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.

Hypersonic Boundary Layer Instability Over a Corner

NASA Technical Reports Server (NTRS)

Balakumar, Ponnampalam; Zhao, Hong-Wu; McClinton, Charles (Technical Monitor)

2001-01-01

A boundary-layer transition study over a compression corner was conducted under a hypersonic flow condition. Due to the discontinuities in boundary layer flow, the full Navier-Stokes equations were solved to simulate the development of disturbance in the boundary layer. A linear stability analysis and PSE method were used to get the initial disturbance for parallel and non-parallel flow respectively. A 2-D code was developed to solve the full Navier-stokes by using WENO(weighted essentially non-oscillating) scheme. The given numerical results show the evolution of the linear disturbance for the most amplified disturbance in supersonic and hypersonic flow over a compression ramp. The nonlinear computations also determined the minimal amplitudes necessary to cause transition at a designed location.

Introduction to boundary-layer theory. [viscous friction loss calculation for turbine blade design

NASA Technical Reports Server (NTRS)

Mcnally, W. D.

1973-01-01

The pressure ratio across a turbine provides a certain amount of ideal energy that is available to the turbine for producing work. The portion of the ideal energy that is not converted to work is considered to be a loss. One of the more important and difficult aspects of turbine design is the prediction of the losses. The primary cause of losses is the boundary layer that develops on the blade and end wall surfaces. Boundary-layer theory is used to calculate the parameters needed to estimate viscous (friction) losses.

Instability of a Supersonic Boundary-Layer with Localized Roughness

NASA Technical Reports Server (NTRS)

Marxen, Olaf; Iaccarino, Gianluca; Shaqfeh, Eric S. G.

2010-01-01

A localized 3-D roughness causes boundary-layer separation and (weak) shocks. Most importantly, streamwise vortices occur which induce streamwise (low U, high T) streaks. Immersed boundary method (volume force) suitable to represent roughness element in DNS. Favorable comparison between bi-global stability theory and DNS for a "y-mode" Outlook: Understand the flow physics (investigate "z-modes" in DNS through sinuous spanwise forcing, study origin of the beat in DNS).

Magnetic Fe, Si, Al-Rich Impact Spherules from the P-T Boundary Layer at Graphite Peak, Antarctica

NASA Technical Reports Server (NTRS)

Petaev, M. I.; Jacobsen, S. B.; Basu, A. R.; Becker, L.

2004-01-01

The geological boundary between Triassic and Permian strata coincides with the greatest life extinction in the Earth's history. Although the cause of the extinction is still the subject of intense debates, recent discoveries in the P-T boundary layer of shocked quartz grains, fullerenes with the extraterrestrial noble gases, Fe metal nuggets, and chondritic meteorite fragments all point to a powerful collision of Earth with a celestial body in the late Permian. Here we report the discovery of magnetic Fe, Si, Al-rich impact spherules which accompany the chondritic meteorite fragments in some samples from the P-T boundary layer at Graphite Peak, Antarctica.

Analyzing the Boundary Thermal Resistance of Epitaxially Grown Fe2VAl/W Layers by Picosecond Time-Domain Thermoreflectance

NASA Astrophysics Data System (ADS)

Hiroi, Satoshi; Choi, Seongho; Nishino, Shunsuke; Seo, Okkyun; Chen, Yanna; Sakata, Osami; Takeuchi, Tsunehiro

2018-06-01

To gain deep insight into the mechanism of phonon scattering at grain boundaries, we investigated the boundary thermal resistance by using picosecond pulsed-laser time-domain thermoreflectance for epitaxially grown W/Fe2VAl/W films. By using radio-frequency magnetron sputtering, we prepared a series of the three-layer films whose Fe2VAl thickness ranged from 1 nm to 37 nm. The fine oscillation of reflectivity associated with the top W layer clearly appeared in synchrotron x-ray reflectivity measurements, indicating a less obvious mixture of elements at the boundary. The areal heat diffusion time, obtained from the time-domain thermoreflectance signal in the rear-heating front-detection configuration, reduced rapidly in samples whose Fe2VAl layer was thinner than 15 nm. The ˜ 10% mismatch in lattice constant between Fe2VAl and W naturally produced the randomly distributed lattice stress near the boundary, causing an effective increase of boundary thermal resistance in the thick samples, but the stress became homogeneous in the thinner layers, which reduced the scattering probability of phonons.

Variation of turbulence in a coastal thermal internal boundary layer

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

SethuRaman, S.; Raynor, G.S.; Brown, R.M.

1981-01-01

Internal boundary layers (IBL) form when an air mass encounters a change in surface characteristics. There are essentially two types of internal boundary layers - one caused by the change in surface roughness and the other by the variation in surface heating. The former is known as the aerodynamic internal boundary layer (AIBL) and the latter the thermal internal boundary layer (TIBL). Change in shear stress generally characterizes the AIBL and change in turbulence the TIBL. Results of some observations of the vertical component of turbulence made in a coastal TIBL over Long Island, New York from 1974 to 1978more » are reported. Vertical turbulence measured by a simple sail plane variometer in a thermal internal boundary layer over Long Island with onshore flows indicates the structure to depend significantly on the land-water temperature difference. The position of the vertical velocity fluctuation maximum seems to vary from one test to another but its variation could not be correlated to other parameters due to lack of a sufficient number of tests. The structure of vertical turbulence was found to be different for sea breeze flows as compared to gradient winds.« less

Particle motion in atmospheric boundary layers of Mars and Earth

NASA Technical Reports Server (NTRS)

White, B. R.; Iversen, J. D.; Greeley, R.; Pollack, J. B.

1975-01-01

To study the eolian mechanics of saltating particles, both an experimental investigation of the flow field around a model crater in an atmospheric boundary layer wind tunnel and numerical solutions of the two- and three-dimensional equations of motion of a single particle under the influence of a turbulent boundary layer were conducted. Two-dimensional particle motion was calculated for flow near the surfaces of both Earth and Mars. For the case of Earth both a turbulent boundary layer with a viscous sublayer and one without were calculated. For the case of Mars it was only necessary to calculate turbulent boundary layer flow with a laminar sublayer because of the low values of friction Reynolds number; however, it was necessary to include the effects of slip flow on a particle caused by the rarefied Martian atmosphere. In the equations of motion the lift force functions were developed to act on a single particle only in the laminar sublayer or a corresponding small region of high shear near the surface for a fully turbulent boundary layer. The lift force functions were developed from the analytical work by Saffman concerning the lift force acting on a particle in simple shear flow.

Control of unsteadiness of a shock wave/turbulent boundary layer interaction by using a pulsed-plasma-jet actuator

NASA Astrophysics Data System (ADS)

Narayanaswamy, Venkateswaran; Raja, Laxminarayan L.; Clemens, Noel T.

2012-07-01

A pulsed-plasma jet actuator is used to control the unsteady motion of the separation shock of a shock wave/boundary layer interaction formed by a compression ramp in a Mach 3 flow. The actuator is based on a plasma-generated synthetic jet and is configured as an array of three jets that can be injected normal to the cross-flow, pitched, or pitched and skewed. The typical peak jet exit velocity of the actuators is about 300 m/s and the pulsing frequencies are a few kilohertz. A study of the interaction between the pulsed-plasma jets and the shock/boundary layer interaction was performed in a time-resolved manner using 10 kHz schlieren imaging. When the actuator, pulsed at StL ≈ 0.04 (f = 2 kHz), was injected into the upstream boundary layer, the separation shock responded to the plasma jet by executing a rapid upstream motion followed by a gradual downstream recovery motion. Schlieren movies of the interaction showed that the separation shock unsteadiness was locked to the pulsing frequency of the actuator, with amplitude of about one boundary layer thickness. Wall-pressure measurements made under the intermittent region showed about a 30% decrease in the overall magnitude of the pressure fluctuations in the low-frequency band associated with unsteady large-scale motion of the separated flow. Furthermore, by increasing the pulsing frequency to 3.3 kHz, the amplitude of the separation shock oscillation was reduced to less than half the boundary layer thickness. Investigation into the effect of the actuator location on the shock wave/boundary layer interaction (SWBLI) showed qualitatively and quantitatively that the actuator placed upstream of the separation shock caused significant modification to the SWBLI unsteadiness, whereas injection from inside the separation bubble did not cause a noticeable effect.

Theoretical Calculation of Viscous-Inviscid Transonic Flows.

DTIC Science & Technology

1980-08-01

Taylor Naval Ship Research and Development Center Aviation and Surface Effects Department / (See reverse side) Bethesda, Maryland 20084 ! CONTROLLING...Interactions ... .......... ... 46 18 -ffect of Boundary Layer on Blade Surface Pressures in a Transonic Fan Rotor Tip Section Cascade...complicated by the viscous effect . The strong viscous-inviscid interaction caused by the shock wave thickens the boundary layer rapidly, and the flow eventually

Advanced boundary layer transition measurement methods for flight applications

NASA Technical Reports Server (NTRS)

Holmes, B. J.; Croom, C. C.; Gail, P. D.; Manuel, G. S.; Carraway, D. L.

1986-01-01

In modern laminar flow flight research, it is important to understand the specific cause(s) of laminar to turbulent boundary-layer transition. Such information is crucial to the exploration of the limits of practical application of laminar flow for drag reduction on aircraft. The transition modes of interest in current flight investigations include the viscous Tollmien-Schlichting instability, the inflectional instability at laminar separation, and the crossflow inflectional instability, as well as others. This paper presents the results to date of research on advanced devices and methods used for the study of laminar boundary-layer transition phenomena in the flight environment. Recent advancements in the development of arrayed hot-film devices and of a new flow visualization method are discussed. Arrayed hot-film devices have been designed to detect the presence of laminar separation, and of crossflow vorticity. The advanced flow visualization method utilizes color changes in liquid-crystal coatings to detect boundary-layer transition at high altitude flight conditions. Flight and wind tunnel data are presented to illustrate the design and operation of these advanced methods. These new research tools provide information on disturbance growth and transition mode which is essential to furthering our understanding of practical design limits for applications of laminar flow technology.

Generation of net sediment transport by velocity skewness in oscillatory sheet flow

NASA Astrophysics Data System (ADS)

Chen, Xin; Li, Yong; Chen, Genfa; Wang, Fujun; Tang, Xuelin

2018-01-01

This study utilizes a qualitative approach and a two-phase numerical model to investigate net sediment transport caused by velocity skewness beneath oscillatory sheet flow and current. The qualitative approach is derived based on the pseudo-laminar approximation of boundary layer velocity and exponential approximation of concentration. The two-phase model can obtain well the instantaneous erosion depth, sediment flux, boundary layer thickness, and sediment transport rate. It can especially illustrate the difference between positive and negative flow stages caused by velocity skewness, which is considerably important in determining the net boundary layer flow and sediment transport direction. The two-phase model also explains the effect of sediment diameter and phase-lag to sediment transport by comparing the instantaneous-type formulas to better illustrate velocity skewness effect. In previous studies about sheet flow transport in pure velocity-skewed flows, net sediment transport is only attributed to the phase-lag effect. In the present study with the qualitative approach and two-phase model, phase-lag effect is shown important but not sufficient for the net sediment transport beneath pure velocity-skewed flow and current, while the asymmetric wave boundary layer development between positive and negative flow stages also contributes to the sediment transport.

A magnetic boundary layer at the magnetopause

NASA Astrophysics Data System (ADS)

Kartalev, M. D.; Simeonov, G.

A new approach in the boundary layer description of the magnetopause is proposed. The magnetopause is considered as a mixing region of two streams of plasma with different parameters. The assumption is made that wave-particle interactions cause the plasma to be resistive. Thus only the magnetic viscosity is supposed to be essential. Other dissipation effects are neglected. The plasma and magnetic field conditions at the outer boundary of the layer can be obtained from the solution of the nondissipative problem for the magnetosheath. The magnetic field is assumed to be known at the inner boundary. No further conditions are needed in our formulation of the problem. The variation of the flow parameters and the magnetic field can be obtained numerically.

Dust transportation in bounday layers on complex areas

NASA Astrophysics Data System (ADS)

Karelsky, Kirill; Petrosyan, Arakel

2017-04-01

This presentation is aimed at creating and realization of new physical model of impurity transfer (solid particles and heavy gases) in areas with non-flat and/or nonstationary boundaries. The main idea of suggested method is to use non-viscous equations for solid particles transport modeling in the vicinity of complex boundary. In viscous atmosphere with as small as one likes coefficient of molecular viscosity, the non-slip boundary condition on solid surface must be observed. This postulates the reduction of velocity to zero at a solid surface. It is unconditionally in this case Prandtle hypothesis must be observed: for rather wide range of conditions in the surface neighboring layers energy dissipation of atmosphere flows is comparable by magnitude with manifestation of inertia forces. That is why according to Prandtle hypothesis in atmosphere movement characterizing by a high Reynolds number the boundary layer is forming near a planet surface, within which the required transition from zero velocities at the surface to magnitudes at the external boundary of the layer that are quite close to ones in ideal atmosphere flow. In that layer fast velocity gradients cause viscous effects to be comparable in magnitude with inertia forces influence. For conditions considered essential changes of hydrodynamic fields near solid boundary caused not only by nonslip condition but also by a various relief of surface: mountains, street canyons, individual buildings. Transport of solid particles, their ascent and precipitation also result in dramatic changes of meteorological fields. As dynamic processes of solid particles transfer accompanying the flow past of complex relief surface by wind flows is of our main interest we are to use equations of non-viscous hydrodynamic. We should put up with on the one hand idea of high wind gradients in the boundary layer and on the other hand disregard of molecular viscosity in two-phase atmosphere equations. We deal with describing high field gradients with the aid of scheme viscosity of numerical algorithm used to model near-surface phenomena. This idea is implemented in the model of ideal gas equations with variable equation of state describing particulates transportation within boundary layer with obstacles.

Dual polarization micropulse lidar observations of the diurnal evolution of atmospheric boundary layer over a tropical coastal station

NASA Astrophysics Data System (ADS)

Rajeev, K.; Mishra, Manoj K.; Sunilkumar, S. V.; Sijikumar, S.

2016-05-01

High-resolution dual polarized micropulse lidar (MPL) observations have been used to investigate the diurnal evolution of atmospheric boundary layer (ABL) during winter (2008-2011) over Thiruvananthapuram (8.5°N, 77°E), a tropical coastal station located at southwest Peninsular India, adjoining the Arabian Sea. The lidar observations are compared with the boundary layer characteristics derived from concurrent balloon-borne radiosonde observations. This study shows that the mixed layer height over this coastal station generally increases from <300 m in the morning to 1500 m by the afternoon. Growth rate of the mixed layer height is rapid ( 350 m/hr) during 09-11 IST and slows down with time to <150 m/hr during 11-14 IST and <90 m/hr during 14-16 IST. Thermal internal boundary layer during the afternoon, caused by sea breeze circulation, extends up to 500 m altitude and is characterized by highly spherical aerosols, while a distinctly non-spherical aerosol layer appear above this altitude, in the return flow arising from the landmass.

Control of secondary instability of the crossflow and Görtler-like vortices (Success and problems)

NASA Astrophysics Data System (ADS)

Kozlov, Viktor V.; Grek, Genrich R.

The secondary instability on a group of crossflow vortices developing in a swept wing boundary layer is described. It is shown that, for travelling waves, there is a region of linear development, and the growth rate of disturbances appreciably depends on the separation between the vortices. Methods of controlling the secondary instability of the vortices by a controlled wave and local suction are proposed and substantiated. The stability of a flat plate boundary layer modulated by G&ou ml;rtler-like stationary vortices is described. Vortices were generated inside the boundary layer by means of roughness elements arranged in a regular array along the spanwise (z) direction. Transition is not caused directly by these structures, but by the growth of small amplitude travelling waves riding on top of the steady vortices. This situation is analogous to the transition process in Görtler and cross-flows. The waves were found to amplify up to a stage where higher harmonics are gener ated, leading to turbulent breakdown and disintegration of the spanwise boundary layer structure. For strong modulations, the observed instability is quite powerful, and can be excited "naturally" by small uncontrollable background disturbances. Controlled oscillations were then introduced by means of a vibrating ribbon, allowing a detailed investigation of the wave characteristics. The instability seems to be associated with the spanwise gradients of the mean flow, , and at all z-positions, the maximum wave amplitude was found at a wall-normal position where the mean velocity is equal to the phase velocity of the wave, U(y)=c, i.e., at the local critical layer. Unstable waves were observed at frequency well above those for which Tollmien-Schlichting (TS) waves amplify in the Blasius boundary layer. Excitation at lower frequencies and milder basic flow modulation showed that TS-type waves may a lso develop. Study of the transition control in that flow by means of riblets shows that the effect of the riblets is to suppress longitudinal vortex structures in a boundary layer. The boundary layer becomes stable with respect to high-frequency travelling waves, which cause the transition in the absence of the riblets.

Experiments on Hypersonic Roughness Induced Transition by Means of Infrared Thermography

NASA Astrophysics Data System (ADS)

Schrijer, F. F. J.; Scarano, F.; van Oudheusden, B. W.; Bannink, W. J.

2005-02-01

Roughness induced boundary layer transition is experimentally investigated in the hypersonic flow regime at M = 9. The primary interest is the possible effect of stepwise geometry imperfections (2D isolated roughness) on (boundary layer) transition which may be caused on the EXPERT vehicle by the difference in thermal expansion due to the different materials used in the vehicle-nose construction. Also 3D isolated and 3D distributed roughness configurations were studied. Quantitative Infra-Red Thermography (QIRT) is used as primary diagnostic technique to measure the surface convective heat transfer and to detect boundary layer laminar-to-turbulent transition. The investigation shows that for a given height of the roughness element, the boundary layer is least sensitive to a step-like disturbance, whereas distributed 3D roughness was found to be effective in triggering transition. The experimental results have been compared to existing hypersonic transition correlations (PANT and Shuttle). Finally a transition criterion is evaluated which is based on the critical roughness height Reynolds number. Usage of this criterion enables a straightforward extrapolation to flight. Key words: hypersonic flow, boundary layer transition.

Exploratory study of in-plane streamline curvature effects on a turbulent boundary layer at a Mach number of 3

NASA Technical Reports Server (NTRS)

Bogdonoff, Seymour M.

1991-01-01

This report on a program to study in-plane streamline curvature effects in a turbulent boundary layer at a Mach number of 3. The original proposal, for a 3-year program to explore in-plane streamline curvature effects on a supersonic turbulent boundary layer using three-dimensional pressure fields generated by fins and wall geometry, ended after one year. The purpose of these tests was to compare these streamline curvature effects to the more classical two-dimensional curvature generated by wall shape and imposed pressure gradients, previously considered primarily in a plane normal to the floor. The studies were carried out in the Mach number of 3, 8 x 8 inch High Reynolds Number Supersonic Tunnel. The usual surface visualization and mean wall static pressures were supplemented by the use of many small high frequency wall static pressure gauges (Kulites) to get some indication of the amplification of boundary layer disturbances by the in-plane streamline curvature caused by the three-dimensional pressure fields imposed on the boundary layer.

Control of a shock wave-boundary layer interaction using localized arc filament plasma actuators

NASA Astrophysics Data System (ADS)

Webb, Nathan Joseph

Supersonic flight is currently possible, but expensive. Inexpensive supersonic travel will require increased efficiency of high-speed air entrainment, an integral part of air-breathing propulsion systems. Although mixed compression inlet geometry can significantly improve entrainment efficiency, numerous Shock Wave-Boundary Layer Interactions (SWBLIs) are generated in this configuration. The boundary layer must therefore develop through multiple regions of adverse pressure gradient, causing it to thicken, and, in severe cases, separate. The associated increase in unsteadiness can have adverse effects on downstream engine hardware. The most severe consequence of these interactions is the increased aerodynamic blockage generated by the thickened boundary layer. If the increase is sufficient, it can choke the flow, causing inlet unstart, and resulting in a loss of thrust and high transient forces on the engine, airframe, and aircraft occupants. The potentially severe consequences associated with SWBLIs require flow control to ensure proper operation. Traditionally, boundary layer bleed has been used to control the interaction. Although this method is effective, it has inherent efficiency penalties. Localized Arc Filament Plasma Actuators (LAFPAs) are designed to generate perturbations for flow control. Natural flow instabilities act to amplify certain perturbations, allowing the LAFPAs to control the flow with minimal power input. LAFPAs also have the flexibility to maintain control over a variety of operating conditions. This work seeks to examine the effectiveness of LAFPAs as a separation control method for an oblique, impinging SWBLI. The low frequency unsteadiness in the reflected shock was thought to be the natural manifestation of a Kelvin-Helmholtz instability in the shear layer above the separation region. The LAFPAs were therefore placed upstream of the interaction to allow their perturbations to convect to the receptivity region (near the shear layer origin/separation line). Streamwise PIV measurements did not show that the boundary layer or separation region were energized by the actuation. The primary effect of the LAFPAs was the displacement of the reflected shock upstream. Jaunet et al. (2012) observed a similar shift in the reflected shock when they heated the wall beneath the boundary layer. A significantly greater power deposition was used in that work, and significantly larger shock displacements were observed. Although the LAFPAs output significantly less power (albeit in an unsteady, highly localized fashion), a parametric sweep strongly pointed to heating as the primary control mechanism. Further investigation and analysis showed that the near-wall heating of the flow by the plasma was the primary control mechanism of the LAFPAs, despite the small power input. The reflected shock was displaced by an increase in the separation region size, which was caused by the degradation of the upstream boundary layer. The LAFPAs degrade the upstream boundary layer through a variety of heating associated mechanisms: 1) Decreasing the density increases the mass flow deficit, 2) The altered skin-friction coefficient acts to retard the flow and make the velocity profile less full, and 3) The heating moves the sonic line further from the wall. Other mechanisms may also play a role.

Large Eddy Simulation of Wake Vortices in the Convective Boundary Layer

NASA Technical Reports Server (NTRS)

Lin, Yuh-Lang; Han, Jongil; Zhang, Jing; Ding, Feng; Arya, S. Pal; Proctor, Fred H.

2000-01-01

The behavior of wake vortices in a convective boundary layer is investigated using a validated large eddy simulation model. Our results show that the vortices are largely deformed due to strong turbulent eddy motion while a sinusoidal Crow instability develops. Vortex rising is found to be caused by the updrafts (thermals) during daytime convective conditions and increases with increasing nondimensional turbulence intensity eta. In the downdraft region of the convective boundary layer, vortex sinking is found to be accelerated proportional to increasing eta, with faster speed than that in an ideal line vortex pair in an inviscid fluid. Wake vortices are also shown to be laterally transported over a significant distance due to large turbulent eddy motion. On the other hand, the decay rate of the, vortices in the convective boundary layer that increases with increasing eta, is larger in the updraft region than in the downdraft region because of stronger turbulence in the updraft region.

Flight-measured laminar boundary-layer transition phenomena including stability theory analysis

NASA Technical Reports Server (NTRS)

Obara, C. J.; Holmes, B. J.

1985-01-01

Flight experiments were conducted on a single-engine turboprop aircraft fitted with a 92-in-chord, 3-ft-span natural laminar flow glove at glove section lift coefficients from 0.15 to 1.10. The boundary-layer transition measurement methods used included sublimating chemicals and surface hot-film sensors. Transition occurred downstream of the minimum pressure point. Hot-film sensors provided a well-defined indication of laminar, laminar-separation, transitional, and turbulent boundary layers. Theoretical calculations of the boundary-layer parameters provided close agreement between the predicted laminar-separation point and the measured transition location. Tollmien-Schlichting (T-S) wave growth n-factors between 15 and 17 were calculated at the predicted point of laminar separation. These results suggest that for many practical airplane cruise conditions, laminar separation (as opposed to T-S instability) is the major cause of transition in predominantly two-dimensional flows.

Unsteady separation and vortex shedding from a laminar separation bubble over a bluff body

NASA Astrophysics Data System (ADS)

Das, S. P.; Srinivasan, U.; Arakeri, J. H.

2013-07-01

Boundary layers are subject to favorable and adverse pressure gradients because of both the temporal and spatial components of the pressure gradient. The adverse pressure gradient may cause the flow to separate. In a closed loop unsteady tunnel we have studied the initiation of separation in unsteady flow past a constriction (bluff body) in a channel. We have proposed two important scalings for the time when boundary layer separates. One is based on the local pressure gradient and the other is a convective time scale based on boundary layer parameters. The flow visualization using a dye injection technique shows the flow structure past the body. Nondimensional shedding frequency (Strouhal number) is calculated based on boundary layer and momentum thicknesses. Strouhal number based on the momentum thickness shows a close agreement with that for flat plate and circular cylinder.

Mach 6 flowfield survey at the engine inlet of a research airplane

NASA Technical Reports Server (NTRS)

Johnson, C. B.; Lawing, P. L.

1977-01-01

A flowfield survey was conducted to better define the nature of vehicle forebody flowfield at the inlet location of an airframe-integrated scramjet engine mounted on the lower surface of a high-speed research airplane to be air launched from a B-52 and rocket boosted to Mach 6. The tests were conducted on a 1/30-scale brass model in a Mach-6 20-in. wind tunnel at Reynolds number of 11,200,000 based on distance to engine inlet. Boundary layer profiles at five spanwise locations indicate that the boundary layer in the area of the forebody centerline is more than twice as thick as the boundary layer at three outboard stations. It is shown that the cold streak found in heating contours on the centerline of the forebody is caused by a thickening of the boundary layer on the centerline, and that this thickening decreases with angle of attack.

Fuselage boundary-layer refraction of fan tones radiated from an installed turbofan aero-engine.

PubMed

Gaffney, James; McAlpine, Alan; Kingan, Michael J

2017-03-01

A distributed source model to predict fan tone noise levels of an installed turbofan aero-engine is extended to include the refraction effects caused by the fuselage boundary layer. The model is a simple representation of an installed turbofan, where fan tones are represented in terms of spinning modes radiated from a semi-infinite circular duct, and the aircraft's fuselage is represented by an infinitely long, rigid cylinder. The distributed source is a disk, formed by integrating infinitesimal volume sources located on the intake duct termination. The cylinder is located adjacent to the disk. There is uniform axial flow, aligned with the axis of the cylinder, everywhere except close to the cylinder where there is a constant thickness boundary layer. The aim is to predict the near-field acoustic pressure, and in particular, to predict the pressure on the cylindrical fuselage which is relevant to assess cabin noise. Thus no far-field approximations are included in the modelling. The effect of the boundary layer is quantified by calculating the area-averaged mean square pressure over the cylinder's surface with and without the boundary layer included in the prediction model. The sound propagation through the boundary layer is calculated by solving the Pridmore-Brown equation. Results from the theoretical method show that the boundary layer has a significant effect on the predicted sound pressure levels on the cylindrical fuselage, owing to sound radiation of fan tones from an installed turbofan aero-engine.

Investigating a 65-Ma-Old Smoking Gun: Deep Drilling of the Chicxulub Impact Structure

NASA Astrophysics Data System (ADS)

Dressler, B. O.; Sharpton, V. L.; Morgan, J.; Buffler, R.; Moran, D.; Smit, J.; Stöffler, D.; Urrutia, J.

The Phanerozoic paleontological record is marked by several biological extinction events. One of them, at the Cretaceous/Tertiary (K/T) boundary, was responsible for the demise of about 5% of genera and 75% of species, including the dinosaurs. These drastic and abrupt changes in the development of life on Earth puzzled paleontologists in the past. Many a cause was put forward to account for them, amongst them climate changes, disease, or overspecialization. About 20 years ago, Alvarez et al. [1980] discovered a high iridium concentration in an Italian K/T boundary clay layer. They proposed that the iridium was derived from an extra-terrestrial impact 65 Ma ago and that the impact was the cause for the K/T boundary extinctions. The iridium layer was subsequently found at K/T boundary locations worldwide. Further evidence for a K/T impact came from the discovery of shocked quartz, nano-diamonds, glass spherules, and nickel-rich spinels in microkrystites in the iridium-rich layer. There was evidence for an impact event, but no crater.

Influence of probe geometry on pitot-probe displacement in supersonic turbulent flow

NASA Technical Reports Server (NTRS)

Allen, J. M.

1975-01-01

An experiment was conducted to determine the varying effects of six different probe-tip and support-shaft configurations on pitot tube displacement. The study was stimulated by discrepancies between supersonic wind-tunnel tests conducted by Wilson and Young (1949) and Allen (1972). Wilson (1973) had concluded that these discrepancies were caused by differences in probe geometry. It is shown that in fact, no major differences in profiles of streamwise velocity over streamwise velocity at boundary-layer edge vs normal coordinate over boundary-layer total thickness result from geometry. The true cause of the discrepancies, however, remains to be discovered.

The structure of a three-dimensional turbulent boundary layer

NASA Technical Reports Server (NTRS)

Degani, A. T.; Smith, F. T.; Walker, J. D. A.

1993-01-01

The three-dimensional turbulent boundary layer is shown to have a self-consistent two-layer asymptotic structure in the limit of large Reynolds number. In a streamline coordinate system, the streamwise velocity distribution is similar to that in two-dimensional flows, having a defect-function form in the outer layer which is adjusted to zero at the wall through an inner wall layer. An asymptotic expansion accurate to two orders is required for the cross-stream velocity which is shown to exhibit a logarithmic form in the overlap region. The inner wall-layer flow is collateral to leading order but the influence of the pressure gradient, at large but finite Reynolds numbers, is not negligible and can cause substantial skewing of the velocity profile near the wall. Conditions under which the boundary layer achieves self-similarity and the governing set of ordinary differential equations for the outer layer are derived. The calculated solution of these equations is matched asymptotically to an inner wall-layer solution and the composite profiles so formed describe the flow throughout the entire boundary layer. The effects of Reynolds number and cross-stream pressure gradient on the crossstream velocity profile are discussed and it is shown that the location of the maximum cross-stream velocity is within the overlap region.

Numerical simulations of the stratified oceanic bottom boundary layer

NASA Astrophysics Data System (ADS)

Taylor, John R.

Numerical simulations are used to consider several problems relevant to the turbulent oceanic bottom boundary layer. In the first study, stratified open channel flow is considered with thermal boundary conditions chosen to approximate a shallow sea. Specifically, a constant heat flux is applied at the free surface and the lower wall is assumed to be adiabatic. When the surface heat flux is strong, turbulent upwellings of low speed fluid from near the lower wall are inhibited by the stable stratification. Subsequent studies consider a stratified bottom Ekman layer over a non-sloping lower wall. The influence of the free surface is removed by using an open boundary condition at the top of the computational domain. Particular attention is paid to the influence of the outer layer stratification on the boundary layer structure. When the density field is initialized with a linear profile, a turbulent mixed layer forms near the wall, which is separated from the outer layer by a strongly stable pycnocline. It is found that the bottom stress is not strongly affected by the outer layer stratification. However, stratification reduces turbulent transport to the outer layer and strongly limits the boundary layer height. The mean shear at the top of the boundary layer is enhanced when the outer layer is stratified, and this shear is strong enough to cause intermittent instabilities above the pycnocline. Turbulence-generated internal gravity waves are observed in the outer layer with a relatively narrow frequency range. An explanation for frequency content of these waves is proposed, starting with an observed broad-banded turbulent spectrum and invoking linear viscous decay to explain the preferential damping of low and high frequency waves. During the course of this work, an open-source computational fluid dynamics code has been developed with a number of advanced features including scalar advection, subgrid-scale models for large-eddy simulation, and distributed memory parallelism.

Numerical investigation of an internal layer in turbulent flow over a curved hill

NASA Technical Reports Server (NTRS)

Kim, S-W.

1989-01-01

The development of an internal layer in a turbulent boundary layer flow over a curved hill is investigated numerically. The turbulence field of the boundary layer flow over the curved hill is compared with that of a turbulent flow over a symmetric airfoil (which has the same geometry as the curved hill except that the leading and trailing edge plates were removed) to study the influence of the strongly curved surface on the turbulence field. The turbulent flow equations are solved by a control-volume based finite difference method. The turbulence is described by a multiple-time-scale turbulence model supplemented with a near-wall turbulence model. Computational results for the mean flow field (pressure distributions on the walls, wall shearing stresses and mean velocity profiles), the turbulence structure (Reynolds stress and turbulent kinetic energy profiles), and the integral parameters (displacement and momentum thicknesses) compared favorably with the measured data. Computational results show that the internal layer is a strong turbulence field which is developed beneath the external boundary layer and is located very close to the wall. Development of the internal layer was more obviously observed in the Reynolds stress profiles and in the turbulent kinetic energy profiles than in the mean velocity profiles. In this regard, the internal layers is significantly different from wall-bounded simple shear layers in which the mean velocity profile characterizes the boundary layer most distinguishably. Development of such an internal layer, characterized by an intense turbulence field, is attributed to the enormous mean flow strain rate caused by the streamline curvature and the strong pressure gradient. In the turbulent flow over the curved hill, the internal layer begin to form near the forward corner of the hill, merges with the external boundary layer, and develops into a new fully turbulent boundary layer as the fluid flows in the downstream direction. For the flow over the symmetric airfoil, the boundary layer began to form from almost the same location as that of the curved hill, grew in its strength, and formed a fully turbulent boundary layer from mid-part of the airfoil and in the downstream region. Computational results also show that the detailed turbulence structure in the region very close to the wall of the curved hill is almost the same as that of the airfoil in most of the curved regions except near the leading edge. Thus the internal layer of the curved hill and the boundary layer of the airfoil were also almost the same. Development of the wall shearing stress and separation of the boundary layer at the rear end of the curved hill mostly depends on the internal layer and is only slightly influenced by the external boundary layer flow.

Correction of Excessive Precipitation Over Steep and High Mountains in a General Circulation Model

NASA Technical Reports Server (NTRS)

Chao, Winston C.

2012-01-01

Excessive precipitation over steep and high mountains (EPSM) is a well-known problem in GCMs and meso-scale models. This problem impairs simulation and data assimilation products. Among the possible causes investigated in this study, we found that the most important one, by far, is a missing upward transport of heat out of the boundary layer due to the vertical circulations forced by the daytime upslope winds, which are forced by the heated boundary layer on subgrid-scale slopes. These upslope winds are associated with large subgrid-scale topographic variation, which is found over steep and high mountains. Without such subgridscale heat ventilation, the resolvable-scale upslope flow in the boundary layer generated by surface sensible heat flux along the mountain slopes is excessive. Such an excessive resolvablescale upslope flow combined with the high moisture content in the boundary layer results in excessive moisture transport toward mountaintops, which in turn gives rise to EPSM. Other possible causes of EPSM that we have investigated include 1) a poorly-designed horizontal moisture flux in the terrain-following coordinates, 2) the condition for cumulus convection being too easily satisfied at mountaintops, 3) the presence of conditional instability of the computational kind, and 4) the absence of blocked flow drag. These are all minor or inconsequential. We have parameterized the ventilation effects of the subgrid-scale heated-slope-induced vertical circulation (SHVC) by removing heat from the boundary layer and depositing it in layers higher up when the topographic variance exceeds a critical value. Test results using NASA/Goddard's GEOS-S GCM have shown that this largely solved the EPSM problem.

Numerical Experiments in Error Control for Sound Propagation Using a Damping Layer Boundary Treatment

NASA Technical Reports Server (NTRS)

Goodrich, John W.

2017-01-01

This paper presents results from numerical experiments for controlling the error caused by a damping layer boundary treatment when simulating the propagation of an acoustic signal from a continuous pressure source. The computations are with the 2D Linearized Euler Equations (LEE) for both a uniform mean flow and a steady parallel jet. The numerical experiments are with algorithms that are third, fifth, seventh and ninth order accurate in space and time. The numerical domain is enclosed in a damping layer boundary treatment. The damping is implemented in a time accurate manner, with simple polynomial damping profiles of second, fourth, sixth and eighth power. At the outer boundaries of the damping layer the propagating solution is uniformly set to zero. The complete boundary treatment is remarkably simple and intrinsically independant from the dimension of the spatial domain. The reported results show the relative effect on the error from the boundary treatment by varying the damping layer width, damping profile power, damping amplitude, propagtion time, grid resolution and algorithm order. The issue that is being addressed is not the accuracy of the numerical solution when compared to a mathematical solution, but the effect of the complete boundary treatment on the numerical solution, and to what degree the error in the numerical solution from the complete boundary treatment can be controlled. We report maximum relative absolute errors from just the boundary treatment that range from O[10-2] to O[10-7].

