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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 1,297 records · Page 72
All sourcesNASA NTRSDOE OSTI
NASA NTRS1986

Natural laminar flow flight experiments on a turbine engine nacelle fairing

Flight experiments are being conducted with the objective to investigate the interactions between acoustic disturbances and laminar flow in the flight environment. In the experiments, the laminar boundary layer on the nacelles will be exposed to discrete and broadband external noises, and the effect of varying noise levels and frequencies on the stability of the laminar flow will be studied. The present paper provides an overview of the complete project and a status report on the results which have been obtained. The flight experiment is conducted with the aid of a modified research aircraft. The phase I flight tests are concerned with a quick and simple determination of natural laminar flow (NLF) behavior on an engine nacelle. Attention is given to instrumentation, the acoustic noise source, flow visualization, and the test results.

Obara, C. J.↗
NASA NTRS1986

Non-linear effects in finite amplitude wave propagation through ducts and nozzles

In this paper an extensive study of non-linear effects in finite amplitude wave propagation through ducts and nozzles is summarized. Some results from earlier studies are included to illustrate the non-linear effects on the transmission characteristics of duct and nozzle terminations. Investigaiations, both experimental and analytical, were carried out to determine the magnitudes of the effects for high intensity pulse propagation. The results derived from these investigations are presented in this paper. They include the effect of the sound intensity on the acoustic characteristics of duct and nozzle terminations, the extent of the non-linearities in the propagation of high intensity impulsive sound inside the duct and out into free field, the acoustic energy dissipation mechanism at a termination as shown by flow visualizations, and quantitative evaluations by experimental and analytical means of the influence of the intensity of a sound pulse on the dissipation of its acoustic power.

Salikuddin, M.↗
NASA NTRS1986

Experimental investigation of rotorcraft hub and shaft fairing drag reduction

A wind-tunnel test was conducted to obtain data on several rotorcraft hub and shaft fairing drag reduction configurations. Aerodynamic loads and moments were acquired for each test configuration. Limited wake pressure measurements and flow visualization (tuft) photographs were obtained for some configurations. All hub and shaft fairing configurations were tested on a 1/5-scale XH-59A model fuselage. Both coaxial and single rotor configurations were tested. All rotor assemblies were modeled with nonrotating hardware. The drag reduction methods tested included cambered elliptical hub fairings, several different shaft fairings, and strakes. Test data show that significant drag reductions can be attained with certain fairing configurations. The lowest drag values for the single rotor configurations were obtained for a cambered elliptical hub fairing with a large thickness airfoil shaft fairing. The lowest coaxial configuration drag values were obtained with cambered elliptical hub fairings and a long chord intermediate shaft fairing.

Young, L. A.↗
NASA NTRS1986

Calculation of asymmetric vortex separation on slender delta wings with a vortex-sheet model

An inviscid vortex-sheet model based on the slender wing theory is developed to examine asymmetric vortex separation at zero sideslip on delta wings. It is found that multiple asymmetric vortex configurations exist at a given angle of attack. Available data on rolling moment measurements and flow visualization are used for correlation to prove the concept.

Lan, C. E.↗
NASA NTRS1986

Flowfield survey over a 75 deg swept delta wing at an angle of attack of 20.5 deg

An experimental investigation of the flowfield over a 75 deg swept delta wing at an angle of attack of 20.5 deg has been conducted. The data include pitot pressure surveys and two types of flow visualization. Surface and flowfield visualization data were obtained at Reynolds number, Rn, ranging from 0.5 to 2.0 million in increments of 0.25 million. Detailed pitot pressure surveys were made at five longitudinal stations at Rn = 0.5, 1.0, and 1.5 million in both the primary and secondary vortices. The results indicate that Reynolds number has only a minor effect on the global structure of the flowfield in the Reynolds number range that was investigated. The boundary layer transitions from laminar to turbulent at the trailing edge of the wing at Rn = 1.0 x 10 to the 6th, and the transition moves forward to x/L = 0.4 at Rn = 2.0 x 10 to the 6th. The positions of the primary vortex cores are insensitive to Reynolds number in this range; however, the lateral position of the secondary vortex core moves outboard aft of the region where the boundary layer transitions from laminar to turbulent.

