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Results for “Skin friction drag”

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 235 records · Page 13
All sourcesNASA NTRSDOE OSTI
NASA NTRS1958

On flow of electrically conducting fluids over a flat plate in the presence of a transverse magnetic field

The use of a magnetic field to control the motion of electrically conducting fluids is studied. The incompressible boundary-layer solutions are found for flow over a flat plate when the magnetic field is fixed relative to the plate or to the fluid. The equations are integrated numerically for the effect of the transverse magnetic field on the velocity and temperature profiles, and hence, the skin friction and rate of heat transfer. It is concluded that the skin friction and the heat-transfer rate are reduced when the transverse magnetic field is fixed relative to the plate and increased when fixed relative to the fluid. The total drag is increased in all of the areas.

Rossow, Vernon J↗
NASA NTRS1995

Instrumentation development for study of Reynolds Analogy in reacting flows

Boundary layers in supersonic reacting flows are not well understood. Recently a technique has been developed which makes more extensive surface measurements practical, increasing the capability to understand the turbulent boundary layer. A significant advance in this understanding would be the formulation of an analytic relation between the transfer of momentum and the transfer of heat for this flow, similar to the Reynolds Analogy that exists for laminar flow. A gauge has been designed and built which allows a thorough experimental investigation of the relative effects of heat transfer and skin friction in the presence of combustion. Direct concurrent measurements made at the same location, combined with local flow conditions, enable a quantitative analysis to obtain a relation between the surface drag and wall heating, as well as identifying possible ways of reducing both.

Deturris, Dianne J.↗
NASA NTRS1987

Riblets for Stars and Stripes

Stars and Stripes racing yacht brought the American's Cup back to the United States. Originating from NASA's drag reduction technology, the boats "secret weapon" was that the hull's underside was coated with riblets. Riblets are small, barely visible grooves on the surface of an airplane intended to reduce skin friction by smoothing the turbulent airflow next to the skin. Grooves are V-shaped with the angle pointing in the direction of the airflow. No deeper than a scratch, they have a pronounced beneficial influence on air turbulence. *No longer commercially available.

Source record↗
NASA NTRS1983

Research on non-planar wall geometries for turbulence control and skin-friction reduction

Eight turbulence-control/drag-reduction concepts under study at NASA Langley Research Center are discussed. These concepts include: slot injection, ion wind, large-eddy breakup devices, riblets, relaminarization, convex curvature, passive porous walls, and rigid wavy walls. Of these concepts, passive porous walls and small wavelength wavy walls are found to increase drag. Riblets, slot injection, and large-eddy breakup devices reduce net turbulent drag, at least for some conditions. The ion wind, relaminarization, and convex curvature studies are still in the early stages and require further work to evaluate their applicability for drag reduction.

Hefner, J. N.↗
NASA NTRS1990

Shock tunnel studies of scramjet phenomena, supplement 5

A series of reports are presented on SCRAMjet studies, shock tunnel studies, and expansion tube studies. The SCRAMjet studies include: (1) Investigation of a Supersonic Combustion Layer; (2) Wall Injected SCRAMjet Experiments; (3) Supersonic Combustion with Transvers, Circular, Wall Jets; (4) Dissociated Test Gas Effects on SCRAMjet Combustors; (5) Use of Silane as a Fuel Additive for Hypersonic Thrust Production, (6) Pressure-length Correlations in Supersonic Combustion; (7) Hot Hydrogen Injection Technique for Shock Tunnels; (8) Heat Release - Wave Interaction Phenomena in Hypersonic Flows; (9) A Study of the Wave Drag in Hypersonic SCRAMjets; (10) Parametric Study of Thrust Production in the Two Dimensional SCRAMjet; (11) The Design of a Mass Spectrometer for use in Hypersonic Impulse Facilities; and (12) Development of a Skin Friction Gauge for use in an Impulse Facility. The shock tunnel studies include: (1) Hypervelocity flow in Axisymmetric Nozzles; (2) Shock Tunnel Development; and (3) Real Gas Efects in Hypervelocity Flows over an Inclined Cone. The expansion tube studies include: (1) Investigation of Flow Characteristics in TQ Expansion Tube; and (2) Disturbances in the Driver Gas of a Shock Tube.