Evaluation of Planetary Boundary Layer Scheme Sensitivities for the Purpose of Parameter Estimation

EPA Science Inventory

Meteorological model errors caused by imperfect parameterizations generally cannot be overcome simply by optimizing initial and boundary conditions. However, advanced data assimilation methods are capable of extracting significant information about parameterization behavior from ...

Visualization of the structural response of a hypersonic turbulent boundary layer to convex curvature

NASA Astrophysics Data System (ADS)

Humble, R. A.; Peltier, S. J.; Bowersox, R. D. W.

2012-10-01

The effects of convex curvature on the outer structure of a Mach 4.9 turbulent boundary layer (Reθ = 4.7 × 104) are investigated using condensate Rayleigh scattering and analyzed using spatial correlations, intermittency, and fractal theory. It is found that the post-expansion boundary layer structure morphology appears subtle, but certain features exhibit a more obvious response. The large-scale flow structures survive the initial expansion, appearing to maintain the same physical size. However, due to the nature of the expansion fan, a differential acceleration effect takes place across the flow structures, causing them to be reoriented, leaning farther away from the wall. The onset of intermittency moves closer towards the boundary layer edge and the region of intermittent flow decreases. It is likely that this reflects the less frequent penetration of outer irrotational fluid into the boundary layer, consistent with a boundary layer that is losing its ability to entrain freestream fluid. The fractal dimension of the turbulent/nonturbulent interface decreases with increasing favorable pressure gradient, indicating that the interface's irregularity decreases. Because fractal scale similarity does not encompass the largest scales, this suggests that the change in fractal dimension is due to the action of the smaller-scales, consistent with the idea that the small-scale flow structures are quenched during the expansion in response to bulk dilatation.

Effects of Cavities and Protuberances on Transition over Hypersonic Vehicles

NASA Technical Reports Server (NTRS)

Chang, Chau-Lyan; Choudhari, Meelan M.; Li, Fei; Venkatachari, Balaji

2011-01-01

Surface protuberances and cavities on a hypersonic vehicle are known to cause several aerodynamic or aerothermodynamic issues. Most important of all, premature transition due to these surface irregularities can lead to a significant rise in surface heating. To help understand laminar-turbulent transition induced by protuberances or cavities on a Crew Exploration Vehicle (CEV) surface, high-fidelity numerical simulations are carried out for both types of trips on a CEV wind tunnel model. Due to the large bluntness, these surface irregularities reside in an accelerating subsonic boundary layer. For the Mach 6 wind tunnel conditions with a roughness Reynolds number Re(sub kk) of 800, it was found that a protuberance with a height to boundary layer thickness ratio of 0.73 leads to strong wake instability and spontaneous vortex shedding, while a cavity with identical geometry only causes a rather weak flow unsteadiness. The same cavity with a larger Reynolds number also leads to similar spontaneous vortex shedding and wake instability. The wake development and the formation of hairpin vortices for both protuberance and cavity were found to be qualitatively similar to that observed for an isolated hemisphere submerged in a subsonic, low speed flat-plate boundary layer. However, the shed vortices and their accompanying instability waves were found to be slightly stabilized downstream by the accelerating boundary layer along the CEV surface. Despite this stabilizing influence, it was found that the wake instability spreads substantially in both wall-normal and azimuthal directions as the flow is evolving towards a transitional state. Similarities and differences between the wake instability behind a protuberance and a cavity are investigated. Computations for the Mach 6 boundary layer over a slender cylindrical roughness element with a height to the boundary layer thickness of about 1.1 also shows spontaneous vortex shedding and strong wake instability. Comparisons of detailed flow structures associated with protuberances at subsonic and supersonic edge Mach numbers indicate distinctively different instability mechanisms.

Boundary-layer transition on cones at angle of attack in a Mach-6 Quiet Tunnel

NASA Astrophysics Data System (ADS)

Swanson, Erick O.

It is desirable for the boundary layer on a re-entry vehicle (RV) to be laminar during as much of its flight as possible, since a turbulent boundary layer causes several problems, such as high heat flux to the vehicle and larger drag forces. Nosetip roughness can cause the boundary layer to transition downstream on the cone. Surface roughness and nosetip bluntness may cause windside-forward transition on maneuvering RVs. The crossflow instability may also influence transition on yawed RVs. The mechanisms through which these phenomena induce transition are poorly understood. Several experiments have been conducted to study these phenomena. The temperature-sensitive-paint (TSP) and oil-flow techniques were used to observe transition and crossflow vortices on cones at angle of attack in the Purdue Boeing/AFOSR Mach-6 Quiet Tunnel. The high-Reynolds number capability of the tunnel was developed to facilitate these experiments. Improvements were made in the use of the temperature-sensitive-paint technique in the Purdue Mach-6 Quiet Tunnel. The measured heat transfer to cones with sharp and spherically-blunt nosetips at 0° angle-of-attack was within 60% of the values from Navier-Stokes computations. Transition was observed on sharp and spherically-blunt cones at 6° angle-of-attack in noisy flow. Crossflow vortices were observed with both TSP and oil flow under noisy conditions in the turbulent boundary layer on a sharp cone. The vortex angles were about 50% of the surface-streamline angles observed using oil dots. TSP was also used to observe crossflow vortices in quiet flow. The vortices were similar to those seen in noisy flow. An array of roughness elements at x = 2 inches (axially) with a spacing of 9° on a yawed sharp cone in noisy flow influenced transition that was apparently induced by the crossflow instability. No influence of the roughness array was observed in quiet flow.

Measurements of thermal updraft intensity over complex terrain using American white pelicans and a simple boundary-layer forecast model

USGS Publications Warehouse

Shannon, H.D.; Young, G.S.; Yates, M.; Fuller, Mark R.; Seegar, W.

2003-01-01

An examination of boundary-layer meteorological and avian aerodynamic theories suggests that soaring birds can be used to measure the magnitude of vertical air motions within the boundary layer. These theories are applied to obtain mixed-layer normalized thermal updraft intensity over both flat and complex terrain from the climb rates of soaring American white pelicans and from diagnostic boundary-layer model-produced estimates of the boundary-layer depth zi and the convective velocity scale w*. Comparison of the flatland data with the profiles of normalized updraft velocity obtained from previous studies reveals that the pelican-derived measurements of thermal updraft intensity are in close agreement with those obtained using traditional research aircraft and large eddy simulation (LES) in the height range of 0.2 to 0.8 zi. Given the success of this method, the profiles of thermal vertical velocity over the flatland and the nearby mountains are compared. This comparison shows that these profiles are statistically indistinguishable over this height range, indicating that the profile for thermal updraft intensity varies little over this sample of complex terrain. These observations support the findings of a recent LES study that explored the turbulent structure of the boundary layer using a range of terrain specifications. For terrain similar in scale to that encountered in this study, results of the LES suggest that the terrain caused less than an 11% variation in the standard deviation of vertical velocity.

Correction of Excessive Precipitation over Steep Mountains in a General Circulation Model (GCM)

NASA Technical Reports Server (NTRS)

Chao, Winston C.

2012-01-01

Excessive precipitation over steep and high mountains (EPSM) is a well-known problem in GCMs and regional climate models even at a resolution as high as 19km. The affected regions include the Andes, the Himalayas, Sierra Madre, New Guinea and others. This problem also shows up in some data assimilation products. Among the possible causes investigated in this study, we found that the most important one, by far, is a missing upward transport of heat out of the boundary layer due to the vertical circulations forced by the daytime subgrid-scale upslope winds, which in turn is forced by heated boundary layer on the slopes. These upslope winds are associated with large subgrid-scale topographic variance, which is found over steep mountains. Without such subgrid-scale heat ventilation, the resolvable-scale upslope flow in the boundary layer generated by surface sensible heat flux along the mountain slopes is excessive. Such an excessive resolvable-scale upslope flow in the boundary layer combined with the high moisture content in the boundary layer results in excessive moisture transport toward mountaintops, which in turn gives rise to excessive precipitation over the affected regions. We have parameterized the effects of subgrid-scale heated-slope-induced vertical circulation (SHVC) by removing heat from the boundary layer and depositing it in the layers higher up when topographic variance exceeds a critical value. Test results using NASA/Goddard's GEOS-5 GCM have shown that the EPSM problem is largely solved.

Effect of Blowing on Boundary Layer of Scarf Inlet

NASA Technical Reports Server (NTRS)

Gerhold, Carl H.; Clark, Lorenzo R.

2004-01-01

When aircraft operate in stationary or low speed conditions, airflow into the engine accelerates around the inlet lip and pockets of turbulence that cause noise and vibration can be ingested. This problem has been encountered with engines equipped with the scarf inlet, both in full scale and in model tests, where the noise produced during the static test makes it difficult to assess the noise reduction performance of the scarf inlet. NASA Langley researchers have implemented boundary layer control in an attempt to reduce the influence of the flow nonuniformity in a 12-in. diameter model of a high bypass fan engine mounted in an anechoic chamber. Static pressures and boundary layer profiles were measured in the inlet and far field acoustic measurements were made to assess the effectiveness of the blowing treatment. The blowing system was found to lack the authority to overcome the inlet distortions. Methods to improve the implementation of boundary layer control to reduce inlet distortion are discussed.

Flow visualization study of a vortex-wing interaction

NASA Technical Reports Server (NTRS)

Mehta, R. D.; Lim, T. T.

1984-01-01

A flow visualization study in water was completed on the interaction of a streamwise vortex with a laminar boundary layer on a two-dimensional wing. The vortex was generated at the tip of a finite wing at incidence, mounted perpendicular to the main wing, and having the same chord as the main wing. The Reynolds number based on wing chord was about 5000. Two different visualization techniques were used. One involved the injection of two different colored dyes into the vortex and the boundary layer. The other technique utilized hydrogen bubbles as an indicator. The position of the vortex was varied in a directional normal to the wing. The angle of attack of the main wing was varied from -5 to +12.5 deg. The vortex induced noticeable cross flows in the wing boundary layer from a distance equivalent to 0.75 chords. When very close to the wing, the vortex entrained boundary layer fluid and caused a cross flow separation which resulted in a secondary vortex.

Is Chicxulub Too Small to be the Source of the K/Pg Boundary Layer and the Cause of the Dinosaur Extinction Event and would the Amazon Basin Considered as an Impact Feature fit the Evidence Better?

NASA Astrophysics Data System (ADS)

Burgener, J. A.

2016-12-01

The Chicxulub impact is well associated with the K/Pg boundary layer and extinction event [Schulte et al., 2010]. However, most agree that Chicxulub is considered to be too small to have caused the extinction in itself [Kring, 2007; Keller, 2014]. Keller [2014] discusses how the K/Pg extinction event may have been due to many factors, of which Chicxulub would be part, but global warming or volcanic fumes or other factors were the main killers. There are several features in the K/Pg layer that require a much higher energy impact than Chicxulub. The worldwide distribution of shocked crystals does not fit Chicxulub - Chicxulub would only send such granules 400 km away [Morgan et al, 2006]. The Fern Spore anomaly extends too far from Chicxulub indicating a much larger fireball and impact [Fleming 1990; Robertson, 2103]. Fireballs falling around the planet have been proposed and dismissed as not possible. [Goldin & Melosh, 2009] and [Adair,2010] rule out a firestorm from ejecta. One of the reasons that Chicxulub is convincingly attributed with the K/Pg boundary layer is the calculation that the size of the impacting asteroid should have been about 10 km in diameter, based on the thickness of the boundary layer and the amount of iridium in the boundary layer [Alvarez, 1980]. Alvarez used the factor from the Krakatoa eruption (0.22) as the amount of asteroid material that would stay in the atmosphere. More recent studies imply that far less than 0.22 of an asteroid would stay in the atmosphere after an impact. When a comet hits at 55 - 72 km/sec, the vast majority of the comet material will be buried deep into the Earth or ejected at speeds in excess of the escape velocity, and very little would remain [Jeffers et al.2001]. Therefore a comet impact should leave a relatively small boundary layer, requiring a much larger impact by a comet to form what Alvaraz calculated for a 10 km asteroid. If a much larger impact occurred at the end of the Cretaceous, it would resolve the challenges of Chicxulub as long as it was near the location of Chicxulub. If the Amazon Basin was considered as an impact, it would be large enough to fit the K/Pg boundary layer details much better than Chicxulub, and it would explain the extinction event without any need to rely on extenuating factors - the impact itself would have been sufficient to cause the extinction.

Roles of drizzle in a one-dimensional third-order turbulence closure model of the nocturnal stratus-topped marine boundary layer

NASA Technical Reports Server (NTRS)

Wang, Shouping; Wang, Qing

1994-01-01

This study focuses on the effects of drizzle in a one-dimensional third-order turbulence closure model of the nocturnal stratus-topped marine boundary layer. When the simulated drizzle rate is relatively small (maximum approximately equal to 0.6 mm/day), steady-state solutions are obtained. The boundary layer stabilizes essentially because drizzle causes evaporative cooling of the subcloud layer. This stabilization considerably reduces the buoyancy flux and turbulence kinetic energy below the stratus cloud. Thus, drizzle tends to decouple the cloud from the subcloud layer in the model, as suggested by many observational studies. In addition, the evaporation of drizzle in the subcloud layer creates small scattered clouds, which are likely to represent cumulus clouds, below the solid stratus cloud in the model. The sensitivity experiments show that these scattered clouds help maintain a coupled boundary layer. When the drizzle rate is relatively large (maximum approximately equal to 0.9 mm/day), the response of the model becomes transient with bursts in turbulent fluxes. This phenomenon is related to the formation of the scattered cloud layer below the solid stratus cloud. It appears that the model is inadequate to represent the heat and moisture transport by strong updrafts covering a small fractional area in cumulus convection.

Intense sub-kilometer-scale boundary layer rolls observed in hurricane fran

PubMed

Wurman; Winslow

1998-04-24

High-resolution observations obtained with the Doppler On Wheels (DOW) mobile weather radar near the point of landfall of hurricane Fran (1996) revealed the existence of intense, sub-kilometer-scale, boundary layer rolls that strongly modulated the near-surface wind speed. It is proposed that these structures are one cause of geographically varying surface damage patterns that have been observed after some landfalling hurricanes and that they cause much of the observed gustiness, bringing high-velocity air from aloft to the lowest observable levels. High-resolution DOW radar observations are contrasted with lower-resolution observations obtained with an operational weather radar, which underestimated peak low-level wind speeds.

The three-dimensional turbulent boundary layer near a plane of symmetry

NASA Technical Reports Server (NTRS)

Degani, A. T.; Smith, F. T.; Walker, J. D. A.

1992-01-01

The asymptotic structure of the three-dimensional turbulent boundary layer near a plane of symmetry is considered in the limit of large Reynolds number. A self-consistent two-layer structure is shown to exist wherein the streamwise velocity is brought to rest through an outer defect layer and an inner wall layer in a manner similar to that in two-dimensional boundary layers. The cross-stream velocity distribution is more complex and two terms in the asymptotic expansion are required to yield a complete profile which is shown to exhibit a logarithmic region. The flow in the inner wall layer is demonstrated to be collateral to leading order; pressure-gradient effects are formally of higher order but can cause the velocity profile to skew substantially near the wall at the large but finite Reynolds numbers encountered in practice. The governing set of ordinary differential equations describing a self-similar flow is derived. The calculated numerical solutions of these equations are matched asymptotically to an inner wall-layer solution and the results show trends that are consistent with experimental observations.

Wave interactions in a three-dimensional attachment line boundary layer

NASA Technical Reports Server (NTRS)

Hall, Philip; Mackerrell, Sharon O.

1988-01-01

The 3-D boundary layer on a swept wing can support different types of hydrodynamic instability. Attention is focused on the so-called spanwise contamination problem, which occurs when the attachment line boundary layer on the leading edge becomes unstable to Tollmien-Schlichting waves. In order to gain insight into the interactions important in that problem, a simplified basic state is considered. This simplified flow corresponds to the swept attachment line boundary layer on an infinite flat plate. The basic flow here is an exact solution of the Navier-Stokes equations and its stability to 2-D waves propagating along the attachment can be considered exactly at finite Reynolds number. This has been done in the linear and weakly nonlinear regimes. The corresponding problem is studied for oblique waves and their interaction with 2-D waves is investigated. In fact, oblique modes cannot be described exactly at finite Reynolds number so it is necessary to make a high Reynolds number approximation and use triple deck theory. It is shown that there are two types of oblique wave which, if excited, cause the destabilization of the 2-D mode and the breakdown of the disturbed flow at a finite distance from the leading edge. First, a low frequency mode related to the viscous stationary crossflow mode is a possible cause of breakdown. Second, a class of oblique wave with frequency comparable with that of the 2-D mode is another cause of breakdown. It is shown that the relative importance of the modes depends on the distance from the attachment line.

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.

Transient interaction between a reaction control jet and a hypersonic crossflow

NASA Astrophysics Data System (ADS)

Miller, Warrick A.; Medwell, Paul R.; Doolan, Con J.; Kim, Minkwan

2018-04-01

This paper presents a numerical study that focuses on the transient interaction between a reaction control jet and a hypersonic crossflow with a laminar boundary layer. The aim is to better understand the underlying physical mechanisms affecting the resulting surface pressure and control force. Implicit large-eddy simulations were performed with a round, sonic, perfect air jet issuing normal to a Mach 5 crossflow over a flat plate with a laminar boundary layer, at a jet-to-crossflow momentum ratio of 5.3 and a pressure ratio of 251. The pressure distribution induced on the flat plate is unsteady and is influenced by vortex structures that form around the jet. A horseshoe vortex structure forms upstream and consists of six vortices: two quasi-steady vortices and two co-rotating vortex pairs that periodically coalesce. Shear-layer vortices shed periodically and cause localised high pressure regions that convect downstream with constant velocity. A longitudinal counter-rotating vortex pair is present downstream of the jet and is formed from a series of trailing vortices which rotate about a common axis. Shear-layer vortex shedding causes periodic deformation of barrel and bow shocks. This changes the location of boundary layer separation which also affects the normal force on the plate.

A closed-form analytical model for predicting 3D boundary layer displacement thickness for the validation of viscous flow solvers

NASA Astrophysics Data System (ADS)

Kumar, V. R. Sanal; Sankar, Vigneshwaran; Chandrasekaran, Nichith; Saravanan, Vignesh; Natarajan, Vishnu; Padmanabhan, Sathyan; Sukumaran, Ajith; Mani, Sivabalan; Rameshkumar, Tharikaa; Nagaraju Doddi, Hema Sai; Vysaprasad, Krithika; Sharan, Sharad; Murugesh, Pavithra; Shankar, S. Ganesh; Nejaamtheen, Mohammed Niyasdeen; Baskaran, Roshan Vignesh; Rahman Mohamed Rafic, Sulthan Ariff; Harisrinivasan, Ukeshkumar; Srinivasan, Vivek

2018-02-01

A closed-form analytical model is developed for estimating the 3D boundary-layer-displacement thickness of an internal flow system at the Sanal flow choking condition for adiabatic flows obeying the physics of compressible viscous fluids. At this unique condition the boundary-layer blockage induced fluid-throat choking and the adiabatic wall-friction persuaded flow choking occur at a single sonic-fluid-throat location. The beauty and novelty of this model is that without missing the flow physics we could predict the exact boundary-layer blockage of both 2D and 3D cases at the sonic-fluid-throat from the known values of the inlet Mach number, the adiabatic index of the gas and the inlet port diameter of the internal flow system. We found that the 3D blockage factor is 47.33 % lower than the 2D blockage factor with air as the working fluid. We concluded that the exact prediction of the boundary-layer-displacement thickness at the sonic-fluid-throat provides a means to correctly pinpoint the causes of errors of the viscous flow solvers. The methodology presented herein with state-of-the-art will play pivotal roles in future physical and biological sciences for a credible verification, calibration and validation of various viscous flow solvers for high-fidelity 2D/3D numerical simulations of real-world flows. Furthermore, our closed-form analytical model will be useful for the solid and hybrid rocket designers for the grain-port-geometry optimization of new generation single-stage-to-orbit dual-thrust-motors with the highest promising propellant loading density within the given envelope without manifestation of the Sanal flow choking leading to possible shock waves causing catastrophic failures.

Method of high speed flow field influence and restrain on laser communication

NASA Astrophysics Data System (ADS)

Meng, Li-xin; Wang, Chun-hui; Qian, Cun-zhu; Wang, Shuo; Zhang, Li-zhong

2013-08-01

For laser communication performance which carried by airplane or airship, due to high-speed platform movement, the air has two influences in platform and laser communication terminal window. The first influence is that aerodynamic effect causes the deformation of the optical window; the second one is that a shock wave and boundary layer would be generated. For subsonic within the aircraft, the boundary layer is the main influence. The presence of a boundary layer could change the air density and the temperature of the optical window, which causes the light deflection and received beam spot flicker. Ultimately, the energy hunting of the beam spot which reaches receiving side increases, so that the error rate increases. In this paper, aerodynamic theory is used in analyzing the influence of the optical window deformation due to high speed air. Aero-optics theory is used to analyze the influence of the boundary layer in laser communication link. Based on this, we focused on working on exploring in aerodynamic and aero-optical effect suppression method in the perspective of the optical window design. Based on planning experimental aircraft types and equipment installation location, we optimized the design parameters of the shape and thickness of the optical window, the shape and size of air-management kit. Finally, deformation of the optical window and air flow distribution were simulated by fluid simulation software in the different mach and different altitude fly condition. The simulation results showed that the optical window can inhibit the aerodynamic influence after optimization. In addition, the boundary layer is smoothed; the turbulence influence is reduced, which meets the requirements of the airborne laser communication.

Unsuccessful initial search for a midmantle chemical boundary with seismic arrays

USGS Publications Warehouse

Vidale, J.E.; Schubert, G.; Earle, P.S.

2001-01-01

Compositional layering of the midmantle has been proposed to account for seismic and geochemical patterns [van der Hilst and Karason, 1999], and inferred radiogenic heat source concentrations [Kellogg et al., 1999]. Compositional layering would require thermal boundary layers both above and below an interface. We construct a minimal 1-D model of a mid-mantle boundary consistent with the observed nearly adiabatic compressional velocity structure [Dziewonksi and Anderson, 1981] and the proposed high heat flow from the lower mantle [Albarede and van der Hilst, 1999; Kellogg et al., 1999]. Ray tracing and reflectivity synthetic seismograms show that a distinct triplication is predicted for short-period P waves. Although topography on a boundary would cause uncertainty in the strength and the range of the triplication, many clear observations would be expected. We examine data from the US West Coast regional networks in the most likely distance range of 60?? to 70?? for a 1770-km-depth boundary, and find no evidence for P wave triplications.

Numerical simulation of adverse-pressure-gradient boundary layer with or without roughness

NASA Astrophysics Data System (ADS)

Mottaghian, Pouya; Yuan, Junlin; Piomelli, Ugo

2014-11-01

Large-eddy and direct numerical simulations are carried out on flat-plate boundary layer over smooth and rough surfaces, with adverse pressure gradient.The deceleration is achieved by imposing a wall-normal freestream velocity profile, and is strong enough to cause separation at the wall. The Reynolds number based on momentum thickness and freestream velocity at inlet is 600. Numerical sandgrain roughness is applied based on an immersed boundary method, yielding a flow that is transitionally rough. The turbulence intensity increases before separation, and reaches a higher value for the rough case, indicating stronger mixing. Roughness also causes higher momentum deficit near the wall, leading to earlier separation. This is consistent with previous observation made on rough-wall flow separation over a ramp. In both cases, the turbulent kinetic energy peaks inside the shear layer above the detachment region, with higher values in the rough case; it then decreases approaching the reattachment region. Near the wall inside the separation bubble, the near-zero turbulent intensity indicates that the turbulent structures are lifted up in the separation region. Compared with the smooth case, the shear layer is farther from the wall and the reattachment length is longer on the rough wall.

Unsteady turbulent boundary layers in swimming rainbow trout.

PubMed

Yanase, Kazutaka; Saarenrinne, Pentti

2015-05-01

The boundary layers of rainbow trout, Oncorhynchus mykiss, swimming at 1.02±0.09 L s(-1) (mean±s.d., N=4), were measured by the particle image velocimetry (PIV) technique at a Reynolds number of 4×10(5). The boundary layer profile showed unsteadiness, oscillating above and beneath the classical logarithmic law of the wall with body motion. Across the entire surface regions that were measured, local Reynolds numbers based on momentum thickness, which is the distance that is perpendicular to the fish surface through which the boundary layer momentum flows at free-stream velocity, were greater than the critical value of 320 for the laminar-to-turbulent transition. The skin friction was dampened on the convex surface while the surface was moving towards a free-stream flow and increased on the concave surface while retreating. These observations contradict the result of a previous study using different species swimming by different methods. Boundary layer compression accompanied by an increase in local skin friction was not observed. Thus, the overall results may not support absolutely the Bone-Lighthill boundary layer thinning hypothesis that the undulatory motions of swimming fish cause a large increase in their friction drag because of the compression of the boundary layer. In some cases, marginal flow separation occurred on the convex surface in the relatively anterior surface region, but the separated flow reattached to the fish surface immediately downstream. Therefore, we believe that a severe impact due to induced drag components (i.e. pressure drag) on the swimming performance, an inevitable consequence of flow separation, was avoided. © 2015. Published by The Company of Biologists Ltd.

Experimental investigation on the influence of boundary layer thickness on the base pressure and near-wake flow features of an axisymmetric blunt-based body

NASA Astrophysics Data System (ADS)

Mariotti, Alessandro; Buresti, Guido

2013-11-01

The influence of the thickness of the boundary layer developing over the surface of an axisymmetric bluff body upon its base pressure and near-wake flow is analyzed experimentally. The model, whose diameter-to-length ratio is d/ l = 0.175, has a forebody with an elliptical contour and a sharp-edged flat base; it is supported above a plate by means of a faired strut. The pressure distributions over the body lateral and base surfaces were obtained using numerous pressure taps, while the boundary layer profiles and the wake velocity field were measured through hot-wire anemometry. The tests were carried out at , at which the boundary layer over the lateral surface of the body becomes turbulent before reaching the base contour. Strips of emery cloth were wrapped in various positions around the body circumference in order to modify the thickness and the characteristics of the boundary layer. The results show that increasing the boundary layer thickness causes a decrease in the base suctions and a corresponding increase in the length of the mean recirculation region present behind the body. In the spectra of the velocity fluctuations measured within and aside the wake, a dominating peak becomes evident in the region downstream of the final part of the recirculation region. The relevant non-dimensional frequency decreases with increasing boundary layer thickness; however, a Strouhal number based on the wake width and the velocity defect at a suitable reference cross section downstream of the recirculation region is found to remain almost constant for the different cases.

Sensitivity of High-Resolution Simulations of Hurricane Bob (1991) to Planetary Boundary Layer Parameterizations

NASA Technical Reports Server (NTRS)

Braun, Scott A.; Tao, Wei-Kuo

1999-01-01

The MM5 mesoscale model is used to simulate Hurricane Bob (1991) using grids nested to high resolution (4 km). Tests are conducted to determine the sensitivity of the simulation to the available planetary boundary layer parameterizations, including the bulk-aerodynamic, Blackadar, Medium-RanGe Forecast (MRF) model, and Burk-Thompson boundary-layer schemes. Significant sensitivity is seen, with minimum central pressures varying by up to 17 mb. The Burk-Thompson and bulk-aerodynamic boundary-layer schemes produced the strongest storms while the MRF scheme produced the weakest storm. Precipitation structure of the simulated hurricanes also varied substantially with the boundary layer parameterizations. Diagnostics of boundary-layer variables indicated that the intensity of the simulated hurricanes generally increased as the ratio of the surface exchange coefficients for heat and momentum, C(sub h)/C(sub M), although the manner in which the vertical mixing takes place was also important. Findings specific to the boundary-layer schemes include: 1) the MRF scheme produces mixing that is too deep and causes drying of the lower boundary layer in the inner-core region of the hurricane; 2) the bulk-aerodynamic scheme produces mixing that is probably too shallow, but results in a strong hurricane because of a large value of C(sub h)/C(sub M) (approximately 1.3); 3) the MRF and Blackadar schemes are weak partly because of smaller surface moisture fluxes that result in a reduced value of C(sub h)/C(sub M) (approximately 0.7); 4) the Burk-Thompson scheme produces a strong storm with C(sub h)/C(sub M) approximately 1; and 5) the formulation of the wind-speed dependence of the surface roughness parameter, z(sub 0), is important for getting appropriate values of the surface exchange coefficients in hurricanes based upon current estimates of these parameters.

Laser transit anemometer measurements on a slender cone in the Langley unitary plan wind tunnel

NASA Technical Reports Server (NTRS)

Humphreys, William M., Jr.; Hunter, William W., Jr.; Covell, Peter F.; Nichols, Cecil E., Jr.

1990-01-01

A laser transit anemometer (LTA) system was used to probe the boundary layer on a slender (5 degree half angle) cone model in the Langley unitary plan wind tunnel. The anemometer system utilized a pair of laser beams with a diameter of 40 micrometers spaced 1230 micrometers apart to measure the transit times of ensembles of seeding particles using a cross-correlation technique. From these measurements, boundary layer profiles around the model were constructed and compared with CFD calculations. The measured boundary layer profiles representing the boundary layer velocity normalized to the edge velocity as a function of height above the model surface were collected with the model at zero angle of attack for four different flow conditions, and were collected in a vertical plane that bisected the model's longitudinal center line at a location 635 mm from the tip of the forebody cone. The results indicate an excellent ability of the LTA system to make velocity measurements deep into the boundary layer. However, because of disturbances in the flow field caused by onboard seeding, premature transition occurred implying that upstream seeding is mandatory if model flow field integrity is to be maintained. A description and results of the flow field surveys are presented.

Laminar-Turbulent Transition Behind Discrete Roughness Elements in a High-Speed Boundary Layer

NASA Technical Reports Server (NTRS)

Choudhari, Meelan M.; Li, Fei; Wu, Minwei; Chang, Chau-Lyan; Edwards, Jack R., Jr.; Kegerise, Michael; King, Rudolph

2010-01-01

Computations are performed to study the flow past an isolated roughness element in a Mach 3.5, laminar, flat plate boundary layer. To determine the effects of the roughness element on the location of laminar-turbulent transition inside the boundary layer, the instability characteristics of the stationary wake behind the roughness element are investigated over a range of roughness heights. The wake flow adjacent to the spanwise plane of symmetry is characterized by a narrow region of increased boundary layer thickness. Beyond the near wake region, the centerline streak is surrounded by a pair of high-speed streaks with reduced boundary layer thickness and a secondary, outer pair of lower-speed streaks. Similar to the spanwise periodic pattern of streaks behind an array of regularly spaced roughness elements, the above wake structure persists over large distances and can sustain strong enough convective instabilities to cause an earlier onset of transition when the roughness height is sufficiently large. Time accurate computations are performed to clarify additional issues such as the role of the nearfield of the roughness element during the generation of streak instabilities, as well as to reveal selected details of their nonlinear evolution. Effects of roughness element shape on the streak amplitudes and the interactions between multiple roughness elements aligned along the flow direction are also investigated.

Boundary Layer Transition in the Leading Edge Region of a Swept Cylinder in High Speed Flow

NASA Technical Reports Server (NTRS)

Coleman, Colin P.

1998-01-01

Experiments were conducted on a 76 degree swept cylinder to establish the behavior of the attachment line transition process in a low-disturbance level, Mach number 1.6 flow. For a near adiabatic wall condition, the attachment-line boundary layer remained laminar up to the highest attainable Reynolds number. The attachment-line boundary layer transition under the influence of trip wires depended on wind tunnel disturbance level, and a transition onset condition for this flow is established. Internal heating raised the surface temperature of the attachment line to induce boundary layer instabilities. This was demonstrated experimentally for the first time and the frequencies of the most amplified disturbances were determined over a range of temperature settings. Results were in excellent agreement to those predicted by a linear stability code, and provide the first experimental verification of theory. Transition onset along the heated attachment line at an R-bar of 800 under quiet tunnel conditions was found to correlate with an N factor of 13.2. Increased tunnel disturbance levels caused the transition onset to occur at lower cylinder surface temperatures and was found to correlate with an approximate N factor of 1 1.9, so demonstrating that the attachment-line boundary layer is receptive to increases in the tunnel disturbance level.

Vortex Formation During Unsteady Boundary-Layer Separation

NASA Astrophysics Data System (ADS)

Das, Debopam; Arakeri, Jaywant H.

1998-11-01

Unsteady laminar boundary-layer separation is invariably accompanied by the formation of vortices. The aim of the present work is to study the vortex formation mechanism(s). An adverse pressure gradient causing a separation can be decomposed into a spatial component ( spatial variation of the velocity external to the boundary layer ) and a temporal component ( temporal variation of the external velocity ). Experiments were conducted in a piston driven 2-D water channel, where the spatial component could be be contolled by geometry and the temporal component by the piston motion. We present results for three divergent channel geometries. The piston motion consists of three phases: constant acceleration from start, contant velocity, and constant deceleration to stop. Depending on the geometry and piston motion we observe different types of unsteady separation and vortex formation.

Tile Surface Thermocouple Measurement Challenges from the Orbiter Boundary Layer Transition Flight Experiment

NASA Technical Reports Server (NTRS)

Campbell, Charles H.; Berger, Karen; Anderson, Brian

2012-01-01

Hypersonic entry flight testing motivated by efforts seeking to characterize boundary layer transition on the Space Shuttle Orbiters have identified challenges in our ability to acquire high quality quantitative surface temperature measurements versus time. Five missions near the end of the Space Shuttle Program implemented a tile surface protuberance as a boundary layer trip together with tile surface thermocouples to capture temperature measurements during entry. Similar engineering implementations of these measurements on Discovery and Endeavor demonstrated unexpected measurement voltage response during the high heating portion of the entry trajectory. An assessment has been performed to characterize possible causes of the issues experienced during STS-119, STS-128, STS-131, STS-133 and STS-134 as well as similar issues encountered during other orbiter entries.

Boundary Layer Flow Control with a One Atmosphere Uniform Glow Discharge Surface Plasma

NASA Technical Reports Server (NTRS)

Roth, J. Reece; Sherman, Daniel M.; Wilkinson, Stephen P.

1998-01-01

Low speed wind tunnel data have been acquired for planar panels covered by a uniform, glow-discharge surface plasma in atmospheric pressure air known as the One Atmosphere Uniform Glow Discharge Plasma (OAUGDP). Streamwise and spanwise arrays of flush, plasma-generating surface electrodes have been studied in laminar, transitional, and fully turbulent boundary layer flow. Plasma between symmetric streamwise electrode strips caused large increases in panel drag, whereas asymmetric spanwise electrode configurations produced a significant thrust. Smoke wire flow visualization and mean velocity diagnostics show the primary cause of the phenomena to be a combination of mass transport and vortical structures induced by strong paraelectric ElectroHydroDynamic (EHD) body forces on the flow.

Vertical axis wind turbine wake in boundary layer flow in a wind tunnel

NASA Astrophysics Data System (ADS)

Rolin, Vincent; Porté-Agel, Fernando

2016-04-01

A vertical axis wind turbine is placed in a boundary layer flow in a wind tunnel, and its wake is investigated. Measurements are performed using an x-wire to measure two components of velocity and turbulence statistics in the wake of the wind turbine. The study is performed at various heights and crosswind positions in order to investigate the full volume of the wake for a range of tip speed ratios. The velocity deficit and levels of turbulence in the wake are related to the performance of the turbine. The asymmetric incoming boundary layer flow causes the rate of recovery in the wake to change as a function of height. Higher shear between the wake and unperturbed flow occurs at the top edge of the wake, inducing stronger turbulence and mixing in this region. The difference in flow relative to the blades causes the velocity deficit and turbulence level to change as a function of crosswind position behind the rotor. The relative difference diminishes with increasing tip speed ratio. Therefore, the wake becomes more homogeneous as tip speed ratio increases.

