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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 289 records · Page 16
All sourcesNASA NTRSDOE OSTI
NASA NTRS1983

Effect of lead-aircraft ground-speed on self-spacing performance using a cockpit display of traffic information

A simulator investigation was conducted to determine the effect of the lead-aircraft ground-speed quantization level on self-spacing performance using a Cockpit Display of Traffic Information (CDTI). The study utilized a simulator employing cathode-ray tubes for the primary flight and navigation displays and highly augmented flight control modes. The pilot's task was to follow, and self-space on, a lead aircraft which was performing an idle-thrust profile descent to an instrument landing system (ILS) approach and landing. The spacing requirement was specified in terms of both a minimum distance and a time interval. The results indicate that the ground-speed quantization level, lead-aircraft scenario, and pilot technique had a significant effect on self-spacing performance. However, the ground-speed quantization level only had a significant effect on the performance when the lead aircraft flew a fast final approach.

Kelly, J. R.↗
NASA NTRS1984

An analytical design procedure for the determination of effective leading edge extensions on thick delta wings

An analytical design procedure for leading edge extensions (LEE) was developed for thick delta wings. This LEE device is designed to be mounted to a wing along the pseudo-stagnation stream surface associated with the attached flow design lift coefficient of greater than zero. The intended purpose of this device is to improve the aerodynamic performance of high subsonic and low supersonic aircraft at incidences above that of attached flow design lift coefficient, by using a vortex system emanating along the leading edges of the device. The low pressure associated with these vortices would act on the LEE upper surface and the forward facing area at the wing leading edges, providing an additional lift and effective leading edge thrust recovery. The first application of this technique was to a thick, round edged, twisted and cambered wing of approximately triangular planform having a sweep of 58 deg and aspect ratio of 2.30. The panel aerodynamics and vortex lattice method with suction analogy computer codes were employed to determine the pseudo-stagnation stream surface and an optimized LEE planform shape.

Farhad Ghaffari↗
NASA NTRS1984

Advanced leading edge thermal-structure concept. Direct bond reusable surface insulation to a composite structure

An advanced leading-edge concept was analyzed using the space shuttle leading edge system as a reference model. The comparison indicates that a direct-bond system utilizing a high temperature (2700 F) fibrous refractory composite insulation tile bonded to a high temperature (PI/graphite) composite structure can result in a weight savings of up to 800 lb. The concern that tile damage or loss during ascent would result in adverse entry aerodynamics if a leading edge tile system were used is addressed. It was found from experiment that missing tiles (as many as 22) on the leading edge would not significantly affect the basic force-and-moment aerodynamic coefficients. Additionally, this concept affords a degree of redundancy to a thermal protection system in that the base structure (being a composite material) ablates and neither melts nor burns through when subjected to entry heating in the event tiles are actually lost or damaged during ascent.

Riccitiello, S. R.↗
NASA NTRS1986

Holder for Tinning Microcircuit Leads

Heat-sinking tool holds microcircuits for lead tinning while protecting circuits from heat of tinning solder. Microcircuit holder dips leads in molten solder. Holder shields microcircuit from solder heat while leads immersed and absorbs heat conducted through leads. Thus keeps microcircuit relatively cool. Application tool was developed for requires tinning not closer than 0.02 in. (0.5 mm) from package body or its glass seals.

Gilbert, G. G.↗
NASA NTRS1986

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

The aerodynamic performance of leading-edge flaps on three delta double-delta wing planforms having aspect ratios of 1.75, 2.11, and 2.50, have been investigated experimentally. The wings were mounted on a generic fuselage without an inlet canopy, or a vertical tail. The Mach numbers of the flow over the wings were 1.60, 1.90 and 2.16. A primary set of full-span leading-edge flaps with similar root and tip chords were tested on each wing, and several alternate flap planforms were tested on the aspect ratio 1.75 wings. It is found that all leading edge geometries were effective in reducing drag lifting over the range of wing aspect ratios and Mach numbers tested. Greater flap performance was obtained when primary flaps were applied to the delta planform. In general, the primary flap geometry yielded better performance than the alternative geometries tested. Flow visualization techniques were found to be useful for identifying the beneficial effects of leading-edge flap deflection on flow separation as well as fuselage interference effects. Black and white photographs of the delta and double-delta planforms are provided.

