Standardized performance tests of collectors of solar thermal energy-a flat-plate collector with a single-tube serpentine flow distribution

NASA Technical Reports Server (NTRS)

Johnson, S.

1976-01-01

This preliminary data report gives basic test results of a flat-plate solar collector whose performance was determined in the NASA-Lewis solar simulator. The collector was tested over ranges of inlet temperatures, fluxes and coolant flow rates. Collector efficienty is correlated in terms of inlet temperature and flux level.

OVERFLOW Validation for Predicting Plume Impingement of Underexpanded Axisymmetric Jets onto Angled Flat Plates

NASA Technical Reports Server (NTRS)

Lee, Henry C.; Klopfer, Goetz

2011-01-01

This report documents how OVERFLOW, a computational fluid dynamics code, predicts plume impingement of underexpanded axisymmetric jets onto both perpendicular and inclined flat plates. The effects of the plume impinging on a range of plate inclinations varying from 90deg to 30deg are investigated and compared to the experimental results in Reference 1 and 2. The flow fields are extremely complex due to the interaction between the shock waves from the free jet and those deflected by the plate. Additionally, complex mixing effects create very intricate structures in the flow. The experimental data is very limited, so these validation studies will focus only on cold plume impingement on flat and inclined plates. This validation study will help quantify the error in the OVERFLOW simulation when applied to stage separation scenarios.

In-Flight Boundary-Layer Transition of a Large Flat Plate at Supersonic Speeds

NASA Technical Reports Server (NTRS)

Banks, D. W.; Frederick, M. A.; Tracy, R. R.; Matisheck, J. R.; Vanecek, N. D.

2012-01-01

A flight experiment was conducted to investigate the pressure distribution, local-flow conditions, and boundary-layer transition characteristics on a large flat plate in flight at supersonic speeds up to Mach 2.00. The tests used a NASA testbed aircraft with a bottom centerline mounted test fixture. The primary objective of the test was to characterize the local flow field in preparation for future tests of a high Reynolds number natural laminar flow test article. A second objective was to determine the boundary-layer transition characteristics on the flat plate and the effectiveness of using a simplified surface coating. Boundary-layer transition was captured in both analog and digital formats using an onboard infrared imaging system. Surface pressures were measured on the surface of the flat plate. Flow field measurements near the leading edge of the test fixture revealed the local flow characteristics including downwash, sidewash, and local Mach number. Results also indicated that the simplified surface coating did not provide sufficient insulation from the metallic structure, which likely had a substantial effect on boundary-layer transition compared with that of an adiabatic surface. Cold wall conditions were predominant during the acceleration to maximum Mach number, and warm wall conditions were evident during the subsequent deceleration.

Characterization of the Time-Dependent Fluid-Structure Interaction of Passive Flow Control of Low Reynolds Number Membrane Wings

DTIC Science & Technology

2013-07-01

plates usually experiences separation near or at the leading-edge, creating an aerodynamic shear layer that either reattaches to form a separation...blunt-body shedding. At low angle-of-attack, however, flat plates do not exhibit strong blunt-body shedding, thus, is an unlikely driver. Additionally...range from 0 – 10% for typical flat plate membrane models in low-Re flow. Two distinct regions of membrane vibration relative to the tensioning

The transference of heat from a hot plate to an air stream

NASA Technical Reports Server (NTRS)

Elias, Franz

1931-01-01

The object of the present study was to define experimentally the field of temperature and velocity in a heated flat plate when exposed to an air stream whose direction is parallel to it, then calculate therefrom the heat transference and the friction past the flat plate, and lastly, compare the test data with the mathematical theory. To ensure comparable results, we were to actually obtain or else approximate: a) two-dimensional flow; b) constant plate temperature in the direction of the stream. To approximate the flow in two dimensions, we chose a relatively wide plate and measured the velocity and temperature in the median plane.

Unsteady laminar boundary-layer calculations on oscillating configurations including backflow. Part 1: Flat plate, oscillating in its own plane

NASA Technical Reports Server (NTRS)

Geissler, W.

1983-01-01

A finite difference method has been developed to calculate the unsteady boundary layer over an oscillating flat plate. Low- and high frequency approximations were used for comparison with numerical results. Special emphasis was placed on the behavior of the flow and on the numerical calculation procedure as soon as reversed flow has occurred over part of the oscillation cycle. The numerical method displayed neither problems nor singular behavior at the beginning of or within the reversed flow region. Calculations, however, came to a limit where the back-flow region reached the plate's leading edge in the case of high oscillation amplitudes. It is assumed that this limit is caused by the special behavior of the flow at the plate's leading edge where the boundary layer equations are not valid.

Flat-plate film cooling from a double jet holes: influence of free-stream turbulence and flow acceleration

NASA Astrophysics Data System (ADS)

Khalatov, A. A.; Borisov, I. I.; Dashevsky, Yu. J.; Panchenko, N. A.; Kovalenko, A. S.

2014-12-01

Results of an experimental study of flat-plate film cooling effectiveness achieved with an inlet double jet scheme are reported. At low ( m = 0.5) and medium ( m = 1.0) blowing ratio the average film cooling effectiveness is about 20 % greater of the traditional two-row scheme of round holes data, while at higher m = 1.5 it is close to it. The free-stream turbulence (≈ 7 %) influences weekly on the average flat-plate film cooling effectiveness. The flow acceleration decreases the film cooling effectiveness down to 25 % when the pressure gradient parameter K is ranged from 0.5·10-6 to 3.5·10-6.

Near Continuum Velocity and Temperature Coupled Compressible Boundary Layer Flow over a Flat Plate

NASA Astrophysics Data System (ADS)

He, Xin; Cai, Chunpei

2017-04-01

The problem of a compressible gas flows over a flat plate with the velocity-slip and temperature-jump boundary conditions are being studied. The standard single- shooting method is applied to obtain the exact solutions for velocity and temperature profiles when the momentum and energy equations are weakly coupled. A double-shooting method is applied if these two equations are closely coupled. If the temperature affects the velocity directly, more significant velocity slip happens at locations closer to the plate's leading edge, and inflections on the velocity profiles appear, indicating flows may become unstable. As a consequence, the temperature-jump and velocity-slip boundary conditions may trigger earlier flow transitions from a laminar to a turbulent flow state.

Air flow in the boundary layer near a plate

NASA Technical Reports Server (NTRS)

Dryden, Hugh L

1937-01-01

The published data on the distribution of speed near a thin flat plate with sharp leading edge placed parallel to the flow (skin friction plate) are reviewed and the results of some additional measurements are described. The purpose of the experiments was to study the basic phenomena of boundary-layer flow under simple conditions.

On the nonlinear stability of viscous modes within the Rayleigh problem on an infinite flat plate

NASA Technical Reports Server (NTRS)

Webb, J. C.; Otto, S. R.; Lilley, G. M.

1994-01-01

The stability has been investigated of the unsteady flow past an infinite flat plate when it is moved impulsively from rest, in its own plane. For small times the instantaneous stability of the flow depends on the linearized equations of motion which reduce in this problem to the Orr-Sommerfeld equation. It is known that the flow for certain values of Reynolds number, frequency and wave number is unstable to Tollmien-Schlichting waves, as in the case of the Blasius boundary layer flow past a flat plate. With increase in time, the unstable waves only undergo growth for a finite time interval, and this growth rate is itself a function of time. The influence of finite amplitude effects is studied by solving the full Navier-Stokes equations. It is found that the stability characteristics are markedly changed both by the consideration of the time evolution of the flow, and by the introduction of finite amplitude effects.

Analysis of turbulent free-convection boundary layer on flat plate

NASA Technical Reports Server (NTRS)

Eckert, E R G; Jackson, Thomas W

1950-01-01

A calculation was made for the flow and heat transfer in the turbulent free-convection boundary layer on a vertical flat plate. Formulas for the heat-transfer coefficient, boundary layer thickness, and the maximum velocity in the boundary layer were obtained.

Measurement and research on the appearance of tongue board based on modification to discuss centrifugal fan air performance

NASA Astrophysics Data System (ADS)

Jwo, Ching-Song; Cheng, Tseng-Tang; Cho, Hung-Pin; Chiang, Wei-Tang; Chen, Sih-Li; Chen, Chien-Wei; Jian, Ling-You

2011-12-01

This paper presents a reduced fan noise method, with increased fan-benefit analysis of various performances. The experimental approach adopts changes in the outlet in the form of two fans (flat tongue and a V-Type tongue plate) in order to measure the noise under the two forms of value and volume of supply air fan, shaft power consumption, operating current, and static pressure. The results showed that the tongue plate and the V-plane tongue plate noise between the value of the measurement location of 6.7 in the tongue plate in the plane below the noise level is about V-tongue plate 1 ~ 1.5dB (A). Air flow rate testing showed that the flat plate and the V-Type tongue plate between the tongue plate V-Type flow rate value, the measurement location of 3.4 in the tongue plate in the plane was more than the V-Type flow rate tongue plate 5 to 5.5%. Shaft power testing of measurement model 3, and measurement model 4, showed that the tongue plate in the plane V-tongue plate was more than 8%, 5%. The measurement models 3 and 4 and 5 showed more than the V-Type plane tongue plate 1%, 2.7%, and 2.6%. The measurement models 6 and 8 showed that, the flat tongue plate is less than the V-tongue plate of 2.9% and 2.3%. Static pressure testing showed that the flat tongue plate in particular measurement models (3,4,8,9), the static value of V-tongue plate than the 11.1% higher, respectively, 9%, 4.3%, and 3.7%. The results summarized above suggest that, in the specific measurement points, when parallel to the tongue plate the V-tongue board has better performance.

Mantle flow through a tear in the Nazca slab inferred from shear wave splitting

NASA Astrophysics Data System (ADS)

Lynner, Colton; Anderson, Megan L.; Portner, Daniel E.; Beck, Susan L.; Gilbert, Hersh

2017-07-01

A tear in the subducting Nazca slab is located between the end of the Pampean flat slab and normally subducting oceanic lithosphere. Tomographic studies suggest mantle material flows through this opening. The best way to probe this hypothesis is through observations of seismic anisotropy, such as shear wave splitting. We examine patterns of shear wave splitting using data from two seismic deployments in Argentina that lay updip of the slab tear. We observe a simple pattern of plate-motion-parallel fast splitting directions, indicative of plate-motion-parallel mantle flow, beneath the majority of the stations. Our observed splitting contrasts previous observations to the north and south of the flat slab region. Since plate-motion-parallel splitting occurs only coincidentally with the slab tear, we propose mantle material flows through the opening resulting in Nazca plate-motion-parallel flow in both the subslab mantle and mantle wedge.

Researcher and Mechanic with Solar Collector in Solar Simulator Cell

NASA Image and Video Library

1976-08-21

Researcher Susan Johnson and a mechanic examine a flat-plate solar collector in the Solar Simulator Cell in the High Temperature Composites Laboratory at the National Aeronautics and Space Administration (NASA) Lewis Research Center. The Solar Simulator Cell allowed the researchers to control the radiation levels, air temperature, airflow, and fluid flow. The flat-plate collector, seen in a horizontal position here, was directed at the solar simulator, seen above Johnson, during the tests. Lewis researchers were studying the efficiency of various flat- plate solar collector designs in the 1970s for temperature control systems in buildings. The collectors consisted of a cover material, absorber plate, and parallel flow configuration. The collector’s absorber material and coating, covers, honeycomb material, mirrors, vacuum, and tube attachment could all be modified. Johnson’s study analyzed 35 collectors. Johnson, a lifelong pilot, joined NASA Lewis in 1974. The flat-plate solar collectors, seen here, were her first research project. Johnson also investigated advanced heat engines for general aviation and evaluated variable geometry combustors and liners. Johnson earned the Cleveland Technical Society’s Technical Achievement Award in 1984.

A Study of Chemically Reactive Species and Thermal Radiation Effects on an Unsteady MHD Free Convection Flow Through a Porous Medium Past a Flat Plate with Ramped Wall Temperature

NASA Astrophysics Data System (ADS)

Pandit, K. K.; Sarma, D.; Singh, S. I.

2017-12-01

An investigation of the effects of a chemical reaction and thermal radiation on unsteady MHD free convection heat and mass transfer flow of an electrically conducting, viscous, incompressible fluid past a vertical infinite flat plate embedded in a porous medium is carried out. The flow is induced by a general time-dependent movement of the vertical plate, and the cases of ramped temperature and isothermal plates are studied. An exact solution of the governing equations is obtained in closed form by the Laplace Transform technique. Some applications of practical interest for different types of plate motions are discussed. The numerical values of fluid velocity, temperature and species concentration are displayed graphically whereas the numerical values of skin friction, Nusselt number and Sherwood number are presented in a tabular form for various values of pertinent flow parameters for both ramped temperature and isothermal plates.

Friction factor data for flat plate tests of smooth and honeycomb surfaces. M.S. Thesis

NASA Technical Reports Server (NTRS)

Ha, Tae Woong

1989-01-01

Friction factors for honeycomb surfaces were measured with a flat plate tester. The flat plate test apparatus was described and a method was discussed for determining the friction factor experimentally. The friction factor model was developed for the flat plate test based on the Fanno Line Flow. The comparisons of the friction factor were plotted for smooth surfaces and six-honeycomb surfaces with three-clearances, 6.9 bar to 17.9 bar range of inlet pressures, and 5,000 to 100,000 range of the Reynolds number. The optimum geometries for the maximum friction factor were found as a function of cell width to cell depth and cell width to clearance ratios.

Flow past a flat plat with a vortex/sink combination

NASA Technical Reports Server (NTRS)

Mourtos, N. J.

1985-01-01

An attempt was made to model the so called leading edge vortex which forms over the leading edge of delta wings at high angles of attack. A simplified model was considered, namely that of a two-dimensional, inviscid, incompressible steady flow around a flat plate at an angle of attack with a stationary vortex detached on top, as well as a sink to simulate the strong spanwise flow. The results appear to agree qualitatively with experiments. A comparison was also made between the lift and the drag of this model and the corresponding results for two classical solutions: (1) that of totally attached flow over the plate with the Kutta condition satisfied at the trailing edge only; and (2) the Helmholtz solution of totally separated flow over the plate.

Aerodynamic characteristics of a Sparrow 3 missile model in the flow field of a generalized parent body at Mach 2.86

NASA Technical Reports Server (NTRS)

Stallings, R. L., Jr.

1984-01-01

Longitudinal aerodynamic characteristics of a Sparrow 3 wing control missile model were measured through a range of separation distances relative to a flat plate surface that represented the parent-body configuration. Measurements were obtained with and without two dimensional circular arc protuberances attached to the flat plate surface. The tests were conducted at a Mach number of 2.86 and a Reynolds number per meter of 6.56 million. The behavior of these longitudinal characteristics with varying separation distance in the flow field created by the flat plate and protuberance was generally as would be expected on the basis of flow field boundaries determined from the second order approximation of Friedrich. In general, varying roll angle from 0 deg to 45 deg caused no significant effect on the store separation characteristics.

Vortical structures of supersonic flow over a delta-wing on a flat plate

NASA Astrophysics Data System (ADS)

Wang, D. P.; Xia, Z. X.; Zhao, Y. X.; Wang, Q. H.; Liu, B.

2013-02-01

Employing the nanoparticle-based planar laser scattering (NPLS), supersonic flow over a delta-winged vortex generator on a flat plate was experimentally investigated in a supersonic quiet wind tunnel at Ma = 2.68. The fine structures of the flow field, shock waves, separation vortices, wake, and boundary layer transition were observed in the NPLS images. According to the time-correlation of the NPLS images and the measurement results of particle image velocimetry, the structural model of the flow field was improved further, and coherent wake structures were observed, which is of significance theoretically and in engineering application.

Efficiency of plasma actuator ionization in shock wave modification in a rarefied supersonic flow over a flat plate

NASA Astrophysics Data System (ADS)

Joussot, Romain; Lago, Viviana; Parisse, Jean-Denis

2014-12-01

This paper describes experimental and numerical investigations focused on the shock wave modification, induced by a dc glow discharge, of a Mach 2 flow under rarefied regime. The model under investigation is a flat plate equipped with a plasma actuator composed of two electrodes. The glow discharge is generated by applying a negative potential to the upstream electrode, enabling the creation of a weakly ionized plasma. The natural flow (i.e. without the plasma) exhibits a thick laminar boundary layer and a shock wave with a hyperbolic shape. Images of the flow obtained with an ICCD camera revealed that the plasma discharge induces an increase in the shock wave angle. Thermal effects (volumetric, and at the surface) and plasma effects (ionization, and thermal non-equilibrium) are the most relevant processes explaining the observed modifications. The effect induced by the heating of the flat plate surface is studied experimentally by replacing the upstream electrode by a heating element, and numerically by modifying the thermal boundary condition of the model surface. The results show that for a similar temperature distribution over the plate surface, modifications induced by the heating element are lower than those produced by the plasma. This difference shows that other effects than purely thermal effects are involved with the plasma actuator. Measurements of the electron density with a Langmuir probe highlight the fact that the ionization degree plays an important role into the modification of the flow. The gas properties, especially the isentropic exponent, are indeed modified by the plasma above the actuator and upstream the flat plate. This leads to a local modification of the flow conditions, inducing an increase in the shock wave angle.

Compressible Navier-Stokes equations: A study of leading edge effects

NASA Technical Reports Server (NTRS)

Hariharan, S. I.; Karbhari, P. R.

1987-01-01

A computational method is developed that allows numerical calculations of the time dependent compressible Navier-Stokes equations.The current results concern a study of flow past a semi-infinite flat plate.Flow develops from given inflow conditions upstream and passes over the flat plate to leave the computational domain without reflecting at the downstream boundary. Leading edge effects are included in this paper. In addition, specification of a heated region which gets convected with the flow is considered. The time history of this convection is obtained, and it exhibits a wave phenomena.

On the rotation and pitching of flat plates

NASA Astrophysics Data System (ADS)

Jin, Yaqing; Ji, Sheng; Chamorro, Leonardo P.

2016-11-01

Wind tunnel experiments were performed to characterize the flow-induced rotation and pitching of various flat plates as a function of the thickness ratio, the location of the axis of rotation and turbulence levels. High-resolution telemetry, laser tachometer, and hotwire were used to get time series of the plates motions and the signature of the wake flow at a specific location. Results show that a minor axis offset can induce high-order modes in the plate rotation under low turbulence due to torque unbalance. The spectral decomposition of the flow velocity in the plate wake reveals the existence of a dominating high-frequency mode that corresponds to a static-like vortex shedding occurring at the maximum plate pitch, where the characteristic length scale is the projected width at maximum pitch. The plate thickness ratio shows inverse relation with the angular velocity. A simple model is derived to explain the linear relation between pitching frequency and wind speed. The spectra of the plate rotation show nonlinear relation with the incoming turbulence, and the dominating role of the generated vortices in the plate motions.

STAN5: A program for numerical computation of two-dimensional internal and external boundary layer flows

NASA Technical Reports Server (NTRS)

Crawford, M. E.; Kays, W. M.

1976-01-01

A large variety of two dimensional flows can be accommodated by the program, including boundary layers on a flat plate, flow inside nozzles and diffusers (for a prescribed potential flow distribution), flow over axisymmetric bodies, and developing and fully developed flow inside circular pipes and flat ducts. The flows may be laminar or turbulent, and provision is made to handle transition.

On the aeroacoustic and flow structures developed on a flat plate with a serrated sawtooth trailing edge

NASA Astrophysics Data System (ADS)

Chong, Tze Pei; Vathylakis, Alexandros

2015-10-01

Results of an experimental study on turbulent flow over a flat plate with a serrated sawtooth trailing edge are presented in this paper. After tripping the boundary layer to become turbulent, the broadband noise sources at the sawtooth serrated trailing edge is studied by several experimental techniques. Broadband noise reduction by the serrated sawtooth trailing edge can be realistically achieved in the flat plate configuration. The variations of wall pressure power spectral density and the spanwise coherence (which relates to the spanwise correlation length) in a sawtooth trailing edge play a minor role in the mechanisms underpinning the reduction of self noise radiation. Conditional-averaging technique was applied in the boundary layer data where a pair of pressure-driven oblique vortical structures near the sawtooth side edges is identified. In the current flat plate configuration, the interaction between the vortical structures and the local turbulent boundary layer results in a redistribution of the momentum transport and turbulent shear stress near the sawtooth side edges as well as the sawtooth tip, thus affecting the efficiency of self noise radiation.

Blade motion and nutrient flux to the kelp, Eisenia arborea.

PubMed

Denny, Mark; Roberson, Loretta

2002-08-01

Marine algae rely on currents and waves to replenish the nutrients required for photosynthesis. The interaction of algal blades with flow often involves dynamic reorientations of the blade surface (pitching and flapping) that may in turn affect nutrient flux. As a first step toward understanding the consequences of blade motion, we explore the effect of oscillatory pitching on the flux to a flat plate and to two morphologies of the kelp Eisenia arborea. In slow flow (equivalent to a water velocity of 2.7 cm s(-1)), pitching increases the time-averaged flux to both kelp morphologies, but not to the plate. In fast flow (equivalent to 20 cm s(-1) in water), pitching has negligible effect on flux regardless of shape. For many aspects of flux, the flat plate is a reliable model for the flow-protected algal blade, but predictions made from the plate would substantially underestimate the flux to the flow-exposed blade. These measurements highlight the complexities of flow-related nutrient transport and the need to understand better the dynamic interactions among nutrient flux, blade motion, blade morphology, and water flow.

Turbulent Combustion Study of Scramjet Problem

DTIC Science & Technology

2015-08-01

boundary layer model for 2D simulations of a supersonic flat plate boundary layer . The inflow O2 has an average density of...flow above the flat plate has a transition from a laminar boundary layer to a turbulent boundary layer at a position downstream from the inlet. The...δ. Chapman [13] estimated the number of cells need to resolve the outer layer is proportional to Re0.4 for flat plat boundary layer and

Active control of noise amplification in the flow over a square leading-edge flat plate utilizing DBD plasma actuator

NASA Astrophysics Data System (ADS)

Yadong, HUANG; Benmou, ZHOU

2018-05-01

Perturbation is generally considered as the flow noise, and its energy can gain transient growth in the separation bubble. The amplified perturbations may cause unstable Kelvin–Helmohltz vortices which induce the three-dimensional transition. Active control of noise amplification via dielectric barrier discharge plasma actuator in the flow over a square leading-edge flat plate is numerically studied. The actuator is installed near the plate leading-edge where the separation bubble is formed. The maximum energy amplification of perturbations is positively correlated with the separation bubble scale which decreases with the increasing control parameters. As the magnitude of noise amplification is reduced, the laminar-turbulent transition is successfully suppressed.

In-Flight Boundary-Layer Transition on a Large Flat Plate at Supersonic Speeds

NASA Technical Reports Server (NTRS)

Banks, Daniel W.; Fredericks, Michael Alan; Tracy, Richard R.; Matisheck, Jason R.; Vanecek, Neal D.

2012-01-01

A flight experiment was conducted to investigate the pressure distribution, local flow conditions, and boundary-layer transition characteristics on a large flat plate in flight at supersonic speeds up to Mach 2.0. The primary objective of the test was to characterize the local flow field in preparation for future tests of a high Reynolds number natural laminar flow test article. The tests used a F-15B testbed aircraft with a bottom centerline mounted test fixture. A second objective was to determine the boundary-layer transition characteristics on the flat plate and the effectiveness of using a simplified surface coating for future laminar flow flight tests employing infrared thermography. Boundary-layer transition was captured using an onboard infrared imaging system. The infrared imagery was captured in both analog and digital formats. Surface pressures were measured with electronically scanned pressure modules connected to 60 surface-mounted pressure orifices. The local flow field was measured with five 5-hole conical probes mounted near the leading edge of the test fixture. Flow field measurements revealed the local flow characteristics including downwash, sidewash, and local Mach number. Results also indicated that the simplified surface coating did not provide sufficient insulation from the metallic structure, which likely had a substantial effect on boundary-layer transition compared with that of an adiabatic surface. Cold wall conditions were predominant during the acceleration to maximum Mach number, and warm wall conditions were evident during the subsequent deceleration. The infrared imaging system was able to capture shock wave impingement on the surface of the flat plate in addition to indicating laminar-to-turbulent boundary-layer transition.

Two-Piece Screens for Decontaminating Granular Material

NASA Technical Reports Server (NTRS)

Backes, Douglas; Poulter, Clay; Godfrey, Max; Dutton, Melinda; Tolman, Dennis

2009-01-01

Two-piece screens have been designed specifically for use in filtering a granular material to remove contaminant particles that are significantly wider or longer than are the desired granules. In the original application for which the twopiece screens were conceived, the granular material is ammonium perchlorate and the contaminant particles tend to be wires and other relatively long, rigid strands. The basic design of the twopiece screens can be adapted to other granular materials and contaminants by modifying critical dimensions to accommodate different grain and contaminant- particle sizes. A two-piece screen of this type consists mainly of (1) a top flat plate perforated with circular holes arranged in a hexagonal pattern and (2) a bottom plate that is also perforated with circular holes (but not in a pure hexagonal pattern) and is folded into an accordion structure. Fabrication of the bottom plate begins with drilling circular holes into a flat plate in a hexagonal pattern that is interrupted, at regular intervals, by parallel gaps. The plate is then folded into the accordion structure along the gaps. Because the folds are along the gaps, there are no holes at the peaks and valleys of the accordion screen. The top flat plate and the bottom accordion plate are secured within a metal frame. The resulting two-piece screen is placed at the bottom opening of a feed hopper containing the granular material to be filtered. Tests have shown that such long, rigid contaminant strands as wires readily can pass through a filter consisting of the flat screen alone and that the addition of the accordion screen below the flat screen greatly increases the effectiveness of removal of wires and other contaminant strands. Part of the reason for increased effectiveness is in the presentation of the contaminant to the filter surface. Testing has shown that wire type contamination will readily align itself parallel to the material direction flow. Since this direction of flow is nearly always perpendicular to the filter surface holes, the contamination is automatically aligned to pass through. The two-filter configuration reduces the likelihood that a given contaminant strand will be aligned with the flow of material by eliminating the perpendicular presentation angle. Thus, for wires of a certain diameter, a two-piece screen is 20 percent more effective than is the corresponding flat perforated plate alone, even if the holes in the flat plate are narrower. An accordion screen alone is similarly effective in catching contaminants, but lumps of agglomerated granules of the desired material often collect in the valleys and clog the screen. The addition of a flat screen above the accordion screen prevents clogging of the accordion screen. Flat wire screens have often been used to remove contaminants from granular materials, and are about as effective as are the corresponding perforated flat plates used alone.

Experimental study of turbulent flow heat transfer and pressure drop in a plate heat exchanger with chevron plates

DOE Office of Scientific and Technical Information (OSTI.GOV)

Muley, A.; Manglik, R.M.

1997-07-01

Experimental data for isothermal pressure drop and heat transfer in single-phase water flows in a plate heat exchanger (PHE) with chevron plates are presented. A single-pass, U-type, counterflow PHE, with three different chevron plate arrangements is employed: two symmetric plate arrangements with {beta} = 30/30{degree} and 60/60{degree}, and a mixed-plate arrangement with {beta} = 30/60{degree}. With water flow rates in the turbulent flow regime (600 < Re < 10{sup 4} and 2 < Pr < 6), effects of the chevron corrugation inclination angle {beta} on Nu and f characteristics of the PHE are investigated. As {beta} increases and compared tomore » a flat-plate pack, up to 2 to 5 times higher Nu are obtained; the concomitant f, however, are 13 to 44 times higher. Based on the experimental data for Re {le} 1,000, predictive correlations of the form Nu = C{sub 1}{beta} Re{sup p1({beta})} Pr{sup 1/3} ({mu}/{mu}{sub w}){sup 0.14} and f = C{sub 2}{beta} Re{sup p2({beta})} are devised. Also, at constant pumping power and depending upon {beta}, the heat transfer is found to be enhanced over 1.8 times that in equivalent flat-plate channels.« less

Correlation of Water Frost Porosity in Laminar Flow over Flat Surfaces

NASA Technical Reports Server (NTRS)

Kandula, Max

2011-01-01

A dimensionless correlation has been proposed for water frost porosity expressing its dependence on frost surface temperature and Reynolds number for laminar forced flow over a flat surface. The correlation is presented in terms of a dimensionless frost surface temperature scaled with the cold plate temperature, and the freezing temperature. The flow Reynolds number is scaled with reference to the critical Reynolds number for laminar-turbulent transition. The proposed correlation agrees satisfactorily with the simultaneous measurements of frost density and frost surface temperature covering a range of plate temperature, ambient air velocity, humidity, and temperature. It is revealed that the frost porosity depends primarily on the frost surface and the plate temperatures and the flow Reynolds number, and is only weakly dependent on the relative humidity. The results also point out the general character of frost porosity displaying a decrease with an increase in flow Reynolds number.

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

NASA Technical Reports Server (NTRS)

Rossow, Vernon J

1958-01-01

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.

Weak incident shock interactions with Mach 8 laminar boundary layers. [of flat plate

NASA Technical Reports Server (NTRS)

Kaufman, L. G., II; Johnson, C. B.

1974-01-01

Weak shock-wave interactions with boundary layers on a flat plate were investigated experimentally in Mach 8 variable-density tunnel for plate-length Reynolds numbers. The undisturbed boundary layers were laminar over the entire plate length. Pressure and heat-transfer distributions were obtained for wedge-generated incident shock waves that resulted in pressure rises ranging from 1.36 to 4.46 (both nonseparated and separated boundary-layer flows). The resulting heat-transfer amplifications ranged from 1.45 to 14. The distributions followed established trends for nonseparated flows, for incipient separation, and for laminar free-interaction pressure rises. The experimental results corroborated established trends for the extent of the pressure rise and for certain peak heat-transfer correlations.

A laser-induced heat flux technique for convective heat transfer measurements in high speed flows

NASA Technical Reports Server (NTRS)

Porro, A. R.; Keith, T. G., Jr.; Hingst, W. R.

1991-01-01

A technique is developed to measure the local convective heat transfer coefficient on a model surface in a supersonic flow field. The technique uses a laser to apply a discrete local heat flux at the model test surface, and an infrared camera system determines the local temperature distribution due to the heating. From this temperature distribution and an analysis of the heating process, a local convective heat transfer coefficient is determined. The technique was used to measure the local surface convective heat transfer coefficient distribution on a flat plate at nominal Mach numbers of 2.5, 3.0, 3.5, and 4.0. The flat plate boundary layer initially was laminar and became transitional in the measurement region. The experimentally determined convective heat transfer coefficients were generally higher than the theoretical predictions for flat plate laminar boundary layers. However, the results indicate that this nonintrusive optical measurement technique has the potential to measure surface convective heat transfer coefficients in high speed flow fields.

Standardized performance tests of collectors of solar thermal energy - A flat-plate copper collector with parallel mylar striping

NASA Technical Reports Server (NTRS)

Johnson, S. M.

1976-01-01

Basic test results are reported for a flat plate solar collector whose performance was determined in a solar simulator. The collector was tested over ranges of inlet temperatures, fluxes and one coolant flow rate. Collector efficiency is correlated in terms of inlet temperature and flux level.

Laminar Horse Shoe Vortex for a Triangular Cylinder Flat Plate Juncture

NASA Astrophysics Data System (ADS)

Younis, Muhammad Yamin; Zhang, H.; Hu, B.; Sohail, Muhammad Amjad; Muhammad, Zaka

2011-09-01

Juncture Flows are 3-D flows which occur when fluid, flowing on a flat surface encounters an obstacle on its way. The flow separates from the surface due to the adverse pressure gradient produced by the obstacle and rolls up to form a vortical structure known as "Horse Shoe Vortex". Studies and research is underway to completely identify and understand different hidden features of the horse shoe vortex. In the present study the structure of horse shoe vortex for a Triangular cylinder flat plate juncture is visualized using particle image velocimetry (PIV). The diameter Reynolds number experimented is within the range of 2 000 ≤ ReA ≤ 8 000. The flow characteristics are studied for the horse shoe vortex and the flow is categorized into different flow regimes. (1) Steady or static vortex system, (2) periodic amalgamating vortex system, and (3) periodic break away vortex system. The range for different vortex systems is also calculated with shedding frequency for the periodic unsteady vortex system. Most importantly the range of Reynolds number for which the above mentioned vortex systems exist is much higher for Sharp leading edge cylinder than for blunt (circular and Elliptical) and flat (Square) leading edge cylinders studied earlier.

DSMC simulations of leading edge flat-plate boundary layer flows at high Mach number

NASA Astrophysics Data System (ADS)

Pradhan, Sahadev, , Dr.

2017-04-01

The flow over a 2D leading-edge flat plate is studied at Mach number Ma =(Uinf / \\setmn √{kBTinf / m}) in the range

DSMC simulations of leading edge flat-plate boundary layer flows at high Mach number

NASA Astrophysics Data System (ADS)

Pradhan, Sahadev, , Dr.

2016-11-01

The flow over a 2D leading-edge flat plate is studied at Mach number Ma = (Uinf /√{kBTinf / m }) in the range

DSMC simulations of leading edge flat-plate boundary layer flows at high Mach number

NASA Astrophysics Data System (ADS)

Pradhan, Sahadev, , Dr.

2017-01-01

The flow over a 2D leading-edge flat plate is studied at Mach number Ma = (Uinf /√{kBTinf / m }) in the range

DSMC simulations of leading edge flat-plate boundary layer flows at high Mach number

NASA Astrophysics Data System (ADS)

Pradhan, Sahadev

2016-10-01

The flow over a 2D leading-edge flat plate is studied at Mach number Ma = (Uinf / {kBTinf /m}) in the range

DSMC simulations of leading edge flat-plate boundary layer flows at high Mach number

NASA Astrophysics Data System (ADS)

Pradhan, Sahadev, , Dr.

The flow over a 2D leading-edge flat plate is studied at Mach number Ma = (Uinf / ∖ sqrt{kBTinf / m})in the range

Flat Plate Boundary Layer Stimulation Using Trip Wires and Hama Strips

NASA Astrophysics Data System (ADS)

Peguero, Charles; Henoch, Charles; Hrubes, James; Fredette, Albert; Roberts, Raymond; Huyer, Stephen

2017-11-01

Water tunnel experiments on a flat plate at zero angle of attack were performed to investigate the effect of single roughness elements, i.e., trip wires and Hama strips, on the transition to turbulence. Boundary layer trips are traditionally used in scale model testing to force a boundary layer to transition from laminar to turbulent flow at a single location to aid in scaling of flow characteristics. Several investigations of trip wire effects exist in the literature, but there is a dearth of information regarding the influence of Hama strips on the flat plate boundary layer. The intent of this investigation is to better understand the effects of boundary layer trips, particularly Hama strips, and to investigate the pressure-induced drag of both styles of boundary layer trips. Untripped and tripped boundary layers along a flat plate at a range of flow speeds were characterized with multiple diagnostic measurements in the NUWC/Newport 12-inch water tunnel. A wide range of Hama strip and wire trip thicknesses were used. Measurements included dye flow visualization, direct skin friction and parasitic drag force, boundary layer profiles using LDV, wall shear stress fluctuations using hot film anemometry, and streamwise pressure gradients. Test results will be compared to the CFD and boundary layer model results as well as the existing body of work. Conclusions, resulting in guidance for application of Hama strips in model scale experiments and non-dimensional predictions of pressure drag will be presented.

Exploiting similarity in turbulent shear flows for turbulence modeling

NASA Technical Reports Server (NTRS)

Robinson, David F.; Harris, Julius E.; Hassan, H. A.

1992-01-01

It is well known that current k-epsilon models cannot predict the flow over a flat plate and its wake. In an effort to address this issue and other issues associated with turbulence closure, a new approach for turbulence modeling is proposed which exploits similarities in the flow field. Thus, if we consider the flow over a flat plate and its wake, then in addition to taking advantage of the log-law region, we can exploit the fact that the flow becomes self-similar in the far wake. This latter behavior makes it possible to cast the governing equations as a set of total differential equations. Solutions of this set and comparison with measured shear stress and velocity profiles yields the desired set of model constants. Such a set is, in general, different from other sets of model constants. The rational for such an approach is that if we can correctly model the flow over a flat plate and its far wake, then we can have a better chance of predicting the behavior in between. It is to be noted that the approach does not appeal, in any way, to the decay of homogeneous turbulence. This is because the asymptotic behavior of the flow under consideration is not representative of the decay of homogeneous turbulence.

Exploiting similarity in turbulent shear flows for turbulence modeling

NASA Astrophysics Data System (ADS)

Robinson, David F.; Harris, Julius E.; Hassan, H. A.

1992-12-01

It is well known that current k-epsilon models cannot predict the flow over a flat plate and its wake. In an effort to address this issue and other issues associated with turbulence closure, a new approach for turbulence modeling is proposed which exploits similarities in the flow field. Thus, if we consider the flow over a flat plate and its wake, then in addition to taking advantage of the log-law region, we can exploit the fact that the flow becomes self-similar in the far wake. This latter behavior makes it possible to cast the governing equations as a set of total differential equations. Solutions of this set and comparison with measured shear stress and velocity profiles yields the desired set of model constants. Such a set is, in general, different from other sets of model constants. The rational for such an approach is that if we can correctly model the flow over a flat plate and its far wake, then we can have a better chance of predicting the behavior in between. It is to be noted that the approach does not appeal, in any way, to the decay of homogeneous turbulence. This is because the asymptotic behavior of the flow under consideration is not representative of the decay of homogeneous turbulence.

An investigation of the flow characteristics in the blade endwall corner region

NASA Technical Reports Server (NTRS)

Hazarika, Birinchi K.; Raj, Rishi S.

1987-01-01

Studies were undertaken to determine the structure of the flow in the blade end wall corner region simulated by attaching two uncambered airfoils on either side of a flat plate with a semicircular leading edge. Detailed measurements of the corner flow were obtained with conventional pressure probes, hot wire anemometry, and flow visualization. The mean velocity profiles and six components of the Reynolds stress tensor were obtained with an inclined single sensor hot wire probe whereas power spectra were obtained with a single sensor oriented normal to the flow. Three streamwise vortices were identified based on the surface streamlines, distortion of total pressure profiles, and variation of mean velocity components in the corner. A horseshoe vortex formed near the leading edge of the airfoil. Within a short distance downstream, a corner vortex was detected between the horseshoe vortex and the surfaces forming the corner. A third vortex was formed at the rear portion of the corner between the corner vortex and the surface of the flat plate. Turbulent shear stress and production of turbulence are negligibly small. A region of negative turbulent shear stress was also observed near the region of low turbulence intensity from the vicinity of the flat plate.

Large volume flow-through scintillating detector

DOEpatents

Gritzo, Russ E.; Fowler, Malcolm M.

1995-01-01

A large volume flow through radiation detector for use in large air flow situations such as incinerator stacks or building air systems comprises a plurality of flat plates made of a scintillating material arranged parallel to the air flow. Each scintillating plate has a light guide attached which transfers light generated inside the scintillating plate to an associated photomultiplier tube. The output of the photomultiplier tubes are connected to electronics which can record any radiation and provide an alarm if appropriate for the application.

An eddy-viscosity treatment of the unsteady turbulent boundary layer on a flat plate in an expansion tube

NASA Technical Reports Server (NTRS)

Gupta, R. N.; Trimpi, R. L.

1974-01-01

An analysis is presented for the relaxation of a turbulent boundary layer on a semiinfinite flat plate after passage of a shock wave and a trailing driver gas-driven gas interface. The problem has special application to expansion tube flows. The flow-governing equations have been transformed into the Lamcrocco variables. The numerical results indicate that a fully turbulent boundary layer relaxes faster to the final steady-state values of heat transfer and skin-friction than a fully laminar boundary layer.

Interaction of a Rectangular Jet with a Flat-Plate Placed Parallel to the Flow

NASA Technical Reports Server (NTRS)

Zaman, K. B. M. Q.; Brown, C. A.; Bridges, J. A.

2013-01-01

An experimental study is carried out addressing the flowfield and radiated noise from the interaction of a large aspect ratio rectangular jet with a flat plate placed parallel to but away from the direct path of the jet. Sound pressure level spectra exhibit an increase in the noise levels for both the 'reflected' and 'shielded' sides of the plate relative to the free-jet case. Detailed cross-sectional distributions of flowfield properties obtained by hot-wire anemometry are documented for a low subsonic condition. Corresponding mean Mach number distributions obtained by Pitot-probe surveys are presented for high subsonic conditions. In the latter flow regime and for certain relative locations of the plate, a flow resonance accompanied by audible tones is encountered. Under the resonant condition the jet cross-section experiences an 'axis-switching' and flow visualization indicates the presence of an organized 'vortex street'. The trends of the resonant frequency variation with flow parameters exhibit some similarities to, but also marked differences with, corresponding trends of the well-known edgetone phenomenon.

Velocity and temperature profiles in near-critical nitrogen flowing past a horizontal flat plate

NASA Technical Reports Server (NTRS)

Simoneau, R. J.

1977-01-01

Boundary layer velocity and temperature profiles were measured for nitrogen near its thermodynamic critical point flowing past a horizontal flat plate. The results were compared measurements made for vertically upward flow. The boundary layer temperatures ranged from below to above the thermodynamic critical temperature. For wall temperatures below the thermodynamic critical temperature there was little variation between the velocity and temperature profiles in three orientations. In all three orientations the point of crossing into the critical temperature region is marked by a significant flattening of the velocity and temperature profiles and also a decrease in heat transfer coefficient.

Influence of end plates on aerodynamic characteristics of bluff bodies

NASA Astrophysics Data System (ADS)

Shmigirilov, Rodion; Ryabinin, Anatoly

2018-05-01

Aerodynamic characteristics of flat plate oriented normally to the flow are studied in the wind tunnel. The experiments are carried out without end plates and with round end plates of different diameter. We obtain that end plates increase the base pressure, the drag coefficient and decrease the length of recirculation region.

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

NASA Technical Reports Server (NTRS)

Rodkiewicz, C. M.; Gupta, R. N.

1971-01-01

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.

Effect of leading-edge geometry on boundary-layer receptivity to freestream sound

NASA Technical Reports Server (NTRS)

Lin, Nay; Reed, Helen L.; Saric, W. S.

1991-01-01

The receptivity to freestream sound of the laminar boundary layer over a semi-infinite flat plate with an elliptic leading edge is simulated numerically. The incompressible flow past the flat plate is computed by solving the full Navier-Stokes equations in general curvilinear coordinates. A finite-difference method which is second-order accurate in space and time is used. Spatial and temporal developments of the Tollmien-Schlichting wave in the boundary layer, due to small-amplitude time-harmonic oscillations of the freestream velocity that closely simulate a sound wave travelling parallel to the plate, are observed. The effect of leading-edge curvature is studied by varying the aspect ratio of the ellipse. The boundary layer over the flat plate with a sharper leading edge is found to be less receptive. The relative contribution of the discontinuity in curvature at the ellipse-flat-plate juncture to receptivity is investigated by smoothing the juncture with a polynomial. Continuous curvature leads to less receptivity. A new geometry of the leading edge, a modified super ellipse, which provides continuous curvature at the juncture with the flat plate, is used to study the effect of continuous curvature and inherent pressure gradient on receptivity.

Numerical study of the flow structures in flat plate and the wall-mounted hump induced by the unsteady DBD plasma

NASA Astrophysics Data System (ADS)

Yu, Jianyang; Liu, Huaping; Wang, Ruoyu; Chen, Fu

2017-01-01

In this work, the dielectric-barrier-discharge plasma actuator was employed to study the flow structures induced by the plasma actuator over a flat plate and a wall-mounted hump. A phenomenological dielectric-barrier-discharge plasma model which regarded the plasma effect as the body force was implemented into the Navier-Stokes equations solved by the method of large eddy simulations. The results show that a series of vortex pairs, which indicated dipole formation and periodicity distribution were generated in the boundary layer when the plasma was applied to the flow over a flat plane. They would enhance the energy exchanged between the near wall region and the free stream. Besides, their spatial trajectories are deeply affected by the actuation strength. When the actuator was engaged in the flow over a wall-mounted hump, the vortex pairs were also produced, which was able to delay flow separation as well as to promote flow reattachment and reduce the generation of a vortex, achieving the goal of reducing dissipation and decreasing flow resistance.

DSMC simulations of leading edge flat-plate boundary layer flows at high Mach number

NASA Astrophysics Data System (ADS)

Pradhan, Sahadev

2016-09-01

The flow over a 2D leading-edge flat plate is studied at Mach number Ma = (Uinf /√{kBTinf / m }) in the range

Skin friction and heat transfer correlations for high-speed low-density flow past a flat plate

NASA Technical Reports Server (NTRS)

Woronowicz, Michael S.; Baganoff, Donald

1991-01-01

The independent and dependent variables associated with drag and heat transfer to a flat plate at zero incidence in high-speed, rarefied flow are analyzed anew to reflect the importance of kinetic effects occurring near the plate surface on energy and momentum transfer, rather than following arguments normally used to describe continuum, higher density flowfields. A new parameter, the wall Knudsen number Knx,w, based on an estimate of the mean free path length of molecules having just interacted with the surface of the plate, is introduced and used to correlate published drag and heat transfer data. The new parameter is shown to provide better correlation than either the viscous interaction parameter X or the widely-used slip parameter Voo for drag and heat transfer data over a wide range of Mach numbers, Reynolds numbers, and plate-to-freestream stagnation temperature ratios.

Resonant Interaction of a Rectangular Jet with a Flat-Plate

NASA Technical Reports Server (NTRS)

Zaman, K. B. M. Q.; Fagan, A. F.; Clem, M. M.; Brown, C. A.

2014-01-01

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.

Application of a Laser Interferometer Skin-Friction Meter in Complex Flows

NASA Technical Reports Server (NTRS)

Monson, D. J.; Driver, D. M.; Szodruch, J.

1981-01-01

A nonintrusive skin-friction meter has been found useful for a variety of complex wind-tunnel flows. This meter measures skin friction with a remotely located laser interferometer that monitors the thickness change of a thin oil film. Its accuracy has been proven in a low-speed flat-plate flow. The wind-tunnel flows described here include sub-sonic separated and reattached flow over a rearward-facing step, supersonic flow over a flat plate at high Reynolds numbers, and supersonic three - dimensional vortical flow over the lee of a delta wing at angle of attack. The data-reduction analysis was extended to apply to three-dimensional flows with unknown flow direction, large pressure and shear gradients, and large oil viscosity changes with time. The skin friction measurements were verified, where possible, with results from more conventional techniques and also from theoretical computations.

Reducing cylinder drag by adding a plate

NASA Astrophysics Data System (ADS)

Frolov, Vladimir A.; Kozlova, Anna S.

2017-10-01

Reducing the drag of bodies is a central problem of modern aerohydrodynamics. The paper presents theoretical and experimental studies of a new method for reducing the drag of a circular cylinder. To reduce the drag we propose to install a flat plate along the flow in front of the cylinder. The theoretical investigation of the drag was carried out using FlowSimulation software. An experimental study of the body drag was performed in an open wind tunnel. The drag coefficient results of the cylinder depended on the different locations of the flat plate relative to the cylinder. The following geometric characteristics of the cylinder/plate are studied: the width of the gap between the cylinder and the plate and the meridional angle of the plate with respect to the cylinder. On the basis of Numerical and Physical Modeling, the values of the drag coefficient for the cylinder/plate are presented. The results included establishment the locations of the cylinder/plate which give the value of the drag coefficient for the combination of the two bodies. That total drag coefficient of the cylinder/plate can be less than the cylinder alone.

Design of a High Viscosity Couette Flow Facility for Patterned Surface Drag Measurements

NASA Astrophysics Data System (ADS)

Johnson, Tyler; Lang, Amy

2009-11-01

Direct drag measurements can be difficult to obtain with low viscosity fluids such as air or water. In this facility, mineral oil is used as the working fluid to increase the shear stress across the surface of experimental models. A mounted conveyor creates a flow within a plexiglass tank. The experimental model of a flat or patterned surface is suspended above a moving belt. Within the gap between the model and moving belt a Couette flow with a linear velocity profile is created. PIV measurements are used to determine the exact velocities and the Reynolds numbers for each experiment. The model is suspended by bars that connect to the pillow block housing of each bearing. Drag is measured by a force gauge connected to linear roller bearings that slide along steel rods. The patterned surfaces, initially consisting of 2-D cavities, are embedded in a plexiglass plate so as to keep the total surface area constant for each experiment. First, the drag across a flat plate is measured and compared to theoretical values for laminar Couette flow. The drag for patterned surfaces is then measured and compared to a flat plate.

Experimental Technique and Assessment for Measuring the Convective Heat Transfer Coefficient from Natural Ice Accretions

NASA Technical Reports Server (NTRS)

Masiulaniec, K. Cyril; Vanfossen, G. James, Jr.; Dewitt, Kenneth J.; Dukhan, Nihad

1995-01-01

A technique was developed to cast frozen ice shapes that had been grown on a metal surface. This technique was applied to a series of ice shapes that were grown in the NASA Lewis Icing Research Tunnel on flat plates. Nine flat plates, 18 inches square, were obtained from which aluminum castings were made that gave good ice shape characterizations. Test strips taken from these plates were outfitted with heat flux gages, such that when placed in a dry wind tunnel, can be used to experimentally map out the convective heat transfer coefficient in the direction of flow from the roughened surfaces. The effects on the heat transfer coefficient for both parallel and accelerating flow will be studied. The smooth plate model verification baseline data as well as one ice roughened test case are presented.

Analysis of Turbulent Flow and Heat Transfer on a Flat Plate at High Mach Numbers with Variable Fluid Properties

NASA Technical Reports Server (NTRS)

Deissler, R. G.; Loeffler, A. L., Jr.

1959-01-01

A previous analysis of turbulent heat transfer and flow with variable fluid properties in smooth passages is extended to flow over a flat plate at high Mach numbers, and the results are compared with experimental data. Velocity and temperature distributions are calculated for a boundary layer with appreciative effects of frictional heating and external heat transfer. Viscosity and thermal conductivity are assumed to vary as a power or the temperature, while Prandtl number and specific heat are taken as constant. Skin-friction and heat-transfer coefficients are calculated and compared with the incompressible values. The rate of boundary-layer growth is obtained for various Mach numbers.

Frost Growth and Densification on a Flat Surface in Laminar Flow with Variable Humidity

NASA Technical Reports Server (NTRS)

Kandula, M.

2012-01-01

Experiments are performed concerning frost growth and densification in laminar flow over a flat surface under conditions of constant and variable humidity. The flat plate test specimen is made of aluminum-6031, and has dimensions of 0.3 mx0.3 mx6.35 mm. Results for the first variable humidity case are obtained for a plate temperature of 255.4 K, air velocity of 1.77 m/s, air temperature of 295.1 K, and a relative humidity continuously ranging from 81 to 54%. The second variable humidity test case corresponds to plate temperature of 255.4 K, air velocity of 2.44 m/s, air temperature of 291.8 K, and a relative humidity ranging from 66 to 59%. Results for the constant humidity case are obtained for a plate temperature of 263.7 K, air velocity of 1.7 m/s, air temperature of 295 K, and a relative humidity of 71.6 %. Comparisons of the data with the author's frost model extended to accommodate variable humidity suggest satisfactory agreement between the theory and the data for both constant and variable humidity.

Vortex detection through pressure measurements

NASA Astrophysics Data System (ADS)

Bhide, Aditi

Vortex Generators (VGs) are known to hinder boundary layer separation, a frequently unwanted phenomenon when it comes to external flows over aircraft wings, on-ground vehicles or internal flows within pipes, diffusers and turbomachinery. Boundary layer separation leads to loss of lift, higher drag and subsequently, energy losses. The vortices generated inhibit boundary layer separation. This thesis is an effort to discern the strength and location of these generated vortices using an array of VGs over a flat plate. Such information may be useful in the future in active control systems for streamwise vortices, which have been proposed to relaminarize turbulent boundary layers. Flow over flat plates, simulated using wind tunnel experiments, is studied for pressure variation using an array of pressure ports mounted over the plate and connected to suitable pressure sensors. Pressure coefficient and Velocity maps are generated using the data obtained from the Kirsten Wind Tunnel data acquisition system. These represent the nature of the flow field over the plate and are used to locate the vortices and determine their strength. It was found that the vortices can be detected using this method and their strength and location can be estimated.

Standard performance tests of collectors of solar thermal energy: A selectively coated, flat-plate copper collector with one transparent cover and a tube-to-tube spacing of 3-7/8 inches

NASA Technical Reports Server (NTRS)

1976-01-01

Basic test results are given of a flat-plate solar collector whose performance was determined in the NASA-Lewis solar simulator. The collector was tested over ranges of inlet temperatures, fluxes, and coolant flow rates. Collector efficiency is correlated in terms of inlet temperature and flux level.

Film Condensation with and Without Body Force in Boundary-Layer Flow of Vapor Over a Flat Plate

NASA Technical Reports Server (NTRS)

Chung, Paul M.

1961-01-01

Laminar film condensation under the simultaneous influence of gas-liquid interface shear and body force (g force) is analyzed over a flat plate. Important parameters governing condensation and heat transfer of pure vapor are determined. Mixtures of condensable vapor and noncondensable gas are also analyzed. The conditions under which the body force has a significant influence on condensation are determined.

Comparisons of the Maxwell and CLL gas/surface interaction models using DSMC

NASA Technical Reports Server (NTRS)

Hedahl, Marc O.; Wilmoth, Richard G.

1995-01-01

The behavior of two different models of gas-surface interactions is studied using the Direct Simulation Monte Carlo (DSMC) method. The DSMC calculations examine differences in predictions of aerodynamic forces and heat transfer between the Maxwell and the Cercignani-Lampis-Lord (CLL) models for flat plate configurations at freestream conditions corresponding to a 140 km orbit around Venus. The size of the flat plate represents one of the solar panels on the Magellan spacecraft, and the freestream conditions correspond to those experienced during aerobraking maneuvers. Results are presented for both a single flat plate and a two-plate configuration as a function of angle of attack and gas-surface accommodation coefficients. The two-plate system is not representative of the Magellan geometry but is studied to explore possible experiments that might be used to differentiate between the two gas-surface interaction models. The Maxwell and CLL models produce qualitatively similar results for the aerodynamic forces and heat transfer on a single flat plate. However, the flow fields produced with the two models are qualitatively different for both the single-plate and two-plate calculations. These differences in the flowfield lead to predictions of the angle of attack for maximum heat transfer in a two plate configuration that are distinctly different for the two gas-surface interactions models.

Vortex dynamics and wall shear stress behaviour associated with an elliptic jet impinging upon a flat plate

NASA Astrophysics Data System (ADS)

Long, J.; New, T. H.

2016-07-01

Vortical structures and dynamics of a Re h = 2100 elliptic jet impinging upon a flat plate were studied at H/ d h = 1, 2 and 4 jet-to-plate separation distances. Flow investigations were conducted along both its major and minor planes using laser-induced fluorescence and digital particle image velocimetry techniques. Results show that the impingement process along the major plane largely consists of primary jet ring-vortex and wall-separated secondary vortex formations, where they subsequently separate from the flat plate at smaller H/ d h = 1 and 2 separation distances. Key vortex formation locations occur closer to the impingement point as the separation distance increases. Interestingly, braid vortices and rib structures begin to take part in the impingement process at H/ d h = 4 and wave instabilities dominate the flow field. In contrast, significantly more coherent primary and secondary vortices with physically larger vortex core sizes and higher vortex strengths are observed along the minor plane, with no signs of braid vortices and rib structures. Lastly, influences of these different flow dynamics on the major and minor plane instantaneous and mean skin friction coefficient levels are investigated to shed light on the effects of separation distance on the wall shear stress distributions.

Direct numerical simulation of laminar-turbulent flow over a flat plate at hypersonic flow speeds

NASA Astrophysics Data System (ADS)

Egorov, I. V.; Novikov, A. V.

2016-06-01

A method for direct numerical simulation of a laminar-turbulent flow around bodies at hypersonic flow speeds is proposed. The simulation is performed by solving the full three-dimensional unsteady Navier-Stokes equations. The method of calculation is oriented to application of supercomputers and is based on implicit monotonic approximation schemes and a modified Newton-Raphson method for solving nonlinear difference equations. By this method, the development of three-dimensional perturbations in the boundary layer over a flat plate and in a near-wall flow in a compression corner is studied at the Mach numbers of the free-stream of M = 5.37. In addition to pulsation characteristic, distributions of the mean coefficients of the viscous flow in the transient section of the streamlined surface are obtained, which enables one to determine the beginning of the laminar-turbulent transition and estimate the characteristics of the turbulent flow in the boundary layer.