Recycling inflow method for simulations of spatially evolving turbulent boundary layers over rough surfaces

NASA Astrophysics Data System (ADS)

Yang, Xiang I. A.; Meneveau, Charles

2016-01-01

The technique by Lund et al. to generate turbulent inflow for simulations of developing boundary layers over smooth flat plates is extended to the case of surfaces with roughness elements. In the Lund et al. method, turbulent velocities on a sampling plane are rescaled and recycled back to the inlet as inflow boundary condition. To rescale mean and fluctuating velocities, appropriate length scales need be identified and for smooth surfaces, the viscous scale lν = ν/uτ (where ν is the kinematic viscosity and uτ is the friction velocity) is employed for the inner layer. Different from smooth surfaces, in rough wall boundary layers the length scale of the inner layer, i.e. the roughness sub-layer scale ld, must be determined by the geometric details of the surface roughness elements and the flow around them. In the proposed approach, it is determined by diagnosing dispersive stresses that quantify the spatial inhomogeneity caused by the roughness elements in the flow. The scale ld is used for rescaling in the inner layer, and the boundary layer thickness δ is used in the outer region. Both parts are then combined for recycling using a blending function. Unlike the blending function proposed by Lund et al. which transitions from the inner layer to the outer layer at approximately 0.2δ, here the location of blending is shifted upwards to enable simulations of very rough surfaces in which the roughness length may exceed the height of 0.2δ assumed in the traditional method. The extended rescaling-recycling method is tested in large eddy simulation of flow over surfaces with various types of roughness element shapes.

Effects of surface roughness on an adverse-pressure-gradient separating turbulent boundary layer

NASA Astrophysics Data System (ADS)

Wu, Wen; Piomelli, Ugo; Turbulence Simulation; Modelling Laboratory Team

2017-11-01

Separating turbulent boundary layers over smooth and rough flat plates are investigated by large-eddy simulations. A suction-blowing velocity distribution is imposed at the top boundary to produce an adverse-to-favourable pressure gradient and a closed separation bubble. Sandgrain roughness in the fully-rough regime is modelled by an immersed boundary method. In the rough-wall case, streamline detachment occurs earlier and the separation region is substantially larger due to the momentum deficit caused by the roughness. The adverse pressure gradient decreases the form drag and causes a thin reversed-flow region below the roughness crest, so that Cf = 0 does not coincide with the detachment of the flow from the surface. The wake regions behind roughness elements affect the intermittency of the near-wall flow, so that upstream of the detachment point the flow can be reversed half of the time, but its average is positive. The separated shear layer exhibits higher turbulent kinetic energy (TKE); the growth of the TKE there begins earlier relative to the separation point, and the peak TKE occurs close to the separation point. The momentum deficit caused by the roughness, again, plays a critical role in these changes. The authors acknowledge the support from Hydro-Québec and the NSERC Collaborative Research & Development program (CRDPJ 418786-11). The simulations were performed at CAC Queen't site. UP also thanks the support of Canada Research Chair Program.

Impact of the Loess Plateau on the atmospheric boundary layer structure and air quality in the North China Plain: a case study.

PubMed

Hu, Xiao-Ming; Ma, ZhiQiang; Lin, Weili; Zhang, Hongliang; Hu, Jianlin; Wang, Ying; Xu, Xiaobin; Fuentes, Jose D; Xue, Ming

2014-11-15

The North China Plain (NCP), to the east of the Loess Plateau, experiences severe regional air pollution. During the daytime in the summer, the Loess Plateau acts as an elevated heat source. The impacts of such a thermal effect on meteorological phenomena (e.g., waves, precipitation) in this region have been discussed. However, its impacts on the atmospheric boundary layer structure and air quality have not been reported. It is hypothesized that the thermal effect of the Plateau likely modulates the boundary layer structure and ambient concentrations of pollutants over the NCP under certain meteorological conditions. Thus, this study investigates such effect and its impacts using measurements and three-dimensional model simulations. It is found that in the presence of daytime westerly wind in the lower troposphere (~1 km above the NCP), warmer air above the Loess Plateau was transported over the NCP and imposed a thermal inversion above the mixed boundary layer, which acted as a lid and suppressed the mixed layer growth. As a result, pollutants accumulated in the shallow mixed layer and ozone was efficiently produced. The downward branch of the thermally-induced Mountain-Plains Solenoid circulation over the NCP contributed to enhancing the capping inversion and exacerbating air pollution. Previous studies have reported that low mixed layer, a factor for elevated pollution in the NCP, may be caused by aerosol scattering and absorption of solar radiation, frontal inversion, and large scale subsidence. The present study revealed a different mechanism (i.e., westerly warm advection) for the suppression of the mixed layer in summer NCP, which caused severe O3 pollution. This study has important implications for understanding the essential meteorological factors for pollution episodes in this region and forecasting these severe events. Copyright © 2014 Elsevier B.V. All rights reserved.

Görtler instability of the axisymmetric boundary layer along a cone

NASA Astrophysics Data System (ADS)

ITOH, Nobutake

2014-10-01

Exact partial differential equations are derived to describe Görtler instability, caused by a weakly concave wall, of axisymmetric boundary layers with similar velocity profiles that are decomposed into a sequence of ordinary differential systems on the assumption that the solution can be expanded into inverse powers of local Reynolds number. The leading terms of the series solution are determined by solving a non-parallel version of Görtler’s eigenvalue problem and lead to a neutral stability curve and finite values of critical Görtler number and wave number for stationary and longitudinal vortices. Higher-order terms of the series solution indicate Reynolds-number dependence of Görtler instability and a limited validity of Görtler’s approximation based on the leading terms only. The present formulation is simply applicable to two-dimensional boundary layers of similar profiles, and critical Görtler number and wave number of the Blasius boundary layer on a flat plate are given by G2c = 1.23 and β2c = 0.288, respectively, if the momentum thickness is chosen as the reference length.

First simultaneous space measurements of atmospheric pollutants in the boundary layer from IASI: a case study in the North China Plain

NASA Astrophysics Data System (ADS)

Boynard, Anne; Clerbaux, Cathy; Clarisse, Lieven; Safieddine, Sarah; Pommier, Matthieu; Van Damme, Martin; Bauduin, Sophie; Oudot, Charlotte; Hadji-Lazaro, Juliette; Hurtmans, Daniel; Coheur, Pierre-François

2014-05-01

An extremely severe and persistent smog episode occurred in January 2013 over China. The levels of air pollution have been dangerously high, reaching 40 times recommended safety levels and have affected health of millions of people. China faced one of the worst periods of air quality in recent history and drew worldwide attention. This pollution episode was caused by the combination of anthropogenic emissions and stable meteorological conditions (absence of wind and temperature inversion) that trapped pollutants in the boundary layer. To characterize this episode, we used the IASI (Infrared Atmospheric Sounding Interferometer) instrument onboard the MetOp-A platform. IASI observations show high concentrations of key trace gases such as carbon monoxide (CO), sulfur dioxide (SO2) and ammonia (NH3) along with ammonium sulfate aerosol. We show that IASI is able to detect boundary layer pollution in case of large negative thermal contrast combined with high levels of pollution. Our findings demonstrate the ability of thermal infrared instrument such as IASI to monitor boundary layer pollutants, which can support air quality evaluation and management.

Review of Orbiter Flight Boundary Layer Transition Data

NASA Technical Reports Server (NTRS)

Mcginley, Catherine B.; Berry, Scott A.; Kinder, Gerald R.; Barnell, maria; Wang, Kuo C.; Kirk, Benjamin S.

2006-01-01

In support of the Shuttle Return to Flight program, a tool was developed to predict when boundary layer transition would occur on the lower surface of the orbiter during reentry due to the presence of protuberances and cavities in the thermal protection system. This predictive tool was developed based on extensive wind tunnel tests conducted after the loss of the Space Shuttle Columbia. Recognizing that wind tunnels cannot simulate the exact conditions an orbiter encounters as it re-enters the atmosphere, a preliminary attempt was made to use the documented flight related damage and the orbiter transition times, as deduced from flight instrumentation, to calibrate the predictive tool. After flight STS-114, the Boundary Layer Transition Team decided that a more in-depth analysis of the historical flight data was needed to better determine the root causes of the occasional early transition times of some of the past shuttle flights. In this paper we discuss our methodology for the analysis, the various sources of shuttle damage information, the analysis of the flight thermocouple data, and how the results compare to the Boundary Layer Transition prediction tool designed for Return to Flight.

Trace Elements in Cretaceous-Tertiary Boundary Clay at Gubbio, Italy

NASA Astrophysics Data System (ADS)

Ebihara, M.; Miura, T.

1992-07-01

In 1980, Alvarez et al. reported high Ir concentrations for the Cretaceous-Tertiary (hereafter, K/T) boundary layer, suggesting an impact of extraterrestrial material as a possible cause of the sudden mass extinction at the end of the Cretaceous period. Since then, high Ir abundances have been reported for K/T layers all over the world. Iridium enrichments were alternatively explained in terms of volcanic eruptions (Officer and Drake, 1982) or sedimentation (Zoller et al, 1982). Thus, abundances of Ir only cannot be critical in explaining the cause of the mass extinctions at the K/T boundary. In contrast to the fairly large number of Ir data for K/T boundary geological materials, only limited data are available for other siderophile elements. Relative abundances of siderophiles must be more informative in considering the causes of extinction, and provide further data on the type of extraterrestrial material of the projectile if siderophile abundances are in favor of an impact as the cause of the mass extinction at the K/T boundary. Thus, we analyzed additional K/T boundary materials for trace elements, including some of the siderophiles. A total of 7 samples collected from the K/T boundary near Gubbio, Italy (three from Bottaccione, four from Contessa) were analyzed. For comparison, we analyzed three additional samples, one from a Cretaceous sediment layer and the remaining two from a Tertiary layer. Four siderophile elements (Ir, Pt, Au, and Pd) were measured by RNAA and more than 25 elements, including 9 lanthanoids, were measured by INAA. The siderophiles listed above and Ni were found to be present in all of the boundary clay samples. They have C1-normalized abundances of 0.02 for Ni, Ir, and Pt, 0.04 for Pd, and Au was exceptionally depleted at 0.005. Both Ni and Ir show fairly small variations in abundances among the clay samples, whereas the other three elements show quite large variations, exceeding error limits. We believe that similar enrichments for these siderophiles in the K/T boundary clays were caused by an impact of extraterrestrial material having siderophiles that have not been largely fractionated. Similar abundance patterns of REE were confirmed not only for clay samples but also for the Cretaceous and Tertiary sediments. This suggests that sedimentation continued in similar circumstances without a large disturbance at the K/T boundary. We confirmed excellent correlations among Ir, As, and Sb abundances in the K/T samples, suggesting that they had a similar solution chemistry when sedimentation occurred. Both As and Sb show similar abundances, even for the Cretaceous as well as the Tertiary sediments, while Ir does not. Neither Pd nor Pt shows any correlation with these elements or with each other. This suggests that Ir was trapped into the clay together with As and Sb, but not with Pd or Pt. It is highly unlikely that these siderophiles were supplied only from sea water, and were eventually greatly enriched in clay materials, with the relative elemental abundances coinciding with those in chondrites. Thus, our data strongly suggest that a large impact of extraterrestrial material (chondritic?) caused the enrichment of siderophiles at K/T boundary. Acknowledgment. We are indebted to M. Ozima and S. Amari for samples analyzed in this work. References Alvarez, L.W., Alvarez, W., Asaro, F., and Michel, H.V. (1980) Science 208, 1095-1108. Officer, C.B. and Drake, C.L. (1982) Science 219, 1383-1390. Zoller, W.H., Parrington, J.R., and Kotra, J.M.P. (1983) Science 222, 1118-1120.

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.

Nature, theory and modelling of geophysical convective planetary boundary layers

NASA Astrophysics Data System (ADS)

Zilitinkevich, Sergej

2015-04-01

Geophysical convective planetary boundary layers (CPBLs) are still poorly reproduced in oceanographic, hydrological and meteorological models. Besides the mean flow and usual shear-generated turbulence, CPBLs involve two types of motion disregarded in conventional theories: 'anarchy turbulence' comprised of the buoyancy-driven plumes, merging to form larger plumes instead of breaking down, as postulated in conventional theory (Zilitinkevich, 1973), large-scale organised structures fed by the potential energy of unstable stratification through inverse energy transfer in convective turbulence (and performing non-local transports irrespective of mean gradients of transporting properties). C-PBLs are strongly mixed and go on growing as long as the boundary layer remains unstable. Penetration of the mixed layer into the weakly turbulent, stably stratified free flow causes turbulent transports through the CPBL outer boundary. The proposed theory, taking into account the above listed features of CPBL, is based on the following recent developments: prognostic CPBL-depth equation in combination with diagnostic algorithm for turbulence fluxes at the CPBL inner and outer boundaries (Zilitinkevich, 1991, 2012, 2013; Zilitinkevich et al., 2006, 2012), deterministic model of self-organised convective structures combined with statistical turbulence-closure model of turbulence in the CPBL core (Zilitinkevich, 2013). It is demonstrated that the overall vertical transports are performed mostly by turbulence in the surface layer and entrainment layer (at the CPBL inner and outer boundaries) and mostly by organised structures in the CPBL core (Hellsten and Zilitinkevich, 2013). Principal difference between structural and turbulent mixing plays an important role in a number of practical problems: transport and dispersion of admixtures, microphysics of fogs and clouds, etc. The surface-layer turbulence in atmospheric and marine CPBLs is strongly enhanced by the velocity shears in horizontal branches of organised structures. This mechanism (Zilitinkevich et al., 2006), was overlooked in conventional local theories, such as the Monin-Obukhov similarity theory, and convective heat/mass transfer law: Nu~Ra1/3, where Nu and Ra are the Nusselt number and Raleigh numbers. References Hellsten A., Zilitinkevich S., 2013: Role of convective structures and background turbulence in the dry convective boundary layer. Boundary-Layer Meteorol. 149, 323-353. Zilitinkevich, S.S., 1973: Shear convection. Boundary-Layer Meteorol. 3, 416-423. Zilitinkevich, S.S., 1991: Turbulent Penetrative Convection, Avebury Technical, Aldershot, 180 pp. Zilitinkevich S.S., 2012: The Height of the Atmospheric Planetary Boundary layer: State of the Art and New Development - Chapter 13 in 'National Security and Human Health Implications of Climate Change', edited by H.J.S. Fernando, Z. Klaić, J.L. McKulley, NATO Science for Peace and Security Series - C: Environmental Security (ISBN 978-94-007-2429-7), Springer, 147-161. Zilitinkevich S.S., 2013: Atmospheric Turbulence and Planetary Boundary Layers. Fizmatlit, Moscow, 248 pp. Zilitinkevich, S.S., Hunt, J.C.R., Grachev, A.A., Esau, I.N., Lalas, D.P., Akylas, E., Tombrou, M., Fairall, C.W., Fernando, H.J.S., Baklanov, and A., Joffre, S.M., 2006: The influence of large convective eddies on the surface layer turbulence. Quart. J. Roy. Met. Soc. 132, 1423-1456. Zilitinkevich S.S., Tyuryakov S.A., Troitskaya Yu. I., Mareev E., 2012: Theoretical models of the height of the atmospheric planetary boundary layer and turbulent entrainment at its upper boundary. Izvestija RAN, FAO, 48, No.1, 150-160 Zilitinkevich, S.S., Elperin, T., Kleeorin, N., Rogachevskii, I., Esau, I.N., 2013: A hierarchy of energy- and flux-budget (EFB) turbulence closure models for stably stratified geophysical flows. Boundary-Layer Meteorol. 146, 341-373.

Vortex instabilities in 3D boundary layers: The relationship between Goertler and crossflow vortices

NASA Technical Reports Server (NTRS)

Bassom, Andrew; Hall, Philip

1990-01-01

The inviscid and viscous stability problems are addressed for a boundary layer which can support both Goertler and crossflow vortices. The change in structure of Goertler vortices is found when the parameter representing the degree of three-dimensionality of the basic boundary layer flow under consideration is increased. It is shown that crossflow vortices emerge naturally as this parameter is increased and ultimately become the only possible vortex instability of the flow. It is shown conclusively that at sufficiently large values of the crossflow there are no unstable Goertler vortices present in a boundary layer which, in the zero crossflow case, is centrifugally unstable. The results suggest that in many practical applications Goertler vortices cannot be a cause of transition because they are destroyed by the 3-D nature of the basic state. In swept wing flows the Goertler mechanism is probably not present for typical angles of sweep of about 20 degrees. Some discussion of the receptivity problem for vortex instabilities in weakly 3-D boundary layers is given; it is shown that inviscid modes have a coupling coefficient marginally smaller than those of the fastest growing viscous modes discussed recently by Denier, Hall, and Seddougui (1990). However the fact that the growth rates of the inviscid modes are the largest in most situations means that they are probably the most likely source of transition.

A comparison of radiative transfer models for predicting the microwave emission from soils

NASA Technical Reports Server (NTRS)

Schmugge, T. J.; Choudhury, B. J.

1981-01-01

Noncoherent and coherent numerical models for predicting emission from soils are compared. Coherent models use the boundary conditions on the electric fields across the layer boundaries to calculate the radiation intensity, and noncoherent models consider radiation intensities directly. Interference may cause different results in the two approaches when coupling between soil layers in coherent models causes greater soil moisture sampling depths. Calculations performed at frequencies of 1.4 and 19.4 GHz show little difference between the models at 19.4 GHz, although differences are apparent at the lower frequency. A definition for an effective emissivity is also given for when a nonuniform temperature profile is present, and measurements made from a tower show good agreement with calculations from the coherent model.

The Sensitivity of Large-Eddy Simulation to Local and Nonlocal Drag Coefficients at the Lower Boundary

NASA Technical Reports Server (NTRS)

Schowalter, D. G.; DeCroix, D. S.; Lin, Y. L.; Arya, S. P.; Kaplan, M. L.

1996-01-01

It was found that the homogeneity of the surface drag coefficient plays an important role in the large scale structure of turbulence in large-eddy simulation of the convective atmospheric boundary layer. Particularly when a ground surface temperature was specified, large horizontal anisotropies occurred when the drag coefficient depended upon local velocities and heat fluxes. This was due to the formation of streamwise roll structures in the boundary layer. In reality, these structures have been found to form when shear is approximately balanced by buoyancy. The present cases, however, were highly convective. The formation was caused by particularly low values of the drag coefficient at the entrance to thermal plume structures.

Airborne measurements of turbulent trace gas fluxes and analysis of eddy structure in the convective boundary layer over complex terrain

NASA Astrophysics Data System (ADS)

Hasel, M.; Kottmeier, Ch.; Corsmeier, U.; Wieser, A.

2005-03-01

Using the new high-frequency measurement equipment of the research aircraft DO 128, which is described in detail, turbulent vertical fluxes of ozone and nitric oxide have been calculated from data sampled during the ESCOMPTE program in the south of France. Based on airborne turbulence measurements, radiosonde data and surface energy balance measurements, the convective boundary layer (CBL) is examined under two different aspects. The analysis covers boundary-layer convection with respect to (i) the control of CBL depth by surface heating and synoptic scale influences, and (ii) the structure of convective plumes and their vertical transport of ozone and nitric oxides. The orographic structure of the terrain causes significant differences between planetary boundary layer (PBL) heights, which are found to exceed those of terrain height variations on average. A comparison of boundary-layer flux profiles as well as mean quantities over flat and complex terrain and also under different pollution situations and weather conditions shows relationships between vertical gradients and corresponding turbulent fluxes. Generally, NO x transports are directed upward independent of the terrain, since primary emission sources are located near the ground. For ozone, negative fluxes are common in the lower CBL in accordance with the deposition of O 3 at the surface. The detailed structure of thermals, which largely carry out vertical transports in the boundary layer, are examined with a conditional sampling technique. Updrafts mostly contain warm, moist and NO x loaded air, while the ozone transport by thermals alternates with the background ozone gradient. Evidence for handover processes of trace gases to the free atmosphere can be found in the case of existing gradients across the boundary-layer top. An analysis of the size of eddies suggests the possibility of some influence of the heterogeneous terrain in mountainous area on the length scales of eddies.

Experimental Evaluation of the Effect of Angle-of-attack on the External Aerodynamics and Mass Capture of a Symmetric Three-engine Air-breathing Launch Vehicle Configuration at Supersonic Speeds

NASA Technical Reports Server (NTRS)

Kim, Hyun D.; Frate, Franco C.

2001-01-01

A subscale aerodynamic model of the GTX air-breathing launch vehicle was tested at NASA Glenn Research Center's 10- by 10-Foot Supersonic Wind Tunnel from Mach 2.0 to 3.5 at various angles-of-attack. The objective of the test was to investigate the effect of angle-of-attack on inlet mass capture, inlet diverter effectiveness, and the flowfield at the cowl lip plane. The flow-through inlets were tested with and without boundary-layer diverters. Quantitative measurements such as inlet mass flow rates and pitot-pressure distributions in the cowl lip plane are presented. At a 3deg angle-of-attack, the flow rates for the top and side inlets were within 8 percent of the zero angle-of-attack value, and little distortion was evident at the cowl lip plane. Surface oil flow patterns showing the shock/boundary-layer interaction caused by the inlet spikes are shown. In addition to inlet data, vehicle forebody static pressure distributions, boundary-layer profiles, and temperature-sensitive paint images to evaluate the boundary-layer transition are presented. Three-dimensional parabolized Navier-Stokes computational fluid dynamics calculations of the forebody flowfield are presented and show good agreement with the experimental static pressure distributions and boundary-layer profiles. With the boundary-layer diverters installed, no adverse aerodynamic phenomena were found that would prevent the inlets from operating at the required angles-of-attack. We recommend that phase 2 of the test program be initiated, where inlet contraction ratio and diverter geometry variations will be tested.

Reversing flow development in a separating turbulent boundary layer

NASA Astrophysics Data System (ADS)

Santos, Leonardo; Lang, Amy; Wahidi, Redha; Bonacci, Andrew

2016-11-01

Fast swimming sharks have micro-structures on their skin consisting of bristling scales. These scales are hypothesized to bristle in response to backflow generated from the separated turbulent boundary layer (TBL) in regions of adverse pressure gradient (APG) on the shark body. Vortices are trapped in the cavities between the scales, which induce momentum exchange between the higher momentum fluid in the outer flow and that in the separated region. This momentum exchange causes reattachment of the separated TBL, causing the scales to return to the unbristled location, and the cycle continues. The rows of scales have widths that are comparable to the spanwise length scale of the intermittent backflow patches that appear in the region of incipient detachment of TBLs. In this experimental investigation, correlations between the shark scale's width and the spanwise size of the low backflow streaks are examined, as well as details of the incipient detachment region. The experiments are conducted in a water tunnel facility and the flow field is measured using PIV. Turbulent boundary layers are subjected to an APG via a rotating cylinder. Separated TBLs are investigated on a flat plate. The authors would like to greatfully acknowledge the Army Research Office for funding this project.

Multilayer graphene as an effective corrosion protection coating for copper

NASA Astrophysics Data System (ADS)

Ravishankar, Vasumathy; Ramaprabhu, S.; Jaiswal, Manu

2018-04-01

Graphene grown by chemical vapor deposition (CVD) has been studied as a protective layer against corrosion of copper. The layer number dependence on the protective nature of graphene has been investigated using techniques such as Tafel analysis and Electroimpedance Spectroscopy. Multiple layers of graphene were achieved by wet transfer above CVD grown graphene. Though this might cause grain boundaries, the sites where corrosion is initiated, to be staggered, wet transfer inherently carries the disadvantage of tearing of graphene, as confirmed by Raman spectroscopy measurements. However, Electroimpedance Spectroscopy (EIS) reflects that graphene protected copper has a layer dependent resistance to corrosion. Decrease in corrosion current (Icorr) for graphene protected copper is presented. There is only small dependence of corrosion current on the layer number, Tafel plots clearly indicate passivation in the presence of graphene, whether it be single layer or multiple layers. Notwithstanding the crystallite size, defect free layers of graphene with staggered grain boundaries combined with passivation could offer good corrosion protection for metals.

A quiet flow Ludwieg tube for study of transition in compressible boundary layers: Design and feasibility

NASA Technical Reports Server (NTRS)

Schneider, Steven P.

1991-01-01

Laminar-turbulent transition in high speed boundary layers is a complicated problem which is still poorly understood, partly because of experimental ambiguities caused by operating in noisy wind tunnels. The NASA Langley experience with quiet tunnel design has been used to design a quiet flow tunnel which can be constructed less expensively. Fabrication techniques have been investigated, and inviscid, boundary layer, and stability computer codes have been adapted for use in the nozzle design. Construction of such a facility seems feasible, at a reasonable cost. Two facilities have been proposed: a large one, with a quiet flow region large enough to study the end of transition, and a smaller and less expensive one, capable of studying low Reynolds number issues such as receptivity. Funding for either facility remains to be obtained, although key facility elements have been obtained and are being integrated into the existing Purdue supersonic facilities.

F-8 supercritical wing flight pressure, Boundary layer, and wake measurements and comparisons with wind tunnel data

NASA Technical Reports Server (NTRS)

Montoya, L. C.; Banner, R. D.

1977-01-01

Data for speeds from Mach 0.50 to Mach 0.99 are presented for configurations with and without fuselage area-rule additions, with and without leading-edge vortex generators, and with and without boundary-layer trips on the wing. The wing pressure coefficients are tabulated. Comparisons between the airplane and model data show that higher second velocity peaks occurred on the airplane wing than on the model wing. The differences were attributed to wind tunnel wall interference effects that caused too much rear camber to be designed into the wing. Optimum flow conditions on the outboard wing section occurred at Mach 0.98 at an angle of attack near 4 deg. The measured differences in section drag with and without boundary-layer trips on the wing suggested that a region of laminar flow existed on the outboard wing without trips.

Parametric study of solar thermal rocket nozzle performance

NASA Technical Reports Server (NTRS)

Pearson, J. Boise; Landrum, D. Brian; Hawk, Clark W.

1995-01-01

This paper details a numerical investigation of performance losses in low-thrust solar thermal rocket nozzles. The effects of nozzle geometry on three types of losses were studied; finite rate dissociation-recombination kinetic losses, two dimensional axisymmetric divergence losses, and compressible viscous boundary layer losses. Short nozzle lengths and supersonic flow produce short residence times in the nozzle and a nearly frozen flow, resulting in large kinetic losses. Variations in geometry have a minimal effect on kinetic losses. Divergence losses are relatively small, and careful shaping of the nozzle can nearly eliminate them. The boundary layer in these small nozzles can grow to a major fraction of nozzle radius, and cause large losses. These losses are attributed to viscous drag on the nozzle walls and flow blockage by the boundary layer, especially in the throat region. Careful shaping of the nozzle can produce a significant reduction in viscous losses.

Similar solutions for the compressible laminar boundary layer with heat transfer and pressure gradient

NASA Technical Reports Server (NTRS)

Cohen, Clarence B; Reshotko, Eli

1956-01-01

Stewartson's transformation is applied to the laminar compressible boundary-layer equations and the requirement of similarity is introduced, resulting in a set of ordinary nonlinear differential equations previously quoted by Stewartson, but unsolved. The requirements of the system are Prandtl number of 1.0, linear viscosity-temperature relation across the boundary layer, an isothermal surface, and the particular distributions of free-stream velocity consistent with similar solutions. This system admits axial pressure gradients of arbitrary magnitude, heat flux normal to the surface, and arbitrary Mach numbers. The system of differential equations is transformed to integral system, with the velocity ratio as the independent variable. For this system, solutions are found by digital computation for pressure gradients varying from that causing separation to the infinitely favorable gradient and for wall temperatures from absolute zero to twice the free-stream stagnation temperature. Some solutions for separated flows are also presented.

Three-dimensional turbulent boundary layers; Proceedings of the Symposium, Berlin, West Germany, March 29-April 1, 1982

NASA Astrophysics Data System (ADS)

Fernholz, H. H.; Krause, E.

Papers are presented on recent research concerning three-dimensional turbulent boundary layers. Topics examined include experimental techniques in three-dimensional turbulent boundary layers, turbulence measurements in ship-model flow, measurements of Reynolds-stress profiles in the stern region of a ship model, the effects of crossflow on the vortex-layer-type three-dimensional flow separation, and wind tunnel investigations of some three-dimensional separated turbulent boundary layers. Also examined are three-dimensional boundary layers in turbomachines, the boundary layers on bodies of revolution spinning in axial flows, the effect on a developed turbulent boundary layer of a sudden local wall motion, three-dimensional turbulent boundary layer along a concave wall, the numerical computation of three-dimensional boundary layers, a numerical study of corner flows, three-dimensional boundary calculations in design aerodynamics, and turbulent boundary-layer calculations in design aerodynamics. For individual items see A83-47012 to A83-47036

Senstitivity analysis of horizontal heat and vapor transfer coefficients for a cloud-topped marine boundary layer during cold-air outbreaks. M.S. Thesis

NASA Technical Reports Server (NTRS)

Chang, Y. V.

1986-01-01

The effects of external parameters on the surface heat and vapor fluxes into the marine atmospheric boundary layer (MABL) during cold-air outbreaks are investigated using the numerical model of Stage and Businger (1981a). These fluxes are nondimensionalized using the horizontal heat (g1) and vapor (g2) transfer coefficient method first suggested by Chou and Atlas (1982) and further formulated by Stage (1983a). In order to simplify the problem, the boundary layer is assumed to be well mixed and horizontally homogeneous, and to have linear shoreline soundings of equivalent potential temperature and mixing ratio. Modifications of initial surface flux estimates, time step limitation, and termination conditions are made to the MABL model to obtain accurate computations. The dependence of g1 and g2 in the cloud topped boundary layer on the external parameters (wind speed, divergence, sea surface temperature, radiative sky temperature, cloud top radiation cooling, and initial shoreline soundings of temperature, and mixing ratio) is studied by a sensitivity analysis, which shows that the uncertainties of horizontal transfer coefficients caused by changes in the parameters are reasonably small.

Separation control in a hypersonic shock wave / turbulent boundary-layer interaction

NASA Astrophysics Data System (ADS)

Schreyer, Anne-Marie; Bermejo-Moreno, Ivan; Kim, Jeonglae; Urzay, Javier

2016-11-01

Hypersonic vehicles play a key role for affordable access to space. The associated flow fields are strongly affected by shock wave/turbulent boundary-layer interactions, and the inherent separation causes flow distortion and low-frequency unsteadiness. Microramp sub-boundary layer vortex generators are a promising means to control separation and diminish associated detrimental effects. We investigate the effect of a microramp on the low-frequency unsteadiness in a fully separated interaction. A large eddy simulation of a 33 ∘ -compression-ramp interaction was performed for an inflow Mach number of 7.2 and a Reynolds number based on momentum thickness of Reθ = 3500 , matching the experiment of Schreyer et al. (2011). For the control case, we introduced a counter-rotating vortex pair, as induced by a single microramp, into the boundary layer through the inflow conditions. We applied a dynamic mode decomposition (DMD) on both cases to identify coherent structures that are responsible for the dynamic behavior. Based on the DMD, we discuss the reduction of the separation zone and the stabilization of the shock motion achieved by the microramp, and contribute to the description of the governing mechanisms. Pursued during the 2016 CTR Summer Program at Stanford University.

Some Insights on Roughness Induced Transition and Control from DNS and Experiments

NASA Astrophysics Data System (ADS)

Suryanarayanan, Saikishan; Ibitayo, Ifeoluwa; Goldstein, David; Brown, Garry

2016-11-01

We study the receptivity and subsequent evolution of an initially laminar flat boundary layer on a flat plate to single and multiple discrete roughness elements (DRE) using a combination of immersed boundary DNS and water channel flow visualization experiments. We examine the transition caused by a single DRE and demonstrate the possibility of suppressing it by an appropriately designed second DRE in both DNS and experiments. The different phases of transition are identified and the roles of Reynolds numbers based on roughness height and boundary layer thickness are investigated. The underlying mechanisms in the observed transition and its control are understood by examining detailed vorticity flux balances. Connections are also made to recent developments in transient growth and streak instability. A unified picture is sought from a parametric study of different DRE dimensions and orientations. The potential applicability of the observations and understanding derived from this study to controlling transition caused by design and environmental roughness over aircraft wings is discussed. Supported by AFOSR # FA9550-15-1-0345.

A comparison of hypersonic vehicle flight and prediction results

NASA Technical Reports Server (NTRS)

Iliff, Kenneth W.; Shafer, Mary F.

1995-01-01

Aerodynamic and aerothermodynamic comparisons between flight and ground test for four hypersonic vehicles are discussed. The four vehicles are the X-15, the Reentry F, the Sandia Energetic Reentry Vehicle Experiment (SWERVE), and the Space Shuttle. The comparisons are taken from papers published by researchers active in the various programs. Aerodynamic comparisons include reaction control jet interaction on the Space Shuttle. Various forms of heating including catalytic, boundary layer, shock interaction and interference, and vortex impingement are compared. Predictions were significantly exceeded for the heating caused by vortex impingement (on the Space Shuttle OMS pods) and for heating caused by shock interaction and interference on the X-15 and the Space Shuttle. Predictions of boundary-layer state were in error on the X-15, the SWERVE, and the Space Shuttle vehicles.

Stability of hypersonic boundary-layer flows with chemistry

NASA Technical Reports Server (NTRS)

Reed, Helen L.; Stuckert, Gregory K.; Haynes, Timothy S.

1993-01-01

The effects of nonequilibrium chemistry and three dimensionality on the stability characteristics of hypersonic flows are discussed. In two-dimensional (2-D) and axisymmetric flows, the inclusion of chemistry causes a shift of the second mode of Mack to lower frequencies. This is found to be due to the increase in size of the region of relative supersonic flow because of the lower speeds of sound in the relatively cooler boundary layers. Although this shift in frequency is present in both the equilibrium and nonequilibrium air results, the equilibrium approximation predicts modes which are not observed in the nonequilibrium calculations (for the flight conditions considered). These modes are superpositions of incoming and outgoing unstable disturbances which travel supersonically relative to the boundary-layer edge velocity. Such solutions are possible because of the finite shock stand-off distance. Their corresponding wall-normal profiles exhibit an oscillatory behavior in the inviscid region between the boundary-layer edge and the bow shock. For the examination of three-dimensional (3-D) effects, a rotating cone is used as a model of a swept wing. An increase of stagnation temperature is found to be only slightly stabilizing. The correlation of transition location (N = 9) with parameters describing the crossflow profile is discussed. Transition location does not correlate with the traditional crossflow Reynolds number. A new parameter that appears to correlate for boundary-layer flow was found. A verification with experiments on a yawed cone is provided.

RACORO Continental Boundary Layer Cloud Investigations: 3. Separation of Parameterization Biases in Single-Column Model CAM5 Simulations of Shallow Cumulus

NASA Technical Reports Server (NTRS)

Lin, Wuyin; Liu, Yangang; Vogelmann, Andrew M.; Fridlind, Ann; Endo, Satoshi; Song, Hua; Feng, Sha; Toto, Tami; Li, Zhijin; Zhang, Minghua

2015-01-01

Climatically important low-level clouds are commonly misrepresented in climate models. The FAst-physics System TEstbed and Research (FASTER) Project has constructed case studies from the Atmospheric Radiation Measurement Climate Research Facility's Southern Great Plain site during the RACORO aircraft campaign to facilitate research on model representation of boundary-layer clouds. This paper focuses on using the single-column Community Atmosphere Model version 5 (SCAM5) simulations of a multi-day continental shallow cumulus case to identify specific parameterization causes of low-cloud biases. Consistent model biases among the simulations driven by a set of alternative forcings suggest that uncertainty in the forcing plays only a relatively minor role. In-depth analysis reveals that the model's shallow cumulus convection scheme tends to significantly under-produce clouds during the times when shallow cumuli exist in the observations, while the deep convective and stratiform cloud schemes significantly over-produce low-level clouds throughout the day. The links between model biases and the underlying assumptions of the shallow cumulus scheme are further diagnosed with the aid of large-eddy simulations and aircraft measurements, and by suppressing the triggering of the deep convection scheme. It is found that the weak boundary layer turbulence simulated is directly responsible for the weak cumulus activity and the simulated boundary layer stratiform clouds. Increased vertical and temporal resolutions are shown to lead to stronger boundary layer turbulence and reduction of low-cloud biases.