Covell, P. F.↗
NASA NTRS1984

Laminar flow control leading edge glove flight test article development

A laminar flow control (LFC) flight test article was designed and fabricated to fit into the right leading edge of a JetStar aircraft. The article was designed to attach to the front spar and fill in approx. 70 inches of the leading edge that are normally occupied by the large slipper fuel tank. The outer contour of the test article was constrained to align with an external fairing aft of the front spar which provided a surface pressure distribution over the test region representative of an LFC airfoil. LFC is achieved by applying suction through a finely perforated surface, which removes a small fraction of the boundary layer. The LFC test article has a retractable high lift shield to protect the laminar surface from contamination by airborne debris during takeoff and low altitude operation. The shield is designed to intercept insects and other particles that could otherwise impact the leading edge. Because the shield will intercept freezing rain and ice, a oozing glycol ice protection system is installed on the shield leading edge. In addition to the shield, a liquid freezing point depressant can be sprayed on the back of the shield.

Pearce, W. E.↗
NASA NTRS1989

Experimental study of pressure and heating rate on a swept cylindrical leading edge resulting from swept shock wave interference

The effects of cylindrical leading edge sweep on surface pressure and heat transfer rate for swept shock wave interference were investigated. Experimental tests were conducted in the Calspan 48-inch Hypersonic Shock Tunnel at a nominal Mach number of 8, nominal unit Reynolds number of 1.5 x 10 to the 6th power per foot, leading edge and incident shock generator sweep angles of 0, 15, and 30 deg, and incident shock generator angle-of-attack fixed at 12.5 deg. Detailed surface pressure and heat transfer rate on the cylindircal leading edge of a swept shock wave interference model were measured at the region of the maximum surface pressure and heat transfer rate. Results show that pressure and heat transfer rate on the cylindrical leading edge of the shock wave interference model were reduced as the sweep was increased over the range of tested parameters. Peak surface pressure and heat transfer rate on the cylinder were about 10 and 30 times the undisturbed flow stagnation point value, respectively, for the 0 deg sweep test. A comparison of the 15 and 30 deg swept results with the 0 deg swept results showed that peak pressure was reduced about 13 percent and 44 percent, respectively, and peak heat transfer rate was reduced about 7 percent and 27 percent, respectively.

Glass, Christopher E.↗
NASA NTRS1990

Computational simulation of flows about hypersonic geometries with sharp leading edges

Hypersonic waverider design has become an important concern in the aerospace industry. As one part of an inverse design effort for waveriders, work has been done to apply existing Euler and Navier-Stokies flow solvers to hypersonic geometries with sharp leading edges. Previously, calculations were done on bodies with rounded leading edges or with conical solutions for the nose initial conditions. In this paper, solutions are computed about waveriders and conical shapes with sharp leading edges without resorting to either shortrcut. All solutions show attached shocks with fully supersonic flows at the nose and along the leading edges. Flows about several waverider shapes are shown, as well as a preliminary cone with inlet calculation to study the shock/inlet interaction.

Jones, Kevin D.↗
NASA NTRS1990

Effect of leading edge roundness on a delta wing in wing-rock motion

The effect of wing leading-edge roundness on wing rock was investigated using flow visualization in a water tunnel. Eighty degree delta wing models were tested on free-to-roll and forced oscillation rigs. The onset of wing rock was delayed by increasing the roundness of the leading edges. The wing rock amplitude and frequency results suggested that damping was increased at lower angles of attack but reduced at higher angles of attack. Vortex lift-off and vortex breakdown, especially during dynamic situations, were strongly affected by the leading edge roundness. Different forms of wing rock motion could be sustained by combinations of vortex breakdown and vortex lift-off. Behaviors of the wing and vortex motions were explained by the influence of leading edge roundness on the separation location, vortex trajectory, and vortex breakdown.