A computational study on the influence of insect wing geometry on bee flight mechanics

PubMed Central

Feaster, Jeffrey; Bayandor, Javid

2017-01-01

ABSTRACT Two-dimensional computational fluid dynamics (CFD) is applied to better understand the effects of wing cross-sectional morphology on flow field and force production. This study investigates the influence of wing cross-section on insect scale flapping flight performance, for the first time, using a morphologically representative model of a bee (Bombus pensylvanicus) wing. The bee wing cross-section was determined using a micro-computed tomography scanner. The results of the bee wing are compared with flat and elliptical cross-sections, representative of those used in modern literature, to determine the impact of profile variation on aerodynamic performance. The flow field surrounding each cross-section and the resulting forces are resolved using CFD for a flight speed range of 1 to 5 m/s. A significant variation in vortex formation is found when comparing the ellipse and flat plate with the true bee wing. During the upstroke, the bee and approximate wing cross-sections have a much shorter wake structure than the flat plate or ellipse. During the downstroke, the flat plate and elliptical cross-sections generate a single leading edge vortex, while the approximate and bee wings generate numerous, smaller structures that are shed throughout the stroke. Comparing the instantaneous aerodynamic forces on the wing, the ellipse and flat plate sections deviate progressively with velocity from the true bee wing. Based on the present findings, a simplified cross-section of an insect wing can misrepresent the flow field and force production. We present the first aerodynamic study using a true insect wing cross-section and show that the wing corrugation increases the leading edge vortex formation frequency for a given set of kinematics. PMID:29061734

A computational study on the influence of insect wing geometry on bee flight mechanics.

PubMed

Feaster, Jeffrey; Battaglia, Francine; Bayandor, Javid

2017-12-15

Two-dimensional computational fluid dynamics (CFD) is applied to better understand the effects of wing cross-sectional morphology on flow field and force production. This study investigates the influence of wing cross-section on insect scale flapping flight performance, for the first time, using a morphologically representative model of a bee ( Bombus pensylvanicus ) wing. The bee wing cross-section was determined using a micro-computed tomography scanner. The results of the bee wing are compared with flat and elliptical cross-sections, representative of those used in modern literature, to determine the impact of profile variation on aerodynamic performance. The flow field surrounding each cross-section and the resulting forces are resolved using CFD for a flight speed range of 1 to 5 m/s. A significant variation in vortex formation is found when comparing the ellipse and flat plate with the true bee wing. During the upstroke, the bee and approximate wing cross-sections have a much shorter wake structure than the flat plate or ellipse. During the downstroke, the flat plate and elliptical cross-sections generate a single leading edge vortex, while the approximate and bee wings generate numerous, smaller structures that are shed throughout the stroke. Comparing the instantaneous aerodynamic forces on the wing, the ellipse and flat plate sections deviate progressively with velocity from the true bee wing. Based on the present findings, a simplified cross-section of an insect wing can misrepresent the flow field and force production. We present the first aerodynamic study using a true insect wing cross-section and show that the wing corrugation increases the leading edge vortex formation frequency for a given set of kinematics. © 2017. Published by The Company of Biologists Ltd.

Euler flow predictions for an oscillating cascade using a high resolution wave-split scheme

NASA Technical Reports Server (NTRS)

Huff, Dennis L.; Swafford, Timothy W.; Reddy, T. S. R.

1991-01-01

A compressible flow code that can predict the nonlinear unsteady aerodynamics associated with transonic flows over oscillating cascades is developed and validated. The code solves the two dimensional, unsteady Euler equations using a time-marching, flux-difference splitting scheme. The unsteady pressures and forces can be determined for arbitrary input motions, although only harmonic pitching and plunging motions are addressed. The code solves the flow equations on a H-grid which is allowed to deform with the airfoil motion. Predictions are presented for both flat plate cascades and loaded airfoil cascades. Results are compared to flat plate theory and experimental data. Predictions are also presented for several oscillating cascades with strong normal shocks where the pitching amplitudes, cascade geometry and interblade phase angles are varied to investigate nonlinear behavior.

Calculation of oblique-shock-wave laminar-boundary-layer interaction on a flat plate

NASA Technical Reports Server (NTRS)

Goldberg, U.; Reshotko, E.

1980-01-01

A finite difference solution to the problem of the interaction between an impinging oblique shock wave and the laminar boundary layer on a flat plate is presented. The boundary layer equations coupled with the Prandtl-Meyer relation for the external flow are used to calculate the flow field. A method for the calculation of the separated flow region is presented and discussed. Comparisons between this theory and the experimental results of other investigators show fairly good agreement. Results are presented for the case of a cooled wall with an oncoming flow at Mach number 2.0 without and with suction. The results show that a small amount of suction greatly reduces the extent of the separated region in the vicinity of the shock impingement location.

Influence of wire-coil inserts on the thermo-hydraulic performance of a flat-plate solar collector

NASA Astrophysics Data System (ADS)

Herrero Martín, R.; García, A.; Pérez-García, J.

2012-11-01

Enhancement techniques can be applied to flat-plate liquid solar collectors towards more compact and efficient designs. For the typical operating mass flow rates in flat-plate solar collectors, the most suitable technique is inserted devices. Based on previous studies from the authors, wire coils were selected for enhancing heat transfer. This type of inserted device provides better results in laminar, transitional and low turbulence fluid flow regimes. To test the enhanced solar collector and compare with a standard one, an experimental side-by-side solar collector test bed was designed and constructed. The testing set up was fully designed following the requirements of EN12975-2 and allow us to accomplish performance tests under the same operating conditions (mass flow rate, inlet fluid temperature and weather conditions). This work presents the thermal efficiency curves of a commercial and an enhanced solar collector, for the standardized mass flow rate per unit of absorber area of 0.02 kg/sm2 (in useful engineering units 144 kg/h for water as working fluid and 2 m2 flat-plate solar collector of absorber area). The enhanced collector was modified inserting spiral wire coils of dimensionless pitch p/D = 1 and wire-diameter e/D = 0.0717. The friction factor per tube has been computed from the overall pressure drop tests across the solar collectors. The thermal efficiency curves of both solar collectors, a standard and an enhanced collector, are presented. The enhanced solar collector increases the thermal efficiency by 15%. To account for the overall enhancement a modified performance evaluation criterion (R3m) is proposed. The maximum value encountered reaches 1.105 which represents an increase in useful power of 10.5% for the same pumping power consumption.

A laser-induced heat flux technique for convective heat transfer measurements in high speed flows

NASA Technical Reports Server (NTRS)

Porro, A. R.; Keith, T. G., Jr.; Hingst, W. R.

1991-01-01

A technique is developed to measure the local convective heat transfer coefficient on a model surface in a supersonic flow field. The technique uses a laser to apply a discrete local heat flux at the model test surface, and an infrared camera system determines the local temperature distribution due to the heating. From this temperature distribution and an analysis of the heating process, a local convective heat transfer coefficient is determined. The technique was used to measure the local surface convective heat transfer coefficient distribution on a flat plate at nominal Mach numbers of 2.5, 3.0, 3.5, and 4.0. The flat plate boundary layer initially was laminar and became transitional in the measurement region. The experimentally determined convective heat transfer coefficients were generally higher than the theoretical predictions for flat plate laminar boundary layers. However, the results indicate that this nonintrusive optical measurement technique has the potential to measure surface convective heat transfer coefficients in high-speed flowfields.

Large Angle Unsteady Aerodynamic Theory of a Flat Plate

NASA Astrophysics Data System (ADS)

Manar, Field; Jones, Anya

2016-11-01

A purely analytical approach is taken for the evaluation of the unsteady loads on a flat plate. This allows for an extremely low cost theoretical prediction of the plate loads in the style of Wagner and Theodorsen, without making the assumption of small angle of attack or small disturbance flow. The forces and moments are evaluated using the time rate of change of fluid momentum, expressed as an integral of the vorticity field. The flow is taken as inviscid and incompressible with isolated vorticity bound to the plate and in the shed wake. The bound vorticity distribution on the plate is solved exactly using conformal mapping of the plate to a cylinder. In keeping with the original assumption of Wagner, the wake vorticity is assumed to remain stationary in an inertial reference frame and convection is disregarded. Formulation in this manner allows for a closed form solution of Wagner's problem valid at all angles of attack. Separation from the leading edge of the plate can also be included to further increase the fidelity of the model at high angles.

Calculation of compressible boundary layer flow about airfoils by a finite element/finite difference method

NASA Technical Reports Server (NTRS)

Strong, Stuart L.; Meade, Andrew J., Jr.

1992-01-01

Preliminary results are presented of a finite element/finite difference method (semidiscrete Galerkin method) used to calculate compressible boundary layer flow about airfoils, in which the group finite element scheme is applied to the Dorodnitsyn formulation of the boundary layer equations. The semidiscrete Galerkin (SDG) method promises to be fast, accurate and computationally efficient. The SDG method can also be applied to any smoothly connected airfoil shape without modification and possesses the potential capability of calculating boundary layer solutions beyond flow separation. Results are presented for low speed laminar flow past a circular cylinder and past a NACA 0012 airfoil at zero angle of attack at a Mach number of 0.5. Also shown are results for compressible flow past a flat plate for a Mach number range of 0 to 10 and results for incompressible turbulent flow past a flat plate. All numerical solutions assume an attached boundary layer.

Numerical techniques for the solution of the compressible Navier-Stokes equations and implementation of turbulence models. [separated turbulent boundary layer flow problems

NASA Technical Reports Server (NTRS)

Baldwin, B. S.; Maccormack, R. W.; Deiwert, G. S.

1975-01-01

The time-splitting explicit numerical method of MacCormack is applied to separated turbulent boundary layer flow problems. Modifications of this basic method are developed to counter difficulties associated with complicated geometry and severe numerical resolution requirements of turbulence model equations. The accuracy of solutions is investigated by comparison with exact solutions for several simple cases. Procedures are developed for modifying the basic method to improve the accuracy. Numerical solutions of high-Reynolds-number separated flows over an airfoil and shock-separated flows over a flat plate are obtained. A simple mixing length model of turbulence is used for the transonic flow past an airfoil. A nonorthogonal mesh of arbitrary configuration facilitates the description of the flow field. For the simpler geometry associated with the flat plate, a rectangular mesh is used, and solutions are obtained based on a two-equation differential model of turbulence.

Standardized performance tests of collectors of solar thermal energy: A selectively coated, flat-plate copper collector with one transparent cover and a tube-to-tube spacing of 5 5/8 inches

NASA Technical Reports Server (NTRS)

1976-01-01

This preliminary data report gives basic test results of a flat-plate solar collector whose performance was determined in the NASA-Lewis solar simulator. The collector was tested over ranges of inlet temperatures, fluxes and coolant flow rates. Collector efficiency is correlated in terms of inlet temperature and flux level.

Acoustic radiation damping of flat rectangular plates subjected to subsonic flows

NASA Technical Reports Server (NTRS)

Lyle, Karen Heitman

1993-01-01

The acoustic radiation damping for various isotropic and laminated composite plates and semi-infinite strips subjected to a uniform, subsonic and steady flow has been predicted. The predictions are based on the linear vibration of a flat plate. The fluid loading is characterized as the perturbation pressure derived from the linearized Bernoulli and continuity equations. Parameters varied in the analysis include Mach number, mode number and plate size, aspect ratio and mass. The predictions are compared with existing theoretical results and experimental data. The analytical results show that the fluid loading can significantly affect realistic plate responses. Generally, graphite/epoxy and carbon/carbon plates have higher acoustic radiation damping values than similar aluminum plates, except near plate divergence conditions resulting from aeroelastic instability. Universal curves are presented where the acoustic radiation damping normalized by the mass ratio is a linear function of the reduced frequency. A separate curve is required for each Mach number and plate aspect ratio. In addition, acoustic radiation damping values can be greater than or equal to the structural component of the modal critical damping ratio (assumed as 0.01) for the higher subsonic Mach numbers. New experimental data were acquired for comparison with the analytical results.

Fluid flow and heat transfer of carbon nanotubes along a flat plate with Navier slip boundary

NASA Astrophysics Data System (ADS)

Khan, W. A.; Khan, Z. H.; Rahi, M.

2014-06-01

Homogeneous flow model is used to study the flow and heat transfer of carbon nanotubes (CNTs) along a flat plate subjected to Navier slip and uniform heat flux boundary conditions. This is the first paper on the flow and heat transfer of CNTs along a flat plate. Two types of CNTs, namely, single- and multi-wall CNTs are used with water, kerosene or engine oil as base fluids. The empirical correlations are used for the thermophysical properties of CNTs in terms of the solid volume fraction of CNTs. For the effective thermal conductivity of CNTs, Xue (Phys B Condens Matter 368:302-307, 2005) model has been used and the results are compared with the existing theoretical models. The governing partial differential equations and boundary conditions are converted into a set of nonlinear ordinary differential equations using suitable similarity transformations. These equations are solved numerically using a very efficient finite difference method with shooting scheme. The effects of the governing parameters on the dimensionless velocity, temperature, skin friction, and Nusselt numbers are investigated and presented in graphical and tabular forms. The numerical results of skin friction and Nusselt numbers are compared with the available data for special cases and are found in good agreement.

Bypass Transitional Flow Calculations Using a Navier-Stokes Solver and Two-Equation Models

NASA Technical Reports Server (NTRS)

Liuo, William W.; Shih, Tsan-Hsing; Povinelli, L. A. (Technical Monitor)

2000-01-01

Bypass transitional flows over a flat plate were simulated using a Navier-Stokes solver and two equation models. A new model for the bypass transition, which occurs in cases with high free stream turbulence intensity (TI), is described. The new transition model is developed by including an intermittency correction function to an existing two-equation turbulence model. The advantages of using Navier-Stokes equations, as opposed to boundary-layer equations, in bypass transition simulations are also illustrated. The results for two test flows over a flat plate with different levels of free stream turbulence intensity are reported. Comparisons with the experimental measurements show that the new model can capture very well both the onset and the length of bypass transition.

Studies of acoustic effects on a flow boundary layer in air

NASA Technical Reports Server (NTRS)

Mechel, F.; Schilz, W.

1986-01-01

Effects of sound fields on the flow boundary layer on a flat plate subjected to a parallel flow are studied. The boundary layer is influenced by controlling the stagnation point flow at the front edge of the plate. Depending on the Reynolds number and sound frequency, excitation or suppression of turbulent is observed. Measurements were taken at wind velocities between 10 and 30 m/sec and sound frequencies between 0.2 and 3.0 kHz.

Hall effects on hydromagnetic free convection flow along a porous flat plate with mass transfer

NASA Astrophysics Data System (ADS)

Hossain, M. A.; Rashid, R. I. M. A.

1987-01-01

Effect of Hall current on the unsteady free convection flow of a viscous incompressible and electrically conducting fluid, in presence of foreign gases (such as H2, CO2, H2O, NH3), along an infinite vertical porous flat plate subjected to a transpiration velocity inversely proportional to the square-root of time is investigated in the presence of a uniform transverse magnetic field. The results are discussed with the effects of the parameters Gc (the Grashof number for mass transfer), m (the Hall parameter) and Sc (the Schmidt number) for Pr = 0.71, which represents air.

Numerical simulation of fluid flow through simplified blade cascade with prescribed harmonic motion using discontinuous Galerkin method

NASA Astrophysics Data System (ADS)

Vimmr, Jan; Bublík, Ondřej; Prausová, Helena; Hála, Jindřich; Pešek, Luděk

2018-06-01

This paper deals with a numerical simulation of compressible viscous fluid flow around three flat plates with prescribed harmonic motion. This arrangement presents a simplified blade cascade with forward wave motion. The aim of this simulation is to determine the aerodynamic forces acting on the flat plates. The mathematical model describing this problem is formed by Favre-averaged system of Navier-Stokes equations in arbitrary Lagrangian-Eulerian (ALE) formulation completed by one-equation Spalart-Allmaras turbulence model. The simulation was performed using the developed in-house CFD software based on discontinuous Galerkin method, which offers high order of accuracy.

Experimental Study of Saddle Point of Attachment in Laminar Juncture Flow

NASA Technical Reports Server (NTRS)

Coon, Michael D.; Tobak, Murray

1995-01-01

An experimental study of laminar horseshoe vortex flows upstream of a cylinder/flat plate juncture has been conducted to verify the existence of saddle-point-of-attachment topologies. In the classical depiction of this flowfield, a saddle point of separation exists on the flat plate upstream of the cylinder, and the boundary layer separates from the surface. Recent computations have indicated that the topology may actually involve a saddle point of attachment on the surface and additional singular points in the flow. Laser light sheet flow visualizations have been performed on the symmetry plane and crossflow planes to identify the saddle-point-of-attachment flowfields. The visualizations reveal that saddle-point-of-attachment topologies occur over a range of Reynolds numbers in both single and multiple vortex regimes. An analysis of the flow topologies is presented that describes the existence and evolution of the singular points in the flowfield.

Vortex shedding experiment with flat and curved bluff plates in water

NASA Technical Reports Server (NTRS)

Reed, D.; Nesman, T.; Howard, P.

1988-01-01

Vortex shedding experiments were conducted in a water flow facility in order to simulate the strong discrete 4000-Hz vibration detected in the Space Shuttle Main Engine (SSME) which is thought to be associated with the SSME LOX inlet tee splitter vanes on the Main Injector. For the case of a flat vane with a blunt trailing edge excited by flow induced vortex shedding, lock-in with the first bending mode of the plate was observed. A curved vane displayed similar behavior, with the lock-in being a more discrete higher amplitude response. Aluminum vanes were employed to decouple the first vane bending mode from the vortex shedding mode. The application of an asymmetric 30-deg trailing edge bevel to both the flat and curved vanes was found to greatly reduce the strength of the shed vortices.

Standardized solar simulator tests of flat plate solar collectors. 1: Soltex collector with two transparent covers

NASA Technical Reports Server (NTRS)

Simon, F.

1975-01-01

A Soltex flat plate solar collector was tested with a solar simulator for inlet temperatures of 77 to 201 F, flux levels of 240 and 350 Btu/hr-sq ft, a collant flow rate of 10.5 lb/hr sq ft, and incident angles of 0 deg, 41.5 deg, and 65.2 deg. Collector performance is correlated in terms of inlet temperature, flux level, and incident angle.

Progress in hypersonic turbulence modeling

NASA Technical Reports Server (NTRS)

Wilcox, David C.

1991-01-01

A compressibility modification is developed for k-omega (Wilcox, 1988) and k-epsilon (Jones and Launder, 1972) models, that is similar to those of Sarkar et al. (1989) and Zeman (1990). Results of the perturbation solution for the compressible wall layer demonstrate why the Sarkar and Zeman terms yield inaccurate skin friction for the flat-plate boundary layer. A new compressibility term is developed which permits accurate predictions of the compressible mixing layer, flat-plate boundary layer, and shock separated flows.

Use of Plasma Actuators as a Moving-Wake Generator

NASA Technical Reports Server (NTRS)

Corke, Thomas C.; Thomas, Flint O.; Klapetzky Michael J.

2007-01-01

The work documented in this report tests the concept of using plasma actuators as a simple and easy way to generate a simulated moving-wake and the disturbances associated with it in turbines. This wake is caused by the blades of the upstream stages of the turbine. Two types of devices, one constructed of arrays of NACA 0018 airfoils, and the one constructed of flat plates were studied. The airfoils or plates were equipped with surface mounted dielectric barrier discharge (DBD) plasma actuators, which were used to generate flow disturbances resembling moving-wakes. CTA hot-wire anemometry and flow visualization using a smoke-wire were used to investigate the wake independence at various spacings and downstream locations. The flat plates were found to produce better results than the airfoils in creating large velocity fluctuations in the free-stream flow. Different dielectric materials, plasma actuator locations, leading edge contours, angles of attack and plate spacings were investigated, some with positive results. The magnitudes of the velocity fluctuations were found to be comparable to existing mechanical moving-wake generators, thus proving the feasibility of using plasma actuators as a moving-wake generator.

A Parametric Study of Jet Interactions with Rarefied Flow

NASA Technical Reports Server (NTRS)

Glass, C. E.

2004-01-01

Three-dimensional computational techniques, in particular the uncoupled CFD-DSMC of the present study, are available to be applied to problems such as jet interactions with variable density regions ranging from a continuum jet to a rarefied free stream. When the value of the jet to free stream momentum flux ratio approximately greater than 2000 for a sharp leading edge flat plate forward separation vortices induced by the jet interaction are present near the surface. Also as the free stream number density n (infinity) decreases, the extent and magnitude of normalized pressure increases and moves upstream of the nozzle exit. Thus for the flat plate model the effect of decreasing n (infinity) is to change the sign of the moment caused by the jet interaction on the flat plate surface.

Reynolds number influence on the formation of vortical structures on a pitching flat plate.

PubMed

Widmann, Alexander; Tropea, Cameron

2017-02-06

The impact of chord-based Reynolds number on the formation of leading-edge vortices (LEVs) on unsteady pitching flat plates is investigated. The influence of secondary flow structures on the shear layer feeding the LEV and the subsequent topological change at the leading edge as the result of viscous processes are demonstrated. Time-resolved velocity fields are measured using particle image velocimetry simultaneously in two fields of view to correlate local and global flow phenomena in order to identify unsteady boundary-layer separation and the subsequent flow structures. Finally, the Reynolds number is identified as a parameter that is responsible for the transition in mechanisms leading to LEV detachment from an aerofoil, as it determines the viscous response of the boundary layer in the vortex-wall interaction.

Reynolds number influence on the formation of vortical structures on a pitching flat plate

PubMed Central

Tropea, Cameron

2017-01-01

The impact of chord-based Reynolds number on the formation of leading-edge vortices (LEVs) on unsteady pitching flat plates is investigated. The influence of secondary flow structures on the shear layer feeding the LEV and the subsequent topological change at the leading edge as the result of viscous processes are demonstrated. Time-resolved velocity fields are measured using particle image velocimetry simultaneously in two fields of view to correlate local and global flow phenomena in order to identify unsteady boundary-layer separation and the subsequent flow structures. Finally, the Reynolds number is identified as a parameter that is responsible for the transition in mechanisms leading to LEV detachment from an aerofoil, as it determines the viscous response of the boundary layer in the vortex–wall interaction. PMID:28163871

Experimental study of turbulent flow heat transfer and pressure drop in plate heat exchanger with chevron plates

DOE Office of Scientific and Technical Information (OSTI.GOV)

Muley, A.; Manglik, R.M.

1999-02-01

Experimental heat transfer and isothermal pressure drop data for single-phase water flows in a plate heat exchanger (PHE) with chevron plates are presented. In a single-pass U-type counterflow PHE, three different chevron plate arrangements are considered: two symmetric plate arrangements with {beta} = 30 deg/30 deg and 60 deg/60 deg, and one mixed-plate arrangement with {beta} = 30 deg/60 deg. For water (2 < Pr < 6) flow rates in the 600 < Re < 10{sup 4} regime, data for Nu and f are presented. The results show significant effects of both the chevron angle {beta} and surface area enlargementmore » factor {phi}. As {beta} increases, and compared to a flat-plate pack, up to two to five times higher Nu are obtained; the concomitant f, however, are 13 to 44 times higher. Increasing {phi} also has a similar, though smaller effect. Based on experimental data for Re {ge} 1000 and 30 deg {le} {beta} {le} 60 deg, predictive correlations of the form Nu = C{sub 1}({beta}) D{sub 1}({phi}) Re{sup p1({beta})} Pr{sup 1/3} ({mu}/{mu}{sub w}){sup 0.14} and f = C{sub 2}({beta}) D{sub 2}({phi}) Re{sup p2({beta})} are devised. Finally, at constant pumping power, and depending upon Re, {beta}, and {phi}, the heat transfer is found to be enhanced by up to 2.8 times that in an equivalent flat-plate channel.« less

Accounting For Compressibility In Viscous Flow In Pipes

NASA Technical Reports Server (NTRS)

Steinle, Frank W.; Gee, Ken; Murthy, Sreedhara V.

1991-01-01

Method developed to account for effects of compressibility in viscous flows through long, circular pipes of uniform diameter. Based on approximation of variations in density and velocity across pipe cross section by profile equations developed for boundary-layer flow between flat plates.

Prediction and measurement of heat transfer rates for the shock-induced unsteady laminar boundary layer on a flat plate

NASA Technical Reports Server (NTRS)

Cook, W. J.

1972-01-01

The unsteady laminar boundary layer induced by the flow-initiating shock wave passing over a flat plate mounted in a shock tube was theoretically and experimentally studied in terms of heat transfer rates to the plate for shock speeds ranging from 1.695 to 7.34 km/sec. The theory presented by Cook and Chapman for the shock-induced unsteady boundary layer on a plate is reviewed with emphasis on unsteady heat transfer. A method of measuring time-dependent heat-transfer rates using thin-film heat-flux gages and an associated data reduction technique are outlined in detail. Particular consideration is given to heat-flux measurement in short-duration ionized shocktube flows. Experimental unsteady plate heat transfer rates obtained in both air and nitrogen using thin-film heat-flux gages generally agree well with theoretical predictions. The experimental results indicate that the theory continues to predict the unsteady boundary layer behavior after the shock wave leaves the trailing edge of the plate even though the theory is strictly applicable only for the time interval in which the shock remains on the plate.

Effect of Dielectric Barrier Discharge Plasma Actuators on Non-equilibrium Hypersonic Flows

DTIC Science & Technology

2014-10-28

goes into the kinetic energy of the electrons rather than heating of the surrounding gas.24 The examples of these include corona discharge and micro...Moreau, G. Artana, and G. Touchard, “Influence of a DC corona discharge on the airflow along an inclined flat plate,” J. Electrostat. 51–52, 300 306...10), 2554 2564 (2007). 42E. Moreau, G. Artana, and G. Touchard, “Surface corona discharge along an insulating flat plate in air applied to

Visualization of leading edge vortices on a series of flat plate delta wings

NASA Technical Reports Server (NTRS)

Payne, Francis M.; Ng, T. Terry; Nelson, Robert C.

1991-01-01

A summary of flow visualization data obtained as part of NASA Grant NAG2-258 is presented. During the course of this study, many still and high speed motion pictures were taken of the leading edge vortices on a series of flat plate delta wings at varying angles of attack. The purpose is to present a systematic collection of photographs showing the state of vortices as a function of the angle of attack for the four models tested.

The Effect of Leading-Edge Sweep and Surface Inclination on the Hypersonic Flow Field Over a Blunt Flat Plate

NASA Technical Reports Server (NTRS)

Creager, Marcus O.

1959-01-01

An investigation of the effects of variation of leading-edge sweep and surface inclination on the flow over blunt flat plates was conducted at Mach numbers of 4 and 5.7 at free-stream Reynolds numbers per inch of 6,600 and 20,000, respectively. Surface pressures were measured on a flat plate blunted by a semicylindrical leading edge over a range of sweep angles from 0 deg to 60 deg and a range of surface inclinations from -10 deg to +10 deg. The surface pressures were predicted within an average error of +/- 8 percent by a combination of blast-wave and boundary-layer theory extended herein to include effects of sweep and surface inclination. This combination applied equally well to similar data of other investigations. The local Reynolds number per inch was found to be lower than the free-stream Reynolds number per inch. The reduction in local Reynolds number was mitigated by increasing the sweep of the leading edge. Boundary-layer thickness and shock-wave shape were changed little by the sweep of the leading edge.

An experimental investigation with artificial sunlight of a solar hot-water heater

NASA Technical Reports Server (NTRS)

Simon, F. F.

1976-01-01

Thermal performance measurements were made of a commercial solar hot water heater in a solar simulator to determine basic performance characteristics of a traditional type of flat plate collector, with and without side reflectors (to increase the solar flux). Information on each of the following was obtained; (1) the effect of flow and incidence angle on the efficiency of a flat plate collector (but only without side reflectors); (2) transient performance under flow and nonflow conditions; (3) the effectiveness of reflectors to increase collector efficiency for a zero radiation angle at fluid temperatures required for solar air conditioning; and (4) the limits of applicability of a collector efficiency correlation based on the Hottel Whillier equation.

A lift formula applied to low-Reynolds-number unsteady flows

NASA Astrophysics Data System (ADS)

Wang, Shizhao; Zhang, Xing; He, Guowei; Liu, Tianshu

2013-09-01

A lift formula for a wing in a rectangular control volume is given in a very simple and physically lucid form, providing a rational foundation for calculation of the lift of a flapping wing in highly unsteady and separated flows at low Reynolds numbers. Direct numerical simulations on the stationary and flapping two-dimensional flat plate and rectangular flat-plate wing are conducted to assess the accuracy of the lift formula along with the classical Kutta-Joukowski theorem. In particular, the Lamb vector integral for the vortex force and the acceleration term of fluid for the unsteady inertial effect are evaluated as the main contributions to the unsteady lift generation of a flapping wing.

Stagnation point properties for non-continuum gaseous jet impinging at a flat plate surface from a planar exit

NASA Astrophysics Data System (ADS)

Cai, Chunpei

2013-10-01

In this paper, we investigate highly rarefied gaseous jet flows out of a planar exit and impinging at a normally set flat plate. Especially, we concentrate on the plate center stagnation point pressure and heat flux coefficients. For a specular reflective plate, the stagnation point pressure coefficient can be represented using two non-dimensional factors: the characteristic gas exit speed ratio S0 and the geometry ratio of H/L, where H is the planar exit semi-height and L is the center-to-center distance from the exit to the plate. For a diffuse reflective plate, the stagnation point pressure and heat flux coefficients involve an extra factor of T0/Tw, i.e., the ratio of exit gas temperature to the plate wall temperature. These results allow us to develop four diagrams, from which we can conveniently obtain the pressure and heat flux coefficients for the stagnation impingement point, at the collisionless flow limit. After normalization with these maximum coefficients, the pressure and heat flux coefficient distributions along the surface essentially degenerate to almost identical curves. As a result, with known plate surface pressure coefficient distributions and these diagrams, we can conveniently construct the heat flux coefficient distributions along the plate surface, and vice versa.

Performance optimization of plate heat exchangers with chevron plates

DOE Office of Scientific and Technical Information (OSTI.GOV)

Muley, A.; Manglik, R.M.

1999-07-01

The enhanced heat transfer performance of a chevron plate heat exchanger (PHE) is evaluated employing (1) energy-conservation based performance evaluation criteria (PECs), and (2) the second-law based minimization of entropy generation principle. Single-phase laminar and turbulent flow convection for three different chevron-plate arrangements are considered. The influence of plate surface corrugation characteristics and their stack arrangements on the heat exchanger's thermal-hydraulic performance is delineated. Based on the different figures of merit, the results show that the extent of heat transfer enhancement increases with flow Re and chevron angle {beta} in laminar flow, but it diminishes with increasing Re in turbulentmore » flows. With up to 2.9 times higher Q, 48% lower A, and entropy generation number N{sub s,a} {lt} 1, relative to an equivalent flat-plate pack, chevron plates are found to be especially suitable in the low to medium flow rates range (20 {le} Re {le} 2,000). Also, there appears to be no significant advantage of using a mixed-plate over a symmetric-plate arrangement.« less

Analysis of Heat Transfer and Pressure Drop for a Gas Flowing Through a set of Multiple Parallel Flat Plates at High Temperatures

NASA Technical Reports Server (NTRS)

Einstein, Thomas H.

1961-01-01

Equations were derived representing heat transfer and pressure drop for a gas flowing in the passages of a heater composed of a series of parallel flat plates. The plates generated heat which was transferred to the flowing gas by convection. The relatively high temperature level of this system necessitated the consideration of heat transfer between the plates by radiation. The equations were solved on an IBM 704 computer, and results were obtained for hydrogen as the working fluid for a series of cases with a gas inlet temperature of 200 R, an exit temperature of 5000 0 R, and exit Mach numbers ranging from 0.2 to O.8. The length of the heater composed of the plates ranged from 2 to 4 feet, and the spacing between the plates was varied from 0.003 to 0.01 foot. Most of the results were for a five- plate heater, but results are also given for nine plates to show the effect of increasing the number of plates. The heat generation was assumed to be identical for each plate but was varied along the length of the plates. The axial variation of power used to obtain the results presented is the so-called "2/3-cosine variation." The boundaries surrounding the set of plates, and parallel to it, were assumed adiabatic, so that all the power generated in the plates went into heating the gas. The results are presented in plots of maximum plate and maximum adiabatic wall temperatures as functions of parameters proportional to f(L/D), for the case of both laminar and turbulent flow. Here f is the Fanning friction factor and (L/D) is the length to equivalent diameter ratio of the passages in the heater. The pressure drop through the heater is presented as a function of these same parameters, the exit Mach number, and the pressure at the exit of the heater.

Stability analysis of the onset of vortex shedding for wakes behind flat plates

NASA Astrophysics Data System (ADS)

Wang, Shuai; Liu, Li; Zhang, Shi-Bo; Wen, Feng-Bo; Zhou, Xun

2018-04-01

Above a critical Reynolds number, wake flows behind flat plates become globally unstable, the leading modal instability in this case is known as Kelvin-Helmholtz mechanism. In this article, both local and BiGlobal linear instability analyses are performed numerically to study the onset of the shedding process. Flat plates with different base shapes are considered to assess geometry effects, and the relation between the critical shedding Reynolds number, Re_cr , and the boundary layer thickness is studied. Three types of base shapes are used: square, triangular and elliptic. It is found that the base shape has a great impact on the growth rate of least stable disturbance mode, thus would influence Re_cr greatly, but it has little effect on the vortex shedding frequency. The shedding frequency is determined mainly by boundary layer thickness and has little dependence on the Reynolds number and base shape. We find that for a fixed Reynolds number, increasing boundary layer thickness acted in two ways to modify the global stability characteristics: It increases the length of the absolute unstable region and it makes the flow less locally absolutely unstable in the near-wake region, and these two effects work against each other to destabilize or stabilize the flow.

Numerical investigation of the self-starting of a vertical axis wind turbine

NASA Astrophysics Data System (ADS)

Tsai, Hsieh-Chen; Colonius, Tim

2014-11-01

The immersed boundary method is used to simulate the incompressible flow around two-dimensional airfoils at sub-scale Reynolds number in order to investigate the self-starting capability of a vertical-axis wind turbine (VAWT). By investigating a single blade fixed at various angle of attacks, the leading edge vortex (LEV) is shown to play an important role in the starting mechanism for both flat-plate and NACA 0018 blades. Depending on the angle of attack of the blade, as the LEV grows, the corresponding low pressure region results in a thrust in the tangential direction, which produces a positive torque to VAWT. Due to the characteristics of the blades, a NACA 0018 blade produces a larger thrust over a wider range of angle of attacks than a flat-plate blade. Therefore, a VAWT with NACA 0018 blades can self-start more easily than one with flat-plate blades. Moreover, by investigating the starting torque of three-bladed VAWTs fixed at various orientations, the optimal orientation that produces the largest torque to start both VAWTs is with a blade parallel to the flow and facing downstream. The simulations are also compared to results from companion water-tunnel experiments at Caltech. This project is supported by Caltech FLOWE center/Gordon and Betty Moore Foundation.

The effect of butterfly-scale inspired patterning on leading-edge vortex growth

NASA Astrophysics Data System (ADS)

Wilroy, Jacob; Lang, Amy

2015-11-01

Leading edge vortices (LEVs) are important for generating thrust and lift in flapping flight, and the surface patterning (scales) on butterfly wings is hypothesized to play a role in the vortex formation of the LEV. To simplify this complex flow problem, an experiment was designed to focus on the alteration of 2-D vortex development with a variation in surface patterning. Specifically, the secondary vorticity generated by the LEV interacting at the patterned surface was studied and the subsequent affect on the growth rate of the circulation in the LEV. For this experiment we used butterfly inspired grooves attached to a flat plate and compared the vortex formation to a smooth plate case as the plate moved vertically. The plate is impulsively started in quiescent water and flow fields at Re = 1500, 3000, and 6000 are examined using Digital Particle Image Velocimetry (DPIV). The vortex formation time is 3.0 and is based on the flat plate travel length and chord length. We would like to thank the National Science Foundation REU Site Award 1358991 for funding this research.

Investigation of Low-Pressure Turbine Endwall Flows: Simulations and Experiments (Postprint)

DTIC Science & Technology

2015-01-01

direction) minor semiaxis of 0.0417Cx (0.25in). Measured in the axial direction, the flat plate leading edge was located at x=-3.958Cx (23.75in) where...for public release; distribution unlimited. plate boundary layer is δ∗ = 1.721s/Re0.5s . For s = 4.833Cx, Reδ∗ = 1.721 √ s/CxRe = 1, 200. At this...boundary which was located at x=-1.4Cx. The following approximations hold for a turbulent flat plate boundary layer: δ99 = 0.37s Re0.2s , δ∗ = 0.046s

Rarefied flow past a flat plate at incidence

NASA Technical Reports Server (NTRS)

Dogra, Virendra K.; Moss, James N.; Price, Joseph M.

1988-01-01

Results of a numerical study using the direct simulation Monte Carlo (DSMC) method are presented for the transitional flow about a flat plate at 40 deg incidence. The plate has zero thickness and a length of 1.0 m. The flow conditions simulated are those experienced by the Shuttle Orbiter during reentry at 7.5 km/s. The range of freestream conditions are such that the freestream Knudsen number values are between 0.02 and 8.4, i.e., conditions that encompass most of the transitional flow regime. The DSMC simulations show that transitional effects are evident when compared with free molecule results for all cases considered. The calculated results demonstrate clearly the necessity of having a means of identifying the effects of transitional flow when making aerodynamic flight measurements as are currently being made with the Space Shuttle Orbiter vehicles. Previous flight data analyses have relied exclusively on adjustments in the gas-surface interaction models without accounting for the transitional effect which can be comparable in magnitude. The present calculations show that the transitional effect at 175 km would increase the Space Shuttle Orbiter lift-drag ratio by 90 percent over the free molecule value.

Fuel cell current collector

DOEpatents

Katz, Murray; Bonk, Stanley P.; Maricle, Donald L.; Abrams, Martin

1991-01-01

A fuel cell has a current collector plate (22) located between an electrode (20) and a separate plate (25). The collector plate has a plurality of arches (26, 28) deformed from a single flat plate in a checkerboard pattern. The arches are of sufficient height (30) to provide sufficient reactant flow area. Each arch is formed with sufficient stiffness to accept compressive load and sufficient resiliently to distribute the load and maintain electrical contact.

Unsteady Boundary-Layer Flow over Jerked Plate Moving in a Free Stream of Viscoelastic Fluid

PubMed Central

Mehmood, Ahmer; Ali, Asif; Saleem, Najma

2014-01-01

This study aims to investigate the unsteady boundary-layer flow of a viscoelastic non-Newtonian fluid over a flat surface. The plate is suddenly jerked to move with uniform velocity in a uniform stream of non-Newtonian fluid. Purely analytic solution to governing nonlinear equation is obtained. The solution is highly accurate and valid for all values of the dimensionless time 0 ≤ τ < ∞. Flow properties of the viscoelastic fluid are discussed through graphs. PMID:24892060

Increasing thermal efficiency of solar flat plate collectors

NASA Astrophysics Data System (ADS)

Pona, J.

A study of methods to increase the efficiency of heat transfer in flat plate solar collectors is presented. In order to increase the heat transfer from the absorber plate to the working fluid inside the tubes, turbulent flow was induced by installing baffles within the tubes. The installation of the baffles resulted in a 7 to 12% increase in collector efficiency. Experiments were run on both 1 sq ft and 2 sq ft collectors each fitted with either slotted baffles or tubular baffles. A computer program was run comparing the baffled collector to the standard collector. The results obtained from the computer show that the baffled collectors have a 2.7% increase in life cycle cost (LCC) savings and a 3.6% increase in net cash flow for use in domestic hot water systems, and even greater increases when used in solar heating systems.

Slip effects on MHD flow and heat transfer of ferrofluids over a moving flat plate

NASA Astrophysics Data System (ADS)

Ramli, Norshafira; Ahmad, Syakila; Pop, Ioan

2017-08-01

In this study, the problem of MHD flow and heat transfer of ferrofluids over a moving flat plate with slip effect and uniform heat flux is considered. The governing ordinary differential equations are solved via shooting method. The effect of slip parameter on the dimensionless velocity, temperature, skin friction and Nusselt numbers are numerically studied for the three selected ferroparticles; magnetite (Fe3O4), cobalt ferrite (CoFe2O4) and Mn-Zn ferrite (Mn-ZnFe2O4) with water-based fluid. The results indicate that dual solutions exist for a plate moving towards the origin. It is found that the slip process delays the boundary layer separation. Moreover, the velocity and thermal boundary-layer thicknesses decrease in the first solution while increase with the increase of the value of slip parameters in second solution.

Direct numerical simulation of transitional and turbulent flow over a heated flat plate using finite-difference schemes

NASA Technical Reports Server (NTRS)

Madavan, Nateri K.

1995-01-01

This report deals with the direct numerical simulation of transitional and turbulent flow at low Mach numbers using high-order-accurate finite-difference techniques. A computation of transition to turbulence of the spatially-evolving boundary layer on a heated flat plate in the presence of relatively high freestream turbulence was performed. The geometry and flow conditions were chosen to match earlier experiments. The development of the momentum and thermal boundary layers was documented. Velocity and temperature profiles, as well as distributions of skin friction, surface heat transfer rate, Reynolds shear stress, and turbulent heat flux, were shown to compare well with experiment. The results indicate that the essential features of the transition process have been captured. The numerical method used here can be applied to complex geometries in a straightforward manner.

Time domain numerical calculations of unsteady vortical flows about a flat plate airfoil

NASA Technical Reports Server (NTRS)

Hariharan, S. I.; Yu, Ping; Scott, J. R.

1989-01-01

A time domain numerical scheme is developed to solve for the unsteady flow about a flat plate airfoil due to imposed upstream, small amplitude, transverse velocity perturbations. The governing equation for the resulting unsteady potential is a homogeneous, constant coefficient, convective wave equation. Accurate solution of the problem requires the development of approximate boundary conditions which correctly model the physics of the unsteady flow in the far field. A uniformly valid far field boundary condition is developed, and numerical results are presented using this condition. The stability of the scheme is discussed, and the stability restriction for the scheme is established as a function of the Mach number. Finally, comparisons are made with the frequency domain calculation by Scott and Atassi, and the relative strengths and weaknesses of each approach are assessed.

Pressure distributions induced by elevon deflections on swept wings and adjacent end-plate surfaces at Mach 6

NASA Technical Reports Server (NTRS)

Kaufman, L. G., II; Johnson, C. B.

1977-01-01

Surface pressure distributions are presented for regions where three-dimensional separated flow effects are prominent on swept-wing-elevon-end-plate models of 0 degree, 50 degree, and 70 degree sweepback, and with 0 degree, 10 degree, 20 degree, and 30 degree elevon deflections. Surface-oil-flow photographs and pressure distributions on the flat-plate wing, elevon, and end-plate surfaces are presented for numerous geometric variations, including various spacings between the elevon and the end plate, with and without a tip fin. The data, for a free-stream Mach number of 6 and a wing-root-chord Reynolds number of 20 x 10 to the sixth power, reveal considerably larger regions of elevon induced loads on the adjacent end-plate surface than would be anticipated by using inviscid flow analyses.

An Experimental Study of Turbulent Skin Friction Reduction in Supersonic Flow Using a Microblowing Technique

NASA Technical Reports Server (NTRS)

Hwang, Danny P.

1999-01-01

A new turbulent skin friction reduction technology, called the microblowing technique has been tested in supersonic flow (Mach number of 1.9) on specially designed porous plates with microholes. The skin friction was measured directly by a force balance and the boundary layer development was measured by a total pressure rake at the tailing edge of a test plate. The free stream Reynolds number was 1.0(10 exp 6) per meter. The turbulent skin friction coefficient ratios (C(sub f)/C(sub f0)) of seven porous plates are given in this report. Test results showed that the microblowing technique could reduce the turbulent skin friction in supersonic flow (up to 90 percent below a solid flat plate value, which was even greater than in subsonic flow).

Surface capillary currents: Rediscovery of fluid-structure interaction by forced evolving boundary theory

NASA Astrophysics Data System (ADS)

Wang, Chunbai; Mitra, Ambar K.

2016-01-01

Any boundary surface evolving in viscous fluid is driven with surface capillary currents. By step function defined for the fluid-structure interface, surface currents are found near a flat wall in a logarithmic form. The general flat-plate boundary layer is demonstrated through the interface kinematics. The dynamics analysis elucidates the relationship of the surface currents with the adhering region as well as the no-slip boundary condition. The wall skin friction coefficient, displacement thickness, and the logarithmic velocity-defect law of the smooth flat-plate boundary-layer flow are derived with the advent of the forced evolving boundary method. This fundamental theory has wide applications in applied science and engineering.

A high performance porous flat-plate solar collector

NASA Technical Reports Server (NTRS)

Lansing, F. L.; Clarke, V.; Reynolds, R.

1979-01-01

A solar collector employing a porous matrix as a solar absorber and heat exchanger is presented and its application in solar air heaters is discussed. The collector is composed of a metallic matrix with a porous surface which acts as a large set of cavity radiators; cold air flows through the matrix plate and exchanges heat with the thermally stratified layers of the matrix. A steady-state thermal analysis of the collector is used to determine collector temperature distributions for the cases of an opaque surface matrix with total absorption of solar energy at the surface, and a diathermanous matrix with successive solar energy absorption at each depth. The theoretical performance of the porous flat plate collector is shown to exceed greatly that of a solid flat plate collector using air as the working medium for any given set of operational conditions. An experimental collector constructed using commercially available, low cost steel wool as the matrix has been found to have thermal efficiencies from 73 to 86%.

Unsteady Separated Flows: Vorticity and Turbulence.

DTIC Science & Technology

1987-04-06

plate, the results are somewhat different . A vortex initiated before : max is obtained in the oscillation cycle yielded convection velocities not...in flat plate m resulted in a 6.25% advance in the cycle where the leading edge vortex was initiated; a value close to that measured using the NACA...three-dimensional model we have used to initiate the three- dimensional study of unsteady flows is a symmetric airfoil (NACA 0015) section fitted witL, a

Cutting process simulation of flat drill

NASA Astrophysics Data System (ADS)

Tamura, Shoichi; Matsumura, Takashi

2018-05-01

Flat drills at a point angle of 180 deg. have recently been developed for drilling of automobile parts with the inclination of the workpiece surfaces. The paper studies the cutting processes of the flat drills in the analytical simulation. A predictive force model is applied to simulation of the cutting force with the chip flow direction. The chip flow model is piled up with orthogonal cuttings in the plane containing the cutting velocities and the chip flow velocities, in which the chip flow direction is determined to minimize the cutting energy. Then, the cutting force is predicted in the determined in the chip flow model. The typical cutting force of the flat drill is discussed with comparing to that of the standard drill. The typical differences are confirmed in the cutting force change during the tool engagement and disengagement. The cutting force, then, is simulated in drilling for an inclined workpiece with a flat drill. The horizontal components in the cutting forces are simulated with changing the inclination angle of the plate. The horizontal force component in the flat drilling is stable to be controlled in terms of the machining accuracy and the tool breakage.

Stream-wise distribution of skin-friction drag reduction on a flat plate with bubble injection

NASA Astrophysics Data System (ADS)

Qin, Shijie; Chu, Ning; Yao, Yan; Liu, Jingting; Huang, Bin; Wu, Dazhuan

2017-03-01

To investigate the stream-wise distribution of skin-friction drag reduction on a flat plate with bubble injection, both experiments and simulations of bubble drag reduction (BDR) have been conducted in this paper. Drag reductions at various flow speeds and air injection rates have been tested in cavitation tunnel experiments. Visualization of bubble flow pattern is implemented synchronously. The computational fluid dynamics (CFD) method, in the framework of Eulerian-Eulerian two fluid modeling, coupled with population balance model (PBM) is used to simulate the bubbly flow along the flat plate. A wide range of bubble sizes considering bubble breakup and coalescence is modeled based on experimental bubble distribution images. Drag and lift forces are fully modeled based on applicable closure models. Both predicted drag reductions and bubble distributions are in reasonable concordance with experimental results. Stream-wise distribution of BDR is revealed based on CFD-PBM numerical results. In particular, four distinct regions with different BDR characteristics are first identified and discussed in this study. Thresholds between regions are extracted and discussed. And it is highly necessary to fully understand the stream-wise distribution of BDR in order to establish a universal scaling law. Moreover, mechanism of stream-wise distribution of BDR is analysed based on the near-wall flow parameters. The local drag reduction is a direct result of near-wall max void fraction. And the near-wall velocity gradient modified by the presence of bubbles is considered as another important factor for bubble drag reduction.

An experimental study of the flow field surrounding a subsonic jet in a cross flow. M.S. Thesis

NASA Technical Reports Server (NTRS)

Dennis, Robert Foster

1993-01-01

An experimental investigation of the flow interaction of a 5.08 cm (2.00 in.) diameter round subsonic jet exhausting perpendicularly to a flat plate in a subsonic cross flow was conducted in the NASA Ames 7x1O ft. Wind Tunnel Number One. Flat plate surface pressures were measured at 400 locations in a 30.48 cm (12.0 in.) concentric circular array surrounding the jet exit. Results from these measurements are provided in tabular and graphical form for jet-to-crossflow velocity ratios ranging from 4 to 12, and for jet exit Mach numbers ranging from 0.50 to 0.93. Laser doppler velocimeter (LDV) three component velocity measurements were made in selected regions in the developed jet plume and near the flat plate surface, at a jet Mach number of 0.50 and jet-to-crossflow velocity ratios of 6 and 8. The results of both pressure and LDV measurements are compared with the results of previous experiments. In addition, pictures of the jet plume shape at jet velocity ratios ranging from 4 to 12 were obtained using schleiren photography. The LDV measurements are consistent with previous work, but more extensive measurements will be necessary to provide a detailed picture of the flow field. The surface pressure results compare closely with previous work and provide a useful characterization of jet induced surface pressures. The results demonstrate the primary influence of jet velocity ratio and the secondary influence of jet Mach number in determining such surface pressures.

Experimental investigation of a jet inclined to a subsonic crossflow

NASA Technical Reports Server (NTRS)

Aoyagi, K.; Snyder, P. K.

1981-01-01

Experimental investigations have been conducted to determine the surface-pressure distribution on a flat plate and a body of revolution with a jet issuing at a large angle to the free stream and to obtain a better understanding of the entrainment mechanism close to the jet exit by quantitative mean velocity surveys. Pressure data were obtained with a flat plate model at several nozzle injection angles using a single round nozzle. For the body of revolution model, data were obtained with a round jet exhausting perpendicular to the crossflow and with two round jets spaced two to six nozzle diameters apart. Mean velocity measurements were obtained with laser velocimeter surveys near the base of a round jet exhausting normal to a flat plate. For the flat plate model, the pressure field shifts downstream and the entrainment effect decreases with decreasing nozzle injection angle. For the body of revolution model with two jets, the jet-induced effect of the rear jet on the surface-pressure distribution was less than the front jet. The flow regions close to the jet are defined by the laser surveys, but further mean velocity surveys are required to understand the entrainment mechanism.

Experimental investigation of supersonic low pressure air plasma flows obtained with different arc-jet operating conditions

NASA Astrophysics Data System (ADS)

Lago, Viviana; Ndiaye, Abdoul-Aziz

2012-11-01

A stationary arc-jet plasma flow at low pressure is used to simulate some properties of the gas flow surrounding a vehicle during its entry into celestial body's atmospheres. This paper presents an experimental study concerning plasmas simulating a re-entry into our planet. Optical measurements have been carried out for several operating plasma conditions in the free stream, and in the shock layer formed in front of a flat cylindrical plate, placed in the plasma jet. The analysis of the spectral radiation enabled the identification of the emitting species, the determination of the rotational and vibrational temperatures in the free-stream and in the shock layer and the determination of the distance of the shock to the flat plate face. Some plasma fluid parameters like, stagnation pressure, specific enthalpy and heat flux have been determined experimentally along the plasma-jet axis.

Mixed convection boundary layer flow over a moving vertical flat plate in an external fluid flow with viscous dissipation effect.

PubMed

Bachok, Norfifah; Ishak, Anuar; Pop, Ioan

2013-01-01

The steady boundary layer flow of a viscous and incompressible fluid over a moving vertical flat plate in an external moving fluid with viscous dissipation is theoretically investigated. Using appropriate similarity variables, the governing system of partial differential equations is transformed into a system of ordinary (similarity) differential equations, which is then solved numerically using a Maple software. Results for the skin friction or shear stress coefficient, local Nusselt number, velocity and temperature profiles are presented for different values of the governing parameters. It is found that the set of the similarity equations has unique solutions, dual solutions or no solutions, depending on the values of the mixed convection parameter, the velocity ratio parameter and the Eckert number. The Eckert number significantly affects the surface shear stress as well as the heat transfer rate at the surface.

Toward Verification of USM3D Extensions for Mixed Element Grids

NASA Technical Reports Server (NTRS)

Pandya, Mohagna J.; Frink, Neal T.; Ding, Ejiang; Parlette, Edward B.

2013-01-01

The unstructured tetrahedral grid cell-centered finite volume flow solver USM3D has been recently extended to handle mixed element grids composed of hexahedral, prismatic, pyramidal, and tetrahedral cells. Presently, two turbulence models, namely, baseline Spalart-Allmaras (SA) and Menter Shear Stress Transport (SST), support mixed element grids. This paper provides an overview of the various numerical discretization options available in the newly enhanced USM3D. Using the SA model, the flow solver extensions are verified on three two-dimensional test cases available on the Turbulence Modeling Resource website at the NASA Langley Research Center. The test cases are zero pressure gradient flat plate, planar shear, and bump-inchannel. The effect of cell topologies on the flow solution is also investigated using the planar shear case. Finally, the assessment of various cell and face gradient options is performed on the zero pressure gradient flat plate case.

Fluid-Dynamic Properties of Some Simple Sharp- and Blunt-Nosed Shapes at Mach Numbers from 16 to 24 in Helium Flow

NASA Technical Reports Server (NTRS)

Henderson, Arthur, Jr.; Johnston, Patrick J.

1959-01-01

The fluid-dynamic characteristics of flat plates, 5 deg and 10 deg wedges, and 5 deg and 10 deg cones have been investigated at Mach numbers from 16.3 to 23.9 in helium flow. The flat-plate results are for a leading-edge Reynolds number range of 584 to 19,500 and show that the induced pressure distribution is essentially linear with the hypersonic viscous interaction parameter bar X within the scope of this investigation. It is also shown that the rate at which the induced pressure varies with bar X is a linear function of the leading-edge Reynolds number. The wedge and cone results show that as the flow-deflection angle increases, the induced-pressure effects decrease and the measured pressures approach those predicted by inviscid shock theory.

Genetic algorithm optimization of a film cooling array on a modern turbine inlet vane

NASA Astrophysics Data System (ADS)

Johnson, Jamie J.

In response to the need for more advanced gas turbine cooling design methods that factor in the 3-D flowfield and heat transfer characteristics, this study involves the computational optimization of a pressure side film cooling array on a modern turbine inlet vane. Latin hypersquare sampling, genetic algorithm reproduction, and Reynolds-Averaged Navier Stokes (RANS) computational fluid dynamics (CFD) as an evaluation step are used to assess a total of 1,800 film cooling designs over 13 generations. The process was efficient due to the Leo CFD code's ability to estimate cooling mass flux at surface grid cells using a transpiration boundary condition, eliminating the need for remeshing between designs. The optimization resulted in a unique cooling design relative to the baseline with new injection angles, compound angles, cooling row patterns, hole sizes, a redistribution of cooling holes away from the over-cooled midspan to hot areas near the shroud, and a lower maximum surface temperature. To experimentally confirm relative design trends between the optimized and baseline designs, flat plate infrared thermography assessments were carried out at design flow conditions. Use of flat plate experiments to model vane pressure side cooling was justified through a conjugate heat transfer CFD comparison of the 3-D vane and flat plate which showed similar cooling performance trends at multiple span locations. The optimized flat plate model exhibited lower minimum surface temperatures at multiple span locations compared to the baseline. Overall, this work shows promise of optimizing film cooling to reduce design cycle time and save cooling mass flow in a gas turbine.