RACORO continental boundary layer cloud investigations. 3. Separation of parameterization biases in single-column model CAM5 simulations of shallow cumulus

DOE PAGES

Lin, Wuyin; Liu, Yangang; Vogelmann, Andrew M.; ...

2015-06-19

Climatically important low-level clouds are commonly misrepresented in climate models. The FAst-physics System TEstbed and Research (FASTER) project has constructed case studies from the Atmospheric Radiation Measurement (ARM) Climate Research Facility's Southern Great Plain site during the RACORO aircraft campaign to facilitate research on model representation of boundary-layer clouds. This paper focuses on using the single-column Community Atmosphere Model version 5 (SCAM5) simulations of a multi-day continental shallow cumulus case to identify specific parameterization causes of low-cloud biases. Consistent model biases among the simulations driven by a set of alternative forcings suggest that uncertainty in the forcing plays only amore » relatively minor role. In-depth analysis reveals that the model's shallow cumulus convection scheme tends to significantly under-produce clouds during the times when shallow cumuli exist in the observations, while the deep convective and stratiform cloud schemes significantly over-produce low-level clouds throughout the day. The links between model biases and the underlying assumptions of the shallow cumulus scheme are further diagnosed with the aid of large-eddy simulations and aircraft measurements, and by suppressing the triggering of the deep convection scheme. It is found that the weak boundary layer turbulence simulated is directly responsible for the weak cumulus activity and the simulated boundary layer stratiform clouds. Increased vertical and temporal resolutions are shown to lead to stronger boundary layer turbulence and reduction of low-cloud biases.« less

Investigation of Separation of the Turbulent Boundary Layer

NASA Technical Reports Server (NTRS)

Schubauer, G B; Klebanoff, P S

1951-01-01

An investigation was conducted on a turbulent boundary layer near a smooth surface with pressure gradients sufficient to cause flow separation. The reynolds number was high, but the speeds were entirely within the incompressible flow range. The investigation consisted of measurements of mean flow, three components of turbulence intensity, turbulent shearing stress, and correlations between two fluctuation components at a point and between the same component of different points. The results are given in the form of tables and graphs. The discussion deals first with separation and then with the more fundamental question of basic concepts of turbulent flow.

Preliminary study of the interactions caused by crossing shock waves and a turbulent boundary layer

NASA Technical Reports Server (NTRS)

Ketchum, A. C.; Bogdonoff, S. M.; Fernando, E. M.; Batcho, P. F.

1989-01-01

The subject research, the first phase of an extended study of the interaction of crossing shock waves with a turbulent boundary layer, has revealed the complexity of the resulting flow. Detailed surface visualization and mean wall static pressure distributions show little resemblance to the inviscid flow approximation, and the exploratory high frequency measurements show that the flow downstream of the theoretical inviscid shock crossing position has a significant unsteady characteristic. Further developments of the (unsteady) high frequency measurements are required to fully characterize the unsteadiness and the requirements to include this component in flowfield modeling.

Measurements in the bottom boundary layer on the Amazon subaqueous delta

USGS Publications Warehouse

Cacchione, D.A.; Drake, D.E.; Kayen, R.W.; Sternberg, R.W.; Kineke, G.C.; Tate, G.B.

1995-01-01

An instrumented bottom tripod (GEOPROBE) recorded flow and suspended sediment data in the bottom boundary layer above the lower foresets of the Amazon subaqueous delta in 65 m mean water depth in February, 1990. After about two weeks of operation the apparent seafloor at the tripod site rapidly elevated over a 14-hour period by about 44 cm. This sudden change, which was detected by an acoustic altimeter and which caused the loss of signals from the lowermost GEOPROBE current and optical sensors, is though to have been caused by the incursion of a dense bottom layer of fluid mud that migrated downslope from shallower sections of the foresets. The fluid-mud migration across the outer part of the foresets, if a repetitive and occasional process in this region, could be a major mechanism for episodic seaward growth of the delta. Current velocity profiles are used to estimate shear velocities, u*, and roughness lengths, zo, during the first two weeks of measurements. -from Authors

Active flow control of subsonic flow in an adverse pressure gradient using synthetic jets and passive micro flow control devices

NASA Astrophysics Data System (ADS)

Denn, Michael E.

Several recent studies have shown the advantages of active and/or passive flow control devices for boundary layer flow modification. Many current and future proposed air vehicles have very short or offset diffusers in order to save vehicle weight and create more optimal vehicle/engine integration. Such short coupled diffusers generally result in boundary layer separation and loss of pressure recovery which reduces engine performance and in some cases may cause engine stall. Deployment of flow control devices can alleviate this problem to a large extent; however, almost all active flow control devices have some energy penalty associated with their inclusion. One potential low penalty approach for enhancing the diffuser performance is to combine the passive flow control elements such as micro-ramps with active flow control devices such as synthetic jets to achieve higher control authority. The goal of this dissertation is twofold. The first objective is to assess the ability of CFD with URANS turbulence models to accurately capture the effects of the synthetic jets and micro-ramps on boundary layer flow. This is accomplished by performing numerical simulations replicating several experimental test cases conducted at Georgia Institute of Technology under the NASA funded Inlet Flow Control and Prediction Technologies Program, and comparing the simulation results with experimental data. The second objective is to run an expanded CFD matrix of numerical simulations by varying various geometric and other flow control parameters of micro-ramps and synthetic jets to determine how passive and active control devices interact with each other in increasing and/or decreasing the control authority and determine their influence on modification of boundary layer flow. The boundary layer shape factor is used as a figure of merit for determining the boundary layer flow quality/modification and its tendency towards separation. It is found by a large number of numerical experiments and the analysis of simulation data that a flow control device's influence on boundary layer quality is a function of three factors: (1) the strength of the longitudinal vortex emanating from the flow control device or devices, (2) the height of the vortex core above the surface and, when a synthetic jet is present, (3) the momentum added to the boundary layer flow.

Discussion of boundary-layer characteristics near the casing of an axial-flow compressor

NASA Technical Reports Server (NTRS)

Mager, Artur; Mahoney, John J; Budinger, Ray E

1951-01-01

Boundary-layer velocity profiles on the casing of an axial-flow compressor behind the guide vanes and rotor were measured and resolved into two components: along the streamline of the flow and perpendicular to it. Boundary-layer thickness and the deflection of the boundary layer at the wall were the generalizing parameters. By use of these results and the momentum-integral equations, the characteristics of boundary on the walls of axial-flow compressor are qualitatively discussed. Important parameters concerning secondary flow in the boundary layer appear to be turning of the flow and the product of boundary-layer thickness and streamline curvature outside the boundary layer. Two types of separation are shown to be possible in three dimensional boundary layer.

An effective absorbing layer for the boundary condition in acoustic seismic wave simulation

NASA Astrophysics Data System (ADS)

Yao, Gang; da Silva, Nuno V.; Wu, Di

2018-04-01

Efficient numerical simulation of seismic wavefields generally involves truncating the Earth model in order to keep computing time and memory requirements down. Absorbing boundary conditions, therefore, are applied to remove the boundary reflections caused by this truncation, thereby allowing for accurate modeling of wavefields. In this paper, we derive an effective absorbing boundary condition for both acoustic and elastic wave simulation, through the simplification of the damping term of the split perfectly matched layer (SPML) boundary condition. This new boundary condition is accurate, cost-effective, and easily implemented, especially for high-performance computing. Stability analysis shows that this boundary condition is effectively as stable as normal (non-absorbing) wave equations for explicit time-stepping finite differences. We found that for full-waveform inversion (FWI), the strengths of the effective absorbing layer—a reduction of the computational and memory cost coupled with a simplistic implementation—significantly outweighs the limitation of incomplete absorption of outgoing waves relative to the SPML. More importantly, we demonstrate that this limitation can easily be overcome through the use of two strategies in FWI, namely variable cell size and model extension thereby fully compensating for the imperfectness of the proposed absorbing boundary condition.

Thermal advection and stratification effects on surface winds and the low level meridional mass transport

NASA Technical Reports Server (NTRS)

Levy, Gad; Tiu, Felice S.

1990-01-01

Statistical tests are performed on the Seasat scatterometer observations to examine if and to what degree thermal advection and stratification effects manifest themselves in these remotely sensed measurements of mean wind and wind stress over the ocean. On the basis of a two layer baroclinic boundary layer model which is presented, it is shown that the thermal advection and stratification of the entire boundary layer as well as the geostrophic forcing influence the modeled near surface wind and wind stress profiles. Evidence of diurnal variation in the stratification under barotropic conditions is found in the data, with the daytime marine boundary layer being more convective than its nighttime counterpart. The temporal and spacial sampling pattern of the satellite makes it impossible to recover the full diurnal cycle, however. The observed effects of the thermal advection are shown to be statistically significant during the day (and presumed more convective) hours, causing a systematic increase in the poleward transport of mass and heat. The statistical results are in a qualitative agreement with the model simulations and cannot be reproduced in randomized control tests.

Enthalpy effects on hypervelocity boundary layers

NASA Astrophysics Data System (ADS)

Adam, Philippe H.

Shots with air and carbon dioxide were carried out in the T5 shock tunnel at GALCIT to study enthalpy effects on hypervelocity boundary layers. The model tested was a 1-meter long, 5-deg half-angle cone. It was instrumented with 51 chromel-constantan coaxial thermocouples and the surface heat transfer rate was computed to deduce the state of the boundary layer. Transitional boundary layers obtained confirm the stabilizing effect of enthalpy. As the reservoir enthalpy is increased, the transition Reynolds number evaluated at the reference conditions increases. This stabilizing effect is more rapid in gases with lower dissociation energy and it seems to level off when no further dissociation can be achieved. Normalizing the reservoir enthalpy with the edge enthalpy appears to collapse the data for all gases onto a single curve. A similar collapse is obtained when normalizing both the transition location and the reservoir enthalpy with the maximum temperature conditions obtained with BLIMPK, a nonequilibrium boundary layer code. The observation that reference conditions are more appropriate to normalize high enthalpy transition data was taken a step further by comparing the tunnel data with results from a reentry experiment. When the edge conditions are used, the tunnel and flight data are around an order of magnitude apart. This is commonly attributed to high disturbance levels in tunnels that cause the boundary layer to transition early. However, when the reference conditions are used instead, the tunnel and flight data come within striking distance of one another although the trends with enthalpy are reversed. This difference could be due to the cone bending and nose blunting. Experimental laminar heat transfer levels were compared to numerical results obtained with BLIMPK. Results for air indicate that the reactions are probably in nonequilibrium and that the wall is catalytic. The catalycity is seen to yield higher surface heat transfer rates than the noncatalytic and frozen chemistry models. The results for carbon dioxide, however, are inconclusive. This is, perhaps, because of inadequate modeling of the reactions. Experimentally, an anomalous yet repeatable, rise in the laminar heat transfer level can be seen at medium enthalpies in carbon dioxide boundary layers.

Evaluating cloud processes in large-scale models: Of idealized case studies, parameterization testbeds and single-column modelling on climate time-scales

NASA Astrophysics Data System (ADS)

Neggers, Roel

2016-04-01

Boundary-layer schemes have always formed an integral part of General Circulation Models (GCMs) used for numerical weather and climate prediction. The spatial and temporal scales associated with boundary-layer processes and clouds are typically much smaller than those at which GCMs are discretized, which makes their representation through parameterization a necessity. The need for generally applicable boundary-layer parameterizations has motivated many scientific studies, which in effect has created its own active research field in the atmospheric sciences. Of particular interest has been the evaluation of boundary-layer schemes at "process-level". This means that parameterized physics are studied in isolated mode from the larger-scale circulation, using prescribed forcings and excluding any upscale interaction. Although feedbacks are thus prevented, the benefit is an enhanced model transparency, which might aid an investigator in identifying model errors and understanding model behavior. The popularity and success of the process-level approach is demonstrated by the many past and ongoing model inter-comparison studies that have been organized by initiatives such as GCSS/GASS. A red line in the results of these studies is that although most schemes somehow manage to capture first-order aspects of boundary layer cloud fields, there certainly remains room for improvement in many areas. Only too often are boundary layer parameterizations still found to be at the heart of problems in large-scale models, negatively affecting forecast skills of NWP models or causing uncertainty in numerical predictions of future climate. How to break this parameterization "deadlock" remains an open problem. This presentation attempts to give an overview of the various existing methods for the process-level evaluation of boundary-layer physics in large-scale models. This includes i) idealized case studies, ii) longer-term evaluation at permanent meteorological sites (the testbed approach), and iii) process-level evaluation at climate time-scales. The advantages and disadvantages of each approach will be identified and discussed, and some thoughts about possible future developments will be given.

Perturbations to the Spatial and Temporal Characteristics of the Diurnally-Varying Atmospheric Boundary Layer Due to an Extensive Wind Farm

NASA Astrophysics Data System (ADS)

Sharma, V.; Parlange, M. B.; Calaf, M.

2017-02-01

The effect of extensive terrestrial wind farms on the spatio-temporal structure of the diurnally-evolving atmospheric boundary layer is explored. High-resolution large-eddy simulations of a realistic diurnal cycle with an embedded wind farm are performed. Simulations are forced by a constant geostrophic velocity with time-varying surface boundary conditions derived from a selected period of the CASES-99 field campaign. Through analysis of the bulk statistics of the flow as a function of height and time, it is shown that extensive wind farms shift the inertial oscillations and the associated nocturnal low-level jet vertically upwards by approximately 200 m; cause a three times stronger stratification between the surface and the rotor-disk region, and as a consequence, delay the formation and growth of the convective boundary layer (CBL) by approximately 2 h. These perturbations are shown to have a direct impact on the potential power output of an extensive wind farm with the displacement of the low-level jet causing lower power output during the night as compared to the day. The low-power regime at night is shown to persist for almost 2 h beyond the morning transition due to the reduced growth of the CBL. It is shown that the wind farm induces a deeper entrainment region with greater entrainment fluxes. Finally, it is found that the diurnally-averaged effective roughness length for wind farms is much lower than the reference value computed theoretically for neutral conditions.

Blunt trauma to large vessels: a mathematical study

PubMed Central

Ismailov, Rovshan M; Shevchuk, Nikolai A; Schwerha, Joseph; Keller, Lawrence; Khusanov, Higmat

2004-01-01

Background Blunt trauma causes short-term compression of some or all parts of the chest, abdomen or pelvis and changes hemodynamics of the blood. Short-term compression caused by trauma also results in a short-term decrease in the diameter of blood vessels. It has been shown that with a sudden change in the diameter of a tube or in the direction of the flow, the slower-moving fluid near the wall stops or reverses direction, which is known as boundary layer separation (BLS). We hypothesized that a sudden change in the diameter of elastic vessel that results from compression may lead not only to BLS but also to other hemodynamic changes that can damage endothelium. Methods We applied Navier-Stokes, multiphase and boundary layer equations to examine such stress. The method of approximation to solve the BL equations was used. Experiments were conducted in an aerodynamic tube, where incident flow velocity and weight of carriage with particles before and after blowing were measured. Results We found that sudden compression resulting from trauma leads to (1) BLS on the curved surface of the vessel wall; (2) transfer of laminar boundary layer into turbulent boundary layer. Damage to the endothelium can occur if compression is at least 25% and velocity is greater than 2.4 m/s or if compression is at least 10% and velocity is greater than 2.9 m/s. Conclusion Our research may point up new ways of reducing the damage from blunt trauma to large vessels. It has the potential for improvement of safety features of motor vehicles. This work will better our understanding of the precise mechanics and critical variables involved in diagnosis and prevention of blunt trauma to large vessels. PMID:15153246

The Effect of Aerosol on Gravity Wave Characteristics above the Boundary Layer over a Tropical Location

NASA Astrophysics Data System (ADS)

Rakshit, G.; Jana, S.; Maitra, A.

2017-12-01

The perturbations of temperature profile over a location give an estimate of the potential energy of gravity waves propagating through the atmosphere. Disturbances in the lower atmosphere due to tropical deep convection, orographic effects and various atmospheric disturbances generates of gravity waves. The present study investigates the gravity wave energy estimated from fluctuations in temperature profiles over the tropical location Kolkata (22°34' N, 88°22' E). Gravity waves are most intense during the pre-monsoon period (March-June) at the present location, the potential energy having high values above the boundary layer (2-4 km) as observed from radiosonde profiles. An increase in temperature perturbation, due to high ambient temperature in the presence of heat absorbing aerosols, causes an enhancement in potential energy. As the present study location is an urban metropolitan city experiencing high level of pollution, pollutant aerosols can go much above the normal boundary layer during daytime due to convection causing an extended boundary layer. The Aerosol Index (AAI) obtained from Global Ozone Monitoring Experiment-2 (GOME-2) on MetOp-A platform at 340 nm and 380 nm confirms the presence of absorbing aerosol particles over the present location. The Hysplit back trajectory analysis shows that the aerosol particles at those heights are of local origin and are responsible for depleting liquid water content due to cloud burning. The aerosol extinction coefficient obtained from CALIPSO data exhibits an increasing trend during 2006-2016 accompanied by a similar pattern of gravity wave energy. Thus the absorbing aerosols have a significant role in increasing the potential energy of gravity wave at an urban location in the tropical region.

Experimental Investigation of Vortex Structures in Wake of Hyperboloid-Shaped Model by Means of 2D Particle Image Velocimetry Measurement

NASA Astrophysics Data System (ADS)

Barraclough, V.; Novotný, J.; Šafařík, P.

2018-06-01

This paper deals with flow around a bluff body of hyperboloid shape. It consists of results gathered in the course of research by means of Particle Image Velocimetry (PIV). The experiments were carried out by means of low-frequency 2D PIV in a range of Reynolds numbers from 40000 to 50000. A hyperboloid-shaped model was measured in a wind tunnel with a modelled atmospheric boundary layer (and additionally, in a low-speed wind tunnel with low turbulence). The model was tested in a subcritical range of Reynolds numbers and various planes in a wake of the model were captured with the intention of getting an estimation of 3D flow structures. The tunnel with the modelled atmospheric boundary layer has a high rate of turbulence, so the influence of the turbulence of incoming flow on the wake could be outlined. The ratio of the height of the model to a thickness of the modelled boundary layer in the tunnel was 1/3, meaning the turbulence in the boundary layer strongly influenced the flow around the model; it suppresses the wake which leads to a lot shorter area of recirculation than low turbulence incoming flow would cause.

Experimental characterization of broadband electrostatic noise due to plasma compression

NASA Astrophysics Data System (ADS)

Dubois, Ami M.; Thomas, Edward, Jr.; Amatucci, William E.; Ganguli, Gurudas

2015-11-01

For a wide variety of laboratory and space plasma environments, theory states that plasmas are unstable to transverse shear flows over a very broad frequency range, where the shear scale length (LE) compared to the ion gyro-radius (ρi) determines the character of the shear-driven instability that may prevail. During active periods in the Earth's magnetosphere, such sheared flows are intensified and broadband electrostatic noise (BEN) is often observed by satellites traversing natural boundary layers. An interpenetrating magnetized plasma configuration is used to create a transverse velocity shear profile similar to that found at natural space plasma boundary layers. The continuous variation and the associated transition of the instability regimes driven by the shear flow mechanism are demonstrated in a single laboratory experiment. For the first time, broadband wave emission, which is correlated to increasing/decreasing stress (i.e., ρi/LE) on a plasma boundary layer, is found under controlled and repeatable conditions. This result provides evidence that the compression/relaxation of a plasma boundary layer leads to a BEN signature and holds out the promise for understanding the cause and effect of the in situ observation of BEN by satellites. This project was supported with funding from the U.S. Department of Energy, the Defense Threat Reduction Agency, and NRL Base Funds.

Air Entrainment and Surface Ripples in a Turbulent Ship Hull Boundary Layer

NASA Astrophysics Data System (ADS)

Masnadi, Naeem; Erinin, Martin; Duncan, James H.

2017-11-01

The air entrainment and free-surface fluctuations caused by the interaction of a free surface and the turbulent boundary layer of a vertical surface-piercing plate is studied experimentally. In this experiment, a meter-wide stainless steel belt travels horizontally in a loop around two rollers with vertically oriented axes. This belt device is mounted inside a large water tank with the water level set just below the top edge of the belt. The belt, rollers, and supporting frame are contained within a sheet metal box to keep the device dry except for one 6-meter-long straight test section. The belt is accelerated suddenly from rest until reaching constant speed in order to create a temporally evolving boundary layer analogous to the spatially evolving boundary layer that would exist along a surface-piercing towed flat plate. Surface ripples are measured using a cinematic laser-induced fluorescence technique with the laser sheet oriented parallel or normal to the belt surface. Air entrainment events and bubble motions are recorded from underneath the water surface using a stereo imaging system. Measurements of small bubbles, that tend to stay submerged for a longer time, are planned via a high-speed digital in-line holographic system. The support of the Office of Naval Research is gratefully acknowledged.

Sensitivity of boundary layer variables to PBL schemes over the central Tibetan Plateau

NASA Astrophysics Data System (ADS)

Xu, L.; Liu, H.; Wang, L.; Du, Q.; Liu, Y.

2017-12-01

Planetary Boundary Layer (PBL) parameterization schemes play critical role in numerical weather prediction and research. They describe physical processes associated with the momentum, heat and humidity exchange between land surface and atmosphere. In this study, two non-local (YSU and ACM2) and two local (MYJ and BouLac) planetary boundary layer parameterization schemes in the Weather Research and Forecasting (WRF) model have been tested over the central Tibetan Plateau regarding of their capability to model boundary layer parameters relevant for surface energy exchange. The model performance has been evaluated against measurements from the Third Tibetan Plateau atmospheric scientific experiment (TIPEX-III). Simulated meteorological parameters and turbulence fluxes have been compared with observations through standard statistical measures. Model results show acceptable behavior, but no particular scheme produces best performance for all locations and parameters. All PBL schemes underestimate near surface air temperatures over the Tibetan Plateau. By investigating the surface energy budget components, the results suggest that downward longwave radiation and sensible heat flux are the main factors causing the lower near surface temperature. Because the downward longwave radiation and sensible heat flux are respectively affected by atmosphere moisture and land-atmosphere coupling, improvements in water vapor distribution and land-atmosphere energy exchange is meaningful for better presentation of PBL physical processes over the central Tibetan Plateau.

Feasibility of generating an artificial burst in a turbulent boundary layer, phase 2

NASA Technical Reports Server (NTRS)

Gad-El-hak, Mohamed

1989-01-01

Various drag accounts for about half of the total drag on commercial aircraft at subsonic cruise conditions. Two avenues are available to achieve drag reduction: either laminar flow control or turbulence manipulation. The present research deals with the latter approach. The primary objective of Phase 2 research was to investigate experimentally the feasibility of substantially reducing the skin-friction drag in a turbulent boundary layer. The method combines the beneficial effects of suction and a longitudinally ribbed surface. At a sufficiently large spanwise separation, the streamwise grooves act as a nucleation site causing a focusing of low-speed streaks over the peaks. Suction is then applied intermittently through longitudinal slots located at selected locations along those peaks to obliterate the low-speed regions and to prevent bursting. Phase 2 research was divided into two tasks. In the first, selective suction from a single streamwise slot was used to eliminate either a single burst-like event or a periodic train of artificially generated bursts in laminar and turbulent boundary layers that develop on a flat plate towed in a water channel. The results indicate that equivalent values of the suction coefficient as low as 0.0006 were sufficient to eliminate the artificially generated bursts in a laminar boundary layer.

Comparison of Methods for Determining Boundary Layer Edge Conditions for Transition Correlations

NASA Technical Reports Server (NTRS)

Liechty, Derek S.; Berry, Scott A.; Hollis, Brian R.; Horvath, Thomas J.

2003-01-01

Data previously obtained for the X-33 in the NASA Langley Research Center 20-Inch Mach 6 Air Tunnel have been reanalyzed to compare methods for determining boundary layer edge conditions for use in transition correlations. The experimental results were previously obtained utilizing the phosphor thermography technique to monitor the status of the boundary layer downstream of discrete roughness elements via global heat transfer images of the X-33 windward surface. A boundary layer transition correlation was previously developed for this data set using boundary layer edge conditions calculated using an inviscid/integral boundary layer approach. An algorithm was written in the present study to extract boundary layer edge quantities from higher fidelity viscous computational fluid dynamic solutions to develop transition correlations that account for viscous effects on vehicles of arbitrary complexity. The boundary layer transition correlation developed for the X-33 from the viscous solutions are compared to the previous boundary layer transition correlations. It is shown that the boundary layer edge conditions calculated using an inviscid/integral boundary layer approach are significantly different than those extracted from viscous computational fluid dynamic solutions. The present results demonstrate the differences obtained in correlating transition data using different computational methods.

Development of Modal Analysis for the Study of Global Modes in High Speed Boundary Layer Flows

NASA Astrophysics Data System (ADS)

Brock, Joseph Michael

Boundary layer transition for compressible flows remains a challenging and unsolved problem. In the context of high-speed compressible flow, transitional and turbulent boundary-layers produce significantly higher surface heating caused by an increase in skin-friction. The higher heating associated with transitional and turbulent boundary layers drives thermal protection systems (TPS) and mission trajectory bounds. Proper understanding of the mechanisms that drive transition is crucial to the successful design and operation of the next generation spacecraft. Currently, prediction of boundary-layer transition is based on experimental efforts and computational stability analysis. Computational analysis, anchored by experimental correlations, offers an avenue to assess/predict stability at a reduced cost. Classical methods of Linearized Stability Theory (LST) and Parabolized Stability Equations (PSE) have proven to be very useful for simple geometries/base flows. Under certain conditions the assumptions that are inherent to classical methods become invalid and the use of LST/PSE is inaccurate. In these situations, a global approach must be considered. A TriGlobal stability analysis code, Global Mode Analysis in US3D (GMAUS3D), has been developed and implemented into the unstructured solver US3D. A discussion of the methodology and implementation will be presented. Two flow configurations are presented in an effort to validate/verify the approach. First, stability analysis for a subsonic cylinder wake is performed and results compared to literature. Second, a supersonic blunt cone is considered to directly compare LST/PSE analysis and results generated by GMAUS3D.

Dry Rainbelts: Understanding Boundary Layer Controls on the ITCZ Using a Dry Dynamical Core

NASA Astrophysics Data System (ADS)

Hill, S. A.; Bordoni, S.; Mitchell, J.

2017-12-01

Though migrations of Earth's Intertropical Convergence Zone (ITCZ) are often interpreted in terms of meridional energy transports, a recent study using an idealized, aquaplanet GCM indicates that the ITCZ's position is also linked to the character of the boundary layer momentum budget. Namely, moist convection within the ITCZ roughly coincides with a transition in the role of relative vorticity advection in the boundary layer, from being of leading-order to lower-order importance. This is insensitive to the presence of mid-latitude eddies or thermal inertia and holds over a range of planetary rotation rates, with this transitional regime and the ITCZ extending farther poleward the slower the planet is rotating. We use an even simpler model, a dry dynamical core, to further refine the theoretical understanding of these results, via simulations analogous to and extending the aforementioned moist cases. The importance of planetary rotation and lack thereof for both baroclinic eddies and thermal inertia emerge in the dry simulations also, implying base causes rooted in simpler, steady-state, solsticial, axisymmetric, dry dynamics. We further elucidate the role of the boundary layer dynamical processes through comparison with arguments dating to at least 1972 (although largely overlooked in recent literature) that convection is forced by convergence driven by a shallowing of the boundary layer depth, with this shallowing resulting from the transition from an advective to an Ekman balance on frictional drag. We discuss the potential links between this dynamical perspective and the popular energetic framework for ITCZ migrations and the resulting implications for moist convection on Earth and other planetary bodies.

Sensitivity of nocturnal boundary layer temperature to tropospheric aerosol surface radiative forcing under clear-sky conditions

NASA Astrophysics Data System (ADS)

Nair, Udaysankar S.; McNider, Richard; Patadia, Falguni; Christopher, Sundar A.; Fuller, Kirk

2011-01-01

Since the middle of the last century, global surface air temperature exhibits an increasing trend, with nocturnal temperatures increasing at a much higher rate. Proposed causative mechanisms include the radiative impact of atmospheric aerosols on the nocturnal boundary layer (NBL) where the temperature response is amplified due to shallow depth and its sensitivity to potential destabilization. A 1-D version of the Regional Atmospheric Modeling System is used to examine the sensitivity of the nocturnal boundary layer temperature to the surface longwave radiative forcing (SLWRF) from urban aerosol loading and doubled atmospheric carbon dioxide concentrations. The analysis is conducted for typical midlatitude nocturnal boundary layer case days from the CASES-99 field experiment and is further extended to urban sites in Pune and New Delhi, India. For the cases studied, locally, the nocturnal SLWRF from urban atmospheric aerosols (2.7-47 W m-2) is comparable or exceeds that caused by doubled atmospheric carbon dioxide (3 W m-2), with the surface temperature response ranging from a compensation for daytime cooling to an increase in the nocturnal minimum temperature. The sensitivity of the NBL to radiative forcing is approximately 4 times higher compared to the daytime boundary layer. Nighttime warming or cooling may occur depending on the nature of diurnal variations in aerosol optical depth. Soil moisture also modulates the magnitude of SLWRF, decreasing from 3 to 1 W m-2 when soil saturation increases from 37% to 70%. These results show the importance of aerosols on the radiative balance of the climate system.

Separation behavior of boundary layers on three-dimensional wings

NASA Technical Reports Server (NTRS)

Stock, H. W.

1981-01-01

An inverse boundary layer procedure for calculating separated, turbulent boundary layers at infinitely long, crabbing wing was developed. The procedure was developed for calculating three dimensional, incompressible turbulent boundary layers was expanded to adiabatic, compressible flows. Example calculations with transsonic wings were made including viscose effects. In this case an approximated calculation method described for areas of separated, turbulent boundary layers, permitting calculation of this displacement thickness. The laminar boundary layer development was calculated with inclined ellipsoids.

Flow Coefficient Behavior for Boundary Layer Bleed Holes and Slots

NASA Technical Reports Server (NTRS)

Willis, B. P.; Davis, D. O.; Hingst, W. R.

1995-01-01

An experimental investigation into the flow coefficient behavior for nine boundary layer bleed orifice configurations is reported. This test was conducted for the purposes of exploring boundary layer control through mass flow removal and does not address issues of stability bleed. Parametric data consist of bleed region flow coefficient as a function of Mach number, bleed plenum pressure, and bleed orifice geometry. Seven multiple hole configurations and two single slot configurations were tested over a supersonic Mach number range of 1.3 to 2.5 (nominal). Advantages gained by using multiple holes in a bleed region instead of a single spanwise slot are discussed and the issue of modeling an entire array of bleed orifices based on the performance of a single orifice is addressed. Preconditioning the flow approaching a 90 degree inclined (normal) hole configuration resulted in a significant improvement in the performance of the configuration. The same preconditioning caused only subtle changes in performance for a 20 degree inclined (slanted) configuration.

Experimental Study of Unsteady Separation in a Laminar Boundary Layer

NASA Astrophysics Data System (ADS)

Bonacci, Andrew; Lang, Amy; Wahidi, Redha; Santos, Leo

2016-11-01

Separation, caused by an adverse pressure gradient, can be a major problem to aircraft. Reversing flow occurs in separated regions and an investigation of how this backflow forms is of interest due to the fact that this could be used as a means of initiating flow control. Specifically, backflow can bristle shark scales which may be linked to a passive, flow actuated separation control mechanism. An experiment was conducted in a water tunnel to replicate separation, with a focus on the reversing flow development near the wall within a laminar boundary layer. Using a rotating cylinder, an adverse pressure gradient was induced creating a separated region over a flat plate. In this experiment the boundary layer grows to sizes great enough that the scale of the flow is increased, making it more measurable to DPIV. In the future, this research can be utilized to better understand flow control mechanisms such as those enabled by shark skin. Funding from Army Research Office and NSF REU site Grant EEC 1358991 is greatly appreciated.

Turbulent heat flux measurements in a transitional boundary layer

NASA Technical Reports Server (NTRS)

Sohn, K. H.; Zaman, K. B. M. Q.; Reshotko, E.

1992-01-01

During an experimental investigation of the transitional boundary layer over a heated flat plate, an unexpected result was encountered for the turbulent heat flux (bar-v't'). This quantity, representing the correlation between the fluctuating normal velocity and the temperature, was measured to be negative near the wall under certain conditions. The result was unexpected as it implied a counter-gradient heat transfer by the turbulent fluctuations. Possible reasons for this anomalous result were further investigated. The possible causes considered for this negative bar-v't' were: (1) plausible measurement error and peculiarity of the flow facility, (2) large probe size effect, (3) 'streaky structure' in the near wall boundary layer, and (4) contributions from other terms usually assumed negligible in the energy equation including the Reynolds heat flux in the streamwise direction (bar-u't'). Even though the energy balance has remained inconclusive, none of the items (1) to (3) appear to be contributing directly to the anomaly.

Evaluation of analytical procedures for prediction of turbulent boundary layers on a porous wall

NASA Technical Reports Server (NTRS)

Towne, C. E.

1974-01-01

An analytical study has been made to determine how well current boundary layer prediction techniques work when there is mass transfer normal to the wall. The data that were considered in this investigation were for two-dimensional, incompressible, turbulent boundary layers with suction and blowing. Some of the bleed data were taken in an adverse pressure gradient. An integral prediction method was used three different porous wall skin friction relations, in addition to a solid-surface relation for the suction cases. A numerical prediction method was also used. Comparisons were made between theoretical and experimental skin friction coefficients, displacement and momentum thicknesses, and velocity profiles. The integral method with one of the porous wall skin friction laws gave very good agreement with data for most of the cases considered. The use of the solid-surface skin friction law caused the integral to overpredict the effectiveness of the bleed. The numerical techniques also worked well for most of the cases.

Summary of experimentally determined facts concerning the behavior of the boundary layer and performance of boundary layer measurements. [considering sailing flight

NASA Technical Reports Server (NTRS)

Vanness, W.

1978-01-01

A summary report of boundary layer studies is presented. Preliminary results of experimental measurements show that: (1) A very thin layer (approximately 0.4 mm) of the boundary layer seems to be accelerated; (2) the static pressure of the outer flow does not remain exactly constant through the boundary layer; and (3) an oncoming boundary layer which is already turbulent at the suction point can again become laminar behind this point without being completely sucked off.

Low Ozone in the Marine Boundary Layer of the Tropical Pacific Ocean

NASA Technical Reports Server (NTRS)

Singh, Hanwant B.; Gregory, G. L.; Andesrson, B.; Browell, E.; Sachse, G. W.; Davis, D. D.; Crawford, J.; Bradshaw, J. D.; Talbot, R.; Blake, D. R.;

Optical based tactile shear and normal load sensor

DOEpatents

Salisbury, Curt Michael

2015-06-09

Various technologies described herein pertain to a tactile sensor that senses normal load and/or shear load. The tactile sensor includes a first layer and an optically transparent layer bonded together. At least a portion of the first layer is made of optically reflective material. The optically transparent layer is made of resilient material (e.g., clear silicone rubber). The tactile sensor includes light emitter/light detector pair(s), which respectively detect either normal load or shear load. Light emitter(s) emit light that traverses through the optically transparent layer and reflects off optically reflective material of the first layer, and light detector(s) detect and measure intensity of reflected light. When a normal load is applied, the optically transparent layer compresses, causing a change in reflected light intensity. When shear load is applied, a boundary between optically reflective material and optically absorptive material is laterally displaced, causing a change in reflected light intensity.

