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Results for “DRAG EFFECT”

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 NTRS1979

An exploratory investigation of the effect of a plastic coating on the profile drag of a practical-metal-construction sailplane airfoil

The Langley low-turbulence pressure tunnel to determine the effect of a plastic coating on the profile drag of a practical-metal-construction sailplane airfoil was investigated. The model was tested with three surface configurations: (1) filled, painted, and sanded smooth; (2) rough bare metal; and (3) plastic-coated. The results are compared with data for the design airfoil (Wortmann FX 67-K-170/17) from another low-turbulence wind tunnel. The investigation was conducted at Reynolds numbers based on airfoil chord of 1.1 x 10 to the 6th power, 2.2 x 10 to the 6th power, and 3.3 x 10 to the 6th power at a Mach number of 0.10.

Somers, D. M.↗
NASA NTRS1996

Recent Laboratory and Numerical Trailing Vortex Studies

Results from two laboratory studies and two numerical studies are presented. In the first laboratory study, measurements of the strength of vortices from a three-dimensional (3-D) model wing are presented. The measurements follow the vortices as they evolve in time from a two-dimensional (2-D) line vortex pair to the development and migration of 3-D vortex rings. It is shown that the resulting vortex rings can contain up to 40 percent of the initial vortex circulation. Thus, the formation of vortex rings may not necessarily signal the end of the wake hazard to following aircraft. In the second laboratory study, we present the results of an experiment which shows how the spanwise drag distribution affects wake-vortex evolution. In this experiment, we modified the spanwise drag distribution on a model wing while keeping the total lift and drag constant. The results show that adding drag on or near the centerline of the wing has a larger effect than adding drag at or near the wingtips. These measurements complement the results of NASA studies in the 1970s. In the first numerical study, results of 3-D numerical calculations are presented which show that the vortex Reynolds number has a significant influence on the evolution and migration of wake vortices. When the Reynolds number is large, 3-D vortex rings evolve from the initially 2-D line vortex pairs. These vortex rings then migrate vertically. When the Reynolds number is lower, the transition of vorticity from 2-D to 3-D is delayed. When the Reynolds number is very low, the vortices never transition to 3-D, and the vertical migration is significantly reduced. It is suggested that this effect may have been important in previous laboratory wake-evolution studies. A second numerical study shows the influence that vertical wind shear can have on trailing vortex evolution.

Delisi, Donald P.↗
NASA NTRS1973

Effects of fineness and closure ratios on boattail drag of circular-arc-afterbody models with jet exhaust at Mach numbers up to 1.3

The effects of variations in fineness ratio and closure ratio on the boattail drag of circular-arc afterbody models were investigated at static conditions and at Mach numbers from 0.40 to 1.30. Jet total-pressure ratio was varied from jet off to about 6, depending on Mach number. Reynolds number based on model maximum diameter varied from about 1.2 million to 2.18 million. Angle of attack was varied from -4 deg to 8 deg. The results indicate that, at subsonic speeds before the drag rise and at a scheduled pressure ratio, the total drag (pressure plus calculated skin friction) is approximately equal for configurations with the same closure ratio. Also, for configurations with the same closure ratio, increasing fineness ratio results in an increased drag-rise Mach number; and for configurations with the same fineness ratio, increasing closure ratio results in an increased drag-rise Mach number.

Reubush, D. E.↗
NASA NTRS1978

A drag-free Lo-Lo satellite system for improved gravity field measurements

At very low altitudes, the effect of atmospheric drag results in drastically reduced orbit lifetimes and considerable uncertainty in satellite motions. The concept suggested herein employs a DISturbance COmpensation System (DISCOS) on each of a pair of satellites at very low altitudes to provide refined measurements of the earth's gravitational field. The DISCOS maintains the satellites in orbit and essentially eliminates motion uncertainties due mostly to drag and to a lesser extent from solar radiation pressure. By a closed-loop measurement of the relative rangerate between the two low satellites, one can determine the earth's gravitational field with a considerably greater accuracy than could be obtained by tracking a single satellite.

Fischell, R. E.↗
NASA NTRS1979

An Exploratory Investigation of the Effect of Plastic Coating on the Profile Drag of a Practical-Metal-Construction Sailplane Airfoil

An exploratory investigation was performed in the Langley low-turbulence pressure tunnel to determine the effect of a plastic coating on the profile drage of a practical-metal-construction sailplaine airfoil. The mode was tested with three surface configurations: (1) filled, painted, and sanded smooth; (2) rough bare metal; and (3) plastic-coated. The investigation was conducted at Reynolds numbers based on airfoil chord of 1,100,000, 2,200,000, and 3,300,000 at a constant Mach number of 0.10. The results indicate that, at all three Reynolds numbers, the order of the drag values of the three surface configurations, starting with the highest drag, was: filled, painted, and sanded smooth; rough bare metal; and plastic-coated.