Flow field and thermal characteristics induced by a rotationally oscillating heated flat plate

NASA Astrophysics Data System (ADS)

Koffi, Moise

The objective of this dissertation is the study the flow and heat transfer in the vicinity of a rectangular flat heated plate of subject to rotational oscillations. Of interest is the effect of the flow field on the thermal characteristics of the plate's surface. A constant heat flux is applied to both sides while the plate is rotated about a fixed edge at a frequency of 2 rad/s in an infinite domain at atmospheric pressure. A computational simulation of the flow with FLUENT reveals a hooked-shape vortex tube around the free edges of the plate, which is confirmed by the flow visualization with smoke particles. During the flapping cycle, vortices form and grow progressively on one face while they shed from the opposite, until they are completely detached from both surfaces at stroke reversal. A data acquisition system uses a numerical computing and programming software (MATLAB) to track the surface temperature recorded by J- type thermocouples at desired locations on the plate. Both experimental and computational results agree with local surface temperature profiles characterized by a transient unsteady periodic variation followed by a steady periodic phase. These characteristics are symmetrical about the median plane of the plate, which is normal to its axis of rotation. The cooling rate of the surface, proportional to the frequency of rotation, depends on the angular position of the plate and the spatial location on the plate's surface. However, the highest heat transfer coefficient is recorded at free edges, especially in the corners swept by strong tip vortices shedding in two orthogonal directions. Conclusions of the present study are used to explain the role of ear flapping in the metabolic heat regulation of large mammals such as elephants. Flow visualization and surface temperature measurements of full size rigid and flexible elephant ear-shape models were carried out. Results indicate improved interaction between the shedding vortex and the model's boundary layer. Therefore the cooling is enhanced using flexible models by 30 percent. However, the huge size of the elephant pinna combined with its large surface to volume ratio and blood perfusion plays a key role in the enhancement of the animal's heat dissipation.

Utilization of Additive Manufacturing for Aerospace Heat Exchangers

DTIC Science & Technology

2016-02-29

is made up of flat plates that are layered on top of each other creating air passages in between the plates where the hot liquid and cold liquid flow...electron beam- based) for two-dimensional scanning of the heat source on the powder layer , stages that decrease the build plate and increase the powder...build plate and result in uneven coating of subsequent powder layers or complete failure of the system to recoat. The perturbations in recoater

The effect of butterfly-scale inspired patterning on leading-edge vortex growth

NASA Astrophysics Data System (ADS)

Wilroy, Jacob; Lang, Amy; Wahidi, Redha

2014-11-01

Leading edge vortices (LEVs) are important for generating thrust and lift in flapping flight, and the surface patterning (scales) on butterfly wings is hypothesized to play a role in the vortex formation of the LEV. To simplify this complex flow problem, we designed an experiment to focus on the alteration of 2-D vortex development with a variation in surface patterning. Specifically we are interested in the secondary vorticity generated by the LEV interacting at the patterned surface and how this can affect the growth rate of the circulation in the LEV. For this experiment we used rapid-prototyped longitudinal and transverse square grooves attached to a flat plate and compared the vortex formation as the plate moved vertically. The plate is impulsively started in quiescent water and flow fields at Re = 1500, 3000, and 6000 are examined using Digital Particle Image Velocimetry (DPIV). The vortex formation time is 0.6 and is based on the flat plate travel length and chord length. Support for this research came from NSF REU Grant 1358991 and CBET 1335848.

Analysis of liquid-metal-jet impingement cooling in a corner region and for a row of jets

NASA Technical Reports Server (NTRS)

Siegel, R.

1975-01-01

A conformal mapping method was used to analyze liquid-metal-jet impingement heat transfer. The jet flow region and energy equation are transformed to correspond to uniform flow in a parallel plate channel with nonuniform heat addition along a portion of one wall. The exact solution for the wall-temperature distribution was obtained in the transformed channel, and the results are mapped back into the physical plane. Two geometries are analyzed. One is for a single slot jet directed either into an interior corner formed by two flat plates, or over the external sides of the corner; the flat plates are uniformly heated, and the corner can have various included angles. The heat-transfer coefficient at the stagnation point at the apex of the plates is obtained as a function of the corner angle, and temperature distributions are calculated along the heated walls. The second geometry is an infinite row of uniformly spaced parallel slot jets impinging normally against a uniformly heated plate. The heat-transfer behavior is obtained as a function of the spacing between the jets. Results are given for several jet Peclet numbers from 5 to 50.

Analysis of unsteady compressible viscous layers

NASA Technical Reports Server (NTRS)

Power, G. D.; Verdon, J. M.; Kousen, K. A.

1990-01-01

The development of an analysis to predict the unsteady compressible flows in blade boundary layers and wakes is presented. The equations that govern the flows in these regions are transformed using an unsteady turbulent generalization of the Levy-Lees transformation. The transformed equations are solved using a finite difference technique in which the solution proceeds by marching in time and in the streamwise direction. Both laminar and turbulent flows are studied, the latter using algebraic turbulence and transition models. Laminar solutions for a flat plate are shown to approach classical asymptotic results for both high and low frequency unsteady motions. Turbulent flat-plate results are in qualitative agreement with previous predictions and measurements. Finally, the numerical technique is also applied to the stator and rotor of a low-speed turbine stage to determine unsteady effects on surface heating. The results compare reasonably well with measured heat transfer data and indicate that nonlinear effects have minimal impact on the mean and unsteady components of the flow.

Development of electromagnetic welding facility of flat plates for nuclear industry

NASA Astrophysics Data System (ADS)

Kumar, Rajesh; Sahoo, Subhanarayan; Sarkar, Biswanath; Shyam, Anurag

2017-04-01

Electromagnetic pulse welding (EMPW) process, one of high speed welding process uses electromagnetic force from discharged current through working coil, which develops a repulsive force between the induced current flowing parallel and in opposite direction. For achieving the successful weldment using this process the design of working coil is the most important factor due to high magnetic field on surface of work piece. In case of high quality flat plate welding factors such as impact velocity, angle of impact standoff distance, thickness of flyer and overlap length have to be chosen carefully. EMPW has wide applications in nuclear industry, automotive industry, aerospace, electrical industries. However formability and weldability still remain major issues. Due to ease in controlling the magnetic field enveloped inside tubes, the EMPW has been widely used for tube welding. In case of flat components control of magnetic field is difficult. Hence the application of EMPW gets restricted. The present work attempts to make a novel contribution by investigating the effect of process parameters on welding quality of flat plates. The work emphasizes the approaches and engineering calculations required to effectively use of actuator in EMPW of flat components.

Direct Measurements of Skin Friction

NASA Technical Reports Server (NTRS)

Dhawan, Satish

1953-01-01

A device has been developed to measure local skin friction on a flat plate by measuring the force exerted upon a very small movable part of the surface of the flat plate. These forces, which range from about 1 milligram to about 100 milligrams, are measured by means of a reactance device. The apparatus was first applied to measurements in the low-speed range, both for laminar and turbulent boundary layers. The measured skin-friction coefficients show excellent agreement with Blasius' and Von Karman's results. The device was then applied to high-speed subsonic flow and the turbulent-skin-friction coefficients were determined up to a Mach number of about 0.8. A few measurements in supersonic flow were also made. This paper describes the design and construction of the device and the results of the measurements.

Parallel DSMC Solution of Three-Dimensional Flow Over a Finite Flat Plate

NASA Technical Reports Server (NTRS)

Nance, Robert P.; Wilmoth, Richard G.; Moon, Bongki; Hassan, H. A.; Saltz, Joel

1994-01-01

This paper describes a parallel implementation of the direct simulation Monte Carlo (DSMC) method. Runtime library support is used for scheduling and execution of communication between nodes, and domain decomposition is performed dynamically to maintain a good load balance. Performance tests are conducted using the code to evaluate various remapping and remapping-interval policies, and it is shown that a one-dimensional chain-partitioning method works best for the problems considered. The parallel code is then used to simulate the Mach 20 nitrogen flow over a finite-thickness flat plate. It is shown that the parallel algorithm produces results which compare well with experimental data. Moreover, it yields significantly faster execution times than the scalar code, as well as very good load-balance characteristics.

Boundary layer flow of air over water on a flat plate

NASA Technical Reports Server (NTRS)

Nelson, John; Alving, Amy E.; Joseph, Daniel D.

1993-01-01

A non-similar boundary layer theory for air blowing over a water layer on a flat plate is formulated and studied as a two-fluid problem in which the position of the interface is unknown. The problem is considered at large Reynolds number (based on x), away from the leading edge. A simple non-similar analytic solution of the problem is derived for which the interface height is proportional to x(sub 1/4) and the water and air flow satisfy the Blasius boundary layer equations, with a linear profile in the water and a Blasius profile in the air. Numerical studies of the initial value problem suggests that this asymptotic, non-similar air-water boundary layer solution is a global attractor for all initial conditions.

Mimicking Natural Laminar to Turbulent Flow Transition: A Systematic CFD Study Using PAB3D

NASA Technical Reports Server (NTRS)

Pao, S. Paul; Abdol-Hamid, Khaled S.

2005-01-01

For applied aerodynamic computations using a general purpose Navier-Stokes code, the common practice of treating laminar to turbulent flow transition over a non-slip surface is somewhat arbitrary by either treating the entire flow as turbulent or forcing the flow to undergo transition at given trip locations in the computational domain. In this study, the possibility of using the PAB3D code, standard k-epsilon turbulence model, and the Girimaji explicit algebraic stresses model to mimic natural laminar to turbulent flow transition was explored. The sensitivity of flow transition with respect to two limiters in the standard k-epsilon turbulence model was examined using a flat plate and a 6:1 aspect ratio prolate spheroid for our computations. For the flat plate, a systematic dependence of transition Reynolds number on background turbulence intensity was found. For the prolate spheroid, the transition patterns in the three-dimensional boundary layer at different flow conditions were sensitive to the free stream turbulence viscosity limit, the reference Reynolds number and the angle of attack, but not to background turbulence intensity below a certain threshold value. The computed results showed encouraging agreements with the experimental measurements at the corresponding geometry and flow conditions.

An analysis of laminar free-convection flow and heat transfer about a flat plate paralled to the direction of the generating body force

NASA Technical Reports Server (NTRS)

Ostrach, Simon

1953-01-01

The free-convection flow and heat transfer (generated by a body force) about a flat plate parallel to the direction of the body force are formally analyzed and the type of flow is found to be dependent on the Grashof number alone. For large Grashof numbers (which are of interest in aeronautics), the flow is of the boundary-layer type and the problem is reduced in a formal manner, which is analogous to Prandtl's forced-flow boundary-layer theory, to the simultaneous solution of two ordinary differential equations subject to the proper boundary conditions. Velocity and temperature distributions for Prandtl numbers of 0.01, 0.72, 0.733, 1, 1, 10, 100, and 1000 are computed, and it is shown that velocities and Nusselt numbers of the order of magnitude of those encountered in forced-convection flows may be obtained in free-convection flows. The theoretical and experimental velocity and temperature distributions are in good agreement. A flow and a heat-transfer parameter, from which the important physical quantities such as shear stress and heat-transfer rate can be computed, are derived as functions of Prandtl number alone.

Dehumidification System with Steam Permeability Films

NASA Astrophysics Data System (ADS)

Ishikwa, Masaaki; Sekimori, Souji; Ogiwara, Shigeaki; Ochiai, Tetsunari; Hirata, Tetsuo

In a factory with a clean room facility in cold regions, dew-condensation on walls of the facility is one of the most serious problems in winter. In this study, a new dehumidification system in which a steam permeability film is located between humid air in a clean room and dry air from outside to exchange steam is proposed. This system can treat a lot of humid air with small energy only for driving fans to flow air. Some films are examined in two kinds of steam exchangers; double tube type and flat p1ate type. Steam permeability resistance and therma1 resistance of each film are first obtained in a double tube type exchanger. An analytica1 model for a flat plate type exchanger is then proposed, which shows good agreement with experimental data. Steam and heat transfer characteristics of a flat plate type exchanger are also evaluated experimentally. One film on a flat plate type exchanger shows dehumidification capacity of 0.033g/s(=120g/h )with its area of 2.232m2.

Development of an economic solar heating system with cost efficient flat plate collectors

NASA Astrophysics Data System (ADS)

Eder-Milchgeisser, W.; Burkart, R.

1980-10-01

Mass produced flat plate solar collectors were worked into the design of a system for heating a swimming pool and/or providing domestic hot water. The collector characteristics, including physical and mechanical data as well as theoretical energy conversion efficiency, are presented. The collector was tested and service life efficiency was determined. The mounting of the collector, depending on roof type, is explained. Both in service and laboratory test results demonstrate the cost effectiveness of the system. Further improvement of efficiency is envisaged with automatic flow control in the solar collector and hot water circuits.

Laminar-Boundary-Layer Oscillations and Transition on a Flat Plate

NASA Technical Reports Server (NTRS)

Schubauer, G B; Skramstad, H K

1948-01-01

This is an account of an investigation in which oscillations were discovered in the laminar boundary layer along a flat plate. These oscillations were found during the course of an experiment in which transition from laminar to turbulent flow was being studied on the plate as the turbulence in the wind stream was being reduced to unusually low values by means of damping screens. The first part of the paper deals with experimental methods and apparatus, measurements of turbulence and sound, and studies of transition. A description is then given of the manner in which oscillations were discovered and how they were found to be related to transition, and then how controlled oscillations were produced and studied in detail.

Hot air impingement on a flat plate using Large Eddy Simulation (LES) technique

NASA Astrophysics Data System (ADS)

Plengsa-ard, C.; Kaewbumrung, M.

2018-01-01

Impinging hot gas jets to a flat plate generate very high heat transfer coefficients in the impingement zone. The magnitude of heat transfer prediction near the stagnation point is important and accurate heat flux distribution are needed. This research studies on heat transfer and flow field resulting from a single hot air impinging wall. The simulation is carried out using computational fluid dynamics (CFD) commercial code FLUENT. Large Eddy Simulation (LES) approach with a subgrid-scale Smagorinsky-Lilly model is present. The classical Werner-Wengle wall model is used to compute the predicted results of velocity and temperature near walls. The Smagorinsky constant in the turbulence model is set to 0.1 and is kept constant throughout the investigation. The hot gas jet impingement on the flat plate with a constant surface temperature is chosen to validate the predicted heat flux results with experimental data. The jet Reynolds number is equal to 20,000 and a fixed jet-to-plate spacing of H/D = 2.0. Nusselt number on the impingement surface is calculated. As predicted by the wall model, the instantaneous computed Nusselt number agree fairly well with experimental data. The largest values of calculated Nusselt number are near the stagnation point and decrease monotonically in the wall jet region. Also, the contour plots of instantaneous values of wall heat flux on a flat plate are captured by LES simulation.

Turbulent Friction in the Boundary Layer of a Flat Plate in a Two-Dimensional Compressible Flow at High Speeds

NASA Technical Reports Server (NTRS)

Frankl, F.; Voishel, V.

1943-01-01

In the present report an investigation is made on a flat plate in a two-dimensional compressible flow of the effect of compressibility and heating on the turbulent frictional drag coefficient in the boundary layer of an airfoil or wing radiator. The analysis is based on the Prandtl-Karman theory of the turbulent boundary later and the Stodola-Crocco, theorem on the linear relation between the total energy of the flow and its velocity. Formulas are obtained for the velocity distribution and the frictional drag law in a turbulent boundary later with the compressibility effect and heat transfer taken into account. It is found that with increase of compressibility and temperature at full retardation of the flow (the temperature when the velocity of the flow at a given point is reduced to zero in case of an adiabatic process in the gas) at a constant R (sub x), the frictional drag coefficient C (sub f) decreased, both of these factors acting in the same sense.

Abstracts, 19th Annual Meeting Society of Engineering Science, Inc. October 27, 28, & 29, 1982.

DTIC Science & Technology

1982-10-01

nickel best syperellys used as turbine disk merlals t Mr Force engines. The types of tess and date are described alang Vth the pre- cedres for...microplar boundary layers. The specific geo- mtries of the flow are the flat plate flew, cross flow on a circular eylinder and longituadinal flow alang

The effect of butterfly-scale inspired patterning on leading-edge vortex growth

NASA Astrophysics Data System (ADS)

Wilroy, Jacob Aaron

Leading edge vortices (LEVs) are important for generating thrust and lift in flapping flight, and the surface patterning (scales) on butterfly wings is hypothesized to play a role in the vortex formation of the LEV. To simplify this complex flow problem, an experiment was designed to focus on the alteration of 2-D vortex development with a variation in surface patterning. Specifically, the secondary vorticity generated by the LEV interacting at the patterned surface was studied, as well as the subsequent effect on the LEV's growth rate and peak circulation. For this experiment, rapid-prototyped grooves based on the scale geometry of the Monarch butterfly (Danaus plexippus) were created using additive manufacturing and were attached to a flat plate with a chordwise orientation, thus increasing plate surface area. The vortex generated by the grooved plate was then compared to a smooth plate case in an experiment where the plate translated vertically through a 2 x 3 x 5 cubic foot tow tank. The plate was impulsively started in quiescent water and flow fields at Rec = 1416, 2833, and 5667 are examined using Digital Particle Image Velocimetry (DPIV). The maximum vortex formation number is 2.8 and is based on the flat plate travel length and chord length. Flow fields from each case show the generation of a secondary vortex whose interaction with the shear layer and LEV caused different behaviors depending upon the surface type. The vortex development process varied for each Reynolds number and it was found that for the lowest Reynolds number case a significant difference does not exist between surface types, however, for the other two cases the grooves affected the secondary vortex's behavior and the LEV's ability to grow at a rate similar to the smooth plate case.

Fuel cell assembly unit for promoting fluid service and electrical conductivity

DOEpatents

Jones, Daniel O.

1999-01-01

Fluid service and/or electrical conductivity for a fuel cell assembly is promoted. Open-faced flow channel(s) are formed in a flow field plate face, and extend in the flow field plate face between entry and exit fluid manifolds. A resilient gas diffusion layer is located between the flow field plate face and a membrane electrode assembly, fluidly serviced with the open-faced flow channel(s). The resilient gas diffusion layer is restrained against entering the open-faced flow channel(s) under a compressive force applied to the fuel cell assembly. In particular, a first side of a support member abuts the flow field plate face, and a second side of the support member abuts the resilient gas diffusion layer. The support member is formed with a plurality of openings extending between the first and second sides of the support member. In addition, a clamping pressure is maintained for an interface between the resilient gas diffusion layer and a portion of the membrane electrode assembly. Preferably, the support member is spikeless and/or substantially flat. Further, the support member is formed with an electrical path for conducting current between the resilient gas diffusion layer and position(s) on the flow field plate face.

Mobility power flow analysis of an L-shaped plate structure subjected to acoustic excitation

NASA Technical Reports Server (NTRS)

Cuschieri, J. M.

1989-01-01

An analytical investigation based on the Mobility Power Flow method is presented for the determination of the vibrational response and power flow for two coupled flat plate structures in an L-shaped configuration, subjected to acoustical excitation. The principle of the mobility power flow method consists of dividing the global structure into a series of subsystems coupled together using mobility functions. Each separate subsystem is analyzed independently to determine the structural mobility functions for the junction and excitation locations. The mobility functions, together with the characteristics of the junction between the subsystems, are then used to determine the response of the global structure and the power flow. In the coupled plate structure considered here, mobility power flow expressions are derived for excitation by an incident acoustic plane wave. In this case, the forces (acoustic pressures) acting on the structure are dependent on the response of the structure because of the scattered pressure component. The interaction between the structure and the fluid leads to the derivation of a corrected mode shape for the plates' normal surface velocity and also for the structure mobility functions. The determination of the scattered pressure components in the expressions for the power flow represents an additional component in the power flow balance for the source plate and the receiver plate. This component represents the radiated acoustical power from the plate structure.

Fluctuating pressures in flow fields of jets

NASA Technical Reports Server (NTRS)

Schroeder, J. C.; Haviland, J. K.

1976-01-01

The powered lift configurations under present development for STOL aircraft are the externally blown flap (EBF), involving direct jet impingement on the aircraft flaps, and the upper surface blown (USB), where the jet flow is attached on the upper surface of the wing and directed downwards. Towards the goal of developing scaling laws to predict unsteady loads imposed on the structural components of these STOL aircraft from small model tests, the near field fluctuating pressure behavior for the simplified cases of a round free cold jet and the same jet impinging on a flat plate was investigated. Examples are given of coherences, phase lags (giving convection velocities), and overall fluctuating pressure levels measured. The fluctuating pressure levels measured on the flat plate are compared to surface fluctuating pressure levels measured on full-scale powered-lift configuration models.

Results of convective heating tests of a longitudinal gap on the Rockwell flat plate model (15-0, insert 7) in the NASA/Ames Research Center

NASA Technical Reports Server (NTRS)

Quan, M.; Lockman, W. K.

1975-01-01

Results are presented which were obtained from tests in a hypersonic wind tunnel to determine aerodynamic heating rates in a gap running parallel or slightly askew to the flow direction. The model used was a flat plate instrumented in thin-skin sections with chromelconstantan thermocouples. Heating rate profiles lengthwise along and down into the gap were obtained, and additional data were obtained from a total temperature probe and rake fabricated during the test to investigate an apparent aerodynamic cooling trend in the gap. Model variables were width, depth, length, and orientation of the gap relative to the flow direction. The tests were conducted at Mach 5.1 and Reynolds numbers per foot of 500,000, 1,000,000, and 2,000,000.

Interference drag in a simulated wing-fuselage juncture

NASA Technical Reports Server (NTRS)

Kubendran, L. R.; Mcmahon, H.; Hubbartt, J. E.

1984-01-01

The interference drag in a wing fuselage juncture as simulated by a flat plate and a body of constant thickness having a 1.5:1 elliptical leading edge is evaluated experimentally. The experimental measurements consist of mean velocity data taken with a hot wire at a streamwise location corresponding to 16 body widths downstream of the body leading edge. From these data, the interference drag is determined by calculating the total momentum deficit (momentum area) in the juncture and also in the two dimensional turbulent boundary layers on the flat plate and body at locations sufficiently far from the juncture flow effect. The interference drag caused by the juncture drag as measured at this particular streamwise station is -3% of the total drag due to the flat plate and body boundary layers in isolation. If the body is considered to be a wing having a chord and span equal to 16 body widths, the interference drag due to the juncture is only -1% of the frictional drag of one surface of such a wing.

Development of a laser-induced heat flux technique for measurement of convective heat transfer coefficients in a supersonic flowfield

NASA Technical Reports Server (NTRS)

Porro, A. Robert; Keith, Theo G., Jr.; Hingst, Warren R.; Chriss, Randall M.; Seablom, Kirk D.

1991-01-01

A technique is developed to measure the local convective heat transfer coefficient on a model surface in a supersonic flow field. The technique uses a laser to apply a discrete local heat flux at the model test surface, and an infrared camera system determines the local temperature distribution due to heating. From this temperature distribution and an analysis of the heating process, a local convective heat transfer coefficient is determined. The technique was used to measure the load surface convective heat transfer coefficient distribution on a flat plate at nominal Mach numbers of 2.5, 3.0, 3.5, and 4.0. The flat plate boundary layer initially was laminar and became transitional in the measurement region. The experimental results agreed reasonably well with theoretical predictions of convective heat transfer of flat plate laminar boundary layers. The results indicate that this non-intrusive optical measurement technique has the potential to obtain high quality surface convective heat transfer measurements in high speed flowfields.

Quantification of the effect of surface heating on shock wave modification by a plasma actuator in a low-density supersonic flow over a flat plate

NASA Astrophysics Data System (ADS)

Joussot, Romain; Lago, Viviana; Parisse, Jean-Denis

2015-05-01

This paper describes experimental and numerical investigations focused on the shock wave modification induced by a dc glow discharge. The model is a flat plate in a Mach 2 air flow, equipped with a plasma actuator composed of two electrodes. A weakly ionized plasma was created above the plate by generating a glow discharge with a negative dc potential applied to the upstream electrode. The natural flow exhibited a shock wave with a hyperbolic shape. Pitot measurements and ICCD images of the modified flow revealed that when the discharge was ignited, the shock wave angle increased with the discharge current. The spatial distribution of the surface temperature was measured with an IR camera. The surface temperature increased with the current and decreased along the model. The temperature distribution was reproduced experimentally by placing a heating element instead of the active electrode, and numerically by modifying the boundary condition at the model surface. For the same surface temperature, experimental investigations showed that the shock wave angle was lower with the heating element than for the case with the discharge switched on. The results show that surface heating is responsible for roughly 50 % of the shock wave angle increase, meaning that purely plasma effects must also be considered to fully explain the flow modifications observed.

Effect of free-stream turbulence on boundary layer transition.

PubMed

Goldstein, M E

2014-07-28

This paper is concerned with the transition to turbulence in flat plate boundary layers due to moderately high levels of free-stream turbulence. The turbulence is assumed to be generated by an (idealized) grid and matched asymptotic expansions are used to analyse the resulting flow over a finite thickness flat plate located in the downstream region. The characteristic Reynolds number Rλ based on the mesh size λ and free-stream velocity is assumed to be large, and the turbulence intensity ε is assumed to be small. The asymptotic flow structure is discussed for the generic case where the turbulence Reynolds number εRλ and the plate thickness and are held fixed (at O(1) and O(λ), respectively) in the limit as [Formula: see text] and ε→0. But various limiting cases are considered in order to explain the relevant transition mechanisms. It is argued that there are two types of streak-like structures that can play a role in the transition process: (i) those that appear in the downstream region and are generated by streamwise vorticity in upstream flow and (ii) those that are concentrated near the leading edge and are generated by plate normal vorticity in upstream flow. The former are relatively unaffected by leading edge geometry and are usually referred to as Klebanoff modes while the latter are strongly affected by leading edge geometry and are more streamwise vortex-like in appearance. © 2014 The Author(s) Published by the Royal Society. All rights reserved.

Orbiter BLT Flight Experiment Wind Tunnel Simulations: Nearfield Flowfield Imaging and Surface Thermography

NASA Technical Reports Server (NTRS)

Danehy, Paul M.; Ivey, Christoper B.; Barthel, Brett F.; Inman, Jennifer A.; Jones, Stephen B.; Watkins, Anthony N.; Goodman, Kyle Z.; McCrea, Andrew C.; Leighty, Bradley D.; Lipford, William K.;

Internal-flow systems for aircraft

NASA Technical Reports Server (NTRS)

Rogallo, F M

1941-01-01

An investigation has been made to determine efficient arrangements for an internal-flow system of an aircraft when such a system operates by itself or in combination with other flow systems. The investigation included a theoretical treatment of the problem and tests in the NACA 5-foot vertical wind tunnel of inlet and outlet openings in a flat plate and in a wing.

Reversing flow causes passive shark scale actuation in a separating turbulent boundary layer

NASA Astrophysics Data System (ADS)

Lang, Amy; Gemmell, Bradford; Motta, Phil; Habegger, Laura; Du Clos, Kevin; Devey, Sean; Stanley, Caleb; Santos, Leo

2017-11-01

Control of flow separation by shortfin mako skin in experiments has been demonstrated, but the mechanism is still poorly understood yet must be to some extent Re independent. The hypothesized mechanisms inherent in the shark skin for controlling flow separation are: (1) the scales, which are capable of being bristled only by reversing flow, inhibit flow reversal events from further development into larger-scale separation and (2) the cavities formed when scales bristle induces mixing of high momentum flow towards the wall thus energizing the flow close to the surface. Two studies were carried out to measure passive scale actuation caused by reversing flow. A small flow channel induced an unsteady, wake flow over the scales prompting reversing flow events and scale actuation. To resolve the flow and scale movements simultaneously we used specialized optics at high magnification (1 mm field of view) at 50,000 fps. In another study, 3D printed models of shark scales, or microflaps (bristling capability up to 50 degrees), were set into a flat plate. Using a tripped, turbulent boundary layer grown over the long flat plate and a localized adverse pressure gradient, a separation bubble was generated within which the microflaps were placed. Passive flow actuation of both shark scales and microflaps by reversing flow was observed. Funding from Army Research Office and NSF REU site Grant.

An analysis of the relaxation of laminar boundary layer on a flat plate after passage of an interface with application to expansion-tube flows

NASA Technical Reports Server (NTRS)

Gupta, R. N.

1972-01-01

The relaxation of the accelerating-gas boundary layer to the test-gas boundary layer over a flat plate in an expansion tube is analyzed. Several combinations of test gas and acceleration gas are considered. The problem is treated in two conically similar limits: (1) when the time lag between the arrival of the shock and the interface at the leading edge of the plate is very large, and (2) when this lag is negligible. The time-dependent laminar-boundary-layer equations of a binary mixture of perfect gases are taken as the flow-governing equations. This coupled set of differential equations, written in terms of the Lam-Crocco variables, has been solved by a line-relaxation finite-difference techniques. The results presented include the Stanton number and the local skin-friction coefficient as functions of shock Mach number and the nondimensional distance-time variable. The results indicate that more than 95 percent of the test-gas boundary layer exists over a length, measured from the leading edge of the plate, equal to about three-tenths of the distance traversed by the interface in the free stream.

Low order physical models of vertical axis wind turbines

NASA Astrophysics Data System (ADS)

Craig, Anna; Dabiri, John; Koseff, Jeffrey

2016-11-01

In order to examine the ability of low-order physical models of vertical axis wind turbines to accurately reproduce key flow characteristics, experiments were conducted on rotating turbine models, rotating solid cylinders, and stationary porous flat plates (of both uniform and non-uniform porosities). From examination of the patterns of mean flow, the wake turbulence spectra, and several quantitative metrics, it was concluded that the rotating cylinders represent a reasonably accurate analog for the rotating turbines. In contrast, from examination of the patterns of mean flow, it was found that the porous flat plates represent only a limited analog for rotating turbines (for the parameters examined). These findings have implications for both laboratory experiments and numerical simulations, which have previously used analogous low order models in order to reduce experimental/computational costs. NSF GRF and SGF to A.C; ONR N000141211047 and the Gordon and Betty Moore Foundation Grant GBMF2645 to J.D.; and the Bob and Norma Street Environmental Fluid Mechanics Laboratory at Stanford University.

Key technique study and application of infrared thermography in hypersonic wind tunnel

NASA Astrophysics Data System (ADS)

LI, Ming; Yang, Yan-guang; Li, Zhi-hui; Zhu, Zhi-wei; Zhou, Jia-sui

2014-11-01

The solutions to some key techniques using infrared thermographic technique in hypersonic wind tunnel, such as temperature measurement under great measurement angle, the corresponding relation between model spatial coordinates and the ones in infrared map, the measurement uncertainty analysis of the test data etc., are studied. The typical results in the hypersonic wind tunnel test are presented, including the comparison of the transfer rates on a thin skin flat plate model with a wedge measured with infrared thermography and thermocouple, the experimental study heating effect on the flat plate model impinged by plume flow and the aerodynamic heating on the lift model.

PLIF Temperature and Velocity Distributions in Laminar Hypersonic Flat-plate Flow

NASA Technical Reports Server (NTRS)

OByrne, S.; Danehy, P. M.; Houwing, A. F. P.

2003-01-01

Rotational temperature and velocity distributions have been measured across a hypersonic laminar flat-plate boundary layer, using planar laser-induced fluorescence. The measurements are compared to a finite-volume computation and a first-order boundary layer computation, assuming local similarity. Both computations produced similar temperature distributions and nearly identical velocity distributions. The disagreement between calculations is ascribed to the similarity solution not accounting for leading-edge displacement effects. The velocity measurements agreed to within the measurement uncertainty of 2 % with both calculated distributions. The peak measured temperature was 200 K lower than the computed values. This discrepancy is tentatively ascribed to vibrational relaxation in the boundary layer.

On the boundary flow using pulsed nanosecond DBD plasma actuators

NASA Astrophysics Data System (ADS)

Zhao, Zi-Jie; Cui, Y. D.; Li, Jiun-Ming; Zheng, Jian-Guo; Khoo, B. C.

2018-05-01

Our previous studies in quiescent air environment [Z. J. Zhao et al., AIAA J. 53(5) (2015) 1336; J. G. Zheng et al., Phys. Fluids 26(3) (2014) 036102] reveal experimentally and numerically that the shock wave generated by the nanosecond pulsed plasma is fundamentally a microblast wave. The shock-induced burst perturbations (overpressure and induced velocity) are found to be restricted to a very narrow region (about 1 mm) behind the shock front and last only for a few microseconds. These results indicate that the pulsed nanosecond dielectric barrier discharge (DBD) plasma actuator has stronger local effects in time and spatial domain. In this paper, we further investigate the effects of pulsed plasma on the boundary layer flow over a flat plate. The present investigation reveals that the nanosecond pulsed plasma actuator generates intense perturbations and tends to promote the laminar boundary over a flat plate to turbulent flow. The heat effect after the pulsed plasma discharge was observed in the external flow, lasting a few milliseconds for a single pulse and reaching a quasi-stable state for multi-pulses.

Generating cycle flow between dark and light zones with double paddlewheels to improve microalgal growth in a flat plate photo-bioreactor.

PubMed

Cheng, Jun; Xu, Junchen; Lu, Hongxiang; Ye, Qing; Liu, Jianzhong; Zhou, Junhu

2018-08-01

Double paddlewheels were proposed to generate cycle flow for increasing horizontal fluid velocity between dark and light zones in a flat plate photo-bioreactor, which strengthened the mass transfer and the mixing effect to improve microalgal growth with 15% CO 2 . Numerical fluid dynamics were used to simulate the cycle flow field with double paddlewheels. The local flow field measured with particle image velocimetry fitted well with the numerical simulation results. The horizontal fluid velocity in the photo-bioreactor was markedly increased from 5.8 × 10 -5  m/s to 0.45 m/s with the rotation of double paddlewheels, resulting in a decreased dark/light cycle period. Therefore, bubble formation time and diameter reduced by 24.4% and 27.4%, respectively. Meanwhile, solution mixing time reduced by 31.3% and mass transfer coefficient increased by 41.2%. The biomass yield of microalgae Nannochloropsis Oceanic increased by 127.1% with double paddlewheels under 15% CO 2 condition. Copyright © 2018 Elsevier Ltd. All rights reserved.

NUCLEAR REACTOR FUEL ELEMENT

DOEpatents

Wheelock, C.W.; Baumeister, E.B.

1961-09-01

A reactor fuel element utilizing fissionable fuel materials in plate form is described. This fuel element consists of bundles of fuel-bearing plates. The bundles are stacked inside of a tube which forms the shell of the fuel element. The plates each have longitudinal fins running parallel to the direction of coolant flow, and interspersed among and parallel to the fins are ribs which position the plates relative to each other and to the fuel element shell. The plate bundles are held together by thin bands or wires. The ex tended surface increases the heat transfer capabilities of a fuel element by a factor of 3 or more over those of a simple flat plate.

Vortex formation and saturation for low-aspect-ratio rotating flat-plate fins

NASA Astrophysics Data System (ADS)

Devoria, Adam C.; Ringuette, Matthew J.

2012-02-01

We investigate experimentally the unsteady, three-dimensional vortex formation of low-aspect-ratio, trapezoidal flat-plate fins undergoing rotation from rest at a 90° angle of attack and Reynolds numbers of O(103). The objectives are to characterize the unsteady three-dimensional vortex structure, examine vortex saturation, and understand the effects of the root-to-tip flow for different velocity programs. The experiments are conducted in a water tank facility, and the diagnostic tools are dye flow visualization and digital particle image velocimetry. The dye visualizations show that the low-aspect-ratio plate produces symmetric ring-like vortices comprised mainly of tip-edge vorticity. They also indicate the presence of the root-to-tip velocity. For large rotational amplitudes, the primary ring-like vortex sheds and a secondary ring-like vortex is generated while the plate is still in motion, indicating saturation of the leading vortex. The time-varying vortex circulation in the flow symmetry plane provides quantitative evidence of vortex saturation. The phenomenon of saturation is observed for several plate velocity programs. The temporal development of the vortex circulation is often complex, which prevents an objective determination of an exact saturation time. This is the result of an interaction between the developing vortex and the root-to-tip flow, which breaks apart the vortex. However, it is possible to define a range of time during which the vortex reaches saturation. A formation-parameter definition is investigated and is found to reasonably predict the state corresponding to the pinch-off of the initial tip vortex across the velocity programs tested. This event is the lower bound on the saturation time range.

Effects of Reynolds number on orifice induced pressure error

NASA Technical Reports Server (NTRS)

Plentovich, E. B.; Gloss, B. B.

1982-01-01

Data previously reported for orifice induced pressure errors are extended to the case of higher Reynolds number flows, and a remedy is presented in the form of a porous metal plug for the orifice. Test orifices with apertures 0.330, 0.660, and 1.321 cm in diam. were fabricated on a flat plate for trials in the NASA Langley wind tunnel at Mach numbers 0.40-0.72. A boundary layer survey rake was also mounted on the flat plate to allow measurement of the total boundary layer pressures at the orifices. At the high Reynolds number flows studied, the orifice induced pressure error was found to be a function of the ratio of the orifice diameter to the boundary layer thickness. The error was effectively eliminated by the insertion of a porous metal disc set flush with the orifice outside surface.

Driving mechanism of unsteady separation shock motion in hypersonic interactive flow

NASA Technical Reports Server (NTRS)

Dolling, D. S.; Narlo, J. C., II

1987-01-01

Wall pressure fluctuations were measured under the steady separation shock waves in Mach 5 turbulent interactions induced by unswept circular cylinders on a flat plate. The wall temperature was adiabatic. A conditional sampling algorithm was developed to examine the statistics of the shock wave motion. The same algorithm was used to examine data taken in earlier studies in the Princeton University Mach 3 blowdown tunnel. In these earlier studies, hemicylindrically blunted fins of different leading-edge diameters were tested in boundary layers which developed on the tunnel floor and on a flat plate. A description of the algorithm, the reasons why it was developed and the sensitivity of the results to the threshold settings, are discussed. The results from the algorithm, together with cross correlations and power spectral density estimates suggests that the shock motion is driven by the low-frequency unsteadiness of the downstream separated, vortical flow.

An experimental investigation with artificial sunlight of a solar hot-water heater

NASA Technical Reports Server (NTRS)

Simon, F. F.

1976-01-01

Thermal performance measurements were made of a commercial solar hot-water heater in a solar simulator. The objective of the test was to determine basic performance characteristics of a traditional type of flat-plate collector, with and without side reflectors (to increase the solar flux). Due to the fact that collector testing in the solar simulator permits control of the variables that affect collector performance, it was possible to obtain information on each of the following: (1) the effect of flow and incidence angle on the efficiency of a flat-plate collector (but only without side reflectors), (2) transient performance under flow and nonflow conditions, (3) the effectiveness of reflectors in increasing collector efficiency for a zero radiation angle at fluid temperatures required for solar air conditioning, and (4) the limits of applicability of a collector efficiency correlation based on the Hottel-Whillier equation (1958).

Hydrodynamic and Thermal Slip Effect on Double-Diffusive Free Convective Boundary Layer Flow of a Nanofluid Past a Flat Vertical Plate in the Moving Free Stream

PubMed Central

Khan, Waqar A.; Uddin, Md Jashim; Ismail, A. I. Md.

2013-01-01

The effects of hydrodynamic and thermal slip boundary conditions on the double-diffusive free convective flow of a nanofluid along a semi-infinite flat solid vertical plate are investigated numerically. It is assumed that free stream is moving. The governing boundary layer equations are non-dimensionalized and transformed into a system of nonlinear, coupled similarity equations. The effects of the controlling parameters on the dimensionless velocity, temperature, solute and nanofluid concentration as well as on the reduced Nusselt number, reduced Sherwood number and the reduced nanoparticle Sherwood number are investigated and presented graphically. To the best of our knowledge, the effects of hydrodynamic and thermal slip boundary conditions have not been investigated yet. It is found that the reduced local Nusselt, local solute and the local nanofluid Sherwood numbers increase with hydrodynamic slip and decrease with thermal slip parameters. PMID:23533566

Double Diffusive Magnetohydrodynamic (MHD) Mixed Convective Slip Flow along a Radiating Moving Vertical Flat Plate with Convective Boundary Condition

PubMed Central

Rashidi, Mohammad M.; Kavyani, Neda; Abelman, Shirley; Uddin, Mohammed J.; Freidoonimehr, Navid

2014-01-01

In this study combined heat and mass transfer by mixed convective flow along a moving vertical flat plate with hydrodynamic slip and thermal convective boundary condition is investigated. Using similarity variables, the governing nonlinear partial differential equations are converted into a system of coupled nonlinear ordinary differential equations. The transformed equations are then solved using a semi-numerical/analytical method called the differential transform method and results are compared with numerical results. Close agreement is found between the present method and the numerical method. Effects of the controlling parameters, including convective heat transfer, magnetic field, buoyancy ratio, hydrodynamic slip, mixed convective, Prandtl number and Schmidt number are investigated on the dimensionless velocity, temperature and concentration profiles. In addition effects of different parameters on the skin friction factor, , local Nusselt number, , and local Sherwood number are shown and explained through tables. PMID:25343360

An experimental study of tip shape effects on the flutter of aft-swept, flat-plate wings

NASA Technical Reports Server (NTRS)

Dansberry, Bryan E.; Rivera, Jose A., Jr.; Farmer, Moses G.

1990-01-01

The effects of tip chord orientation on wing flutter are investigated experimentally using six cantilever-mounted, flat-plate wing models. Experimentally determined flutter characteristics of the six models are presented covering both the subsonic and transonic Mach number ranges. While all models have a 60 degree leading edge sweep, a 40.97 degree trailing edge sweep, and a root chord of 34.75 inches, they are subdivided into two series characterized by a higher aspect ratio and a lower aspect ratio. Each series is made up of three models with tip chord orientations which are parallel to the free-stream flow, perpendicular to the model mid-chord line, and perpendicular to the free-stream flow. Although planform characteristics within each series of models are held constant, structural characteristics such as mode shapes and natural frequencies are allowed to vary.

Numerical analysis of conjugate heat transfer due to oblique impingement of turbulent slot jet onto a flat plate

NASA Astrophysics Data System (ADS)

Shashikant, Patel, Devendra Kumar; Kumar, Jayesh; Kumar, Vishwajeet

2018-04-01

The conjugate heat transfer due to oblique impingement of two-dimensional, steady state, incompressible, turbulent slot jet on a uniformly heated flat plate has been studied in the present work. The standard high Reynolds number two-equation k - ɛ eddy viscosity model has been used for numerical simulation. The Reynolds number based on the hydraulic diameter of nozzle exit and turbulent intensity maintained at 9, 900 and 2% respectively. The angle of inclination 30°, 45°, 60° and, 75° degrees are considered for the numerical study. A uniform temperature higher than the jet exit temperature is provided to the bottom surface of the plate. The flow field have been studied using the contour plots of pressure and velocity in the fluid domain. The influence of inclination on the distribution of the local Nusselt number over the surface of impingement have been presented. It is found that the angle of impingement influences the flow field and heat transfer characteristics more in the downhill direction of the stagnation zone compared to the uphill direction.

Radiated flow of chemically reacting nanoliquid with an induced magnetic field across a permeable vertical plate

NASA Astrophysics Data System (ADS)

Mahanthesh, B.; Gireesha, B. J.; Athira, P. R.

Impact of induced magnetic field over a flat porous plate by utilizing incompressible water-copper nanoliquid is examined analytically. Flow is supposed to be laminar, steady and two-dimensional. The plate is subjected to a regular free stream velocity as well as suction velocity. Flow formulation is developed by considering Maxwell-Garnetts (MG) and Brinkman models of nanoliquid. Impacts of thermal radiation, viscous dissipation, temperature dependent heat source/sink and first order chemical reaction are also retained. The subjected non-linear problems are non-dimensionalized and analytic solutions are presented via series expansion method. The graphs are plotted to analyze the influence of pertinent parameters on flow, magnetism, heat and mass transfer fields as well as friction factor, current density, Nusselt and Sherwood numbers. It is found that friction factor at the plate is more for larger magnetic Prandtl number. Also the rate of heat transfer decayed with increasing nanoparticles volume fraction and the strength of magnetism.

Numerical simulation of supersonic water vapor jet impinging on a flat plate

NASA Astrophysics Data System (ADS)

Kuzuu, Kazuto; Aono, Junya; Shima, Eiji

2012-11-01

We investigated supersonic water vapor jet impinging on a flat plate through numerical simulation. This simulation is for estimating heating effect of a reusable sounding rocket during vertical landing. The jet from the rocket bottom is supersonic, M=2 to 3, high temperature, T=2000K, and over-expanded. Atmospheric condition is a stationary standard air. The simulation is base on the full Navier-Stokes equations, and the flow is numerically solved by an unstructured compressible flow solver, in-house code LS-FLOW-RG. In this solver, the transport properties of muti-species gas and mass conservation equations of those species are considered. We employed DDES method as a turbulence model. For verification and validation, we also carried out a simulation under the condition of air, and compared with the experimental data. Agreement between our results and the experimental data are satisfactory. Through this simulation, we calculated the flow under some exit pressure conditions, and discuss the effects of pressure ratio on flow structures, heat transfer and so on. Furthermore, we also investigated diffusion effects of water vapor, and we confirmed that these phenomena are generated by the interaction of atmospheric air and affects the heat transfer to the surrounding environment.

Thin walled channel

DOE Office of Scientific and Technical Information (OSTI.GOV)

Crowther, R.L.; Johansson, E.B.

1988-06-07

A fuel assembly is described comprising fuel rods positioned in a spaced array by upper and lower tie-plates, an open ended flow channel surrounding the array for conducting coolant upward about the fuel rods, the open ended channel having a polygon shaped cross section with flat side sections connected between the corner sections; means separate from the channel connecting the upper and lower tie-plates together and maintaining the fuel rods in spaced array independent of the flow channel, improvement in the flow channel comprising: four corners having a first thickness; four sides having a second and reduced thickness from themore » corner thickness, the sides welded to the corner sections.« less

Effects of mass transfer on MHD three dimensional flow of a Prandtl liquid over a flat plate in the presence of chemical reaction

NASA Astrophysics Data System (ADS)

Ganesh Kumar, K.; Rizwan-ul-Haq; Rudraswamy, N. G.; Gireesha, B. J.

The present study addresses the three-dimensional flow of a Prandtl fluid over a Riga plate in the presence of chemical reaction and convective condition. The converted set of boundary layer equations are solved numerically by RKF four-fifth method. Obtained numerical results for flow and mass transfer characteristics are discussed for various physical parameters. Additionally, the skin friction coefficient and Sherwood number are also presented. It is found that, the momentum boundary layer thickness is dominant for higher values of α and solutal boundary layer is low for higher Schmidt number and chemical reaction parameter.

Numerical study of large-eddy breakup and its effect on the drag characteristics of boundary layers

NASA Technical Reports Server (NTRS)

Kinney, R. B.; Taslim, M. E.; Hung, S. C.

1985-01-01

The break-up of a field of eddies by a flat-plate obstacle embedded in a boundary layer is studied using numerical solutions to the two-dimensional Navier-Stokes equations. The flow is taken to be incompressible and unsteady. The flow field is initiated from rest. A train of eddies of predetermined size and strength are swept into the computational domain upstream of the plate. The undisturbed velocity profile is given by the Blasius solution. The disturbance vorticity generated at the plate and wall, plus that introduced with the eddies, mix with the background vorticity and is transported throughout the entire flow. All quantities are scaled by the plate length, the unidsturbed free-stream velocity, and the fluid kinematic viscosity. The Reynolds number is 1000, the Blasius boundary layer thickness is 2.0, and the plate is positioned a distance of 1.0 above the wall. The computational domain is four units high and sixteen units long.

Transmission and Incidence Losses for a Slotted Plate

NASA Technical Reports Server (NTRS)

Wilson, Jack; Chima, Rodrick V.; Skews, Beric W.

1998-01-01

The objective of this work is to find a model of the stagnation pressure loss resulting from flow through a slotted plate, which is effectively a cascade of flat plate airfoils, particularly at very large angles of incidence. Data from a published experiment is examined, and compared with control volume analysis, and CFD code calculations. An assumption that the loss can be separated into a transmission loss and an incidence loss seems to be justified by the data. Both the data and the CFD code results are consistent with an incidence loss model in which the flow component normal to the slot axis is lost. However, the experimental transmission loss is much larger than calculated values.

Application of a new K-tau model to near wall turbulent flows

NASA Technical Reports Server (NTRS)

Thangam, S.; Abid, R.; Speziale, Charles G.

1991-01-01

A recently developed K-tau model for near wall turbulent flows is applied to two severe test cases. The turbulent flows considered include the incompressible flat plate boundary layer with the adverse pressure gradients and incompressible flow past a backward facing step. Calculations are performed for this two-equation model using an anisotropic as well as isotropic eddy-viscosity. The model predictions are shown to compare quite favorably with experimental data.

Standardized performance tests of collectors of solar thermal energy: An evacuated flatplate copper collector with a serpentine flow distribution

NASA Technical Reports Server (NTRS)

Johnson, S. M.

1976-01-01

Basic test results are given for a flat plate solar collector whose performance was determined in the NASA-Lewis solar simulator. The collector was tested over ranges of inlet temperatures, fluxes and one coolant flow rate. Collector efficiency is correlated in terms of inlet temperature and flux level.

78 FR 50378 - Diffusion-Annealed, Nickel-Plated Flat-Rolled Steel Products From Japan: Postponement of...

Federal Register 2010, 2011, 2012, 2013, 2014

2013-08-19

...-Plated Flat-Rolled Steel Products From Japan: Postponement of Preliminary Determination of Antidumping... investigation of diffusion-annealed, nickel-plated flat-rolled steel products from Japan. See Diffusion- Annealed, Nickel-Plated Flat-Rolled Steel Products From Japan: Initiation of Antidumping Duty Investigation...

Axially shaped channel and integral flow trippers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Crowther, R.L.; Johansson, E.B.; Matzner, B.

1988-06-07

A fuel assembly is described comprising fuel rods positioned in spaced array by upper and lower tie-plates, an open ended flow channel surrounding the array for conducting coolant upward between a lower support plate having coolant communicated thereto to an upper support grid having a steam/water outlet communicated thereto. The flow channel surrounds the array for conducting coolant about the fuel rods. The open ended channel has a polygon shaped cross section with the channel constituting a closed conduit with flat side sections connected at corners to form the enclosed conduit; means separate from the channel for connecting the uppermore » and lower tie-plates together and maintaining the fuel rods in spaced array independent of the flow channel. The improvement in the flow channel comprises tapered side walls. The tapered side walls extend from an average thick cross section adjacent the lower support plate to an average thin cross section adjacent the upper core grid whereby the channel is reduced in thickness adjacent the upper core grid to correspond with the reduced pressure adjacent the upper core grid.« less

Axially shaped channel and integral flow trippers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Crowther, R.L. Jr.; Johansson, E.B.; Matzner, B.

1992-02-11

This patent describes a fuel assembly. It comprises: fuel rods positioned in spaced array by upper and lower tie-plates, and open ended flow channel surrounding the array for conducting coolant upward between a lower support plate having coolant communicated thereto to an upper support grid having a steam/water outlet communicated thereto. The flow channel surrounding the array for conducting coolant about the fuel rods; the open ended channel having a polygon shaped cross section with the channel constituting a closed conduit with flat side sections connected at corners to form the enclosed conduit; means separate from the channel for connectingmore » the upper and lower tie-plates together and maintaining the fuel rods in spaced array independent of the flow channel, the improvement in the flow channel comprising tapered side walls, the tapered side walls extending from an average thick cross section adjacent the lower support plate to an average thin cross section adjacent the upper core grid whereby the channel is reduced in thickness adjacent the upper core grid to correspond with the reduced pressure adjacent the upper core grid.« less

Vortex boundary-layer interactions

NASA Technical Reports Server (NTRS)

Bradshaw, P.

1986-01-01

Parametric studies to identify a vortex generator were completed. Data acquisition in the first chosen configuration, in which a longitudinal vortex pair generated by an isolated delta wing starts to merge with a turbulent boundary layer on a flat plate fairly close to the leading edge is nearly completed. Work on a delta-wing/flat-plate combination, consisting of a flow visualization and hot wire measurements taken with a computer controlled traverse gear and data logging system were completed. Data taking and analysis have continued, and sample results for another cross stream plane are presented. Available data include all mean velocity components, second order mean products of turbulent fluctuations, and third order mean products. Implementation of a faster data logging system was accomplished.

Transmission of heat from a flat plate to a fluid flowing at a high velocity

NASA Technical Reports Server (NTRS)

Crocco, Luigi

1932-01-01

The writer, starting with the consideration of the hydrodynamic and thermodynamic equations for the turbulent boundary layer of a flat plate when it is necessary to take into account the heat produced by friction, arrives at the conclusion that the transmission of the heat follows the same law that is valid when the frictional heat is negligible, provided the temperature of the fluid is considered to be that which the fluid would reach if arrested adiabatically. It is then shown how the same law holds good for faired bodies, and some applications of the law are made to the problems of flight at very high speeds.

78 FR 75371 - Diffusion-Annealed, Nickel-Plated Flat-Rolled Steel Products From Japan; Scheduling of the Final...

Federal Register 2010, 2011, 2012, 2013, 2014

2013-12-11

...-Plated Flat-Rolled Steel Products From Japan; Scheduling of the Final Phase of an Antidumping... imports from Japan of diffusion-annealed, nickel- plated flat-rolled steel products, provided for... diffusion-annealed, nickel- plated flat-rolled steel products from Japan are being sold in the United States...

78 FR 23905 - Diffusion-Annealed, Nickel-Plated Flat-Rolled Steel Products From Japan: Initiation of...

Federal Register 2010, 2011, 2012, 2013, 2014

2013-04-23

...-Plated Flat-Rolled Steel Products From Japan: Initiation of Antidumping Duty Investigation AGENCY: Import... products from Japan (``certain nickel-plated, flat-rolled steel''), filed in proper form by Thomas Steel... Antidumping Duty Petition on Diffusion-Annealed, Nickel- Plated Steel Flat-Rolled Products from Japan, dated...

Measurements of store forces and moments and cavity pressures for a generic store in and near a box cavity at subsonic and transonic speeds

NASA Technical Reports Server (NTRS)

Stallings, Robert L., Jr.; Plentovich, E. B.; Tracy, M. B.; Hemsch, Michael J.

1995-01-01

An experimental force and moment study was conducted in the Langley 8-Foot Transonic Pressure Tunnel for a generic store in and near rectangular box cavities contained in a flat-plate configuration at subsonic and transonic speeds. Surface pressures were measured inside the cavities and on the flat plate. The length-to-height ratios were 5.42, 6.25, 10.83, and 12.50. The corresponding width-to-height ratios were 2.00, 2.00, 4.00, and 4.00. The free-stream Mach number range was from 0.20 to 0.95. Surface pressure measurements inside the cavities indicated that the flow fields for the shallow cavities were either closed or transitional near the transitional/closed boundary. For the deep cavities, the flow fields were either open or near the open/transitional boundary. The presence of the store did not change the type of flow field and had only small effects on the pressure distributions. For transitional or open transitional flow fields, increasing the free-stream Mach number resulted in large reductions in pitching-moment coefficient. Values of pitching-moment coefficient were always much greater for closed flow fields than for open flow fields.

Investigation of the Flow Structure on a Flat Plate Induced by Unsteady Plasma Actuation with DNS Methods

NASA Astrophysics Data System (ADS)

Yu, Jianyang; Chen, Fu; Liu, Huaping; Song, Yanping

2015-12-01

An investigation into the flow characteristic on a flat plate induced by an unsteady plasma was conducted with the methods of direct numerical simulations (DNS). A simplified model of dielectric barrier discharge (DBD) plasma was applied and its parameters were calibrated with the experimental results. In the simulations, effects of the actuation frequency on the flow were examined. The instantaneous flow parameters were also drawn to serve as a detailed study on the behavior when the plasma actuator was applied to the flow. The result shows that induced by the unsteady actuation, a series of vortex pairs which showed dipole formation and periodicity distribution were formed in the boundary layer. The production of these vortex pairs indicated a strong energy exchange between the main flow and the boundary layer. They moved downstream under the action of the free stream and decayed under the influence of the fluid viscosity. The distance of the neighboring vortices was found to be determined by the actuation frequency. Interaction of the neighboring vortices would be ignored when the actuation frequency was too small to make a difference. supported by the Foundation for Innovative Research Groups of National Natural Science Foundation of China (No. 51121004) and National Natural Science Foundation of China (No. 50976026)

Corrugated cover plate for flat plate collector

DOEpatents

Hollands, K. G. Terry; Sibbitt, Bruce

1978-01-01

A flat plate radiant energy collector is providing having a transparent cover. The cover has a V-corrugated shape which reduces the amount of energy reflected by the cover away from the flat plate absorber of the collector.

Local distribution of wall static pressure and heat transfer on a smooth flat plate impinged by a slot air jet

NASA Astrophysics Data System (ADS)

M, Adimurthy; Katti, Vadiraj V.