Orbiter Entry Aeroheating Working Group Viscous CFD Boundary Layer Transition Trailblazer Solutions

NASA Technical Reports Server (NTRS)

Wood, William A.; Erickson, David W.; Greene, Francis A.

2007-01-01

Boundary layer transition correlations for the Shuttle Orbiter have been previously developed utilizing a two-layer boundary layer prediction technique. The particular two-layer technique that was used is limited to Mach numbers less than 20. To allow assessments at Mach numbers greater than 20, it is proposed to use viscous CFD to the predict boundary layer properties. This report addresses if the existing Orbiter entry aeroheating viscous CFD solutions, which were originally intended to be used for heat transfer rate predictions, adequately resolve boundary layer edge properties and if the existing two-layer results could be leveraged to reduce the number of needed CFD solutions. The boundary layer edge parameters from viscous CFD solutions are extracted along the wind side centerline of the Space Shuttle Orbiter at reentry conditions, and are compared with results from the two-layer boundary layer prediction technique. The differences between the viscous CFD and two-layer prediction techniques vary between Mach 6 and 18 flight conditions and Mach 6 wind tunnel conditions, and there is not a straightforward scaling between the viscous CFD and two-layer values. Therefore: it is not possible to leverage the existing two-layer Orbiter flight boundary layer data set as a substitute for a viscous CFD data set; but viscous CFD solutions at the current grid resolution are sufficient to produce a boundary layer data set suitable for applying edge-based boundary layer transition correlations.

Transonic Shock-Wave/Boundary-Layer Interactions on an Oscillating Airfoil

NASA Technical Reports Server (NTRS)

Davis, Sanford S.; Malcolm, Gerald N.

1980-01-01

Unsteady aerodynamic loads were measured on an oscillating NACA 64A010 airfoil In the NASA Ames 11 by 11 ft Transonic Wind Tunnel. Data are presented to show the effect of the unsteady shock-wave/boundary-layer interaction on the fundamental frequency lift, moment, and pressure distributions. The data show that weak shock waves induce an unsteady pressure distribution that can be predicted quite well, while stronger shock waves cause complex frequency-dependent distributions due to flow separation. An experimental test of the principles of linearity and superposition showed that they hold for weak shock waves while flows with stronger shock waves cannot be superimposed.

Calculation methods for compressible turbulent boundary layers, 1976

NASA Technical Reports Server (NTRS)

Bushnell, D. M.; Cary, A. M., Jr.; Harris, J. E.

1977-01-01

Equations and closure methods for compressible turbulent boundary layers are discussed. Flow phenomena peculiar to calculation of these boundary layers were considered, along with calculations of three dimensional compressible turbulent boundary layers. Procedures for ascertaining nonsimilar two and three dimensional compressible turbulent boundary layers were appended, including finite difference, finite element, and mass-weighted residual methods.

Shear Stress induced Stretching of Red Blood Cells by Oscillating Bubbles within a Narrow Gap

NASA Astrophysics Data System (ADS)

Li, Fenfang; Mohammadzadeh, Milad; Ohl, Claus-Dieter; Claus-Dieter Ohl Team

2013-11-01

The flow pattern, especially the boundary layer caused by the expanding/contracting bubble in a narrow gap (15 μm) and the resultant stretching of red blood cells is investigated in this work. High speed recordings show that a red blood cell (biconcave shape, thickness of 1-2 μm) can be elongated to five times its original length by a laser-induced cavitation bubble within the narrow gap. However, flexible cancer cells in suspension (RKO, spherical shape, diameter of 10-15 μm) are hardly elongated under the same experimental condition. We hypothesize that the shear stress at the boundary layer is crucial for this elongation to occur. Therefore, in order to resolve the related fluid dynamics, we conducted numerical simulations using the finite element method (Fluent). The rapidly expanding/contracting vapor bubble is successfully modeled by employing viscosity and surface tension. The transient pressure inside the bubble and the velocity profile of the flow is obtained. We observe strong shear near the upper and lower boundary during the bubble oscillation. The flow fields are compared with analytical solutions to transient and pulsating flows in 2D. In the experiment the red blood cells sit within the lower boundary layer, thus are probably elongated by this strong shear flow. In contrast, the spherical cancer cells are of comparable size to the gap height so that they are lesser affected by this boundary layer flow.

A general integral form of the boundary-layer equation for incompressible flow with an application to the calculation of the separation point of turbulent boundary layers

NASA Technical Reports Server (NTRS)

Tetervin, Neal; Lin, Chia Chiao

1951-01-01

A general integral form of the boundary-layer equation, valid for either laminar or turbulent incompressible boundary-layer flow, is derived. By using the experimental finding that all velocity profiles of the turbulent boundary layer form essentially a single-parameter family, the general equation is changed to an equation for the space rate of change of the velocity-profile shape parameter. The lack of precise knowledge concerning the surface shear and the distribution of the shearing stress across turbulent boundary layers prevented the attainment of a reliable method for calculating the behavior of turbulent boundary layers.

Microgravity Effects on Plant Boundary Layers

NASA Technical Reports Server (NTRS)

Stutte, Gary; Monje, Oscar

2005-01-01

The goal of these series of experiment was to determine the effects of microgravity conditions on the developmental boundary layers in roots and leaves and to determine the effects of air flow on boundary layer development. It is hypothesized that microgravity induces larger boundary layers around plant organs because of the absence of buoyancy-driven convection. These larger boundary layers may affect normal metabolic function because they may reduce the fluxes of heat and metabolically active gases (e.g., oxygen, water vapor, and carbon dioxide. These experiments are to test whether there is a change in boundary layer associated with microgravity, quantify the change if it exists, and determine influence of air velocity on boundary layer thickness under different gravity conditions.

Assessment of surface turbulent fluxes using geostationary satellite surface skin temperatures and a mixed layer planetary boundary layer scheme

NASA Technical Reports Server (NTRS)

Diak, George R.; Stewart, Tod R.

1989-01-01

A method is presented for evaluating the fluxes of sensible and latent heating at the land surface, using satellite-measured surface temperature changes in a composite surface layer-mixed layer representation of the planetary boundary layer. The basic prognostic model is tested by comparison with synoptic station information at sites where surface evaporation climatology is well known. The remote sensing version of the model, using satellite-measured surface temperature changes, is then used to quantify the sharp spatial gradient in surface heating/evaporation across the central United States. An error analysis indicates that perhaps five levels of evaporation are recognizable by these methods and that the chief cause of error is the interaction of errors in the measurement of surface temperature change with errors in the assigment of surface roughness character. Finally, two new potential methods for remote sensing of the land-surface energy balance are suggested which will relay on space-borne instrumentation planned for the 1990s.

Boundary layer friction of solvate ionic liquids as a function of potential.

PubMed

Li, Hua; Rutland, Mark W; Watanabe, Masayoshi; Atkin, Rob

2017-07-01

Atomic force microscopy (AFM) has been used to investigate the potential dependent boundary layer friction at solvate ionic liquid (SIL)-highly ordered pyrolytic graphite (HOPG) and SIL-Au(111) interfaces. Friction trace and retrace loops of lithium tetraglyme bis(trifluoromethylsulfonyl)amide (Li(G4) TFSI) at HOPG present clearer stick-slip events at negative potentials than at positive potentials, indicating that a Li + cation layer adsorbed to the HOPG lattice at negative potentials which enhances stick-slip events. The boundary layer friction data for Li(G4) TFSI shows that at HOPG, friction forces at all potentials are low. The TFSI - anion rich boundary layer at positive potentials is more lubricating than the Li + cation rich boundary layer at negative potentials. These results suggest that boundary layers at all potentials are smooth and energy is predominantly dissipated via stick-slip events. In contrast, friction at Au(111) for Li(G4) TFSI is significantly higher at positive potentials than at negative potentials, which is comparable to that at HOPG at the same potential. The similarity of boundary layer friction at negatively charged HOPG and Au(111) surfaces indicates that the boundary layer compositions are similar and rich in Li + cations for both surfaces at negative potentials. However, at Au(111), the TFSI - rich boundary layer is less lubricating than the Li + rich boundary layer, which implies that anion reorientations rather than stick-slip events are the predominant energy dissipation pathways. This is confirmed by the boundary friction of Li(G4) NO 3 at Au(111), which shows similar friction to Li(G4) TFSI at negative potentials due to the same cation rich boundary layer composition, but even higher friction at positive potentials, due to higher energy dissipation in the NO 3 - rich boundary layer.

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

Tethered balloon-based black carbon profiles within the lower troposphere of Shanghai in the 2013 East China smog

NASA Astrophysics Data System (ADS)

Li, Juan; Fu, Qingyan; Huo, Juntao; Wang, Dongfang; Yang, Wen; Bian, Qinggen; Duan, Yusen; Zhang, Yihua; Pan, Jun; Lin, Yanfen; Huang, Kan; Bai, Zhipeng; Wang, Sheng-Hsiang; Fu, Joshua S.; Louie, Peter K. K.

2015-12-01

A Tethered balloon-based field campaign was launched for the vertical observation of air pollutants within the lower troposphere of 1000 m for the first time over a Chinese megacity, Shanghai in December of 2013. A custom-designed instrumentation platform for tethered balloon observation and ground-based observation synchronously operated for the measurement of same meteorological parameters and typical air pollutants. One episodic event (December 13) was selected with specific focus on particulate black carbon, a short-lived climate forcer with strong warming effect. Diurnal variation of the mixing layer height showed very shallow boundary of less than 300 m in early morning and night due to nocturnal inversion while extended boundary of more than 1000 m from noon to afternoon. Wind profiles showed relatively stagnant synoptic condition in the morning, frequent shifts between upward and downward motion at noon and in the afternoon, and dominant downward motion with sea breeze in the evening. Characteristics of black carbon vertical profiles during four different periods of a day were analyzed and compared. In the morning, surface BC concentration averaged as high as 20 μg/m3 due to intense traffic emissions from the morning rush hours and unfavorable meteorological conditions. A strong gradient of BC concentrations with altitude was observed from the ground to the top of boundary layer at around 250-370 m. BC gradients turned much smaller above the boundary layer. BC profiles measured during noon and afternoon were the least dependent on heights. The largely extended boundary layer with strong vertical convection was responsible for a well mixing of BC particles in the whole measured column. BC profiles were similar between the early-evening and late-evening phases. The lower troposphere was divided into two stratified air layers with contrasted BC vertical distributions. Profiles at night showed strong gradients from the relatively high surface concentrations to low concentrations near the top of the boundary layer around 200 m. Above the boundary layer, BC increased with altitudes and reached a maximum at the top of 1000 m. Prevailing sea breeze within the boundary layer was mainly responsible for the quick cleanup of BC in the lower altitudes. In contrast, continental outflow via regional transport was the major cause of the enhanced BC aloft. This study provides a first insight of the black carbon vertical profiles over Eastern China, which will have significant implications for narrowing the gaps between the source emissions and observations as well as improving estimations of BC radiative forcing and regional climate.

Mass and energy transfer across the Earth's magnetopause caused by vortex-induced reconnection: Mass and energy transfer by K-H vortex

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

Nakamura, T. K. M.; Eriksson, S.; Hasegawa, H.

When the interplanetary magnetic field (IMF) is strongly northward, a boundary layer that contains a considerable amount of plasma of magnetosheath origin is often observed along and earthward of the low-latitude magnetopause. Such a pre-existing boundary layer, with a higher density than observed in the adjacent magnetosphere, reduces the local Alfvén speed and allows the Kelvin-Helmholtz instability (KHI) to grow more strongly. We employ a three-dimensional fully kinetic simulation to model an event observed by the Magnetospheric Multiscale (MMS) mission in which the spacecraft detected substantial KH waves between a pre-existing boundary layer and the magnetosheath during strong northward IMF.more » Initial results of this simulation [Nakamura et al., 2017] have successfully demonstrated ion-scale signatures of magnetic reconnection induced by the non-linearly developed KH vortex, which are quantitatively consistent with MMS observations. Furthermore, we quantify the simulated mass and energy transfer processes driven by this vortex-induced reconnection (VIR) and show that during this particular MMS event (i) mass enters a new mixing layer formed by the VIR more efficiently from the pre-existing boundary layer side than from the magnetosheath side, (ii) mixed plasmas within the new mixing layer convect tailward along the magnetopause at more than half the magnetosheath flow speed, and (iii) energy dissipation in localized VIR dissipation regions results in a strong parallel electron heating within the mixing layer. Finally, the quantitative agreements between the simulation and MMS observations allow new predictions that elucidate how the mass and energy transfer processes occur near the magnetopause during strong northward IMF.« less

Mass and energy transfer across the Earth's magnetopause caused by vortex-induced reconnection: Mass and energy transfer by K-H vortex

DOE PAGES

Nakamura, T. K. M.; Eriksson, S.; Hasegawa, H.; ...

2017-10-23

When the interplanetary magnetic field (IMF) is strongly northward, a boundary layer that contains a considerable amount of plasma of magnetosheath origin is often observed along and earthward of the low-latitude magnetopause. Such a pre-existing boundary layer, with a higher density than observed in the adjacent magnetosphere, reduces the local Alfvén speed and allows the Kelvin-Helmholtz instability (KHI) to grow more strongly. We employ a three-dimensional fully kinetic simulation to model an event observed by the Magnetospheric Multiscale (MMS) mission in which the spacecraft detected substantial KH waves between a pre-existing boundary layer and the magnetosheath during strong northward IMF.more » Initial results of this simulation [Nakamura et al., 2017] have successfully demonstrated ion-scale signatures of magnetic reconnection induced by the non-linearly developed KH vortex, which are quantitatively consistent with MMS observations. Furthermore, we quantify the simulated mass and energy transfer processes driven by this vortex-induced reconnection (VIR) and show that during this particular MMS event (i) mass enters a new mixing layer formed by the VIR more efficiently from the pre-existing boundary layer side than from the magnetosheath side, (ii) mixed plasmas within the new mixing layer convect tailward along the magnetopause at more than half the magnetosheath flow speed, and (iii) energy dissipation in localized VIR dissipation regions results in a strong parallel electron heating within the mixing layer. Finally, the quantitative agreements between the simulation and MMS observations allow new predictions that elucidate how the mass and energy transfer processes occur near the magnetopause during strong northward IMF.« less

The Edge Detectors Suitable for Retinal OCT Image Segmentation

PubMed Central

Yang, Jing; Gao, Qian; Zhou, Sheng

2017-01-01

Retinal layer thickness measurement offers important information for reliable diagnosis of retinal diseases and for the evaluation of disease development and medical treatment responses. This task critically depends on the accurate edge detection of the retinal layers in OCT images. Here, we intended to search for the most suitable edge detectors for the retinal OCT image segmentation task. The three most promising edge detection algorithms were identified in the related literature: Canny edge detector, the two-pass method, and the EdgeFlow technique. The quantitative evaluation results show that the two-pass method outperforms consistently the Canny detector and the EdgeFlow technique in delineating the retinal layer boundaries in the OCT images. In addition, the mean localization deviation metrics show that the two-pass method caused the smallest edge shifting problem. These findings suggest that the two-pass method is the best among the three algorithms for detecting retinal layer boundaries. The overall better performance of Canny and two-pass methods over EdgeFlow technique implies that the OCT images contain more intensity gradient information than texture changes along the retinal layer boundaries. The results will guide our future efforts in the quantitative analysis of retinal OCT images for the effective use of OCT technologies in the field of ophthalmology. PMID:29065594

Investigation of Hypersonic Nozzle Flow Uniformity Using NO Fluorescence

NASA Technical Reports Server (NTRS)

O'Byrne, S.; Danehy, P. J.; Houwing, A. F. P.

2005-01-01

Planar laser-induced fluorescence visualisation is used to investigate nonuniformities in the flow of a hypersonic conical nozzle. Possible causes for the nonuniformity are outlined and investigated, and the problem is shown to be due to a small step at the nozzle throat. Entrainment of cold boundary layer gas is postulated as the cause of the signal nonuniformity.

Large scale motions of multiple limit-cycle high Reynolds number annular and toroidal rotor/stator cavities

NASA Astrophysics Data System (ADS)

Bridel-Bertomeu, Thibault; Gicquel, L. Y. M.; Staffelbach, G.

2017-06-01

Rotating cavity flows are essential components of industrial applications but their dynamics are still not fully understood when it comes to the relation between the fluid organization and monitored pressure fluctuations. From computer hard-drives to turbo-pumps of space launchers, designed devices often produce flow oscillations that can either destroy the component prematurely or produce too much noise. In such a context, large scale dynamics of high Reynolds number rotor/stator cavities need better understanding especially at the flow limit-cycle or associated statistically stationary state. In particular, the influence of curvature as well as cavity aspect ratio on the large scale organization and flow stability at a fixed rotating disc Reynolds number is fundamental. To probe such flows, wall-resolved large eddy simulation is applied to two different rotor/stator cylindrical cavities and one annular cavity. Validation of the predictions proves the method to be suited and to capture the disc boundary layer patterns reported in the literature. It is then shown that in complement to these disc boundary layer analyses, at the limit-cycle the rotating flows exhibit characteristic patterns at mid-height in the homogeneous core pointing the importance of large scale features. Indeed, dynamic modal decomposition reveals that the entire flow dynamics are driven by only a handful of atomic modes whose combination links the oscillatory patterns observed in the boundary layers as well as in the core of the cavity. These fluctuations form macro-structures, born in the unstable stator boundary layer and extending through the homogeneous inviscid core to the rotating disc boundary layer, causing its instability under some conditions. More importantly, the macro-structures significantly differ depending on the configuration pointing the need for deeper understanding of the influence of geometrical parameters as well as operating conditions.

Effect of canopy and topography induced wakes on land-atmosphere fluxes of momentum and scalars

NASA Astrophysics Data System (ADS)

Markfort, C. D.; Zhang, W.; Porté-Agel, F.; Stefan, H. G.

2012-04-01

Wakes shed from natural and anthropogenic landscape features affect land-atmosphere fluxes of momentum and scalars, including water vapor and trace gases (e.g. CO2). Canopies and bluff bodies, such as forests, buildings and topography, cause boundary layer flow separation, and lead to a break down of standard Monin-Obukhov similarity relationships in the atmospheric boundary layer (ABL). Wakes generated by these land surface features persist for significant distances (>100 typical length scales) and affect a large fraction of the Earth's terrestrial surface. This effect is currently not accounted for in land-atmosphere models, and little is known about how heterogeneity of wake-generating features affect land surface fluxes. Additionally flux measurements, made in wake-affected regions, do not satisfy the homogeneous flow requirements for the standard eddy correlation (EC) method. This phenomenon, often referred to as wind sheltering, has been shown to affect momentum and kinetic energy fluxes at the lake-atmosphere interface (Markfort et al. 2010). This presentation will highlight results from controlled wind tunnel experiments of neutral and thermally stratified boundary layers, using particle image velocimetry (PIV) and custom x-wire/cold-wire anemometry, to understand how the physical structure of upstream bluff bodies and porous canopies as well as how thermal stability affect the flow separation zone, boundary layer recovery and surface fluxes. We have found that there is a nonlinear relationship between canopy length/porosity and flow separation downwind of a canopy to clearing transition. Results will provide the basis for new parameterizations to account for wake effects on land-atmosphere fluxes and corrections for the EC measurements over open fields, lakes, and wetlands. Key words: Atmospheric boundary layer; Wakes; Stratification; Land-Atmosphere Parameterization; Canopy

Three-dimensional instability analysis of boundary layers perturbed by streamwise vortices

NASA Astrophysics Data System (ADS)

Martín, Juan A.; Paredes, Pedro

2017-12-01

A parametric study is presented for the incompressible, zero-pressure-gradient flat-plate boundary layer perturbed by streamwise vortices. The vortices are placed near the leading edge and model the vortices induced by miniature vortex generators (MVGs), which consist in a spanwise-periodic array of small winglet pairs. The introduction of MVGs has been experimentally proved to be a successful passive flow control strategy for delaying laminar-turbulent transition caused by Tollmien-Schlichting (TS) waves. The counter-rotating vortex pairs induce non-modal, transient growth that leads to a streaky boundary layer flow. The initial intensity of the vortices and their wall-normal distances to the plate wall are varied with the aim of finding the most effective location for streak generation and the effect on the instability characteristics of the perturbed flow. The study includes the solution of the three-dimensional, stationary, streaky boundary layer flows by using the boundary region equations, and the three-dimensional instability analysis of the resulting basic flows by using the plane-marching parabolized stability equations. Depending on the initial circulation and positioning of the vortices, planar TS waves are stabilized by the presence of the streaks, resulting in a reduction in the region of instability and shrink of the neutral stability curve. For a fixed maximum streak amplitude below the threshold for secondary instability (SI), the most effective wall-normal distance for the formation of the streaks is found to also offer the most stabilization of TS waves. By setting a maximum streak amplitude above the threshold for SI, sinuous shear layer modes become unstable, as well as another instability mode that is amplified in a narrow region near the vortex inlet position.

A study of tornadic thunderstorm interactions with thermal boundaries

NASA Technical Reports Server (NTRS)

Maddox, R. A.; Hoxit, L. R.; Chappell, C. F.

1980-01-01

A study of tornadic thunderstorm interactions with thermal boundaries using a model of subcloud wind profiles is presented. Within a hot, moist, and conditionally unstable air mass, warm thermal advection and surface friction cause the winds to veer and increase with height, while within a cool, moist air mass cool thermal advection and friction combine to produce a wind profile that has maximum speeds near the surface and veers little with height. The spatial distribution of different wind profiles and moisture contents within the boundary layer may act together to maximize mesoscale moisture contents, convergence, and cyclonic vorticity within a narrow mixing zone along the thermal boundary.

Unsteady Heat-Flux Measurements of Second-Mode Instability Waves in a Hypersonic Boundary Layer

NASA Technical Reports Server (NTRS)

Kergerise, Michael A.; Rufer, Shann J.

2016-01-01

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 in agreement 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 developed 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.

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.

The evaporatively driven cloud-top mixing layer

NASA Astrophysics Data System (ADS)

Mellado, Juan Pedro

2010-11-01

Turbulent mixing caused by the local evaporative cooling at the top cloud-boundary of stratocumuli will be discussed. This research is motivated by the lack of a complete understanding of several phenomena in that important region, which translates into an unacceptable variability of order one in current models, including those employed in climate research. The cloud-top mixing layer is a simplified surrogate to investigate, locally, particular aspects of the fluid dynamics at the boundary between the stratocumulus clouds and the upper cloud-free air. In this work, direct numerical simulations have been used to study latent heat effects. The problem is the following: When the cloud mixes with the upper cloud-free layer, relatively warm and dry, evaporation tends to cool the mixture and, if strong enough, the buoyancy reversal instability develops. This instability leads to a turbulent convection layer growing next to the upper boundary of the cloud, which is, in several aspects, similar to free convection below a cold horizontal surface. In particular, results show an approximately self-preserving behavior that is characterized by the molecular buoyancy flux at the inversion base, fact that helps to explain the difficulties found when doing large-eddy simulations of this problem using classical subgrid closures.

The Influence of Low Wall Temperature on Boundary-Layer Transition and Local Heat Transfer on 2-Inch-Diameter Hemispheres at a Mach Number of 4.95 and a Reynolds Number per Foot of 73.2 x 10(exp 6)

NASA Technical Reports Server (NTRS)

Cooper, Morton; Mayo, Edward E.; Julius, Jerome D.

1960-01-01

Measurements of the location of boundary-layer transition and the local heat transfer have been made on 2-inch-diameter hemispheres in the Langley gas dynamics laboratory at a Mach number of 4.95, a Reynolds number per foot of 73.2 x 10(exp 6), and a stagnation temperature of approximately 400 F. The transient-heating thin-skin calorimeter technique was used, and the initial values of the wall-to-stream stagnation- temperature ratios were 0.16 (cold-model tests) and 0.65 (hot-model test). During two of the four cold tests, the boundary-layer flow changed from turbulent to laminar over large regions of the hemisphere as the model heated. On the basis of a detailed consideration of the magnitude of roughness possibly present during these two cold tests, it appears that this destabilizing effect of low wall temperatures (cooling) was not caused by roughness as a dominant influence. This idea of a decrease in boundary-layer stability with cooling has been previously suggested. (See, for example, NASA Memorandum 10-8-58E.) For the laminar data obtained during the early part of the hot test, the correlation of the local-heating data with laminar theory was excellent.

Boundary Layer Regimes Conducive to Formation of Dust Devils on Mars

NASA Astrophysics Data System (ADS)

Williams, B.; Nair, U. S.

2014-12-01

Dust devils on Mars contribute to maintenance of background atmospheric aerosol loading and thus dust radiative forcing, which is an important modulator of Martian climate. Dust devils also cause surface erosion and change in surface albedo which impacts radiative energy budget. Thus there is a need for parameterizing dust devil impacts in Martian climate models. In this context it is important to understand environmental conditions that are favorable for formation of dust devils on Mars and associated implications for diurnal, seasonal, and geographical variation of dust devil occurrence. On earth, prior studies show that thresholds of ratio of convective and friction scale velocities may be used to identify boundary layer regimes that are conducive to formation of dust devils. On earth, a w*/u* ratio in excess of 5 is found to be conducive for formation of dust devils. In this study, meteorological observations collected during the Viking Lander mission are used to constrain Martian boundary layer model simulations, which is then used to estimate w*/u* ratio. The w*/u* ratio is computed for several case days during which dust devil occurrence was detected. A majority of dust devils occurred in convective boundary layer regimes characterized by w*/u* ratios exceeding 10. The above described analysis is being extended to other mars mission landing sites and results from the extended analysis will also be presented.

The flow field around a pair of cubic roughness elements with different spacings immersed in turbulent boundary layer

NASA Astrophysics Data System (ADS)

Agarwal, Karuna; Gao, Jian; Katz, Joseph

2017-11-01

The shape, size, and spacing between roughness elements in turbulent boundary layers affect the associated drag and noise. Understanding them require data on the flow structure around these elements. Dual-view tomographic holography is used to study the 3D 3-component velocity field around a pair of cubic roughness elements immersed in a turbulent boundary layer at Reτ = 2500 . These a = 1 mm high cubes correspond to 4% of the half channel height and 90 wall units (δν = 11 μ m). Tests are performed for spanwise spacings of a, 1.5 a and 2.5 a. The sample volume is 385δν × 250δν × 190δν and the vector spacing is 5.4δν. Conversed statistics is obtained by recording 1500 realizations in volumes centered upstream, downstream and around a cube. The boundary layer separating upstream of the cube does not reattach until the wake region, resulting in formation of a vortical ``canopy'' that engulfs each cube. It is dominated by spanwise vorticity above the cube and separated region, bounded by vertical vorticity on the sides. Flow channeling in the space between cubes causes asymmetry in the vorticity distributions along the inner and outer walls. The legs of horseshoe vortices remain near the wall between cubes, but grow and expand in the wake region. Funded by NSF and ONR.

Free-stream disturbance, continuous Eigenfunctions, boundary-layer instability and transition

NASA Technical Reports Server (NTRS)

Grosch, C. E.

1980-01-01

A rational foundation is presented for the application of the linear shear flows to transition prediction, and an explicit method is given for carrying out the necessary calculations. The expansions used are shown to be complete. Sample calculations show that a typical boundary layer is very sensitive to vorticity disturbances in the inner boundary layer, near the critical layer. Vorticity disturbances three or four boundary layer thicknesses above the boundary are nearly uncoupled from the boundary layer in that the amplitudes of the discrete Tollmien-Schlicting waves are an extremely small fraction of the amplitude of the disturbance.

Use of Microgravity to Control the Microstructure of Eutectics

NASA Technical Reports Server (NTRS)

Wilcox, William R.; Regel, Liya L.; Smith, Reginald W.

1999-01-01

The long term goal of this project is to be able to control the microstructure of directionally solidified eutectic alloys, through an improved understanding of the influence of convection. Prior experimental results on the influence of microgravity on the microstructure of fibrous eutectics have been contradictory. Theoretical work at Clarkson University showed that buoyancy-driven convection in the vertical Bridgman configuration is not vigorous enough to alter the concentration field in the melt sufficiently to cause a measurable change in microstructure when the eutectic grows at minimum supercooling. Currently, there are four other hypotheses that might explain the observed changes in microstructure of fibrous eutectics caused by convection: (1) Disturbance of the concentration boundary layer arising from an off-eutectic melt composition and growth at the extremum; (2) Disturbance of the concentration boundary layer of a habit-modifying impurity; (3) Disturbance of the concentration boundary layer arising from an off-eutectic interfacial composition due to non-extremum growth; and (4) A fluctuating freezing rate combined with differences in the kinetics of fiber termination and fiber formation. We favor the last of these hypotheses. Thus, the primary objective of the present grant is to determine experimentally and theoretically the influence of a periodically varying freezing rate on eutectic solidification. A secondary objective is to determine the influence of convection on the microstructure of at least one other eutectic alloy that might be suitable for flight experiments.

Archaeological Graves Revealing By Means of Seismic-electric Effect

NASA Astrophysics Data System (ADS)

Boulytchov, A.

[a4paper,12pt]article english Seismic-electric effect was applied in field to forecast subsurface archaeological cul- tural objects. A source of seismic waves were repeated blows of a heavy hammer or powerful signals of magnetostrictive installation. Main frequency used was 500 Hz. Passed a soil layer and reached a second boundary between upper clayey-sand sedi- ments and archaeological object, the seismic wave caused electromagnetic fields on the both boundaries what in general is due to dipole charge separation owe to an im- balance of streaming currents induced by the seismic wave on opposite sides of a boundary interface. According to theoretical works of Pride the electromagnetic field appears on a boundary between two layers with different physical properties in the time of seismic wave propagation. Electric responses of electromagnetic fields were measured on a surface by pair of grounded dipole antennas or by one pivot and a long wire antenna acting as a capacitive pickup. The arrival times of first series of responses correspond to the time of seismic wave propagation from a source to a boundary between soil and clayey-sand layers. The arrival times of second row of responses correspond to the time of seismic wave way from a source to a boundary of clayey-sand layer with the archaeological object. The method depths successfully investigated were between 0.5-10 m. Similar electromagnetic field on another type of geological structure was also revealed by Mikhailov et al., Massachusetts, but their signals registered from two frontiers were too faint and not evident in comparing with ours ones that occurred to be perfect and clear. Seismic-electric method field experi- ments were successfully provided for the first time on archaeological objects.

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.

Observations of the magnetopause current layer: Cases with no boundary layer and tests of recent models

NASA Technical Reports Server (NTRS)

Eastman, Timothy E.

1995-01-01

Evidence for the probable existence of magnetospheric boundary layers was first presented by Hones, et al. (1972), based on VELA satellite plasma observations (no magnetic field measurements were obtained). This magnetotail boundary layer is now known to be the tailward extension of the high-latitude boundary layer or plasma mantle (first uniquely identified using HEOS 2 plasma and field observations by Rosenbauer et al., 1975) and the low-latitude boundary layer (first uniquely identified using IMP 6 plasma and field observations by Eastman et al., 1976). The magnetospheric boundary layer is the region of magnetosheath-like plasma located Earthward of, but generally contiguous with the magnetopause. This boundary layer is typically identified by comparing low-energy (less than 10 keV) ion spectra across the magnetopause. Low-energy electron measurements are also useful for identifying the boundary layer because the shocked solar wind or magnetosheath has a characteristic spectral signature for electrons as well. However, there are magnetopause crossings where low-energy electrons might suggest a depletion layer outside the magnetopause even though the traditional field-rotation signature indicates that this same region is a boundary layer Earthward of the current layer. Our analyses avoided crossings which exhibit such ambiguities. Pristine magnetopause crossings are magnetopause crossings for which the current layer is well defined and for which there is no adjoining magnetospheric boundary layer as defined above. Although most magnetopause models to date apply to such crossings, few comparisons between such theory and observations of pristine magnetopause crossings have been made because most crossings have an associated magnetospheric boundary layer which significantly affects the applicable boundary conditions for the magnetopause current layer. Furthermore, almost no observational studies of magnetopause microstructure have been done even though key theoretical issues have been discussed for over two decades. This is because plasma instruments deployed prior to the ISEE and AMPTE missions did not have the required time resolution and most ISEE investigations to-date have focused on tests of MHD plasma models, especially reconnection. More recently, many phenomenological and theoretical models have been developed to explain the existence and characteristics of the magnetospheric boundary layers with only limited success to date. The cases with no boundary layer treated in this study provide a contrary set of conditions to those observed with a boundary layer. For the measured parameters of such cases, a successful boundary layer model should predict no plasma penetration across the magnetopause. Thus, this research project provides the first direct observational tests of magnetopause models using pristine magnetopause crossings and provides important new results on magnetopause microstructure and associated kinetic processes.

Measurements and Modeling of the Mean and Turbulent Flow Structure in High-Speed Rough-Wall Non-Equilibrium Boundary Layers

DTIC Science & Technology

2010-01-25

study builds on three basic bodies of knowledge: (1) supersonic rough wall boundary layers, (2) distorted supersonic turbulent boundary layers, and...with the boundary layer turbulence . The present study showed that secondary distortions associated with such waves significantly affect the transport...38080 14. ABSTRACT The response of a supersonic high Reynolds number turbulent boundary layer flow subjected to mechanical distortions was

Understanding the Fundamental Roles of Momentum and Vorticity Injections in Flow Control

DTIC Science & Technology

2016-09-02

production by pitched and skewed jets in a turbulent boundary layer . AIAA Journal 30, 640–647. DISTRIBUTION A: Distribution approved for public release...adverse pressure gradient along the suction surface, which ultimately results in a separated boundary layer . Such behavior of the boundary layer can... boundary layer either directly or by utilizing free stream momentum to energize the boundary layer (Gad-el-Hak, 2000a). Directly adding momentum to the

Large-eddy substitution via vortex cancellation for wall turbulence control

NASA Technical Reports Server (NTRS)

Mcginley, C. B.; Beeler, G. B.

1985-01-01

A system of co-rotating longitudinal vortices was used to introduce streamline (as opposed to wall) curvature into a turbulent wall flow. Two methods of vortex cancellation, unwinding and self-annihilation, were tested as a means of removing the vortices once they had processed most of the incoming turbulent boundary layer. Vortex unwinding, which uses vorticity of the opposite sign, was shown to be a viable method for cancelling the co-rotating vortices. Vortex self-annihilation, caused by interference effects resulting from a close initial spanwise vortex spacing, eliminated the vortices within 60 delta downstream. In each case, reductions in boundary layer entrainment were found once the vortices were cancelled.

Effect of an isolated semi-arid pine forest on the boundary layer height

NASA Astrophysics Data System (ADS)

Brugger, Peter; Banerjee, Tirtha; Kröniger, Konstantin; Preisler, Yakir; Rotenberg, Eyal; Tatarinov, Fedor; Yakir, Dan; Mauder, Matthias

2017-04-01

Forests play an important role for earth's climate by influencing the surface energy balance and CO2 concentrations in the atmosphere. Semi-arid forests and their effects on the local and regional climate are studied within the CliFF project (Climate Feedbacks and benefits of semi-arid Forests). This requires understanding of the atmospheric boundary layer over semi-arid forests, because it links the surface and the free atmosphere and determines the exchange of momentum, heat and trace gases. Our study site, Yatir, is a semi-arid isolated pine forest in the Negev desert in Israel. Higher roughness and lower albedo compared to the surrounding shrubland make it interesting to study the influences of the semi-arid Yatir forest on the boundary layer. Previous studies of the forest focused on the energy balance and secondary circulations. This study focuses on the boundary layer structure above the forest, in particular the boundary layer height. The boundary layer height is an essential parameter for many applications (e.g. construction of convective scaling parameters or air pollution modeling). We measured the boundary layer height upwind, over and downwind of the forest. In addition we measured at two sites wind profiles within the boundary layer and turbulent fluxes at the surface. This allows us to quantify the effects of the forest on boundary layer compared to the surrounding shrubland. Results show that the forest increases the boundary layer height in absence of a strong boundary layer top inversion. A model of the boundary layer height based on eddy-covariance data shows some agreement to the measurements, but fails during anticyclonic conditions and the transition to the nocturnal boundary layer. More complex models accounting for large scale influences are investigated. Further influences of the forest and surrounding shrubland on the turbulent transport of energy are discussed in a companion presentation (EGU2017-2219).