Somers, D. M.↗
NASA NTRS1974

Effects of viscoelasticity on cavitation in drag reducing fluids

To study cavitation inception in polymer solutions, a blow-down water tunnel with short running times was used. Tests were made using 1/4 and 1/2 inch diameter models of hemispherical-nose cylinders. To accurately detect the inception of cavitation, a reliable technique was developed using a continuously operating He-Ne gas laser. The laser beam was adjusted to grazing incidence with the model at the minimum pressure point where cavitation inception was to be expected. A sensitive photocell was placed at ninety degrees to detect the beam. As incipient cavitation occurred, the bubbles caused scattering of the laser beam which was picked up by the photocell. Static pressure near the model in the working section of the tunnel was measured using a solid-state pressure pick-up. The signals from the photocell and the pressure pick-up were recorded on an oscillograph. Velocity field visualization was achieved using one microsecond duration light pulses scattered by small polystryrene latex spheres in the flow.

Ting, R. Y.↗
NASA NTRS1981

Factors Influencing the Predicted Performance of Advanced Propeller Designs

The assumptions on which conventional propeller aerodynamic performance analyses are based can be seriously violated when advanced high speed propellers are analyzed. Studies were performed using a lifting line representation for the propeller to determine the sensitivity of predicted propeller performance to various assumptions in the analysis. Items studied include the method of determining blade section lift and the effects of blade section drag, camber and blade sweep. The effects of nonuniform flow into the propeller and compressibility were also studied. Comparisons of analytical and experimental results are presented to demonstrate the overall validity of the results.

Bober, L. J.↗
NASA NTRS1981

Factors influencing the predicted performance of advanced propeller designs

The assumptions on which conventional propeller aerodynamic performance analyses are based can be seriously violated when advanced high speed propellers are analyzed. Studies have been performed using a lifting line representation for the propeller to determine the sensitivity of predicted propeller performance to various assumptions in the analysis. Items which have been studied include the method of determining blade section lift and the effects of blade section drag, camber and blade sweep. The effects of nonuniform flow into the propeller and compressibility have also been studied. Comparisons of analytical and experimental results are presented to demonstrate the overall validity of the results.

Bober, L. J.↗
NASA NTRS1985

Effect of flow oscillations on cavity drag and a technique for their control

Experiments to relate the state of the shear layer to cavity drag have been performed in a water channel using a 4" axisymmetric cavity model. Detailed flow measurements in various cavity flow oscillation phases, amplitude amplification along the flow direction, distribution of shear stress, and other momentum flux obtained by laser Doppler velocimeter are presented. Measurements show exponential dependence of cavity drag on the length of the cavity. A jump in the cavity drag coefficient is observed as the cavity flow shows a bluff body wake type behavior. Natural and forced oscillations are introduced by a sinusoidally heated thin-film strip which excites the Tollmein-Schlichting waves in the boundary layer upstream of the gap. For a large gap, self-sustained periodic oscillations are observed, while for smaller gaps, which do not oscillate naturally, periodical oscillations can be obtained by external forcing through the strip heater. The drag of the cavity can be increased by one order of magnitude in the non-oscillating case through external forcing. Also, it is possible to completely eliminate mode switching by external forcing. For the first time, it is demonstrated that amplitude of cavity flow Kelvin-Helmholtz wave is dampened or cancelled by introduction of external perturbation of natural flow frequency but different phase.

Gharib, M.↗
NASA NTRS1987

The effect of flow oscillations on cavity drag

An experimental investigation of flow over an axisymmetric cavity shows that self-sustained, periodic oscillations of the cavity shear layer are associated with low cavity drag. In this low-drag mode the flow regulates itself to fix the mean-shear-layer stagnation point at the downstream corner. Above a critical value of the cavity width-to-depth ratio there is an abrupt and large increase of drag due to the onset of the 'wake mode' of instability. It is also shown by measurement of the momentum balance how the drag of the cavity is related to the state of the shear layer, as defined by the mean momentum transport and the Reynolds stress, and how these are related to the amplifying oscillations in the shear layer. The cavity shear layer is found to be different, in several respects, from a free shear layer.

Gharib, M.↗
NASA NTRS1990

Wind-tunnel investigation on the effect of a crescent planform on drag

Lift and drag forces were compared for elliptic and crescent wing models at cruise and climb conditions in the NASA/Langley 14 x 22-ft subsonic tunnel. The force measurements were obtained for an angle-of-attack range from -3 to 10 deg at a Reynolds number of about 1.7 million. The results indicate that for attached flow conditions, the crescent wing with its highly swept tips generates less lift-dependent drag than the elliptic wing for given lift force, wing span, and freestream conditions. The drag reduction is thought to be the result of the favorable influence of trailing wake deformations on the pressure distribution of the highly swept outboard region of the crescent wing.

Van Dam, C. P.↗