2017-02-01

Local distribution of wall static pressure and heat transfer on a smooth flat plate impinged by a normal slot air jet is experimental investigated. Present study focuses on the influence of jet-to-plate spacing ( Z/D h ) (0.5-10) and Reynolds number (2500-20,000) on the fluid flow and heat transfer distribution. A single slot jet with an aspect ratio ( l/b) of about 22 is chosen for the current study. Infrared Thermal Imaging technique is used to capture the temperature data on the target surface. Local heat transfer coefficients are estimated from the thermal images using `SMART VIEW' software. Wall static pressure measurement is carried out for the specified range of Re and Z/D h . Wall static pressure coefficients are seen to be independent of Re in the range between 5000 and 15,000 for a given Z/D h . Nu values are higher at the stagnation point for all Z/D h and Re investigated. For lower Z/D h and higher Re, secondary peaks are observed in the heat transfer distributions. This may be attributed to fluid translating from laminar to turbulent flow on the target plate. Heat transfer characteristics are explained based on the simplified flow assumptions and the pressure data obtained using Differential pressure transducer and static pressure probe. Semi-empirical correlation for the Nusselt number in the stagnation region is proposed.

Couette flow of an incompressible fluid in a porous channel with mass transfer

NASA Astrophysics Data System (ADS)

Niranjana, N.; Vidhya, M.; Govindarajan, A.

2018-04-01

The present discussion deals with the study of couette flow through a porous medium of a viscous incompressible fluid between two infinite horizontal parallel porous flat plates with heat and mass transfer. The stationary plate and the plate in uniform motion are subjected to transverse sinusoidal injection and uniform suction of the fluid. Due to this type of injection velocity, the flow becomes three dimensional. The analytical solutions of the nonlinear partial differential equations of this problem are obtained by using perturbation technique. Expressions for the velocity, temperature fields and the rate of heat and mass transfers are obtained. Effects of the following parameters Schmidt number (Sc), Modified Grashof number (Gm) on the velocity, temperature and concentration fields are obtained numerically and depicted through graphs. The rate of heat and mass transfer are also analyzed.

An Assessment of the Usefulness of Water Tunnels for Aerodynamic Investigations

DTIC Science & Technology

2012-12-01

a wide range of research projects, including the prediction of the performance of gas- turbine engines under conditions of pulsating flow, parametric...number-insensitive flows is water-tunnel testing of a thin rectangular flat plate having an aspect ratio of 2 – see Figure 4 from Kaplan , Altman & Ol... Kaplan , Altman & Ol, (2007). 7. Flow Over Circular-Type Bodies 7.1 Circular Cylinders The flow around a circular cylinder located at right angles

A numerical study of incompressible juncture flows

NASA Technical Reports Server (NTRS)

Kwak, D.; Rogers, S. E.; Kaul, U. K.; Chang, J. L. C.

1986-01-01

The laminar, steady juncture flow around single or multiple posts mounted between two flat plates is simulated using the three dimensional incompressible Navier-Stokes code, INS3D. The three dimensional separation of the boundary layer and subsequent formation and development of the horseshoe vortex is computed. The computed flow compares favorably with the experimental observation. The recent numerical study to understand and quantify the juncture flow relevant to the Space Shuttle main engine power head is summarized.

Analytical and experimental study of flow phenomena in noncavitating rocket pump inducers

NASA Technical Reports Server (NTRS)

Lakshminarayana, B.

1981-01-01

The flow processes in rocket pump inducers are summarized. The experimental investigations were carried out with air as the test medium. The major characteristics features of the rocket pump inducers are low flow coefficient (0.05 to 0.2) large stagger angle (70 deg to 85 deg) and high solidity blades of little or no camber. The investigations are concerned with the effect of viscosity not the effects of cavitation. Flow visualization, conventional and hot wire probe measurement inside and at the exit of the blade passage, were the analytical methods used. The experiment was carried out using four three and two bladed inducers with cambered blades. Both the passage and the exit flow were measured. The basic research and boundary layer investigation was carried out using a helical flat plate (of some dimensions as the inducer blades tested), and flat plate helical inducer (four bladed). Detailed mean and turbulence flow field inside the passage as well as the exit of the rotor were derived from these measurement. The boundary layer, endwall, and other passage data reveal extremely complex nature of the flow, with major effects of viscosity present across the entire passage. Several analyses were carried out to predict the flow field in inducers. These included an approximate analysis, the shear pumping analysis, and a numerical solution of exact viscous equations with approximate modeling for the viscous terms.

Turbulence Modeling Validation, Testing, and Development

NASA Technical Reports Server (NTRS)

Bardina, J. E.; Huang, P. G.; Coakley, T. J.

1997-01-01

The primary objective of this work is to provide accurate numerical solutions for selected flow fields and to compare and evaluate the performance of selected turbulence models with experimental results. Four popular turbulence models have been tested and validated against experimental data often turbulent flows. The models are: (1) the two-equation k-epsilon model of Wilcox, (2) the two-equation k-epsilon model of Launder and Sharma, (3) the two-equation k-omega/k-epsilon SST model of Menter, and (4) the one-equation model of Spalart and Allmaras. The flows investigated are five free shear flows consisting of a mixing layer, a round jet, a plane jet, a plane wake, and a compressible mixing layer; and five boundary layer flows consisting of an incompressible flat plate, a Mach 5 adiabatic flat plate, a separated boundary layer, an axisymmetric shock-wave/boundary layer interaction, and an RAE 2822 transonic airfoil. The experimental data for these flows are well established and have been extensively used in model developments. The results are shown in the following four sections: Part A describes the equations of motion and boundary conditions; Part B describes the model equations, constants, parameters, boundary conditions, and numerical implementation; and Parts C and D describe the experimental data and the performance of the models in the free-shear flows and the boundary layer flows, respectively.

Progress Towards a Cartesian Cut-Cell Method for Viscous Compressible Flow

NASA Technical Reports Server (NTRS)

Berger, Marsha; Aftosmis, Michael J.

2011-01-01

The proposed paper reports advances in developing a method for high Reynolds number compressible viscous flow simulations using a Cartesian cut-cell method with embedded boundaries. This preliminary work focuses on accuracy of the discretization near solid wall boundaries. A model problem is used to investigate the accuracy of various difference stencils for second derivatives and to guide development of the discretization of the viscous terms in the Navier-Stokes equations. Near walls, quadratic reconstruction in the wall-normal direction is used to mitigate mesh irregularity and yields smooth skin friction distributions along the body. Multigrid performance is demonstrated using second-order coarse grid operators combined with second-order restriction and prolongation operators. Preliminary verification and validation for the method is demonstrated using flat-plate and airfoil examples at compressible Mach numbers. Simulations of flow on laminar and turbulent flat plates show skin friction and velocity profiles compared with those from boundary-layer theory. Airfoil simulations are performed at laminar and turbulent Reynolds numbers with results compared to both other simulations and experimental data

A qualitative study of vortex trapping capability for lift enhancement on unconventional wing

NASA Astrophysics Data System (ADS)

Salleh, M. B.; Kamaruddin, N. M.; Mohamed-Kassim, Z.

2018-05-01

Lift enhancement by using passive vortex trapping technique offers great advantage in small aircraft design as it can improve aerodynamics performance and reduce weight of the wing. To achieve this aim, a qualitative study on the flow structures across wing models with cavities has been performed using smoke wire visualisation technique. An experiment has been conducted at low Reynolds number of 26,000 with angle of attack (α) = 0°, 5°, 10° and 15° to investigate the vortex trapping capability of semi-circular leading edge (SCLE) flat-plate wing model and elliptical leading edge (ELE) flat-plate wing model with cavities, respectively. Results from the qualitative study indicated unique characteristics in the flow structures between the tested wing models. The SCLE wing models were able to trap stable rotating vortices for α ≤ 10° whereas the ability of ELE wing models to suppress flow separation allowed stable clockwise vortices to be trapped inside the cavities even at α > 10°. The trapped vortices found to have the potential to increase lift on the unconventional wing models.

Measurements of forces, moments, and pressures on a generic store separating from a box cavity at supersonic speeds

NASA Technical Reports Server (NTRS)

Stallings, Robert L., Jr.; Wilcox, Floyd J., Jr.; Forrest, Dana K.

1991-01-01

An experimental investigation was conducted to measure the forces, moments, and pressure distributions on the generic store separating from a rectangular box cavity contained in a flat plate surface at supersonic speeds. Pressure distributions inside the cavity and oil flow and vapor-screen photographs of the cavity flow field were also obtained. The measurements were obtained for the store separating from a flat plate surface, from two shallow cavities having length to depth ratios (L/h) of 16.778 and 12.073, and from a deep cavity having L/h = 6.730. Measurements for the shallow cavities were obtained both with and without rectangular doors attached to sides of the cavities. The tests were conducted at free stream Mach numbers of 1.69, 2.00 and 2.65 for a free stream Reynolds number per foot of 2 x 10(exp 6). Presented here are a discussion of the results, a complete tabulation of the pressure data, figures of both the pressure and force and moment data, and representative oil flow and vapor screen photographs.

An experimental investigation of heat transfer to reusable surface insulation tile array gaps in a turbulent boundary layer with pressure gradient. M.S. Thesis

NASA Technical Reports Server (NTRS)

Throckmorton, D. A.

1975-01-01

An experimental investigation was performed to determine the effect of pressure gradient on the heat transfer to space shuttle reusable surface insulation (RSI) tile array gaps under thick, turbulent boundary layer conditions. Heat transfer and pressure measurements were obtained on a curved array of full-scale simulated RSI tiles in a tunnel wall boundary layer at a nominal freestream Mach number of 10.3 and freestream unit Reynolds numbers of 1.6, 3.3, and and 6.1 million per meter. Transverse pressure gradients were induced over the model surface by rotating the curved array with respect to the flow. Definition of the tunnel wall boundary layer flow was obtained by measurement of boundary layer pitot pressure profiles, and flat plate wall pressure and heat transfer. Flat plate wall heat transfer data were correlated and a method was derived for prediction of smooth, curved array heat transfer in the highly three-dimensional tunnel wall boundary layer flow and simulation of full-scale space shuttle vehicle pressure gradient levels was assessed.

Relaxation of an unsteady turbulent boundary layer on a flat plate in an expansion tube

NASA Technical Reports Server (NTRS)

Gurta, R. N.; Trimpi, R. L.

1974-01-01

An analysis is presented for the relaxation of a turbulent boundary layer on a semi-infinite flat plate after passage of a shock wave and a trailing driver gas-driven gas interface. The problem has special application to expansion-tube flows. The flow-governing equations have been transformed into the Crocco variables, and a time-similar solution is presented in terms of the dimensionless distance-time variable alpha and the dimensionless velocity variable beta. An eddy-viscosity model, similar to that of time-steady boundary layers, is applied to the inner and outer regions of the boundary layer. A turbulent Prandtl number equal to the molecular Prandtl number is used to relate the turbulent heat flux to the eddy viscosity. The numerical results, obtained by using the Gauss-Seidel line-relaxation method, indicate that a fully turbulent boundary layer relaxes faster to the final steady-state values of heat transfer and skin friction than a laminar boundary layer. The results also give a fairly good estimate of the local skin friction and heat transfer for near steady-flow conditions.

An experimental study of large-scale vortices over a blunt-faced flat plate in pulsating flow

NASA Astrophysics Data System (ADS)

Hwang, K. S.; Sung, H. J.; Hyun, J. M.

Laboratory measurements are made of flow over a blunt flat plate of finite thickness, which is placed in a pulsating free stream, U=Uo(1+Aocos 2πfpt). Low turbulence-intensity wind tunnel experiments are conducted in the ranges of Stp<=1.23 and Ao<=0.118 at ReH=560. Pulsation is generated by means of a woofer speaker. Variations of the time-mean reattachment length xR as functions of Stp and Ao are scrutinized by using the forward-time fraction and surface pressure distributions (Cp). The shedding frequency of large-scale vortices due to pulsation is measured. Flow visualizations depict the behavior of large-scale vortices. The results for non-pulsating flows (Ao=0) are consistent with the published data. In the lower range of Ao, as Stp increases, xR attains a minimum value at a particular pulsation frequency. For large Ao, the results show complicated behaviors of xR. For Stp>=0.80, changes in xR are insignificant as Ao increases. The shedding frequency of large-scale vortices is locked-in to the pulsation frequency. A vortex-pairing process takes place between two neighboring large-scale vortices in the separated shear layer.

Numerical Simulations of Flow Separation Control in Low-Pressure Turbines using Plasma Actuators

NASA Technical Reports Server (NTRS)

Suzen, Y. B.; Huang, P. G.; Ashpis, D. E.

2007-01-01

A recently introduced phenomenological model to simulate flow control applications using plasma actuators has been further developed and improved in order to expand its use to complicated actuator geometries. The new modeling approach eliminates the requirement of an empirical charge density distribution shape by using the embedded electrode as a source for the charge density. The resulting model is validated against a flat plate experiment with quiescent environment. The modeling approach incorporates the effect of the plasma actuators on the external flow into Navier Stokes computations as a body force vector which is obtained as a product of the net charge density and the electric field. The model solves the Maxwell equation to obtain the electric field due to the applied AC voltage at the electrodes and an additional equation for the charge density distribution representing the plasma density. The new modeling approach solves the charge density equation in the computational domain assuming the embedded electrode as a source therefore automatically generating a charge density distribution on the surface exposed to the flow similar to that observed in the experiments without explicitly specifying an empirical distribution. The model is validated against a flat plate experiment with quiescent environment.

Air-Induced Drag Reduction at High Reynolds Numbers: Velocity and Void Fraction Profiles

NASA Astrophysics Data System (ADS)

Elbing, Brian; Mäkiharju, Simo; Wiggins, Andrew; Dowling, David; Perlin, Marc; Ceccio, Steven

2010-11-01

The injection of air into a turbulent boundary layer forming over a flat plate can reduce the skin friction. With sufficient volumetric fluxes an air layer can separate the solid surface from the flowing liquid, which can produce drag reduction in excess of 80%. Several large scale experiments have been conducted at the US Navy's Large Cavitation Channel on a 12.9 m long flat plate model investigating bubble drag reduction (BDR), air layer drag reduction (ALDR) and the transition between BDR and ALDR. The most recent experiment acquired phase velocities and void fraction profiles at three downstream locations (3.6, 5.9 and 10.6 m downstream from the model leading edge) for a single flow speed (˜6.4 m/s). The profiles were acquired with a combination of electrode point probes, time-of-flight sensors, Pitot tubes and an LDV system. Additional diagnostics included skin-friction sensors and flow-field image visualization. During this experiment the inlet flow was perturbed with vortex generators immediately upstream of the injection location to assess the robustness of the air layer. From these, and prior measurements, computational models can be refined to help assess the viability of ALDR for full-scale ship applications.

Three-Dimensional Thermal Boundary Layer Corrections for Circular Heat Flux Gauges Mounted in a Flat Plate with a Surface Temperature Discontinuity

NASA Technical Reports Server (NTRS)

Kandula, M.; Haddad, G. F.; Chen, R.-H.

2006-01-01

Three-dimensional Navier-Stokes computational fluid dynamics (CFD) analysis has been performed in an effort to determine thermal boundary layer correction factors for circular convective heat flux gauges (such as Schmidt-Boelter and plug type)mounted flush in a flat plate subjected to a stepwise surface temperature discontinuity. Turbulent flow solutions with temperature-dependent properties are obtained for a free stream Reynolds number of 1E6, and freestream Mach numbers of 2 and 4. The effect of gauge diameter and the plate surface temperature have been investigated. The 3-D CFD results for the heat flux correction factors are compared to quasi-21) results deduced from constant property integral solutions and also 2-D CFD analysis with both constant and variable properties. The role of three-dimensionality and of property variations on the heat flux correction factors has been demonstrated.

Surface Microwave and Surface Transversal Pulsed-Periodic Discharges in Supersonic Flow

DTIC Science & Technology

2004-03-01

plasmas of different types of gas discharges near the surface of Aerodynamic models and in the boundary layers. Also, the contractor will develop modes...regions near the surface. The following experimental work will be done in supersonic air flow (Mɚ) at pressures between 1 and 200 Torr: a...198 CHAPTER IX NUMERICAL CALCULATION OF CHARACTERISTICS OF SUPERSONIC FLOW NEAR A FLAT PLATE WITH MICROWAVE DISCHARGE ON ITS SURFACE

Three-dimensional couette flow of dusty fluid with heat transfer in the presence of magnetic field

NASA Astrophysics Data System (ADS)

Gayathri, R.; Govindarajan, A.; Sasikala, R.

2018-04-01

This paper is focused on the mathematical modelling of three-dimensional couette flow and heat transfer of a dusty fluid between two infinite horizontal parallel porous flat plates in the presence of an induced magnetic field. The problem is formulated using a continuum two-phase model and the resulting equations are solved analytically. The lower plate is stationary while the upper plate is undergoing uniform motion in its plane. These plates are, respectively subjected to transverse exponential injection and its corresponding removal by constant suction. Due to this type of injection velocity, the flow becomes three dimensional. The closed-form expressions for velocity and temperature fields of both the fluid and dust phase are obtained by solving the governing partial differentiation equations using the perturbation method. A selective set of graphical results is presented and discussed to show interesting features of the problem. It is found that the velocity profiles of both fluid and dust particles decrease due to the increase of (magnetic parameter) Hartmann number.

Direct measurements of local bed shear stress in the presence of pressure gradients

NASA Astrophysics Data System (ADS)

Pujara, Nimish; Liu, Philip L.-F.

2014-07-01

This paper describes the development of a shear plate sensor capable of directly measuring the local mean bed shear stress in small-scale and large-scale laboratory flumes. The sensor is capable of measuring bed shear stress in the range 200 Pa with an accuracy up to 1 %. Its size, 43 mm in the flow direction, is designed to be small enough to give spatially local measurements, and its bandwidth, 75 Hz, is high enough to resolve time-varying forcing. Typically, shear plate sensors are restricted to use in zero pressure gradient flows because secondary forces on the edge of the shear plate caused by pressure gradients can introduce large errors. However, by analysis of the pressure distribution at the edges of the shear plate in mild pressure gradients, we introduce a new methodology for correcting for the pressure gradient force. The developed sensor includes pressure tappings to measure the pressure gradient in the flow, and the methodology for correction is applied to obtain accurate measurements of bed shear stress under solitary waves in a small-scale wave flume. The sensor is also validated by measurements in a turbulent flat plate boundary layer in open channel flow.

Reconfiguration of a flexible flat plate under snow loading

NASA Astrophysics Data System (ADS)

Gosselin, Frédérick; de Langre, Emmanuel

2015-11-01

Snow and wind constitute two of the main sources of mechanical loading on terrestrial plants. Plants bend and twist with large amplitude to bear these loads. For the past ten years, various authors have sought to decompose the problem of plant reconfiguration under fluid flow into its fundamental mechanical ingredients by studying the reconfiguration of simple flexible structures such as beams, plates, rods and strips. Here, we adopt a similar approach to these studies and consider the snow interception of a flexible flat plate. We performed two sets of experiments on thin flexible rectangular plates supported at their center: in the first one, a plate was subjected to real snowing events; in the second one, a plate was loaded with glass beads acting as a granular media similar to snow. Moreover, a theoretical model coupling the Elastica formulation to a loading with a set angle of repose is developed. The model is found to be in good agreement with the experiments on glass beads. Asymptotic scaling laws can be found similarly to the Vogel exponents of reconfiguring structures. For the real snow loading, it is found that the cohesive force in snow which is highly dependent on the snow temperature complicate things greatly.

Modulation of radial blood flow during Braille character discrimination task.

PubMed

Murata, Jun; Matsukawa, K; Komine, H; Tsuchimochi, H

2012-03-01

Human hands are excellent in performing sensory and motor function. We have hypothesized that blood flow of the hand is dynamically regulated by sympathetic outflow during concentrated finger perception. To identify this hypothesis, we measured radial blood flow (RBF), radial vascular conductance (RVC), heart rate (HR), and arterial blood pressure (AP) during Braille reading performed under the blind condition in nine healthy subjects. The subjects were instructed to read a flat plate with raised letters (Braille reading) for 30 s by the forefinger, and to touch a blank plate as control for the Braille discrimination procedure. HR and AP slightly increased during Braille reading but remained unchanged during the touching of the blank plate. RBF and RVC were reduced during the Braille character discrimination task (decreased by -46% and -49%, respectively). Furthermore, the changes in RBF and RVC were much greater during the Braille character discrimination task than during the touching of the blank plate (decreased by -20% and -20%, respectively). These results have suggested that the distribution of blood flow to the hand is modulated via sympathetic nerve activity during concentrated finger perception.

Numerical Investigation of an Oscillating Flat Plate Airfoil

NASA Astrophysics Data System (ADS)

Mohaghegh, Fazlolah; Janechek, Matthew; Buchholz, James; Udaykumar, Hs

2017-11-01

This research investigates the vortex dynamics of a plunging flat plate airfoil by analyzing the vorticity transport in 2D simulations. A horizontal airfoil is subject to a freestream flow at Re =10000. A prescribed vertical sinusoidal motion is applied to the airfoil. Smoothed Profile Method (SPM) models the fluid-structure interaction. SPM as a diffuse interface model considers a thickness for the interface and applies a smooth transition from solid to fluid. As the forces on the airfoil are highly affected by the interaction of the generated vortices from the surface, it is very important to find out whether a diffuse interface solver can model a flow dominated by vorticities. The results show that variation of lift coefficient with time agrees well with the experiment. Study of vortex evolution shows that similar to experiments, when the plate starts moving downward from top, the boundary layer is attached to the surface and the leading-edge vortex (LEV) is very small. By time, LEV grows and rolls up and a secondary vortex emerges. Meanwhile, the boundary layer starts to separate and finally LEV detaches from the surface. In overall, SPM as a diffuse interface model can predict the lift force and vortex pattern accurately.

Influence of nanofluids on the efficiency of Flat-Plate Solar Collectors (FPSC)

NASA Astrophysics Data System (ADS)

Nejad, Marjan B.; Mohammed, H. A.; Sadeghi, O.; Zubeer, Swar A.

2017-11-01

A numerical investigation is performed using finite volume method to study the laminar heat transfer in a three-dimensional flat-plate solar collector using different nanofluids as working fluids. Three nanofluids with different types of nanoparticles (Ag, MWCNT and Al2O3 dispersed in water) with 1-2 wt% volume fractions are analyzed. A constant heat flux, equivalent to solar radiation absorbed by the collector, is applied at the top surface of the absorber plate. In this study, several parameters including boundary conditions (different volume flow rates, different fluid inlet temperatures and different solar irradiance at Skudai, Malaysia), different types of nanoparticles, and different solar collector tilt angles are investigated to identify their effects on the heat transfer performance of FPSC. The numerical results reveal that the three types of nanofluid enhance the thermal performance of solar collector compared to pure water and FPSC with Ag nanofluid has the best thermal performance enhancement. For all the cases, the collector efficiency increased with the increase of volume flow rate while fluid outlet temperature decreased. It is found that FPSC with tilt angle of 10° and fluid inlet temperature of 301.15 K has the best thermal performance.

Planar Laser-Induced Iodine Fluorescence Measurements in Rarefied Hypersonic Flow

NASA Technical Reports Server (NTRS)

Cecil, Eric; McDaniel, James C.

2005-01-01

A planar laser-induced fluorescence (PLIF) technique is discussed and applied to measurement of time-averaged values of velocity and temperature in an I(sub 2)-seeded N(sub 2) hypersonic free jet facility. Using this technique, a low temperature, non-reacting, hypersonic flow over a simplified model of a reaction control system (RCS) was investigated. Data are presented of rarefied Mach 12 flow over a sharp leading edge flat plate at zero incidence, both with and without an interacting jet issuing from a nozzle built into the plate. The velocity profile in the boundary layer on the plate was resolved. The slip velocity along the plate, extrapolated from the velocity profile data, varied from nearly 100% down to 10% of the freestream value. These measurements are compared with results of a DSMC solution. The velocity variation along the centerline of a jet issuing from the plate was measured and found to match closely with the correlation of Ashkenas and Sherman. The velocity variation in the oblique shock terminating the jet was resolved sufficiently to measure the shock wave thickness.

Comments on Reynolds number effects in wall-bounded shear layers

NASA Technical Reports Server (NTRS)

Bandyopadhyay, Promode R.

1991-01-01

The effect of Reynolds number on the structure of turbulent boundary layers and channel flows is discussed. Published data are reexamined in light of the following questions: (1) does the boundary layer turbulence structure change after the well known Reynolds number limit viz, when Re(theta) is greater than 6000?; (2) is it possible to disturb a high Reynolds number flat plate turbulent boundary layer near the wall such that the recovery length is O(100 delta)?; and (3) how close is the numerically simulated low Reynolds number flat plate turbulence structure to that observed experimentally? The turbulence structure appears to change continuously with Reynolds number virtually throughout the bounday layer and sometimes in unexpected manners at high Reynolds numbers.

A direct numerical method for predicting concentration profiles in a turbulent boundary layer over a flat plate. M.S. Thesis

NASA Technical Reports Server (NTRS)

Dow, J. W.

1972-01-01

A numerical solution of the turbulent mass transport equation utilizing the concept of eddy diffusivity is presented as an efficient method of investigating turbulent mass transport in boundary layer type flows. A FORTRAN computer program is used to study the two-dimensional diffusion of ammonia, from a line source on the surface, into a turbulent boundary layer over a flat plate. The results of the numerical solution are compared with experimental data to verify the results of the solution. Several other solutions to diffusion problems are presented to illustrate the versatility of the computer program and to provide some insight into the problem of mass diffusion as a whole.

Source Term Model for Steady Micro Jets in a Navier-Stokes Computer Code

NASA Technical Reports Server (NTRS)

Waithe, Kenrick A.

2005-01-01

A source term model for steady micro jets was implemented into a non-proprietary Navier-Stokes computer code, OVERFLOW. The source term models the mass flow and momentum created by a steady blowing micro jet. The model is obtained by adding the momentum and mass flow created by the jet to the Navier-Stokes equations. The model was tested by comparing with data from numerical simulations of a single, steady micro jet on a flat plate in two and three dimensions. The source term model predicted the velocity distribution well compared to the two-dimensional plate using a steady mass flow boundary condition, which was used to simulate a steady micro jet. The model was also compared to two three-dimensional flat plate cases using a steady mass flow boundary condition to simulate a steady micro jet. The three-dimensional comparison included a case with a grid generated to capture the circular shape of the jet and a case without a grid generated for the micro jet. The case without the jet grid mimics the application of the source term. The source term model compared well with both of the three-dimensional cases. Comparisons of velocity distribution were made before and after the jet and Mach and vorticity contours were examined. The source term model allows a researcher to quickly investigate different locations of individual or several steady micro jets. The researcher is able to conduct a preliminary investigation with minimal grid generation and computational time.

Development of a high-performance boiling heat exchanger by improved liquid supply to narrow channels.

PubMed

Ohta, Haruhiko; Ohno, Toshiyuki; Hioki, Fumiaki; Shinmoto, Yasuhisa

2004-11-01

A two-phase flow loop is a promising method for application to thermal management systems for large-scale space platforms handling large amounts of energy. Boiling heat transfer reduces the size and weight of cold plates. The transportation of latent heat reduces the mass flow rate of working fluid and pump power. To develop compact heat exchangers for the removal of waste heat from electronic devices with high heat generation density, experiments on a method to increase the critical heat flux for a narrow heated channel between parallel heated and unheated plates were conducted. Fine grooves are machined on the heating surface in a transverse direction to the flow and liquid is supplied underneath flattened bubbles by the capillary pressure difference from auxiliary liquid channels separated by porous metal plates from the main heated channel. The critical heat flux values for the present heated channel structure are more than twice those for a flat surface at gap sizes 2 mm and 0.7 mm. The validity of the present structure with auxiliary liquid channels is confirmed by experiments in which the liquid supply to the grooves is interrupted. The increment in the critical heat flux compared to those for a flat surface takes a maximum value at a certain flow rate of liquid supply to the heated channel. The increment is expected to become larger when the length of the heated channel is increased and/or the gravity level is reduced.

The oblique impingement of an axisymmetric jet. [flow characteristics of jet flow over flat plates

NASA Technical Reports Server (NTRS)

Foss, J. F.; Kleis, S. J.

1976-01-01

The mechanics of the oblique impingement of an axisymmetric jet on a plane surface are examined in detail. The stagnation point is discussed. A schematic drawing of the problem and coordinate system used to describe the flow field are given. The kinematic features of the flow above the plate are examined in the context of the conservation of mass, the vorticity of the jet, and the vorticity introduced by the jetplate interaction. The dynamic features of the flow are examined in terms of the surface pressure distribution and the cause-effect relationships which exist between the pressure and velocity/vorticity distributions. Flow calculations performed are given. The investigation is relevant to the flow resulting from the interaction of the propulsion jet with the main airfoil (STOL aircraft), and is appropriate to an over- or under- wing configuration.

78 FR 31577 - Diffusion-Annealed, Nickel-Plated Flat-Rolled Steel Products From Japan

Federal Register 2010, 2011, 2012, 2013, 2014

2013-05-24

..., Nickel-Plated Flat-Rolled Steel Products From Japan Determination On the basis of the record \\1... imports from Japan of diffusion-annealed, nickel-plated flat-rolled steel products, provided for primarily... flat-rolled steel products from Japan. Accordingly, effective March 27, 2013, the Commission instituted...

Double diffusive magnetohydrodynamic (MHD) mixed convective slip flow along a radiating moving vertical flat plate with convective boundary condition.

PubMed

Rashidi, Mohammad M; Kavyani, Neda; Abelman, Shirley; Uddin, Mohammed J; Freidoonimehr, Navid

2014-01-01

In this study combined heat and mass transfer by mixed convective flow along a moving vertical flat plate with hydrodynamic slip and thermal convective boundary condition is investigated. Using similarity variables, the governing nonlinear partial differential equations are converted into a system of coupled nonlinear ordinary differential equations. The transformed equations are then solved using a semi-numerical/analytical method called the differential transform method and results are compared with numerical results. Close agreement is found between the present method and the numerical method. Effects of the controlling parameters, including convective heat transfer, magnetic field, buoyancy ratio, hydrodynamic slip, mixed convective, Prandtl number and Schmidt number are investigated on the dimensionless velocity, temperature and concentration profiles. In addition effects of different parameters on the skin friction factor, [Formula: see text], local Nusselt number, [Formula: see text], and local Sherwood number [Formula: see text] are shown and explained through tables.

An analysis of oscillatory hydromagnetic couette flow through a porous medium in a rotating system

NASA Astrophysics Data System (ADS)

Rajesh, K.; Govindarajan, A.; Vidhya, M.; Siva, E. P.

2018-04-01

Analysis of an exact solution of oscillatory Ekman boundary layer flow through a porous medium bounded by two horizontal flat plates is found. One of the plates is at rest and the other one is oscillating in its own plane. The whole of the system rotates about an axis normal to the plates. The effects of Coriolis force and the permeability of the porous medium on the flow field are studied. It is seen that even in the special case of resonance (w = 2Ω) the solution obtained by Mazumder is incorrect as contended by Ganapathy. It is found that the amplitude of the resultant velocity |A0| for the steady part increases with either an increase in the permeability parameter k0 (or) an increase in the rotation parameter R. But the above profiles have a reverse trend when there is an increase in the Hartmann number.

Simulation of the Transverse Injection of a Pulsed Jet from the Surface of a Flat Plate into a Supersonic Flow

NASA Astrophysics Data System (ADS)

Volkov, K. N.; Emelyanov, V. N.; Yakovchuk, M. S.

2017-11-01

The transverse injection of a pulsed jet into a supersonic flow for thrust vectoring in solid rocket motors is investigated. The gas flow through the injection nozzle is controlled by a piston which performs reciprocating motion. Reynolds-averaged Navier-Stokes equations and the ( k- ɛ) turbulence model equations are discretized using the finite volume method and moving grids. The pressure distributions on the plate surface obtained using various approaches to the description of the flow field and difference schemes are compared. The solution obtained for the case of injection of a pulsed jet is compared with the solution for the case where a valve prevents gas flow through the injection nozzle. The dependence of the control force produced by gas injection on time is investigated.

Fluid flow induced by periodic temperature oscillation over a flat plate: Comparisons with the classical Stokes problems

NASA Astrophysics Data System (ADS)

Pal, Debashis; Chakraborty, Suman

2015-05-01

We delineate the dynamics of temporally and spatially periodic flow over a flat plate originating out of periodic thermoviscous expansion of the fluid, as a consequence of a thermal wave applied on the plate wall. We identify two appropriate length scales, namely, the wavelength of the temperature wave and the thermal penetration depth, so as to bring out the complex thermo-physical interaction between the fluid and the solid boundaries. Our results reveal that the entire thermal fluctuation and the subsequent thermoviscous actuation remain confined within a "thermo-viscous boundary layer." Based on the length scales and the analytical solution for the temperature field, we demarcate three different layers, namely, the wall layer (which is further sub-divided into various sub-layers, based on the temperature field), the intermediate layer, and the outer layer. We show that the interactions between the pressure oscillation and temperature-dependent viscosity yield a unidirectional time-averaged (mean) flow within the wall layer opposite to the direction of motion of the thermal wave. We also obtain appropriate scalings for the time-averaged velocity, which we further substantiate by full scale numerical simulations. Our analysis may constitute a new design basis for simultaneous control of the net throughput and mixing over a solid boundary, by the judicious employment of a traveling temperature wave.

Effects of transverse oscillatory waves on turbulent boundary waves

NASA Technical Reports Server (NTRS)

Matulevich, Jonathan; Jacobs, Harold R.

1994-01-01

Studies of the interaction of unsteady (oscillatory) flows with the growth of a turbulent boundary layer on a flat plate have primarily dealt with an oscillatory component in the primary flow direction. Past studies of the 2-D flow have shown little or no increase in the time averaged heat transfer. The present paper deals with a steady axial and an oscillatory transverse flow. It is shown that for such flows the temporal variation for both the turbulent skin friction and heat transfer are such as to yield increased time averaged values.

The response of a laminar boundary layer in supersonic flow to small amplitude progressive waves

NASA Technical Reports Server (NTRS)

Duck, Peter W.

1989-01-01

The effect of a small amplitude progressive wave on the laminar boundary layer on a semi-infinite flat plate, due to a uniform supersonic freestream flow, is considered. The perturbation to the flow divides into two streamwise zones. In the first, relatively close to the leading edge of the plate, on a transverse scale comparable to the boundary layer thickness, the perturbation flow is described by a form of the unsteady linearized compressible boundary layer equations. In the freestream, this component of flow is governed by the wave equation, the solution of which provides the outer velocity conditions for the boundary layer. This system is solved numerically, and also the asymptotic structure in the far downstream limit is studied. This reveals a breakdown and a subsequent second streamwise zone, where the flow disturbance is predominantly inviscid. The two zones are shown to match in a proper asymptotic sense.

On the aeroacoustic tonal noise generation mechanism of a sharp-edged plate.

PubMed

Moreau, Danielle J; Brooks, Laura A; Doolan, Con J

2011-04-01

This letter presents an experimental study on the tonal noise generated by a sharp-edged flat plate at low-to-moderate Reynolds number. Flow and far-field noise data reveal that, in this particular case, the tonal noise appears to be governed by vortex shedding processes. Also related to the existence of the tonal noise is a region of separated flow slightly upstream of the trailing edge. Hydrodynamic fluctuations at selected vortex shedding frequencies are strongly amplified by the inflectional mean velocity profile in the separated shear layer. The amplified hydrodynamic fluctuations are diffracted by the trailing edge, producing strong tonal noise.

The effect of free-stream turbulence on heat transfer from a flat plate

NASA Technical Reports Server (NTRS)

Sugawara, Sugao; Sato, Takashi; Komatsu, Hiroyasu; Osaka, Hiroichi

1958-01-01

Turbulence was generated by using screens, and the turbulence percentage was measured by a hot-wire anemometer both in the boundary layer and the free stream. The local heat-transfer coefficient was measured at 12 locations along the plate for the cases of various turbulence levels. The transition Reynolds number from laminar to turbulent flow decreases as the main-stream turbulence level increases. In the range of laminar heat transfer the effect of turbulence in the main flow was not great, but in the range of turbulent heat transfer the heat-transfer coefficient increases according to the increase of turbulence.

Unified nonlinear approach to both weak and strong-interaction problems. [heat transfer in hypersonic flow

NASA Technical Reports Server (NTRS)

Gupta, R. N.; Rodkiewicz, C. M.

1975-01-01

The numerical results are obtained for heat transfer, skin-friction, and viscous interaction induced pressure for a step-wise accelerated flat plate in hypersonic flow. In the unified approach here the results are presented for both weak and strong-interaction problems without employing any linearization scheme. With the help of the numerical method used in this work an accurate prediction of wall shear can be made for the problems with plate velocity changes of 1% or larger. The obtained results indicate that the transient contribution to the induced pressure for helium is greater than that for air.

Structurally integrated steel solar collector

DOEpatents

Moore, Stanley W.

1977-03-08

Herein is disclosed a flat plate solar heat collector unit. The solar collector is integrated as a structural unit so that the collector also functions as the building roof. The functions of efficient heat collection, liquid coolant flow passages, roof structural support and building insulation are combined into one unit.

Dilatation-dissipation corrections for advanced turbulence models

NASA Technical Reports Server (NTRS)

Wilcox, David C.

1992-01-01

This paper analyzes dilatation-dissipation based compressibility corrections for advanced turbulence models. Numerical computations verify that the dilatation-dissipation corrections devised by Sarkar and Zeman greatly improve both the k-omega and k-epsilon model predicted effect of Mach number on spreading rate. However, computations with the k-gamma model also show that the Sarkar/Zeman terms cause an undesired reduction in skin friction for the compressible flat-plate boundary layer. A perturbation solution for the compressible wall layer shows that the Sarkar and Zeman terms reduce the effective von Karman constant in the law of the wall. This is the source of the inaccurate k-gamma model skin-friction predictions for the flat-plate boundary layer. The perturbation solution also shows that the k-epsilon model has an inherent flaw for compressible boundary layers that is not compensated for by the dilatation-dissipation corrections. A compressibility modification for k-gamma and k-epsilon models is proposed that is similar to those of Sarkar and Zeman. The new compressibility term permits accurate predictions for the compressible mixing layer, flat-plate boundary layer, and a shock separated flow with the same values for all closure coefficients.

Unsteady separated stagnation-point flow and heat transfer of a viscous fluid over a moving flat surface

NASA Astrophysics Data System (ADS)

Dholey, S.

2018-04-01

In this paper, we have investigated numerically the laminar unsteady separated stagnation-point flow and heat transfer of a viscous fluid over a moving flat surface in the presence of a time dependent free stream velocity which causes the unsteadiness of this flow problem. The plate is assumed to move in the same or opposite direction of the free stream velocity. The flow is therefore governed by the velocity ratio parameter λ (ratio of the plate velocity to the free stream velocity) and the unsteadiness parameter β. When the plate surface moves in the same direction of the free stream velocity (i.e., when λ > 0), the solution of this flow problem continues for any given value of β. On the other hand, when they move in opposite directions (i.e., when λ < 0), the solution does not exist after a certain value of λ depending upon the values of β. In this case, separation appears inside the layer only for a negative value of β, and for a positive value of β, the boundary layer solution is terminated after a certain distance from the plate surface with an attached flow solution with no point of inflection. The concerning issue of the steady flow (β = 0) case has also been considered and two types of attached flow solutions have been found—one with a point of inflection and the other with no point of inflection, in a definite range of λ (-1.246 58 ≤ λ ≤ -1.07). However, this range decreases with an increase in |β| when β < 0. A novel result which arises from the heat transfer analysis is that for a given value of λ(= 0), first the heat transfer rate increases with the increase of the Prandtl number Pr and after attaining a maximum value, it decreases and finally tends to be zero for large values of Pr depending upon the values of β > 0. On the contrary, for a given value of β(≤ 0), the rate of heat transfer increases consistently with the increase of Pr.

Effect of thermal radiation on laminar boundary layer flow over a permeable flat plate with Newtonian heating

NASA Astrophysics Data System (ADS)

Khairul Anuar Mohamed, Muhammad; Zuki Salleh, Mohd; Noar, Nor Aida Zuraimi Md; Ishak, Anuar

2017-09-01

The laminar boundary layer flow over a permeable flat plat with the presence of thermal radiation and Newtonian heating is numerically studied. The non linear partial differential equations that governed the model are transformed to ordinary differential equations before being solved numerically by Runge-Kutta-Fehlberg (RKF) method using Maple software. The influenced and characteristic of pertinent parameters which are the Prandtl number, the suction/blowing parameter, the thermal radiation parameter and the conjugate parameter are analyzed and discussed. It is found that the presence of thermal radiation and blowing parameter has increased the value of wall temperature. Meanwhile, the trend is contrary with the suction effect.

Heat transfer in porous medium embedded with vertical plate: Non-equilibrium approach - Part A

DOE Office of Scientific and Technical Information (OSTI.GOV)

Badruddin, Irfan Anjum; Quadir, G. A.

2016-06-08

Heat transfer in a porous medium embedded with vertical flat plate is investigated by using thermal non-equilibrium model. Darcy model is employed to simulate the flow inside porous medium. It is assumed that the heat transfer takes place by natural convection and radiation. The vertical plate is maintained at isothermal temperature. The governing partial differential equations are converted into non-dimensional form and solved numerically using finite element method. Results are presented in terms of isotherms and streamlines for various parameters such as heat transfer coefficient parameter, thermal conductivity ratio, and radiation parameter.

Skin-friction gauge for use in hypervelocity impulse facilities

NASA Technical Reports Server (NTRS)

Kelly, G. M.; Simmons, J. M.; Paull, A.

1992-01-01

A transducer is presented which can measure as rise-time of about 20 microsec, and is thereby applicable to measurements in the high-enthalpy flows associated with hypervelocity impulse facilities. Results are presented which demonstrate the effectiveness of the concept in the case of skin-friction measurements conducted on a flat plate at Mach 3.2. The calibration used was against theoretical skin-friction values in a simple flow.

Flow Phenomena in the Very Near Wake of a Flat Plate with a Circular Trailing Edge

NASA Technical Reports Server (NTRS)

Rai, Man Mohan

2014-01-01

The very near wake of a flat plate with a circular trailing edge, exhibiting pronounced shedding of wake vortices, is investigated with data from a direct numerical simulation. The separating boundary layers are turbulent and statistically identical thus resulting in a wake that is symmetric in the mean. The focus here is on the instability of the detached shear layers, the evolution of rib-vortex induced localized regions of reverse flow that detach from the main body of reverse flow in the trailing edge region and convect downstream, and phaseaveraged velocity statistics in the very near wake. The detached shear layers are found to exhibit unstable behavior intermittently, including the development of shear layer vortices as in earlier cylinder flow investigations with laminar separating boundary layers. Only a small fraction of the separated turbulent boundary layers undergo this instability, and form the initial shed vortices. Pressure spectra within the shear layers show a broadband peak at a multiple of shedding frequency. Phase-averaged intensity and shear stress distributions of the randomly fluctuating component of velocity are compared with those obtained in the near wake. The distributions of the production terms in the transport equations for the turbulent stresses are also provided.

Calculating forces on thin flat plates with incomplete vorticity-field data

NASA Astrophysics Data System (ADS)

Limacher, Eric; Morton, Chris; Wood, David

2016-11-01

Optical experimental techniques such as particle image velocimetry (PIV) permit detailed quantification of velocities in the wakes of bluff bodies. Patterns in the wake development are significant to force generation, but it is not trivial to quantitatively relate changes in the wake to changes in measured forces. Key difficulties in this regard include: (i) accurate quantification of velocities close to the body, and (ii) the effect of missing velocity or vorticity data in regions where optical access is obscured. In the present work, we consider force formulations based on the vorticity field, wherein mathematical manipulation eliminates the need for accurate near-body velocity information. Attention is restricted to nominally two dimensional problems, namely (i) a linearly accelerating flat plate, investigated using PIV in a water tunnel, and (ii) a pitching plate in a freestream flow, as investigated numerically by Wang & Eldredge (2013). The effect of missing vorticity data on the pressure side of the plate has a significant impact on the calculation of force for the pitching plate test case. Fortunately, if the vorticity on the pressure side remains confined to a thin boundary layer, simple corrections can be applied to recover a force estimate.

Generalized wall function and its application to compressible turbulent boundary layer over a flat plate

NASA Astrophysics Data System (ADS)

Liu, J.; Wu, S. P.

2017-04-01

Wall function boundary conditions including the effects of compressibility and heat transfer are improved for compressible turbulent boundary flows. Generalized wall function formulation at zero-pressure gradient is proposed based on coupled velocity and temperature profiles in the entire near-wall region. The parameters in the generalized wall function are well revised. The proposed boundary conditions are integrated into Navier-Stokes computational fluid dynamics code that includes the shear stress transport turbulence model. Numerical results are presented for a compressible boundary layer over a flat plate at zero-pressure gradient. Compared with experimental data, the computational results show that the generalized wall function reduces the first grid spacing in the directed normal to the wall and proves the feasibility and effectivity of the generalized wall function method.

Skin friction reduction in supersonic flow by injection through slots, porous sections and combinations of the two

NASA Technical Reports Server (NTRS)

Schetz, J. A.; Vanovereem, J.

1975-01-01

An experimental study of skin friction reduction in a Mach 3.0 air steam with gaseous injection through a tangential slot, a porous wall section, and combinations of the two was conducted. The primary data obtained were wall shear values measured directly with a floating element balance and also inferred from Preston Tube measurements. Detailed profiles at several axial stations, wall pressure distributions and schlieren photographs are presented. The data indicate that a slot provides the greatest skin friction reduction in comparison with a reference flat plate experiment. The porous wall section arrangement suffers from an apparent roughness-induced rise in skin friction at low injection rates compared to the flat plate. The combination schemes demonstrated a potential for gain.

ON THE MODIFICATION OF THE LOW FLOW-RATE PM10 DICHOTOMOUS SAMPLER INLET

EPA Science Inventory

A popular flat-topped inlet used for the collection of atmospheric particulate matter was modified to reduce water intrusion during rain and snow events. Simple alterations in the intake region of this inlet were made, including a larger drain hole, a one piece top plate, and ...

An Idealized Direct-Contact Biomass Pyrolysis Reactor Model

NASA Technical Reports Server (NTRS)

Miller, R. S.; Bellan, J.

1996-01-01

A numerical study is performed in order to assess the performance of biomass pyrolysis reactors which utilize direct particle-wall thermal conduction heating. An idealized reactor configuration consisting of a flat-plate turbulent boundary layer flow with particle convection along the heated wall and incorporating particle re-entrainment is considered.

Prediction of an internal boundary layer on a flat plate after a step change in roughness using a near-wall RANS model

NASA Astrophysics Data System (ADS)

Chu, Minghan; Meng, Fanxiao; Bergstrom, Donald J.

2017-11-01

An in-house computational fluid dynamics code was used to simulate turbulent flow over a flat plate with a step change in roughness, exhibiting a smooth-rough-smooth configuration. An internal boundary layer (IBL) is formed at the transition from the smooth to rough (SR) and then the rough to smooth (RS) surfaces. For an IBL the flow far above the surface has experienced a wall shear stress that is different from the local value. Within a Reynolds-Averaged-Navier-Stokes (RANS) formulation, the two-layer k- ɛ model of Durbin et al. (2001) was implemented to analyze the response of the flow to the change in surface condition. The numerical results are compared to experimental data, including some in-house measurements and the seminal work of Antonia and Luxton (1971,72). This problem captures some aspects of roughness in industrial and environmental applications, such as corrosion and the earth's surface heterogeneity, where the roughness is often encountered as discrete distributions. It illustrates the challenge of incorporating roughness models in RANS that are capable of responding to complex surface roughness profiles.

Drag Measurements over Embedded Cavities in a Low Reynolds Number Couette Flow

NASA Astrophysics Data System (ADS)

Gilmer, Caleb; Lang, Amy; Jones, Robert

2010-11-01

Recent research has revealed that thin-walled, embedded cavities in low Reynolds number flow have the potential to reduce the net viscous drag force acting on the surface. This reduction is due to the formation of embedded vortices allowing the outer flow to pass over the surface via a roller bearing effect. It is also hypothesized that the scales found on butterfly wings may act in a similar manner to cause a net increase in flying efficiency. In this experimental study, rectangular embedded cavities were designed as a means of successfully reducing the net drag across surfaces in a low Reynolds number flow. A Couette flow was generated via a rotating conveyor belt immersed in a tank of high viscosity mineral oil above which the plates with embedded cavities were placed. Drag induced on the plate models was measured using a force gauge and compared directly to measurements acquired over a flat plate. Various cavity aspect ratios and gap heights were tested in order to determine the conditions under which the greatest drag reductions occurred.

Process For Controlling Flow Rate Of Viscous Materials Including Use Of Nozzle With Changeable Openings

DOEpatents

Ellingson, William A.; Forster, George A.

1999-11-02

Apparatus and a method for controlling the flow rate of viscous materials through a nozzle includes an apertured main body and an apertured end cap coupled together and having an elongated, linear flow channel extending the length thereof. An end of the main body is disposed within the end cap and includes a plurality of elongated slots concentrically disposed about and aligned with the flow channel. A generally flat cam plate having a center aperture is disposed between the main body and end cap and is rotatable about the flow channel. A plurality of flow control vane assemblies are concentrically disposed about the flow channel and are coupled to the cam plate. Each vane assembly includes a vane element disposed adjacent the end of the flow channel. Rotation of the cam plate in a first direction causes a corresponding rotation of each of the vane elements for positioning the individual vane elements over the aperture in the end cap blocking flow through the flow channel, while rotation in an opposite direction removes the vane elements from the aperture and positions them about the flow channel in a nested configuration in the full open position, with a continuous range of vane element positions available between the full open and closed positions.

Finite element analysis of periodic transonic flow problems

NASA Technical Reports Server (NTRS)

Fix, G. J.

1978-01-01

Flow about an oscillating thin airfoil in a transonic stream was considered. It was assumed that the flow field can be decomposed into a mean flow plus a periodic perturbation. On the surface of the airfoil the usual Neumman conditions are imposed. Two computer programs were written, both using linear basis functions over triangles for the finite element space. The first program uses a banded Gaussian elimination solver to solve the matrix problem, while the second uses an iterative technique, namely SOR. The only results obtained are for an oscillating flat plate.

A numerical study of the 2- and 3-dimensional unsteady Navier-Stokes equations in velocity-vorticity variables using compact difference schemes

NASA Technical Reports Server (NTRS)

Gatski, T. B.; Grosch, C. E.

1984-01-01

A compact finite-difference approximation to the unsteady Navier-Stokes equations in velocity-vorticity variables is used to numerically simulate a number of flows. These include two-dimensional laminar flow of a vortex evolving over a flat plate with an embedded cavity, the unsteady flow over an elliptic cylinder, and aspects of the transient dynamics of the flow over a rearward facing step. The methodology required to extend the two-dimensional formulation to three-dimensions is presented.

Long Hole Film Cooling Dataset for CFD Development - Flow and Film Effectiveness

NASA Technical Reports Server (NTRS)

Shyam, Vikram; Poinsatte, Phillip; Thurman, Douglas; Ameri, Ali

2014-01-01

An experiment investigating flow and heat transfer of long (length to diameter ratio of 18) cylindrical film cooling holes has been completed. In this paper, the thermal field in the flow and on the surface of the film cooled flat plate is presented for nominal freestream turbulence intensities of 1.5 and 8 percent. The holes are inclined at 30 deg above the downstream direction, injecting chilled air of density ratio 1.0 onto the surface of a flat plate. The diameter of the hole is 0.75 in. (approx. 0.02 m) with center to center spacing (pitch) of 3 hole diameters. Coolant was injected into the mainstream flow at nominal blowing ratios of 0.5, 1.0, 1.5, and 2.0. The Reynolds number of the freestream was approximately 11,000 based on hole diameter. Thermocouple surveys were used to characterize the thermal field. Infrared thermography was used to determine the adiabatic film effectiveness on the plate. Hotwire anemometry was used to provide flowfield physics and turbulence measurements. The results are compared to existing data in the literature. The aim of this work is to produce a benchmark dataset for Computational Fluid Dynamics (CFD) development to eliminate the effects of hole length to diameter ratio and to improve resolution in the near-hole region. In this report, a Time Filtered Navier Stokes (TFNS), also known as Partially Resolved Navier Stokes (PRNS), method that was implemented in the Glenn-HT code is used to model coolant-mainstream interaction. This method is a high fidelity unsteady method that aims to represent large scale flow features and mixing more accurately.

Fluorescence Visualization of Hypersonic Flow Past Triangular and Rectangular Boundary-layer Trips

NASA Technical Reports Server (NTRS)

Danehy, Paul M.; Garcia, A. P.; Borg, Stephen E.; Dyakonov, Artem A.; Berry, Scott A.; Inman, Jennifer A.; Alderfer, David W.

2007-01-01

Planar laser-induced fluorescence (PLIF) flow visualization has been used to investigate the hypersonic flow of air over surface protrusions that are sized to force laminar-to-turbulent boundary layer transition. These trips were selected to simulate protruding Space Shuttle Orbiter heat shield gap-filler material. Experiments were performed in the NASA Langley Research Center 31-Inch Mach 10 Air Wind Tunnel, which is an electrically-heated, blowdown facility. Two-mm high by 8-mm wide triangular and rectangular trips were attached to a flat plate and were oriented at an angle of 45 degrees with respect to the oncoming flow. Upstream of these trips, nitric oxide (NO) was seeded into the boundary layer. PLIF visualization of this NO allowed observation of both laminar and turbulent boundary layer flow downstream of the trips for varying flow conditions as the flat plate angle of attack was varied. By varying the angle of attack, the Mach number above the boundary layer was varied between 4.2 and 9.8, according to analytical oblique-shock calculations. Computational Fluid Dynamics (CFD) simulations of the flowfield with a laminar boundary layer were also performed to better understand the flow environment. The PLIF images of the tripped boundary layer flow were compared to a case with no trip for which the flow remained laminar over the entire angle-of-attack range studied. Qualitative agreement is found between the present observed transition measurements and a previous experimental roughness-induced transition database determined by other means, which is used by the shuttle return-to-flight program.

Numerical study focusing on the entropy analysis of MHD squeezing flow of a nanofluid model using Cattaneo–Christov theory

NASA Astrophysics Data System (ADS)

Akmal, N.; Sagheer, M.; Hussain, S.

2018-05-01

The present study gives an account of the heat transfer characteristics of the squeezing flow of a nanofluid between two flat plates with upper plate moving vertically and the lower in the horizontal direction. Tiwari and Das nanofluid model has been utilized to give a comparative analysis of the heat transfer in the Cu-water and Al2O3-water nanofluids with entropy generation. The modeling is carried out with the consideration of Lorentz forces to observe the effect of magnetic field on the flow. The Joule heating effect is included to discuss the heat dissipation in the fluid and its effect on the entropy of the system. The nondimensional ordinary differential equations are solved using the Keller box method to assess the numerical results which are presented by the graphs and tables. An interesting observation is that the entropy is generated more near the lower plate as compared with that at the upper plate. Also, the heat transfer rate is found to be higher for the Cu nanoparticles in comparison with the Al2O3 nanoparticles.

When Boundary Layers Collide: Plumes v. Subduction Zones

NASA Astrophysics Data System (ADS)

Moresi, L. N.; Betts, P. G.; Miller, M. S.; Willis, D.; O'Driscoll, L.

2014-12-01

Many subduction zones retreat while hotspots remain sufficiently stable in the mantle to provide an approximate reference frame. As a consequence, the mantle can be thought of as an unusual convecting system which self-organises to promote frequent collisions of downgoing material with upwellings. We present three 3D numerical models of subduction where buoyant material from a plume head and an associated ocean-island chain or plateau produce flat slab subduction and deformation of the over-riding plate. We observe transient instabilities of the convergent margin including: contorted trench geometry; trench migration parallel with the plate margin; folding of the subducting slab and orocline development at the convergent margin; and transfer of the plateau to the overriding plate. The presence of plume material beneath the oceanic plateau causes flat subduction above the plume, resulting in a "bowed" shaped subducting slab. In the absence of a plateau at the surface, the slab can remain uncoupled from the over-riding plate during very shallow subduction and hence there is very little shortening at the surface or advance of the plate boundary. In plateau-only models, plateau accretion at the edge of the overriding plate results in trench migration around the edge of the plateau before subduction re-establishes directly behind the trailing edge of the plateau. The plateau shortens during accretion and some plateau material subducts. In a plateau-plus-plume model, accretion is associated with rapid trench advance as the flat slab drives the plateau into the margin. This indentation stops once a new convergent boundary forms close to the original trench location. A slab window formed beneath the accreted plateau allows plume material to flow from beneath the subducting plate to the underside of the overriding plate. In all of these models the subduction zone maintains a relatively stable configuration away from the buoyancy anomalies within the downgoing plate. The models provide a dynamic context for plateau and plume accretion in accretionary orogenic systems.

