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Results for “boundary effects”

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 343 records · Page 19
All sourcesNASA NTRSDOE OSTI
NASA NTRS1958

Effectiveness of Boundary-layer Control, Obtained by Blowing over a Plain Rear Flap in Combination with a Forward Slotted Flap, in Deflecting a Slipstream Downward for Vertical Take-off

The wing employed in this investigation had a 67-percent-chord slotted flap in combination with a 33-percent-chord plain rear flap equipped with a full-span blowing nozzle. The tests were conducted in a static-thrust facility at the Langley Aeronautical Laboratory. The investigation indicated that the plain rear flap alone with a low momentum coefficient for boundary-layer control provided larger turning angles than the combined slotted and plain flaps without boundary-layer control.

HIGH-LIFT DEVICES - COMPLETE WINGS↗
NASA NTRS2013

Effect of Boundary-Layer Bleed Hole Inclination Angle and Scaling on Flow Coefficient Behavior

Phase II data results of the Fundamental Inlet Bleed Experiments study at NASA Glenn Research Center are presented which include flow coefficient behavior for 21 bleed hole configurations. The bleed configurations are all round holes with hole diameters ranging from 0.795 to 6.35 mm, hole inclination angles from 20deg to 90deg, and thickness-to-diameter ratios from 0.25 to 2.0. All configurations were tested at a unit Reynolds number of 2.46 10(exp 7)/m and at discrete local Mach numbers of 1.33, 1.62, 1.98, 2.46, and 2.92. Interactions between the design parameters of hole diameter, hole inclination angle, and thickness-to-diameter as well as the interactions between the flow parameters of pressure ratio and Mach number upon the flow coefficient are examined, and a preliminary statistical model is proposed. An existing correlation is also examined with respect to this data.

Eichorn, Michael B.↗
NASA NTRS2019

The Effect of Incoming Boundary Layer Characteristics on the Performance of a Distributed Propulsion System

An experimental study is conducted in an effort to advance the understanding of flow physics associated with a boundary layer ingesting, distributed propulsion system. The influence of incoming boundary layer thickness and flow distortions are studied on the flow downstream and the overall performance of the system. The propulsion model, fabricated using additive manufacturing and integrated with electrical fans, is mounted on a flat plate and tested at subsonic speeds. Detailed characterization of the incoming boundary layer and subsequent assessment of the downstream flow field is performed using hotwire anemometry. Modification of the incoming boundary layer is achieved by placing tripping devices, such as rods and vortex generating ramps, near the leading edge of the flat plate. The overall performance of the system for different incoming flow conditions is analyzed by comparing magnitudes of exhaust velocities as well as estimated propulsive power to the corresponding baseline values. For a constant input power to the fans, smaller upstream flow distortions and moderately thickened boundary layers result in marginal changes in the flow field downstream. On the other hand, notable reductions in downstream flow velocities and propulsive power are observed in the case of a significantly thicker and/or distorted incoming boundary layer. It is hoped that this study will serve as a database for this technologically relevant flow field that has not been explored adequately before.

Propulsion↗
NASA NTRS2021

Effects of Pseudostreamer Boundary Dynamics on Heliospheric Field and Wind

Interchange reconnection has been proposed as a mechanism for the generation of the slow solar wind, and a key contributor to determining its characteristic qualities. In this paper we study the implications of interchange reconnection for the structure of the plasma and field in the heliosphere. We use the Adaptively Refined Magnetohydrodynamic Solver (ARMS) to simulate the coronal magnetic evolution in a coronal topology containing both a pseudostreamer and helmet streamer. We begin with a geometry containing a low-latitude coronal hole that is separated from the main polar coronal hole by a pseudostreamer. We drive the system by imposing rotating flows at the Solar surface within and around the low-latitude coronal hole, which leads to a corrugation (at low altitudes) of the separatrix surfaces that separate open from closed magnetic flux. Interchange reconnection is induced both at the null points and separators of the pseudostreamer, and at the global helmet streamer. Wedemonstrate that a preferential occurrence of interchange reconnection in the “lanes” between our driving cells leads to a filamentary pattern of newly-opened flux in the heliosphere. These flux bundles connect to but extend far from the separatrix-web (S-Web) arcs at the source surface. We propose that the pattern of granular and supergranular flows on the photosphere should leave an observable imprint in the heliosphere.

V Aslanyan↗
NASA NTRS2022

Numerical Study of the Turbulent Prandtl Number in Supersonic Plane-Channel Flow – the Effect of Thermal Boundary Conditions

Direct numerical simulation is used to investigate the turbulent Prandtl number Prt above cold (isothermal) and hot (adiabatic) walls in a family of supersonic channel flows. A range of Reynolds numbers and mean temperature/density variations is considered. The value of Prt away from the wall approaches 0.85 above both the isothermal and adiabatic walls, with the width of the Prt = 0.85 region increasing with wall-variable-based Reynolds number Reτw (the latter strongly affected by the thermal boundary condition). The variable, near-wall Prt profiles from both the present and previous, passive-scalar simulations collapse as a function of the semilocal y∗ wall scaling proposed by Huang et al., with the y∗-dependence weakly parameterized by Reτw.

Turbulence↗
NASA NTRS1972

Effects of casing boundary-layer removal on noise of a turbofan rotor

The effect of casing boundary-layer removal on noise produced by a turbofan rotor was measured. The outlet guide vanes were removed for these tests. A comparison was made between the noise measurements when the boundary layer was bled off and under zero bleed conditions. When the boundary layer was removed, overall sound pressure level was reduced 2 dB with moderate blade loading and 3 dB with heavier blade loading. An analysis of the changes in the spectral density with bleed is presented.

Goldstein, A. W.↗
NASA NTRS1980

Experiments on initial and boundary conditions

Effects of three different models for the treatment of subsonic boundary conditions, applied to the problem of flow in a channel with a bump, are discussed. A preliminary discussion of the numerical treatment of the corners is presented.

Moretti, G.↗
NASA NTRS1977

The effects of the laminar/turbulent boundary layer states on the development of a plane mixing layer

The effect of the laminar/turbulent boundary layer state on the mean and rms velocities of a developing plane mixing layer was investigated. The use of commonly accepted nondimensional representations of the data confirm (at least) an approximately self-preserving condition. It is suggested that the effects of the laminar/turbulent initial condition persist in the self-preserving region.

Foss, J. F.↗