Spatial Linear Instability of Confluent Wake/Boundary Layers

NASA Technical Reports Server (NTRS)

Liou, William W.; Liu, Feng-Jun; Rumsey, C. L. (Technical Monitor)

2001-01-01

The spatial linear instability of incompressible confluent wake/boundary layers is analyzed. The flow model adopted is a superposition of the Blasius boundary layer and a wake located above the boundary layer. The Orr-Sommerfeld equation is solved using a global numerical method for the resulting eigenvalue problem. The numerical procedure is validated by comparing the present solutions for the instability of the Blasius boundary layer and for the instability of a wake with published results. For the confluent wake/boundary layers, modes associated with the boundary layer and the wake, respectively, are identified. The boundary layer mode is found amplified as the wake approaches the wall. On the other hand, the modes associated with the wake, including a symmetric mode and an antisymmetric mode, are stabilized by the reduced distance between the wall and the wake. An unstable mode switching at low frequency is observed where the antisymmetric mode becomes more unstable than the symmetric mode when the wake velocity defect is high.

A nonperturbing boundary-layer transition detection

NASA Astrophysics Data System (ADS)

Ohare, J. E.

1985-01-01

A laser interferometer technique is being applied to the characterization of boundary-layer conditions on models in supersonic and hypersonic wind tunnels in the von Karman Facility at Arnold Engineering Development Center (AEDC). The Boundary-Layer Transition Detector (BLTD), based on lateral interferometry, is applicable for determining the turbulence frequency spectrum of boundary layers in compressible flow. The turbulence, in terms of air density fluctuations, is detected by monitoring interferometric fringe phase shifts (in real time) formed by one beam which passes through the boundary layer and a reference beam which is outside the boundary layer. This technique is nonintrusive to the flow field unlike other commonly used methods such as pitot tube probing and hot-wire anemometry. Model boundary-layer data are presented at Mach 8 and compared with data recorded using other methods during boundary-layer transition from laminar to turbulent flow. Spectra from the BLTD reveal the presence of a high-frequency peak during transition, which is characteristic of spectra obtained with hot wires. The BLTD is described along with operational requirements and limitations.

A Nonperturbing Boundary-Layer Transition Detector

NASA Astrophysics Data System (ADS)

O'Hare, J. E.

1986-01-01

A laser interferometer technique is being applied to the characterization of boundary-layer conditions on models in supersonic and hypersonic wind tunnels in the von Kaman Facility at Arnold Engineering Development Center (AEDC). The Boundary-Layer Transition Detector (BLTD), based on lateral interferometry, is applicable for determining the turbulence frequency spectrum of boundary layers in compressible flow. The turbulence, in terms of air density fluctuations, is detected by monitoring interferometric fringe phase shifts (in real time) formed by one beam which passes through the boundary layer and a reference beam which is outside the boundary layer. This technique is nonintrusive to the flow field unlike other commonly used methods such as pitot tube probing and hot-wire anemometry. Model boundary-layer data are presented at Mach 8 and compared with data recorded using other methods during boundary-layer transition from laminar to turbulent flow. Spectra from the BLTD reveal the presence of a high-frequency peak during transition, which is characteristic of spectra obtained with hot wires. The BLTD is described along with operational requirements and limitations.

Comparison of theoretical and experimental boundary-layer development in a Mach 2.5 mixed-compression inlet

NASA Technical Reports Server (NTRS)

Hingst, W. R.; Towne, C. E.

1974-01-01

An analytical investigation was made of the boundary layer flow in an axisymmetric Mach 2.5 mixed compression inlet, and the results were compared with experimental measurements. The inlet tests were conducted in the Lewis 10- by 10-foot supersonic wind tunnel at a unit Reynolds number of 8.2 million/m. The inlet incorporated porous bleed regions for boundary layer control, and the effect of this bleed was taken into account in the analysis. The experimental boundary layer data were analyzed by using similarity laws from which the skin friction coefficient was obtained. The boundary layer analysis included predictions of laminar and turbulent boundary layer growth, transition, and the effects of the shock boundary layer interactions. In addition, the surface static pressures were compared with those obtained from an inviscid characteristics program. The results of investigation showed that the analytical techniques gave satisfactory predictions of the boundary layer flow except in regions that were badly distorted by the terminal shock.

Boundary layers in centrifugal compressors. [application of boundary layer theory to compressor design

NASA Technical Reports Server (NTRS)

Dean, R. C., Jr.

1974-01-01

The utility of boundary-layer theory in the design of centrifugal compressors is demonstrated. Boundary-layer development in the diffuser entry region is shown to be important to stage efficiency. The result of an earnest attempt to analyze this boundary layer with the best tools available is displayed. Acceptable prediction accuracy was not achieved. The inaccuracy of boundary-layer analysis in this case would result in stage efficiency prediction as much as four points low. Fluid dynamic reasons for analysis failure are discussed with support from flow data. Empirical correlations used today to circumnavigate the weakness of the theory are illustrated.

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

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

NASA Technical Reports Server (NTRS)

1987-01-01

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

In-flight transition measurement on a 10 deg cone at Mach numbers from 0.5 to 2.0

NASA Technical Reports Server (NTRS)

Fisher, D. F.; Dougherty, N. S., Jr.

1982-01-01

Boundary layer transition measurements were made in flight on a 10 deg transition cone tested previously in 23 wind tunnels. The cone was mounted on the nose of an F-15 aircraft and flown at Mach numbers room 0.5 to 2.0 and altitudes from 1500 meters (5000 feet) to 15,000 meters (50,000 feet), overlapping the Mach number/Reynolds number envelope of the wind tunnel tests. Transition was detected using a traversing pitot probe in contact with the surface. Data were obtained near zero cone incidence and adiabatic wall temperature. Transition Reynolds number was found to be a function of Mach number and of the ratio of wall temperature to adiabatic all temperature. Microphones mounted flush with the cone surface measured free-stream disturbances imposed on the laminar boundary layer and identified Tollmien-Schlichting waves as the probable cause of transition. Transition Reynolds number also correlated with the disturbance levels as measured by the cone surface microphones under a laminar boundary layer as well as the free-stream impact.

Effect of wakes from moving upstream rods on boundary layer separation from a high lift airfoil

NASA Astrophysics Data System (ADS)

Volino, Ralph J.

2011-11-01

Highly loaded airfoils in turbines allow power generation using fewer airfoils. High loading, however, can cause boundary layer separation, resulting in reduced lift and increased aerodynamic loss. Separation is affected by the interaction between rotating blades and stationary vanes. Wakes from upstream vanes periodically impinge on downstream blades, and can reduce separation. The wakes include elevated turbulence, which can induce transition, and a velocity deficit, which results in an impinging flow on the blade surface known as a ``negative jet.'' In the present study, flow through a linear cascade of very high lift airfoils is studied experimentally. Wakes are produced with moving rods which cut through the flow upstream of the airfoils, simulating the effect of upstream vanes. Pressure and velocity fields are documented. Wake spacing and velocity are varied. At low Reynolds numbers without wakes, the boundary layer separates and does not reattach. At high wake passing frequencies separation is largely suppressed. At lower frequencies, ensemble averaged velocity results show intermittent separation and reattachment during the wake passing cycle. Supported by NASA.

High-Speed Boundary-Layer Transition: Study of Stationary Crossflow Using Spectral Analysis

NASA Astrophysics Data System (ADS)

McGuire, Patrick Joseph

Crossflow instability is primary cause of boundary-layer transition on swept wings used in high-speed applications. Delaying the downstream location of transition would drastically reduce the viscous drag over the wing surface, and subsequently improves the overall aircraft efficiency. By studying the development of instability growth rates and how they interact with the surroundings, researchers can control the crossflow transition location. Experiments on the 35° swept-wing model were performed in the NASA Langley 20-Inch Supersonic Wind Tunnel with Mach 2.0 flow conditions and 20 μm tall discrete roughness elements (DRE) with varying spacing placed along the leading edge. Fluorene was used as the sublimating chemical in the surface flow visualization technique to observe the transition front and stationary crossflow vortex patterns in the laminar flow region. Spatial spectral decomposition was completed on high-resolution images of sublimating chemical runs using a newly developed image processing technique. Streamwise evolution of the vortex track wavelengths within the laminar boundary-layer region was observed. The spectral information was averaged to produce dominant modes present throughout the laminar region.

Correlation of transonic-cone Preston-tube data and skin friction. [characterizing the flow quality of a transonic wind tunnel

NASA Technical Reports Server (NTRS)

Reed, T. D.

1981-01-01

The distribution of Preston tube pressures within turbulent boundary layers along the surface of a sharp-nosed, ten degree cone was correlated with theoretical values of turbulent skin friction for freestream Mach numbers less than one. The mini-basic computer code, the Wu and Lock computer code, and the STAN-5 computer code were used to analyze the data and to solve the boundary layer conservation equations. The skin friction which results from using Preston tube pressures in the correlation equation, has a rms error of 1.125 percent. It was found that the effective center of the probe is not a constant but increases as the surface distance increases. For a specified unit Reynolds number, the effective center of the probe decreases as the Mach number increases. The variation of the fluid (air) properties across the face of the probe may be neglected for subsonic flows. The possible transverse errors caused by the use of the concept of a virtual origin for the turbulent boundary layer were investigated and found to be negligible.

Flow Measurements over a Biomimetic Surface Roughness Microgeometry

NASA Astrophysics Data System (ADS)

Lang, Amy; Hidalgo, Pablo; Westcott, Matthew

2007-11-01

Certain species of sharks (e.g. shortfin mako) have a skin structure that results in a bristling of their denticles (scales) during increased swimming speeds. This unique surface geometry results in the formation of a 3D array of cavities* (d-type roughness geometry) within the shark skin, thus causing it to potentially act as a means of boundary layer control. Initial work is confined to scaling up the geometry from 0.2 mm on the shark skin to 2 cm, with a scaling down in characteristic velocity from 10 - 20 m/s to 10 - 20 cm/s for laminar flow boundary layer water tunnel studies over a shark skin model. The hypothesized formation of cavity vortices within the shark skin replica has been measured using DPIV. We have also shown that with the sufficient growth of a boundary layer upstream of the model (local Re = 200,000), transition is not tripped by the surface and the flow skips over the cavities. Support for this research by a NSF SGER grant (CTS-0630489), Lindbergh Foundation Grant and a University of Alabama RAC grant is gratefully acknowledged. * Patent pending.

Flight test results of riblets at supersonic speeds

NASA Technical Reports Server (NTRS)

Zuniga, Fanny A.; Anderson, Bianca T.; Bertelrud, Arild

1992-01-01

A flight experiment to test and evaluate the skin friction drag characteristics of a riblet surface in turbulent flow at supersonic speeds was conducted at NASA Dryden. Riblets of groove sizes 0.0030 and 0.0013 in. were mounted on the F-104G flight test fixture. The test surfaces were surveyed with boundary layer rakes and pressure orifices to examine the boundary layer profiles and pressure distributions of the flow. Skin friction reductions caused by the riblet surface were reported based on measured differences of momentum thickness between the smooth and riblet surfaces obtained from the boundary layer data. Flight test results for the 0.0030 in. riblet show skin friction reductions of 4 to 8 % for Mach numbers ranging from 1.2 to 1.6 and Reynolds numbers ranging from 2 to 3.4 million per unit foot. The results from the 0.0013 in. riblets show skin friction reductions of 4 to 15 % for Mach 1.2 to 1.4 and Reynolds numbers ranging from 3.6 to 6 million per unit foot.

A Combined CFD/Characteristic Method for Prediction and Design of Hypersonic Inlet with Nose Bluntness

NASA Astrophysics Data System (ADS)

Gao, Wenzhi; Li, Zhufei; Yang, Jiming

Leading edge bluntness is widely used in hypersonic inlet design for thermal protection[1]. Detailed research of leading edge bluntness on hypersonic inlet has been concentrated on shock shape correlation[2], boundary layer flow[3], inlet performance[4], etc. It is well known that blunted noses cause detached bow shocks which generate subsonic regions around the noses and entropy layers in the flowfield.

Detection of Frictional Heating on Faults Using Raman Spectra of Carbonaceous Material

NASA Astrophysics Data System (ADS)

Ito, K.; Ujiie, K.; Kagi, H.

2017-12-01

Raman spectra of carbonaceous material (RSCM) have been used as geothermometer in sedimentary and metamorphic rocks. However, it remains poorly understood whether RSCM are useful for detecting past frictional heating on faults. To detect increased heating during seismic slip, we examine the thrust fault in the Jurassic accretionary complex, central Japan. The thrust fault zone includes 10 cm-thick cataclasite and a few mm-thick dark layer. The cataclasite is characterized by fragments of black and gray chert in the black carbonaceous mudstone matrix. The dark layer is marked by intensely cracked gray chert fragments in the dark matrix of carbonaceous mudstone composition, which bounds the fractured gray chert above from the cataclasite below. The RSCM are analyzed for carbonaceous material in the cataclasite, dark layer, and host rock <10 mm from cataclasite and dark layer boundaries. The result indicates that there is no increased carbonization in the cataclasite. In contrast, the dark layer and part of host rocks <2 mm from the dark layer boundaries show prominent increase in carbonization. The absent of increased carbonization in the cataclasite could be attributed to insufficient frictional heating associated with distributed shear and/or faulting at low slip rates. The dark layer exhibits the appearance of fault and injection veins, and the dark layer boundaries are irregularly embayed or intensely cracked; these features have been characteristically observed in pseudotachylytes. Therefore, the increased carbonization in the dark layer is likely resulted from increased heating during earthquake faulting. The intensely cracked fragments in the dark layer and cracked wall rocks may reflect thermal fracturing in chert, which is caused by heat conduction from the molten zone. We suggest that RSCM are useful for the detection of increased heating on faults, particularly when the temperature is high enough for frictional melting and thermal fracturing.

Evaluation of the heat balance constituents of the upper mixed layer in the North Atlantic

NASA Astrophysics Data System (ADS)

Polonsky, A. B.; Sukhonos, P. A.

2016-11-01

Different physical mechanisms which cause interannual and interdecadal temperature anomalies in the upper mixed layer (UML) of the North Atlantic are investigated using the data of ORA-S3 reanalysis for the period of 1959-2011. It is shown that the annual mean heat budget in UML is mainly caused by the balance between advective heat transfer and horizontal turbulent mixing (estimated as a residual term in the equation of thermal balance). The local UML temperature change and contribution from the heat fluxes on the lower boundary of the UML to the heat budget of the upper layer are insignificant for the time scale under consideration. The contribution of the heat fluxes on the upper UML boundary to the low-frequency variability of the upper layer temperature in the whole North Atlantic area is substantially less than 30%. Areas like the northwestern part of the Northern Subtropical Anticyclonic Gyre (NSAG), where their contribution exceeds 30-60%, are exceptions. The typical time scales of advective heat transfer variability are revealed. In the NSAG area, an interannual variability associated with the North Atlantic Oscillation dominates, while in the North Atlantic subpolar gyre, an interdecadal variability of advective transfers with periods of more than 30 years prevails.

Interaction of Atmospheric Turbulence with Blade Boundary Layer Dynamics on a 5MW Wind Turbine using Blade-Boundary-Layer-Resolved CFD with hybrid URANS-LES.

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

Vijayakumar, Ganesh; Brasseur, James; Lavely, Adam

We describe the response of the NREL 5 MW wind turbine blade boundary layer to the passage of atmospheric turbulence using blade-boundary-layer-resolved computational fluid dynamics with hybrid URANS-LES modeling.

Semiconductor P-I-N detector

DOEpatents

Sudharsanan, Rengarajan; Karam, Nasser H.

2001-01-01

A semiconductor P-I-N detector including an intrinsic wafer, a P-doped layer, an N-doped layer, and a boundary layer for reducing the diffusion of dopants into the intrinsic wafer. The boundary layer is positioned between one of the doped regions and the intrinsic wafer. The intrinsic wafer can be composed of CdZnTe or CdTe, the P-doped layer can be composed of ZnTe doped with copper, and the N-doped layer can be composed of CdS doped with indium. The boundary layers is formed of an undoped semiconductor material. The boundary layer can be deposited onto the underlying intrinsic wafer. The doped regions are then typically formed by a deposition process or by doping a section of the deposited boundary layer.

Practical calculation of laminar and turbulent bled-off boundary layers

NASA Technical Reports Server (NTRS)

Eppler, R.

1978-01-01

Bleed-off of boundary layer material is shown to be an effective means for reducing drag by conserving the laminar boundary layer and preventing separation of the turbulent boundary layer. The case in which the two effects of bleed-off overlap is examined. Empirical methods are extended to the case of bleed-off. Laminar and turbulent boundary layers are treated simultaneously and the approximation differential equations are solved without an uncertain error. The case without bleed-off is also treated.

Tables for correcting airfoil data obtained in the Langley 0.3-meter transonic cryogenic tunnel for sidewall boundary-layer effects

NASA Technical Reports Server (NTRS)

Jenkins, R. V.; Adcock, J. B.

1986-01-01

Tables for correcting airfoil data taken in the Langley 0.3-meter Transonic Cryogenic Tunnel for the presence of sidewall boundary layer are presented. The corrected Mach number and the correction factor are minutely altered by a 20 percent change in the boundary layer virtual origin distance. The sidewall boundary layer displacement thicknesses measured for perforated sidewall inserts and without boundary layer removal agree with the values calculated for solid sidewalls.

The Role of Boundary-Layer and Cumulus Convection on Dust Emission, Mixing, and Transport Over Desert Regions

NASA Astrophysics Data System (ADS)

Takemi, T.; Yasui, M.

2005-12-01

Recent studies on dust emission and transport have been concerning the small-scale atmospheric processes in order to incorporate them as a subgrid-scale effect in large-scale numerical prediction models. In the present study, we investigated the dynamical processes and mechanisms of dust emission, mixing, and transport induced by boundary-layer and cumulus convection under a fair-weather condition over a Chinese desert. We performed a set of sensitivity experiments as well as a control simulation in order to examine the effects of vertical wind shear, upper-level wind speed, and moist convection by using a simplified and idealized modeling framework. The results of the control experiment showed that surface dust emission was at first caused before the noon time by intense convective motion which not only developed in the boundary layer but also penetrated into the free troposphere. In the afternoon hours, boundary-layer dry convection actively mixed and transported dust within the boundary layer. Some of the convective cells penetrated above the boundary layer, which led to the generation of cumulus clouds and hence gradually increased the dust content in the free troposphere. Coupled effects of the dry and moist convection played an important role in inducing surface dust emission and transporting dust vertically. This was clearly demonstrated through the comparison of the results between the control and the sensitivity experiments. The results of the control simulation were compared with lidar measurements. The simulation well captured the observed diurnal features of the upward transport of dust. We also examined the dependence of the simulated results on grid resolution: the grid size was changed from 250 m up to 4 km. It was found that there was a significant difference between the 2-km and 4-km grids. If a cumulus parameterization was added to the 4-km grid run, the column content was comparable to the other cases. This result suggests that subgrid parameterizations are required if the grid size is larger than the order of 1 km in a fair-weather condition.

Discussion of Boundary-Layer Characteristics Near the Wall of an Axial-Flow Compressor

NASA Technical Reports Server (NTRS)

Mager, Artur; Mohoney, John J; Budinger, Ray E

1952-01-01

The boundary-layer velocity profiles in the tip region of an axial-flow compressor downstream of the guide vanes and downstream of the rotor were measured by use of total-pressure and claw-type yaw probes. These velocities were resolved into two components: one along the streamline of the flow outside the boundary layer, and the other perpendicular to it. The affinity among all profiles was thus demonstrated with the boundary-layer thickness and the deflection of the boundary layer at the wall as the generalizing parameters. By use of these results and the momentum-integral equations, boundary-layer characteristics on the walls of an axial-flow compressor were qualitatively evaluated.

Experimental Investigation of Separated and Transitional Boundary Layers Under Low-Pressure Turbine Airfoil Conditions

NASA Technical Reports Server (NTRS)

Hultgren, Lennart S.; Volino, Ralph J.

2002-01-01

Modern low-pressure turbine airfoils are subject to increasingly stronger pressure gradients as designers impose higher loading in an effort to improve efficiency and to reduce part count. The adverse pressure gradients on the suction side of these airfoils can lead to boundary-layer separation, particularly under cruise conditions. Separation bubbles, notably those which fail to reattach, can result in a significant degradation of engine efficiency. Accurate prediction of separation and reattachment is hence crucial to improved turbine design. This requires an improved understanding of the transition flow physics. Transition may begin before or after separation, depending on the Reynolds number and other flow conditions, has a strong influence on subsequent reattachment, and may even eliminate separation. Further complicating the problem are the high free-stream turbulence levels in a real engine environment, the strong pressure gradients along the airfoils, the curvature of the airfoils, and the unsteadiness associated with wake passing from upstream stages. Because of the complicated flow situation, transition in these devices can take many paths that can coexist, vary in importance, and possibly also interact, at different locations and instances in time. The present work was carried out in an attempt to systematically sort out some of these issues. Detailed velocity measurements were made along a flat plate subject to the same nominal dimensionless pressure gradient as the suction side of a modern low-pressure turbine airfoil ('Pak-B'). The Reynolds number based on wetted plate length and nominal exit velocity, Re, was varied from 50;000 to 300; 000, covering cruise to takeoff conditions. Low, 0.2%, and high, 7%, inlet free-stream turbulence intensities were set using passive grids. These turbulence levels correspond to about 0.2% and 2.5% turbulence intensity in the test section when normalized with the exit velocity. The Reynolds number and free-stream turbulence level do not have a significant effect on the location of boundary-layer separation unless they are high enough to induce transition upstream of separation. The location and extent of the transition zone, in contrast, depend strongly on Re and TI. The beginning of reattachment closely follows the onset of transition. Under low free-stream turbulence conditions the boundary layer is laminar at separation and then begins to exhibit fluctuations in a finite frequency band in the shear layer over the separation bubble. These fluctuations are due to instability waves. The fluctuations grow in magnitude, higher harmonics are generated, and finally lead to a breakdown to turbulence. Transition begins in the shear layer, but quickly spreads to the near wall region and causes the boundary layer to reattach. The transition is rapid and the resulting turbulence contains a full range of high and low frequencies. Under high free-stream turbulence conditions, slowly growing low-frequency fluctuations are induced in the pretransitional boundary layer by the free-stream. The separation bubbles are considerably thinner than in the low TI cases, resulting in thinner boundary layers at the end of the test wall. At Re=50,000 and 100,000, the pre-transitional boundary layer separates at about the same location as in the low TI cases. Transition occurs through a bypass mode, begins upstream of the corresponding low-TI location, and proceeds in a manner similar to that of an attached boundary layer. Under high TI at Re=200,000 and 300,000, transition begins before separation. The boundary layer may separate, but if it does the separation bubble is very short and does not significantly affect the downstream development of the boundary layer. A comparison is made to previous work in a simulated cascade.

Prediction of turbulent shear layers in turbomachines

NASA Technical Reports Server (NTRS)

Bradshaw, P.

1974-01-01

The characteristics of turbulent shear layers in turbomachines are compared with the turbulent boundary layers on airfoils. Seven different aspects are examined. The limits of boundary layer theory are investigated. Boundary layer prediction methods are applied to analysis of the flow in turbomachines.

Study of boundary-layer transition using transonic-cone preston tube data

NASA Technical Reports Server (NTRS)

Reed, T. D.; Moretti, P. M.

1980-01-01

The laminar boundary layer on a 10 degree cone in a transonic wind tunnel was studied. The inviscid flow and boundary layer development were simulated by computer programs. The effects of pitch and yaw angles on the boundary layer were examined. Preston-tube data, taken on the boundary-layer-transition cone in the NASA Ames 11 ft transonic wind tunnel, were used to develope a correlation which relates the measurements to theoretical values of laminar skin friction. The recommended correlation is based on a compressible form of the classical law-of-the-wall. The computer codes successfully simulates the laminar boundary layer for near-zero pitch and yaw angles. However, in cases of significant pitch and/or yaw angles, the flow is three dimensional and the boundary layer computer code used here cannot provide a satisfactory model. The skin-friction correlation is thought to be valid for body geometries other than cones.

Stability of boundary layer flow based on energy gradient theory

NASA Astrophysics Data System (ADS)

Dou, Hua-Shu; Xu, Wenqian; Khoo, Boo Cheong

2018-05-01

The flow of the laminar boundary layer on a flat plate is studied with the simulation of Navier-Stokes equations. The mechanisms of flow instability at external edge of the boundary layer and near the wall are analyzed using the energy gradient theory. The simulation results show that there is an overshoot on the velocity profile at the external edge of the boundary layer. At this overshoot, the energy gradient function is very large which results in instability according to the energy gradient theory. It is found that the transverse gradient of the total mechanical energy is responsible for the instability at the external edge of the boundary layer, which induces the entrainment of external flow into the boundary layer. Within the boundary layer, there is a maximum of the energy gradient function near the wall, which leads to intensive flow instability near the wall and contributes to the generation of turbulence.

Wind and boundary layers in Rayleigh-Bénard convection. II. Boundary layer character and scaling.

PubMed

van Reeuwijk, Maarten; Jonker, Harm J J; Hanjalić, Kemo

2008-03-01

The scaling of the kinematic boundary layer thickness lambda(u) and the friction factor C(f) at the top and bottom walls of Rayleigh-Bénard convection is studied by direct numerical simulation (DNS). By a detailed analysis of the friction factor, a new parameterisation for C(f) and lambda(u) is proposed. The simulations were made of an L/H=4 aspect-ratio domain with periodic lateral boundary conditions at Ra=(10(5), 10(6), 10(7), 10(8)) and Pr=1. The continuous spectrum, as well as significant forcing due to Reynolds stresses, clearly indicates a turbulent character of the boundary layer, while viscous effects cannot be neglected, judging from the scaling of classical integral boundary layer parameters with Reynolds number. Using a conceptual wind model, we find that the friction factor C(f) should scale proportionally to the thermal boundary layer thickness as C(f) proportional variant lambda(Theta)/H, while the kinetic boundary layer thickness lambda(u) scales inversely proportionally to the thermal boundary layer thickness and wind Reynolds number lambda(u)/H proportional variant (lambda(Theta)/H)(-1)Re(-1). The predicted trends for C(f) and lambda(u) are in agreement with DNS results.

Lidar Measurements of Wind, Moisture and Boundary Layer Evolution in a Dryline During IHOP2002

NASA Technical Reports Server (NTRS)

Demoz, Belay; Evans, Keith; DiGirolamo, Paolo; Wang, Zhien; Whiteman, David; Schwemmer, Geary; Gentry, Bruce; Miller, David

2003-01-01

Variability in the convective boundary layer moisture, wind and temperature fields and their importance in the forecasting and understanding of storms have been discussed in the literature. These variations have been reported in relation to frontal zones, stationary boundaries and during horizontal convective rolls. While all three vary substantially in the convective boundary layer, moisture poses a particular challenge. Moisture or water vapor concentration (expressed as a mass mixing ratio, g/kg), is conserved in all meteorological processes except condensation and evaporation. The water vapor mixing ratio often remains distinct across an air -mass boundary even when the temperature difference is indistinct. These properties make it an ideal choice in visualizing and understanding many of the atmosphere's dynamic features. However, it also presents a unique measurement challenge because water vapor content can vary by more than three orders of magnitude in the troposphere. Characterization of the 3D-distribution of water vapor is also difficult as water vapor observations can suffer from large sampling errors and substantial variability both in the vertical and horizontal. This study presents groundbased measurements of wind, boundary layer structure and water vapor mixing ratio measurements observed by three co-located lidars. This presentation will focus on the evolution and variability of moisture and wind in the boundary layer during a dry line event that occurred on 22 May 2002. These data sets and analyses are unique in that they combine simultaneous measurements of wind, moisture and CBL structure to study the detailed thermal variability in and around clear air updrafts during a dryline event. It will quantify the variation caused by, in and around buoyant plumes and across a dryline. The data presented here were collected in the panhandle of Oklahoma as part of the International BO Project (IHOP-2002), a field experiment that took place over the Southern Great Plains (SGP) of the United States from 13 May to 30 June 2002. The chief goal of IHOP-2002 is to improve characterization of the four-dimensional (4-D) distribution of water vapor and its application to improving the understanding and prediction of convection

Lidar Measurements of Wind, Moisture, and Boundary Layer Evolution in a Dry Line during 1HOP 2002

NASA Technical Reports Server (NTRS)

Demoz, Belay; Evans, Keith; DiGirolamo, Paolo; Wang, Zhe-In; Whiteman, David; Schwemmer, Geary; Gentry, Bruce; Miller, David; Palm, Stephen

2002-01-01

Variability in the convective boundary layer moisture, wind and temperature fields and their importance in the forecasting and understanding of storms have been discussed in the literature. These . variations have been reported in relation to frontal zones, stationary boundaries and during horizontal convective rolls. While all three vary substantially in the convective boundary layer, moisture poses a particular challenge. Moisture or water vapor concentration (expressed as a mass mixing ratio, g/kg), is conserved in all meteorological processes except condensation and evaporation. The water vapor mixing ratio often remains distinct across an air-mass boundary even when the temperature difference is indistinct. These properties make it an ideal choice in visualizing and understanding many of the atmosphere's dynamic features. However, it also presents a unique measurement challenge because water vapor content can vary by more than three orders of magnitude in the troposphere. Characterization of the 3D-distribution of water vapor is also difficult as water vapor observations can suffer from large sampling errors and substantial variability both in the vertical and horizontal. This study presents ground-based measurements of wind, boundary layer structure and water vapor mixing ratio measurements observed by three co-located lidars. This presentation will focus on the evolution and variability of moisture and wind in the boundary layer during a dry line event that occurred on 22 May 2002. These data sets and analyses are unique in that they combine simultaneous measurements of wind, moisture and CBL structure to study the detailed thermal variability in and around clear air updrafts during a dryline event. It will quantify the variation caused by, in and around buoyant plumes and across a dryline. The data presented here were collected in the panhandle of Oklahoma as part of the International H2O Project (MOP-2002), a field experiment that took place over the Southern Great Plains (SGP) of the United States from 13 May to 30 June 2002. The chief goal of MOP-2002 is to improve characterization of the four-dimensional (4-D) distribution of water vapor and its application to improving the understanding and prediction of convection

Magnetic field reversals, polar wander, and core-mantle coupling.

PubMed

Courtillot, V; Besse, J

1987-09-04

True polar wander, the shifting of the entire mantle relative to the earth's spin axis, has been reanalyzed. Over the last 200 million years, true polar wander has been fast (approximately 5 centimeters per year) most of the time, except for a remarkable standstill from 170 to 110 million years ago. This standstill correlates with a decrease in the reversal frequency of the geomagnetic field and episodes of continental breakup. Conversely, true polar wander is high when reversal frequency increases. It is proposed that intermittent convection modulates the thickness of a thermal boundary layer at the base of the mantle and consequently the core-to-mantle heat flux. Emission of hot thermals from the boundary layer leads to increases in mantle convection and true polar wander. In conjunction, cold thermals released from a boundary layer at the top of the liquid core eventually lead to reversals. Changes in the locations of subduction zones may also affect true polar wander. Exceptional volcanism and mass extinctions at the Cretaceous-Tertiary and Permo-Triassic boundaries may be related to thermals released after two unusually long periods with no magnetic reversals. These environmental catastrophes may therefore be a consequence of thermal and chemical couplings in the earth's multilayer heat engine rather than have an extraterrestrial cause.

Unsteady transonic viscous-inviscid interaction using Euler and boundary-layer equations

NASA Technical Reports Server (NTRS)

Pirzadeh, Shahyar; Whitfield, Dave

1989-01-01

The Euler code is used extensively for computation of transonic unsteady aerodynamics. The boundary layer code solves the 3-D, compressible, unsteady, mean flow kinetic energy integral boundary layer equations in the direct mode. Inviscid-viscous coupling is handled using porosity boundary conditions. Some of the advantages and disadvantages of using the Euler and boundary layer equations for investigating unsteady viscous-inviscid interaction is examined.

Improving graph-based OCT segmentation for severe pathology in retinitis pigmentosa patients

NASA Astrophysics Data System (ADS)

Lang, Andrew; Carass, Aaron; Bittner, Ava K.; Ying, Howard S.; Prince, Jerry L.

2017-03-01

Three dimensional segmentation of macular optical coherence tomography (OCT) data of subjects with retinitis pigmentosa (RP) is a challenging problem due to the disappearance of the photoreceptor layers, which causes algorithms developed for segmentation of healthy data to perform poorly on RP patients. In this work, we present enhancements to a previously developed graph-based OCT segmentation pipeline to enable processing of RP data. The algorithm segments eight retinal layers in RP data by relaxing constraints on the thickness and smoothness of each layer learned from healthy data. Following from prior work, a random forest classifier is first trained on the RP data to estimate boundary probabilities, which are used by a graph search algorithm to find the optimal set of nine surfaces that fit the data. Due to the intensity disparity between normal layers of healthy controls and layers in various stages of degeneration in RP patients, an additional intensity normalization step is introduced. Leave-one-out validation on data acquired from nine subjects showed an average overall boundary error of 4.22 μm as compared to 6.02 μm using the original algorithm.

Feedback effects of boundary-layer meteorological factors on cumulative explosive growth of PM2.5 during winter heavy pollution episodes in Beijing from 2013 to 2016

NASA Astrophysics Data System (ADS)

Zhong, Junting; Zhang, Xiaoye; Dong, Yunsheng; Wang, Yaqiang; Liu, Cheng; Wang, Jizhi; Zhang, Yangmei; Che, Haochi

2018-01-01

In January 2013, February 2014, December 2015 and December 2016 to 10 January 2017, 12 persistent heavy aerosol pollution episodes (HPEs) occurred in Beijing, which received special attention from the public. During the HPEs, the precise cause of PM2.5 explosive growth (mass concentration at least doubled in several hours to 10 h) is uncertain. Here, we analyzed and estimated relative contributions of boundary-layer meteorological factors to such growth, using ground and vertical meteorological data. Beijing HPEs are generally characterized by the transport stage (TS), whose aerosol pollution formation is primarily caused by pollutants transported from the south of Beijing, and the cumulative stage (CS), in which the cumulative explosive growth of PM2.5 mass is dominated by stable atmospheric stratification characteristics of southerly slight or calm winds, near-ground anomalous inversion, and moisture accumulation. During the CSs, observed southerly weak winds facilitate local pollutant accumulation by minimizing horizontal pollutant diffusion. Established by TSs, elevated PM2.5 levels scatter more solar radiation back to space to reduce near-ground temperature, which very likely causes anomalous inversion. This surface cooling by PM2.5 decreases near-ground saturation vapor pressure and increases relative humidity significantly; the inversion subsequently reduces vertical turbulent diffusion and boundary-layer height to trap pollutants and accumulate water vapor. Appreciable near-ground moisture accumulation (relative humidity > 80 %) would further enhance aerosol hygroscopic growth and accelerate liquid-phase and heterogeneous reactions, in which incompletely quantified chemical mechanisms need more investigation. The positive meteorological feedback noted on PM2.5 mass explains over 70 % of cumulative explosive growth.