Detached Eddy Simulation of Film Cooling over a GE Flat Plate

NASA Technical Reports Server (NTRS)

Roy, Subrata

2005-01-01

The detached eddy simulation of film cooling has been utilized for a proprietary GE plate-pipe configuration. The blowing ratio was 2.02, the velocity ratio was 1.26, and the temperature ratio was 1.61. Results indicate that the mixing processes downstream of the hole are highly anisotropic. DES solution shows its ability to depict the dynamic nature of the flow and capture the asymmetry present in temperature and velocity distributions. Further, comparison between experimental and DES time-averaged effectiveness is satisfactory. Numerical values of span-averaged effectiveness show better prediction of the experimental values at downstream locations than a steady state Glenn HT solution. While the DES method shows obvious promise, there are several issues that need further investigation. Despite an accurate prediction in the hole vicinity, the simulation still falls short in the region x = 10d to 100d. This should be investigated. Also the model used flat plate. Actual turbine blade should be modeled in the future if additional finding is available.

Effects of the inclination angle on the performance of flat plate solar collector

NASA Astrophysics Data System (ADS)

Ambarita, H.; Siregar, R. E. T.; Ronowikarto, A. D.; Setyawan, E. Y.

2018-03-01

Double glasses cover is typically used in a flat plate solar collector to decrease heat losses to ambient. The working principal of the cover is to allow the solar irradiation hit the plate absorber and blocks it using natural convection mechanism in the enclosure between the glasses. The performance of the enclosure to block the heat loss to the surrounding affected by the inclination angle of the collector. The objective of this study is to explore the effect of the inclination angle to the performance of the solar collector. Numerical simulation using commercial code Computational Fluid Dynamic (CFD) has been carried out to explore the fluid flow and heat transfer characteristics in the enclosure. In the result, streamline, vector velocity, and contour temperature are plotted. It was shown that the inclination angle strongly affects the performance of the collector. The average heat transfer coefficient decreases with increasing inclination angle. This fact suggests that too high inclination angle is not recommended for solar collector.

Relaxation of the accelerating-gas boundary layer to the test-gas boundary layer on a flat plate in an expansion tube

NASA Technical Reports Server (NTRS)

Gupta, R. N.; Trimpi, R. L.

1973-01-01

An analytic investigation of the relaxation of the accelerating-gas boundary layer to the test-gas boundary layer over a flat plate mounted in an expansion tube has been conducted. In this treatment, nitrogen has been considered as the test gas and helium as the accelerating gas. The problem is analyzed in two conically similar limits: (1) when the time lag between the arrival of the shock and the interface at the leading edge of the plate is very large, and (2) when this time lag is negligible. The transient laminar boundary-layer equations of a perfect binary-gas mixture are taken as the flow governing equations. These coupled equations have been solved numerically by Gauss-Seidel line-relaxation method. The results predict the transient behavior as well as the time required for an all-helium accelerating-gas boundary layer to relax to an all-nitrogen boundary layer.

Heat Transfer on a Flat Plate with Uniform and Step Temperature Distributions

NASA Technical Reports Server (NTRS)

Bahrami, Parviz A.

2005-01-01

Heat transfer associated with turbulent flow on a step-heated or cooled section of a flat plate at zero angle of attack with an insulated starting section was computationally modeled using the GASP Navier-Stokes code. The algebraic eddy viscosity model of Baldwin-Lomax and the turbulent two-equation models, the K- model and the Shear Stress Turbulent model (SST), were employed. The variations from uniformity of the imposed experimental temperature profile were incorporated in the computations. The computations yielded satisfactory agreement with the experimental results for all three models. The Baldwin- Lomax model showed the closest agreement in heat transfer, whereas the SST model was higher and the K-omega model was yet higher than the experiments. In addition to the step temperature distribution case, computations were also carried out for a uniformly heated or cooled plate. The SST model showed the closest agreement with the Von Karman analogy, whereas the K-omega model was higher and the Baldwin-Lomax was lower.

Evaluation of finger plate and flat plate connection design.

DOT National Transportation Integrated Search

2016-01-01

This project investigates the cause(s) of premature deterioration of MoDOT finger plate and flat plate expansion devices : under high traffic volumes and then uses that information to design new Load and Resistance Factor Design (LRFD) : finger plate...

Effect of diffuser vane shape on the performance of a centrifugal compressor stage

NASA Astrophysics Data System (ADS)

Reddy, T. Ch Siva; Ramana Murty, G. V.; Prasad, M. V. S. S. S. M.

2014-04-01

The present paper reports the results of experimental investigations on the effect of diffuser vane shape on the performance of a centrifugal compressor stage. These studies were conducted on the chosen stage having a backward curved impeller of 500 mm tip diameter and 24.5 mm width and its design flow coefficient is ϕd=0.0535. Three different low solidity diffuser vane shapes namely uncambered aerofoil, constant thickness flat plate and circular arc cambered constant thickness plate were chosen as the variants for diffuser vane shape and all the three shapes have the same thickness to chord ratio (t/c=0.1). Flow coefficient, polytropic efficiency, total head coefficient, power coefficient and static pressure recovery coefficient were chosen as the parameters for evaluating the effect of diffuser vane shape on the stage performance. The results show that there is reasonable improvement in stage efficiency and total head coefficient with the use of the chosen diffuser vane shapes as compared to conventional vaneless diffuser. It is also noticed that the aero foil shaped LSD has shown better performance when compared to flat plate and circular arc profiles. The aerofoil vane shape of the diffuser blade is seen to be tolerant over a considerable range of incidence.

Strong coupling strategy for fluid-structure interaction problems in supersonic regime via fixed point iteration

NASA Astrophysics Data System (ADS)

Storti, Mario A.; Nigro, Norberto M.; Paz, Rodrigo R.; Dalcín, Lisandro D.

2009-03-01

In this paper some results on the convergence of the Gauss-Seidel iteration when solving fluid/structure interaction problems with strong coupling via fixed point iteration are presented. The flow-induced vibration of a flat plate aligned with the flow direction at supersonic Mach number is studied. The precision of different predictor schemes and the influence of the partitioned strong coupling on stability is discussed.

Pressure and thermal distributions on wings and adjacent surfaces induced by elevon deflections at Mach 6

NASA Technical Reports Server (NTRS)

Kaufman, L. G., II; Johnson, C. B.

1979-01-01

Surface pressure distributions and heat transfer distributions were obtained on wing half-models in regions where three dimensional separated flow effects are prominent. Unswept and 50 deg and 70 deg swept semispan wings were tested, for trailing-edge-elevon ramp angles of 0 deg, 10 deg, 20 deg, and 30 deg, with and without cylindrical and flat plate center bodies and with and without various wing-tip plates and fins. The data, obtained for a free stream Mach number of 6 and a wing-root-chord Reynolds number of 18.5 million, reveal considerably larger regions of increased pressure and thermal loads than would be anticipated using non-separated flow analyses.

Applicability of the independence principle to subsonic turbulent flow over a swept rearward-facing step

NASA Technical Reports Server (NTRS)

Selby, G. V.

1983-01-01

Prandtl (1946) has concluded that for yawed laminar incompressible flows the streamwise flow is independent of the spanwise flow. However, Ashkenas and Riddell (1955) have reported that for turbulent flow the 'independence principle' does not apply to yawed flat plates. On the other hand, it was also found that this principle may be applicable to many turbulent flows. As the sweep angle is increased, a sweep angle is reached which defines the interval over which the 'independence principle' is valid. The results obtained in the present investigation indicate the magnitude of the critical angle for subsonic turbulent flow over a swept rearward-facing step.

Use of a rotating cylinder to induce laminar and turbulent separation over a flat plate

NASA Astrophysics Data System (ADS)

Afroz, F.; Lang, A.; Jones, E.

2017-06-01

An innovative and easy technique using a rotating cylinder system has been implemented in a water tunnel experiment to generate an adverse pressure gradient (APG). The strength of the APG was varied through adjustment in the rotation speed and location of the cylinder. Then the technique was used for inducing a laminar separation bubble (LSB) and turbulent boundary layer (TBL) separation over a flat plate. A theoretical model to predict the pressure variation induced on the plate consists of an inviscid flow over a reverse doublet-like configuration of two counter rotating cylinders. This model quantified the pressure distribution with changes of cylinder speed and location. The dimensionless velocity ratio (VR) of the cylinder rotation rate to the mainstream velocity and gap to diameter ratio \\tfrac{G}{D} were chosen as the two main ways of varying the strength of the APG, which affects the nature and extent of the LSB as well as TBL separation. The experimental parametric study, using time-resolved digital particle image velocimetry, was then conducted in a water tunnel. The variation in height (h), length (l), and the separation point (S) of the LSB was documented due to the variation in the APG. The similar type of experimental parametric study was used to explore the unsteady, turbulent separation bubble in a 2D plane aligned with the flow and perpendicular to the plate. The mean detachment locations of TBL separation are determined by two different definitions: (i) back-flow coefficient (χ) = 50%, and (ii) location of start of negative mean skin friction coefficient (C f). They are in good agreement and separation bubble characteristics agreed well with results obtained using different methods thus proving the validity of the technique.

Flowfield measurements in a separated and reattached flat plate turbulent boundary layer

NASA Technical Reports Server (NTRS)

Patrick, William P.

1987-01-01

The separation and reattachment of a large-scale, two-dimensional turbulent boundary layer at low subsonic speed on a flat plate has been studied experimentally. The separation bubble was 55 cm long and had a maximum bubble thickness, measured to the height of the mean dividing streamline, of 17 cm, which was twice the thickness of the inlet boundary layer. A combination of laser velocimetry, hot-wire anemometry, pneumatic probing techniques, and flow visualization were used as diagnostics. Principal findings were that an outer inviscid rotational flow was defined which essentially convected over the blockage associated with the inner, viscously dominated bubble recirculation region. A strong backflow region in which the flow moved upstream 100 percent of the time was measured near the test surface over the central 35 percent of the bubble. A laminar backflow boundary layer having pseudo-turbulent characteristics including a log-linear velocity profile was generated under the highly turbulent backflow. Velocity profile shapes in the reversed flow region matched a previously developed universal backflow profile at the upstream edge of the separation region but not in the steady backflow region downstream. A smoke flow visualization movie and hot-film measurements revealed low frequency nonperiodic flapping at reattachment. However, forward flow fraction data at reattachment and mean velocity profiles in the redeveloping boundary layer downstream of reattachment correlated with backward-facing step data when the axial dimension was scaled by the distance from the maximum bubble thickness to reattachment.

Experimental Study of Transitional Flow Behavior in a Simulated Low Pressure Turbine

NASA Technical Reports Server (NTRS)

Sohn, Ki Hyeon; DeWitt, Kenneth J.

1998-01-01

A detailed investigation of the flow physics occurring on the suction side of a simulated Low Pressure Turbine (LPT) blade was performed. A contoured upper wall was designed to simulate the pressure distribution of an actual LPT airfoil onto a flat lower plate. The experiments were carried out for the Reynolds numbers of 35,000, 70,000, 100,000 and 250,000 with four levels of freestream turbulence ranging from 1% to 4%. For the three lower Reynolds numbers, the boundary layer on the flat plate was separated and formed a bubble. The size of laminar separation bubble was measured to be inversely proportional to the freestream turbulence levels and Reynolds numbers. However, no separation was observed for the Re = 250,000 case. The transition on a separated flow was found to proceed through the formation of turbulent spots in the free shear layer as evidenced in the intermittency profiles for Re = 35,000, 70,000 and 100,000. Spectral data show no evidence of Kelvin-Helmholtz or Tollmien-Schlichting instability waves in the free shear layer over a separation bubble (bypass transition). However, the flow visualization revealed the large vortex structures just outside of the bubble and their development to turbulent flow for Re = 50,000, which is similar to that in the free shear layer (separated-flow transition). Therefore, it is fair to say that the bypass and separated-flow transition modes coexist in the transitional flows over the separation bubble for certain conditions. Transition onset and end locations and length determined from intermittency profiles decrease as Reynolds number and freestream turbulence levels increase.

Experimental Study of Transitional Flow Behavior in a Simulated Low Pressure Turbine

NASA Technical Reports Server (NTRS)

Sohn, Ki Hyeon; DeWitt, Kenneth J.

2007-01-01

A detailed investigation of the flow physics occurring on the suction side of a simulated Low Pressure Turbine (LPT) blade was performed. A contoured upper wall was designed to simulate the pressure distribution of an actual LPT airfoil onto a flat lower plate. The experiments were carried out for the Reynolds numbers of 35,000, 70,000, 100,000, and 250,000 with four levels of freestream turbulence ranging from 1 to 4 percent. For the three lower Reynolds numbers, the boundary layer on the flat plate was separated and formed a bubble. The size of laminar separation bubble was measured to be inversely proportional to the freestream turbulence levels and Reynolds numbers. However, no separation was observed for the Re = 250,000 case. The transition on a separated flow was found to proceed through the formation of turbulent spots in the free shear layer as evidenced in the intermittency profiles for Re = 35,000, 70,000, and 100,000. Spectral data show no evidence of Kelvin-Helmholtz of Tollmien-Schlichting instability waves in the free shear layer over a separation bubble (bypass transition). However, the flow visualization revealed the large vortex structures just outside of the bubble and their development to turbulent flow for Re = 50,000, which is similar to that in the free shear layer (separated-flow transition). Therefore, it is fair to say that the bypass and separated-flow transition modes coexist in the transition flows over the separation bubble of certain conditions. Transition onset and end locations and length determined from intermittency profiles decreased as Reynolds number and freestream turbulence levels increase.

Multidisciplinary Computational Aerodynamics

DTIC Science & Technology

2013-10-01

flat plate. These wings exhibit large aspect ratio and a highly corrugated structure. Several wind tunnel studies have shown possible advantages...Advances in Turbines Aero-thermo-mechanical Design and Analysis”, IGT Institute, Vancouver, June 2011 Rizzetta: Invited Seminar, University of...pressure turbines for high- altitude aircraft, distributed-roughness transition, flapping wing aerodynamics and laser turrets. Flow Structure and Unsteady

Standardized performance tests of collectors of solar thermal energy: A selectively coated, steel collector with one transparent cover

NASA Technical Reports Server (NTRS)

1976-01-01

Basic test results are presented of a flat-plate solar collector whose performance was determined in solar simulator. The collector was tested over ranges of inlet temperatures, fluxes and coolant flow rates. Collector efficiency was correlated in terms of inlet temperature and flux level.

Experimental investigation of turbulent wall jet

NASA Astrophysics Data System (ADS)

Andre, Matthieu A.; Bardet, Philippe M.

2011-11-01

Water jet flowing on a flat plate surrounded by quiescent air constitutes a standard case for the study of the interaction between turbulence and the liquid-air interface. This is of particular interest in the understanding of heat and mass transfers across interfaces. The structure of the surface has a great influence on the rate of the transfers which is critical for chemical processes like separation or absorption; pool-type nuclear reactor; climate modeling etc. This study focuses on high Froude (8 to 12) and Weber (3300 to 7400) numbers at which the surface exhibits small wavelength and large amplitude deformations, such as ligaments, surface break up with air entrainment and droplets projection. The experiment features a high velocity (up to 7.5 m/s) water wall jet (19.05mm thick at the nozzle exit) flowing on a flat plate (Re =105 to 1 . 5 .105). High speed movies and PLIF visualization show the evolution of the surface from smooth to 2D structures, then 3D disturbances as the turbulence arising from the wall interacts with the surface.

On the Environmental Realizability of Algebraically Growing Disturbances and Their Relation to Klebanoff Modes

NASA Technical Reports Server (NTRS)

Goldstein, Marvin E.; Wundrow, David W.

1998-01-01

A theoretical explanation of some experimentally observed phenomena associated with the so-called Klebanoff modes is obtained by analyzing the flow over a finite thickness flat plate resulting from a small-amplitude distortion imposed on the upstream mean flow. The analysis shows (among other things) how the stretching of the vortex lines around the plate leads to streamwise vorticity at the plate surface, which then produces a streamwise velocity perturbation within the boundary layer that can be related to the experimentally observed Klebanoff mode. The complete evolution of this flow must be found by solving the boundary-region equations of Kemp (1951) and Davis and Rubin (1980), but a limiting analytical solution can also be obtained. Since the initial growth of the boundary-layer disturbance is nearly algebraic, our results demonstrate how the algebraically growing disturbances promoted by Landahl and others can be generated by a realistic external-disturbance environment. The relationship between these results and various bypass transition mechanisms is discussed.

An Experimental Device for Generating High Frequency Perturbations in Supersonic Wind Tunnels

NASA Technical Reports Server (NTRS)

Melcher, Kevin J.; Ibrahim, Mounir B.

1996-01-01

This paper describes the analytical study of a device that has been proposed as a mechanism for generating gust-like perturbations in supersonic wind tunnels. The device is envisioned as a means to experimentally validate dynamic models and control systems designed for high-speed inlets. The proposed gust generator is composed of two flat trapezoidal plates that modify the properties of the flow ingested by the inlet. One plate may be oscillated to generate small perturbations in the flow. The other plate is held stationary to maintain a constant angle-of-attack. Using an idealized approach, design equations and performance maps for the new device were developed from the compressible flow relations. A two-dimensional CFD code was used to confirm the correctness of these results. The idealized approach was then used to design and evaluate a new gust generator for a 3.05-meter by 3.05-meter (10-foot by 10-foot) supersonic wind tunnel.

Estimation of spatially varying heat transfer coefficient from a flat plate with flush mounted heat sources using Bayesian inference

NASA Astrophysics Data System (ADS)

Jakkareddy, Pradeep S.; Balaji, C.

2016-09-01

This paper employs the Bayesian based Metropolis Hasting - Markov Chain Monte Carlo algorithm to solve inverse heat transfer problem of determining the spatially varying heat transfer coefficient from a flat plate with flush mounted discrete heat sources with measured temperatures at the bottom of the plate. The Nusselt number is assumed to be of the form Nu = aReb(x/l)c . To input reasonable values of ’a’ and ‘b’ into the inverse problem, first limited two dimensional conjugate convection simulations were done with Comsol. Based on the guidance from this different values of ‘a’ and ‘b’ are input to a computationally less complex problem of conjugate conduction in the flat plate (15mm thickness) and temperature distributions at the bottom of the plate which is a more convenient location for measuring the temperatures without disturbing the flow were obtained. Since the goal of this work is to demonstrate the eficiacy of the Bayesian approach to accurately retrieve ‘a’ and ‘b’, numerically generated temperatures with known values of ‘a’ and ‘b’ are treated as ‘surrogate’ experimental data. The inverse problem is then solved by repeatedly using the forward solutions together with the MH-MCMC aprroach. To speed up the estimation, the forward model is replaced by an artificial neural network. The mean, maximum-a-posteriori and standard deviation of the estimated parameters ‘a’ and ‘b’ are reported. The robustness of the proposed method is examined, by synthetically adding noise to the temperatures.

Unsteady conjugate heat transfer analysis for impinging jet cooling

NASA Astrophysics Data System (ADS)

Tejero, F.; Flaszyński, P.; Szwaba, R.; Telega, J.

2016-10-01

The paper presents the numerical investigations of the heat transfer on a flat plate cooled by a single impinging jet. The thermal conductivity of the plate was modified from a high thermal case (steel -λ= 35 W/m/K) to a low one (steel alloy Inconel -λ= 9.8 W/m/K). The numerical simulations results are compared with the experimental data from the Institute of Fluid-Flow Machinery Polish Academy of Sciences, Gdansk (Poland). The numerical simulations are carried out by means of Ansys/Fluent and k-ω SST turbulence model and the temperature evolution on the target plate is investigated by conjugated heat transfer computations.

RF current sensor

DOEpatents

Moore, James A.; Sparks, Dennis O.

1998-11-10

An RF sensor having a novel current sensing probe and a voltage sensing probe to measure voltage and current. The current sensor is disposed in a transmission line to link all of the flux generated by the flowing current in order to obtain an accurate measurement. The voltage sensor is a flat plate which operates as a capacitive plate to sense voltage on a center conductor of the transmission line, in which the measured voltage is obtained across a resistance leg of a R-C differentiator circuit formed by the characteristic impedance of a connecting transmission line and a capacitance of the plate, which is positioned proximal to the center conductor.

Ionospheric plasma flow about a system of electrically biased flat plates. M.S. Thesis - Cleveland State Univ. Final Report

NASA Technical Reports Server (NTRS)

Herr, Joel L.

1993-01-01

The steady state interaction of two electrically biased parallel plates immersed in a flowing plasma characteristic of low earth orbit is studied numerically. Fluid equations are developed to describe the motion of the cold positively charged plasma ions, and are solved using finite-differences in two dimensions on a Cartesian grid. The behavior of the plasma electrons is assumed to be described by the Maxwell-Boltzmann distribution. Results are compared to an analytical and a particle simulation technique for a simplified flow geometry consisting of a single semi-infinite negatively biased plate. Comparison of the extent of the electrical disturbance into the flowing plasma and the magnitude of the current collected by the plate is very good. The interaction of two equally biased parallel plates is studied as a function of applied potential. The separation distance at which the current collected by either plate decreases by five and twenty percent is determined as a function of applied potential. The percent decreases were based on a non-interacting case. The decrease in overall current is caused by a decrease in ionic density in the region between the plates. As the separation between the plates decreases, the plates collect the ions at a faster rate than they are supplied to the middle region by the oncoming plasma flow. The docking of spacecraft in orbit is simulated by moving two plates of unequal potential toward one another in a quasi-static manner. One plate is held at a large negative potential while the other floats electrically in the resulting potential field. It is found that the floating plate does not charge continuously negative as it approaches the other more negatively biased plate. Instead, it charges more and then less negative as ionic current decreases and then increases respectively upon approach. When the two plates come into contact, it is expected that the electrically floating plate will charge rapidly negative to a potential near that of the other plate.

On the role of tip curvature on flapping plates.

PubMed

Martin, Nathan; Gharib, Morteza

2018-01-09

During the flapping motion of a fish's tail, the caudal fin exhibits antero-posterior bending and dorso-ventral bending, the latter of which is referred to as chord-wise bending herein. The impact of chord-wise tip curvature on the hydrodynamic forces for flapping plates is investigated to explore potential mechanisms to improve the maneuverability or the performance of autonomous underwater vehicles. First, actuated chord-wise tip curvature is explored. Comparison of rigid curved geometries to a rigid flat plate as a baseline suggests that an increased curvature decreases the generated forces. An actuated plate with a dynamic tip curvature is created to illustrate a modulation of this decrease in forces. Second, the impact of curvature is isolated using curved plates with an identical planform area. Comparison of rigid curved geometries as a baseline corroborates the result that an increased curvature decreases the generated forces, with the exception that presenting a concave geometry into the flow increases the thrust and the efficiency. A passively-actuated plate is designed to capitalize on this effect by presenting a concave geometry into the flow throughout the cycle. The dynamically and passively actuated plates show potential to improve the maneuverability and the efficiency of autonomous underwater vehicles, respectively.

Comparison of DAC and MONACO DSMC Codes with Flat Plate Simulation

NASA Technical Reports Server (NTRS)

Padilla, Jose F.

2010-01-01

Various implementations of the direct simulation Monte Carlo (DSMC) method exist in academia, government and industry. By comparing implementations, deficiencies and merits of each can be discovered. This document reports comparisons between DSMC Analysis Code (DAC) and MONACO. DAC is NASA's standard DSMC production code and MONACO is a research DSMC code developed in academia. These codes have various differences; in particular, they employ distinct computational grid definitions. In this study, DAC and MONACO are compared by having each simulate a blunted flat plate wind tunnel test, using an identical volume mesh. Simulation expense and DSMC metrics are compared. In addition, flow results are compared with available laboratory data. Overall, this study revealed that both codes, excluding grid adaptation, performed similarly. For parallel processing, DAC was generally more efficient. As expected, code accuracy was mainly dependent on physical models employed.

Experimental studies of hypersonic shock-wave boundary-layer interactions

NASA Technical Reports Server (NTRS)

Lu, Frank K.

1992-01-01

Two classes of shock-wave boundary-layer interactions were studied experimentally in a shock tunnel in which a low Reynolds number, turbulent flow at Mach 8 was developed on a cold, flat test surface. The two classes of interactions were: (1) a swept interaction generated by a wedge ('fin') mounted perpendicularly on the flat plate; and (2) a two-dimensional, unseparated interaction induced by a shock impinging near an expansion corner. The swept interaction, with wedge angles of 5-20 degrees, was separated and there was also indication that the strongest interactions prossessed secondary separation zones. The interaction spread out extensively from the inviscid shock location although no indication of quasi-conical symmetry was evident. The surface pressure from the upstream influence to the inviscid shock was relatively low compared to the inviscid downstream value but it rose rapidly past the inviscid shock location. However, the surface pressure did not reach the downstream inviscid value and reasons were proposed for this anomalous behavior compared to strongly separated, supersonic interactions. The second class of interactions involved weak shocks impinging near small expansion corners. As a prelude to studying this interaction, a hypersonic similarity parameter was identified for the pure, expansion corner flow. The expansion corner severely damped out surface pressure fluctuations. When a shock impinged upstream of the corner, no significant changes to the surface pressure were found as compared to the case when the shock impinged on a flat plate. But, when the shock impinged downstream of the corner, a close coupling existed between the two wave systems, unlike the supersonic case. This close coupling modified the upstream influence. Regardless of whether the shock impinged ahead or behind the corner, the downstream region was affected by the close coupling between the shock and the expansion. Not only was the mean pressure distribution modified but the unsteadiness in the surface pressure was reduced compared to the flat-plate case.

Drag measurements of an axisymmetric nacelle mounted on a flat plate at supersonic speeds

NASA Technical Reports Server (NTRS)

Flamm, Jeffrey D.; Wilcox, Floyd J., Jr.

1995-01-01

An experimental investigation was conducted to determine the effect of diverter wedge half-angle and nacelle lip height on the drag characteristics of an assembly consisting of a nacelle fore cowl from a typical high-speed civil transport (HSCT) and a diverter mounted on a flat plate. Data were obtained for diverter wedge half-angles of 4.0 deg, 6.0 deg, and 8.0 deg and ratios of the nacelle lip height above a flat plate to the boundary-layer thickness (h(sub n)/delta) of approximately 0.87 to 2.45. Limited drag data were also obtained on a complete nacelle/diverter configuration that included fore and aft cowls. Although the nacelle/diverter drag data were not corrected for base pressures or internal flow drag, the data are useful for comparing the relative drag of the configuration tested. The tests were conducted in the Langley Unitary Plan Wind Tunnel at Mach numbers of 1.50, 1.80, 2.10, and 2.40 and Reynolds numbers ranging from 2.00 x 10(exp 6) to 5.00 x 10(exp 6) per foot. The results of this investigation showed that the nacelle/diverter drag essentially increased linearly with increasing h(sub n)/delta except near 1.0 where the data showed a nonlinear behavior. This nonlinear behavior was probably caused by the interaction of the shock waves from the nacelle/diverter configuration with the flat-plate boundary layer. At the lowest h(sub n)/delta tested, the diverter wedge half-angle had virtually no effect on the nacelle/diverter drag. However, as h(sub n)/delta increased, the nacelle/diverter drag increased as diverter wedge half-angle increased.

Numerical investigation of the aerodynamic and structural characteristics of a corrugated wing

NASA Astrophysics Data System (ADS)

Hord, Kyle

Previous experimental studies on static, bio-inspired corrugated wings have shown that they produce favorable aerodynamic properties such as delayed stall compared to streamlined wings and flat plates at high Reynolds numbers (Re ≥ 4x104). The majority of studies have been carried out with scaled models of dragonfly forewings from the Aeshna Cyanea in either wind tunnels or water channels. In this thesis, the aerodynamics of a corrugated airfoil was studied using computational fluid dynamics methods at a low Reynolds number of 1000. Structural analysis was also performed using the commercial software SolidWorks 2009. The flow field is described by solving the incompressible Navier-Stokes equations on an overlapping grid using the pressure-Poisson method. The equations are discretized in space with second-order accurate central differences. Time integration is achieved through the second-order Crank-Nicolson implicit method. The complex vortex structures that form in the corrugated airfoil valleys and around the corrugated airfoil are studied in detail. Comparisons are made with experimental measurements from corrugated wings and also with simulations of a flat plate. Contrary to the studies at high Reynolds numbers, our study shows that at low Reynolds numbers the wing corrugation does not provide any aerodynamic benefit compared to a smoothed flat plate. Instead, the corrugated profile generates more pressure drag which is only partially offset by the reduction of friction drag, leading to more total drag than the flat plate. Structural analysis shows that the wing corrugation can increase the resistance to bending moments on the wing structure. A smoothed structure has to be three times thicker to provide the same stiffness. It was concluded the corrugated wing has the structural benefit to provide the same resistance to bending moments with a much reduced weight.

Collation of quarterly reports on air flat plate collectors

NASA Technical Reports Server (NTRS)

1977-01-01

The solar 2 air flat plate collectors are described. The development and fabrication of a prototype air flat plate collector subsystem containing 320 square feet of collector area are described. Three instrumented panels were completely assembled with glazing and insulation. Manufacture of the last seven prototype collectors was completed in October 1977.

Flat-plate solar array progress and plans

NASA Technical Reports Server (NTRS)

Callaghan, W. T.

1984-01-01

The results of research into the technology of flat-plate solar arrays undertaken in the Flat-Plate Solar Array Project under the sponsorship of the U.S. Department of Energy are surveyed. Topics examined include Si refinement, ribbon-sheet substrate formation, module process sequences, environmental isolation, module engineering and testing, and photovoltaic-array economics.

Biomechanics of Tetrahymena escaping from a dead end

PubMed Central

Kikuchi, Kenji

2018-01-01

Understanding the behaviours of swimming microorganisms in various environments is important for understanding cell distribution and growth in nature and industry. However, cell behaviour in complex geometries is largely unknown. In this study, we used Tetrahymena thermophila as a model microorganism and experimentally investigated cell behaviour between two flat plates with a small angle. In this configuration, the geometry provided a ‘dead end' line where the two flat plates made contact. The results showed that cells tended to escape from the dead end line more by hydrodynamics than by a biological reaction. In the case of hydrodynamic escape, the cell trajectories were symmetric as they swam to and from the dead end line. Near the dead end line, T. thermophila cells were compressed between the two flat plates while cilia kept beating with reduced frequency; those cells again showed symmetric trajectories, although the swimming velocity decreased. These behaviours were well reproduced by our computational model based on biomechanics. The mechanism of hydrodynamic escape can be understood in terms of the torque balance induced by lubrication flow. We therefore conclude that a cell's escape from the dead end was assisted by hydrodynamics. These findings pave the way for understanding cell behaviour and distribution in complex geometries. PMID:29491169

Large area x-ray detectors for cargo radiography

NASA Astrophysics Data System (ADS)

Bueno, C.; Albagli, D.; Bendahan, J.; Castleberry, D.; Gordon, C.; Hopkins, F.; Ross, W.

2007-04-01

Large area x-ray detectors based on phosphors coupled to flat panel amorphous silicon diode technology offer significant advances for cargo radiologic imaging. Flat panel area detectors provide large object coverage offering high throughput inspections to meet the high flow rate of container commerce. These detectors provide excellent spatial resolution when needed, and enhanced SNR through low noise electronics. If the resolution is reduced through pixel binning, further advances in SNR are achievable. Extended exposure imaging and frame averaging enables improved x-ray penetration of ultra-thick objects, or "select-your-own" contrast sensitivity at a rate many times faster than LDAs. The areal coverage of flat panel technology provides inherent volumetric imaging with the appropriate scanning methods. Flat panel area detectors have flexible designs in terms of electronic control, scintillator selection, pixel pitch, and frame rates. Their cost is becoming more competitive as production ramps up for the healthcare, nondestructive testing (NDT), and homeland protection industries. Typically used medical and industrial polycrystalline phosphor materials such as Gd2O2S:Tb (GOS) can be applied to megavolt applications if the phosphor layer is sufficiently thick to enhance x-ray absorption, and if a metal radiator is used to augment the quantum detection efficiency and reduce x-ray scatter. Phosphor layers ranging from 0.2-mm to 1-mm can be "sandwiched" between amorphous silicon flat panel diode arrays and metal radiators. Metal plates consisting of W, Pb or Cu, with thicknesses ranging from 0.25-mm to well over 1-mm can be used by covering the entire area of the phosphor plate. In some combinations of high density metal and phosphor layers, the metal plate provides an intensification of 25% in signal due to electron emission from the plate and subsequent excitation within the phosphor material. This further improves the SNR of the system.

Active control of panel vibrations induced by boundary-layer flow

NASA Technical Reports Server (NTRS)

Chow, Pao-Liu

1991-01-01

Some problems in active control of panel vibration excited by a boundary layer flow over a flat plate are studied. In the first phase of the study, the optimal control problem of vibrating elastic panel induced by a fluid dynamical loading was studied. For a simply supported rectangular plate, the vibration control problem can be analyzed by a modal analysis. The control objective is to minimize the total cost functional, which is the sum of a vibrational energy and the control cost. By means of the modal expansion, the dynamical equation for the plate and the cost functional are reduced to a system of ordinary differential equations and the cost functions for the modes. For the linear elastic plate, the modes become uncoupled. The control of each modal amplitude reduces to the so-called linear regulator problem in control theory. Such problems can then be solved by the method of adjoint state. The optimality system of equations was solved numerically by a shooting method. The results are summarized.

Three-Dimensional Unsteady Separation at Low Reynolds Numbers

DTIC Science & Technology

1990-07-01

novel, robust adaptive- grid technique for incompressible flow (Shen & Reed 1990a "Shepard’s Interpolation for Solution-Adaptive Methods" submitted to...3-D adaptive- grid schemes developed for flat plate for full, unsteady, incompressible Navier Stokes. 4. 2-D and 3-D unsteady, vortex-lattice code...perforated to tailor suction through wall. Honeycomb and contractiong uide flow uniformly crons "a dn muwet a m Fiur32 c ic R n R ev lving -disc seals

Near Field Trailing Edge Tone Noise Computation

NASA Technical Reports Server (NTRS)

Loh, Ching Y.

2002-01-01

Blunt trailing edges in a flow often generate tone noise due to wall-jet shear layer and vortex shedding. In this paper, the space-time conservation element (CE/SE) method is employed to numerically study the near-field noise of blunt trailing edges. Two typical cases, namely, flow past a circular cylinder (aeolian noise problem) and flow past a flat plate of finite thickness are considered. The computed frequencies compare well with experimental data. For the aeolian noise problem, comparisons with the results of other numerical approaches are also presented.

On the effect of boundary layer growth on the stability of compressible flows

NASA Technical Reports Server (NTRS)

El-Hady, N. M.

1981-01-01

The method of multiple scales is used to describe a formally correct method based on the nonparallel linear stability theory, that examines the two and three dimensional stability of compressible boundary layer flows. The method is applied to the supersonic flat plate layer at Mach number 4.5. The theoretical growth rates are in good agreement with experimental results. The method is also applied to the infinite-span swept wing transonic boundary layer with suction to evaluate the effect of the nonparallel flow on the development of crossflow disturbances.

Numerical Simulation of a Spatially Evolving Supersonic Turbulent Boundary Layer

NASA Technical Reports Server (NTRS)

Gatski, T. B.; Erlebacher, G.

2002-01-01

The results from direct numerical simulations of a spatially evolving, supersonic, flat-plate turbulent boundary-layer flow, with free-stream Mach number of 2.25 are presented. The simulated flow field extends from a transition region, initiated by wall suction and blowing near the inflow boundary, into the fully turbulent regime. Distributions of mean and turbulent flow quantities are obtained and an analysis of these quantities is performed at a downstream station corresponding to Re(sub x)= 5.548 x10(exp 6) based on distance from the leading edge.

Sound radiated by the interaction of non-homogeneous turbulence on a transversely sheared flow with leading and trailing edges of semi-infinite flat plate

NASA Astrophysics Data System (ADS)

Afsar, Mohammed; Sassanis, Vasilis

2017-11-01

The small amplitude unsteady motion on a transversely sheared mean flow is determined by two arbitrary convected quantities with a particular choice of gauge in which the Fourier transform of the pressure is linearly-related to a scalar potential whose integral solution can be written in terms of one of these convected quantities. This formulation becomes very useful for studying Rapid-distortion theory problems involving solid surface interaction. Recent work by Goldstein et al. (JFM, 2017) has shown that the convected quantities are related to the turbulence by exact conservation laws, which allow the upstream boundary conditions for interaction of a turbulent shear flow with a solid-surface (for example) to be derived self-consistently with appropriate asymptotic separation of scales. This result requires the imposition of causality on an intermediate variable within the conservation laws that represents the local particle displacement. In this talk, we use the model derived in Goldstein et al. for trailing edge noise and compare it to leading edge noise on a semi-infinite flat plate positioned parallel to the level curves of the mean flow. Since the latter represents the leading order solution for the aerofoil interaction problem, these results are expected to be generic. M.Z.A. would also like to thank Strathclyde University for financial support from the Chancellor's Fellowship.

Micromachined silicon electrostatic chuck

DOEpatents

Anderson, R.A.; Seager, C.H.

1996-12-10

An electrostatic chuck is faced with a patterned silicon plate, created by micromachining a silicon wafer, which is attached to a metallic base plate. Direct electrical contact between the chuck face (patterned silicon plate`s surface) and the silicon wafer it is intended to hold is prevented by a pattern of flat-topped silicon dioxide islands that protrude less than 5 micrometers from the otherwise flat surface of the chuck face. The islands may be formed in any shape. Islands may be about 10 micrometers in diameter or width and spaced about 100 micrometers apart. One or more concentric rings formed around the periphery of the area between the chuck face and wafer contain a low-pressure helium thermal-contact gas used to assist heat removal during plasma etching of a silicon wafer held by the chuck. The islands are tall enough and close enough together to prevent silicon-to-silicon electrical contact in the space between the islands, and the islands occupy only a small fraction of the total area of the chuck face, typically 0.5 to 5 percent. The pattern of the islands, together with at least one hole bored through the silicon veneer into the base plate, will provide sufficient gas-flow space to allow the distribution of the helium thermal-contact gas. 6 figs.

Thin-layer approximation and algebraic model for separated turbulent flows

NASA Technical Reports Server (NTRS)

Baldwin, B.; Lomax, H.

1978-01-01

An algebraic turbulence model for two- and three-dimensional separated flows is specified that avoids the necessity for finding the edge of the boundary layer. Properties of the model are determined and comparisons made with experiment for an incident shock on a flat plate, separated flow over a compression corner, and transonic flow over an airfoil. Separation and reattachment points from numerical Navier-Stokes solutions agree with experiment within one boundary-layer thickness. Use of law-of-the-wall boundary conditions does not alter the predictions significantly. Applications of the model to other cases are contained in companion papers.

Test code for the assessment and improvement of Reynolds stress models

NASA Technical Reports Server (NTRS)

Rubesin, M. W.; Viegas, J. R.; Vandromme, D.; Minh, H. HA

1987-01-01

An existing two-dimensional, compressible flow, Navier-Stokes computer code, containing a full Reynolds stress turbulence model, was adapted for use as a test bed for assessing and improving turbulence models based on turbulence simulation experiments. To date, the results of using the code in comparison with simulated channel flow and over an oscillating flat plate have shown that the turbulence model used in the code needs improvement for these flows. It is also shown that direct simulation of turbulent flows over a range of Reynolds numbers are needed to guide subsequent improvement of turbulence models.

A Hierarchical Multiscale Particle Computational Method for Simulation of Nanoscale Flows on 3D Unstructured Grids

DTIC Science & Technology

2009-08-14

3 is presented in Figure 12. These cases simulate the smallest na- nochannels with H = 0.1 /im and correspond to the near free -molecular flow with a...nal energy flux (or heat transfer rate) from a free stream with p, T.S to a flat plate with surface temperature T aligned with the flow is, 25 S2... Simulation of Nanoscale Flows on 3D Unstructured Grids 5a. CONTRACT NUMBER 5b. GRANT NUMBER FA9950-06-1-0236 5c. PROGRAM ELEMENT NUMBER 6. AUTHOR(S

46 CFR 154.1320 - Sighting ports, tubular gauge glasses, and flat plate type gauge glasses.

Code of Federal Regulations, 2011 CFR

2011-10-01

... 46 Shipping 5 2011-10-01 2011-10-01 false Sighting ports, tubular gauge glasses, and flat plate type gauge glasses. 154.1320 Section 154.1320 Shipping COAST GUARD, DEPARTMENT OF HOMELAND SECURITY... glasses, and flat plate type gauge glasses. (a) Cargo tanks may have sighting ports as a secondary means...

46 CFR 154.1320 - Sighting ports, tubular gauge glasses, and flat plate type gauge glasses.

Code of Federal Regulations, 2010 CFR

2010-10-01

... 46 Shipping 5 2010-10-01 2010-10-01 false Sighting ports, tubular gauge glasses, and flat plate type gauge glasses. 154.1320 Section 154.1320 Shipping COAST GUARD, DEPARTMENT OF HOMELAND SECURITY... glasses, and flat plate type gauge glasses. (a) Cargo tanks may have sighting ports as a secondary means...

Long Hole Film Cooling Dataset for CFD Development . Part 1; Infrared Thermography and Thermocouple Surveys

NASA Technical Reports Server (NTRS)

Shyam, Vikram; Thurman, Douglas; Poinsatte, Phillip; Ameri, Ali; Eichele, Peter; Knight, James

2013-01-01

An experiment investigating flow and heat transfer of long (length to diameter ratio of 18) cylindrical film cooling holes has been completed. In this paper, the thermal field in the flow and on the surface of the film cooled flat plate is presented for nominal freestream turbulence intensities of 1.5 and 8 percent. The holes are inclined at 30deg above the downstream direction, injecting chilled air of density ratio 1.0 onto the surface of a flat plate. The diameter of the hole is 0.75 in. (0.01905 m) with center to center spacing (pitch) of 3 hole diameters. Coolant was injected into the mainstream flow at nominal blowing ratios of 0.5, 1.0, 1.5, and 2.0. The Reynolds number of the freestream was approximately 11,000 based on hole diameter. Thermocouple surveys were used to characterize the thermal field. Infrared thermography was used to determine the adiabatic film effectiveness on the plate. Hotwire anemometry was used to provide flowfield physics and turbulence measurements. The results are compared to existing data in the literature. The aim of this work is to produce a benchmark dataset for Computational Fluid Dynamics (CFD) development to eliminate the effects of hole length to diameter ratio and to improve resolution in the near-hole region. In this report, a Time-Filtered Navier Stokes (TFNS), also known as Partially Resolved Navier Stokes (PRNS), method that was implemented in the Glenn-HT code is used to model coolant-mainstream interaction. This method is a high fidelity unsteady method that aims to represent large scale flow features and mixing more accurately.

Fluid dynamics and convective heat transfer in impinging jets through implementation of a high resolution liquid crystal technique

NASA Technical Reports Server (NTRS)

Kim, K.; Wiedner, B.; Camci, C.

1993-01-01

A combined convective heat transfer and fluid dynamics investigation in a turbulent round jet impinging on a flat surface is presented. The experimental study uses a high resolution liquid crystal technique for the determination of the convective heat transfer coefficients on the impingement plate. The heat transfer experiments are performed using a transient heat transfer method. The mean flow and the character of turbulent flow in the free jet is presented through five hole probe and hot wire measurements, respectively. The flow field character of the region near the impingement plate plays an important role in the amount of convective heat transfer. Detailed surveys obtained from five hole probe and hot wire measurements are provided. An extensive validation of the liquid crystal based heat transfer method against a conventional technique is also presented. After a complete documentation of the mean and turbulent flow field, the convective heat transfer coefficient distributions on the impingement plate are presented. The near wall of the impingement plate and the free jet region is treated separately. The current heat transfer distributions are compared to other studies available from the literature. The present paper contains complete sets of information on the three dimensional mean flow, turbulent velocity fluctuations, and convective heat transfer to the plate. The experiments also prove that the present nonintrusive heat transfer method is highly effective in obtaining high resolution heat transfer maps with a heat transfer coefficient uncertainty of 5.7 percent.

Polygons on a rotating fluid surface.

PubMed

Jansson, Thomas R N; Haspang, Martin P; Jensen, Kåre H; Hersen, Pascal; Bohr, Tomas

2006-05-05

We report a novel and spectacular instability of a fluid surface in a rotating system. In a flow driven by rotating the bottom plate of a partially filled, stationary cylindrical container, the shape of the free surface can spontaneously break the axial symmetry and assume the form of a polygon rotating rigidly with a speed different from that of the plate. With water, we have observed polygons with up to 6 corners. It has been known for many years that such flows are prone to symmetry breaking, but apparently the polygonal surface shapes have never been observed. The creation of rotating internal waves in a similar setup was observed for much lower rotation rates, where the free surface remains essentially flat [J. M. Lopez, J. Fluid Mech. 502, 99 (2004). We speculate that the instability is caused by the strong azimuthal shear due to the stationary walls and that it is triggered by minute wobbling of the rotating plate.

Manipulation of Turbulent Boundary Layers Using Synthetic Jets

NASA Astrophysics Data System (ADS)

Berger, Zachary; Gomit, Guillaume; Lavoie, Philippe; Ganapathisubramani, Bharath

2015-11-01

This work focuses on the application of active flow control, in the form of synthetic jet actuators, of turbulent boundary layers. An array of 2 synthetic jets are oriented in the spanwise direction and located approximately 2.7 meters downstream from the leading edge of a flat plate. Actuation is applied perpendicular to the surface of the flat plate with varying blowing ratios and reduced frequencies (open-loop). Two-component large window particle image velocimetry (PIV) was performed at the University of Southampton, in the streamwise-wall-normal plane. Complementary stereo PIV measurements were performed at the University of Toronto Institute for Aerospace Studies (UTIAS), in the spanwise-wall-normal plane. The freestream Reynolds number is 3x104, based on the boundary layer thickness. The skin friction Reynolds number is 1,200 based on the skin friction velocity. The experiments at Southampton allow for the observation of the control effects as the flow propagates downstream. The experiments at UTIAS allow for the observation of the streamwise vorticity induced from the actuation. Overall the two experiments provide a 3D representation of the flow field with respect to actuation effects. The current work focuses on the comparison of the two experiments, as well as the effects of varying blowing ratios and reduced frequencies on the turbulent boundary layer. Funded Supported by Airbus.

Further Development of a New, Flux-Conserving Newton Scheme for the Navier-Stokes Equations

NASA Technical Reports Server (NTRS)

Scott, James R.

1996-01-01

This paper is one of a series of papers describing the development of a new numerical approach for solving the steady Navier-Stokes equations. The key features in the current development are (1) the discrete representation of the dependent variables by way of high order polynomial expansions, (2) the retention of all derivatives in the expansions as unknowns to be explicitly solved for, (3) the automatic balancing of fluxes at cell interfaces, and (4) the discrete simulation of both the integral and differential forms of the governing equations. The main purpose of this paper is, first, to provide a systematic and rigorous derivation of the conditions that are used to simulate the differential form of the Navier-Stokes equations, and second, to extend our previously-presented internal flow scheme to external flows and nonuniform grids. Numerical results are presented for high Reynolds number flow (Re = 100,000) around a finite flat plate, and detailed comparisons are made with the Blasius flat plate solution and Goldstein wake solution. It is shown that the error in the streamwise velocity decreases like r(sup alpha)(Delta)y(exp 2), where alpha approx. 0.25 and r = delta(y)/delta(x) is the grid aspect ratio.

Diffusion of drag-reducing polymer solutions within a rough-walled turbulent boundary layer

NASA Astrophysics Data System (ADS)

Elbing, Brian R.; Dowling, David R.; Perlin, Marc; Ceccio, Steven L.

2010-04-01

The influence of surface roughness on diffusion of wall-injected, drag-reducing polymer solutions within a turbulent boundary layer was studied with a 0.94 m long flat-plate test model at speeds of up to 10.6 m s-1 and Reynolds numbers of up to 9×106. The surface was hydraulically smooth, transitionally rough, or fully rough. Mean concentration profiles were acquired with planar laser induced fluorescence, which was the primary flow diagnostic. Polymer concentration profiles with high injection concentrations (≥1000 wppm) had the peak concentration shifted away from the wall, which was partially attributed to a lifting phenomenon. The diffusion process was divided into three zones—initial, intermediate, and final. Studies of polymer injection into a polymer ocean at concentrations sufficient for maximum drag reduction indicated that the maximum initial zone length is of the order of 100 boundary layer thicknesses. The intermediate zone results indicate that friction velocity and roughness height are important scaling parameters in addition to flow and injection conditions. Lastly, the current results were combined with those in Petrie et al. ["Polymer drag reduction with surface roughness in flat-plate turbulent boundary layer flow," Exp. Fluids 35, 8 (2003)] to demonstrate that the influence of polymer degradation increases with increased surface roughness.

Heat Transfer Analysis for Stationary Boundary Layer Slip Flow of a Power-Law Fluid in a Darcy Porous Medium with Plate Suction/Injection

PubMed Central

Aziz, Asim; Ali, Yasir; Aziz, Taha; Siddique, J. I.

2015-01-01

In this paper, we investigate the slip effects on the boundary layer flow and heat transfer characteristics of a power-law fluid past a porous flat plate embedded in the Darcy type porous medium. The nonlinear coupled system of partial differential equations governing the flow and heat transfer of a power-law fluid is transformed into a system of nonlinear coupled ordinary differential equations by applying a suitable similarity transformation. The resulting system of ordinary differential equations is solved numerically using Matlab bvp4c solver. Numerical results are presented in the form of graphs and the effects of the power-law index, velocity and thermal slip parameters, permeability parameter, suction/injection parameter on the velocity and temperature profiles are examined. PMID:26407162

Experimental investigation of jet-induced loads on a flat plate in hover out-of-ground effect

NASA Technical Reports Server (NTRS)

Kuhlman, J. M.; Warcup, R. W.

1979-01-01

Effects of varying jet decay rate on jet-induced loads on a flat plate located in the plane of the jet exit perpendicular to the jet axis were investigated using a small-scale laboratory facility. Jet decay rate has been varied through use of two cylindrical centerbodies having either a flat or hemispherical tip, which were submerged various distances below the flat plate jet exit plane. Increased jet decay rate, caused by the presence of a center-body or plug in the jet nozzle, led to an increased jet-induced lift loss on the flat plate. Jet-induced lift losses reached 1 percent of the jet thrust for the quickest jet decay rates for plate areas equal to 100 times the effective jet exit area. The observed lift loss versus jet decay rate trend agreed well with results of previous investigations.

Global stability analysis of axisymmetric boundary layer over a circular cylinder

NASA Astrophysics Data System (ADS)

Bhoraniya, Ramesh; Vinod, Narayanan

2018-05-01

This paper presents a linear global stability analysis of the incompressible axisymmetric boundary layer on a circular cylinder. The base flow is parallel to the axis of the cylinder at inflow boundary. The pressure gradient is zero in the streamwise direction. The base flow velocity profile is fully non-parallel and non-similar in nature. The boundary layer grows continuously in the spatial directions. Linearized Navier-Stokes (LNS) equations are derived for the disturbance flow quantities in the cylindrical polar coordinates. The LNS equations along with homogeneous boundary conditions forms a generalized eigenvalues problem. Since the base flow is axisymmetric, the disturbances are periodic in azimuthal direction. Chebyshev spectral collocation method and Arnoldi's iterative algorithm is used for the solution of the general eigenvalues problem. The global temporal modes are computed for the range of Reynolds numbers and different azimuthal wave numbers. The largest imaginary part of the computed eigenmodes is negative, and hence, the flow is temporally stable. The spatial structure of the eigenmodes shows that the disturbance amplitudes grow in size and magnitude while they are moving towards downstream. The global modes of axisymmetric boundary layer are more stable than that of 2D flat-plate boundary layer at low Reynolds number. However, at higher Reynolds number they approach 2D flat-plate boundary layer. Thus, the damping effect of transverse curvature is significant at low Reynolds number. The wave-like nature of the disturbance amplitudes is found in the streamwise direction for the least stable eigenmodes.

Boundary Layer Measurements in a Supersonic Wind Tunnel Using Doppler Global Velocimetry

NASA Technical Reports Server (NTRS)

Meyers, James F.; Lee, Joseph W.; Cavone, Angelo A.

2010-01-01

A modified Doppler Global Velocimeter (DGV) was developed to measure the velocity within the boundary layer above a flat plate in a supersonic flow. Classic laser velocimetry (LV) approaches could not be used since the model surface was composed of a glass-ceramic insulator in support of heat-transfer measurements. Since surface flare limited the use of external LV techniques and windows placed in the model would change the heat transfer characteristics of the flat plate, a novel approach was developed. The input laser beam was divided into nine equal power beams and each transmitted through optical fibers to a small cavity within the model. The beams were then directed through 1.6-mm diameter orifices to form a series of orthogonal beams emitted from the model and aligned with the tunnel centerline to approximate a laser light sheet. Scattered light from 0.1-micron diameter water condensation ice crystals was collected by four 5-mm diameter lenses and transmitted by their respective optical fiber bundles to terminate at the image plane of a standard two-camera DGV receiver. Flow measurements were made over a range from 0.5-mm above the surface to the freestream at Mach 3.51 in steady state and heat pulse injected flows. This technique provides a unique option for measuring boundary layers in supersonic flows where seeding the flow is problematic or where the experimental apparatus does not provide the optical access required by other techniques.

Hypervelocity flows of argon produced in a free piston driven expansion tube

NASA Technical Reports Server (NTRS)

Neely, A. J.; Stalker, R. J.

1992-01-01

An expansion tube with a free piston driver has been used to generate quasi-steady hypersonic flows in argon at flow velocities in excess of 9 km/s. Irregular test flow unsteadiness has limited the performance of previous expansion tubes. Test section measurements of pitot pressure, static pressure, and flat plate heat transfer rates are used to confirm the presence of quasi-steady flow, and comparisons are made with predictions for the equilibrium flow of an ideal, ionizing, monatomic gas. The results of this work indicate that expansion tubes can be used to generate quasi-steady hypersonic flows in argon at speeds in excess of Earth orbital velocity.

Experimental analysis of a Flat Plate Pulsating Heat Pipe with Self-ReWetting Fluids during a parabolic flight campaign

NASA Astrophysics Data System (ADS)

Cecere, Anselmo; De Cristofaro, Davide; Savino, Raffaele; Ayel, Vincent; Sole-Agostinelli, Thibaud; Marengo, Marco; Romestant, Cyril; Bertin, Yves

2018-06-01

A Flat Plate Pulsating Heat Pipe (FPPHP) filled with an ordinary liquid (water) and a self-rewetting mixture (dilutes aqueous solutions of long-chain alcohols with unusual surface tension behavior) is investigated under variable gravity conditions on board a 'Zero-g' plane during the 65th Parabolic Flight Campaign of the European Space Agency. The FPPHP thermal performance in terms of evaporator and condenser temperatures, start-up levels and flow regimes is characterized for the two working fluids and a power input ranging from 0 to 200 W (up to 17 W/cm2 at the heater/evaporator wall interface). The experimental set-up also includes a transparent plate enabling the visualization of the oscillating flow patterns during the experiments. For a low power input (4 W/cm2), the pulsating heat pipe filled with pure water is not able to work under low-g conditions, because the evaporator immediately exhibits dry-out conditions and the fluid oscillations stops, preventing heat transfer between the hot and cold side and resulting in a global increase of the temperatures. On the other hand, the FPPHP filled with the self-rewetting fluid runs also during the microgravity phase. The liquid rewets several times the evaporator zone triggering the oscillatory regime. The self-rewetting fluid helps both the start-up and the thermal performance of the FPPHP in microgravity conditions.

Enhanced heat transfer characteristics of viscous liquid flows in a chevron plate heat exchanger

DOE Office of Scientific and Technical Information (OSTI.GOV)

Muley, A.; Manglik, R.M.; Metwally, H.M.

