse. Results of these operations are presented and spacecraft responses compared.

Purvis, C. K.↗
NASA NTRS1977

Acoustics-turbulence interaction

An investigation of the instability frequency was undertaken. Measurements revealed that the hot wire probe induces and sustains stable upstream oscillation of the free shear layer. The characteristics of the free shear layer tone are found to be different from the slit jet wedge edgetone phenomenon. The shear tone induced by a plane wedge in a plane free shear layer was then examined in order to further document the phenomenon. The eigenvalues and eigenfunctions of the tone fundamental show agreement with the spatial stability theory. A comprehensive summary of the results is also included.

Hussain, A. K. M. F.↗
NASA NTRS1977

Experimental clean combustor program: Turbulence characteristics of compressor discharge flows

The results of turbulence measurements at the entrance to the diffuser duct of a large gas turbine are presented. Hot film and hot wire measurements were conducted over a compressor discharge temperature range of 450K to 608K. It was found that the turbulent intensity at the I.D. and midspan locations increases gradually from 6 + or - 1 percent at idle to 7 + or - 1 percent at approach; the turbulent intensity at the O.D. location increases from 7.5 + or - 0.5 percent at idle to 15 + or - 0.5 percent at approach. The energy in the velocity waves is uniformly distributed over a 0.1 to 5 kHz bandwidth, and the cut-off frequency is not a strong function of the engine operation. The axial length of the Fourier components within this bandwidth varies from 0.021 to 1.05m. The turbulence near the diffuser O.D. is of sufficient amplitude and scale to affect the flow to the front end sections of the burner.

Follansbee, P. S.↗
NASA NTRS1978

Dynamic stall experiments on the NACA 0012 airfoil

The flow over a NACA 0012 airfoil undergoing large oscillations in pitch was experimentally studied at a Reynolds number of and over a range of frequencies and amplitudes. Hot-wire probes and surface-pressure transducers were used to clarify the role of the laminar separation bubble, to delineate the growth and shedding of the stall vortex, and to quantify the resultant aerodynamic loads. In addition to the pressure distributions and normal force and pitching moment data that have often been obtained in previous investigations, estimates of the unsteady drag force during dynamic stall have been derived from the surface pressure measurements. Special characteristics of the pressure response, which are symptomatic of the occurrence and relative severity of moment stall, have also been examined.

Mcalister, K. W.↗
NASA NTRS1977

Mean Velocity, Turbulence Intensity and Turbulence Convection Velocity Measurements for a Convergent Nozzle in a Free Jet Wind Tunnel. Comprehensive Data Report

The effect of flight on the mean flow and turbulence properties of a 0.056m circular jet were determined in a free jet wind tunnel. The nozzle exit velocity was 122 m/sec, and the wind tunnel velocity was set at 0, 12, 37, and 61 m/sec. Measurements of flow properties including mean velocity, turbulence intensity and spectra, and eddy convection velocity were carried out using two linearized hot wire anemometers. This report contains the raw data and graphical presentations. The final technical report includes a description of the test facilities, test hardware, along with significant test results and conclusions.

Mccolgan, C. J.↗
NASA NTRS1978

Mean velocity, turbulence intensity and turbulence convection velocity measurements for a convergent nozzle in a free jet wind tunnel

The effect of light on the mean flow and turbulence properties of a 0.056 m circular jet were determined in a free jet wind tunnel. The nozzle exit velocity was 122 m/sec, and the wind tunnel velocity was set at 0, 12, 37, and 61 m/sec. Measurements of flow properties including mean velocity, turbulence intensity and spectra, and eddy convection velocity were carried out using two linearized hot wire anemometers. Normalization factors were determined for the mean velocity and turbulence convection velocity.

Mccolgan, C. J.↗
NASA NTRS1976

USB flow characteristics related to noise generation

The effects of nozzle and flap geometry on upper surface blown flow field characteristics related to noise generation were examined experimentally using static models. Flow attachment and spreading characteristics were observed using flow visualization techniques. Velocity and turbulence profiles in the trailing edge wake were measured using hot-wire anemometry, and the effects of the geometric variables on peak velocity and turbulence intensity were determined. It is shown that peak trailing edge velocity is a function of the ratio of flow length to modified hydraulic diameter.

