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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 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

Sidewall boundary-layer removal effects on wall adaptation in the Langley 0.3-meter transonic cryogenic tunnel

This paper describes the Langley 0.3-m transonic cryogenic tunnel sidewall boundary-layer removal system and is integrated operation with the adaptive wall adjustment. Empty test section measurements show the sidewall boundary-layer displacement thickness at the model station is reduced from about 1.0 to 0.6 percent of the test section width when the maximum boundary-layer removal conditions are applied. Tests with a supercritical airfoil model show the iterative top and bottom wall adaptation process performs satisfactorily with sidewall boundary-layer removal.

Murthy, A. V.↗
NASA NTRS1991

Real gas effects on hypersonic boundary-layer stability

High-temperature effects alter the physical and transport properties of a gas, air in particular, due to vibrational excitation and gas dissociation, and thus the chemical reactions have to be considered in order to compute the flow field. Linear stability of high-temperature boundary layers is investigated under the assumption of chemical equilibrium and this gas model is labeled here as real gas model. In this model, the system of stability equations remains of the same order as for the perfect gas and the effect of chemical reactions is introduced only through mean flow and gas property variations. Calculations are performed for Mach 10 and 15 boundary layers and the results indicate that real gas effects cause the first mode instability to stabilize while the second mode is made more unstable. It is also found that the second mode instability shifts to lower frequencies. There is a slight destabilizing influence of real gas on the Goertler instability as compared to the perfect gas results.

Malik, M. R.↗
NASA NTRS1990

Analysis of the leading edge effects on the boundary layer transition

A general theory of boundary layer control by surface heating is presented. Some analytical results for a simplified model, i.e., the optimal control of temperature fluctuations in a shear flow are described. The results may provide a clue to the effectiveness of the active feedback control of a boundary layer flow by wall heating. In a practical situation, the feedback control may not be feasible from the instrumentational point of view. In this case the vibrational control introduced in systems science can provide a useful alternative. This principle is briefly explained and applied to the control of an unstable wavepacket in a parallel shear flow.

Chow, Pao-Liu↗
NASA NTRS1978

Effect of grain boundaries in silicon on minority-carrier diffusion length and solar-cell efficiency

The spatial variation of minority-carrier diffusion length in the vicinity of a grain boundary for a polycrystalline silicon sheet has been measured by the use of the EBIC technique. The effect of such a variation on solar-cell output has then been computed as a function of grain size. Calculations show that the cell output drops considerably for grain size smaller than three times the bulk diffusion length.

Daud, T.↗
NASA NTRS1993

Spatial simulation of boundary layer instability - Effects of surface roughness

The effects of an isolated, two-dimensional roughness element on the spatial development of instability waves in boundary layers are investigated by numerically integrating the two-dimensional, time-dependent, incompressible Navier-Stokes equations, using a finite difference/Chebyshev discretization. It is shown that (high) inviscid frequencies have higher growth rates than Tollmien-Schlichting frequencies, indicating that disturbances growing in the separation zone are controlled by the inviscid instability of the shear layer at the edge of the separation zone.

Danabasoglu, G.↗
NASA NTRS2010

Effect of Dynamic Sector Boundary Changes on Air Traffic Controllers

The effect of dynamic sector boundary changes on air traffic controller workload was investigated with data from a human-in-the-loop simulation. Multiple boundary changes were made during simulated operations, and controller rating of workload was recorded. Analysis of these data showed an increase of 16.9% in controller workload due to boundary changes. This increased workload was correlated with the number of aircraft handoffs and change in sector volume. There was also a 12.7% increase in average workload due to the changed sector design after boundary changes. This increase was correlated to traffic flow crossing points getting closer to sector boundaries and an increase in the number of flights with short dwell time in a sector. This study has identified some of the factors that affect controller workload when sector boundaries are changed, but more research is needed to better understand their relationships.

Jung, Jaewoo↗
NASA NTRS1951

Deplacement effect of the laminar boundary layer and the pressure drag

The displacement effect of the boundary layer on the outer frictionless flow is discussed for both steady and unsteady flows. The analysis is restricted to cases in which the potential flow pressure distribution remains valid for the boundary-layer calculation. Formulas are given for the dependence of the pressure drag, friction drag, and total drag of circular cylinders on the time from the start of motion for cases in which the velocity varies as a power of the time. Formulas for the locations and for the time for the appearance of the separation point are given for two dimensional bodies of arbitrary shape.

THEORIES - BOUNDARY LAYER - LAMINAR↗
NASA NTRS1982

Curvature effects and turbulent boundary layers

Results are examined from an experiment conducted to determine quantitatively the secondary factors which affect the response of a turbulent boundary layer to convex curvature and to examine the recovery process after curvature ended. The variation of Stanton number with streamwise distance and with enthalpy thickness Reynolds number for the baseline case is shown. The effect of delta sub .99/R on the velocity of the potential core would have if we extended to the wall with no viscous effects, of free stream acceleration, of an unheated starting length, and of boundary layer maturity are discussed. Mixing length and turbulent Prandtl number models are reviewed.