1999-11-01

Thermal processing and manufacturing in the chemical, foods, pharmaceutical, hygiene products, and biochemical industries invariably involve heating and cooling of highly viscous fluid media. These fluids tend to flow in the low Reynolds number regime, inherently have relatively low heat transfer coefficients, and are often temperature sensitive and prone to thermal degradation in the presence of large temperature differences. In recent times, plate heat exchangers (PHEs) have found increasing usage in such applications, primarily due to their features that promote enhanced heat transfer, and provide for the flexibility in altering their unit thermal size with ease, close approach temperature operation,more » and mitigation of thermal degradation of the process fluid. Here, steady-state heat transfer and pressure drop data for single-phase viscous fluid flows (2 {le} Re {le} 400) in a single-pass U-type counterflow plate heat exchanger (PHE) with chevron plates are presented. With vegetable oil as test fluid (130 {lt} Pr {lt} 290), three different plate arrangements are employed: two symmetric ({beta} = 30 deg/30 deg and 60 deg/60 deg) and one mixed ({beta} = 30 deg/60 deg). The effects of chevron angle {beta}, corrugation aspect ratio {gamma}, and flow conditions (Re, Pr, {mu}/{mu}{sub w}) on Nu and f characteristics of the PHE are delineated. The results show a rather complex influence of plate surface corrugations on the enhanced thermal-hydraulic behavior. Relative to the performance of equivalent flat-plate packs, chevron plates sustain up to 2.9 times higher heat transfer rates on a fixed geometry and constant pumping power basis, and require up to 48% less surface area for the fixed heat load and pressure drop constraint.« less

The Hydrodynamic Characteristics of Modified Rectangular Flat Plates Having Aspect Ratios of 1.00, 0.25, and 0.125 and Operating near a Free Water Surface

NASA Technical Reports Server (NTRS)

Wadlin, Kenneth L; Ramsen, John A; Vaughan, Victor L , Jr

1955-01-01

Report presents the results of an investigation conducted to determine the hydrodynamic forces and moments acting on modified rectangular flat plates with aspect ratios of 1.00, 0.25, and 0.125 mounted on a single strut and operating at several depths of submersion. A simple method has been developed by modification of Falkner's vortex-lattice theory which enables the prediction of the lift characteristics in unseparated flow at large depths. This method shows good agreement with experimental data from the present tests and with aerodynamic data at all angles investigated for aspect ratios of 1.00 and 0.25 and at angles up to 16 degrees for aspect ratio 0.125. Above 16 degrees for aspect ratio 0.125, the predicted lift proved too high.

Numerical solution for the interaction of shock wave with laminar boundary layer in two-dimensional flow on a flat plate. Ph.D. Thesis

NASA Technical Reports Server (NTRS)

Landau, U.

1984-01-01

The finite difference computation method was investigated for solving problems of interaction between a shock wave and a laminar boundary layer, through solution of the complete Navier-Stokes equations. This method provided excellent solutions, was simple to perform and needed a relatively short solution time. A large number of runs for various flow conditions could be carried out from which the interaction characteristics and principal factors that influence interaction could be studied.

Heat-flux gage measurements on a flat plate at a Mach number of 4.6 in the VSD high speed wind tunnel, a feasibility test (LA28). [wind tunnel tests of measuring instruments for boundary layer flow

NASA Technical Reports Server (NTRS)

1975-01-01

The feasibility of employing thin-film heat-flux gages was studied as a method of defining boundary layer characteristics at supersonic speeds in a high speed blowdown wind tunnel. Flow visualization techniques (using oil) were employed. Tabulated data (computer printouts), a test facility description, and photographs of test equipment are given.

A study of the effect of a boundary layer profile on the dynamic response and acoustic radiation of flat panels. Ph.D. Thesis - Virginia Univ.

NASA Technical Reports Server (NTRS)

Mixson, J. S.

1973-01-01

The response of a thin, elastic plate to a harmonic force which drives the plate from below and a compressible air stream with a viscous boundary layer flowing parallel to the upper surface along the length was investigated. Equations governing the forced response of the coupled plate-aerodynamic system are derived along with appropriate boundary conditions. Calculations of basic solution parameters for a linear velocity profile and for a Blasius profile showed that the same system response could be obtained from each profile if appropriate values of boundary layer thickness were chosen for each profile.

Capacitively coupled RF voltage probe having optimized flux linkage

DOEpatents

Moore, James A.; Sparks, Dennis O.

1999-02-02

An RF sensor having a novel current sensing probe and a voltage sensing probe to measure voltage and current. The current sensor is disposed in a transmission line to link all of the flux generated by the flowing current in order to obtain an accurate measurement. The voltage sensor is a flat plate which operates as a capacitive plate to sense voltage on a center conductor of the transmission line, in which the measured voltage is obtained across a resistance leg of a R-C differentiator circuit formed by the characteristic impedance of a connecting transmission line and a capacitance of the plate, which is positioned proximal to the center conductor.

Investigation of the flow-field of two parallel round jets impinging normal to a flat surface

NASA Astrophysics Data System (ADS)

Myers, Leighton M.

The flow-field features of dual jet impingement were investigated through sub-scale model experiments. The experiments were designed to simulate the environment of a Short Takeoff, and Vertical Landing, STOVL, aircraft performing a hover over the ground, at different heights. Two different dual impinging jet models were designed, fabricated, and tested. The Generation 1 Model consisted of two stainless-steel nozzles, in a tandem configuration, each with an exit diameter of approximately 12.7 mm. The front convergent nozzle was operated at the sonic Mach number of 1.0, while the rear C-D nozzle was generally operated supersonically. The nozzles were embedded in a rectangular flat plate, referred to as the lift plate, which represents a generic lifting surface. The lift plate was instrumented with 36 surface pressure taps, which were used to examine the flow entrainment and recirculation patterns caused by varying the stand-off distance from the nozzle exits to a flat ground surface. The stand-off distance was adjusted with a sliding rail frame that the ground plane was mounted to. Typical dimensionless stand-off distances (ground plane separation) were H/DR = 2 to 24. A series of measurements were performed with the Generation 1 model, in the Penn State High Speed Jet Aeroacoustics Laboratory, to characterize the basic flow phenomena associated with dual jet impingement. The regions of interest in the flow-field included the vertical jet plume(s), near impingement/turning region, and wall jet outwash. Other aspects of interest included the loss of lift (suckdown) that occurs as the ground plane separation distance becomes small, and azimuthal variation of the acoustic noise radiation. Various experimental methods and techniques were used to characterize the flow-field, including flow-visualization, pressure rake surveys, surface mounted pressure taps, laser Doppler velocimetry, and acoustic microphone arrays. A second dual impinging jet scale model, Generation 2, was designed and fabricated with a 50% increase in nozzle exit diameter. The primary design improvement is the ability to quickly and easily exchange the nozzles of the model. This allowed experiments to be performed with rapid-prototyped nozzles that feature more realistic geometry to that of tactical military aircraft engines. One such nozzle, which was designed and demonstrated by previous researchers to reduce jet noise in a free-jet, was incorporated into the model. The nozzle, featuring deflected seals, was installed in the Generation 2 model and its effect on suckdown was evaluated.

Forced Convection and Sedimentation Past a Flat Plate

NASA Technical Reports Server (NTRS)

Pelekasis, Nikolaos A.; Acrivos, Andreas

1995-01-01

The steady laminar flow of a well-mixed suspension of monodisperse solid spheres, convected steadily past a horizontal flat plate and sedimenting under the action of gravity, is examined. It is shown that, in the limit as Re approaches infinity and epsilon approaches 0, where Re is the bulk Reynolds number and epsilon is the ratio of the particle radius a to the characteristic length scale L, the analysis for determining the particle concentration profile has several aspects in common with that of obtaining the temperature profile in forced-convection heat transfer from a wall to a fluid stream moving at high Reynolds and Prandtl numbers. Specifically, it is found that the particle concentration remains uniform throughout the O(Re(exp -1/2)) thick Blasius boundary layer except for two O(epsilon(exp 2/3)) thin regions on either side of the plate, where the concentration profile becomes non-uniform owing to the presence of shear-induced particle diffusion which balances the particle flux due to convection and sedimentation. The system of equations within this concentration boundary layer admits a similarity solution near the leading edge of the plate, according to which the particle concentration along the top surface of the plate increases from its value in the free stream by an amount proportional to X(exp 5/6), with X measuring the distance along the plate, and decreases in a similar fashion along the underside. But, unlike the case of gravity settling on an inclined plate in the absence of a bulk flow at infinity considered earlier, here the concentration profile remains continuous everywhere. For values of X beyond the region near the leading edge, the particle concentration profile is obtained through the numerical solution of the relevant equations. It is found that, as predicted from the similarity solution, there exists a value of X at which the particle concentration along the top side of the plate attains its maximum value phi(sub m) and that, beyond this point, a stagnant sediment layer will form that grows steadily in time. This critical value of X is computed as a function of phi(sub s), the particle volume fraction in the free stream. In contrast, but again in conformity with the similarity solution, for values of X sufficiently far removed from the leading edge along the underside of the plate, a particle-free region is predicted to form adjacent to the plate. This model, with minor modifications, can be used to describe particle migration in other shear flows, as, for example, in the case of crossflow microfiltration.

Experimental studies on the tripping behavior of narrow T-stiffened flat plates subjected to hydrostatic pressure and underwater shock

NASA Technical Reports Server (NTRS)

Budweg, H. L.; Shin, Y. S.

1987-01-01

An experimental investigation was conducted to determine the static and dynamic responses of a specific stiffened flat plate design. The air-backed rectangular flat plates of 6061-T6 aluminum with an externally machined longitudinal narrow-flanged T-stiffener and clamped boundary conditions were subjected to static loading by water hydropump pressure and shock loading from an eight pound TNT charge detonated underwater. The dynamic test plate was instrumented to measure transient strains and free field pressure. The static test plate was instrumented to measure transient strains, plate deflection, and pressure. Emphasis was placed upon forcing static and dynamic stiffener tripping, obtaining relevant strain and pressure data, and studying the associated plate-stiffener behavior.

A finite element computation of turbulent boundary layer flows with an algebraic stress turbulence model

NASA Technical Reports Server (NTRS)

Kim, Sang-Wook; Chen, Yen-Sen

1988-01-01

An algebraic stress turbulence model and a computational procedure for turbulent boundary layer flows which is based on the semidiscrete Galerkin FEM are discussed. In the algebraic stress turbulence model, the eddy viscosity expression is obtained from the Reynolds stress turbulence model, and the turbulent kinetic energy dissipation rate equation is improved by including a production range time scale. Good agreement with experimental data is found for the examples of a fully developed channel flow, a fully developed pipe flow, a flat plate boundary layer flow, a plane jet exhausting into a moving stream, a circular jet exhausting into a moving stream, and a wall jet flow.

Convective diffusion in protein crystal growth

NASA Technical Reports Server (NTRS)

Baird, J. K.; Meehan, E. J., Jr.; Xidis, A. L.; Howard, S. B.

1986-01-01

A protein crystal modeled as a flat plate suspended in the parent solution, with the normal to the largest face perpendicular to gravity and the protein concentration in the solution adjacent to the plate taken to be the equilibrium solubility, is studied. The Navier-Stokes equation and the equation for convective diffusion in the boundary layer next to the plate are solved to calculate the flow velocity and the protein mass flux. The local rate of growth of the plate is shown to vary significantly with depth due to the convection. For an aqueous solution of lysozyme at a concentration of 40 mg/ml, the boundary layer at the top of a 1-mm-high crystal has a thickness of 80 microns at 1 g, and 2570 microns at 10 to the -6th g.

Receptivity of flat-plate boundary layer in a non-uniform free stream (vorticity normal to the plate)

NASA Technical Reports Server (NTRS)

Kogan, M. N.

1994-01-01

Recent progress in both the linear and nonlinear aspects of stability theory has highlighted the importance of the receptivity problem. One of the most unclear aspects of receptivity study is the receptivity of boundary-layer flow normal to vortical disturbances. Some experimental and theoretical results permit the proposition that quasi-steady outer-flow vortical disturbances may trigger by-pass transition. In present work such interaction is investigated for vorticity normal to a leading edge. The interest in these types of vortical disturbances arise from theoretical work, where it was shown that small sinusoidal variations of upstream velocity along the spanwise direction can produce significant variations in the boundary-layer profile. In the experimental part of this work, such non-uniform flow was created and the laminar-turbulent transition in this flow was investigated. The experiment was carried out in a low-turbulence direct-flow wind tunnel T-361 at the Central Aerohydrodynamic Institute (TsAGI). The non-uniform flow was produced by laminar or turbulent wakes behind a wire placed normal to the plate upstream of the leading edge. The theoretical part of the work is devoted to studying the unstable disturbance evolution in a boundary layer with strongly non-uniform velocity profiles similar to that produced by outer-flow vorticity. Specifically, the Tollmien-Schlichting wave development in the boundary layer flow with spanwise variations of velocity is investigated.

Development of a selective thin film and of a hermetically sealed flat plate solar collector with gas filling

NASA Astrophysics Data System (ADS)

Zernial, W.

1982-12-01

The industrial productibility of a selective absorbing thin film was investigated on the basis of reactive cathodic sputtering of Ni. On substrates of 1.8 sq m of Al, Cu, steel and stainless steel, solar absorption values up to 97% were achieved at emissivities of 5 to 10%. A prototype flat plate collector for high temperatures with two covers and hermetical sealing was developed. The technical data of the collector were measured, dependent on the selectivity of the absorber, gas fillings of dry air, argon or SF6 and the geometry and were compared with those of an evacuated flat plate collector. A hermetical sealed double flat plate collector for low temperatures was developed which has the advantage of lower no load temperatures and higher energy gain for heating swimming pool water compared with a conventional flat plate collector. The insolation values on collectors were measured and were used for a calculation of the energy gains of different collector types.

Experimental study of surface pressures induced on a flat plate and a body of revolution by various dual jet configurations. [wind tunnel tudies of a jet in a cross flow for V/STOL applications

NASA Technical Reports Server (NTRS)

Schetz, J. A.; Jakubowski, A. K.

1982-01-01

The effect of the angle of a jet to a crossflow, the performance of dual jet configurations, and a jet injected from a body of revolution as opposed to a flat plate were investigated during experiments conducted in the 7x10 tunnel at NASA Ames at Velocities from 14.5 m/sec to 35.8 m/sec (47.6 to 117.4 ft/sec.). Pressure distributions are presented for single and dual jets over a range of velocity ratios from 2 to 10, spacings from 2 to 6 diameters and injection angles of 90, 75, 60, and 105 degrees. For the body of revolution tests, the ratio of the jet to body diameters was set as large (1/2) in order to be more representative of V/STOL aircraft applications. Flat plate tests involved dual jets both aligned and in side by side configurations. The effects of the various parameters and the differences between the axisymmetric and planar body geometrics on the nature, size, shape, and strength of the interaction regions on the body surfaces are shown. Some flowfield measurements are also presented, and it is shown that a simple analysis is capable of predicting the trajectories of the jets.

Investigation of Heat Transfer to a Flat Plate in a Shock Tube.

DTIC Science & Technology

1987-12-01

2 Objectives and Scope . . . . . .. .. .. .... 5 11. Theory ............... ....... 7 Shock Tube Principles........... 7 Boundary Layer Theory ...in *excess of theory , but the rounded edge flat plate exhibited data which matched or was less than what theory predicted for each Mach number tested...normal shock advancing along an infinite flat plate. For x< Ugt there is a region of interaction between the downstream influence of the leading edge

Elastic Buckling under Combined Stresses of Flat Plates with Integral Waffle-Like Stiffening

NASA Technical Reports Server (NTRS)

Dow, Norris F.; Levin, L. Ross; Troutman, John L.

1953-01-01

Theory and experiment were compared and found in good agreement for the elastic Buckling under combined stresses of long flat plates with integral waffle-like stiffening in a variety of configurations. For such flat plates, 45deg waffle stiffening was found to be the most effective of the configurations for the proportions considered over the widest range of combinations of compression and shear.

Elastic Buckling Under Combined Stresses of Flat Plates with Integral Waffle-like Stiffening

NASA Technical Reports Server (NTRS)

Dow, Norris F; Levin, L Ross; Troutman, John L

1954-01-01

Theory and experiment were compared and found in good agreement for the elastic buckling under combined stresses of long flat plates with integral waffle-like stiffening in a variety of configurations. For such flat plates, 45 degree waffle stiffening was found to be the most effective of the configurations for the proportions considered over the widest range of combinations of compression and shear.

High Reynolds number analysis of flat plate and separated afterbody flow using non-linear turbulence models

NASA Technical Reports Server (NTRS)

Carlson, John R.

1996-01-01

The ability of the three-dimensional Navier-Stokes method, PAB3D, to simulate the effect of Reynolds number variation using non-linear explicit algebraic Reynolds stress turbulence modeling was assessed. Subsonic flat plate boundary-layer flow parameters such as normalized velocity distributions, local and average skin friction, and shape factor were compared with DNS calculations and classical theory at various local Reynolds numbers up to 180 million. Additionally, surface pressure coefficient distributions and integrated drag predictions on an axisymmetric nozzle afterbody were compared with experimental data from 10 to 130 million Reynolds number. The high Reynolds data was obtained from the NASA Langley 0.3m Transonic Cryogenic Tunnel. There was generally good agreement of surface static pressure coefficients between the CFD and measurement. The change in pressure coefficient distributions with varying Reynolds number was similar to the experimental data trends, though slightly over-predicting the effect. The computational sensitivity of viscous modeling and turbulence modeling are shown. Integrated afterbody pressure drag was typically slightly lower than the experimental data. The change in afterbody pressure drag with Reynolds number was small both experimentally and computationally, even though the shape of the distribution was somewhat modified with Reynolds number.

Application of the High Gradient hydrodynamics code to simulations of a two-dimensional zero-pressure-gradient turbulent boundary layer over a flat plate

NASA Astrophysics Data System (ADS)

Kaiser, Bryan E.; Poroseva, Svetlana V.; Canfield, Jesse M.; Sauer, Jeremy A.; Linn, Rodman R.

2013-11-01

The High Gradient hydrodynamics (HIGRAD) code is an atmospheric computational fluid dynamics code created by Los Alamos National Laboratory to accurately represent flows characterized by sharp gradients in velocity, concentration, and temperature. HIGRAD uses a fully compressible finite-volume formulation for explicit Large Eddy Simulation (LES) and features an advection scheme that is second-order accurate in time and space. In the current study, boundary conditions implemented in HIGRAD are varied to find those that better reproduce the reduced physics of a flat plate boundary layer to compare with complex physics of the atmospheric boundary layer. Numerical predictions are compared with available DNS, experimental, and LES data obtained by other researchers. High-order turbulence statistics are collected. The Reynolds number based on the free-stream velocity and the momentum thickness is 120 at the inflow and the Mach number for the flow is 0.2. Results are compared at Reynolds numbers of 670 and 1410. A part of the material is based upon work supported by NASA under award NNX12AJ61A and by the Junior Faculty UNM-LANL Collaborative Research Grant.

Three-dimensional characterization and control of Tollmien-Schlichting waves on a flat plate

NASA Astrophysics Data System (ADS)

Tuna, Burak; Amitay, Michael

2014-11-01

Tollmien-Schlichting (T-S) waves are instability waves inside the boundary layer which are the prime mechanism for the transition from laminar to turbulent flows. The T-S waves grow in amplitude and develop three-dimensionality as they advect downstream. At sufficiently large amplitude they break up into turbulent spots, followed by a turbulent flow, which yields a drag increase. The present work aims to identify the T-S waves and reduce their amplitude to delay transition to turbulence. For that propose, Piezoelectric-Driven Oscillating Surface (PDOS) actuator was developed; Two PDOS actuators were used are two stream wise locations. The upstream PDOS was used to excite and phase-lock the T-S waves, and the downstream PDOS was used to cancel the T-S waves by applying an anti phase disturbance at the proper amplitude. Stereoscopic particle image velocimetry (SPIV) was used to identify the three-dimensional development of the T-S waves along the flat plate. Moreover, the SPIV results showed that reduction of peak values of velocity fluctuations due to the T-S waves could be achieved, and this reduction corresponds to a delay of laminar to turbulent transition.

Quadratic Convective Flow of a Micropolar Fluid along an Inclined Plate in a Non-Darcy Porous Medium with Convective Boundary Condition

NASA Astrophysics Data System (ADS)

RamReddy, Ch.; Naveen, P.; Srinivasacharya, D.

2017-06-01

The objective of the present study is to investigate the effect of nonlinear variation of density with temperature and concentration on the mixed convective flow of a micropolar fluid over an inclined flat plate in a non-Darcy porous medium in the presence of the convective boundary condition. In order to analyze all the essential features, the governing non-dimensional partial differential equations are transformed into a system of ordinary differential equations using a local non-similarity procedure and then the resulting boundary value problem is solved using a successive linearisation method (SLM). By insisting the comparison between vertical, horizontal and inclined plates, the physical quantities of the flow and its characteristics are exhibited graphically and quantitatively with various parameters. An increase in the micropolar parameter and non-Darcy parameter tend to increase the skin friction and the reverse change is observed in wall couple stress, mass and heat transfer rates. The influence of the nonlinear concentration parameter is more prominent on all the physical characteristics of the present model, compared with that of nonlinear temperature parameter.

Mobility power flow analysis of an L-shaped plate structure subjected to distributed loading

NASA Technical Reports Server (NTRS)

Cuschieri, J. M.; Cimmerman, B.

1990-01-01

An analytical investigation based in the Mobility Power Flow (MPF) method is presented for the determination of the vibrational response and power flow for two coupled flat plate structures in an L-shaped configuration, subjected to distributed excitation. The principle of the MPF method consists of dividing the global structure into a series of subsystems coupled together using mobility functions. Each separate subsystem is analyzed independently to determine the structural mobility functions for the junction and excitation locations. The mobility functions, together with the characteristics of the junction between the subsystems, are then used to determine the response of the global structure and the MPF. In the considered coupled plate structure, MPF expressions are derived for distributed mechanical excitation which is independent of the structure response. However using a similar approach with some modifications excitation by an acoustic plane wave can be considered. Some modifications are required to deal with the latter case are necessary because the forces (acoustic pressure) acting on the structure are dependent on the response of the structure due to the presence of the scattered pressure.

Skin friction enhancement in a model problem of undulatory swimming

NASA Astrophysics Data System (ADS)

Ehrenstein, Uwe; Eloy, Christophe

2013-10-01

To calculate the energy costs of swimming, it is crucial to evaluate the drag force originating from skin friction. In this paper we examine the assumption, known as the 'Bone-Lighthill boundary-layer thinning hypothesis', that undulatory swimming motions induce a drag increase because of the compression of the boundary layer. Studying analytically an incoming flow along a flat plate moving at a normal velocity as a limit case of a yawed cylinder in uniform flow under the laminar boundary layer assumption, we demonstrate that the longitudinal drag scales as the square root of the normal velocity component. This analytical prediction is interpreted in the light of a three-dimensional numerical simulation result for a plate of finite length and width. An analogous two-dimensional Navier-Stokes problem by artificially accelerating the flow in a channel of finite height is proposed and solved numerically, showing the robustness of the analytical results. Solving the problem for an undulatory plate motion similar to fish swimming, we find a drag enhancement which can be estimated to be of the order of 20 %.

Fuel cell separator plate with bellows-type sealing flanges

DOEpatents

Louis, G.A.

1984-05-29

A fuel cell separator includes a rectangular flat plate having two unitary upper sealing flanges respectively comprising opposite marginal edges of the plate folded upwardly and back on themselves and two lower sealing flanges respectively comprising the other two marginal edges of the plate folded downwardly and back on themselves. Each of the sealing flanges includes a flat wall spaced from the plate and substantially parallel thereto and two accordion-pleated side walls, one of which interconnects the flat wall with the plate and the other of which steps just short of the plate, these side walls affording resilient compressibility to the sealing flange in a direction generally normal to the plane of the plate. Four corner members close the ends of the sealing flanges. An additional resiliently compressible reinforcing member may be inserted in the passages formed by each of the sealing flanges with the plate.

Fuel cell separator plate with bellows-type sealing flanges

DOEpatents

Louis, George A.

1986-08-05

A fuel cell separator includes a rectangular flat plate having two unitary upper sealing flanges respectively comprising opposite marginal edges of the plate folded upwardly and back on themselves and two lower sealing flanges respectively comprising the other two marginal edges of the plate folded downwardly and back on themselves. Each of the sealing flanges includes a flat wall spaced from the plate and substantially parallel thereto and two accordion-pleated side walls, one of which interconnects the flat wall with the plate and the other of which stops just short of the plate, these side walls affording resilient compressibility to the sealing flange in a directiongenerally normal to the plane of the plate. Four corner members close the ends of the sealing flanges. An additional resiliently compressible reinforcing member may be inserted in the passages formed by each of the sealing flanges with the plate.

Effect of specific surface microstructures on substrate endothelialisation and thrombogenicity: Importance for stent design.

PubMed

Lutter, Christoph; Nothhaft, Matthias; Rzany, Alexander; Garlichs, Christoph D; Cicha, Iwona

2015-01-01

In coronary artery disease, highly stenosed arteries are frequently treated by stent implantation, which thereafter necessitates a dual-antiplatelet therapy (DAPT) in order to prevent stent-thrombosis. We hypothesized that specific patterns of microstructures on stents can accelerate endothelialisation thereby reducing their thrombogenicity and the DAPT duration. Differently designed, 2-5 μm high elevations or hollows were lithographically etched on silicon plates, subsequently coated with silicon carbide. Smooth silicon plates and bare metal substrates were used as controls. To assess attachment and growth of human umbilical vein endothelial cells under static or flow conditions, actin cytoskeleton was visualised with green phalloidin. Endothelial migration was assessed in a modified barrier assay. To investigate surface thrombogenicity, platelets were incubated on the structured surfaces in static and flow conditions, and visualised with fluorescein-conjugated P-selectin antibody. Images were taken with incident-light fluorescent microscope for non-transparent objects. Compared to smooth surface, flat cubic elevations (5 μm edge length) improved endothelial cell attachment and growth under static and dynamic conditions, whereas smaller, spiky structures (2 μm edge length) had a negative influence on endothelialisation. Endothelial cell migration was fastest on flat cubic elevations, hollows, and smooth surfaces, whereas spiky structures and bare metal had a negative effect on endothelial migration. Thrombogenicity assays under static and flow conditions showed that platelet adhesion was reduced on the flat elevations and the smooth surface, as compared to the spiky structures, the hollow design and the bare metal substrates. Surface microstructures strongly influence endothelialisation of substrates. Designing stents with surface topography which accelerates endothelialisation and reduces thrombogenicity may be of clinical benefit by improving the safety profile of coronary interventions.

Influence of leading edge bluntness on hypersonic flow in a generic internal-compression inlet

NASA Astrophysics Data System (ADS)

Borovoy, V.; Egorov, I.; Mosharov, V.; Radchenko, V.; Skuratov, A.; Struminskaya, I.

2015-06-01

Flow and heat transfer inside a generic inlet are investigated experimentally. The cross section of the inlet is rectangular. The inlet is installed on a flat plat at a significant distance from the leading edge. The experiments are performed in TsAGI wind tunnel UT-1M working in the Ludwieg tube mode at Mach number M∞ = 5 and Reynolds numbers (based on the plate length L = 320 mm) Re∞L = 23 · 106 and 13 · 106. Steady flow duration is 40 ms. Optical panoramic methods are used for investigation of flow outside and inside the inlet as well. For this purpose, the cowl and one of two compressing wedges are made of a transparent material. Heat flux distribution is measured by thin luminescent Temperature Sensitive Paint (TSP). Surface flow and shear stress visualization is performed by viscous oil containing luminophor particles. The investigation shows that at high contraction ratio of the inlet, an increase of plate or cowl bluntness to some critical value leads to sudden change of the flow structure.

Two-dimensional steady bow waves in water of finite depth

NASA Astrophysics Data System (ADS)

Kao, John

1998-12-01

In this study, the two-dimensional steady bow flow in water of arbitrary finite depth has been investigated. The two-dimensional bow is assumed to consist of an inclined flat plate connected downstream to a horizontal semi-infinite draft plate. The bottom of the channel is assumed to be a horizontal plate; the fluid is assumed to be inviscid, incompressible; and the flow irrotational. For the angle of incidence α (held by the bow plate) lying between 0o and 60o, the local flow analysis near the stagnation point shows that the angle lying between the free surface and the inclined plate, β, must always be equal to 120o, otherwise no solution can exist. Moreover, we further find that the local flow solution does not exist if /alpha > 60o, and that on the inclined plate there exists a negative pressure region adjacent to the stagnation point for /alpha < 30o. Singularities at the stagnation point and the upstream infinity are found to have multiple branch-point singularities of irrational orders. A fully nonlinear theoretical model has been developed in this study for evaluating the incompressible irrotational flow satisfying the free-surface conditions and two constraint equations. To solve the bow flow problem, successive conformal mappings are first used to transform the flow domain into the interior of a unit semi-circle in which the unknowns can be represented as the coefficients of an infinite series. A total error function equivalent to satisfying the Bernoulli equation is defined and solved by minimizing the error function and applying the method of Lagrange's multiplier. Smooth solutions with monotonic free surface profiles have been found and presented here for the range of 35o < /alpha < 60o, a draft Froude number Frd less than 0.5, and a water-depth Froude number Frh less than 0.4. The dependence of the solution on these key parameters is examined. Our results may be useful in designing the optimum bow shape.

Engineering applications and analysis of vibratory motion fourth order fluid film over the time dependent heated flat plate

NASA Astrophysics Data System (ADS)

Mohmand, Muhammad Ismail; Mamat, Mustafa Bin; Shah, Qayyum

2017-07-01

This article deals with the time dependent analysis of thermally conducting and Magneto-hydrodynamic (MHD) liquid film flow of a fourth order fluid past a vertical and vibratory plate. In this article have been developed for higher order complex nature fluids. The governing-equations have been modeled in the terms of nonlinear partial differential equations with the help of physical boundary circumstances. Two different analytical approaches i.e. Adomian decomposition method (ADM) and the optimal homotopy asymptotic method (OHAM), have been used for discoveryof the series clarification of the problems. Solutions obtained via two diversemethods have been compared using the graphs, tables and found an excellent contract. Variants of the embedded flow parameters in the solution have been analysed through the graphical diagrams.

An integral wall model for Large Eddy Simulation (iWMLES) and applications to developing boundary layers over smooth and rough plates

NASA Astrophysics Data System (ADS)

Yang, Xiang; Sadique, Jasim; Mittal, Rajat; Meneveau, Charles

2014-11-01

A new wall model for Large-Eddy-Simulations is proposed. It is based on an integral boundary layer method that assumes a functional form for the local mean velocity profile. The method, iWMLES, evaluates required unsteady and advective terms in the vertically integrated boundary layer equations analytically. The assumed profile contains a viscous or roughness sublayer, and a logarithmic layer with an additional linear term accounting for inertial and pressure gradient effects. The iWMLES method is tested in the context of a finite difference LES code. Test cases include developing turbulent boundary layers on a smooth flat plate at various Reynolds numbers, over flat plates with unresolved roughness, and a sample application to boundary layer flow over a plate that includes resolved roughness elements. The elements are truncated cones acting as idealized barnacle-like roughness elements that often occur in biofouling of marine surfaces. Comparisons with data show that iWMLES provides accurate predictions of near-wall velocity profiles in LES while, similarly to equilibrium wall models, its cost remains independent of Reynolds number and is thus significantly lower compared to standard zonal or hybrid wall models. This work is funded by ONR Grant N00014-12-1-0582 (Dr. R. Joslin, program manager).

Effect of controlled spanwise bending on the stability of the leading-edge vortex

NASA Astrophysics Data System (ADS)

Bhattacharya, Samik; Scofield, Tyler

2017-11-01

When an airfoil is accelerated from rest at a high angle of attack, a leading-edge vortex (LEV) forms, which soon gets destabilized and convects downstream. In this work, we control the spanwise bending of a flat plate wing to actively influence the vorticity transfer from the LEV. Our aim is to investigate the effect of spanwise curvature variation on the geometry, growth, and stability of the LEV during the acceleration phase. A 3D printed flat-plate with a chord of 5 cm and span of 15 cm is towed in a small fish tank at different angles of attack greater than 15°. The plate starts from rest and reaches a Reynolds number of 5000 after travelling different multiples and submultiples of chord-length. We carry out dye-flow visualization and measure the circulation build up and the convection velocity of the LEV with the help of particle image velocimetry (PIV). The unsteady loads coming on to the wing is measured with a force sensor. An analytical scheme for computing the load from the measured displacement of the plate is presented and compared with the force sensor data. Preliminary results indicate that controlled curvature variation can influence the formation and stability of an LEV.

Advanced solar box and flat plate collector cookers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Grupp, M.; Bergler, H.

Several new solar cooker systems have been developed at Synopsis during the last years: advanced box type cookers, featuring an optimized heat transfer from the absorber into the cooking vessel; flat plate cookers, based on a particular two-way collector with air as transfer fluid; flat plate cookers with heat-pipe transfer; specialized cookers for the baking of bread and flat bread. The working principle of these cookers is described, the structure of a thermal simulation model and results of thermal tests are presented. The results of the first year of local production and use of advanced boxes in India are reported.

Connecting the surface to the deep: Flat-slab subduction dynamics and the evolution of western Amazonia

NASA Astrophysics Data System (ADS)

Eakin, C. M.

2017-12-01

Plate tectonics is primarily driven by the subduction of cold dense oceanic slabs. It has yet to be fully understood however how variations in slab morphology and buoyancy influence the surrounding mantle dynamics, and what difference if any is seen at the surface. An excellent natural laboratory to answer such questions is found along the Andean margin where the world's largest flat slab is presently subducting beneath much of Peru. Following the deployment of broadband seismic arrays across the region, mantle flow both beneath and above the flat-slab is investigated using targeted shear-wave splitting techniques that detect seismic anisotropy and the pattern of mantle deformation. The along strike change in slab dip angle and buoyancy content is found to exert a strong control over the surrounding mantle flow field. Modeling of the induced mantle flow, and the dynamic topography at the surface that results, predicts a wave of dynamic subsidence that propagates away from the trench as the flat slab develops. This is found to correlate well with the record of widespread sediment deposition across western Amazonia during the Miocene. A combination of uplift, flexure and dynamic topography during slab flattening is proposed to explain the overall landscape evolution of the region and the subsequent configuration of the transcontinental Amazon drainage system we see today.

78 FR 69371 - Diffusion-Annealed, Nickel-Plated Flat-Rolled Steel Products From Japan: Preliminary...

Federal Register 2010, 2011, 2012, 2013, 2014

2013-11-19

... Memorandum 1. Background 2. Scope of the Investigation 3. Respondent Selection 4. Discussion of Methodology a...: Scope of the Investigation The diffusion-annealed, nickel-plated flat-rolled steel products included in this investigation are flat-rolled, cold-reduced steel products, regardless of chemistry; whether or...

Effects of the foil flatness on the stress-strain characteristics of U10Mo alloy based monolithic mini-plates

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hakan Ozaltun; Pavel Medvedev

The effects of the foil flatness on stress-strain behavior of monolithic fuel mini-plates during fabrication and irradiation were studied. Monolithic plate-type fuels are a new fuel form being developed for research and test reactors to achieve higher uranium densities. This concept facilitates the use of low-enriched uranium fuel in the reactor. These fuel elements are comprised of a high density, low enrichment, U–Mo alloy based fuel foil encapsulated in a cladding material made of Aluminum. To evaluate the effects of the foil flatness on the stress-strain behavior of the plates during fabrication, irradiation and shutdown stages, a representative plate frommore » RERTR-12 experiments (Plate L1P756) was considered. Both fabrication and irradiation processes of the plate were simulated by using actual irradiation parameters. The simulations were repeated for various foil curvatures to observe the effects of the foil flatness on the peak stress and strain magnitudes of the fuel elements. Results of fabrication simulations revealed that the flatness of the foil does not have a considerable impact on the post fabrication stress-strain fields. Furthermore, the irradiation simulations indicated that any post-fabrication stresses in the foil would be relieved relatively fast in the reactor. While, the perfectly flat foil provided the slightly better mechanical performance, overall difference between the flat-foil case and curved-foil case was not significant. Even though the peak stresses are less affected, the foil curvature has several implications on the strain magnitudes in the cladding. It was observed that with an increasing foil curvature, there is a slight increase in the cladding strains.« less

Boundary-Layer Bypass Transition Over Large-Scale Bodies

DTIC Science & Technology

2016-12-16

shape of the streamwise velocity profile compared to the flat- plate boundary layer. The research showed that the streamwise wavenumber plays a key role...many works on the suppression of the transitional boundary layer. Most of the results in the literature are for the flat- plate boundary layer but the...behaviour of the velocity and pressure changes with the curvature. This work aims to extend the results of the flat- plate boundary layer to a Rankine

Vortex flow hysteresis

NASA Technical Reports Server (NTRS)

Cunningham, A. M., Jr.

1986-01-01

An experimental study was conducted to quantify the hysteresis associated with various vortex flow transition points and to determine the effect of planform geometry. The transition points observed consisted of the appearance (or disappearance) of trailing edge vortex burst and the transition to (or from) flat plate or totally separated flows. Flow visualization with smoke injected into the vortices was used to identify the transitions on a series of semi-span models tested in a low speed tunnel. The planforms tested included simple deltas (55 deg to 80 deg sweep), cranked wings with varying tip panel sweep and dihedral, and a straked wing. High speed movies at 1000 frames per second were made of the vortex flow visualization in order to better understand the dynamics of vortex flow, burst and transition.

Relative potentials of concentrating and two-axis tracking flat-plate photovoltaic arrays for central-station applications

NASA Technical Reports Server (NTRS)

Borden, C. S.; Schwartz, D. L.

1984-01-01

The purpose of this study is to assess the relative economic potentials of concenrating and two-axis tracking flat-plate photovoltaic arrays for central-station applications in the mid-1990's. Specific objectives of this study are to provide information on concentrator photovoltaic collector probabilistic price and efficiency levels to illustrate critical areas of R&D for concentrator cells and collectors, and to compare concentrator and flat-plate PV price and efficiency alternatives for several locations, based on their implied costs of energy. To deal with the uncertainties surrounding research and development activities in general, a probabilistic assessment of commercially achievable concentrator photovoltaic collector efficiencies and prices (at the factory loading dock) is performed. The results of this projection of concentrator photovoltaic technology are then compared with a previous flat-plate module price analysis (performed early in 1983). To focus this analysis on specific collector alternatives and their implied energy costs for different locations, similar two-axis tracking designs are assumed for both concentrator and flat-plate options.

Pressure and heating-rate distributions on a corrugated surface in a supersonic turbulent boundary layer

NASA Technical Reports Server (NTRS)

Sawyer, J. W.

1977-01-01

Drag and heating rates on wavy surfaces typical of current corrugated plate designs for thermal protection systems were determined experimentally. Pressure-distribution, heating-rate, and oil-flow tests were conducted in the Langley Unitary Plan wind tunnel at Mach numbers of 2.4 and 4.5 with the corrugated surface exposed to both thick and thin turbulent boundary layers. Tests were conducted with the corrugations at cross-flow angles from 0 deg to 90 deg to the flow. Results show that for cross-flow angles of 30 deg or less, the pressure drag coefficients are less than the local flat-plate skin-friction coefficients and are not significantly affected by Mach number, Reynolds number, or boundary-layer thickness over the ranges investigated. For cross-flow angles greater than 30 deg, the drag coefficients increase significantly with cross-flow angle and moderately with Reynolds number. Increasing the Mach number causes a significant reduction in the pressure drag. The average and peak heating penalties due to the corrugated surface are small for cross-flow angles of 10 deg or less but are significantly higher for the larger cross-flow angles.

Solar-heated and cooled savings and loan building-1-Leavenworth, Kanasas

NASA Technical Reports Server (NTRS)

1981-01-01

Report describes heating and cooling system which furnishes 90 percent of annual heating load, 70 percent of cooling load, and all hot water for two-story building. Roof-mounted flat-plate collectors allow three distinct flow rates and are oriented south for optimum energy collection. Building contains fully automated temperature controls is divided into five temperature-load zones, each with independent heat pump.

Receptivity of Flat-Plate Boundary Layer in a Non-Uniform Free Stream (Vorticity Normal to the Plate)

NASA Technical Reports Server (NTRS)

Kogan, M. N.; Ustinov, M. V.

1997-01-01

Work is devoted to study of free-stream vorticity normal to leading edge interaction with boundary layer over plate and resulting flow distortion influence on laminar-turbulent transition. In experiments made the wake behind the vertically stretched wire was used as a source of vortical disturbances and its effect on the boundary layer over the horizontally mounted plate with various leading edge shapes was investigated. The purpose of experiments was to check the predictions of theoretical works of M.E. Goldstein, et. al. This theory shows that small free-stream inhomogeneity interacting with leading edge produces considerable distortion of boundary layer flow. In general, results obtained confirms predictions of Goldstein's theory, i.e., the amplification of steady vortical disturbances in boundary layer caused by vortex lines stretching was observed. Experimental results fully coincide with predictions of theory for large Reynolds number, relatively sharp leading edge and small disturbances. For large enough disturbances the flow distortion caused by symmetric wake unexpectedly becomes antisymmetric in spanwise direction. If the leading edge is too blunt the maximal distortion takes place immediately at the nose and no further amplification was observed. All these conditions and results are beyond the scope of Goldstein's theory.

Experimental Studies on the Effects of Thermal Bumps in the Flow-Field around a Flat Plate using a Hypersonic Wind Tunnel

DTIC Science & Technology

2012-07-01

Form Approved OMB No. 0704-0188 Public reporting burden for this collection of information is estimated to average 1 hour per response, including the...PLEASE DO NOT RETURN YOUR FORM TO THE ABOVE ADDRESS. 1 . REPORT DATE (DD-MM-YYYY) 12 July 2012 2. REPORT TYPE Final Report 3. DATES COVERED...From – To) 1 October 2008 – 31 January 2012 4. TITLE AND SUBTITLE Experimental Studies on the Effects of Thermal Bumps in the Flow-Field around a

Skin-Friction Measurements in Incompressible Flow

NASA Technical Reports Server (NTRS)

Smith, Donald W.; Walker, John H.

1959-01-01

Experiments have been conducted to measure the local surface-shear stress and the average skin-friction coefficient in Incompressible flow for a turbulent boundary layer on a smooth flat plate having zero pressure gradient. Data were obtained for a range of Reynolds numbers from 1 million to 45 million. The local surface-shear stress was measured by a floating-element skin-friction balance and also by a calibrated total head tube located on the surface of the test wall. The average skin-friction coefficient was obtained from boundary-layer velocity profiles.

A study of wind effects on collector performance

DOE Office of Scientific and Technical Information (OSTI.GOV)

Onur, N.; Hewitt, J.C. Jr.

1980-08-01

Convective heat transfer experiments have been run on flat-plate collectors for tilt angles ranging from the horizontal to the vertical and for five different flow velocities. Experimental data are used to evaluate the currently used models, namely, those of Jurges (1924), Drake (1948), and Sparrow et al (1970-79), and it is shown that although none of these models provides an exact fit, they do represent bounds for the present data. It is also shown that the effect of flow from the northern quadrants provides an additional heat loss reduction of 10 to 20%.

Cascade aeroacoustics including steady loading effects

NASA Astrophysics Data System (ADS)

Chiang, Hsiao-Wei D.; Fleeter, Sanford

A mathematical model is developed to analyze the effects of airfoil and cascade geometry, steady aerodynamic loading, and the characteristics of the unsteady flow field on the discrete frequency noise generation of a blade row in an incompressible flow. The unsteady lift which generates the noise is predicted with a complex first-order cascade convected gust analysis. This model was then applied to the Gostelow airfoil cascade and variations, demonstrating that steady loading, cascade solidity, and the gust direction are significant. Also, even at zero incidence, the classical flat plate cascade predictions are unacceptable.

Flow visualization of film cooling with spanwise injection from a small array of holes and compound-angle injection from a large array

NASA Technical Reports Server (NTRS)

Russell, L. M.

1978-01-01

Film injection from discrete holes in a smooth, flat plate was studied for two configurations: (1) spanwise injection through a four hole staggered array; and (2) compound angle injection through a 49 hole staggered array. The ratio of boundary layer thicknesses to hole diameter and the Reynolds number were typical of gas turbine film cooling applications. Streaklines showing the motion of the injected air were obtained by photographing small, neutrally buoyant, helium-filled soap bubbles that followed the flow field.

Experimental studies on the aerodynamic performance and dynamic response of flow direction sensing vanes

NASA Technical Reports Server (NTRS)

Barna, P. S.; Crossman, G. R.

1976-01-01

Systematic investigations were performed on a variety of aerodynamic surfaces to obtain their potential for possible application to wind vanes. Among the surfaces tested were: (1) single vanes consisting of flat plates of various planforms having aspect ratios between 0.5 and 5; (2) bi-vanes with aspect ratio 2.5; (3) various cone and box vanes; and (4) various cruciform configurations. The models were subjected to windtunnel tests. In addition to lift and drag force measurements, damping and frequency test were performed under a variety of flow conditions.

Disturbances to Air-Layer Skin-Friction Drag Reduction at High Reynolds Numbers

NASA Astrophysics Data System (ADS)

Dowling, David; Elbing, Brian; Makiharju, Simo; Wiggins, Andrew; Perlin, Marc; Ceccio, Steven

2009-11-01

Skin friction drag on a flat surface may be reduced by more than 80% when a layer of air separates the surface from a flowing liquid compared to when such an air layer is absent. Past large-scale experiments utilizing the US Navy's Large Cavitation Channel and a flat-plate test model 3 m wide and 12.9 m long have demonstrated air layer drag reduction (ALDR) on both smooth and rough surfaces at water flow speeds sufficient to reach downstream-distance-based Reynolds numbers exceeding 100 million. For these experiments, the incoming flow conditions, surface orientation, air injection geometry, and buoyancy forces all favored air layer formation. The results presented here extend this prior work to include the effects that vortex generators and free stream flow unsteadiness have on ALDR to assess its robustness for application to ocean-going ships. Measurements include skin friction, static pressure, airflow rate, video of the flow field downstream of the injector, and profiles of the flowing air-water mixture when the injected air forms bubbles, when it is in transition to an air layer, and when the air layer is fully formed. From these, and the prior measurements, ALDR's viability for full-scale applications is assessed.

Convective heat transfer studies at high temperatures with pressure gradient for inlet flow Mach number of 0.45

NASA Technical Reports Server (NTRS)

Pedrosa, A. C. F.; Nagamatsu, H. T.; Hinckel, J. A.

1984-01-01

Heat transfer measurements were determined for a flat plate with and without pressure gradient for various free stream temperatures, wall temperature ratios, and Reynolds numbers for an inlet flow Mach number of 0.45, which is a representative inlet Mach number for gas turbine rotor blades. A shock tube generated the high temperature and pressure air flow, and a variable geometry test section was used to produce inlet flow Mach number of 0.45 and accelerate the flow over the plate to sonic velocity. Thin-film platinum heat gages recorded the local heat flux for laminar, transition, and turbulent boundary layers. The free stream temperatures varied from 611 R (339 K) to 3840 R (2133 K) for a T(w)/T(r,g) temperature ratio of 0.87 to 0.14. The Reynolds number over the heat gages varied from 3000 to 690,000. The experimental heat transfer data were correlated with laminar and turbulent boundary layer theories for the range of temperatures and Reynolds numbers and the transition phenomenon was examined.

Bypass transition in compressible boundary layers

NASA Technical Reports Server (NTRS)

Vandervegt, J. J.

1992-01-01

Transition to turbulence in aerospace applications usually occurs in a strongly disturbed environment. For instance, the effects of free-stream turbulence, roughness and obstacles in the boundary layer strongly influence transition. Proper understanding of the mechanisms leading to transition is crucial in the design of aircraft wings and gas turbine blades, because lift, drag and heat transfer strongly depend on the state of the boundary layer, laminar or turbulent. Unfortunately, most of the transition research, both theoretical and experimental, has focused on natural transition. Many practical flows, however, defy any theoretical analysis and are extremely difficult to measure. Morkovin introduced in his review paper the concept of bypass transition as those forms of transition which bypass the known mechanisms of linear and non-linear transition theories and are currently not understood by experiments. In an effort to better understand the mechanisms leading to transition in a disturbed environment, experiments are conducted studying simpler cases, viz. the effects of free stream turbulence on transition on a flat plate. It turns out that these experiments are very difficult to conduct, because generation of free stream turbulence with sufficiently high fluctuation levels and reasonable homogeneity is non trivial. For a discussion see Morkovin. Serious problems also appear due to the fact that at high Reynolds numbers the boundary layers are very thin, especially in the nose region of the plate where the transition occurs, which makes the use of very small probes necessary. The effects of free-stream turbulence on transition are the subject of this research and are especially important in a gas turbine environment, where turbulence intensities are measured between 5 and 20 percent, Wang et al. Due to the fact that the Reynolds number for turbine blades is considerably lower than for aircraft wings, generally a larger portion of the blade will be in a laminar transitional state. The effects of large free stream turbulence in compressible boundary layers at Mach numbers are examined both in the subsonic and transonic regime using direct numerical simulations. The flow is computed over a flat plate and curved surface. while many applications operate in the transonic regime. Due the nature of their numerical scheme, a non-conservation formulation of the Navier-Stokes equations, it is a non-trivial extension to compute flow fields in the transonic regime. This project aims at better understanding the effects of large free-stream turbulence in compressible boundary layers at mach number both in the subsonic and transonic regime using direct numerical simulations. The present project aims at computing the flow over a flat plate and curved surface. This research will provide data which can be used to clarify mechanisms leading to transition in an environment with high free stream turbulence. This information is useful for the development of turbulence models, which are of great importance for CFD applications, and are currently unreliable for more complex flows, such as transitional flows.

Properties of Special Types of Radiators

NASA Technical Reports Server (NTRS)

Parsons, S R

1921-01-01

This report discusses the general performance characteristics of three special classes of radiators: those with flat plate water tubes, fin and tube types, and types that whistle in an air stream. Curves and tables show the performance of representative radiators of each class and compare the flat plate and whistling types. Empirical equations are given for estimating the performance of flat plate radiators of various dimensions. This report also contains a brief discussion, with curves, showing the effect of yawing on the properties of a radiator.

Improved Thermal-Vacuum Compatible Flat Plate Radiometric Souce for System-Level Testing of Optical Sensors

NASA Technical Reports Server (NTRS)

Schwarz, Mark A.; Kent, Craig J.; Bousquet, Robert; Brown, Steven W.

2015-01-01

This work describes the development of an improved vacuum compatible flat plate radiometric source used for characterizing and calibrating remote optical sensors, in situ, throughout their testing period. The original flat plate radiometric source was developed for use by the VIIRS instrument during the NPOESS Preparatory Project (NPP). Following this effort, the FPI has had significant upgrades in order to improve both the radiometric throughput and uniformity. Results of the VIIRS testing with the reconfigured FPI are reported and discussed.

Lift Production on Flapping and Rotary Wings at Low Reynolds Numbers

DTIC Science & Technology

2016-02-26

though parameter variations were also performed. For the rotating cases, the wing was an aspect ratio 2 rectangular flat plate , and the root cutout (i.e...rectangular flat plate . 2 U (Side View) (a) 1A: Rectilinear pitch U (Side View) (b) 1B: Rectilinear surge (Top View) (Side View) (c) 2A: Rotational...0.5c φ (b) A=2 flat plate wing Figure 2: Schematic of the AVT-202 rotating wing kinematics and geometry, from Ref. 12. 3.2 Experimental Setup Rotating

Streamline curvature in supersonic shear layers

NASA Technical Reports Server (NTRS)

Kibens, V.

1992-01-01

Results of an experimental investigation in which a curved shear layer was generated between supersonic flow from a rectangular converging/diverging nozzle and the freestream in a series of open channels with varying radii of curvature are reported. The shear layers exhibit unsteady large-scale activity at supersonic pressure ratios, indicating increased mixing efficiency. This effect contrasts with supersonic flow in a straight channel, for which no large-scale vortical structure development occurs. Curvature must exceed a minimum level before it begins to affect the dynamics of the supersonic shear layer appreciably. The curved channel flows are compared with reference flows consisting of a free jet, a straight channel, and wall jets without sidewalls on a flat and a curved plate.

High enthalpy, hypervelocity flows of air and argon in an expansion tube

NASA Technical Reports Server (NTRS)

Neely, A. J; Stalker, R. J.; Paull, A.

1991-01-01

An expansion tube with a free piston driver has been used to generate quasi-steady hypersonic flows in argon and air at flow velocities in excess of 9 km/s. Irregular test flow unsteadiness has limited the performance of previous expansion tubes, and it has been found that this can be avoided by attention to the interaction between the test gas accelerating expansion and the contact surface in the primary shock tube. Test section measurements of pitot pressure, static pressure and flat plate heat transfer are reported. An approximate analytical theory has been developed for predicting the velocities achieved in the unsteady expansion of the ionizing or dissociating test gas.

A User’s Guide to the PLTEMP/ANL Code

DOE Office of Scientific and Technical Information (OSTI.GOV)

Olson, A. P.; Kalimullah, M.; Feldman, E. E.

2016-07-25

PLTEMP/ANL V4.2 is a program that obtains a steady-state flow and temperature solution for a nuclear reactor core, or for a single fuel assembly. It is based on an evolutionary sequence of codes originally used for plate temperatures, hence “PLTEMP”, developed at Argonne National Laboratory over several decades. Fueled and non-fueled regions are modeled. Each fuel assembly consists of one or more plates or tubes separated by coolant channels. The fuel plates may have one to five layers of different materials, each with heat generation. The width of a fuel plate may be divided into multiple longitudinal stripes, each withmore » its own axial power shape. The temperature solution is effectively 2-dimensional. It begins with a one-dimensional solution across all coolant channels and fuel plates or tubes within a given fuel assembly, at the entrance to the assembly. The temperature solution is repeated for each axial node along the length of the fuel assembly. The geometry may be either slab or radial, corresponding to fuel assemblies made of a series of flat (or slightly curved) plates, or of nested tubes. A variety of thermal-hydraulic correlations are available with which to determine safety margins such as onset-of-nucleate boiling ratio(ONBR), departure from nucleate boiling ratio (DNBR), and onset of flow instability ratio (OFIR). Coolant properties for either light or heavy water are obtained from FORTRAN functions rather than from tables. The code is intended for thermal-hydraulic analysis of research reactor performance in the sub-cooled boiling regime. Both turbulent and laminar flow regimes can be modeled. Options to calculate both forced flow and natural circulation are available. A general search capability is available (Appendix XII) to greatly reduce the reactor analyst’s time.« less

A finite element solver for 3-D compressible viscous flows

NASA Technical Reports Server (NTRS)

Reddy, K. C.; Reddy, J. N.; Nayani, S.

1990-01-01

Computation of the flow field inside a space shuttle main engine (SSME) requires the application of state of the art computational fluid dynamic (CFD) technology. Several computer codes are under development to solve 3-D flow through the hot gas manifold. Some algorithms were designed to solve the unsteady compressible Navier-Stokes equations, either by implicit or explicit factorization methods, using several hundred or thousands of time steps to reach a steady state solution. A new iterative algorithm is being developed for the solution of the implicit finite element equations without assembling global matrices. It is an efficient iteration scheme based on a modified nonlinear Gauss-Seidel iteration with symmetric sweeps. The algorithm is analyzed for a model equation and is shown to be unconditionally stable. Results from a series of test problems are presented. The finite element code was tested for couette flow, which is flow under a pressure gradient between two parallel plates in relative motion. Another problem that was solved is viscous laminar flow over a flat plate. The general 3-D finite element code was used to compute the flow in an axisymmetric turnaround duct at low Mach numbers.

Method of manufacturing lightweight thermo-barrier material

NASA Technical Reports Server (NTRS)

Blair, Winford (Inventor)

1987-01-01

A method of manufacturing thermal barrier structures comprising at least three dimpled cores separated by flat plate material with the outer surface of the flat plate material joined together by diffusion bonding.

Viscous flow drag reduction; Symposium, Dallas, Tex., November 7, 8, 1979, Technical Papers

NASA Technical Reports Server (NTRS)

Hough, G. R.

1980-01-01

The symposium focused on laminar boundary layers, boundary layer stability analysis of a natural laminar flow glove on the F-111 TACT aircraft, drag reduction of an oscillating flat plate with an interface film, electromagnetic precipitation and ducting of particles in turbulent boundary layers, large eddy breakup scheme for turbulent viscous drag reduction, blowing and suction, polymer additives, and compliant surfaces. Topics included influence of environment in laminar boundary layer control, generation rate of turbulent patches in the laminar boundary layer of a submersible, drag reduction of small amplitude rigid surface waves, and hydrodynamic drag and surface deformations generated by liquid flows over flexible surfaces.