Casey, R.↗
NASA NTRS1987

Use of LEBU-devices for drag reduction at flight conditions

The practical aspects of drag reduction using LEBU (large-eddy break-up) devices, turbulence manipulators, etc. in flight are discussed with the help of experience from previous flight tests. These tests have shown that appreciable reductions in local skin friction exist under flight conditions, and that the turbulence-manipulating effects can be found for swept tandem devices in transonic as well as supersonic flows. The unsteady loads experienced with the devices are discussed in connection with the frequencies occurring in this type of real flight conditions.

Bertelrud, A.↗
NASA NTRS1986

Boundary layer control by acoustic excitation

An experimental program in which the effectiveness of a single large eddy break-up device (LEBU) blade is enhanced by proper acoustic excitation is described. An acoustic pulse, phase-locked to the incident large eddies and directed at the LEBU can enhance the large eddy cancellation process and can in effect lead to a decrease in the skin friction coefficient. Cross-correlation data and turbulence intensity measurements show that this acoustic excitation causes eddy cancellation at the trailing edge of the manipulator plate. It is concluded that both reduced turbulent boundary layer mixing and significant drag reduction can be achieved upon proper acoustic input to a LEBU.

Papathanasiou, A. G.↗
NASA NTRS1977

Experimental subsonic drag properties of the space shuttle orbiter TPS tiles

The drag characteristics of the space shuttle orbiter thermal protection system (TPS) tiles were studied experimentally in subsonic flow. Full-scale tiles were mounted to a 3.05 x 3.5 m test board in four configurations plus a completely smooth case. Pressure gradients were produced by tilting the board relative to the freestream. The drags due to steps, slots, and gaps between the tiles were evaluated at various orientations, pressure gradients, and Reynolds numbers. Results showed that the contribution of gaps and slots were minor compared to those of typical steps. The results for skin friction did not correlate as a fully rough surface. Thus, the surface area of the TPS tiles was sufficient to allow smooth-wall Reynolds number effects even though the steps between tiles could double the skin friction.

Norton, D. J.↗
NASA NTRS1989

Airfoil profile drag increase due to acoustic excitation

A two-dimensional airfoil (NACA-0009) is subjected to high intensity pure-tone sound over a 1-5 kHz frequency range while immersed in a flow with 240 ft/sec velocity in a quiet flow facility with a Reynolds number of 3 million. Wake dynamic pressures are determined, and the momentum deficit is used to calculate a two-dimensional drag coefficient. Significant increases in drag are observed when the airfoil is subjected to high-intensity sound at critical frequencies. The increased drag is accompanied by movement of the natural transition location. When the transition is fixed by roughness at 10 percent chord, no further transition movement is observed in response to an acoustic Tollmien-Schlichting disturbance. However, a 4 percent increase in the sectional drag coefficient is noted. It is believed to be due to the sound exciting the flow near the airfoil surface (shear layer), thus causing the existing turbulence to become more intense, possess a higher mixing rate (momentum), and increase the skin friction.

Shearin, John G.↗
NASA NTRS1985

Emmons spot forcing for turbulent drag reduction

An Emmons spot-generation wind tunnel system has been designed to trigger closely spaced Emmons spots in the spanwise and longitudinal directions of an aerodynamic surface. For certain combinations of generator frequencies and amplitude, hole size, and hole spacing, experimental results indicate smaller turbulence scales and a reduction in skin friction of about 15 percent.