Brown, W. H.↗
NASA NTRS1978

Measurement of the turbulence intensity behind a two-dimensional cascade and in a three-stage axial blower

Turbulence intensity (Tu) measurements were made in two-dimensional and rotating cascades of blades in a low-speed cascade wind tunnel using hot-wire probes as sensors. The local Tu at Re = 1.6x100000 was determined in the wake zone behind a two-dimensional cascade. Then the values were recomputed for a rotating cascade, giving a mean turbulence intensity of 6.5% at 1/10 chord downstream and 2.9% at one chord. Fans were used for measurements on the rotating cascade. Re was equal to 7x100000. Frequency analysis was employed to separate the actual Tu of the entry flow from the effects caused by interaction with the rotor blades, showing that the true Tu increased from a few tenths of a percent to 6.6% in the 1st rotor, and from 7.2 to 9.3% in the 2d rotor. The Tu behind the 3d rotor was equal to 8.9%.

Kiock, R.↗
NASA NTRS1978

Measurements of noise produced by flow past lifting surfaces

Wind tunnel studies have been conducted to determine the specific locations of aerodynamic noise production within the flow field about various lifting-surface configurations. The models tested included low aspect ratio shapes intended to represent aircraft flaps, a finite aspect ratio NACA 0012 wing, and a multi-element wing section consisting of a main section, a leading edge flap, and dual trailing edge flaps. Turbulence was induced on the models by surface roughness. Lift and drag were measured for the flap models. Hot-wire anemometry was used for study of the flap-model vortex roll-up. Apparent noise source distributions were measured by use of a directional microphone system, located outside the tunnel, which was scanned about the flow region to be analyzed under computer control. These distributions exhibited a diversity of pattern, suggesting that several flow processes are important to lifting-surface noise production. Speculation concerning these processes is offered.

Kendall, J. M.↗
NASA NTRS1978

Wall region of a relaxing three-dimensional incompressible turbulent boundary layer

A three-dimensional turbulent boundary layer relaxing behind a transverse hump (shaped as a 30-deg swept 5-ft chord wing-type model) was studied in a low-speed wind tunnel. Data obtained with hot-wire probes showed that the apparent dimensionless velocity profiles in the viscous sublayer prevail universally; evidence for wall similarity in the relaxing flow field was confirmed in the form of a log law. An unusual region of slightly decreasing cross-flow angle was found in collateral regions, and a near-wall noncollateral flow was posited. Streamwise relaxation of the mean flow field was also investigated.

Hebbar, K. S.↗
NASA NTRS1979

Exploratory investigation of the effect of porous surfaces on hypersonic turbulent boundary layers

Four different test surfaces were studied to determine the effect of porous walls on the characteristics of a hypersonic turbulent flat-plate boundary layer. The investigation was an attempt to decrease the surface shear of the boundary layer by transmitting fluctuating pressure energy through the wall and absorbing it in a cavity beneath the wall. Pitot surveys were made at two locations, schlieren photographs of the boundary layer were taken, and hot-wire measurements in the flow above the boundary layer were made to determine whether the surfaces affected the turbulent boundary layer. Neither an increase nor a decrease in surface shear or boundary-layer growth was detected. Tabulations of the pitot data are included.

Watson, R. D.↗
NASA NTRS1979

Study of mean- and turbulent-velocity fields in a large-scale turbine-vane passage

Laser-Doppler velocimetry, and to a lesser extent hot-wire anemometry, were employed to measure three components of the mean velocity and the six turbulent stresses at four planes within the turbine inlet-guide-vane passage. One variation in the turbulent inlet boundary layer thickness and one variation in the blade aspect ratio (span/axial chord) were studied. A longitudinal vortex (passage vortex) was clearly identified in the exit plane of the passage for the three test cases. The maximum turbulence intensities within the longitudinal vortex were found to be on the order of 2 to 4 percent, with large regions appearing nonturbulent. Because a turbulent wall boundary layer was the source of vorticity that produced the passage vortex, these low turbulence levels were not anticipated. For the three test cases studied, the lateral velocity field extended significantly beyond the region of the longitudinal velocity defect. Changing the inlet boundary layer thickness produced a difference in the location, the strength, and the extent of the passage vortex. Changing the aspect ratio of the blade passage had a measurable but less significant effect. The experiment was performed in a 210 mm pitch, 272 mm axial chord model in low speed wind tunnel at an inlet Mach number of 0.07.