Kjelgaard, S. O.↗
NASA NTRS1987

Simulation of fluid flows during growth of organic crystals in microgravity

Several counter diffusion type crystal growth experiments were conducted in space. Improvements in crystal size and quality are attributed to reduced natural convection in the microgravity environment. One series of experiments called DMOS (Diffusive Mixing of Organic Solutions) was designed and conducted by researchers at the 3M Corporation and flown by NASA on the space shuttle. Since only limited information about the mixing process is available from the space experiments, a series of ground based experiments was conducted to further investigate the fluid dynamics within the DMOS crystal growth cell. Solutions with density differences in the range of 10 to the -7 to 10 to the -4 power g/cc were used to simulate microgravity conditions. The small density differences were obtained by mixing D2O and H2O. Methylene blue dye was used to enhance flow visualization. The extent of mixing was measured photometrically using the 662 nm absorbance peak of the dye. Results indicate that extensive mixing by natural convection can occur even under microgravity conditions. This is qualitatively consistent with results of a simple scaling analysis. Quantitave results are in close agreement with ongoing computational modeling analysis.

Roberts, Gary D.↗
NASA NTRS1987

Investigation of empennage buffeting

Theoretical methods of predicting aircraft buffeting are reviewed. For the buffeting due to leading-edge vortex breakdown, a method is developed to convert test data of mean square values of fluctuating normal force to buffeting vortex strength through an unsteady lifting-surface theory and unsteady suction analogy. The resulting buffeting vortex from the leading-edge extension of an F-18 configuration is used to generate a fluctuating flow field which produces unsteady pressure distribution on the vertical tails. The root mean square values of root bending moment on the vertical tails are calculated for a rigid configuration. Results from a flow visualization and hot films study in a water tunnel facility using a 1/48 scale model of an F-18 are included in an appendix. The results confirm that the LEX vortex is the dominant forcing function of fin buffet at high angles of attack.

Lan, C. Edward↗
NASA NTRS1987

Investigation of leading-edge flap performance on delta and double-delta wings at supersonic speeds

An investigation of the aerodynamic performance of leading-edge flaps on three clipped delta and three clipped double-delta wing planforms with aspect ratios of 1.75, 2.11, and 2.50 was conducted in the Langley Unitary Plan Wind Tunnel at Mach numbers of 1.60, 1.90, and 2.16. A primary set of fullspan leading-edge flaps with similar root and tip chords were investigated on each wing, and several alternate flap planforms were investigated on the aspect-ratio-1.75 wings. All leading-edge flap geometries were effective in reducing the drag at lifting conditions over the range of wing aspect ratios and Mach numbers tested. Application of a primary flap resulted in better flap performance with the double-delta planform than with the delta planform. The primary flap geometry generally yielded better performance than the alternate flap geometries tested. Trim drag due to flap-induced pitching moments was found to reduce the leading-edge flap performance more for the delta planform than for the double-delta planform. Flow-visualization techniques showed that leading-edge flap deflection reduces crossflow shock-induced separation effects. Finally, it was found that modified linear theory consistently predicts only the effects of leading-edge flap deflection as related to pitching moment and lift trends.

Covell, Peter F.↗
NASA NTRS1987

Investigation of dynamic ground effect

An experimental investigation of dynamic ground effect was conducted in the Univ. of Kansas wind tunnel using delta wings of 60, 70, 75 deg sweep; the XB-70 wing; and the F-104A wing. Both static and dynamic tests were made. Test data were compared to other test data, including dynamic flight test data of the XB-70 and F-104A. Limited flow visualization test were conducted. A significant dynamic effect was found for highly swept delta wings.

