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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 1,171 records · Page 65
All sourcesNASA NTRSDOE OSTI
NASA NTRS1974

The development of experimental techniques for the study of helicopter rotor noise

The features of existing wind tunnels involved in noise studies are discussed. The acoustic characteristics of the MIT low noise open jet wind tunnel are obtained by employing calibration techniques: one technique is to measure the decay of sound pressure with distance in the far field; the other technique is to utilize a speaker, which was calibrated, as a sound source. The sound pressure level versus frequency was obtained in the wind tunnel chamber and compared with the corresponding calibrated values. Fiberglas board-block units were installed on the chamber interior. The free field was increased significantly after this treatment and the chamber cut-off frequency was reduced to 160 Hz from the original designed 250 Hz. The flow field characteristics of the rotor-tunnel configuration were studied by using flow visualization techniques. The influence of open-jet shear layer on the sound transmission was studied by using an Aeolian tone as the sound source. A dynamometer system was designed to measure the steady and low harmonics of the rotor thrust. A theoretical Mach number scaling formula was developed to scale the rotational noise and blade slap noise data of model rotors to full scale helicopter rotors.

Widnall, S. E.↗
NASA NTRS1975

Vortex shedding from a blunt trailing edge with equal and unequal external mean velocities

A flow visualization study showed that strong Karman vortices are developed behind the blunt trailing edge of a plate when the free stream velocities over both surfaces are equal. These vortices tend to disappear when the surface velocities are unequal. This observation provided an explanation for the occurrence and disappearance of the lip noise often present in coaxial jets. Vortex formation and lip noise occurred at a Strouhal number of about 0.2 based on the lip thickness and the average of the external steady-state velocities. Results from theoretical calculations of the vortex formation, based on an inviscid, incompressible analysis of the motion of point vortices, were in good agreement with the experimental observations.

Brinich, P. F.↗
NASA NTRS1975

The effect of wing dihedral and section suction distribution on vortex bursting

Eleven semi-span wing models were tested in the 1/8-scale model of the Langley V/STOL tunnel to qualitatively study vortex bursting. Flow visualization was achieved by using helium filled soap bubbles introduced upstream of the model. The angle of attack range was from 0 deg to 45 deg. The results show that the vortex is unstable, that is, the bursting point location is not fixed at a given angle of attack but moves within certain bounds. Upstream of the trailing edge, the bursting point location has a range of two inches; downstream, the range is about six inches. Anhedral and dihedral appear to have an insignificant effect on the vortex and its bursting point location. Altering the section suction distribution by improving the triangularity generally increases the angle of attack at which vortex bursting occurs at the trailing edge.

Washburn, K. E.↗
NASA NTRS1975

The development of experimental techniques for the study of helicopter rotor noise

The acoustic characteristics of a low noise open jet wind tunnel have been obtained by employing two different calibration techniques. One technique is to measure the decay of sound pressure with distance in far field. The other technique is to utilize a calibrated speaker as a sound source. The sound pressure level vs frequency was obtained in the wind tunnel testing chamber and compared with the corresponding calibrated values. The results of two different techniques agree with each other. Fiberglass board-block units were installed on the testing chamber interior. The free field was increased significantly after this treatment and the testing chamber cut-off frequency was reduced to 160 Hz from the original designed 250 Hz. The flow field characteristics of the rotor-tunnel configuration were studied by using flow visualization techniques.

Harris, W. L.↗
NASA NTRS1975

Experimental study of the effect of span loading on aircraft wakes

Measurements were made in the NASA-Ames 40- by 80-Foot Wind Tunnel of the rolling moment induced on a following model in the wake 13.6 spans behind a subsonic transport model for a variety of trailing edge flap settings of the generator. It was found that the rolling moment on the following model was reduced substantially, compared to the conventional landing configuration, by reshaping the span loading on the generating model to approximate a span loading, found in earlier studies, which resulted in reduced wake velocities. This was accomplished by retracting the outboard trailing edge flaps. It was concluded, based on flow visualization conducted in the wind tunnel as well as in a water tow facility, that this flap arrangement redistributes the vorticity shed by the wing along the span to form three vortex pairs that interact to disperse the wake.

Corsiglia, V. R.↗
NASA NTRS1975

Wing Tip Vortex Drag

Optimization of L/D through minimizing induced drag through a detailed flow study together with force, pressure and vorticity measurements is considered. Flow visualization with neutral helium bubbles provides an excellent means of observing the effects of configuration changes.

