Search NASA⌕ Search

SEARCH · Search NASA

Results for “FLAT PLATE”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 235 records · Page 13
All sourcesNASA NTRSDOE OSTI
NASA NTRS2014

Resonant Interaction of a Rectangular Jet with a Flat-Plate

A resonant interaction between a large aspect ratio rectangular jet and a flat-plate is addressed in this experimental study. The plate is placed parallel to but away from the direct path of the jet. At high subsonic conditions and for certain relative locations of the plate, the resonance accompanied by an audible tone is encountered. The trends of the tone frequency variation exhibit some similarities to, but also marked differences from, corresponding trends of the well-known edge-tone phenomenon. Under the resonant condition flow visualization indicates a periodic flapping motion of the jet column. Phase-averaged Mach number data obtained near the plate's trailing edge illustrate that the jet cross-section goes through large contortions within the period of the tone. Farther downstream a clear 'axis switching' takes place. These results suggest that the assumption of two-dimensionality should be viewed with caution in any analysis of the flow.

Zaman, K. B. M. Q.↗
NASA NTRS2018

Intermittency and Cessation of Vortex Shedding in the Wake of a Thin Flat Plate with a Circular Trailing Edge

The near and very near wake of thin flat plates with both sharp and circular trailing edges (TEs) are investigated with direct numerical simulations (DNSs). The TE is circular in two of the cases (IN & NS) and sharp in one of them (ST). The separating boundary layers are turbulent in all cases. The objectives of this study are twofold. The first is to explore the effect of significantly reducing Re(sub D) (Reynolds number based on circular TE diameter, D) on the flow in the TE region, and the shedding process (Cases IN and NS). The second is to better understand the reasons underlying the findings of an earlier experimental wake investigation (sharp TE) where (1) the center-line values in normal intensity, and the peak in shear stress profiles in the cross-stream direction, were found to first increase in the streamwise direction (x), from that obtained at the TE, before diminishing further downstream, and (2) a broadband peak was observed in centerline cross-stream velocity (v) spectra (indicating quasi-periodicity, possibly due to vortices or wave-like motions). Case ST from the present study showed a near wake instability resulting in spanwise vortices (with a streamwise component). The instability is intermittent and contributes to both the broadband peak in the v spectrum and the initial increases in normal intensity and shear stress (as in the experiment). Case NS, with the lower value of ReD is an "essentially" non-shedding case where the flow in the TE region continually changes direction (upward/downward) because of turbulence. Case IN, with twice the value of ReD as Case NS, also exhibits a swaying motion in the TE region. In addition, vortex shedding is initiated during periods when the flow direction changes rapidly. Shedding in this case is intermittent. It results in a peak in the v spectrum obtained at the centerline (x/D = 1.0).

direct numerical simulations↗
NASA NTRS2022

Linear Disturbance Amplification Over Blunted Flat Plates in High-Speed Flows

Modal and nonmodal instability characteristics of cylindrically blunted flat plates with varying leading edge radii are described for Mach 4 and Mach 6 freestream conditions. The selection of leading edge radii and freestream parameters is informed by experimental conditions. The investigation of this 2D problem provides a slow entropy layer swallowing which allows for an isolated development of perturbations seeded upstream within different wall-normal regions of the flow. At both Mach numbers, a decrease in modal instability amplification was seen as the leading edge radius was increased. Nonmodal analysis reveals amplifying perturbations in the boundary layer as well as in the entropy layer. The medium bluntness regime exhibits the strongest amplification of nonmodal disturbances that is nonmonotonic in character. Small amplitude boundary forcing at the plate surface or volumetric forcing at various wall-normal heights was used to account for receptivity effects. While wall forcing effectively induced modal instabilities, only an actuation above the boundary layer captured disturbances that amplify within the entropy layer. The optimal nonmodal theory’s entropy-layer disturbance evolution exhibited outstanding agreement with controlled forcing, including receptivity effects. The evolution of entropy-layer disturbances from the optimal nonmodal theory showed excellent agreement with the results of receptivity to controlled forcing. Therefore, the nonmodal optimal growth analysis may provide a useful as well as efficient technique to identify the complete disturbance spectrum in blunt hypersonic configurations, where both modal and nonmodal disturbances can amplify in the boundary-layer and entropy-layer regions.