Bailey, D. A.↗
NASA NTRS1979

Structure of the Turbulent Separated Flow Around a Stalled Airfoil

Hot-wire measurements were made in the boundary layer, the separated region, and the near wake for flow past a NACA 4412 airfoil at maximum lift. The Reynolds number based on chord was 1,500,000. Special care was taken to achieve a two-dimensional mean flow. Data were obtained at several thousand locations in the flow field. These data include intermittency, two components of mean velocity, and mean values for three double, four triple, and five quadruple products of two velocity fluctuations. No information was obtained about the third (spanwise) velocity component. Smoothing and interpolating routines were used to determine intermittency, two components of mean velocity, and mean values of three double, four triple, and five quadruple products of two velocity fluctuations on a fine rectangular mesh aligned with the airfoil chord. The data are presented in contour plots, in three-dimensional plots, and in tabular form. The format used to store the experimental data in digital form is described and a computer program which illustrates how this data can be accessed is presented.

Wadcock, A. J.↗
NASA NTRS1979

Full-coverage film cooling: 3-dimensional measurements of turbulence structure and prediction of recovery region hydrodynamics

Hydrodynamic measurements were made with a triaxial hot-wire in the full-coverage region and the recovery region following an array of injection holes inclined downstream, at 30 degrees to the surface. The data were taken under isothermal conditions at ambient temperature and pressure for two blowing ratios: M = 0.9 and M = 0.4. Profiles of the three main velocity components and the six Reynolds stresses were obtained at several spanwise positions at each of the five locations down the test plate. A one-equation model of turbulence (using turbulent kinetic energy with an algebraic mixing length) was used in a two-dimensional computer program to predict the mean velocity and turbulent kinetic energy profiles in the recovery region. A new real-time hotwire scheme was developed to make measurements in the three-dimensional turbulent boundary layer over the full-coverage surface.

Yavuzkurt, S.↗
NASA NTRS1979

Turbulence characteristics of compressor discharge flows

Turbulence measurements were conducted in a large gas turbine engine (JT9D) at the entrance to the diffuser duct, joining the compressor discharge to the combustor inlet. Hot film probe and hot wire probe measurements were obtained at temperatures from 450K (350F) (idle) to 608K (635F) (rich approach). At I.D. (25 percent span) and mid-span locations, the turbulence intensity increased slightly from 6 + or - percent at idle condition to 7 or - 1 percent at rich approach. At O.D. (75 percent span) the turbulent intensity increased more rapidly, from 7.5 + or - 0.5 percent at idle to 15 + or - 0.5 percent at rich approach. The spectra showed turbulent energy distributed uniformly over a 0.1 to 5 KHz bandwidth (down 3db) at all operating conditions, corresponding to random turbulence with velocity wave lengths of 2 cm to 1 meter travelling at the mean velocity of 100 m/sec. Tests results are given in tables and graphs.

Grant, H. P.↗
NASA NTRS1979

Longitudinal vortices in a transitioning boundary layer

Naturally occurring spanwise variations of the streamwise velocity component, characteristic of longitudinal vortices embedded in a transitioning boundary layer were explored using hot-wire anemometers. A vibrating ribbon introduced stable or unstable Tollmien-Schlichting waves into the laminar boundary layer. These damped or growing disturbances always developed a strong three dimensional pattern even though no spanwise perturbations were artificially induced. Changing the radius of the leading edge and other modifications to the flat plate, wind tunnel and boundary layer did not alter the spanwise wavelength of the vortices.

Anders, J. B.↗