Goodman, W. L.↗
NASA NTRS1983

An experimental study of changes in the structure of a turbulent boundary layer due to surface geometry changes

This investigation attempts to observe changes in the flow structure of a nominally zero pressure gradient turbulent boundary layer by altering the surface of a smooth plate with small triangular riblets oriented in the direction of flow and protruding just above the viscous sublayer. Hot-wire measurements show a reduction in the local skin friction over the riblet valleys by about 40% compared to the smooth surface near the end of the plate. Local skin friction increases by about 10% over the riblet peaks. Results showing the effects of the riblets on the mean, root-mean-square and skewness factor distributions of the streamwise velocity are presented. The mean profile displays characteristics similar to those of drag reducing additives; the streamwise turbulence intensity is reduced by approximately 10-15% near the surface by the riblets; the skewness factor distribution is virtually unchanged. A comparison of results from an application of the VITA 'burst' detection technique to smooth and riblet surface data is also presented although the results are rather inconclusive. Flow visualization of 'bursting' over both surfaces, while dramatically revealing the structure, reveals little difference resulting from the presence of the riblet.

Source record↗
NASA NTRS1979

Advanced air transport concepts

The concepts of laminar flow control, very large all-wing aircraft, an aerial relay transportation system and alternative fuels, which would enable large improvements in fuel conservation in air transportation in the 1990's are discussed. Laminar boundary layer control through suction would greatly reduce skin friction and has been reported to reduce fuel consumption by up to 29%. Distributed load aircraft, in which all fuel and payload are carried in the wing and the fuselage is absent, permit the use of lighter construction materials and the elimination of fuselage and tail drag. Spanloader aircraft with laminar flow control could be used in an aerial relay transportation system which would employ a network of continuously flying liners supplied with fuel, cargo and crews by smaller feeder aircraft. Liquid hydrogen and methane fuels derived from coal are shown to be more weight efficient and less costly than coal-derived synthetic jet fuels.

Molloy, J. K.↗
NASA NTRS1988

Computational and experimental studies of LEBUs at high device Reynolds numbers

The present paper summarizes computational and experimental studies for large-eddy breakup devices (LEBUs). LEBU optimization (using a computational approach considering compressibility, Reynolds number, and the unsteadiness of the flow) and experiments with LEBUs at high Reynolds numbers in flight are discussed. The measurements include streamwise as well as spanwise distributions of local skin friction. The unsteady flows around the LEBU devices and far downstream are characterized by strain-gage measurements on the devices and hot-wire readings downstream. Computations are made with available time-averaged and quasi-stationary techniques to find suitable device profiles with minimum drag.

Bertelrud, Arild↗
NASA NTRS2014

Direct Numerical Simulations of High-Speed Turbulent Boundary Layers over Riblets

Direct numerical simulations (DNS) of spatially developing turbulent boundary layers over riblets with a broad range of riblet spacings are conducted to investigate the effects of riblets on skin friction at high speeds. Zero-pressure gradient boundary layers under two flow conditions (Mach 2:5 with T(sub w)/T(sub r) = 1 and Mach 7:2 with T(sub w)/T(sub r) = 0:5) are considered. The DNS results show that the drag-reduction curve (delta C(sub f)/C(sub f) vs l(sup +)(sub g )) at both supersonic speeds follows the trend of low-speed data and consists of a `viscous' regime for small riblet size, a `breakdown' regime with optimal drag reduction, and a `drag-increasing' regime for larger riblet sizes. At l l(sup +)(sub g) approx. 10 (corresponding to s+ approx 20 for the current triangular riblets), drag reduction of approximately 7% is achieved at both Mach numbers, and con rms the observations of the few existing experiments under supersonic conditions. The Mach- number dependence of the drag-reduction curve occurs for riblet sizes that are larger than the optimal size, with smaller slopes of (delta C(sub f)/C(sub f) for larger freestream Mach numbers. The Reynolds analogy holds with 2(C(sub h)=C(sub f) approximately equal to that of at plates for both drag-reducing and drag-increasing configurations.