Moffat, R. J.↗
NASA NTRS1987

Flight survey of the 757 wing noise field and its effects on laminar boundary layer transition. Volume 1: Program description and data analysis

It was previously observed that an incident acoustic field on a wing with laminar flow can cause transition to turbulent flow if the fluctuating acoustic velocities are of sufficient amplitude and in the critical frequency range for an unstable laminar boundary layer. A section of a wing was modified with a natural laminar flow (NLF) glove to allow direct measurement of the effect of varying engine noise on the extent of laminar flow. The flight test program was completed in June, 1985. At each flight condition, the engine power was varied from about 2600 r/min (idle) to about 4500 r/min (maximum continuous power). The spectral data provides considerable insight into the influences of the various sound sources that contribute to the overall noise levels. Additional analysis will be required to assess the impact of these sources on boundary layer transition. These results demonstrate that substantial laminar flow on the wing of a transport configuration with wing-mounted engines can be obtained.

Source record↗
NASA NTRS1989

The structure of sheared turbulence near a plane boundary

The effects of shear on the structure of turbulence near a plane boundary are examined. Inhomogeneous rapid distortion theory is applied to a uniform-shear boundary layer (USBL) with a slip velocity condition at the surface. The effects of blocking the vertical component of the turbulence by the boundary in a USBL are compared with the effects in a shear-free boundary layer. It is shown that the blocking is only slightly modified by the presence of shear. The shear does alter the way in which the boundary influences the horizontal components and the turbulent shear stress near the horizontal component.

Lee, Moon Joo↗
NASA NTRS1956

Investigation of the Effectiveness of Boundary-layer Control by Blowing over a Combination of Sliding and Plain Flaps in Deflecting a Propeller Slipstream Downward for Vertical Take-off

An investigation was conducted in order to determine the effectiveness of blowing a jet of air over the flaps of a wing equipped with a 50-percent-chord sliding flap and a 25-percent-chord plain flap in deflecting a propeller slipstream downward for vertical take-off and the results are presented herein. The effects of a leading-edge slat, ground proximity, end plate, and propeller position were also investigated. The tests were conducted in a static-thrust facility at the Langley Aeronautical Laboratory.

AIRPLANES - PERFORMANCE↗
NASA NTRS1984

Effect of mixed (boundary) pixels on crop proportion estimation

In estimating acreage proportions of crop types in a segment using Landsat data, considerable problem is caused by the presence of mixed pixels. Due to lack of understanding of their spectral characteristics, mixed pixels have been treated in the past as pure while clustering and classifying the segment data. This paper examines this approach of treating mixed pixels as pure pixels and the effect of mixed pixels on the bias and variance of a crop type proportion estimate. First, the spectral response of a boundary pixel is modeled and an analytical expression for the bias and variance of a proportion estimate is obtained. This is followed by a numerical illustration of the effect of mixed pixels on bias and variance. It is shown that as the size of the mixed pixel class increases in a segment, the variance increases, however, such increase does not always affect the bias of the proportion estimate.

Chhikara, R. S.↗
NASA NTRS2009

On the Effects of Surface Roughness on Boundary Layer Transition

Surface roughness can influence laminar-turbulent transition in many different ways. This paper outlines selected analyses performed at the NASA Langley Research Center, ranging in speed from subsonic to hypersonic Mach numbers and highlighting the beneficial as well as adverse roles of the surface roughness in technological applications. The first theme pertains to boundary-layer tripping on the forebody of a hypersonic airbreathing configuration via a spanwise periodic array of trip elements, with the goal of understanding the physical mechanisms underlying roughness-induced transition in a high-speed boundary layer. The effect of an isolated, finite amplitude roughness element on a supersonic boundary layer is considered next. The other set of flow configurations examined herein corresponds to roughness based laminar flow control in subsonic and supersonic swept wing boundary layers. A common theme to all of the above configurations is the need to apply higher fidelity, physics based techniques to develop reliable predictions of roughness effects on laminar-turbulent transition.

Choudhari, Meelan M.↗
NASA NTRS1948

The Effect of Boundary-layer Control by Suction and Several High-lift Devices on the Longitudinal Aerodynamic Characteristics of a 47.5 Degree Sweptback Wing-fuselage Combination

An investigation has been made in the Langley full-scale tunnel of a 47.5 degree sweptback wing-fuselage combination equipped for boundary-layer control by suction. The wing aspect ratio was 3.5, the taper ratio was 0.5, and the airfoil sections normal to the quarter-chord line were NACA 64(sub 1)-A112. The wing configurations tested included the wing with various combinations of extensible leading-edge and split flaps. The effect of Reynolds number, suction-slot location and suction flow coefficient on the aerodynamic characteristics was determined for the model at zero yaw over a range of angle of attack.

WING-FUSELAGE COMBINATIONS - AIRPLANES↗
NASA NTRS1972

Effects of roughness on heating and boundary-layer transition. Part 2: effects of discrete roughness on heating

A preliminary investigation on the effects of roughness on heating in delta wing orbiters was conducted on the windward surface of the vehicle. The purpose of the experiment was to determine the feasibility of using parametric relationships obtained from discrete roughness effects on heating in flat plates and cones, to complex shuttle configurations. An attempt was also made to characterize what parameters were needed to influence roughness. Experimental results show that effective roughness Reynolds numbers are less than or equal to those of flat plates at the same edge Mach number, but, the roughness correlations for plates and cones cannot be applied to the shuttle configuration.

Mateer, G. G.↗