Estimation of Stresses in a Dry Sand Layer Tested on Shaking Table

NASA Astrophysics Data System (ADS)

Sawicki, Andrzej; Kulczykowski, Marek; Jankowski, Robert

2012-12-01

Theoretical analysis of shaking table experiments, simulating earthquake response of a dry sand layer, is presented. The aim of such experiments is to study seismic-induced compaction of soil and resulting settlements. In order to determine the soil compaction, the cyclic stresses and strains should be calculated first. These stresses are caused by the cyclic horizontal acceleration at the base of soil layer, so it is important to determine the stress field as function of the base acceleration. It is particularly important for a proper interpretation of shaking table tests, where the base acceleration is controlled but the stresses are hard to measure, and they can only be deduced. Preliminary experiments have shown that small accelerations do not lead to essential settlements, whilst large accelerations cause some phenomena typical for limit states, including a visible appearance of slip lines. All these problems should be well understood for rational planning of experiments. The analysis of these problems is presented in this paper. First, some heuristic considerations about the dynamics of experimental system are presented. Then, the analysis of boundary conditions, expressed as resultants of respective stresses is shown. A particular form of boundary conditions has been chosen, which satisfies the macroscopic boundary conditions and the equilibrium equations. Then, some considerations are presented in order to obtain statically admissible stress field, which does not exceed the Coulomb-Mohr yield conditions. Such an approach leads to determination of the limit base accelerations, which do not cause the plastic state in soil. It was shown that larger accelerations lead to increase of the lateral stresses, and the respective method, which may replace complex plasticity analyses, is proposed. It is shown that it is the lateral stress coefficient K0 that controls the statically admissible stress field during the shaking table experiments.

Inventory of File gfs.t06z.smartguam00.tm00.grib2

Science.gov Websites

boundary layer WDIR analysis Wind Direction (from which blowing) [degtrue] 013 planetary boundary layer WIND analysis Wind Speed [m/s] 014 planetary boundary layer RH analysis Relative Humidity [%] 015 planetary boundary layer DIST analysis Geometric Height [m] 016 surface 4LFTX analysis Best (4 layer) Lifted

Observations of the Summertime Boundary Layer over the Ross Ice Shelf, Antarctica Using SUMO UAVs

NASA Astrophysics Data System (ADS)

Nigro, M. A.; Cassano, J. J.; Jolly, B.; McDonald, A.

2014-12-01

During January 2014 Small Unmanned Meteorological Observer (SUMO) unmanned aerial vehicles (UAVs) were used to observe the boundary layer over the Ross Ice Shelf, Antarctica. A total of 41 SUMO flights were completed during a 9-day period with a maximum of 11 flights during a single day. Flights occurred as frequently as every 1.5 hours so that the time evolution of the boundary layer could be documented. On almost all of the flights the boundary layer was well mixed from the surface to a depth of less than 50 m to over 350 m. The depth of the well-mixed layer was observed to both increase and decrease over the course of an individual day suggesting that processes other than entrainment were altering the boundary layer depth. The well-mixed layer was observed to both warm and cool during the field campaign indicating that advective processes as well as surface fluxes were acting to control the temporal evolution of the boundary layer temperature. Only a small number of weakly stably stratified boundary layers were observed. Strong, shallow inversions, of up to 6 K, were observed above the top of the boundary layer. Observations from a 30 m automatic weather station and two temporary automatic weather stations 10 km south and west of the main field campaign location provide additional data for understanding the boundary layer evolution observed by the SUMO UAVs during this 9-day period. This presentation will discuss the observed evolution of the summertime boundary layer as well as comment on lessons learned operating the SUMO UAVs at a remote Antarctic field camp.

INDIVIDUAL TURBULENT CELL INTERACTION: BASIS FOR BOUNDARY LAYER ESTABLISHMENT

EPA Science Inventory

Boundary layers are important in determining the forces on objects in flowing fluids, mixing characteristics, and other phenomena. For example, benthic boundary layers are frequently active resuspension layers that determine bottom turbidity and transniissivity. Traditionally, bo...

Boundary-layer receptivity due to distributed surface imperfections of a deterministic or random nature

NASA Technical Reports Server (NTRS)

Choudhari, Meelan

1992-01-01

Acoustic receptivity of a Blasius boundary layer in the presence of distributed surface irregularities is investigated analytically. It is shown that, out of the entire spatial spectrum of the surface irregularities, only a small band of Fourier components can lead to an efficient conversion of the acoustic input at any given frequency to an unstable eigenmode of the boundary layer flow. The location, and width, of this most receptive band of wavenumbers corresponds to a relative detuning of O(R sub l.b.(exp -3/8)) with respect to the lower-neutral instability wavenumber at the frequency under consideration, R sub l.b. being the Reynolds number based on a typical boundary-layer thickness at the lower branch of the neutral stability curve. Surface imperfections in the form of discrete mode waviness in this range of wavenumbers lead to initial instability amplitudes which are O(R sub l.b.(exp 3/8)) larger than those caused by a single, isolated roughness element. In contrast, irregularities with a continuous spatial spectrum produce much smaller instability amplitudes, even compared to the isolated case, since the increase due to the resonant nature of the response is more than that compensated for by the asymptotically small band-width of the receptivity process. Analytical expressions for the maximum possible instability amplitudes, as well as their expectation for an ensemble of statistically irregular surfaces with random phase distributions, are also presented.

Analysis of ferrite nanoparticles in the flow of ferromagnetic nanofluid.

PubMed

Muhammad, Noor; Nadeem, Sohail; Mustafa, M T

2018-01-01

Theoretical analysis has been carried out to establish the heat transport phenomenon of six different ferromagnetic MnZnFe2O4-C2H6O2 (manganese zinc ferrite-ethylene glycol), NiZnFe2O4-C2H6O2 (Nickel zinc ferrite-ethylene glycol), Fe2O4-C2H6O2 (magnetite ferrite-ethylene glycol), NiZnFe2O4-H2O (Nickel zinc ferrite-water), MnZnFe2O4-H2O (manganese zinc ferrite-water), and Fe2O4-H2O (magnetite ferrite-water) nanofluids containing manganese zinc ferrite, Nickel zinc ferrite, and magnetite ferrite nanoparticles dispersed in a base fluid of ethylene glycol and water mixture. The performance of convective heat transfer is elevated in boundary layer flow region via nanoparticles. Magnetic dipole in presence of ferrites nanoparticles plays a vital role in controlling the thermal and momentum boundary layers. In perspective of this, the impacts of magnetic dipole on the nano boundary layer, steady, and laminar flow of incompressible ferromagnetic nanofluids are analyzed in the present study. Flow is caused by linear stretching of the surface. Fourier's law of heat conduction is used in the evaluation of heat flux. Impacts of emerging parameters on the magneto-thermomechanical coupling are analyzed numerically. Further, it is evident that Newtonian heating has increasing behavior on the rate of heat transfer in the boundary layer. Comparison with available results for specific cases show an excellent agreement.

Natural laminar flow flight experiments on a swept wing business jet-boundary layer stability analyses

NASA Technical Reports Server (NTRS)

Rozendaal, R. A.

1986-01-01

The linear boundary layer stability analyses and their correlation with data of 18 cases from a natural laminar flow (NLF) flight test program using a Cessna Citation 3 business jet are described. The transition point varied from 5% to 35% chord for these conditions, and both upper and lower wing surfaces were included. Altitude varied from 10,000 to 43,000 ft and Mach number from 0.3 to 0.8. Four cases were at nonzero sideslip. Although there was much scatter in the results, the analyses of boundary layer stability at the 18 conditions led to the conclusion that crossflow instability was the primary cause of transition. However, the sideslip cases did show some interaction of crossflow and Tollmien-Schlichting disturbances. The lower surface showed much lower Tollmien-Schlichting amplification at transition than the upper surface, but similar crossflow amplifications. No relationship between Mach number and disturbance amplification at transition could be found. The quality of these results is open to question from questionable wing surface quality, inadequate density of transition sensors on the wing upper surface, and an unresolved pressure shift in the wing pressure data. The results of this study show the need for careful preparation for transition experiments. Preparation should include flow analyses of the test surface, boundary layer disturbance amplification analyses, and assurance of adequate surface quality in the test area. The placement of necessary instruments and usefulness of the resulting data could largely be determined during the pretest phase.

Fully nonlinear development of the most unstable goertler vortex in a three dimensional boundary layer

NASA Technical Reports Server (NTRS)

Otto, S. R.; Bassom, Andrew P.

1992-01-01

The nonlinear development is studied of the most unstable Gortler mode within a general 3-D boundary layer upon a suitably concave surface. The structure of this mode was first identified by Denier, Hall and Seddougui (1991) who demonstrated that the growth rate of this instability is O(G sup 3/5) where G is the Gortler number (taken to be large here), which is effectively a measure of the curvature of the surface. Previous researchers have described the fate of the most unstable mode within a 2-D boundary layer. Denier and Hall (1992) discussed the fully nonlinear development of the vortex in this case and showed that the nonlinearity causes a breakdown of the flow structure. The effect of crossflow and unsteadiness upon an infinitesimal unstable mode was elucidated by Bassom and Hall (1991). They demonstrated that crossflow tends to stabilize the most unstable Gortler mode, and for certain crossflow/frequency combinations the Gortler mode may be made neutrally stable. These vortex configurations naturally lend themselves to a weakly nonlinear stability analysis; work which is described in a previous article by the present author. Here we extend the ideas of Denier and Hall (1992) to the three-dimensional boundary layer problem. It is found that the numerical solution of the fully nonlinear equations is best conducted using a method which is essentially an adaption of that utilized by Denier and Hall (1992). The influence of crossflow and unsteadiness upon the breakdown of the flow is described.

Skin-Friction Measurements at Subsonic and Transonic Mach Numbers with Embedded-Wire Gages

DTIC Science & Technology

1981-01-01

Model ................................... 17 9. Boundary-Layer Rake Installation on EBOR Model...boundary-layer total pressure rake eliminates this bulky mechanism and the long data acquisition time, but it introduces interferences which affect the...its construction. Further, boundary-layer rakes are restricted to measurements in thick boundary layers. Surface pressure probes such as Stanton tubes

Mechanics of Boundary Layer Transition. Part 5: Boundary Layer Stability theory in incompressible and compressible flow

NASA Technical Reports Server (NTRS)

Mack, L. M.

1967-01-01

The fundamentals of stability theory, its chief results, and the physical mechanisms at work are presented. The stability theory of the laminar boundary determines whether a small disturbance introduced into the boundary layer will amplify or damp. If the disturbance damps, the boundary layer remains laminar. If the disturbance amplifies, and by a sufficient amount, then transition to turbulence eventually takes place. The stability theory establishes those states of the boundary layer which are most likely to lead to transition, identifys those frequencies which are the most dangerous, and indicates how the external parameters can best be changed to avoid transition.

Three dimensional flow field inside compressor rotor, including blade boundary layers

NASA Technical Reports Server (NTRS)

Galmes, J. M.; Pouagere, M.; Lakshminarayana, B.

1982-01-01

The Reynolds stress equation, pressure strain correlation, and dissipative terms and diffusion are discussed in relation to turbulence modelling using the Reynolds stress model. Algebraic modeling of Reynolds stresses and calculation of the boundary layer over an axial cylinder are examined with regards to the kinetic energy model for turbulence modelling. The numerical analysis of blade and hub wall boundary layers, and an experimental study of rotor blade boundary layer in an axial flow compressor rotor are discussed. The Patankar-Spalding numerical method for two dimensional boundary layers is included.

Boundary-layer effects in composite laminates. I - Free-edge stress singularities. II - Free-edge stress solutions and basic characteristics

NASA Technical Reports Server (NTRS)

Wang, S. S.; Choi, I.

1982-01-01

The fundamental nature of the boundary-layer effect in fiber-reinforced composite laminates is formulated in terms of the theory of anisotropic elasticity. The basic structure of the boundary-layer field solution is obtained by using Lekhnitskii's stress potentials (1963). The boundary-layer stress field is found to be singular at composite laminate edges, and the exact order or strength of the boundary layer stress singularity is determined using an eigenfunction expansion method. A complete solution to the boundary-layer problem is then derived, and the convergence and accuracy of the solution are analyzed, comparing results with existing approximate numerical solutions. The solution method is demonstrated for a symmetric graphite-epoxy composite.

Modification in drag of turbulent boundary layers resulting from manipulation of large-scale structures

NASA Technical Reports Server (NTRS)

Corke, T. C.; Guezennec, Y.; Nagib, H. M.

1981-01-01

The effects of placing a parallel-plate turbulence manipulator in a boundary layer are documented through flow visualization and hot wire measurements. The boundary layer manipulator was designed to manage the large scale structures of turbulence leading to a reduction in surface drag. The differences in the turbulent structure of the boundary layer are summarized to demonstrate differences in various flow properties. The manipulator inhibited the intermittent large scale structure of the turbulent boundary layer for at least 70 boundary layer thicknesses downstream. With the removal of the large scale, the streamwise turbulence intensity levels near the wall were reduced. The downstream distribution of the skin friction was also altered by the introduction of the manipulator.

Validation of High-Speed Turbulent Boundary Layer and Shock-Boundary Layer Interaction Computations with the OVERFLOW Code

NASA Technical Reports Server (NTRS)

Oliver, A. B.; Lillard, R. P.; Blaisdell, G. A.; Lyrintizis, A. S.

2006-01-01

The capability of the OVERFLOW code to accurately compute high-speed turbulent boundary layers and turbulent shock-boundary layer interactions is being evaluated. Configurations being investigated include a Mach 2.87 flat plate to compare experimental velocity profiles and boundary layer growth, a Mach 6 flat plate to compare experimental surface heat transfer,a direct numerical simulation (DNS) at Mach 2.25 for turbulent quantities, and several Mach 3 compression ramps to compare computations of shock-boundary layer interactions to experimental laser doppler velocimetry (LDV) data and hot-wire data. The present paper describes outlines the study and presents preliminary results for two of the flat plate cases and two small-angle compression corner test cases.

The influence of free-stream turbulence on turbulent boundary layers with mild adverse pressure gradients

NASA Technical Reports Server (NTRS)

Hoffmann, J. A.; Kassir, S. M.; Larwood, S. M.

1989-01-01

The influence of near isotropic free-stream turbulence on the shape factors and skin friction coefficients of turbulent boundary layers is presented for the cases of zero and mild adverse pressure gradients. With free-stream turbulence, improved fluid mixing occurs in boundary layers with adverse pressure gradients relative to the zero pressure gradient condition, with the same free-stream turbulence intensity and length scale. Stronger boundary layers with lower shape factors occur as a result of a lower ratio of the integral scale of turbulence to the boundary layer thickness, and to vortex stretching of the turbulent eddies in the free-stream, both of which act to improve the transmission of momentum from the free-stream to the boundary layers.

The roll-up and merging of coherent structures in shallow mixing layers

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

Lam, M. Y., E-mail: celmy@connect.ust.hk; Ghidaoui, M. S.; Kolyshkin, A. A.

2016-09-15

The current study seeks a fundamental explanation to the development of two-dimensional coherent structures (2DCSs) in shallow mixing layers. A nonlinear numerical model based on the depth-averaged shallow water equations is used to investigate the temporal evolution of shallow mixing layers, where the mapping from temporal to spatial results is made using the velocity at the center of the mixing layers. The flow is periodic in the streamwise direction. Transmissive boundary conditions are used in the cross-stream boundaries to prevent reflections. Numerical results are compared to linear stability analysis, mean-field theory, and secondary stability analysis. Results suggest that the onsetmore » and development of 2DCS in shallow mixing layers are the result of a sequence of instabilities governed by linear theory, mean-field theory, and secondary stability theory. The linear instability of the shearing velocity gradient gives the onset of 2DCS. When the perturbations reach a certain amplitude, the flow field of the perturbations changes from a wavy shape to a vortical (2DCS) structure because of nonlinearity. The development of the vertical 2DCS does not appear to follow weakly nonlinear theory; instead, it follows mean-field theory. After the formation of 2DCS, separate 2DCSs merge to form larger 2DCS. In this way, 2DCSs grow and shallow mixing layers develop and grow in scale. The merging of 2DCS in shallow mixing layers is shown to be caused by the secondary instability of the 2DCS. Eventually 2DCSs are dissipated by bed friction. The sequence of instabilities can cause the upscaling of the turbulent kinetic energy in shallow mixing layers.« less

On the boundary conditions on a shock wave for hypersonic flow around a descent vehicle

NASA Astrophysics Data System (ADS)

Golomazov, M. M.; Ivankov, A. A.

2013-12-01

Stationary hypersonic flow around a descent vehicle is examined by considering equilibrium and nonequilibrium reactions. We study how physical-chemical processes and shock wave conditions for gas species influence the shock-layer structure. It is shown that conservation conditions of species on the shock wave cause high-temperature and concentration gradients in the shock layer when we calculate spacecraft deceleration trajectory in the atmosphere at 75 km altitude.

Bubble dynamics in a compressible liquid in contact with a rigid boundary

PubMed Central

Wang, Qianxi; Liu, Wenke; Zhang, A. M.; Sui, Yi

2015-01-01

A bubble initiated near a rigid boundary may be almost in contact with the boundary because of its expansion and migration to the boundary, where a thin layer of water forms between the bubble and the boundary thereafter. This phenomenon is modelled using the weakly compressible theory coupled with the boundary integral method. The wall effects are modelled using the imaging method. The numerical instabilities caused by the near contact of the bubble surface with the boundary are handled by removing a thin layer of water between them and joining the bubble surface with its image to the boundary. Our computations correlate well with experiments for both the first and second cycles of oscillation. The time history of the energy of a bubble system follows a step function, reducing rapidly and significantly because of emission of shock waves at inception of a bubble and at the end of collapse but remaining approximately constant for the rest of the time. The bubble starts being in near contact with the boundary during the first cycle of oscillation when the dimensionless stand-off distance γ = s/Rm < 1, where s is the distance of the initial bubble centre from the boundary and Rm is the maximum bubble radius. This leads to (i) the direct impact of a high-speed liquid jet on the boundary once it penetrates through the bubble, (ii) the direct contact of the bubble at high temperature and high pressure with the boundary, and (iii) the direct impingement of shock waves on the boundary once emitted. These phenomena have clear potential to damage the boundary, which are believed to be part of the mechanisms of cavitation damage. PMID:26442148

Increased Jet Noise Due to a "Nominally Laminar" State of Nozzle Exit Boundary Layer

NASA Technical Reports Server (NTRS)

Zaman, K. B. M. Q.

2017-01-01

A set of 2-in. diameter nozzles is used to investigate the effect of varying exit boundary layer state on the radiated noise from high-subsonic jets. It is confirmed that nozzles involving turbulent boundary layers are the quietest while nozzles involving a "nominally laminar" boundary layer are loud especially on the high-frequency side of the sound pressure level spectrum. The latter boundary layer state involves a "Blasius-like" mean velocity profile but higher turbulence intensities compared to those in the turbulent state. The higher turbulence in the initial region of the jet shear layer leads to increased high-frequency noise. The results strongly suggest that an anomaly noted with subsonic jet noise databases in the literature is due to a similar effect of differences in the initial boundary layer state.

Increased Jet Noise Due to a "Nominally Laminar" State of Nozzle Exit Boundary Layer

NASA Technical Reports Server (NTRS)

Zaman, K. B. M. Q.

2017-01-01

A set of 2-inch diameter nozzles is used to investigate the effect of varying exit boundary layer state on the radiated noise from high-subsonic jets. It is confirmed that nozzles involving turbulent boundary layers are the quietest while nozzles involving a nominally-laminar boundary layer are loud especially on the high-frequency side of the sound pressure level spectrum. The latter boundary layer state involves a Blasius-like mean velocity profile but higher turbulence intensities compared to those in the turbulent state. The higher turbulence in the initial region of the jet shear layer leads to increased high-frequency noise. The results strongly suggest that an anomaly noted with subsonic jet noise databases in the literature is due to a similar effect of differences in the initial boundary layer state.

Average Skin-Friction Drag Coefficients from Tank Tests of a Parabolic Body of Revolution (NACA RM-10)

NASA Technical Reports Server (NTRS)

Mottard, Elmo J; Loposer, J Dan

1954-01-01

Average skin-friction drag coefficients were obtained from boundary-layer total-pressure measurements on a parabolic body of revolution (NACA rm-10, basic fineness ratio 15) in water at Reynolds numbers from 4.4 x 10(6) to 70 x 10(6). The tests were made in the Langley tank no. 1 with the body sting-mounted at a depth of two maximum body diameters. The arithmetic mean of three drag measurements taken around the body was in good agreement with flat-plate results, but, apparently because of the slight surface wave caused by the body, the distribution of the boundary layer around the body was not uniform over part of the Reynolds number range.

Some effects of finite spatial resolution on skin friction measurements in turbulent boundary layers

NASA Technical Reports Server (NTRS)

Westphal, Russell V.

1988-01-01

The effects of finite spatial resolution often cause serious errors in measurements in turbulent boundary layers, with particularly large effects for measurements of fluctuating skin friction and velocities within the sublayer. However, classical analyses of finite spatial resolution effects have generally not accounted for the substantial inhomogeneity and anisotropy of near-wall turbulence. The present study has made use of results from recent computational simulations of wall-bounded turbulent flows to examine spatial resolution effects for measurements made at a wall using both single-sensor probes and those employing two sensing volumes in a V shape. Results are presented to show the effects of finite spatial resolution on a variety of quantitites deduced from the skin friction field.

Key vortical structure causing laminar-turbulent transition in a boundary layer disturbed by a short-duration jet

NASA Astrophysics Data System (ADS)

Yoshikawa, Joe; Nishio, Yu; Izawa, Seiichiro; Fukunishi, Yu

2018-01-01

Numerical simulations are carried out to discover the flow structure that plays an important role in the laminar-turbulent transition process of a boundary layer on a flat plate. The boundary layer is destabilized by ejecting a short-duration jet from a hole in the surface. When the jet velocity is set to 20% of the uniform-flow velocity, a laminar-turbulent transition takes place, whereas in the 18% case, the disturbances created by the jet decay downstream. It is found that in both cases, hairpin vortices are generated; however, these first-generation hairpins do not directly cause the transition. Only in the 20% case does a new hairpin vortex of a different shape with wider distance between the legs appear. The new hairpin grows with time and evokes the generation of vortical structures one after another around it, turning the flow turbulent. It is found that the difference between the two cases is whether or not one of the first-generation hairpin vortices gets connected with the nearby longitudinal vortices. Only when the connection is successful is the new hairpin vortex with wider distance between the legs created. For each of several cases tested with changing jet-ejecting conditions, no difference is found in the importance of the role of the hairpin structure. Therefore, we conclude that the hairpin vortex with widespread legs is a key structure in the transition to turbulence.

Subsidence in the Nocturnal Boundary Layer.

NASA Astrophysics Data System (ADS)

Carlson, Merrilee A.; Stull, Roland B.

1986-08-01

Nights with clear skies and strong radiative cooling that favor the formation of statically stable nocturnal boundary layers (NBL) are also those nights most likely to have subsidence, because of the presence of synoptic high-pressure regions. The divergence associated with subsidence laterally removes some of the chilled nocturnal boundary layer air causing the NBL to not grow as rapidly as would otherwise be expected. An equivalent interpretation is that subsidence-induced heating partially counteracts the radiative and turbulent cooling.A new form of nocturnal integral depth scale, HT, is introduced that incorporates the heating and cooling contributions at night. This scale can be used with a variety of idealized temperature profile shapes, including slab, linear, and exponential. It is shown that observed values of subsidence for two case studies can reduce the NBL growth rate, as measured by HT/t, by 5 to 50% and can cause corresponding errors in the estimation of accumulated cooling unless there is a proper accounting of subsidence.Subsidence plays a very minor role close to the ground, but for the case studies presented here its heating rate increases with height and becomes of comparable magnitude to the cooling rates of turbulence and radiation within the top third of the NBL. Although no adequate measurements of horizontal advective effects were available for the case studies used here, it appears from an energy balance that advection must not be neglected because its magnitude can be as large as turbulence and radiation.

Proterozoic crustal boundary in the southern part of the Illinois Basin

USGS Publications Warehouse

Heigold, P.C.; Kolata, Dennis R.

1993-01-01

Recently acquired COCORP and proprietary seismic reflection data in the southern part of the Illinois Basin, combined with other geological and geophysical data, indicate that a WNW-trending Proterozoic terrane boundary (40 km wide) lies within basement. The boundary is characterized by the termination of subhorizontal Proterozoic reflectors and associated diffraction patterns along a line coinciding with the major magnetic lineament in this region (South Central Magnetic Lineament). North of the boundary, where reflectors thought to represent a sequence of layered Proterozoic rocks in the upper crust are widespread and as much as 11 km thick, total magnetic intensity values are relatively high, suggesting layers of rock with high magnetic susceptibility. To the south, the Proterozoic rocks are acoustically transparent on seismic reflection sections and total magnetic intensity values are relatively low. Moreover, relatively high Bouguer gravity anomaly values to the south may be caused by a dense, altered, lower crustal layer similar to that interpreted from deep seismic refraction studies to underlie the northern Mississippi Embayment. The boundary lies along the projected trend of the northern margin of the Early Proterozoic Central Plains orogen and we suggest that it marks the convergent margin of this orogen. Reactivation of the boundary and the associated zone of weakness during late Paleozoic times apparently resulted in structural deformation in the southern part of the Illinois Basin, including movement along the Cottage Grove Fault System and Ste. Genevieve Fault Zone and igneous activity at Hicks Dome. In addition to the role played by this crustal boundary in the evolution of the Illinois Basin, its location between the Wabash Valley Seismic Zone to the northeast and the New Madrid Seismic Zone to the southwest may be a significant factor in present-day seismicity. ?? 1993.

Turbulent properties of oceanic near-surface stable boundary layers subject to wind, fresh water, and thermal forcing.

NASA Astrophysics Data System (ADS)

St. Laurent, Louis; Clayson, Carol Anne

2015-04-01

The near-surface oceanic boundary layer is generally regarded as convectively unstable due to the effects of wind, evaporation, and cooling. However, stable conditions also occur often, when rain or low-winds and diurnal warming provide buoyancy to a thin surface layer. These conditions are prevalent in the tropical and subtropical latitude bands, and are underrepresented in model simulations. Here, we evaluate cases of oceanic stable boundary layers and their turbulent processes using a combination of measurements and process modeling. We focus on the temperature, salinity and density changes with depth from the surface to the upper thermocline, subject to the influence of turbulent processes causing mixing. The stabilizing effects of freshwater from rain as contrasted to conditions of high solar radiation and low winds will be shown, with observations providing surprising new insights into upper ocean mixing in these regimes. Previous observations of freshwater lenses have demonstrated a maximum of dissipation near the bottom of the stable layer; our observations provide a first demonstration of a similar maximum near the bottom of the solar heating-induced stable layer and a fresh-water induced barrier layer. Examples are drawn from recent studies in the tropical Atlantic and Indian oceans, where ocean gliders equipped with microstructure sensors were used to measure high resolution hydrographic properties and turbulence levels. The limitations of current mixing models will be demonstrated. Our findings suggest that parameterizations of near-surface mixing rates during stable stratification and low-wind conditions require considerable revision, in the direction of larger diffusivities.

Investigation of corner shock boundary layer interactions to understand inlet unstart

NASA Astrophysics Data System (ADS)

Funderburk, Morgan

2015-11-01

Inlet unstart is a detrimental phenomenon in dual-mode ramjet/scramjet engines that causes severe loss of thrust, large transient structural load, and potentially a loss of the aircraft. In order to analyze the effects that the corner shock boundary layer interaction (SBLI) has on initiating and perpetuating inlet unstart, a qualitative and quantitative investigation into mean and dynamic features of corner SBLI at various Mach numbers is made. Surface streakline visualization showed that the corner SBLI is highly three-dimensional with a dominant presence of corner separation vortex. Further, the peak r.m.s. pressure was located at the periphery of corner separation vortex, suggesting that the unsteady loading is caused by the corner vortex. Power spectral densities of wall-pressure fluctuations in the peak r.m.s. location were analyzed in order to characterize the dominant frequencies of oscillation of the flow structures and to unravel the dynamic interactions between them in order to expand the operating margin of future hypersonic air breathing vehicles.

ANGULAR MOMENTUM TRANSPORT BY ACOUSTIC MODES GENERATED IN THE BOUNDARY LAYER. I. HYDRODYNAMICAL THEORY AND SIMULATIONS

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

Belyaev, Mikhail A.; Rafikov, Roman R.; Stone, James M., E-mail: rrr@astro.princeton.edu

The nature of angular momentum transport in the boundary layers of accretion disks has been one of the central and long-standing issues of accretion disk theory. In this work we demonstrate that acoustic waves excited by supersonic shear in the boundary layer serve as an efficient mechanism of mass, momentum, and energy transport at the interface between the disk and the accreting object. We develop the theory of angular momentum transport by acoustic modes in the boundary layer, and support our findings with three-dimensional hydrodynamical simulations, using an isothermal equation of state. Our first major result is the identification ofmore » three types of global modes in the boundary layer. We derive dispersion relations for each of these modes that accurately capture the pattern speeds observed in simulations to within a few percent. Second, we show that angular momentum transport in the boundary layer is intrinsically nonlocal, and is driven by radiation of angular momentum away from the boundary layer into both the star and the disk. The picture of angular momentum transport in the boundary layer by waves that can travel large distances before dissipating and redistributing angular momentum and energy to the disk and star is incompatible with the conventional notion of local transport by turbulent stresses. Our results have important implications for semianalytical models that describe the spectral emission from boundary layers.« less

Nonequilibrium chemistry boundary layer integral matrix procedure

NASA Technical Reports Server (NTRS)

Tong, H.; Buckingham, A. C.; Morse, H. L.

1973-01-01

The development of an analytic procedure for the calculation of nonequilibrium boundary layer flows over surfaces of arbitrary catalycities is described. An existing equilibrium boundary layer integral matrix code was extended to include nonequilibrium chemistry while retaining all of the general boundary condition features built into the original code. For particular application to the pitch-plane of shuttle type vehicles, an approximate procedure was developed to estimate the nonequilibrium and nonisentropic state at the edge of the boundary layer.

Differential analysis for the turbulent boundary layer on a compressor blade element (including boundary-layer separation)

NASA Technical Reports Server (NTRS)

Schmidt, J. F.; Todd, C. A.

1974-01-01

A two-dimensional differential analysis is developed to approximate the turbulent boundary layer on a compressor blade element with strong adverse pressure gradients, including the separated region with reverse flow. The predicted turbulent boundary layer thicknesses and velocity profiles are in good agreement with experimental data for a cascade blade, even in the separated region.

Similarity theory of the buoyantly interactive planetary boundary layer with entrainment

NASA Technical Reports Server (NTRS)

Hoffert, M. I.; Sud, Y. C.

1976-01-01

A similarity model is developed for the vertical profiles of turbulent flow variables in an entraining turbulent boundary layer of arbitrary buoyant stability. In the general formulation the vertical profiles, internal rotation of the velocity vector, discontinuities or jumps at a capping inversion and bulk aerodynamic coefficients of the boundary layer are given by solutions to a system of ordinary differential equations in the similarity variable. To close the system, a formulation for buoyantly interactive eddy diffusivity in the boundary layer is introduced which recovers Monin-Obukhov similarity near the surface and incorporates a hypothesis accounting for the observed variation of mixing length throughout the boundary layer. The model is tested in simplified versions which depend only on roughness, surface buoyancy, and Coriolis effects by comparison with planetary-boundary-layer wind- and temperature-profile observations, measurements of flat-plate boundary layers in a thermally stratified wind tunnel and observations of profiles of terms in the turbulent kinetic-energy budget of convective planetary boundary layers. On balance, the simplified model reproduced the trend of these various observations and experiments reasonably well, suggesting that the full similarity formulation be pursued further.

Assessment of a 3-D boundary layer code to predict heat transfer and flow losses in a turbine

NASA Technical Reports Server (NTRS)

Anderson, O. L.

1984-01-01

Zonal concepts are utilized to delineate regions of application of three-dimensional boundary layer (DBL) theory. The zonal approach requires three distinct analyses. A modified version of the 3-DBL code named TABLET is used to analyze the boundary layer flow. This modified code solves the finite difference form of the compressible 3-DBL equations in a nonorthogonal surface coordinate system which includes coriolis forces produced by coordinate rotation. These equations are solved using an efficient, implicit, fully coupled finite difference procedure. The nonorthogonal surface coordinate system is calculated using a general analysis based on the transfinite mapping of Gordon which is valid for any arbitrary surface. Experimental data is used to determine the boundary layer edge conditions. The boundary layer edge conditions are determined by integrating the boundary layer edge equations, which are the Euler equations at the edge of the boundary layer, using the known experimental wall pressure distribution. Starting solutions along the inflow boundaries are estimated by solving the appropriate limiting form of the 3-DBL equations.

Spatial variations in larch needle and soil δ15N at a forest-grassland boundary in northern Mongolia.

PubMed

Fujiyoshi, Lei; Sugimoto, Atsuko; Tsukuura, Akemi; Kitayama, Asami; Lopez Caceres, M Larry; Mijidsuren, Byambasuren; Saraadanbazar, Ariunaa; Tsujimura, Maki

2017-03-01

The spatial patterns of plant and soil δ 15 N and associated processes in the N cycle were investigated at a forest-grassland boundary in northern Mongolia. Needles of Larix sibirica Ledeb. and soils collected from two study areas were analysed to calculate the differences in δ 15 N between needle and soil (Δδ 15 N). Δδ 15 N showed a clear variation, ranging from -8 ‰ in the forest to -2 ‰ in the grassland boundary, and corresponded to the accumulation of organic layer. In the forest, the separation of available N produced in the soil with 15 N-depleted N uptake by larch and 15 N-enriched N immobilization by microorganisms was proposed to cause large Δδ 15 N, whereas in the grassland boundary, small Δδ 15 N was explained by the transport of the most available N into larch. The divergence of available N between larch and microorganisms in the soil, and the accumulation of diverged N in the organic layer control the variation in Δδ 15 N.

Effects of boundary layer on flame propagation generated by forced ignition behind an incident shock wave

NASA Astrophysics Data System (ADS)

Ishihara, S.; Tamura, S.; Ishii, K.; Kataoka, H.

2016-09-01

To study the effects of the boundary layer on the deflagration to detonation transition (DDT) process, the mixture behind an incident shock wave was ignited using laser breakdown. Ignition timing was controlled so that the interaction of the resulting flame with a laminar or turbulent boundary layer could be examined. In the case of the interaction with a laminar boundary layer, wrinkling of the flame was observed after the flame reached the corner of the channel. On the other hand, interaction with the turbulent boundary layer distorted the flame front and increased the spreading rate of the flame followed by prompt DDT. The inner structure of the turbulent boundary layer plays an important role in the DDT process. The region that distorted the flame within the turbulent boundary layer was found to be the intermediate region 0.01< y/δ < 0.4, where y is the distance from the wall and δ is the boundary layer thickness. The flame disturbance by the turbulent motions is followed by the flame interaction with the inner layer near the wall, which in turn generates a secondary-ignition kernel that produced a spherical accelerating flame, which ultimately led to the onset of detonation. After the flame reached the intermediate region, the time required for DDT was independent of the ignition position. The effect of the boundary layer on the propagating flame, thus, became relatively small after the accelerating flame was generated.

Turbulent boundary layer in high Rayleigh number convection in air.

PubMed

du Puits, Ronald; Li, Ling; Resagk, Christian; Thess, André; Willert, Christian

2014-03-28

Flow visualizations and particle image velocimetry measurements in the boundary layer of a Rayleigh-Bénard experiment are presented for the Rayleigh number Ra=1.4×1010. Our visualizations indicate that the appearance of the flow structures is similar to ordinary (isothermal) turbulent boundary layers. Our particle image velocimetry measurements show that vorticity with both positive and negative sign is generated and that the smallest flow structures are 1 order of magnitude smaller than the boundary layer thickness. Additional local measurements using laser Doppler velocimetry yield turbulence intensities up to I=0.4 as in turbulent atmospheric boundary layers. From our observations, we conclude that the convective boundary layer becomes turbulent locally and temporarily although its Reynolds number Re≈200 is considerably smaller than the value 420 underlying existing phenomenological theories. We think that, in turbulent Rayleigh-Bénard convection, the transition of the boundary layer towards turbulence depends on subtle details of the flow field and is therefore not universal.

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.