Design, construction and evaluation of a system of forced solar water heating.

NASA Astrophysics Data System (ADS)

Hernández, E.; Bautista, G. A.; Ortiz, I. L.

2016-07-01

The main purpose of this project was to design, construct and evaluate a system of forced solar water heating for domestic consumption, at the Universidad Pontificia Bolivariana-Bucaramanga, Colombia; using solar energy. This is a totally system independent of the electrical grid and an important characteristic is the heating water doesn't mix with the consumption water. The system receives the solar radiation through a flat-plate collector, which it transmits the heat to the water that it flow with impulse from the centrifugal pump of 12VDC, the water circulates toward helical serpentine it is inside of the tank of the storage whose capacity is 100 liters of water. The temperature of the tank is regulated with a controller in such a way that de-energized the pump when it gets the temperature required. The performance thermal or efficiency of the system was evaluated like a relationship between the delivered energy to the water in storage tank and the incident energy in the flat-plate collector.

Mixed convection-radiation interaction in boundary-layer flow over horizontal surfaces

NASA Astrophysics Data System (ADS)

Ibrahim, F. S.; Hady, F. M.

1990-06-01

The effect of buoyancy forces and thermal radiation on the steady laminar plane flow over an isothermal horizontal flat plate is investigated within the framework of first-order boundary-layer theory, taking into account the hydrostatic pressure variation normal to the plate. The fluid considered is a gray, absorbing-emitting but nonscattering medium, and the Rosseland approximation is used to describe the radiative heat flux in the energy equation. Both a hot surface facing upward and a cold surface facing downward are considered in the analysis. Numerical results for the local Nusselt number, the local wall shear stress, the local surface heat flux, as well as the velocity and temperature distributions are presented for gases with a Prandtl number of 0.7 for various values of the radiation-conduction parameter, the buoyancy parameter, and the temperature ratio parameter.

Transient heat transfer in viscous rarefied gas between concentric cylinders. Effect of curvature

NASA Astrophysics Data System (ADS)

Gospodinov, P.; Roussinov, V.; Dankov, D.

2015-10-01

The thermoacoustic waves arising in cylindrical or planar Couette rarefied gas flow between rotating cylinders is studied in the cases of suddenly cylinder (active) wall velocity direction turn on. An unlimited increase in the radius of the inner cylinder flow can be interpreted as Couette flow between the two flat plates. Based on the developed in previous publications Navier-Stockes-Fourier (NSF) model and Direct Simulation Monte Carlo (DSMC) method and their numerical solutions, are considered transient processes in the gas phase. Macroscopic flow characteristics (velocity, density, temperature) are received. The cylindrical flow cases for fixed velocity and temperature of the both walls are considered. The curvature effects over the wave's distribution and attenuation are studied numerically.

The Stability of Particulate Ladden Laminar Boundary-Layer Flows

NASA Technical Reports Server (NTRS)

Acrivos, Andreas

1996-01-01

During the course of this investigation, the following two topics were studied theoretically: (1) forced convection and sedimentation past a flat plate, and (2) the effect of rain on airfoil performance. The prototype of the first topic is that of air flowing past the wing section of an aircraft under heavy rain and high windshear. The long-range objective of this project was to identify the various factors determining the dynamics of the flow and then to develop a theoretical framework for modeling such systems. The second topic focused on the idea that the presence of the gas-liquid interface (being the air flow around the airfoil and the thin liquid film created by the rain) accelerates flow separation and thus induces performance losses.

Hydrodynamics of metachronal paddling in crustaceans

NASA Astrophysics Data System (ADS)

Santhanakrishnan, A.; Lai, H. K.; Samaee, M.; Lewis, T. J.; Guy, R. D.

2016-02-01

Long-tailed crustaceans such as crayfish and krill swim by rhythmically paddling a set of four to five limbs (swimmerets) originating from their abdomen. Despite variations in limb size and stroke frequency, movements of ipsilateral limbs always maintain a tail-to-head metachronal rhythm with an approximate quarter-period inter-limb phase difference. Relatively few studies have examined the fluid dynamics of metachronal limb stroke for the range of Reynolds numbers at which crustaceans operate. The objective of this study is to investigate metachronal paddling as a function of Reynolds number (Re) for quantifying hydrodynamic scalability of this swimming mechanism, including the effect of hinges on paddles as seen in crustacean swimmerets. Our approach included experiments on a scaled physical model and computational fluid dynamics (CFD) simulations using the immersed boundary (IB) method. The scaled robotic model of metachronal paddling consisted of a rectangular aquarium tank fitted above with four stepper motors coupled to a four-bar linkage that actuated four acrylic paddles immersed in water-glycerin fluid medium. 2D particle image velocimetry (PIV) was used for quantitative flow visualization in the experiments. The swimmerets were modeled in CFD simulations as rigid 1D rods in a 2D fluid. The inter-limb phase difference was varied from 0% (synchronous paddling) through 50% across Re range of O(10-1000). Two types of experimental limb models were tested, including a simple flat plate and a `split-paddle' structure with two flat plates connected halfway with hinges. Our results show that the natural tail-to-head metachronal rhythm with an approximate quarter-period phase difference is the most effective and efficient rhythm across a wide range of Reynolds numbers. Limb models with hinges generated increased horizontal flow compared to the simple flat plate paddles, suggesting that asymmetry between power and return stroke is important to augment thrust.

Proceedings of the Flat-Plate Solar Array Project Research Forum on the Design of Flat-Plate Photovoltaic Arrays for Central Stations

NASA Technical Reports Server (NTRS)

1983-01-01

The Flat Plate Solar Array Project, focuses on advancing technologies relevant to the design and construction of megawatt level central station systems. Photovoltaic modules and arrays for flat plate central station or other large scale electric power production facilities require the establishment of a technical base that resolves design issues and results in practical and cost effective configurations. Design, qualification and maintenance issues related to central station arrays derived from the engineering and operating experiences of early applications and parallel laboratory reserch activities are investigated. Technical issues are examined from the viewpoint of the utility engineer, architect/engineer and laboratory researcher. Topics on optimum source circuit designs, module insulation design for high system voltages, array safety, structural interface design, measurements, and array operation and maintenance are discussed.

Improved Thermal-Vacuum Compatible Flat Plate Radiometric Source For System-Level Testing Of Optical Sensors

NASA Technical Reports Server (NTRS)

Schwarz, Mark A.; Kent, Craig J.; Bousquet, Robert; Brown, Steven W.

2016-01-01

In this work, we describe an improved thermal-vacuum compatible flat plate radiometric source which has been developed and utilized for the characterization and calibration of remote optical sensors. This source is unique in that it can be used in situ, in both ambient and thermal-vacuum environments, allowing it to follow the sensor throughout its testing cycle. The performance of the original flat plate radiometric source was presented at the 2009 SPIE1. Following the original efforts, design upgrades were incorporated into the source to improve both radiometric throughput and uniformity. The pre-thermal-vacuum (pre-TVAC) testing results of a spacecraft-level optical sensor with the improved flat plate illumination source, both in ambient and vacuum environments, are presented. We also briefly discuss potential FPI configuration changes in order to improve its radiometric performance.

Acoustic Radiation from High-Speed Turbulent Boundary Layers in a Tunnel-Like Environment

NASA Technical Reports Server (NTRS)

Duan, Lian; Choudhari, Meelan M.; Zhang, Chao

2015-01-01

Direct numerical simulation of acoustic radiation from a turbulent boundary layer in a cylindrical domain will be conducted under the flow conditions corresponding to those at the nozzle exit of the Boeing/AFOSR Mach-6 Quiet Tunnel (BAM6QT) operated under noisy-flow conditions with a total pressure p(sub t) of 225 kPa and a total temperature of T(sub t) equal to 430 K. Simulations of acoustic radiation from a turbulent boundary layer over a flat surface are used as a reference configuration to illustrate the effects of the cylindrical enclosure. A detailed analysis of acoustic freestream disturbances in the cylindrical domain will be reported in the final paper along with a discussion pertaining to the significance of the flat-plate acoustic simulations and guidelines concerning the modeling of the effects of an axisymmetric tunnel wall on the noise field.

The effect of butterfly scales on flight efficiency and leading edge vortex formation

NASA Astrophysics Data System (ADS)

Lang, Amy; Wilroy, Jacob; Wahidi, Redha; Slegers, Nathan; Heilman, Micahel; Cranford, Jacob

2016-11-01

It is hypothesized that the scales on a butterfly wing lead to increased flight efficiency. Recent testing of live butterflies tracked their motion over 246 flights for 11 different specimens. Results show a 37.8 percent mean decrease in flight efficiency and a flapping amplitude reduction of 6.7 percent once the scales were removed. This change could be largely a result of how the leading edge vortex (LEV) interacts with the wing. To simplify this complex flow problem, an experiment was designed to focus on the alteration of 2-D vortex development with a variation in surface patterning. Specifically, the secondary vorticity generated by the LEV interacting at the patterned surface was studied, as well as the subsequent effect on the LEV's growth rate and peak circulation. For this experiment butterfly inspired grooves were created using additive manufacturing and were attached to a flat plate with a chordwise orientation, thus increasing plate surface area. The vortex generated by the grooved plate was then compared to a smooth case as the plate translated vertically through a tow tank at Re = 1500, 3000, and 6000. Using DPIV, the vortex formation was documented and a maximum vortex formation time of 4.22 was found based on the flat plate travel distance and chord length. Results indicate that the patterned surface slows down the growth of the vortex which corroborates the flight test results. Funding from NSF CBET Fluid Dynamcis is gratefully acknowledged.

Research on Aero-Thermodynamic Distortion Induced Structural Dynamic Response of Multistage Compressor Blading

DTIC Science & Technology

1992-03-01

of realistic reduced frequency values for the ftost time. 14. SUIUECT TEIEMS IS. NUMBER OF PAGES Unsteady Aerodynamic, 143 Flow Induced Vibrations 16...Flat Plate APPENDIX X. Prediction of Turbulence Generated Random Vibrational 106 Response of Turbomachinery Blading 3 APPENDIX XI. Viscous Oscillating...failure is fatigue caused by vibrations at levels exceeding3 material endurance limits. These vibrations occur when a periodic forcing function, with

Numerical Simulation of Hypersonic Boundary Layer Receptivity, Transient Growth and Transition With Surface Roughness

DTIC Science & Technology

2009-12-31

of receptivity of the Mach 5.92 flow over a flat plate to two- dimensional wall perturbations with surface roughness: 1) amplitude...contain a significantly large intervalθ compared with the normal grid spacing h∆ , which may lead to a deterioration of accuracy of the method... of hypersonic boundary layer receptivity, transient growth and transition with surface roughness. The main approach is to use

Comment on “A similarity solution for laminar thermal boundary layer over a flat plate with a convective surface boundary condition” by A. Aziz, Comm. Nonlinear Sci. Numer. Simul. 2009;14:1064-8

NASA Astrophysics Data System (ADS)

Magyari, Eugen

2011-01-01

In a recent paper published in this Journal the title problem has been investigated numerically. In the present paper the exact solution for the temperature boundary layer is given in terms of the solution of the flow problem (the Blasius problem) in a compact integral form.

Studies on Impingement Effects of Low Density Jets on Surfaces — Determination of Shear Stress and Normal Pressure

NASA Astrophysics Data System (ADS)

Sathian, Sarith. P.; Kurian, Job

2005-05-01

This paper presents the results of the Laser Reflection Method (LRM) for the determination of shear stress due to impingement of low-density free jets on flat plate. For thin oil film moving under the action of aerodynamic boundary layer the shear stress at the air-oil interface is equal to the shear stress between the surface and air. A direct and dynamic measurement of the oil film slope is measured using a position sensing detector (PSD). The thinning rate of oil film is directly measured which is the major advantage of the LRM over LISF method. From the oil film slope history, direct calculation of the shear stress is done using a three-point formula. For the full range of experiment conditions Knudsen numbers varied till the continuum limit of the transition regime. The shear stress values for low-density flows in the transition regime are thus obtained using LRM and the measured values of shear show fair agreement with those obtained by other methods. Results of the normal pressure measurements on a flat plate in low-density jets by using thermistors as pressure sensors are also presented in the paper. The normal pressure profiles obtained show the characteristic features of Newtonian impact theory for hypersonic flows.

The flow of a power-law fluid in the near-wake of a flat plate

NASA Astrophysics Data System (ADS)

Zhou, Min; Ladeinde, Foluso; Bluestein, Danny

2006-08-01

The analysis of the near-wake flow downstream of a flat plate is reported in this paper for the case of a non-Newtonian (power-law) constitutive model. To our knowledge, the present paper is the first to address this problem, as previous work on near-wakes has been limited to the use of a Newtonian model. The motivation for this work comes from the biomedical engineering problem of blood flow around the bileaflet of a mechanical heart valve. In the present paper, the series method has been used to calculate the flow near the centerline of the wake, while an asymptotic method has been used for larger distances from the centerline. The effects of power-law inlet conditions on the wake flow are reported for various values of the power-law index n, within the range 0.7≤n ≤1.3. The present analysis has been successfully validated by comparing the results for n =1 to the near-wake results by Goldstein [Proc. Cambridge Philos. Soc. 26, 1 (1930)]. We generalized the equations for arbitrary values of n, without any special considerations for n =1. Therefore, the accurate results observed for n =1 validate our procedure as a whole. The first major finding is that a fluid with smaller n develops faster downstream, such that decreasing n leads to monotonically increasing velocities compared to fluids with large n values. Another finding is that the non-Newtonian effects become more significant as the downstream distance increases. Finally, these effects tend to be more pronounced in the vicinity of the wake centerline compared to larger y locations.

Unsteady heat-flux measurements of second-mode instability waves in a hypersonic flat-plate boundary layer

NASA Astrophysics Data System (ADS)

Kegerise, Michael A.; Rufer, Shann J.

2016-08-01

In this paper, we report on the application of the atomic layer thermopile (ALTP) heat-flux sensor to the measurement of laminar-to-turbulent transition in a hypersonic flat-plate boundary layer. The centerline of the flat-plate model was instrumented with a streamwise array of ALTP sensors, and the flat-plate model was exposed to a Mach 6 freestream over a range of unit Reynolds numbers. Here, we observed an unstable band of frequencies that are associated with second-mode instability waves in the laminar boundary layer that forms on the flat-plate surface. The measured frequencies, group velocities, phase speeds, and wavelengths of these instability waves are consistent with data previously reported in the literature. Heat flux time series, and the Morlet wavelet transforms of them, revealed the wave-packet nature of the second-mode instability waves. In addition, a laser-based radiative heating system was used to measure the frequency response functions (FRF) of the ALTP sensors used in the wind tunnel test. These measurements were used to assess the stability of the sensor FRFs over time and to correct spectral estimates for any attenuation caused by the finite sensor bandwidth.

CFD Simulations of the IHF Arc-Jet Flow: Compression-Pad Separation Bolt Wedge Tests

NASA Technical Reports Server (NTRS)

Gokcen, Tahir; Skokova, Kristina A.

2017-01-01

This paper reports computational analyses in support of two wedge tests in a high enthalpy arc-jet facility at NASA Ames Research Center. These tests were conducted using two different wedge models, each placed in a free jet downstream of a corresponding different conical nozzle in the Ames 60-MW Interaction Heating Facility. Each panel test article included a metallic separation bolt imbedded in Orion compression-pad and heatshield materials, resulting in a circular protuberance over a flat plate. The protuberances produce complex model flowfields, containing shock-shock and shock-boundary layer interactions, and multiple augmented heating regions on the test plate. As part of the test calibration runs, surface pressure and heat flux measurements on water-cooled calibration plates integrated with the wedge models were also obtained. Surface heating distributions on the test articles as well as arc-jet test environment parameters for each test configuration are obtained through computational fluid dynamics simulations, consistent with the facility and calibration measurements. The present analysis comprises simulations of the non-equilibrium flow field in the facility nozzle, test box, and flow field over test articles, and comparisons with the measured calibration data.

Investigating the Feedback Path in a Jet-Surface Resonant Interaction

NASA Technical Reports Server (NTRS)

Zaman, Khairul; Fagan, Amy; Bridges, James; Brown, Cliff

2015-01-01

A resonant interaction between an 8:1 aspect ratio rectangular jet and flat-plates, placed parallel to the jet, is addressed in this study. For certain relative locations of the plates, the resonance takes place with accompanying audible tones. Even when the tone is not audible the sound pressure level spectra is often marked by conspicuous peaks. The frequencies of the spectral peaks, as functions of the streamwise length of the plate and its relative location to the jet as well as the jet Mach number, are explored in an effort of understand the flow mechanism. It is demonstrated that the tones are not due to a simple feedback between the plates trailing edge and the nozzle exit; the leading edge also comes into play in determining the frequency. An acoustic feedback path, involving diffraction from the leading edge, appears to explain the frequencies of some of the spectral peaks.

Core assembly storage structure

DOEpatents

Jones, Jr., Charles E.; Brunings, Jay E.

1988-01-01

A structure for the storage of core assemblies from a liquid metal-cooled nuclear reactor. The structure comprises an enclosed housing having a substantially flat horizontal top plate, a bottom plate and substantially vertical wall members extending therebetween. A plurality of thimble members extend downwardly through the top plate. Each thimble member is closed at its bottom end and has an open end adjacent said top plate. Each thimble member has a length and diameter greater than that of the core assembly to be stored therein. The housing is provided with an inlet duct for the admission of cooling air and an exhaust duct for the discharge of air therefrom, such that when hot core assemblies are placed in the thimbles, the heat generated will by convection cause air to flow from the inlet duct around the thimbles and out the exhaust duct maintaining the core assemblies at a safe temperature without the necessity of auxiliary powered cooling equipment.

High temperature thermocouple and heat flux gauge using a unique thin film-hardware hot juncture

NASA Technical Reports Server (NTRS)

Liebert, C. H.; Holanda, R.; Hippensteele, S. A.; Andracchio, C. A.

1984-01-01

A special thin film-hardware material thermocouple (TC) and heat flux gauge concept for a reasonably high temperature and high flux flat plate heat transfer experiment was fabricated and tested to gauge temperatures of 911 K. This concept was developed for minimal disturbance of boundary layer temperature and flow over the plates and minimal disturbance of heat flux through the plates. Comparison of special heat flux gauge Stanton number output at steady-state conditions with benchmark literature data was good and agreement was within a calculated uncertainty of the measurement system. Also, good agreement of special TC and standard TC outputs was obtained and the results are encouraging. Oxidation of thin film thermoelements was a primary failure mode after about 5 of operation.

High-temperature thermocouple and heat flux gauge using a unique thin film-hardware hot junction

NASA Technical Reports Server (NTRS)

Liebert, C. H.; Holanda, R.; Hippensteele, S. A.; Andracchio, C. A.

1985-01-01

A special thin film-hardware material thermocouple (TC) and heat flux gauge concept for a reasonably high temperature and high flux flat plate heat transfer experiment was fabricated and tested to gauge temperatures of 911 K. This concept was developed for minimal disturbance of boundary layer temperature and flow over the plates and minimal disturbance of heat flux through the plates. Comparison of special heat flux gauge Stanton number output at steady-state conditions with benchmark literature data was good and agreement was within a calculated uncertainty of the measurement system. Also, good agreement of special TC and standard TC outputs was obtained and the results are encouraging. Oxidation of thin film thermoelements was a primary failure mode after about 5 of operation.

Turbulent boundary layer heat transfer experiments: Convex curvature effects, including introduction and recovery

NASA Technical Reports Server (NTRS)

Simon, T. W.; Moffat, R. J.; Johnston, J. P.; Kays, W. M.

1980-01-01

Heat transfer rates were measured through turbulent and transitional boundary layers on an isothermal, convexly curved wall and downstream flat plate. The effect of convex curvature on the fully turbulent boundary layer was a reduction of the local Stanton numbers 20-50% below those predicted for a flat wall under the same circumstances. The recovery of the heat transfer rates on the downstream flat wall was extremely slow. After 60 cm of recovery length, the Stanton number was still typically 15-20% below the flat wall predicted value. Various effects important in the modeling of curved flows were studied separately. These are: (1) the effect of initial boundary layer thickness; (2) the effect of freestream velocity; (3) the effect of freestream acceleration; (4) the effect of unheated starting length; and (5) the effect of the maturity of the boundary layer. Regardless of the initial state, curvature eventually forced the boundary layer into an asymptotic curved condition. The slope, minus one, is believed to be significant.

Turbulent boundary layer heat transfer experiments: Convex curvature effects including introduction and recovery

NASA Technical Reports Server (NTRS)

Simon, T. W.; Moffat, R. J.; Johnston, J. P.; Kays, W. M.

1982-01-01

Measurements were made of the heat transfer rate through turbulent and transitional boundary layers on an isothermal, convexly curved wall and downstream flat plate. The effect of convex curvature on the fully turbulent boundary layer was a reduction of the local Stanton numbers 20% to 50% below those predicted for a flat wall under the same circumstances. The recovery of the heat transfer rates on the downstream flat wall was extremely slow. After 60 cm of recovery length, the Stanton number was still typically 15% to 20% below the flat wall predicted value. Various effects important in the modeling of curved flows were studied separately. These are: the effect of initial boundary layer thickness, the effect of freestream velocity, the effect of freestream acceleration, the effect of unheated starting length, and the effect of the maturity of the boundary layer. An existing curvature prediction model was tested against this broad heat transfer data base to determine where it could appropriately be used for heat transfer predictions.

Comparison of Mixing Characteristics for Several Fuel Injectors on an Open Plate and in a Ducted Flowpath Configuration at Hypervelocity Flow Conditions

NASA Technical Reports Server (NTRS)

Drozda, Tomasz G.; Shenoy, Rajiv R.; Passe, Bradley J.; Baurle, Robert A.; Drummond, J. Philip

2017-01-01

In order to reduce the cost and complexity associated with fuel injection and mixing experiments for high-speed flows, and to further enable optical access to the test section for nonintrusive diagnostics, the Enhanced Injection and Mixing Project (EIMP) utilizes an open flat plate configuration to characterize inert mixing properties of various fuel injectors for hypervelocity applications. The experiments also utilize reduced total temperature conditions to alleviate the need for hardware cooling. The use of "cold" flows and non-reacting mixtures for mixing experiments is not new, and has been extensively utilized as a screening technique for scramjet fuel injectors. The impact of reduced facility-air total temperature, and the use of inert fuel simulants, such as helium, on the mixing character of the flow has been assessed in previous numerical studies by the authors. Mixing performance was characterized for three different injectors: a strut, a ramp, and a flushwall. The present study focuses on the impact of using an open plate to approximate mixing in the duct. Toward this end, Reynolds-averaged simulations (RAS) were performed for the three fuel injectors in an open plate configuration and in a duct. The mixing parameters of interest, such as mixing efficiency and total pressure recovery, are then computed and compared for the two configurations. In addition to mixing efficiency and total pressure recovery, the combustion efficiency and thrust potential are also computed for the reacting simulations.

Frost characteristics and heat transfer on a flat plate under freezer operating conditions: Part 1, Experimentation and correlations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mao, Y.; Besant, R.W.; Chen, H.

1999-07-01

An experimental investigation of frost growth on a flat, cold surface supplied by subfreezing, turbulent, humid, parallel flow of air is presented. The operating conditions are typical of many commercial freezers. A test loop was constructed to perform the tests, and the frost height, frost mass concentration, and cold surface heat flux were measured using specially designed and calibrated instrumentation. Twenty tests were done for steady operating conditions, each starting with no initial frost accumulation, and were run for two to six hours giving 480 data samples. Measured results show that the frost characteristics differ significantly with frost growth datamore » taken previously for room temperature airflow. Depending on the temperature of the cold plate and the relative humidity of the subfreezing supply air, the frost could appear to be either smooth or rough. Smooth frost, which occurred at warmer plate temperatures and lower supply air relative humidities, gave rise to frost growth that was much thinner and denser than that for the rough, thick, low-density frost. Frost growth characteristics are correlated as a function of five independent variables (time, distance from the leading edge, cold plate temperature ratio, humidity ratio, and Reynolds number). These correlations are presented separately for the full data set, the rough frost data, and the smooth frost data.« less

Micromachined silicon electrostatic chuck

DOEpatents

Anderson, Robert A.; Seager, Carleton H.

1996-01-01

An electrostatic chuck is faced with a patterned silicon plate 11, created y micromachining a silicon wafer, which is attached to a metallic base plate 13. Direct electrical contact between the chuck face 15 (patterned silicon plate's surface) and the silicon wafer 17 it is intended to hold is prevented by a pattern of flat-topped silicon dioxide islands 19 that protrude less than 5 micrometers from the otherwise flat surface of the chuck face 15. The islands 19 may be formed in any shape. Islands may be about 10 micrometers in diameter or width and spaced about 100 micrometers apart. One or more concentric rings formed around the periphery of the area between the chuck face 15 and wafer 17 contain a low-pressure helium thermal-contact gas used to assist heat removal during plasma etching of a silicon wafer held by the chuck. The islands 19 are tall enough and close enough together to prevent silicon-to-silicon electrical contact in the space between the islands, and the islands occupy only a small fraction of the total area of the chuck face 15, typically 0.5 to 5 percent. The pattern of the islands 19, together with at least one hole 12 bored through the silicon veneer into the base plate, will provide sufficient gas-flow space to allow the distribution of the helium thermal-contact gas.

Convective Heat Transfer from Castings of Ice Roughened Surfaces in Horizontal Flight

NASA Technical Reports Server (NTRS)

Dukhan, Nihad; Vanfossen, G. James, Jr.; Masiulaniec, K. Cyril; Dewitt, Kenneth J.

1995-01-01

A technique was developed to cast frozen ice shapes that had been grown on a metal surface. This technique was applied to a series of ice shapes that were grown in the NASA Lewis Icing Research Tunnel on flat plates. Eight different types of ice growths, characterizing different types of roughness, were obtained from these plates, from which aluminum castings were made. Test strips taken from these castings were outfitted with heat flux gages, such that when placed in a dry wind tunnel, they could be used to experimentally map out the convective heat transfer coefficient in the direction of flow from the roughened surfaces. The effects on the heat transfer coefficient for parallel flow, which simulates horizontal flight, were studied. The results of this investigation can be used to help size heaters for wings, helicopter rotor blades, jet engine intakes, etc., or de-icing for anti-icing applications where the flow is parallel to the iced surface.

CFD Simulations of the IHF Arc-Jet Flow: Compression-Pad/Separation Bolt Wedge Tests

NASA Technical Reports Server (NTRS)

Gokcen, Tahir; Skokova, Kristina A.

2017-01-01

This paper reports computational analyses in support of two wedge tests in a high enthalpy arc-jet facility at NASA Ames Research Center. These tests were conducted using two different wedge models, each placed in a free jet downstream of a corresponding different conical nozzle in the Ames 60-MW Interaction Heating Facility. Panel test articles included a metallic separation bolt imbedded in the compression-pad and heat shield materials, resulting in a circular protuberance over a flat plate. As part of the test calibration runs, surface pressure and heat flux measurements on water-cooled calibration plates integrated with the wedge models were also obtained. Surface heating distributions on the test articles as well as arc-jet test environment parameters for each test configuration are obtained through computational fluid dynamics simulations, consistent with the facility and calibration measurements. The present analysis comprises simulations of the non-equilibrium flow field in the facility nozzle, test box, and flow field over test articles, and comparisons with the measured calibration data.

Experiments to verify nonparallel stability theory at Virginia Polytechnic Institute and State University, Blacksburg, Virginia

NASA Technical Reports Server (NTRS)

Saric, William S.

1988-01-01

The effects of normal mass injection and suction on boundary-layer stability and transition are studied on a flat plate. Titanium panels, in which 0.063 mm diameter holes were drilled on 0.635 mm centers, are inserted in the plate. Suction level and distribution are variable. Disturbances are introduced by means of a vibrating ribbon and measurements of both mean- and disturbance-flow velocities are made with a hot wire. Disturbance amplitudes are measured as a function of Reynolds number, frequency, and suction characteristics, and are compared with the previous results obtained over a Dynapore surface. Transition measurements under natural and forced conditions are also made. The stabilizing effects of suction are documented. It is also shown that very high local flow rates through the suction holes (which approach a hole Reynolds number of 300) do not destabilize the flow. On the other hand, weak blowing lowers the transition Reynolds number, but is found not to cause serious problems.

On the stability of a time dependent boundary layer

NASA Technical Reports Server (NTRS)

Otto, S. R.

1993-01-01

The aim of this article is to determine the stability characteristics of a Rayleigh layer, which is known to occur when the fluid above a flat plate has a velocity imparted to it (parallel to the plate). This situation is intrinsically unsteady, however, as a first approximation we consider the instantaneous stability of the flow. The Orr-Sommerfeld equation is found to govern fixed downstream wavelength linear perturbations to the basic flow profile. By the solution of this equation, we can determine the Reynolds numbers at which the flow is neutrally stable; this quasisteady approach is only formally applicable for infinite Reynolds numbers. We shall consider the large Reynolds number limit of the original problem and use a three deck mentality to determine the form of the modes. The results of the two calculations are compared, and the linear large Reynolds number analysis is extended to consider the effect of weak nonlinearity in order to determine whether the system is subcritical or supercritical.

Development and Experimental Evaluation of Passive Fuel Cell Thermal Control

NASA Technical Reports Server (NTRS)

Colozza, Anthony J.; Jakupca, Ian J.; Castle, Charles H.; Burke, Kenneth A.

2014-01-01

To provide uniform cooling for a fuel cell stack, a cooling plate concept was evaluated. This concept utilized thin cooling plates to extract heat from the interior of a fuel cell stack and move this heat to a cooling manifold where it can be transferred to an external cooling fluid. The advantages of this cooling approach include a reduced number of ancillary components and the ability to directly utilize an external cooling fluid loop for cooling the fuel cell stack. A number of different types of cooling plates and manifolds were developed. The cooling plates consisted of two main types; a plate based on thermopyrolytic graphite (TPG) and a planar (or flat plate) heat pipe. The plates, along with solid metal control samples, were tested for both thermal and electrical conductivity. To transfer heat from the cooling plates to the cooling fluid, a number of manifold designs utilizing various materials were devised, constructed, and tested. A key aspect of the manifold was that it had to be electrically nonconductive so it would not short out the fuel cell stack during operation. Different manifold and cooling plate configurations were tested in a vacuum chamber to minimize convective heat losses. Cooling plates were placed in the grooves within the manifolds and heated with surface-mounted electric pad heaters. The plate temperature and its thermal distribution were recorded for all tested combinations of manifold cooling flow rates and heater power loads. This testing simulated the performance of the cooling plates and manifold within an operational fuel cell stack. Different types of control valves and control schemes were tested and evaluated based on their ability to maintain a constant temperature of the cooling plates. The control valves regulated the cooling fluid flow through the manifold, thereby controlling the heat flow to the cooling fluid. Through this work, a cooling plate and manifold system was developed that could maintain the cooling plates within a minimal temperature band with negligible thermal gradients over power profiles that would be experienced within an operating fuel cell stack.

Effects of the foil flatness on irradiation performance of U10Mo monolithic mini-plates

DOE PAGES

Ozaltun, Hakan; Medvedev, Pavel G.; Rabin, Barry H.

2015-09-03

Monolithic plate-type fuels comprise of a high density, low enrichment, U10Mo fuel foil encapsulated in a cladding material. This concept generates several fabrication challenges such as flatness, centering or thickness variation. There are concerns, if these parameters have implications on overall performance. To investigate these inquiries, the effects of the foil flatness were studied. For this, a representative plate was simulated for an ideal case. The simulations were repeated for additional cases with various foil curvatures to evaluate the effects on the irradiation performance. The results revealed that the stresses and strains induced by fabrication process are not affected bymore » the flatness of the foil. Furthermore, fabrication stresses in the foil are relieved relatively fast in the reactor. The effects of the foil flatness on peak irradiation stressstrains are minimal. There is a slight increase in temperature for the case with maximum curvature. The major impact is on the displacement characteristics. Furthermore, while the case with a flat foil produces a symmetrical swelling, if the foil is curved, more swelling occurs on the thin-cladding side and the plate bows during irradiation.« less

Stress analyses of flat plates with attached nozzles. Vol. 3. Experimental stress analyses of a flat plate with two closely spaced nozzles of equal diameter attached

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bryson, J.W.; Swinson, W.F.

1975-12-01

The complete test results for a flat plate with two closely spaced nozzles attached are presented. Test loadings were 1:1, 1:2, and 2:1 biaxial planar tension loadings on the plate, axial thrust loadings applied separately to the nozzles, and bending moment loadings applied to the nozzles both within and normal to the plane of symmetry containing the nozzle axes. The test plate was 36 x 36 x 0.375 in., and the attached nozzles had outer diameters of 2.625 in. and wall thicknesses of 0.250 in. The nozzles were located in the center of the plate with their centers 3.0 in.more » apart and were considered to be free of weld distortions and irregularities in the junction region. 6 references. (auth)« less

Steady boundary layer slip flow along with heat and mass transfer over a flat porous plate embedded in a porous medium.

PubMed

Aziz, Asim; Siddique, J I; Aziz, Taha

2014-01-01

In this paper, a simplified model of an incompressible fluid flow along with heat and mass transfer past a porous flat plate embedded in a Darcy type porous medium is investigated. The velocity, thermal and mass slip conditions are utilized that has not been discussed in the literature before. The similarity transformations are used to transform the governing partial differential equations (PDEs) into a nonlinear ordinary differential equations (ODEs). The resulting system of ODEs is then reduced to a system of first order differential equations which was solved numerically by using Matlab bvp4c code. The effects of permeability, suction/injection parameter, velocity parameter and slip parameter on the structure of velocity, temperature and mass transfer rates are examined with the aid of several graphs. Moreover, observations based on Schmidt number and Soret number are also presented. The result shows, the increase in permeability of the porous medium increase the velocity and decrease the temperature profile. This happens due to a decrease in drag of the fluid flow. In the case of heat transfer, the increase in permeability and slip parameter causes an increase in heat transfer. However for the case of increase in thermal slip parameter there is a decrease in heat transfer. An increase in the mass slip parameter causes a decrease in the concentration field. The suction and injection parameter has similar effect on concentration profile as for the case of velocity profile.

Steady Boundary Layer Slip Flow along with Heat and Mass Transfer over a Flat Porous Plate Embedded in a Porous Medium

PubMed Central

Aziz, Asim; Siddique, J. I.; Aziz, Taha

2014-01-01

In this paper, a simplified model of an incompressible fluid flow along with heat and mass transfer past a porous flat plate embedded in a Darcy type porous medium is investigated. The velocity, thermal and mass slip conditions are utilized that has not been discussed in the literature before. The similarity transformations are used to transform the governing partial differential equations (PDEs) into a nonlinear ordinary differential equations (ODEs). The resulting system of ODEs is then reduced to a system of first order differential equations which was solved numerically by using Matlab bvp4c code. The effects of permeability, suction/injection parameter, velocity parameter and slip parameter on the structure of velocity, temperature and mass transfer rates are examined with the aid of several graphs. Moreover, observations based on Schmidt number and Soret number are also presented. The result shows, the increase in permeability of the porous medium increase the velocity and decrease the temperature profile. This happens due to a decrease in drag of the fluid flow. In the case of heat transfer, the increase in permeability and slip parameter causes an increase in heat transfer. However for the case of increase in thermal slip parameter there is a decrease in heat transfer. An increase in the mass slip parameter causes a decrease in the concentration field. The suction and injection parameter has similar effect on concentration profile as for the case of velocity profile. PMID:25531301

Fabrication Techniques and Principles for Flat Plate Antennas

DOT National Transportation Integrated Search

1973-09-01

The report documents the fabrication techniques and principles selected to produce one and ten million flat plate antennas per year. An engineering analysis of the reliability, electrical integrity, and repeatability is made, and a cost analysis summ...

Unsteady force estimation using a Lagrangian drift-volume approach

NASA Astrophysics Data System (ADS)

McPhaden, Cameron J.; Rival, David E.

2018-04-01

A novel Lagrangian force estimation technique for unsteady fluid flows has been developed, using the concept of a Darwinian drift volume to measure unsteady forces on accelerating bodies. The construct of added mass in viscous flows, calculated from a series of drift volumes, is used to calculate the reaction force on an accelerating circular flat plate, containing highly-separated, vortical flow. The net displacement of fluid contained within the drift volumes is, through Darwin's drift-volume added-mass proposition, equal to the added mass of the plate and provides the reaction force of the fluid on the body. The resultant unsteady force estimates from the proposed technique are shown to align with the measured drag force associated with a rapid acceleration. The critical aspects of understanding unsteady flows, relating to peak and time-resolved forces, often lie within the acceleration phase of the motions, which are well-captured by the drift-volume approach. Therefore, this Lagrangian added-mass estimation technique opens the door to fluid-dynamic analyses in areas that, until now, were inaccessible by conventional means.

Using thermal and compositional modeling to assess the role of water in Alaskan flat slab subduction

NASA Astrophysics Data System (ADS)

Robinson, S. E.; Porter, R. C.; Hoisch, T. D.

2017-12-01

Although plate tectonic theory is well established in the geosciences, the mechanisms and details of various plate-tectonics related phenomena are not always well understood. In some ( 10%) convergent plate boundaries, subduction of downgoing oceanic plates is characterized by low angle geometries and is termed "flat slab subduction." The mechanism(s) driving this form of subduction are not well understood. The goal of this study is to explore the role that water plays in these flat slab subduction settings. This is important for a better understanding of the behavior of these systems and for assessing volcanic hazards associated with subduction and slab rollback. In southern Alaska, the Pacific Plate is subducting beneath the North American plate at a shallow angle. This low-angle subduction within the region is often attributed to the subduction of the Yakutat block, a terrane accreting to the south-central coast of Alaska. This flat slab region is bounded by the Aleution arc to the west and the strike-slip Queen Charlotte fault to the east. Temperature and compositional models for a 500-km transect across this subduction zone in Alaska were run for ten million years (the length of time that flat slab subduction has been ongoing in Alaska) and allow for interpretation of present-day conditions at depth. This allows for an evaluation of two hypotheses regarding the role of water in flat-slab regions: (1) slab hydration and dehydration help control slab buoyancy which influences whether flat slab subduction will be maintained or ended. (2) slab hydration/dehydration of the overlying lithosphere impacts deformation within the upper plate as water encourages plate deformation. Preliminary results from thermal modeling using Thermod8 show that cooling of the mantle to 500 °C is predicted down to 100 km depth at 10 million years after the onset of low-angle subduction (representing present-day). Results from compositional modeling in Perple_X show the maximum amount of water that can be held in the system assuming crustal (basalt and metabasalt) and mantle (peridotite) compositions. These models will be compared with seismic velocity models created from EarthScope Transportable Array data in the region in order to determine amounts of serpentinite and other water-bearing rocks within the flat slab subduction system.

Performance of Renormalization Group Algebraic Turbulence Model on Boundary Layer Transition Simulation

NASA Technical Reports Server (NTRS)

Ahn, Kyung H.

1994-01-01

The RNG-based algebraic turbulence model, with a new method of solving the cubic equation and applying new length scales, is introduced. An analysis is made of the RNG length scale which was previously reported and the resulting eddy viscosity is compared with those from other algebraic turbulence models. Subsequently, a new length scale is introduced which actually uses the two previous RNG length scales in a systematic way to improve the model performance. The performance of the present RNG model is demonstrated by simulating the boundary layer flow over a flat plate and the flow over an airfoil.

Experimental and predicted cavitation performance of an 80.6 deg helical inducer in high temperature water

NASA Technical Reports Server (NTRS)

Kovich, G.

1972-01-01

The cavitating performance of a stainless steel 80.6 degree flat-plate helical inducer was investigated in water over a range of liquid temperatures and flow coefficients. A semi-empirical prediction method was used to compare predicted values of required net positive suction head in water with experimental values obtained in water. Good agreement was obtained between predicted and experimental data in water. The required net positive suction head in water decreased with increasing temperature and increased with flow coefficient, similar to that observed for a like inducer in liquid hydrogen.

Representation of turbulent shear stress by a product of mean velocity differences

NASA Technical Reports Server (NTRS)

Braun, W. H.

1977-01-01

A quadratic form in the mean velocity for the turbulent shear stress is presented. It is expressed as the product of two velocity differences whose roots are the maximum velocity in the flow and a cutoff velocity below which the turbulent shear stress vanishes. Application to pipe and channel flows yields the centerline velocity as a function of pressure gradient, as well as the velocity profile. The flat plate, boundary-layer problem is solved by a system of integral equations to obtain friction coefficient, displacement thickness, and momentum-loss thickness. Comparisons are made with experiment.

An abbreviated Reynolds stress turbulence model for airfoil flows

NASA Technical Reports Server (NTRS)

Gaffney, R. L., Jr.; Hassan, H. A.; Salas, M. D.

1990-01-01

An abbreviated Reynolds stress turbulence model is presented for solving turbulent flow over airfoils. The model consists of two partial differential equations, one for the Reynolds shear stress and the other for the turbulent kinetic energy. The normal stresses and the dissipation rate of turbulent kinetic energy are computed from algebraic relationships having the correct asymptotic near wall behavior. This allows the model to be integrated all the way to the wall without the use of wall functions. Results for a flat plate at zero angle of attack, a NACA 0012 airfoil and a RAE 2822 airfoil are presented.

An experimental study of a three-dimensional shock wave/turbulent boundary-layer interaction at a hypersonic Mach number

NASA Technical Reports Server (NTRS)

Kussoy, M. I.; Horstman, K. C.; Kim, K.-S.

1991-01-01

Experimental data for a series of three-dimensional shock-wave/turbulent-boundary-layer interaction flows at Mach 8.2 are presented. The test bodies, composed of sharp fins fastened to a flat-plate test surface, were designed to generate flows with varying degrees of pressure gradient, boundary-layer separation, and turning angle. The data include surface-pressure, heat-transfer, and skin-friction distributions, as well as limited mean flowfield surveys both in the undisturbed and interaction regimes. The data were obtained for the purpose of validating computational models of these hypersonic interactions.

The interaction of moderately strong shock waves with thick perforated walls of low porosity

NASA Technical Reports Server (NTRS)

Grant, D. J.

1972-01-01

A theoretical prediction is given of the flow through thick perforated walls of low porosity resulting from the impingement of a moderately strong traveling shock wave. The model was a flat plate positioned normal to the direction of the flow. Holes bored in the plate parallel to the direction of the flow provided nominal hole length-to-diameter ratios of 10:1 and an axial porosity of 25 percent of the flow channel cross section. The flow field behind the reflected shock wave was assumed to behave as a reservoir producing a quasi-steady duct flow through the model. Rayleigh and Fanno duct flow theoretical computations for each of three possible auxiliary wave patterns that can be associated with the transmitted shock (to satisfy contact surface compatibility) were used to provide bounding solutions as an alternative to the more complex influence coefficients method. Qualitative and quantitative behavior was verified in a 1.5- by 2.0-in. helium shock tube. High speed Schlieren photography, piezoelectric pressure-time histories, and electronic-counter wave speed measurements were used to assess the extent of correlation with the theoretical flow models. Reduced data indicated the adequacy of the bounding theory approach to predict wave phenomena and quantitative response.

The remarkable ability of turbulence model equations to describe transition

NASA Technical Reports Server (NTRS)

Wilcox, David C.

1992-01-01

This paper demonstrates how well the k-omega turbulence model describes the nonlinear growth of flow instabilities from laminar flow into the turbulent flow regime. Viscous modifications are proposed for the k-omega model that yield close agreement with measurements and with Direct Numerical Simulation results for channel and pipe flow. These modifications permit prediction of subtle sublayer details such as maximum dissipation at the surface, k approximately y(exp 2) as y approaches 0, and the sharp peak value of k near the surface. With two transition specific closure coefficients, the model equations accurately predict transition for an incompressible flat-plate boundary layer. The analysis also shows why the k-epsilon model is so difficult to use for predicting transition.

Boundary-layer development and transition due to free-stream exothermic reactions in shock-induced flows

NASA Technical Reports Server (NTRS)

Hall, J. L.

1974-01-01

A study of the effect of free-stream thermal-energy release from shock-induced exothermic reactions on boundary-layer development and transition is presented. The flow model is that of a boundary layer developing behind a moving shock wave in two-dimensional unsteady flow over a shock-tube wall. Matched sets of combustible hydrogen-oxygen-nitrogen mixtures and inert hydrogen-nitrogen mixtures were used to obtain transition data over a range of transition Reynolds numbers from 1,100,000 to 21,300,000. The heat-energy is shown to significantly stabilize the boundary layer without changing its development character. A method for application of this data to flat-plate steady flows is included.

Velocity field of a round jet in a cross flow for various jet injection angles and velocity ratios. [Langley V/STOL tunnel

NASA Technical Reports Server (NTRS)

Fearn, R. L.; Weston, R. P.

1979-01-01

A subsonic round jet injected from a flat plate into a subsonic crosswind of the same temperature was investigated. Velocity and pressure measurements in planes perpendicular to the path of the jet were made for nominal jet injection angles of 45 deg, 60 deg, 75 deg, 90 deg, and 105 deg and for jet/cross flow velocity ratios of four and eight. The velocity measurements were obtained to infer the properties of the vortex pair associated with a jet in a cross flow. Jet centerline and vortex trajectories were determined and fit with an empirical equation that includes the effects of jet injection angle, jet core length, and jet/cross flow velocity ratios.

Implementation of Advanced Two Equation Turbulence Models in the USM3D Unstructured Flow Solver

NASA Technical Reports Server (NTRS)

Wang, Qun-Zhen; Massey, Steven J.; Abdol-Hamid, Khaled S.

2000-01-01

USM3D is a widely-used unstructured flow solver for simulating inviscid and viscous flows over complex geometries. The current version (version 5.0) of USM3D, however, does not have advanced turbulence models to accurately simulate complicated flow. We have implemented two modified versions of the original Jones and Launder k-epsilon "two-equation" turbulence model and the Girimaji algebraic Reynolds stress model in USM3D. Tests have been conducted for three flat plate boundary layer cases, a RAE2822 airfoil and an ONERA M6 wing. The results are compared with those from direct numerical simulation, empirical formulae, theoretical results, and the existing Spalart-Allmaras one-equation model.

Numerical modeling of Farallon Plate flat-slab subduction: Influence of lithosphere structure and rheology on slab dynamics

NASA Astrophysics Data System (ADS)

Liu, X.; Currie, C. A.

2017-12-01

The subducted Farallon plate is believed to have evolved to a flat geometry underneath North America plate during Late Cretaceous, triggering Laramide deformation within the continental interior. However, the mechanism that caused the oceanic slab to flatten and the factors that control the flat-slab depth remain uncertain. In this work, we use 2D thermal-mechanical models using the SOPALE code to study the subduction dynamics from 90 Ma to 50 Ma. During this period, an oceanic plateau (Shatsky Conjugate) is inferred to have subducted beneath western North America and interacted with the continental lithosphere, including areas of thicker lithosphere such as the Colorado Plateau and Wyoming Craton. Based on seismic tomography and plate reconstruction data sets, we built a set of models to examine the influence of the structure and rheology of the oceanic and continental plates on slab dynamics. Models include a 600 km wide oceanic plateau consisting of 18 km thick crust and a 36 km thick underlying harzburgite layer, and we ran a series of model experiments to test different continental thicknesses (80 km, 120 km, & 180 km) and continental mantle lithosphere strengths (approximating conditions from wet olivine to dry olivine). Consistent with earlier studies, we find that creation of a long flat slab requires a buoyant oceanic plateau (i.e., non-eclogitized crust) and trenchward motion of the continent. In addition, our models demonstrate the upper plate has an important control on slab dynamics. A flat slab requires either a thin continent or, if the continent is thick, its mantle lithosphere must be relatively weak so that it can be displaced by the flattening slab. The depth of the flat slab is mainly controlled by two factors: (1) the continental thickness and (2) the strength of the continental mantle lithosphere. For the same initial lithosphere thickness (120 km), a shallower flat slab ( 90 km depth) occurs for the weakest mantle lithosphere ( wet olivine) compared to 120 km depth for strong ( dry) mantle lithosphere because the flat slab removes the lowermost weak lithosphere. Moreover, an even deeper slab ( 130 km) can be found underneath the weakest but thicker continental lithosphere (180 km). Future models will focus on how the flat slab may induce hydration and deformation for the overriding continental plate.

LES/RANS Modeling of Aero-Optical Effects in a Supersonic Cavity Flow

DTIC Science & Technology

2016-06-13

the wind tunnel is not modeled in the cavity simulation, a separate turbulent boundary layer simulation with identical free-stream conditions was...the wind tunnel experiments were provided by Dr. Donald J. Wittich and the testbed geometries were modeled by Mr. Jeremy Stanford. Dr. Maziar Hemati...and an auxiliary flat plate simulation is performed to replicate the effects of the wind - tunnel boundary layer on the computed optical path

Aero-Mechanical Coupling in a High-Speed Compressor

DTIC Science & Technology

2010-02-01

compressor for which this facility is being designed is a scale model of a single stage of a civil jet engine . A strong non-synchronous blade vibration was...Flutter and resonant vibration characteristics of engine blades . Journal of engineering for gas turbines and power, 119. Thermann, H. and Niehuis, R...changes in airfoil lift associated with the unsteady flow. The blade aerodynamics are approximated by a flat plate, however more complex shapes can be

Turbulent transport modeling of shear flows around an aerodynamic wing. Development of turbulent near-wall model and its application to recirculating flows

NASA Technical Reports Server (NTRS)

Amano, R. S.

1982-01-01

Progress in implementing and refining two near-wall turbulence models in which the near-wall region is divided into either two or three zones is outlined. These models were successfully applied to the computation of recirculating flows. The research was further extended to obtaining experimental results of two different recirculating flow conditions in order to check the validity of the present models. Two different experimental apparatuses were set up: axisymmetric turbulent impinging jets on a flat plate, and turbulent flows in a circular pipe with a abrupt pipe expansion. It is shown that generally better results are obtained by using the present near-wall models, and among the models the three-zone model is superior to the two-zone model.

Turbulent flow around a wing-fuselage type juncture

NASA Technical Reports Server (NTRS)

Kubendran, L. R.; Mcmahon, H. M.; Hubbartt, J. E.

1985-01-01

The flow over a 58-mm-thick uniform-thickness winglike body having a 1.5:1 elliptical leading edge and joined to a large flat plate (representing an aircraft fuselage) is characterized experimentally at freestream velocity 15 m/s, corresponding to Reynolds number 940,000/m, using hot-wire anemometry. The results are presented graphically, and it is found that the horseshoe vortex formed by the separation of the fuselage boundary layer ahead of the wing leading edge is effective in transporting turbulence and modifying the mean-flow characteristics and the turbulent-stress distribution. It is suggested that the slenderness ratio of the leading edge is the dominant factor affecting the strength and location of the vortex.

Heat transfer and fluid mechanics measurements in transitional boundary layer flows

NASA Technical Reports Server (NTRS)

Wang, T.; Simon, T. W.; Buddhavarapu, J.

1985-01-01

Experimental results are presented to document hydrodynamic and thermal development of flat-plate boundary layers undergoing natural transition. Local heat transfer coefficients, skin friction coefficients and profiles of velocity, temperature and Reynolds normal and shear stresses are presented. A case with no transition and transitional cases with 0.68% and 2.0% free-stream disturbance intensities were investigated. The locations of transition are consistent with earlier data. A late-laminar state with significant levels of turbulence is documented. In late-transitional and early-turbulent flows, turbulent Prandtl number and conduction layer thickness values exceed, and the Reynolds analogy factor is less than, values previously measured in fully turbulent flows.

Solving Navier-Stokes Equations with Advanced Turbulence Models on Three-Dimensional Unstructured Grids

NASA Technical Reports Server (NTRS)

Wang, Qun-Zhen; Massey, Steven J.; Abdol-Hamid, Khaled S.; Frink, Neal T.

1999-01-01

USM3D is a widely-used unstructured flow solver for simulating inviscid and viscous flows over complex geometries. The current version (version 5.0) of USM3D, however, does not have advanced turbulence models to accurately simulate complicated flows. We have implemented two modified versions of the original Jones and Launder k-epsilon two-equation turbulence model and the Girimaji algebraic Reynolds stress model in USM3D. Tests have been conducted for two flat plate boundary layer cases, a RAE2822 airfoil and an ONERA M6 wing. The results are compared with those of empirical formulae, theoretical results and the existing Spalart-Allmaras one-equation model.

Unsteady boundary-layer injection

NASA Technical Reports Server (NTRS)

Telionis, D. P.; Jones, G. S.

1981-01-01

The boundary-layer equations for two-dimensional incompressible flow are integrated numerically for the flow over a flat plate and a Howarth body. Injection is introduced either impulsively or periodically along a narrow strip. Results indicate that injection perpendicular to the wall is transmitted instantly across the boundary layer and has little effect on the velocity profile parallel to the wall. The effect is a little more noticeable for flows with adverse pressure gradients. Injection parallel to the wall results in fuller velocity profiles. Parallel and oscillatory injection appears to influence the mean. The amplitude of oscillation decreases with distance from the injection strip but further downstream it increases again in a manner reminiscent of an unstable process.

Stability of a laminar premixed supersonic free shear layer with chemical reactions

NASA Technical Reports Server (NTRS)

Menon, S.; Anderson, J. D., Jr.; Pai, S. I.

1984-01-01

The stability of a two-dimensional compressible supersonic flow in the wake of a flat plate is discussed. The fluid is a multi-species mixture which is undergoing finite rate chemical reactions. The spatial stability of an infinitesimal disturbance in the fluid is considered. Numerical solutions of the eigenvalue stability equations for both reactive and nonreactive supersonic flows are presented and discussed. The chemical reactions have significant influence on the stability behavior. For instance, a neutral eigenvalue is observed near the freestream Mach number of 2.375 for the nonreactive case, but disappears when the reaction is turned on. For reactive flows, the eigenvalues are not very dependent on the free stream Mach number.

On the accuracy of Whitham's method. [for steady ideal gas flow past cones

NASA Technical Reports Server (NTRS)

Zahalak, G. I.; Myers, M. K.

1974-01-01

The steady flow of an ideal gas past a conical body is studied by the method of matched asymptotic expansions and by Whitham's method in order to assess the accuracy of the latter. It is found that while Whitham's method does not yield a correct asymptotic representation of the perturbation field to second order in regions where the flow ahead of the Mach cone of the apex is disturbed, it does correctly predict the changes of the second-order perturbation quantities across a shock (the first-order shock strength). The results of the analysis are illustrated by a special case of a flat, rectangular plate at incidence.

Various mechanisms to induce present-day shallow flat subduction and implications for the younger Earth: a numerical parameter study

NASA Astrophysics Data System (ADS)

van Hunen, Jeroen; van den Berg, Arie P.; Vlaar, Nico J.

2004-08-01

Shallow flat subduction is a relatively common feature at present-day subduction zones. Several mechanisms to explain this feature have been proposed, and can be subdivided into three groups: overthrusting of the subducting plate, subduction of a plume-generated oceanic plateau, and slab suction forces. We developed a numerical model to investigate these mechanisms and tested it through a comparison of the model results with the observations of the Peru flat slab where all three mechanisms seem to be contributing. The ratio of contributions of overthrusting continent to plateau subduction is in the range of 1:1 to 1:2, and the role of plate suction forces is likely to be significant. By applying the overthrusting continent and plateau subduction mechanisms separately, we were able to determine the most important model parameters for each of the mechanisms. Overthrusting easily results in flat subduction, and the flat slab length is primarily a function of slab age, overriding plate motion and mantle viscosity. An oceanic plateau is much less likely to cause flat subduction, and favorable conditions for flat subduction include a young slab age, long-lived plateau buoyancy after subduction, a strong mantle, and addition of slab suction forces that are large enough to further reduce the subduction dip angle, once the plateau initiates this flattening. Furthermore, we found that even though today flat subduction can be explained with the dominant model parameters within a reasonable range, for a slightly hotter, younger Earth, these flat subduction conditions are much less favorable, and so this style of subduction was probably not present in the past. This contradicts earlier predictions that flat subduction was a more wide-spread phenomenon in the early stages of plate tectonics in a younger earth.

Investigation of the effects of pressure gradient, temperature and wall temperature ratio on the stagnation point heat transfer for circular cylinders and gas turbine vanes

NASA Technical Reports Server (NTRS)

Nagamatsu, H. T.; Duffy, R. E.