Muirhead, V. U.↗
NASA NTRS1975

Design and preliminary tests of a blade tip air mass injection system for vortex modification and possible noise reduction on a full-scale helicopter rotor

Full-scale tests were conducted on the Langley helicopter rotor test facility as part of a study to evaluate the effectiveness of a turbulent blade tip air mass injection system in alleviating the impulsive noise (blade slap) caused by blade-vortex interaction. Although blade-slap conditions could not be induced during these tests, qualitative results from flow visualization studies using smoke showed that the differential velocity between the jet velocity and the rotor tip speed was a primary parameter controlling the vortex modification.

Pegg, R. J.↗
NASA NTRS1975

An investigation in MSFC 14-inch TWT to determine the static stability characteristics of 0.004-scale model (74-OTS) space shuttle vehicle 5 configuration (IA33), volume 1

Wind tunnel tests were conducted to: (1) determine the static stability characteristics of the Shuttle Vehicle 5 configuration; (2) determine the effect on the Vehicle 5 aerodynamic characteristics of External Tank (ET) and Solid Rocket Booster (SRB) nose shape, SRB nozzle shroud flare angle, orbiter to tank fairing, and sting location; (3) provide flow visualization using thin film oil paint; and (4) determine rudder, body flap, and inboard and outboard elevon hinge moments. The mated vehicle model was mounted in three different ways: (1) the orbiter mounted on the balance with the SRB's attached to the tank and the tank in turn attached to the orbiter; (2) the tank mounted on the balance (with the sting protruding through the tank base) with the SRB's and orbiter attached to the tank, and (3) with the tank mounted on the balance and the balance in turn supported by a forked sting entering the nozzle of each SRB, extending forward into the SRB's then crossing over to the tank to provide a balance socket. Data were obtained for Mach numbers from 0.6 through 4.96 at angles-of-attack and -sideslip from -10 to 10 degrees.

Allen, E. C.↗
NASA NTRS1975

Intrepretation of surface features and surface processes on Mars

Eolian erosion and deposition on earth was studied in order to interpret the eolian land forms of Mars. Emphasis of the wind tunnel studies was on the flow field around models of eolian forms. Areas of the wind tunnel studies include: simulation of the atmospheric boundary layer; velocity profile measurements around different models in the desert boundary layer, and estimating shear stress distributions on the model surfaces; flow visualization techniques; streamline mapping using tuft photographs; and roughness contrasts.

Gad-El-hak, M.↗
NASA NTRS1975

Heat-flux gage measurements on a flat plate at a Mach number of 4.6 in the VSD high speed wind tunnel, a feasibility test (LA28)

The feasibility of employing thin-film heat-flux gages was studied as a method of defining boundary layer characteristics at supersonic speeds in a high speed blowdown wind tunnel. Flow visualization techniques (using oil) were employed. Tabulated data (computer printouts), a test facility description, and photographs of test equipment are given.

Source record↗
NASA NTRS1975

An investigation of the 0.0091 scale External Tank ogive nose (MSFC model 470) in the MSFC 14 inch TWT to determine the pressure distribution around the External Tank Nose (TA3F), volume 1

The model tested was a 0.0091 scale representation of the ogive nose section of the External Tank with nose cap and lightning rod and protuberances. Pressure distribution around the nose cap was determined. Pressure data were also obtained along the ogive nose. Data were obtained over an angle of attack range of + or -5 degrees and over a Mach number range of .6 to 4.96. The Reynolds number per unit length (ft.) ranged from 4.1 million to 4.96 million. There were 22 pressure ports in a single row. Circumferential positions of 0, 22.5, 45, 67.5 and 90 degrees were simulated by rotating the model. The LO2 feed line and LO2 recirculation line were simulated. The effects of the nose spike were investigated over a range of Mach numbers. The data will be useful for venting analyses. Photographs showing flow visualization of the test configuration are given.

Ramsey, P. E.↗
NASA NTRS1975

Investigation of rotor blade element airloads for a teetering rotor in the blade stall regime (second wind tunnel test)

A test was conducted in the NASA-Ames 7 x 10 ft low speed wind tunnel on a seven-foot diameter model of a teetering rotor. The objectives of the test were: (1) acquire pressure data for correlation with laser and flow visualization measurements; (2) explore rotor propulsive force limits by varying the advance ratio at constant lift and propulsive force coefficients; (3) obtain additional data to define the differences between teetering and articulated rotors; and (4) verify the acceleration sensitivity of experimental transducers. Results are presented.