Boundary layer transition↗
NASA NTRS2022

Linear Disturbance Amplification Over Blunted Flat Plates in High-Speed Flows

Modal and nonmodal instability characteristics of cylindrically blunted flat plates with varying leading edge radii are described for Mach 4 and Mach 6 freestream conditions. The selection of leading edge radii and freestream parameters is informed by experimental conditions. The investigation of this 2D problem provides a slow entropy layer swallowing which allows for an isolated development of perturbations seeded upstream within different wall-normal regions of the flow. At both Mach numbers, a decrease in modal instability amplification was seen as the leading edge radius was increased. Nonmodal analysis reveals amplifying perturbations in the boundary layer as well as in the entropy layer. The medium bluntness regime exhibits the strongest amplification of nonmodal disturbances that is nonmonotonic in character. Small amplitude boundary forcing at the plate surface or volumetric forcing at various wall-normal heights was used to account for receptivity effects. While wall forcing effectively induced modal instabilities, only an actuation above the boundary layer captured disturbances that amplify within the entropy layer. The optimal nonmodal theory’s entropy-layer disturbance evolution exhibited outstanding agreement with controlled forcing, including receptivity effects. The evolution of entropy-layer disturbances from the optimal nonmodal theory showed excellent agreement with the results of receptivity to controlled forcing. Therefore, the nonmodal optimal growth analysis may provide a useful as well as efficient technique to identify the complete disturbance spectrum in blunt hypersonic configurations, where both modal and nonmodal disturbances can amplify in the boundary-layer and entropy-layer regions.

Boundary layer transition↗
NASA NTRS1971

Time dependent shear stress and temperature distribution over an insulated flat plate moving at hypersonic speed.

The laminar two-dimensional flow over a stepwise accelerated flat plate moving with hypersonic speed at zero angle of attack is analysed. The governing equations in the self-similar form are linearized and solved numerically for small times. The solutions obtained are the deviations of the velocity and the temperature profiles from those of steady state. The presented results may be used to find the first order boundary layer induced pressure on the plate.

Rodkiewicz, C. M.↗
NASA NTRS1976

Recommendations for the performance rating of flat plate terrestrial photovoltaic solar panels

A review of recommendations for standardizing the performance rating of flat plate terrestrial solar panels is given to develop an international standard code of practice for performance rating. Required data to characterize the performance of a solar panel are listed. Other items discussed are: (1) basic measurement procedures; (2) performance measurement in natural sunlight and simulated sunlight; (3) standard solar cells; (4) the normal incidence method; (5) global method and (6) definition of peak power.

Treble, F. C.↗
NASA NTRS1977

Gravitational effects on chemically reacting laminar boundary layer flows over a horizontal flat plate

A theoretical study of the chemically reacting laminar boundary layer flow over a horizontal flat plate with gravitationally induced buoyant force is presented. A diffusion flame sheet model was used to describe the combustion process. The effects of gravity on the purely force convection flow can be characterized by a dimensionless coordinate quantity, which is involved in the generation of the governing equations. A numerical solution of the zero and first order governing equations subject to the appropriate physical boundary conditions was obtained. It is shown that the cross stream buoyancy induced body force acts effectively to produce a streamwise pressure gradient in the fluid adjacent to the plate surface. It is concluded that buoyancy plays an important role in boundary layer diffusion flames.

Lavid, M.↗
NASA NTRS1979

Environmental requirements for flat plate photovoltaic modules for terrestrial applications

The environmental test requirements that have been developed for flat plate modules purchased through Department of Energy funding are described. Concurrent with the selection of the initial qualification tests from space program experience - temperature cycling and humidity - surveys of existing photovoltaic systems in the field revealed that arrays were experiencing the following failure modes: interconnect breakage, delamination, and electrical termination corrosion. These coupled with application-dependent considerations led to the development of additional qualification tests, such as cyclic pressure loading, warped mounting surface, and hail. Rationale for the selection of tests, their levels and durations is described. Comparisons between field-observed degradation and test-induced degradation show a positive correlation with some of the observed field effects. Also, the tests are proving useful for detecting design, process, and workmanship deficiencies. The status of study efforts for the development of environmental requirements for field-related problems is reviewed.

Hoffman, A. R.↗
NASA NTRS1984

Designing Flat-Plate Photovoltaic Arrays

Report presents overview of state of art in design techniques for flat-plate solar photovoltaic modules and arrays. Paper discusses design requirements, design analyses, and test methods identified and developed for this technology over past several years in effort to reduce cost and improve utility and reliability for broad spectrum of terrestrial applications.

Ross, R. G., Jr.↗
NASA NTRS1989

Relaminarization of turbulent flow on a flat plate by localized surface heating

Relaminarization of a turbulent boundary layer in air on a flat plate is demonstrated experimentally using localized surface heating. Localized heating is achieved by electrically heating a wire embedded in a thermally insulated substrate (Space Shuttle Tile) on the surface. The stability of the flow downstream of the applied control point increases with decreasing stream temperature in the flow direction. The mean and perturbation velocity profiles without control show that the flow is turbulent. With control, these profiles sequentially change from intermittently turbulent to a fully laminar state. In the relaminarization stage, the turbulent energy is dissipated by molecular transport due to viscous and conductivity mechanisms. The new profile adjusts to a lower Reynolds number based on the momentum thickness than that of the previous turbulent state.

Maestrello, Lucio↗