1984-01-01

Low and high pressure shock tubes were designed and constructed for the purpose of obtaining heat transfer data over a temperature range of 390 to 2500 K, pressures of 0.3 to 42 atm, and Mach numbers of 0.15 to 1.5 with and without pressure gradient. A square test section with adjustable top and bottom walls was constructed to produce the favorable and adverse pressure gradient over the flat plate with heat gages. A water cooled gas turbine nozzle cascade which is attached to the high pressure shock tube was obtained to measuse the heat flux over pressure and suction surfaces. Thin-film platinum heat gages with a response time of a few microseconds were developed and used to measure the heat flux for laminar, transition, and turbulent boundary layers. The laminar boundary heat flux on the shock tube wall agreed with Mirel's flat plate theory. Stagnation point heat transfer for circular cylinders at low temperature compared with the theoretical prediction, but for a gas temperature of 922 K the heat fluxes were higher than the predicted values. Preliminary flat plate heat transfer data were measured for laminar, transition, and turbulent boundary layers with and without pressure gradients for free-stream temperatures of 350 to 2575 K and flow Mach numbers of 0.11 to 1.9. The experimental heat flux data were correlated with the laminar and turbulent theories and the agreement was good at low temperatures which was not the case for higher temperatures.

Llinas’ Phase Reset Mechanism Delays the Onset of Chaos in Shark and Dolphin Wall Turbulence

DTIC Science & Technology

2014-02-10

eruption due to plate tectonics . (The plate becomes locally thin and is unable to prevent the high-pressure hot magma from erupting.) The vorticity...flat plate value. The spacing between riblet peaks s+= 10 is used unless noted. KM gives the "strength" of the riblets, where the terms "weak" and...exhibit spanwise variations in skin friction coefficients and integral boundary layer properties, even in flat plate experiments where great care has

Design and installation package for the Sunmat Flat Plate solar collector

NASA Technical Reports Server (NTRS)

1978-01-01

The information used in evaluating the design of a liquid flat plate solar collector is reported. Included in this package are subsystem performance specification, installation, operation and maintenance manuals, collector sizing guides, and detailed drawings of the single-glazed collector.

Certification and verification for Calmac flat plate solar collector

NASA Technical Reports Server (NTRS)

1978-01-01

Information used in the certification and verification of the Calmac Flat Plate Collector is presented. Contained are such items as test procedures and results, information on materials used, installation, operation, and maintenance manuals, and other information pertaining to the verification and certification.

On the flow generated by rotating flat plates of low aspect ratio

NASA Astrophysics Data System (ADS)

DeVoria, Adam C.

Low-aspect-ratio propulsors typically allow for high maneuverability at low-to-moderate speeds. This has made them the subject of much recent research aimed at employing such appendages on autonomous vehicles which are required to navigate tumultuous environments. This experimental investigation focuses on the fluid dynamic aspects associated with overly-simplified versions of such biologically-inspired propulsors. In doing so, fundamental contributions are made to the research area. The unsteady, three-dimensional flow of a low-aspect-ratio, trapezoidal flat plate undergoing rotation from rest at a 90° angle of attack and Reynolds numbers of O(103) is investigated experimentally. The objectives are to develop a straightforward protocol for vortex saturation, and to understand the effects of the root-to-tip flow for different velocity programs. The experiments are conducted in a glass-walled tank, and digital particle image velocimetry is used to obtain planar velocity measurements. A formation-parameter definition is investigated and is found to reasonably predict the state corresponding to the pinch-off of the initial tip vortex across the velocity programs tested. The flow in the region near the tip is relatively insensitive to Reynolds number over the range studied. The component normal to the plate is unaffected by total rotational amplitude while the tangential component has dependence on this angle. Also, an estimate of the first tip-vortex pinch-off time is obtained from the near-tip velocity data and agrees very well with values estimated using circulation. The angle of incidence of the bulk root-to-tip flow relative to the plate normal becomes more oblique with increasing rotational amplitude. Accordingly, the peak magnitude of the tangential velocity is also increased and as a result advects fluid momentum away from the plate at a higher rate. The more oblique impingement of the root-to-tip flow for increasing rotational amplitude is shown to have a distinct effect on the associated fluid dynamic force normal to the plate. For impulsive plate deceleration the time that a non-negligible force exists decreases, while for non-impulsive plate deceleration both this time and the relative force magnitude decrease for larger rotational amplitudes. In a separate set of experiments, force measurements are conducted on a similar plate that performs an advancing stroke from rest followed by a returning stroke. The parameters varied are the rotational amplitude of the motion and the rest time between the advancing and returning strokes. The unsteady normal forces track with the angular acceleration of the plate, with the added mass force peak in the returning stroke being larger than that in the advancing stroke. However, as the rest time is increased, the normal forces generated in each stroke become dynamically similar. The maximum total impulse is calculated from the force measurements and rapidly decays from its largest value at zero rest time and asymptotes to a constant with increased rest time. The direction of this impulse is also calculated and quickly approaches the direction about which the plate motion is symmetric. The largest additional impulse contribution obtained from executing a returning stroke within a finite time is approximately 18%. Increases in rotational amplitude initially increase the maximum total impulse, but it then plateaus at an amplitude of around 90 degrees. For non-zero rest times, any maxima of the impulse in a fixed direction are weak and necessarily reduced from the maximum possible impulse. For a nearly 100 degrees range of directions, the impulse is largest for rotational amplitudes between 75--90 degrees. The results are also applied to three types of propulsive configurations.

Adaptive multigrid domain decomposition solutions for viscous interacting flows

NASA Technical Reports Server (NTRS)

Rubin, Stanley G.; Srinivasan, Kumar

1992-01-01

Several viscous incompressible flows with strong pressure interaction and/or axial flow reversal are considered with an adaptive multigrid domain decomposition procedure. Specific examples include the triple deck structure surrounding the trailing edge of a flat plate, the flow recirculation in a trough geometry, and the flow in a rearward facing step channel. For the latter case, there are multiple recirculation zones, of different character, for laminar and turbulent flow conditions. A pressure-based form of flux-vector splitting is applied to the Navier-Stokes equations, which are represented by an implicit lowest-order reduced Navier-Stokes (RNS) system and a purely diffusive, higher-order, deferred-corrector. A trapezoidal or box-like form of discretization insures that all mass conservation properties are satisfied at interfacial and outflow boundaries, even for this primitive-variable, non-staggered grid computation.

Three-flat test with plates in horizontal posture

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vannoni, Maurizio; Molesini, Giuseppe

2008-04-20

Measuring flats in the horizontal posture with interferometers is analyzed in detail, taking into account the sag produced by gravity. A mathematical expression of the bending is provided for a plate supported at three unevenly spaced locations along the edge. It is shown that the azimuthal terms of the deformation can be recovered from a three-flat measuring procedure, while the pure radial terms can only be estimated. The effectiveness of the iterative algorithm for data processing is also demonstrated. Experimental comparison on a set of three flats in horizontal and upright posture is provided.

Computation of saddle point of attachment

NASA Technical Reports Server (NTRS)

Hung, Ching-Mao; Sung, Chao-Ho; Chen, Chung-Lung

1991-01-01

Low-speed flows over a cylinder mounted on a flat plate are studied numerically in order to confirm the existence of a saddle point of attachment in the flow before an obstacle, to analyze the flow characteristics near the saddle point theoretically, and to address the significance of the saddle point of attachment to the construction of external flow structures, the interpretation of experimental surface oil-flow patterns, and the theoretical definition of three-dimensional flow separation. Two numerical codes, one for an incompressible flow and another for a compressible flow, are used for various Mach numbers, Reynolds numbers, grid sizes, and numbers of grid points. It is pointed out that the potential presence of a saddle point of attachment means that a line of 'oil accumulation' from both sides of a skin-friction line emanating outward from a saddle point can be either a line of separation or a line of attachment.

On the instability of hypersonic flow past a flat plate

NASA Technical Reports Server (NTRS)

Blackaby, Nicholas; Cowley, Stephen; Hall, Philip

1990-01-01

The instability of hypersonic boundary-layer flows over flat plates is considered. The viscosity of the fluid is taken to be governed by Sutherland's law, which gives a much more accurate representation of the temperature dependence of fluid viscosity at hypersonic speeds than Chapman's approximate linear law; although at lower speeds the temperature variation of the mean state is less pronounced so that the Chapman law can be used with some confidence. Attention is focussed on the so-called (vorticity) mode of instability of the viscous hypersonic boundary layer. This is thought to be the fastest growing inviscid disturbance at hypersonic speeds; it is also believed to have an asymptotically larger growth rate than any viscous or centrifugal instability. As a starting point the instability of the hypersonic boundary layer which exists far downstream from the leading edge of the plate is investigated. In this regime the shock that is attached to the leading edge of the plate plays no role, so that the basic boundary layer is non-interactive. It is shown that the vorticity mode of instability of this flow operates on a significantly different lengthscale than that obtained if a Chapman viscosity law is assumed. In particular, it is found that the growth rate predicted by a linear viscosity law overestimates the size of the growth rate by O(M(exp 2). Next, the development of the vorticity mode as the wavenumber decreases is described, and it is shown that acoustic modes emerge when the wavenumber has decreased from it's O(1) initial value to O(M (exp -3/2). Finally, the inviscid instability of the boundary layer near the leading edge in the interaction zone is discussed and particular attention is focussed on the strong interaction region which occurs sufficiently close to the leading edge. It is found that the vorticity mode in this regime is again unstable, and that it is concentrated in the transition layer at the edge of the boundary layer where the temperature adjusts from its large, O(M(exp 2), value in the viscous boundary layer, to its O(1) free stream value. The existence of the shock indirectly, but significantly, influences the instability problem by modifying the basic flow structure in this layer.

Comparisons of the Maxwell and CLL Gas/Surface Interaction Models Using DSMC

NASA Technical Reports Server (NTRS)

Hedahl, Marc O.

1995-01-01

Two contrasting models of gas-surface interactions are studied using the Direct Simulation Monte Carlo (DSMC) method. The DSMC calculations examine differences in predictions of aerodynamic forces and heat transfer between the Maxwell and Cercignani-Lampis-Lord (CLL) models for flat plate configurations at freestream conditions corresponding to a 140 km orbit around Venus. The size of the flat plate is that of one of the solar panels on the Magellan spacecraft, and the freestream conditions are one of those experienced during aerobraking maneuvers. Results are presented for both a single flat plate and a two-plate configuration as a function of angle of attack and gas-surface accommodation coefficients. The two plate system is not representative of the Magellan geometry, but is studied to explore possible experiments that might be used to differentiate between the two gas surface interaction models.

Free vibration of rectangular plates with a small initial curvature

NASA Technical Reports Server (NTRS)

Adeniji-Fashola, A. A.; Oyediran, A. A.

1988-01-01

The method of matched asymptotic expansions is used to solve the transverse free vibration of a slightly curved, thin rectangular plate. Analytical results for natural frequencies and mode shapes are presented in the limit when the dimensionless bending rigidity, epsilon, is small compared with in-plane forces. Results for different boundary conditions are obtained when the initial deflection is: (1) a polynomial in both directions, and (2) the product of a polynomial and a trigonometric function, and arbitrary. For the arbitrary initial deflection case, the Fourier series technique is used to define the initial deflection. The results obtained show that the natural frequencies of vibration of slightly curved plates are coincident with those of perfectly flat, prestressed rectangular plates. However, the eigenmodes are very different from those of initially flat prestressed rectangular plates. The total deflection is found to be the sum of the initial deflection, the deflection resulting from the solution of the flat plate problem, and the deflection resulting from the static problem.

78 FR 16832 - Corrosion-Resistant Carbon Steel Flat Products From Germany and the Republic of Korea: Revocation...

Federal Register 2010, 2011, 2012, 2013, 2014

2013-03-19

.... Excluded from the scope of the orders are flat-rolled steel products either plated or coated with tin, lead, chromium, chromium oxides, both tin and lead (``terne plate''), or both chromium and chromium oxides (``tin...

Model 0102 Flat Plate Antenna for Use in Automobile Radar Anticipatory Crash Sensors

DOT National Transportation Integrated Search

1973-09-01

The report analyzed alternative methods of construction and production costs for a flat plate antenna based on the use of etched circuit techniques. The antenna is proposed for use in certain new automotive radar anticipatory crash sensor systems now...

LDEF transverse flat plate heat pipe experiment /S1005/. [Long Duration Exposure Facility

NASA Technical Reports Server (NTRS)

Robinson, G. A., Jr.

1979-01-01

The paper describes the Transverse Flat Plate Heat Pipe Experiment. A transverse flat plate heat pipe is a thermal control device that serves the dual function of temperature control and mounting base for electronic equipment. In its ultimate application, the pipe would be a lightweight structure member that could be configured in a platform or enclosure and provide temperature control for large space structures, flight experiments, equipment, etc. The objective of the LDEF flight experiment is to evaluate the zero-g performance of a number of transverse flat plate heat pipe modules. Performance will include: (1) the pipes transport capability, (2) temperature drop, and (3) ability to maintain temperature over varying duty cycles and environments. Performance degradation, if any, will be monitored over the length of the LDEF mission. This information is necessary if heat pipes are to be considered for system designs where they offer benefits not available with other thermal control techniques, such as minimum weight penalty, long-life heat pipe/structural members.

Analysis of behavior of simply supported flat plates compressed beyond the buckling load into the plastic range

NASA Technical Reports Server (NTRS)

Mayers, J; Budiansky, Bernard

1955-01-01

An analysis is presented of the postbuckling behavior of a simply supported square flat plate with straight edges compressed beyond the buckling load into the plastic range. The method of analysis involves the application of a variational principle of the deformation theory of plasticity in conjunction with computations carried out on a high-speed calculating machine. Numerical results are obtained for several plate proportions and for one material. The results indicate plate strengths greater than those that have been found experimentally on plates that do not satisfy straight-edge conditions. (author)

Computational and experimental investigation of two-dimensional scramjet inlets and hypersonic flow over a sharp flat plate

NASA Astrophysics Data System (ADS)

Messitt, Donald G.

1999-11-01

The WIND code was employed to compute the hypersonic flow in the shock wave boundary layer merged region near the leading edge of a sharp flat plate. Solutions were obtained at Mach numbers from 9.86 to 15.0 and free stream Reynolds numbers of 3,467 to 346,700 in-1 (1.365 · 105 to 1.365 · 107 m-1) for perfect gas conditions. The numerical results indicated a merged shock wave and viscous layer near the leading edge. The merged region grew in size with increasing free stream Mach number, proportional to Minfinity 2/Reinfinity. Profiles of the static pressure in the merged region indicated a strong normal pressure gradient (∂p/∂y). The normal pressure gradient has been neglected in previous analyses which used the boundary layer equations. The shock wave near the leading edge was thick, as has been experimentally observed. Computed shock wave locations and surface pressures agreed well within experimental error for values of the rarefaction parameter, chi/M infinity2 < 0.3. A preliminary analysis using kinetic theory indicated that rarefied flow effects became important above this value. In particular, the WIND solution agreed well in the transition region between the merged flow, which was predicted well by the theory of Li and Nagamatsu, and the downstream region where the strong interaction theory applied. Additional computations with the NPARC code, WIND's predecessor, demonstrated the ability of the code to compute hypersonic inlet flows at free stream Mach numbers up to 20. Good qualitative agreement with measured pressure data indicated that the code captured the important physical features of the shock wave - boundary layer interactions. The computed surface and pitot pressures fell within the combined experimental and numerical error bounds for most points. The calculations demonstrated the need for extremely fine grids when computing hypersonic interaction flows.

Fast PSP measurements of wall-pressure fluctuation in low-speed flows: improvements using proper orthogonal decomposition

NASA Astrophysics Data System (ADS)

Peng, Di; Wang, Shaofei; Liu, Yingzheng

2016-04-01

Fast pressure-sensitive paint (PSP) is very useful in flow diagnostics due to its fast response and high spatial resolution, but its applications in low-speed flows are usually challenging due to limitations of paint's pressure sensitivity and the capability of high-speed imagers. The poor signal-to-noise ratio in low-speed cases makes it very difficult to extract useful information from the PSP data. In this study, unsteady PSP measurements were made on a flat plate behind a cylinder in a low-speed wind tunnel (flow speed from 10 to 17 m/s). Pressure fluctuations (Δ P) on the plate caused by vortex-plate interaction were recorded continuously by fast PSP (using a high-speed camera) and a microphone array. Power spectrum of pressure fluctuations and phase-averaged Δ P obtained from PSP and microphone were compared, showing good agreement in general. Proper orthogonal decomposition (POD) was used to reduce noise in PSP data and extract the dominant pressure features. The PSP results reconstructed from selected POD modes were then compared to the pressure data obtained simultaneously with microphone sensors. Based on the comparison of both instantaneous Δ P and root-mean-square of Δ P, it was confirmed that POD analysis could effectively remove noise while preserving the instantaneous pressure information with good fidelity, especially for flows with strong periodicity. This technique extends the application range of fast PSP and can be a powerful tool for fundamental fluid mechanics research at low speed.

Rapid Fabrication of Flat Plate Cavity Phosphor Thermography Test Models for Shuttle Return-to-Flight Aero-Heating

NASA Technical Reports Server (NTRS)

Buck, Gregory M.; Powers, Michael A.; Nevins, Stephen C.; Griffith, Mark S.; Wainwright, Gary A.

2006-01-01

Methods, materials and equipment are documented for fabricating flat plate test models at NASA Langley Research Center for Shuttle return-to-flight aeroheating experiments simulating open and closed cavity interactions in Langley s hypersonic 20-Inch Mach 6 air wind tunnel. Approximately 96 silica ceramic flat plate cavity phosphor thermography test models have been fabricated using these methods. On one model, an additional slot is machined through the back of the plate and into the cavity and vented into an evacuated plenum chamber to simulate a further opening in the cavity. After sintering ceramic to 2150 F, and mounting support hardware, a ceramic-based two-color thermographic phosphor coating is applied for global temperature and heat transfer measurements, with fiducial markings for image registration.

Computation of Tone Noise From Supersonic Jet Impinging on Flat Plates

NASA Technical Reports Server (NTRS)

Loh, Ching Y.; Blech, Richard A. (Technical Monitor)

2005-01-01

A supersonic jet impinging normally on a flat plate has both practical importance and theoretical interests. The physical phenomenon is not fully understood yet. Research concentrates either on the hydrodynamics (e.g., lift loss for STOVL) or on the aeroacoustic loading. In this paper, a finite volume scheme - the space-time conservation element and solution element (CE/SE) method - is employed to numerically study the near-field noise of an underexpanded supersonic jet from a converging nozzle impinging normally on a flat plate. The numerical approach is of the MILES type (monotonically integrated large eddy simulation). The computed results compare favorably with the experimental findings.

Effects of design on cost of flat-plate solar photovoltaic arrays for terrestrial central station power applications

NASA Technical Reports Server (NTRS)

Tsou, P.; Stolte, W.

1978-01-01

The paper examines the impact of module and array designs on the balance-of-plant costs for flat-plate terrestrial central station power applications. Consideration is given to the following types of arrays: horizontal, tandem, augmented, tilt adjusted, and E-W tracking. The life-cycle cost of a 20-year plant life serves as the costing criteria for making design and cost tradeoffs. A tailored code of accounts is developed for determining consistent photovoltaic power plant costs and providing credible photovoltaic system cost baselines for flat-plate module and array designs by costing several varying array design approaches.

Experimental study on flat plate air solar collector using a thin sand layer

NASA Astrophysics Data System (ADS)

Lati, Moukhtar; Boughali, Slimane; Bouguettaia, Hamza; Mennouche, Djamel; Bechki, Djamel

2016-07-01

A flat plate air solar collector was constructed in the laboratory of New and Renewable Energy in Arid Zones LENREZA, Ouargla University-South East Algeria. The absorber of the flat plate air solar collector was laminated with a thin layer of local sand. This acted as a thermal storage system (packed bed) with a collecting area of 2.15 m2 (0.86 m × 2.5 m). It was noticed that the solar heater integrated with the thermal storage material delivered comparatively higher temperatures; thus, giving a better efficiency than the air heater without the thermal storage system.

Unsteady Airloads in Separated and Transonic Flow

DTIC Science & Technology

1977-07-01

pressure distributions on a cylindrical body with a square flat plate airbrake." January, 1956 RAE T.N. Aero 2396 7-5 FIG. 1 FATIGUE DESIGN STATUS INHERENT...These findings correlate very well with the experiences of Magnus and Yoshihara (Ref., 11), Laval (Ref., 12) and Krupp and Murman (Ref. 13), who in their...followed. In this respect the ideas developed by Magnus and Yoshihara (Ref, 21) deserve attention, since their relatively simple "viscous ramp" model

Computational Fluid Dynamics (CFD) Simulations of a Finned Projectile with Microflaps for Flow Control

DTIC Science & Technology

2016-04-01

fields associated with these control mechanisms for US Army weapons are complex, involving 3-dimensional (3-D) shock- boundary layer interactions...distribution over the rear finned section and thus produce control forces and moments. Dykes et al.6 used a flat - plate fin interaction design of...cells—tetrahedrals, triangular prisms, and pyramids—were used in the mesh. Grid points shown in Fig. 3a were clustered in the boundary layer region

Parametric study of beam refraction problems across laser anemometer windows

NASA Technical Reports Server (NTRS)

Owen, A. K.

1986-01-01

The experimenter is often required to view flows through a window with a different index of refraction than either the medium being observed or the medium that the laser anemometer is immersed in. The refraction that occurs at the window surfaces may lead to undesirable changes in probe volume position or beam crossing angle and can lead to partial or complete beam uncrossing. This report describes the results of a parametric study of this problem using a ray tracing technique to predict these changes. The windows studied were a flat plate and a simple cyclinder. For the flat-plate study: (1) surface thickness, (2) beam crossing angle, (3) bisecting line - surface normal angle, and (4) incoming beam plane surface orientation were varied. For the cylindrical window additional parameters were also varied: (1) probe volume immersion, (2) probe volume off-radial position, and (3) probe volume position out of the R-theta plane of the lens. A number of empirical correlations were deduced to aid the interested reader in determining the movement, uncrossing, and change in crossing angle for a particular situation.

A parametric study of the beam refraction problems across laser anemometer windows

NASA Technical Reports Server (NTRS)

Owen, Albert K.

1986-01-01

The experimenter is often required to view flows through a window with a different index of refraction than either the medium being observed or the medium that the laser anemometer is immersed in. The refraction that occurs at the window surfaces may lead to undesirable changes in probe volume position or beam crossing angle and can lead to partial or complete beam uncrossing. This report describes the results of a parametric study of this problem using a ray tracing technique to predict these changes. The windows studied were a flat plate and a simple cylinder. For the flat-plate study: (1) surface thickness, (2) beam crossing angle, (3) bisecting line - surface normal angle, and (4) incoming beam plane surface orientation were varied. For the cylindrical window additional parameters were also varied: (1) probe volume immersion, (2) probe volume off-radial position, and (3) probe volume position out of the r-theta plane of the lens. A number of empirical correlations were deduced to aid the reader in determining the movement, uncrossing, and change in crossing angle for a particular situations.

A lifting surface computer code with jet-in-crossflow interference effects. Volume 1: Theoretical description

NASA Technical Reports Server (NTRS)

Furlong, K. L.; Fearn, R. L.

1983-01-01

A method is proposed to combine a numerical description of a jet in a crossflow with a lifting surface panel code to calculate the jet/aerodynamic-surface interference effects on a V/STOL aircraft. An iterative technique is suggested that starts with a model for the properties of a jet/flat plate configuration and modifies these properties based on the flow field calculated for the configuration of interest. The method would estimate the pressures, forces, and moments on an aircraft out of ground effect. A first-order approximation to the method suggested is developed and applied to two simple configurations. The first-order approximation is a noniterative precedure which does not allow for interactions between multiple jets in a crossflow and also does not account for the influence of lifting surfaces on the jet properties. The jet/flat plate model utilized in the examples presented is restricted to a uniform round jet injected perpendicularly into a uniform crossflow for a range of jet-to-crossflow velocity ratios from three to ten.

Modeling of the heat transfer in bypass transitional boundary-layer flows

NASA Technical Reports Server (NTRS)

Simon, Frederick F.; Stephens, Craig A.

1991-01-01

A low Reynolds number k-epsilon turbulence model and conditioned momentum, energy and turbulence equations were used to predict bypass transition heat transfer on a flat plate in a high-disturbance environment with zero pressure gradient. The use of conditioned equations was demonstrated to be an improvement over the use of the global-time-averaged equations for the calculation of velocity profiles and turbulence intensity profiles in the transition region of a boundary layer. The approach of conditioned equations is extended to include heat transfer and a modeling of transition events is used to predict transition onset and the extent of transition on a flat plate. The events, which describe the boundary layer at the leading edge, result in boundary-layer regions consisting of: (1) the laminar, (2) pseudolaminar, (3) transitional, and (4) turbulent boundary layers. The modeled transition events were incorporated into the TEXSTAN 2-D boundary-layer code which is used to numerically predict the heat transfer. The numerical predictions in general compared well with the experimental data and revealed areas where additional experimental information is needed.

Gating geometry studies of thin-walled 17-4PH investment castings

DOE Office of Scientific and Technical Information (OSTI.GOV)

Maguire, M.C.; Zanner, F.J.

1992-11-01

The ability to design gating systems that reliably feed and support investment castings is often the result of ``cut-and-try`` methodology. Factors such as hot tearing, porosity, cold shuts, misruns, and shrink are defects often corrected by several empirical gating design iterations. Sandia National Laboratories is developing rules that aid in removing the uncertainty involved in the design of gating systems for investment castings. In this work, gating geometries used for filling of thin walled investment cast 17-4PH stainless steel flat plates were investigated. A full factorial experiment evaluating the influence of metal pour temperature, mold preheat temperature, and mold channelmore » thickness were conducted for orientations that filled a horizontal flat plate from the edge. A single wedge gate geometry was used for the edge-gated configuration. Thermocouples placed along the top of the mold recorded metal front temperatures, and a real-time x-ray imaging system tracked the fluid flow behavior during filling of the casting. Data from these experiments were used to determine the terminal fill volumes and terminal fill times for each gate design.« less

Gating geometry studies of thin-walled 17-4PH investment castings

DOE Office of Scientific and Technical Information (OSTI.GOV)

Maguire, M.C.; Zanner, F.J.

1992-01-01

The ability to design gating systems that reliably feed and support investment castings is often the result of cut-and-try'' methodology. Factors such as hot tearing, porosity, cold shuts, misruns, and shrink are defects often corrected by several empirical gating design iterations. Sandia National Laboratories is developing rules that aid in removing the uncertainty involved in the design of gating systems for investment castings. In this work, gating geometries used for filling of thin walled investment cast 17-4PH stainless steel flat plates were investigated. A full factorial experiment evaluating the influence of metal pour temperature, mold preheat temperature, and mold channelmore » thickness were conducted for orientations that filled a horizontal flat plate from the edge. A single wedge gate geometry was used for the edge-gated configuration. Thermocouples placed along the top of the mold recorded metal front temperatures, and a real-time x-ray imaging system tracked the fluid flow behavior during filling of the casting. Data from these experiments were used to determine the terminal fill volumes and terminal fill times for each gate design.« less

Aeolian processes aboard a space station: Saltation and particle trajectory analysis

NASA Technical Reports Server (NTRS)

White, B. R.; Greeley, R.; Iversen, J. D.; Leach, R. N.

1986-01-01

The Carousel wind tunnel (CWT) proposed to study aeolian processes aboard a space station consists of two concentric rotating drums. The space between the two drums comprises the wind tunnel test section. Differential rates of rotation of the two drums would provide a wind velocity with respect to either drum surface. Preliminary results of measured velocity profiles made in a CWT prototype indicate that the wall bounded boundary layer profiles are suitable to simulate flat plate turbulent boundary layer flow. The two dimensional flat plate Cartesian coordinate equations of motion of a particle moving through the air are explained. In order to assess the suitability of CWT in the analysis of the trajectories of windblown particles, a series of calculations were conducted comparing cases for gravity with those of zero gravity. Results from the calculations demonstrate that a wind tunnel of the carousel design could be fabricted to operate in a space station environment and that experiments could be conducted which would yield significant results contributing to the understanding of the physics of particle dynamics.

Relationship between the changes in blood flow and volume in the finger during a Braille character discrimination task.

PubMed

Murata, J; Murata, S; Soma, M; Nakae, H; Sato, Y; Kogo, H; Umeki, N

2017-11-01

We hypothesized that skin blood flow (SBF) of fingers are modulated during concentrated finger perception and that the changes in SBF reflect fluctuations in finger volume (FV). The aim of this study, therefore, was examine the relationship between the changes in SBF and FV during Braille reading. We measured SBF of the finger, cutaneous vascular conductance (CVC), FV, and arterial blood pressure during Braille reading performed under blind conditions in thirty healthy subjects. The subjects were instructed to read a flat plate with raised letters (Braille reading) for 15 seconds using their forefinger, and to touch a blank plate as a control for the Braille discrimination procedure. Arterial blood pressure slightly increased during Braille reading but remained unchanged during the touching of the blank plate. SBF, CVC, and FV were reduced during Braille reading (decreased by -26%, -29%, and -0.3 mL/100 mL respectively). Furthermore, a significant relationship was observed between the changes in SBF and FV (r=.613) during Braille reading. These results suggested that SBF of fingers is modulated during concentrated finger perception, and that the variability of blood flow reflects the response in FV. © 2017 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.

The use of transition region characteristics to improve the numerical simulation of heat transfer in bypass transitional flows

NASA Technical Reports Server (NTRS)

Simon, Frederick F.

1993-01-01

A method is presented for improving the numerical prediction of bypass transition heat transfer on a flat plate in a high-disturbance environment with zero or favorable pressure gradient. The method utilizes low Reynolds number k-epsilon turbulence models in combination with the characteristic parameters of the transition region. The parameters representing the characteristics of the transition region used are the intermittency, transition length and turbulent spot properties. An analysis is made of the transition length in terms of turbulent spot variables. The nondimensional spot formation rate, required for the prediction of the transition length, is shown by the analysis to be a function of the spot spreading angle, the dimensionless spot velocity ratio and the dimensionless spot area ratio. The intermittency form of the k-epsilon equations were derived from conditionally averaged equations which have been shown to be an improvement over global-time-averaged equations for the numerical calculation of the transition region. The numerical predictions are in general good agreement with the experimental data and indicate the potential use of the method in accelerating flows. Turbulence models of the k-epsilon type are known to underpredict the transition length. The present work demonstrates how incorporating transition region characteristics improves the ability of two-equation turbulence models to simulate bypass transition for flat plates with potential application to turbine vanes and blades.

Acoustic Receptivity of Mach 4.5 Boundary Layer with Leading- Edge Bluntness

NASA Technical Reports Server (NTRS)

Malik, Mujeeb R.; Balakumar, Ponnampalam

2007-01-01

Boundary layer receptivity to two-dimensional slow and fast acoustic waves is investigated by solving Navier-Stokes equations for Mach 4.5 flow over a flat plate with a finite-thickness leading edge. Higher order spatial and temporal schemes are employed to obtain the solution whereby the flat-plate leading edge region is resolved by providing a sufficiently refined grid. The results show that the instability waves are generated in the leading edge region and that the boundary-layer is much more receptive to slow acoustic waves (by almost a factor of 20) as compared to the fast waves. Hence, this leading-edge receptivity mechanism is expected to be more relevant in the transition process for high Mach number flows where second mode instability is dominant. Computations are performed to investigate the effect of leading-edge thickness and it is found that bluntness tends to stabilize the boundary layer. Furthermore, the relative significance of fast acoustic waves is enhanced in the presence of bluntness. The effect of acoustic wave incidence angle is also studied and it is found that the receptivity of the boundary layer on the windward side (with respect to the acoustic forcing) decreases by more than a factor of 4 when the incidence angle is increased from 0 to 45 deg. However, the receptivity coefficient for the leeward side is found to vary relatively weakly with the incidence angle.

Flat slabs seen from above: aeromagnetic data in Central Mexico

NASA Astrophysics Data System (ADS)

Manea, M.; Manea, V. C.

2006-12-01

The aeromagnetic map of Mexico shows a magnetic "quiet zone" in Guerrero and Oaxaca (Central Mexico), characterized by a general lack of short-wavelength magnetic anomalies. In order to investigate the magnetic quiet zone in relation with the thermal sources, spectral analysis has been applied to the aeromagnetic data. The results show the existence of deep magnetic sources (30-40 km) which we consider to be the Currie depth (corresponding to a temperature of 575-600°). Above the Curie temperature spontaneous magnetization vanishes and the minerals exhibit only a small paramagnetic susceptibility. Our estimates of magnetic basal depth are consistent with the heat flow measurements in the area (20-30 mW/m2). In order to explain such deep magnetic source and small heat flow estimates, we infer the thermal structure associated with the subduction of the Cocos plate beneath Central Mexico, using a finite element approach. The modeling results show that the 575-600°C isotherm is subhorisontal due to the flat slab regime in the area. Also, the heat flow estimates from thermal models and spectral analysis of aeromagnetic anomalies are in good agreement. We conclude that the magnetic quiet zone is associated with a flat slab subduction regime in Central Mexico, and proved to be an important constraint for the thermal structure associated with subduction zones.

Experimental Study of Unsteady Flow Separation in a Laminar Boundary Layer

NASA Astrophysics Data System (ADS)

Bonacci, Andrew; Lang, Amy; Wahidi, Redha; Santos, Leonardo

2017-11-01

Flow separation, caused by an adverse pressure gradient, is a major problem in many applications. Reversing flow near the wall is the first sign of incipient separation and can bristle shark scales which may be linked to a passive, flow actuated separation control mechanism. An investigation of how this backflow forms and how it interacts with shark skin is of interest due to the fact that this could be used as a bioinspired means of initiating flow control. A water tunnel experiment aims to study unsteady separation with a focus on the reversing flow development near the wall within a flat plate laminar boundary layer (Re on order of 105) as an increasing adverse pressure gradient is induced by a rotating cylinder. Unsteady reversing flow development is documented using DPIV. Funding was provided by the National Science Foundation under the Research Experience for Undergraduates (REU) program (EEC 1659710) and the Army Research Office.

Mean velocities and Reynolds stresses in a juncture flow

NASA Technical Reports Server (NTRS)

Mcmahon, H.; Hubbartt, J.; Kubendran, L.

1982-01-01

Values of three mean velocity components and six turbulence stresses measured in a juncture flow are presented and discussed. The juncture flow is generated by a constant thickness body, having an elliptical leading edge, which is mounted perpendicular to a large flat plate along which a turbulent boundary layer is growing. The measurements were carried out at two streamwise stations in the juncture and were made using two single sensor hot-wire probes. The secondary flow in the juncture results in a considerable distortion in the mean velocity profiles. The secondary flow also transports turbulence in the juncture flow and has a large effect on the turbulence stresses. From visual inspection of the results, there is considerable evidence of similarity between the turbulent shear stresses and the mean flow strain rates. There is some evidence of similarity between the variations in the turbulent stress components.

Standarized performance tests of collectors of solar thermal energy: A steel flat-plate collector with two transparent covers and a proprietary coating

NASA Technical Reports Server (NTRS)

1976-01-01

Basic test results of a flat-plate solar collector whose performance was determined in the NASA-Lewis solar simulator are given. The collector was tested over ranges of inlet temperature and flux level.

a Lattice Boltzmann Study of the 2d Boundary Layer Created by AN Oscillating Plate

NASA Astrophysics Data System (ADS)

Cappietti, L.; Chopard, B.

We study the applicability of the Lattice Boltzmann Method (LBM) to simulate the 2D laminar boundary layer induced by an oscillating flat plate. We also investigate the transition to the disturbed laminar regime that occurs with a rough oscillating plate. The simulations were performed in two cases: first with a fluid otherwise at rest and second in presence of superimposed current. The generation of coherent vortex structures and their evolution are commented. The accuracy of the method was checked by comparisons with the exact analytical solution of the Navier-Stokes equations for the so-called Stokes' Second Problem. The comparisons show that LBM reproduces this time varying flow with first order accuracy. In the case of the wavy-plate, the results show that a mechanism of vortex-jet formations, low speed-streak and shear instability sustain a systems of stationary vortices outside the boundary layer. The vortex-jet takes place at the end of the decelerating phase whereas the boundary layer turns out to be laminar when the plate accelerates. In the presence of the superimposed current, the vortex-jet mechanism is still effective but the vortices outside the boundary layer are only present during part of the oscillating period. During the remaining part, the flow turns out to be laminar although a wave perturbation in the velocity field is present.

Evolution of the long-wavelength, subduction-driven topography of South America since 150 Ma

NASA Astrophysics Data System (ADS)

Flament, N. E.; Gurnis, M.; Williams, S.; Bower, D. J.; Seton, M.; Müller, D.

2014-12-01

Subduction to the west of South America spans 6000 km along strike and has been active for over 250 Myr. The influence of the history of subduction on the geodynamics of South America has been profound, driving mountain building and arc volcanism in the Andean Cordillera. Here, we investigate the long-wavelength changes in the topography of South America associated with subduction and plate motion and their interplay with the lithospheric deformation associated with the opening of the South Atlantic. We pay particular attention to the topographic expression of flat-lying subduction zones. We develop time-dependent geodynamic models of mantle flow and lithosphere deformation to investigate the evolution of South American dynamic and total topography since the late Jurassic (150 Ma). Our models are semi-empirical because the computational cost of fully dynamic, evolutionary models is still prohibitive. We impose the kinematics of global plate reconstructions with deforming continents in forward global mantle convection models with compositionally distinct crust and continental lithosphere embedded within the thermal lithosphere. The shallow thermal structure of subducting slabs is imposed, allowing us to investigate the evolution of dynamic topography around flat slab segments in time-dependent models. Multiple cases are used to investigate how the evolution of South American dynamic topography is influenced by mantle viscosity, the kinematics of the opening of the South Atlantic and alternative scenarios for recent and past flat-slab subduction. We predict that the migration of South America over sinking oceanic lithosphere resulted in continental tilt to the west until ~ 45 Ma, inverting to an eastward tilt thereafter. This first-order result is consistent with the reversal of the drainage of the Amazon River system. We investigate which scenarios of flat-slab subduction since the Eocene are compatible with geological constraints on the evolution of the Solimoes Basin, the Chaco Basin, the Sierras Pampeanas and the Central Patagonian Basin. To broadly constrain mantle viscosity, we compare models to the total subsidence inferred from well data offshore Argentina and Brazil, and to mantle tomography, since the initial and boundary conditions are based on independent plate reconstructions.

Impact of current speed on mass flux to a model flexible seagrass blade

NASA Astrophysics Data System (ADS)

Lei, Jiarui; Nepf, Heidi

2016-07-01

Seagrass and other freshwater macrophytes can acquire nutrients from surrounding water through their blades. This flux may depend on the current speed (U), which can influence both the posture of flexible blades (reconfiguration) and the thickness of the flux-limiting diffusive layer. The impact of current speed (U) on mass flux to flexible blades of model seagrass was studied through a combination of laboratory flume experiments, numerical modeling and theory. Model seagrass blades were constructed from low-density polyethylene (LDPE), and 1, 2-dichlorobenzene was used as a tracer chemical. The tracer mass accumulation in the blades was measured at different unidirectional current speeds. A numerical model was used to estimate the transfer velocity (K) by fitting the measured mass uptake to a one-dimensional diffusion model. The measured transfer velocity was compared to predictions based on laminar and turbulent boundary layers developing over a flat plate parallel to flow, for which K∝U0.5 and ∝U, respectively. The degree of blade reconfiguration depended on the dimensionless Cauchy number, Ca, which is a function of both the blade stiffness and flow velocity. For large Ca, the majority of the blade was parallel to the flow, and the measured transfer velocity agreed with laminar boundary layer theory, K∝U0.5. For small Ca, the model blades remained upright, and the flux to the blade was diminished relative to the flat-plate model. A meadow-scale analysis suggests that the mass exchange at the blade scale may control the uptake at the meadow scale.

An experimental study of near wall flow parameters in the blade end-wall corner region

NASA Technical Reports Server (NTRS)

Bhargava, Rakesh K.; Raj, Rishi S.

1989-01-01

The near wall flow parameters in the blade end-wall corner region is investigated. The blade end-wall corner region was simulated by mounting an airfoil section (NACA 65-015 base profile) symmetric blades on both sides of the flat plate with semi-circular leading edge. The initial 7 cm from the leading edge of the flat plate was roughened by gluing No. 4 floor sanding paper to artificially increase the boundary layer thickness on the flat plate. The initial flow conditions of the boundary layer upstream of the corner region are expected to dictate the behavior of flow inside the corner region. Therefore, an experimental investigation was extended to study the combined effect of initial roughness and increased level of free stream turbulence on the development of a 2-D turbulent boundary layer in the absence of the blade. The measurement techniques employed in the present investigation included, the conventional pitot and pitot-static probes, wall taps, the Preston tube, piezoresistive transducer and the normal sensor hot-wire probe. The pitot and pitot-static probes were used to obtain mean velocity profile measurements within the boundary layer. The measurements of mean surface static pressure were obtained with the surface static tube and the conventional wall tap method. The wall shear vector measurements were made with a specially constructed Preston tube. The flush mounted piezoresistive type pressure transducer were employed to measure the wall pressure fluctuation field. The velocity fluctuation measurements, used in obtaining the wall pressure-velocity correlation data, were made with normal single sensor hot-wire probe. At different streamwise stations, in the blade end-wall corner region, the mean values of surface static pressure varied more on the end-wall surface in the corner region were mainly caused by the changes in the curvature of the streamlines. The magnitude of the wall shear stress in the blade end-wall corner region increased significantly in the close vicinity of the corner line. The maximum value of the wall shear stress and its location from the corner line, on both the surfaces forming the corner region, were observed to change along the corner. These observed changes in the maximum values of the wall shear stress and its location from the corner line could be associated with the stretching and attenuation of the horseshoe vortex. The wall shear stress vectors in the blade end-wall corner region were observed to be more skewed on the end-wall surface as compared to that on the blade surface. The differences in the wall shear stress directions obtained with the Preston tube and flow visualization method were within the range in which the Preston tube was found to be insensitive to the yaw angle.

An assessment and application of turbulence models for hypersonic flows

NASA Technical Reports Server (NTRS)

Coakley, T. J.; Viegas, J. R.; Huang, P. G.; Rubesin, M. W.

1990-01-01

The current approach to the Accurate Computation of Complex high-speed flows is to solve the Reynolds averaged Navier-Stokes equations using finite difference methods. An integral part of this approach consists of development and applications of mathematical turbulence models which are necessary in predicting the aerothermodynamic loads on the vehicle and the performance of the propulsion plant. Computations of several high speed turbulent flows using various turbulence models are described and the models are evaluated by comparing computations with the results of experimental measurements. The cases investigated include flows over insulated and cooled flat plates with Mach numbers ranging from 2 to 8 and wall temperature ratios ranging from 0.2 to 1.0. The turbulence models investigated include zero-equation, two-equation, and Reynolds-stress transport models.

Wake measurements in a strong adverse pressure gradient

NASA Technical Reports Server (NTRS)

Hoffenberg, R.; Sullivan, John P.; Schneider, S. P.

1994-01-01

The behavior of wakes in adverse pressure gradients is critical to the performance of high-lift systems for transport aircraft. Wake deceleration is known to lead to sudden thickening and the onset of reversed flow; this 'wake bursting' phenomenon can occur while surface flows remain attached. Although 'wake bursting' is known to be important for high-lift systems, no detailed measurements of 'burst' wakes have ever been reported. Wake bursting has been successfully achieved in the wake of a flat plate as it decelerated in a two-dimensional diffuser, whose sidewalls were forced to remain attached by use of slot blowing. Pilot probe surveys, L.D.V. measurements, and flow visualization have been used to investigate the physics of this decelerated wake, through the onset of reversed flow.

Supersonic Flow Field Investigation Using a Fiber-optic based Doppler Global Velocimeter

NASA Technical Reports Server (NTRS)

Meyers, James F.; Lee, Joseph W.; Fletcher, Mark T.; Cavone, Angelo A.; AscencionGuerreroViramontes, J.

2006-01-01

A three-component fiber-optic based Doppler Global Velocimeter was constructed, evaluated and used to measure shock structures about a low-sonic boom model in a Mach 2 flow. The system was designed to have maximum flexibility in its ability to measure flows with restricted optical access and in various facilities. System layout is described along with techniques developed for production supersonic testing. System evaluation in the Unitary Plan Wind Tunnel showed a common acceptance angle of f4 among the three views with velocity measurement resolutions comparable with free-space systems. Flow field measurements of shock structures above a flat plate with an attached ellipsoid-cylinder store and a low-sonic boom model are presented to demonstrate the capabilities of the system during production testing.

An experimental study of an explosively driven flat plate launcher

NASA Astrophysics Data System (ADS)

Rae, Philip; Haroz, Erik; Armstrong, Chris; Perry, Lee; M Division Team

2017-06-01

For some upcoming experiments it is desired to impact a large explosive assembly with one or more moderate diameter flat metal plates traveling at high velocity (2-3 km s-1). The time of arrival of these plates will need to carefully controlled and delayed (i.e. the time(s) of arrival known to approximately a microsecond). For this reason, producing a flyer plate from more traditional gun assemblies is not possible. Previous researchers have demonstrated the ability to throw reasonably flat metal flyers from the so-called Forest flyer geometry. The defining characteristics of this design are a carefully controlled reduction in explosive area from a larger explosive plane-wave-lens and booster pad to a smaller flyer plate to improve the planarity of the drive available and an air gap between the explosive booster and the plate to reduce the peak tensile stresses generated in the plate to suppress spalling. This experimental series comprised a number of different design variants and plate and explosive drive materials. The aim was to calibrate a predictive computational modeling capability on this kind of system in preparation for later more radical design ideas best tested in a computer before undertaking the expensive business of construction.

PIV-based estimation of unsteady loads on a flat plate at high angle of attack using momentum equation approaches

NASA Astrophysics Data System (ADS)

Guissart, A.; Bernal, L. P.; Dimitriadis, G.; Terrapon, V. E.

2017-05-01

This work presents, compares and discusses results obtained with two indirect methods for the calculation of aerodynamic forces and pitching moment from 2D Particle Image Velocimetry (PIV) measurements. Both methodologies are based on the formulations of the momentum balance: the integral Navier-Stokes equations and the "flux equation" proposed by Noca et al. (J Fluids Struct 13(5):551-578, 1999), which has been extended to the computation of moments. The indirect methods are applied to spatio-temporal data for different separated flows around a plate with a 16:1 chord-to-thickness ratio. Experimental data are obtained in a water channel for both a plate undergoing a large amplitude imposed pitching motion and a static plate at high angle of attack. In addition to PIV data, direct measurements of aerodynamic loads are carried out to assess the quality of the indirect calculations. It is found that indirect methods are able to compute the mean and the temporal evolution of the loads for two-dimensional flows with a reasonable accuracy. Nonetheless, both methodologies are noise sensitive, and the parameters impacting the computation should thus be chosen carefully. It is also shown that results can be improved through the use of dynamic mode decomposition (DMD) as a pre-processing step.

Aerodynamic properties of a flat plate with cavity for optical-propagation studies

NASA Technical Reports Server (NTRS)

Buell, D. A.

1979-01-01

Transonic wind-tunnel tests were performed on a flat plate with and without a cube-shaped cavity and antiresonance devices. Measurements were made of the optical propagation and aerodynamic properties of the boundary and shear layers. The model and its velocity profiles and pressures are described.

Proceedings of the Flat-Plate Solar Array Project Research Forum on Photovoltaic Metallization Systems

NASA Technical Reports Server (NTRS)

1983-01-01

A photovoltaic Metallization Research forum, under the sponsorship of the Flat-Plate Solar Array Project consisted of five sessions, covering: (1) the current status of metallization systems, (2) system design, (3) thick-film metallization, (4) advanced techniques, and (5) future metallization challenges.

Designing Flat-Plate Photovoltaic Arrays

NASA Technical Reports Server (NTRS)

Ross, R. G., Jr.

1984-01-01

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.

Safety review package for University of Central Florida flat-plate heat pipe experiment

NASA Technical Reports Server (NTRS)

Chow, Louis C.

1998-01-01

A flat-plate heat pipe (FPHP) experiment has been set up for micro-gravity tests on a NASA supplied aircraft. This report presents an analysis on various components of the experimental setup to certify that it will satisfy the flight safety and operation requirements.

Unsteady magnetohydrodynamic free convection flow of a second grade fluid in a porous medium with ramped wall temperature.

PubMed

Samiulhaq; Ahmad, Sohail; Vieru, Dumitru; Khan, Ilyas; Shafie, Sharidan

2014-01-01

Magnetic field influence on unsteady free convection flow of a second grade fluid near an infinite vertical flat plate with ramped wall temperature embedded in a porous medium is studied. It has been observed that magnitude of velocity as well as skin friction in case of ramped temperature is quite less than the isothermal temperature. Some special cases namely: (i) second grade fluid in the absence of magnetic field and porous medium and (ii) Newtonian fluid in the presence of magnetic field and porous medium, performing the same motion are obtained. Finally, the influence of various parameters is graphically shown.

The effect of small streamwise velocity distortion on the boundary layer flow over a thin flat plate with application to boundary layer stability theory

NASA Technical Reports Server (NTRS)

Goldstein, M. E.; Leib, S. J.; Cowley, S. J.

1990-01-01

Researchers show how an initially linear spanwise disturbance in the free stream velocity field is amplified by leading edge bluntness effects and ultimately leads to a small amplitude but linear spanwise motion far downstream from the edge. This spanwise motion is imposed on the boundary layer flow and ultimately causes an order-one change in its profile shape. The modified profiles are highly unstable and can support Tollmein-Schlichting wave growth well upstream of the theoretical lower branch of the neutral stability curve for a Blasius boundary layer.

A Modified Mixing Length Turbulence Model for Zero and Adverse Pressure Gradients. M.S. Thesis - Akron Univ., 1993

NASA Technical Reports Server (NTRS)

Conley, Julianne M.; Leonard, B. P.

1994-01-01

The modified mixing length (MML) turbulence model was installed in the Proteus Navier-Stokes code, then modified to make it applicable to a wider range of flows typical of aerospace propulsion applications. The modifications are based on experimental data for three flat-plate flows having zero, mild adverse, and strong adverse pressure gradients. Three transonic diffuser test cases were run with the new version of the model in order to evaluate its performance. All results are compared with experimental data and show improvements over calculations made using the Baldwin-Lomax turbulence model, the standard algebraic model in Proteus.

Imaging the Peruvian flat slab with Rayliegh wave tomography

NASA Astrophysics Data System (ADS)

Knezevic Antonijevic, Sanja

In subduction zones the oceanic plates descend at a broad range of dip angles. A "flat slab" is an oceanic plate that starts to subduct steeply, but bends at 100 km depth and continues almost horizontally for several hundred kilometers. This unusual slab geometry has been linked to various geologic features, including the cessation of arc volcanism, basement core uplifts removed far from subducting margins, and the formation of high plateaus. Despite the prevalence of flat slabs worldwide since the Proterozoic, questions on how flat slabs form, persist, and re-steepen remains a topic of ongoing research. Even less clear is how this phenomenon relates to unusual features observed at the surface. To better understand the causes and consequences of slab flattening I focus on the Peruvian flat slab. This is not only the biggest flat slab region today, but due to the oblique angle at which the Nazca Plate subducts under the South American Plate, it also provides unique opportunity to get insights into the temporal evolution of the flat slab. Using ambient noise and earthquake-generated Rayleigh waves recorded at several contemporary dense seismic networks, I was able to perform unprecedentedly high resolution imaging of the subduction zone in southern Peru. Surprisingly, instead of imaging a vast flat slab region as expected, I found that the flat slab tears and re-steepens north of the subducting Nazca Ridge. The change in slab geometry is associated with variations in the slab's internal strain along strike, as inferred from slab-related anisotropy. Based on newly-discovered features I discuss the critical role of the subducting ridges in the formation and longevity of flat slabs. The slab tear created a new mantle pathway between the torn slab and the flat slab remnant to the east, and is possibly linked to the profound low velocity anomaly located under the eastern corner of the flat slab. Finally, I re-evaluate the connection between slab flattening and volcanic patterns at the surface. These findings have important implications for all present-day and paleo-flat slab regions, such as the one proposed for the western United States during the Laramide orogeny 80-55 Ma.

About the coupling of turbulence closure models with averaged Navier-Stokes equations

NASA Technical Reports Server (NTRS)

Vandromme, D.; Ha Minh, H.

1986-01-01

The MacCormack implicit predictor-corrector model (1981) for numerical solution of the coupled Navier-Stokes equations for turbulent flows is extended to nonconservative multiequation turbulence models, as well as the inclusion of second-order Reynolds stress turbulence closure. A scalar effective pressure turbulent contribution to the pressure field is defined to approximate the effects of the Reynolds stress in strongly sheared flows. The Jacobian matrices of the transport equations are diagonalized to reduce the required computer memory and run time. Techniques are defined for including turbulence in the diagonalization. Application of the method is demonstrated with solutions generated for transonic nozzle flow and for the interaction between a supersonic flat plate boundary layer and a 12 deg compression-expansion ramp.

Development of a three-dimensional Navier-Stokes code on CDC star-100 computer

NASA Technical Reports Server (NTRS)

Vatsa, V. N.; Goglia, G. L.

1978-01-01

A three-dimensional code in body-fitted coordinates was developed using MacCormack's algorithm. The code is structured to be compatible with any general configuration, provided that the metric coefficients for the transformation are available. The governing equations are developed in primitive variables in order to facilitate the incorporation of physical boundary conditions and turbulence-closure models. MacCormack's two-step, unsplit, time-marching algorithm is used to solve the unsteady Navier-Stokes equations until steady-state solution is achieved. Cases discussed include (1) flat plate in supersonic free stream; (2) supersonic flow along an axial corner; (3) subsonic flow in an axial corner at M infinity = 0.95; and (4) supersonic flow in an axial corner at M infinity 1.5.

Film cooling effectiveness and heat transfer with injection through holes

NASA Technical Reports Server (NTRS)

Eriksen, V. L.

1971-01-01

An experimental investigation of the local film cooling effectiveness and heat transfer downstream of injection of air through discrete holes into a turbulent boundary layer of air on a flat plate is reported. Secondary air is injected through a single hole normal to the main flow and through both a single hole and a row of holes spaced at three diameter intervals with an injection angle of 35 deg to the main flow. Two values of the mainstream Reynolds number are used; the blowing rate is varied from 0.1 to 2.0. Photographs of a carbon dioxide-water fog injected into the main flow at an angle of 90 deg are also presented to show interaction between the jet and mainstream.

Unsteady-flow-field predictions for oscillating cascades

NASA Technical Reports Server (NTRS)

Huff, Dennis L.

1991-01-01

The unsteady flow field around an oscillating cascade of flat plates with zero stagger was studied by using a time marching Euler code. This case had an exact solution based on linear theory and served as a model problem for studying pressure wave propagation in the numerical solution. The importance of using proper unsteady boundary conditions, grid resolution, and time step size was shown for a moderate reduced frequency. Results show that an approximate nonreflecting boundary condition based on linear theory does a good job of minimizing reflections from the inflow and outflow boundaries and allows the placement of the boundaries to be closer to the airfoils than when reflective boundaries are used. Stretching the boundary to dampen the unsteady waves is another way to minimize reflections. Grid clustering near the plates captures the unsteady flow field better than when uniform grids are used as long as the 'Courant Friedrichs Levy' (CFL) number is less than 1 for a sufficient portion of the grid. Finally, a solution based on an optimization of grid, CFL number, and boundary conditions shows good agreement with linear theory.

Apparatus and method for rapid cooling of large area substrates in vacuum

DOEpatents

Barth, Kurt L.; Enzenroth, Robert A.; Sampath, Walajabad S.

2012-11-06

The present invention is directed to an apparatus and method for rapid cooling of a large substrate in a vacuum environment. A first cooled plate is brought into close proximity with one surface of a flat substrate. The spatial volume between the first cooling plate and the substrate is sealed and brought to a higher pressure than the surrounding vacuum level to increase the cooling efficiency. A second cooled plate is brought into close proximity with the opposite surface of the flat substrate. A second spatial volume between the second cooling plate and the substrate is sealed and the gas pressure is equalized to the gas pressure in the first spatial volume. The equalization of the gas pressure on both sides of the flat substrate eliminates deflection of the substrate and bending stress in the substrate.