Chang, Ray Chung↗
NASA NTRS1987

An experimental low Reynolds number comparison of a Wortmann FX67-K170 airfoil, a NACA 0012 airfoil and a NACA 64-210 airfoil in simulated heavy rain

Wind tunnel experiments were conducted on Wortmann FX67-K170, NACA 0012, and NACA 64-210 airfoils at rain rates of 1000 mm/hr and Reynolds numbers of 310,000 to compare the aerodynamic performance degradation of the airfoils and to attempt to identify the various mechanisms which affect performance in heavy rain conditions. Lift and drag were measured in dry and wet conditions, a variety of flow visualization techniques were employed, and a computational code which predicted airfoil boundary layer behavior was used. At low angles of attack, the lift degradation in wet conditions varied significantly between the airfoils. The Wortmann section had the greatest overall lift degradation and the NACA 64-210 airfoil had the smallest. At high angles of attack, the NACA 64-210 and 0012 airfoils had improved aerodynamic performance in rain conditions due to an apparent reduction of the boundry layer separation. Performance degradation in heavy rain for all three airfoils at low angles of attack could be emulated by forced boundary layer transition near the leading edge. The secondary effect occurs at time scales consistent with top surface water runback times. The runback layer is thought to effectively alter the airfoil geometry. The severity of the performance degradation for the airfoils varied. The relative differences appeared to be related to the susceptibility of each airfoil to premature boundary layer transition.

Craig, Anthony P.↗
NASA NTRS1987

Measurement of the effect of manufacturing deviations on natural laminar flow for a single engine general aviation airplane

Renewed interest in natural laminar flow (NLF) had rekindled designer concern that manufacuring deviations may destroy the effectiveness of NLF for an operational aircraft. Experiments are summarized that attemtped to measure total drag changes associated with three different wing surface conditions on an aircraft typical of current general aviation high performance singles. The speed power technique was first used in an attempt to quantify the changes in total drag. Predicted and measured boundary layer transition locations for three different wing surface conditions were also compared, using two different forms of flow visualization. The three flight test phases included: assessment of an unpainted airframe, flight tests of the same aircraft after painstakingly filling and sanding the wings to design contours, and similar measurement after this aricraft was painted. In each flight phase, transition locations were monitored using with sublimating chemicals or pigmented oil. Two-dimensional drag coefficients were estimated using the Eppler-Somers code and measured with a wake rake in a method very similar to Jones' pitot traverse method. The net change in two-dimensional drag coefficient was approximately 20 counts between the unpainted aircraft and the hand-smoothed aircraft for typical cruise flight conditions.

Source record↗
NASA NTRS1986

The influence of free-stream turbulence on separation of turbulent boundary layers in incompressible, two-dimensional flow

Experiments were conducted to determine if free-stream turbulence scale affects separation of turbulent boundary layers. In consideration of possible interrelation between scale and intensity of turbulence, the latter characteristic also was varied and its role was evaluated. Flow over a 2-dimensional airfoil in a subsonic wind tunnel was studied with the aid of hot-wire anemometry, liquid-film flow visualization, a Preston tube, and static pressure measurements. Profiles of velocity, relative turbulence intensity, and integral scale in the boundary layer were measured. Detachment boundary was determined for various angles of attack and free-stream turbulence. The free-stream turbulence intensity and scale were found to spread into the entire turbulent boundary layer, but the effect decreased as the airfoil surface was approached. When the changes in stream turbulence were such that the boundary layer velocity profiles were unchanged, detachment location was not significantly affected by the variations of intensity and scale. Pressure distribution remained the key factor in determining detachment location.

Potter, J. Leith↗
NASA NTRS1987

Implementation and validation of a wake model for vortex-surface interactions in low speed forward flight

The wake model was implemented using a VAX 750 and a Microvax II workstation. Online graphics capability using a DISSPLA graphics package. The rotor model used by Beddoes was significantly extended to include azimuthal variations due to forward flight and a simplified scheme for locating critical points where vortex elements are placed. A test case was obtained for validation of the predictions of induced velocity. Comparison of the results indicates that the code requires some more features before satisfactory predictions can be made over the whole rotor disk. Specifically, shed vorticity due to the azimuthal variation of blade loading must be incorporated into the model. Interactions between vortices shed from the four blades of the model rotor must be included. The Scully code for calculating the velocity field is being modified in parallel with these efforts to enable comparison with experimental data. To date, some comparisons with flow visualization data obtained at Georgia Tech were performed and show good agreement for the isolated rotor case. Comparison of time-resolved velocity data obtained at Georgia Tech also shows good agreement. Modifications are being implemented to enable generation of time-averaged results for comparison with NASA data.