Dadone, L. U.↗
NASA NTRS1974

RSRA sixth scale wind tunnel test

The sixth scale model of the Sikorsky/NASA/Army rotor systems research aircraft was tested in an 18-foot section of a large subsonic wind tunnel for the purpose of obtaining basic data in the areas of performance, stability, and body surface loads. The model was mounted in the tunnel on the struts arranged in tandem. Basic testing was limited to forward flight with angles of yaw from -20 to +20 degrees and angles of attack from -20 to +25 degrees. Tunnel test speeds were varied up to 172 knots (q = 96 psf). Test data were monitored through a high speed static data acquisition system, linked to a PDP-6 computer. This system provided immediate records of angle of attack, angle of yaw, six component force and moment data, and static and total pressure information. The wind tunnel model was constructed of aluminum structural members with aluminum, fiberglass, and wood skins. Tabulated force and moment data, flow visualization photographs, tabulated surface pressure data are presented for the basic helicopter and compound configurations. Limited discussions of the results of the test are included.

Flemming, R.↗
NASA NTRS1976

Vortex interactions in multiple vortex wakes behind aircraft

A flow visualization technique has been developed which allows the nature of lift-generated wakes behind aircraft models to be investigated. Several different configurations of a 0.61-m span model of a Boeing 747-type transport aircraft were tested to allow observation of typical vortex interactions and merging in multiple vortex wakes. The vortices were identified by emitting tracer dyes from selected locations on the model. Wing span loading and model attitude were found to effect both vortex motions within the wake and resulting far-field wake velocity. Landing gear deployment caused a far-field reformation of vorticity behind a model configuration which dissipated concentrated vorticity in the near-field wake. A modified landing configuration was developed which appeared to significantly alleviate the concentrated wake vorticity.

Ciffone, D. L.↗
NASA NTRS1976

Vortex shedding from a blunt trailing edge with equal and unequal external mean velocities

A flow-visualization study has shown that strong Karman vortices develop behind the blunt trailing edge of a plate when the free-stream velocities over both surfaces are equal and that the vortices tend to disappear when the surface velocities are unequal. This observation provides an explanation for the occurence and disappearance of certain discrete tones often found to be present in the noise spectra of coaxial jets. Both the vortex formation and the tones occur at a Strouhal number based on the lip thickness and the average of the external steady-state velocities of about 0.2. Results from theoretical calculations of the vortex formation, based on an inviscid incompressible analysis of the motion of point vortices, were in good agreement with the experimental observations.

Boldman, D. R.↗
NASA NTRS1976

Float-zone processing in a weightless environment

The results were reported of investigations to: (1) test the validity of analyses which set maximum practical diameters for Si crystals that can be processed by the float zone method in a near weightless environment, (2) determine the convective flow patterns induced in a typical float zone, Si melt under conditions perceived to be advantageous to the crystal growth process using flow visualization techniques applied to a dimensionally scaled model of the Si melt, (3) revise the estimates of the economic impact of space produced Si crystal by the float zone method on the U.S. electronics industry, and (4) devise a rational plan for future work related to crystal growth phenomena wherein low gravity conditions available in a space site can be used to maximum benefit to the U.S. electronics industry.

Fowle, A. A.↗
NASA NTRS1976

Pressure distribution on a 1- by 3-meter semispan wing at sweep angles from 0 deg to 40 deg in subsonic flow

A 1- by 3-meter semispan wing of taper ratio 1.0 with NACA 0012 airfoil section contours was tested in the Langley V/STOL tunnel to measure the pressure distribution at five sweep angles, 0 deg, 10 deg, 20 deg, 30 deg, and 40 deg, through an angle-of-attack range from -6 deg to 20 deg. The pressure data are presented as plots of pressure coefficients at each static-pressure tap location on the wing. Flow visualization wing-tuft photographs are also presented for a wing of 40 deg sweep. A comparison between theory and experiment using two inviscid theories and a viscous theory shows good agreement for pressure distributions, normal forces, and pitching moments for the wing at 0 deg sweep.

Yip, L. P.↗
NASA NTRS1976

Aerodynamic validation of a SCAR design

Wind tunnel test of the McDonnell Douglas Supersonic Cruise Aircraft, designed for a cruise Mach number of 2.2, was conducted in the NASA Ames Unitary Plan Wind Tunnels. Extensive force, pressure, and flow visualization data were obtained over a Mach number range from 0.5 to 2.4. Comparisons between theory and measurements of both forces and pressure concentrate on the results obtained in the supersonic tunnel. Schlieren and tuft pictures are presented to help provide an understanding of the nonlinearities observed at off-design conditions.

Roensch, R. L.↗