Ng, T. Terry↗
NASA NTRS1991

Leading-edge receptivity for blunt-nose bodies

This research program investigates boundary-layer receptivity in the leading-edge region for bodies with blunt leading edges. Receptivity theory provides the link between the unsteady distrubance environment in the free stream and the initial amplitudes of the instability waves in the boundary layer. This is a critical problem which must be addressed in order to develop more accurate prediction methods for boundary-layer transition. The first phase of this project examines the effects of leading-edge bluntness and aerodynamic loading for low Mach number flows. In the second phase of the project, the investigation is extended to supersonic Mach numbers. Singular perturbation techniques are utilized to develop an asymptotic theory for high Reynolds numbers. In the first year, the asymptotic theory was developed for leading-edge receptivity in low Mach number flows. The case of a parabolic nose is considered. Substantial progress was made on the Navier-Sotkes computations. Analytical solutions for the steady and unsteady potential flow fields were incorporated into the code, greatly expanding the types of free-stream disturbances that can be considered while also significantly reducing the the computational requirements. The time-stepping algorithm was modified so that the potential flow perturbations induced by the unsteady pressure field are directly introduced throughout the computational domain, avoiding an artificial 'numerical diffusion' of these from the outer boundary. In addition, the start-up process was modified by introducing the transient Stokes wave solution into the downstream boundary conditions.

Kerschen, Edward J.↗
NASA NTRS1991

Simulation of brush insert for leading-edge-passage convective heat transfer

Current and proposed high speed aircraft have high leading edge heat transfer (to 160 MW/sq m, 100 Btu/sq in/sec) and surface temperatures to 1370 K (2000 F). Without cooling, these surfaces could not survive. In one proposal the coolant hydrogen is circulated to the leading edge through a passage and returned to be consumed by the propulsion system. Simulated flow studies and visualizations have shown flow separation within the passage with a stagnation locus that isolates a zone of recirculation at the most critical portion of the passage, namely the leading edge itself. A novel method is described for mitigating the flow separation and the isolated recirculation zones by using a brush insert in the flow passage near the leading edge zone, thus providing a significant increase in heat transfer.

Hendricks, R. C.↗
NASA NTRS1990

Preliminary thermal/structural analysis of a carbon-carbon/refractory-metal heat-pipe-cooled wing leading edge

This study presents preliminary thermal/structural analyses of a carbon-carbon/refractory-metal heat-pipe-cooled wing leading edge concept designed for an air breathing single-stage-to-orbit hypersonic vehicle. The concept features chordwise (i.e., normal to the leading edge) and spanwise (i.e., parallel to the leading edge) refractory-metal heat pipes which are completely embedded within a carbon-carbon primary structure. Studies of the leading edge were performed using nonlinear thermal and linear structural three-dimensional finite element analyses. The concept was shown to be thermally feasible within the limits of the assumptions made in the analyses when internal radiative cooling is present during ascent, and a three-dimensional carbon-carbon architecture is used. In addition, internal radiative cooling was found not to be necessary during descent. The linear stress analysis indicated excessively large thermal stresses in the rafractory metal walls of the heat pipes even though a soft layer of carbon was included between the heat pipe and the carbon-carbon structure in an attempt to reduce the thermal stresses. A nonlinear structural analysis may be necessary to properly model the response of the refractory-metal heat pipes.

Glass, David E.↗
NASA NTRS1990

Lead-ruthenium pyrochlores as oxygen electrocatalysts

An investigation of lead-ruthenium pyrochlores of the structure Pb2(Ru/2-x/Pb/x/) O7-y for use as oxygen electrocatalysts in alkaline media is discussed. Lead-ruthenium pyrochlore mixed metal oxides were prepared and characterized by X-ray diffraction, BET surface area, dry powder conductivity, and chemical stability. Gas diffusion electrodes were developed specifically for the lead-ruthenium pyrochlore materials. Also investigated were the effects of varying electrode fabrication parameters on the oxygen reduction performance of the lead-ruthenium pyrochlore electrocatalyst. Long-term stability performance was also evaluated. The oxygen reduction performance of the pyrochlore electrocatalyst is considerably higher than that of the state-of-the-art gold-platinum alloy electrocatalyst currently used by NASA. Furthermore, the pyrochlore electrocatalysts are attractive candidates for high-performance pressurized alkaline fuel cells.