Duan, Lian↗
NASA NTRS1976

Ground simulation and tunnel blockage for a jet-flapped, basic STOL model tested to very high lift coefficients

Ground effects experiments and large/small-tunnel interference studies were carried out on a model with a 20-inch (50.8 cm) span wing. The wing, which includes a highly deflected knee-blown flap can be fitted with unflapped tips and slats. A low-mounted tailplane can be fitted to the aft fuselage. Three-component balance meaurements, made with a fixed ground equipped with a single boundary-layer blowing slot, were compared with datum, moving-ground results. Good comparisons were obtained up to model blowing momentum coefficients of approximately two, after which the particular floor blowing settings used proved insufficient to prevent floor separation in the vicinity of the model. Skin friction measurements, taken routinely along the floor centerline, proved invaluable during the analysis of results, and their use is recommended as input to determination of floor BLC setting. A careful investigation was made of pitching moments, including tail-on, close-to-ground cases, with favorable results. Drag proved the most sensitive to the change from a moving to the boundary-layer controlled ground.

Hackett, J. E.↗
NASA NTRS1994

Computational prediction of isolated performance of an axisymmetric nozzle at Mach number 0.90

An improved ability to predict external propulsive performance was incorporated into the three-dimensional Navier-Stokes code PAB3D. The improvements are the ability to account for skin friction and external pressure forces. Performance parameters for two axisymmetric supersonic cruise nozzle configurations were calculated to test the improved methodology. Internal and external flow-field regions were computed using a two-equation kappa-epsilon turbulent viscous-stress model. The computed thrust-minus-drag ratios were within 1 percent of the absolute level of experimental data and the trends of data were predicted accurately. The predicted trend of integrated nozzle pressure drag matched the trend of the integrated experimental pressure drag over a range of nozzle pressure ratios, but absolute drag levels were not accurately predicted.

Carlson, John R.↗
NASA NTRS1999

Effects of Convoluted Divergent Flap Contouring on the Performance of a Fixed-Geometry Nonaxisymmetric Exhaust Nozzle

An investigation was conducted in the model preparation area of the Langley 16-Foot Transonic Tunnel to determine the effects of convoluted divergent-flap contouring on the internal performance of a fixed-geometry, nonaxisymmetric, convergent-divergent exhaust nozzle. Testing was conducted at static conditions using a sub-scale nozzle model with one baseline and four convoluted configurations. All tests were conducted with no external flow at nozzle pressure ratios from 1.25 to approximately 9.50. Results indicate that baseline nozzle performance was dominated by unstable, shock-induced, boundary-layer separation at overexpanded conditions. Convoluted configurations were found to significantly reduce, and in some cases totally alleviate separation at overexpanded conditions. This result was attributed to the ability of convoluted contouring to energize and improve the condition of the nozzle boundary layer. Separation alleviation offers potential for installed nozzle aeropropulsive (thrust-minus-drag) performance benefits by reducing drag at forward flight speeds, even though this may reduce nozzle thrust ratio as much as 6.4% at off-design conditions. At on-design conditions, nozzle thrust ratio for the convoluted configurations ranged from 1% to 2.9% below the baseline configuration; this was a result of increased skin friction and oblique shock losses inside the nozzle.

Asbury, Scott C.↗
NASA NTRS1981

Fundamental studies of antimisting fuels

Research is currently being undertaken to determine the various physical characteristics of antimisting fuel. It is an endeavor to prevent post-crash fuel mist fires. The following studies were done: (1) drop and jet breakup studies using an image processing technique, (2) flammability of fuel mist under simulated plane crash conditions; (3) skin friction measurements; (4) determination of the tensile viscosity of non-Newtonian antimisting fuel as a function of the extensional rate; and (5) water compatibility measurements. The results indicate that the mechanism which prevents antimisting fuel breakup is related to the time-dependent tensile viscosity of antimisting fuel under stress. Drag reduction phenomenon was also observed at Reynolds numbers higher than 20,000. Uptake of water by the antimisting fuel is higher than that for the neat fuel. In addition, its rate of absorption depends on the concurrent degree of agitation.

Sarohia, V.↗