Komerath, Narayanan M.↗
NASA NTRS1985

Free vorticity field-boundary layer conversions: Effect of boundary configuration and scale

Progress was made on further flow visualization of vortex-leading edge interaction, in conjunction with characterization of the unsteady pressure field. The range of scale of an elliptical leading edge, relative to the incident primary vortex, was determined. The scale of the incident vortex was characterized in terms of mean shear layer parameters. An overview of the interaction mechanism for the range of thin to thick leading-edges is given. The interaction mechanism corresponding to the case where the incident vortex is above the leading-edge is given for hydrogen bubble wires well upstream of and at the tip of the leading edge. A sample of the instantaneous pressure distribution for the case where the incident vortex dives beneath the edge is presented. The effect of scale of the incident vortex relative to that of the leading-edge was examined. The circulation and length scale of the incident vortices in the street are being characterized.

Rockwell, D.↗
NASA NTRS1987

Welding arc and plasma studies using real time, multipass holographic interferometry

Flow visualization of the plasma process in a welding arc is being studied with a multipass Argon ion interferometer. High speed movies at 10,000 frames per/sec are taken. The multipass interferometer and several interferograms of the plasma near the electrode of the welding are given. Digitization of the fringes is currently done by hand.

Deason, Vance↗
NASA NTRS1987

Holographic, particle imaging and data reduction at Spectron Development Laboratores

Spectron has been deeply involved in the development and use of a wide variety of particle and flow diagnostic, electro optical instruments. Holography and imaging systems have played an important role in this work, but the extraction of data from images and holograms have always presented a limit to their use. Systems and techniques were devised to speed up and automate the extraction of data from holographic and conventional interferograms, particle images and holograms, and other types of optical flow visualization techniques. An IBM/AI based image analyzer was developed that is capable of automatically analyzing many useful image types including interferograms. A key feature of this system is the low total cost of the required hardware. In the particle field work, a commercial diffraction field analyzer was adopted to the image reconstructed from a hologram. This could expand the use of holography in particle diagnostics greatly.

Trolinger, James D.↗
NASA NTRS1987

Two opposed lateral jets injected into swirling crossflow

Experiments have been conducted to obtain the time-mean and turbulent quantities of opposed lateral jets in a low speed, nonreacting flowfield. A jet-to-crossflow velocity ratio of R = 4 was used throughout the experiments, with swirl vane angles of 0 (swirler removed), 45 and 70 degrees used with the crossflow. Flow visualization techniques used were neutrally-buoyant helium-filled soap bubbles and multispark photography in order to obtain the gross flowfield characteristics. Measurements of time-mean and turbulent quantities were obtained utilizing a six-orientation single hot-wire technique. For the nonswirling case, the jets were found not to penetrate past the test-section centerline, in contrast to the single lateral jet with the same jet-to-crossflow velocity ratio. In the swirling cases, the crossflow remains in a narrow region near the wall of the test section. The opposed jets are swept from their vertical courses into spiral trajectories close to the confining walls. Extensive results are presented in r-x plane plots.

Lilley, D. G.↗
NASA NTRS1987

A drag reduction method for turbulent boundary layers

A novel method to reduce skin friction drag in a turbulent boundary layer is presented. The technique combines the beneficial effects of a longitudinally ribbed surface and suction. The streamwise grooves act as a nucleation site causing a focusing of low-speed streaks over the peaks. Suction is then applied intermittently through longitudinal slots located at selected locations along those peaks to obliterate the low-speed regions and to prevent bursting. During the first phase of the present research, selective suction from a single streamwise slot was used to eliminate either a single burst-like event or a periodic train of artificially generated bursts in laminar and turbulent boundary layers. The experiments were conducted using a flat plate towed in an 18-m water channel. Flow visualization and hot-film probe measurements were used together with pattern recognition algorithms to demonstrate the feasibility of the drag-reducing method.

Gad-El-hak, Mohamed↗