Anderson, E. B.↗
NASA NTRS1991

Computational studies of a fluid spike as a leading edge protection device for shock-shock interference heating

The effectiveness of a fluid spike as a device to protect leading edges of hypersonic atmospheric flight vehicles from high aerothermal loads produced by complex shock-shock interference is studied. The two-dimensional Navier-Stokes equations are solved using an unstructured cell-centered, fully implicit, flux-difference split algorithm. Adaptively generated unstructured meshes are employed. A type IV shock-shock interference for Mach 8 flow on a cylindrical leading edge with and without a small contraflow supersonic jet (fluid spike) placed at two different locations on the body is solved. A typical flow past a blunt body with a type IV shock-shock interference produces very high pressures and heat fluxes on the leading edge. Present results indicate that a fluid spike displaces the bow shock further in front of the body and modifies the shock-shock interference pattern. This leads to reduced peak pressures and heat fluxes on the body.

Prabhu, Ramadas K.↗
NASA NTRS1992

Heat transfer characteristics of hypersonic waveriders with an emphasis on the leading edge effects

The heat transfer characteristics in surface radiative equilibrium and the aerodynamic performance of blunted hypersonic waveriders are studied along two constant dynamic pressure trajectories for four different Mach numbers. The inviscid leading edge drag was found to be a small (4 to 8 percent) but not negligible fraction of the inviscid drag of the vehicle. Although the viscous drag at the leading edge can be neglected, the presence of the leading edge will influence the transition pattern of the upper and the lower surfaces and therefore affect the viscous drag of the entire vehicle. For an application similar to the National Aerospace Plane (NASP), the present study demonstrates that the waverider remains a valuable concept at high Mach numbers if a state-of-the-art active cooling device is used along the leading edge. At low Mach number (less than 5), the study shows the surface radiative cooling might be sufficient. In all cases, radiative cooling is sufficient for the upper and lower surfaces of the vehicle if ceramic composites are used as thermal protection.

Vanmol, Denis O.↗
NASA NTRS1992

Increased heat transfer to elliptical leading edges due to spanwise variations in the freestream momentum - Numerical and experimental results

A study of the effect of spanwise variation on leading edge heat transfer is presented. Experimental and numerical results are given for a circular leading edge and for a 3:1 elliptical leading edge. It is demonstrated that increases in leading edge heat transfer due to spanwise variations in freestream momentum are comparable to those due to freestream turbulence.

Rigby, D. L.↗
NASA NTRS1993

Manipulation of upstream rotor leading edge vortex and its effects on counter rotating propeller noise

The leading edge vortex of a counter rotating propeller (CRP) model was altered by using shrouds and by turning the upstream rotors to a forward sweep configuration. Performance, flow, and acoustic data were used to determine the effect of vortex impingement on the noise signature of the CRP system. Forward sweep was found to eliminate the leading edge vortex of the upstream blades. Removal of the vortex had little effect on the tone noise at the forward and rear blade passing frequencies (BPF's) but significantly altered both the sound pressure level and directivity of the interaction tone which occurs at the sum of the two BPF's. A separate manipulation of the leading edge vortex performed by installing shrouds of various inlet length on the CRP verified that diverting the vortex path increases the noise level of the interaction tone. An unexpected link has been established between the interaction tone and the leading edge vortex-blade interaction phenomenon.

Squires, Becky↗
NASA NTRS1993

Electrical conductivity in directionally solidified lead-9 and -20 wt pct copper alloys

Composites consisting of aligned copper dendrites in a lead matrix have been produced by directional solidification processing for potential application as grids in lead-acid batteries. To promote a uniform composite of aligned copper dendrites in a protective lead matrix, two alloy compositions, Pb-9 and -20 wt pct Cu, have been directionally solidified through a temperature gradient of 4.5 K/mm at constant growth velocities which ranged from 1 to 100 micron/s. With slow growth rates (below about 10 microns/s), the copper dendrites were generally columnar and continuous along the sample length; at higher velocities (above 60 microns/s), they assumed an intricate and equiaxed morphology. In accordance with copper content and growth rate, the electrical conductivity of the directionally solidified composites was found to be as much as a 2.5 times that of pure lead. The results are compared with that predicted by a model based on a geometrical dendrite.

Kim, Shinwoo↗