Generating Inviscid and Viscous Fluid Flow Simulations over a Surface Using a Quasi-simultaneous Technique

NASA Technical Reports Server (NTRS)

Sturdza, Peter (Inventor); Martins-Rivas, Herve (Inventor); Suzuki, Yoshifumi (Inventor)

2014-01-01

A fluid-flow simulation over a computer-generated surface is generated using a quasi-simultaneous technique. The simulation includes a fluid-flow mesh of inviscid and boundary-layer fluid cells. An initial fluid property for an inviscid fluid cell is determined using an inviscid fluid simulation that does not simulate fluid viscous effects. An initial boundary-layer fluid property a boundary-layer fluid cell is determined using the initial fluid property and a viscous fluid simulation that simulates fluid viscous effects. An updated boundary-layer fluid property is determined for the boundary-layer fluid cell using the initial fluid property, initial boundary-layer fluid property, and an interaction law. The interaction law approximates the inviscid fluid simulation using a matrix of aerodynamic influence coefficients computed using a two-dimensional surface panel technique and a fluid-property vector. An updated fluid property is determined for the inviscid fluid cell using the updated boundary-layer fluid property.

A nonperturbing boundary-layer transition detector

NASA Astrophysics Data System (ADS)

Ohare, J. E.

1985-11-01

A laser interferometer technique is being applied to the characterization of boundary-layer conditions on models in supersonic and hypersonic wind tunnels. The boundary-layer transition detector (BLTD), based on lateral interferometry, is applicable for determining the turbulence frequency spectrum of boundary layers in compressible flow. The turbulence, in terms of air density fluctuations, is detected by monitoring interferometric fringe phase shifts (in real time) formed by one beam which passes through the boundary layer and a reference beam which is outside the boundary layer. This technique is nonintrusive to the flow field unlike other commonly used methods such as pitot tube probing and hot-wire anemometry. Data which depict boundary-layer transition from laminar to turbulent flow are presented to provide comparisons of the BLTD with other measurement methods. Spectra from the BLTD reveals the presence of a high-frequency peak during transition which is characteristic of spectra obtained with hot wires. The BLTD is described along with operational requirements and limitations.

Mean velocity and turbulence measurements in a 90 deg curved duct with thin inlet boundary layer

NASA Technical Reports Server (NTRS)

Crawford, R. A.; Peters, C. E.; Steinhoff, J.; Hornkohl, J. O.; Nourinejad, J.; Ramachandran, K.

1985-01-01

The experimental database established by this investigation of the flow in a large rectangular turning duct is of benchmark quality. The experimental Reynolds numbers, Deans numbers and boundary layer characteristics are significantly different from previous benchmark curved-duct experimental parameters. This investigation extends the experimental database to higher Reynolds number and thinner entrance boundary layers. The 5% to 10% thick boundary layers, based on duct half-width, results in a large region of near-potential flow in the duct core surrounded by developing boundary layers with large crossflows. The turbulent entrance boundary layer case at R sub ed = 328,000 provides an incompressible flowfield which approaches real turbine blade cascade characteristics. The results of this investigation provide a challenging benchmark database for computational fluid dynamics code development.

A mathematical analysis of drug dissolution in the USP flow through apparatus

NASA Astrophysics Data System (ADS)

McDonnell, David; D'Arcy, D. M.; Crane, L. J.; Redmond, Brendan

2018-03-01

This paper applies boundary layer theory to the process of drug dissolution in the USP (United States Pharmacopeia) Flow Through Apparatus. The mass transfer rate from the vertical planar surface of a compact within the device is examined. The theoretical results obtained are then compared with those of experiment. The paper also examines the effect on the dissolution process caused by the interaction between natural and forced convection within the apparatus and the introduction of additional boundaries.

A comparison of no-slip, stress-free and inviscid models of rapidly rotating fluid in a spherical shell

PubMed Central

Livermore, Philip W.; Bailey, Lewis M.; Hollerbach, Rainer

2016-01-01

We investigate how the choice of either no-slip or stress-free boundary conditions affects numerical models of rapidly rotating flow in Earth’s core by computing solutions of the weakly-viscous magnetostrophic equations within a spherical shell, driven by a prescribed body force. For non-axisymmetric solutions, we show that models with either choice of boundary condition have thin boundary layers of depth E1/2, where E is the Ekman number, and a free-stream flow that converges to the formally inviscid solution. At Earth-like values of viscosity, the boundary layer thickness is approximately 1 m, for either choice of condition. In contrast, the axisymmetric flows depend crucially on the choice of boundary condition, in both their structure and magnitude (either E−1/2 or E−1). These very large zonal flows arise from requiring viscosity to balance residual axisymmetric torques. We demonstrate that switching the mechanical boundary conditions can cause a distinct change of structure of the flow, including a sign-change close to the equator, even at asymptotically low viscosity. Thus implementation of stress-free boundary conditions, compared with no-slip conditions, may yield qualitatively different dynamics in weakly-viscous magnetostrophic models of Earth’s core. We further show that convergence of the free-stream flow to its asymptotic structure requires E ≤ 10−5. PMID:26980289

Compressible Boundary Layer Investigation for Ramjet/scramjet Inlets and Nozzles

NASA Astrophysics Data System (ADS)

Goldfeld, M. A.; Starov, A. V.; Semenova, Yu. V.

2005-02-01

The results of experimental investigation of a turbulent boundary layer on compression and expansion surfaces are presented. They include the study of the shock wave and/or expansion fan action upon the boundary layer, boundary layer separation and its relaxation. Complex events of paired interactions and the flow on compression convex-concave surfaces were studied [M. Goldfeld, 1993]. The possibility and conditions of the boundary layer relaminarization behind the expansion fan and its effect on the relaxation length are presented. Different model configurations for wide range conditions were investigated. Comparison of results for different interactions was carried out.

Heat transfer through turbulent boundary layers - The effects of introduction of and recovery from convex curvature

NASA Technical Reports Server (NTRS)

Simon, T. W.; Moffat, R. J.

1979-01-01

Measurements have been made of the heat transfer through a turbulent boundary layer on a convexly curved isothermal wall and on a flat plate following the curved section. Data were taken for one free-stream velocity and two different ratios of boundary layer thickness to radius of curvature delta/R = 0.051 and delta/R = 0.077. Only small differences were observed in the distribution of heat transfer rates for the two boundary layer thicknesses tested, although differences were noted in the temperature distributions within the boundary layer

F-16XL ship #1 - CAWAP boundary layer rakes and hot film on left wing

NASA Technical Reports Server (NTRS)

1996-01-01

This photo shows the boundary layer hot film and the boundary layer rakes on the left wing of NASA's single-seat F-16XL (ship #1) used for the Cranked-Arrow Wing Aerodynamic Project (CAWAP) at Dryden Flight Research Center, Edwards, California. The modified airplane features a delta 'cranked-arrow' wing with strips of tubing along the leading edge to the trailing edge to sense static on the wing and obtain pressure distribution data. The right wing receives data on pressure distribution and the left wing has three types of instrumentation - preston tubes to measure local skin friction, boundary layer rakes to measure boundary layer profiles (the layer where the air interacts with the surfaces of a moving aircraft), and hot films to determine boundary layer transition locations. The first flight of CAWAP occurred on November 21, 1995, and the test program ended in April 1996.

An Experimental Investigation of the Confluent Boundary Layer on a High-Lift System

NASA Technical Reports Server (NTRS)

Thomas, F. O.; Nelson, R. C.

1997-01-01

This paper describes a fundamental experimental investigation of the confluent boundary layer generated by the interaction of a leading-edge slat wake with the boundary layer on the main element of a multi-element airfoil model. The slat and airfoil model geometry are both fully two-dimensional. The research reported in this paper is performed in an attempt to investigate the flow physics of confluent boundary layers and to build an archival data base on the interaction of the slat wake and the main element wall layer. In addition, an attempt is made to clearly identify the role that slat wake / airfoil boundary layer confluence has on lift production and how this occurs. Although complete LDV flow surveys were performed for a variety of slat gap and overhang settings, in this report the focus is on two cases representing both strong and weak wake boundary layer confluence.

Molecular carbon isotope variations in core samples taken at the Permian-Triassic boundary layers in southern China

NASA Astrophysics Data System (ADS)

Wang, Ruiliang; Zhang, Shuichang; Brassell, Simon; Wang, Jiaxue; Lu, Zhengyuan; Ming, Qingzhong; Wang, Xiaomei; Bian, Lizeng

2012-07-01

Stable carbon isotope composition (δ13C) of carbonate sediments and the molecular (biomarker) characteristics of a continuous Permian-Triassic (PT) layer in southern China were studied to obtain geochemical signals of global change at the Permian-Triassic boundary (PTB). Carbonate carbon isotope values shifted toward positive before the end of the Permian period and then shifted negative above the PTB into the Triassic period. Molecular carbon isotope values of biomarkers followed the same trend at and below the PTB and remained negative in the Triassic layer. These biomarkers were acyclic isoprenoids, ranging from C15 to C40, steranes (C27 dominates) and terpenoids that were all significantly more abundant in samples from the Permian layer than those from the Triassic layer. The Triassic layer was distinguished by the dominance of higher molecular weight (waxy) n-alkanes. Stable carbon isotope values of individual components, including n-alkanes and acyclic isoprenoids such as phytane, isop-C25, and squalane, are depleted in δ13C by up to 8-10‰ in the Triassic samples as compared to the Permian. Measured molecular and isotopic variations of organic matter in the PT layers support the generally accepted view of Permian oceanic stagnation followed by a massive upwelling of toxic deep waters at the PTB. A series of large-scale (global) outgassing events may be associated with the carbon isotope shift we measured. This is also consistent with the lithological evidence we observed of white thin-clay layers in this region. Our findings, in context with a generally accepted stagnant Permian ocean, followed by massive upwelling of toxic deep waters might be the major causes of the largest global mass extinction event that occurred at the Permian-Triassic boundary.

Towards Natural Transition in Compressible Boundary Layers

DTIC Science & Technology

2016-06-29

AFRL-AFOSR-CL-TR-2016-0011 Towards natural transition in compressible boundary layers Marcello Faraco de Medeiros FUNDACAO PARA O INCREMENTO DA...to 29-03-2016 Towards natural transition in compressible boundary layers FA9550-11-1-0354 Marcello A. Faraco de Medeiros Germán Andrés Gaviria...unlimited. 109 Final report Towards natural transition in compressible boundary layers Principal Investigator: Marcello Augusto Faraco de Medeiros

Inventory of File nam.t00z.smartconus00.tm00.grib2

Science.gov Websites

(Eta model reduction) [Pa] 014 planetary boundary layer WDIR analysis Wind Direction (from which blowing) [degtrue] 015 planetary boundary layer WIND analysis Wind Speed [m/s] 016 planetary boundary layer RH analysis Relative Humidity [%] 017 planetary boundary layer DIST analysis Geometric Height [m

Evaluation of the Atmospheric Boundary-Layer Electrical Variability

NASA Astrophysics Data System (ADS)

Anisimov, Sergey V.; Galichenko, Sergey V.; Aphinogenov, Konstantin V.; Prokhorchuk, Aleksandr A.

2017-12-01

Due to the chaotic motion of charged particles carried by turbulent eddies, electrical quantities in the atmospheric boundary layer (ABL) have short-term variability superimposed on long-term variability caused by sources from regional to global scales. In this study the influence of radon exhalation rate, aerosol distribution and turbulent transport efficiency on the variability of fair-weather atmospheric electricity is investigated via Lagrangian stochastic modelling. For the mid-latitude lower atmosphere undisturbed by precipitation, electrified clouds, or thunderstorms, the model is capable of reproducing the diurnal variation in atmospheric electrical parameters detected by ground-based measurements. Based on the analysis of field observations and numerical simulation it is found that the development of the convective boundary layer, accompanied by an increase in turbulent kinetic energy, forms the vertical distribution of radon and its decaying short-lived daughters to be approximately coincident with the barometric law for several eddy turnover times. In the daytime ABL the vertical distribution of atmospheric electrical conductivity tends to be uniform except within the surface layer, due to convective mixing of radon and its radioactive decay products. At the same time, a decrease in the conductivity near the ground is usually observed. This effect leads to an enhanced ground-level atmospheric electric field compared to that normally observed in the nocturnal stably-stratified boundary layer. The simulation showed that the variability of atmospheric electric field in the ABL associated with internal origins is significant in comparison to the variability related to changes in global parameters. It is suggested that vertical profiles of electrical quantities can serve as informative parameters on ABL turbulent dynamics and can even more broadly characterize the state of the environment.

Asymmetric simple exclusion process with position-dependent hopping rates: Phase diagram from boundary-layer analysis.

PubMed

Mukherji, Sutapa

2018-03-01

In this paper, we study a one-dimensional totally asymmetric simple exclusion process with position-dependent hopping rates. Under open boundary conditions, this system exhibits boundary-induced phase transitions in the steady state. Similarly to totally asymmetric simple exclusion processes with uniform hopping, the phase diagram consists of low-density, high-density, and maximal-current phases. In various phases, the shape of the average particle density profile across the lattice including its boundary-layer parts changes significantly. Using the tools of boundary-layer analysis, we obtain explicit solutions for the density profile in different phases. A detailed analysis of these solutions under different boundary conditions helps us obtain the equations for various phase boundaries. Next, we show how the shape of the entire density profile including the location of the boundary layers can be predicted from the fixed points of the differential equation describing the boundary layers. We discuss this in detail through several examples of density profiles in various phases. The maximal-current phase appears to be an especially interesting phase where the boundary layer flows to a bifurcation point on the fixed-point diagram.

Asymmetric simple exclusion process with position-dependent hopping rates: Phase diagram from boundary-layer analysis

NASA Astrophysics Data System (ADS)

Mukherji, Sutapa

2018-03-01

In this paper, we study a one-dimensional totally asymmetric simple exclusion process with position-dependent hopping rates. Under open boundary conditions, this system exhibits boundary-induced phase transitions in the steady state. Similarly to totally asymmetric simple exclusion processes with uniform hopping, the phase diagram consists of low-density, high-density, and maximal-current phases. In various phases, the shape of the average particle density profile across the lattice including its boundary-layer parts changes significantly. Using the tools of boundary-layer analysis, we obtain explicit solutions for the density profile in different phases. A detailed analysis of these solutions under different boundary conditions helps us obtain the equations for various phase boundaries. Next, we show how the shape of the entire density profile including the location of the boundary layers can be predicted from the fixed points of the differential equation describing the boundary layers. We discuss this in detail through several examples of density profiles in various phases. The maximal-current phase appears to be an especially interesting phase where the boundary layer flows to a bifurcation point on the fixed-point diagram.

Boundary Layer

NASA Technical Reports Server (NTRS)

Loitsianskii. L. G.

1956-01-01

The fundamental, practically the most important branch of the modern mechanics of a viscous fluid or a gas, is that branch which concerns itself with the study of the boundary layer. The presence of a boundary layer accounts for the origin of the resistance and lift force, the breakdown of the smooth flow about bodies, and other phenomena that are associated with the motion of a body in a real fluid. The concept of boundary layer was clearly formulated by the founder of aerodynamics, N. E. Joukowsky, in his well-known work "On the Form of Ships" published as early as 1890. In his book "Theoretical Foundations of Air Navigation," Joukowsky gave an account of the most important properties of the boundary layer and pointed out the part played by it in the production of the resistance of bodies to motion. The fundamental differential equations of the motion of a fluid in a laminar boundary layer were given by Prandtl in 1904; the first solutions of these equations date from 1907 to 1910. As regards the turbulent boundary layer, there does not exist even to this day any rigorous formulation of this problem because there is no closed system of equations for the turbulent motion of a fluid. Soviet scientists have done much toward developing a general theory of the boundary layer, and in that branch of the theory which is of greatest practical importance at the present time, namely the study of the boundary layer at large velocities of the body in a compressed gas, the efforts of the scientists of our country have borne fruit in the creation of a new theory which leaves far behind all that has been done previously in this direction. We shall herein enumerate the most important results by Soviet scientists in the development of the theory of the boundary layer.

Hypersonic Boundary Layer Transition Measurements Using NO2 approaches NO Photo-dissociation Tagging Velocimetry

NASA Technical Reports Server (NTRS)

Bathel, Brett F.; Johansen, Craig T.; Danehy, Paul M.; Inman, Jennifer A.; Jones, Stephen B.; Goyne, Christopher P.

2011-01-01

Measurements of instantaneous and mean streamwise velocity profiles in a hypersonic laminar boundary layer as well as a boundary layer undergoing laminar-to-turbulent transition were obtained over a 10-degree half-angle wedge model. A molecular tagging velocimetry technique consisting of a NO2 approaches?NO photo-dissociation reaction and two subsequent excitations of NO was used. The measurement of the transitional boundary layer velocity profiles was made downstream of a 1-mm tall, 4-mm diameter cylindrical trip along several lines lying within a streamwise measurement plane normal to the model surface and offset 6-mm from the model centerline. For laminar and transitional boundary layer measurements, the magnitudes of streamwise velocity fluctuations are compared. In the transitional boundary layer the fluctuations were, in general, 2-4 times larger than those in the laminar boundary layer. Of particular interest were fluctuations corresponding to a height of approximately 50% of the laminar boundary layer thickness having a magnitude of nearly 30% of the mean measured velocity. For comparison, the measured fluctuations in the laminar boundary layer were approximately 5% of the mean measured velocity at the same location. For the highest 10% signal-to-noise ratio data, average single-shot uncertainties using a 1 ?Es and 50 ?Es interframe delay were 115 m/s and 3 m/s, respectively. By averaging single-shot measurements of the transitional boundary layer, uncertainties in mean velocity as low as 39 m/s were obtained in the wind tunnel. The wall-normal and streamwise spatial resolutions were 0.14-mm (2 pixel) and 0.82-mm (11 pixels), respectively. These measurements were performed in the 31-inch Mach 10 Air Wind Tunnel at the NASA Langley Research Center.

Laminar-turbulent transition tripped by step on transonic compressor profile

NASA Astrophysics Data System (ADS)

Flaszynski, Pawel; Doerffer, Piotr; Szwaba, Ryszard; Piotrowicz, Michal; Kaczynski, Piotr

2018-02-01

The shock wave boundary layer interaction on the suction side of transonic compressor blade is one of the main objectives of TFAST project (Transition Location Effect on Shock Wave Boundary Layer Interaction). The experimental and numerical results for the flow structure investigations are shown for the flow conditions as the existing ones on the suction side of the compressor profile. The two cases are investigated: without and with boundary layer tripping device. In the first case, boundary layer is laminar up to the shock wave, while in the second case the boundary layer is tripped by the step. Numerical results carried out by means of Fine/Turbo Numeca with Explicit Algebraic Reynolds Stress Model including transition modeling are compared with schlieren, Temperature Sensitive Paint and wake measurements. Boundary layer transition location is detected by Temperature Sensitive Paint.

Sound-turbulence interaction in transonic boundary layers

NASA Astrophysics Data System (ADS)

Lelostec, Ludovic; Scalo, Carlo; Lele, Sanjiva

2014-11-01

Acoustic wave scattering in a transonic boundary layer is investigated through a novel approach. Instead of simulating directly the interaction of an incoming oblique acoustic wave with a turbulent boundary layer, suitable Dirichlet conditions are imposed at the wall to reproduce only the reflected wave resulting from the interaction of the incident wave with the boundary layer. The method is first validated using the laminar boundary layer profiles in a parallel flow approximation. For this scattering problem an exact inviscid solution can be found in the frequency domain which requires numerical solution of an ODE. The Dirichlet conditions are imposed in a high-fidelity unstructured compressible flow solver for Large Eddy Simulation (LES), CharLESx. The acoustic field of the reflected wave is then solved and the interaction between the boundary layer and sound scattering can be studied.

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.

Year-Long Vertical Velocity Statistics Derived from Doppler Lidar Data for the Continental Convective Boundary Layer

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

Berg, Larry K.; Newsom, Rob K.; Turner, David D.

One year of Coherent Doppler Lidar (CDL) data collected at the U.S. Department of Energy’s Atmospheric Radiation Measurement (ARM) site in Oklahoma is analyzed to provide profiles of vertical velocity variance, skewness, and kurtosis for cases of cloud-free convective boundary layers. The variance was scaled by the Deardorff convective velocity scale, which was successful when the boundary layer depth was stationary but failed in situations when the layer was changing rapidly. In this study the data are sorted according to time of day, season, wind direction, surface shear stress, degree of instability, and wind shear across the boundary-layer top. Themore » normalized variance was found to have its peak value near a normalized height of 0.25. The magnitude of the variance changes with season, shear stress, and degree of instability, but was not impacted by wind shear across the boundary-layer top. The skewness was largest in the top half of the boundary layer (with the exception of wintertime conditions). The skewness was found to be a function of the season, shear stress, wind shear across the boundary-layer top, with larger amounts of shear leading to smaller values. Like skewness, the vertical profile of kurtosis followed a consistent pattern, with peak values near the boundary-layer top (also with the exception of wintertime data). The altitude of the peak values of kurtosis was found to be lower when there was a large amount of wind shear at the boundary-layer top.« less

Towards a Viscous Wall Model for Immersed Boundary Methods

NASA Technical Reports Server (NTRS)

Brehm, Christoph; Barad, Michael F.; Kiris, Cetin C.

2016-01-01

Immersed boundary methods are frequently employed for simulating flows at low Reynolds numbers or for applications where viscous boundary layer effects can be neglected. The primary shortcoming of Cartesian mesh immersed boundary methods is the inability of efficiently resolving thin turbulent boundary layers in high-Reynolds number flow application. The inefficiency of resolving the thin boundary is associated with the use of constant aspect ratio Cartesian grid cells. Conventional CFD approaches can efficiently resolve the large wall normal gradients by utilizing large aspect ratio cells near the wall. This paper presents different approaches for immersed boundary methods to account for the viscous boundary layer interaction with the flow-field away from the walls. Different wall modeling approaches proposed in previous research studies are addressed and compared to a new integral boundary layer based approach. In contrast to common wall-modeling approaches that usually only utilize local flow information, the integral boundary layer based approach keeps the streamwise history of the boundary layer. This allows the method to remain effective at much larger y+ values than local wall modeling approaches. After a theoretical discussion of the different approaches, the method is applied to increasingly more challenging flow fields including fully attached, separated, and shock-induced separated (laminar and turbulent) flows.

Investigations on entropy layer along hypersonic hyperboloids using a defect boundary layer

NASA Technical Reports Server (NTRS)

Brazier, J. P.; Aupoix, B.; Cousteix, J.

1992-01-01

A defect approach coupled with matched asymptotic expansions is used to derive a new set of boundary layer equations. This method ensures a smooth matching of the boundary layer with the inviscid solution. These equations are solved to calculate boundary layers over hypersonic blunt bodies involving the entropy gradient effect. Systematic comparisons are made for both axisymmetric and plane flows in several cases with different Mach and Reynolds numbers. After a brief survey of the entropy layer characteristics, the defect boundary layer results are compared with standard boundary layer and full Navier-Stokes solutions. The entropy gradient effects are found to be more important in the axisymmetric case than in the plane one. The wall temperature has a great influence on the results through the displacement effect. Good predictions can be obtained with the defect approach over a cold wall in the nose region, with a first order solution. However, the defect approach gives less accurate results far from the nose on axisymmetric bodies because of the thinning of the entropy layer.

Temporal and Spatial Response of a Turbulent Boundary Layer to Forcing by Synthetic Jets

NASA Astrophysics Data System (ADS)

Hanson, Ronald; Ganapathisubramani, Bharathram; Lavoie, Philippe

2016-11-01

In this experimental study we examine the spatial and temporal response of a turbulent boundary layer affected by a single, and pair of, synthetic jet actuator(s). The spatial signature of the boundary layer mean-flow has been previously shown to result from large vortical motions caused by the interaction between the synthetic jets and the cross flow. By means of hot-wire measurements, phase-locked to the synthetic jet input, the propagation of the unsteady disturbance can be quantified over the actuation cycle of a synthetic jet. Using long samples both the phase-locked variation of the periodic (actuation cycle) and turbulent fluctuations are examined. It is shown that both the mean flow and turbulence characteristics are markedly different across the span, owing to the three dimensionality of the upstream input. Further, the disturbance shape and phase of the phase-locked disturbance varies significantly with forcing level, in part owing to the disruption of the mean velocity. Particular focus is given to the interaction occurring between the near-wall and outer region scales, which vary across the span, with respect to various forcing conditions. The financial support of Airbus is gratefully acknowledged.

Diurnal changes in urban boundary layer environment induced by urban greening

NASA Astrophysics Data System (ADS)

Song, Jiyun; Wang, Zhi-Hua

2016-11-01

Urban green infrastructure has been widely used for mitigating adverse environmental problems as well as enhancing urban sustainability of cities worldwide. Here we develop an integrated urban-land-atmosphere modeling framework with the land surface processes parameterized by an advanced urban canopy model and the atmospheric processes parameterized by a single column model. The model is then applied to simulate a variety of forms of green infrastructure, including urban lawns, shade trees, green and cool roofs, and their impact on environmental changes in the total urban boundary layer (UBL) for a stereotypical desert city, viz. Phoenix, Arizona. It was found that green roofs have a relatively uniform cooling effect proportional to their areal coverage. In particular, a reduction of UBL temperature of 0.3 °C and 0.2 °C per 10% increase of green roof coverage was observed at daytime and nighttime, respectively. In contrast, the effect of greening of street canyons is constrained by the overall abundance of green infrastructure and the energy available for evapotranspiration. In addition, the increase in urban greening causes boundary-layer height to decrease during daytime but increase at nighttime, leading to different trends of changes in urban air quality throughout a diurnal cycle.

Heat transfer, velocity-temperature correlation, and turbulent shear stress from Navier-Stokes computations of shock wave/turbulent boundary layer interaction flows

NASA Technical Reports Server (NTRS)

Wang, C. R.; Hingst, W. R.; Porro, A. R.

1991-01-01

The properties of 2-D shock wave/turbulent boundary layer interaction flows were calculated by using a compressible turbulent Navier-Stokes numerical computational code. Interaction flows caused by oblique shock wave impingement on the turbulent boundary layer flow were considered. The oblique shock waves were induced with shock generators at angles of attack less than 10 degs in supersonic flows. The surface temperatures were kept at near-adiabatic (ratio of wall static temperature to free stream total temperature) and cold wall (ratio of wall static temperature to free stream total temperature) conditions. The computational results were studied for the surface heat transfer, velocity temperature correlation, and turbulent shear stress in the interaction flow fields. Comparisons of the computational results with existing measurements indicated that (1) the surface heat transfer rates and surface pressures could be correlated with Holden's relationship, (2) the mean flow streamwise velocity components and static temperatures could be correlated with Crocco's relationship if flow separation did not occur, and (3) the Baldwin-Lomax turbulence model should be modified for turbulent shear stress computations in the interaction flows.

Soft repulsive mixtures under gravity: Brazil-nut effect, depletion bubbles, boundary layering, nonequilibrium shaking

NASA Astrophysics Data System (ADS)

Kruppa, Tobias; Neuhaus, Tim; Messina, René; Löwen, Hartmut

2012-04-01

A binary mixture of particles interacting via long-ranged repulsive forces is studied in gravity by computer simulation and theory. The more repulsive A-particles create a depletion zone of less repulsive B-particles around them reminiscent to a bubble. Applying Archimedes' principle effectively to this bubble, an A-particle can be lifted in a fluid background of B-particles. This "depletion bubble" mechanism explains and predicts a brazil-nut effect where the heavier A-particles float on top of the lighter B-particles. It also implies an effective attraction of an A-particle towards a hard container bottom wall which leads to boundary layering of A-particles. Additionally, we have studied a periodic inversion of gravity causing perpetuous mutual penetration of the mixture in a slit geometry. In this nonequilibrium case of time-dependent gravity, the boundary layering persists. Our results are based on computer simulations and density functional theory of a two-dimensional binary mixture of colloidal repulsive dipoles. The predicted effects also occur for other long-ranged repulsive interactions and in three spatial dimensions. They are therefore verifiable in settling experiments on dipolar or charged colloidal mixtures as well as in charged granulates and dusty plasmas.

Soft repulsive mixtures under gravity: brazil-nut effect, depletion bubbles, boundary layering, nonequilibrium shaking.

PubMed

Kruppa, Tobias; Neuhaus, Tim; Messina, René; Löwen, Hartmut

2012-04-07

A binary mixture of particles interacting via long-ranged repulsive forces is studied in gravity by computer simulation and theory. The more repulsive A-particles create a depletion zone of less repulsive B-particles around them reminiscent to a bubble. Applying Archimedes' principle effectively to this bubble, an A-particle can be lifted in a fluid background of B-particles. This "depletion bubble" mechanism explains and predicts a brazil-nut effect where the heavier A-particles float on top of the lighter B-particles. It also implies an effective attraction of an A-particle towards a hard container bottom wall which leads to boundary layering of A-particles. Additionally, we have studied a periodic inversion of gravity causing perpetuous mutual penetration of the mixture in a slit geometry. In this nonequilibrium case of time-dependent gravity, the boundary layering persists. Our results are based on computer simulations and density functional theory of a two-dimensional binary mixture of colloidal repulsive dipoles. The predicted effects also occur for other long-ranged repulsive interactions and in three spatial dimensions. They are therefore verifiable in settling experiments on dipolar or charged colloidal mixtures as well as in charged granulates and dusty plasmas.

Direct Numerical Simulations of Concentration and Temperature Polarization in Direct Contact Membrane Distillation

NASA Astrophysics Data System (ADS)

Lou, Jincheng; Tilton, Nils

2017-11-01

Membrane distillation (MD) is a method of desalination with boundary layers that are challenging to simulate. MD is a thermal process in which warm feed and cool distilled water flow on opposite sides of a hydrophobic membrane. The temperature difference causes water to evaporate from the feed, travel through the membrane, and condense in the distillate. Two challenges to MD are temperature and concentration polarization. Temperature polarization represents a reduction in the transmembrane temperature difference due to heat transfer through the membrane. Concentration polarization describes the accumulation of solutes near the membrane. These phenomena reduce filtration and lead to membrane fouling. They are difficult to simulate due to the coupling between the velocity, temperature, and concentration fields on the membrane. Unsteady regimes are particularly challenging because noise at the outlets can pollute the near-membrane flow fields. We present the development of a finite-volume method for the simulation of fluid flow, heat, and mass transport in MD systems. Using the method, we perform a parametric study of the polarization boundary layers, and show that the concentration boundary layer shows self-similar behavior that satisfies power laws for the downstream growth. Funded by the U.S. Bureau of Reclamation.

Effect of Surface Roughness on Polymer Drag Reduction with a High-Reynolds-Number Turbulent Boundary Layer

NASA Astrophysics Data System (ADS)

Elbing, Brian; Dowling, David; Solomon, Michael; Bian, Sherry; Ceccio, Steven

2007-11-01

A recent experiment at the U.S. Navy's Large Cavitation Channel (LCC) investigated the effect of wall roughness on wall-injection polymer drag reduction (PDR) within a high-Reynolds-number (10^7 to 2x10^8 based on downstream distance) turbulent boundary layer (TBL). Testing was performed in two parts: 1) PDR experiment on a 12.9 m long, 3.05 m wide hydro-dynamically smooth flat plate and 2) PDR experiment on the same model with the entire surface roughened. The roughness was produced by blowing glass beads into epoxy paint that was applied to the entire model. The roughened model had an average roughness height ranging between 307 and 1154 μm. Drag reduction was determined using six, stream-wise located integrated skin-friction balances. In addition to skin-friction measurements, sampling was performed at three stream-wise located ports. The sampling ports were used to determine the amount of degradation, if any, caused by the turbulent flow on the polymer. Both the skin-friction measurements and sampling analysis indicates that wall roughness in a turbulent boundary layer significantly increases degradation of the polymer solution.

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.

Inventory of File gfs.t06z.smartguam15.tm00.grib2

Science.gov Websites

hour fcst Visibility [m] 014 planetary boundary layer WDIR 15 hour fcst Wind Direction (from which blowing) [degtrue] 015 planetary boundary layer WIND 15 hour fcst Wind Speed [m/s] 016 planetary boundary layer RH 15 hour fcst Relative Humidity [%] 017 planetary boundary layer DIST 15 hour fcst Geometric

Physical modeling of the atmospheric boundary layer in the UNH Flow Physics Facility

NASA Astrophysics Data System (ADS)

Taylor-Power, Gregory; Gilooly, Stephanie; Wosnik, Martin; Klewicki, Joe; Turner, John

2016-11-01

The Flow Physics Facility (FPF) at UNH has test section dimensions W =6.0m, H =2.7m, L =72m. It can achieve high Reynolds number boundary layers, enabling turbulent boundary layer, wind energy and wind engineering research with exceptional spatial and temporal instrument resolution. We examined the FPF's ability to experimentally simulate different types of the atmospheric boundary layer (ABL) using upstream roughness arrays. The American Society for Civil Engineers defines standards for simulating ABLs for different terrain types, from open sea to dense city areas (ASCE 49-12). The standards require the boundary layer to match a power law shape, roughness height, and power spectral density criteria. Each boundary layer type has a corresponding power law exponent and roughness height. The exponent and roughness height both increase with increasing roughness. A suburban boundary layer was chosen for simulation and a roughness element fetch was created. Several fetch lengths were experimented with and the resulting boundary layers were measured and compared to standards in ASCE 49-12: Wind Tunnel Testing for Buildings and Other Structures. Pitot tube and hot wire anemometers were used to measure average and fluctuating flow characteristics. Velocity profiles, turbulence intensity and velocity spectra were found to compare favorably.

Effect of Pulsed Plasma Jets on the Recovering Boundary Layer Downstream of a Reflected Shock Interaction

NASA Astrophysics Data System (ADS)

Greene, Benton; Clemens, Noel; Magari, Patrick; Micka, Daniel; Ueckermann, Mattheus

2015-11-01

Shock-induced turbulent boundary layer separation can have many detrimental effects in supersonic inlets including flow distortion and instability, structural fatigue, poor pressure recovery, and unstart. The current study investigates the effect of pulsed plasma jets on the recovering boundary layer downstream of a reflected shock wave-boundary layer interaction. The effects of pitch and skew angle of the jet as well as the heating parameter and discharge time scale are tested using several pulsing frequencies. In addition, the effect of the plasma jets on the undisturbed boundary layer at 6 mm and 11 mm downstream of the jets is measured. A pitot-static pressure probe is used to measure the velocity profile of the boundary layer 35 mm downstream of the plasma jets, and the degree of boundary layer distortion is compared between the different models and run conditions. Additionally, the effect of each actuator configuration on the shape of the mean separated region is investigated using surface oil flow visualization. Previous studies with lower energy showed a weak effect on the downstream boundary layer. The current investigation will attempt to increase this effect using a higher-energy discharge. Funded by AFRL through and SBIR in collaboration with Creare, LLC.

Some Effects of Leading-Edge Sweep on Boundary-Layer Transition at Supersonic Speeds

NASA Technical Reports Server (NTRS)

Chapman, Gray T.

1961-01-01

The effects of crossflow and shock strength on transition of the laminar boundary layer behind a swept leading edge have been investigated analytically and with the aid of available experimental data. An approximate method of determining the crossflow Reynolds number on a leading edge of circular cross section at supersonic speeds is presented. The applicability of the critical crossflow criterion described by Owen and Randall for transition on swept wings in subsonic flow was examined for the case of supersonic flow over swept circular cylinders. A wide range of applicability of the subsonic critical values is indicated. The corresponding magnitude of crossflow velocity necessary to cause instability on the surface of a swept wing at supersonic speeds was also calculated and found to be small. The effects of shock strength on transition caused by Tollmien-Schlichting type of instability are discussed briefly. Changes in local Reynolds number, due to shock strength, were found analytically to have considerably more effect on transition caused by Tollmien-Schlichting instability than on transition caused by crossflow instability. Changes in the mechanism controlling transition from Tollmien-Schlichting instability to crossflow instability were found to be possible as a wing is swept back and to result in large reductions in the length of laminar flow.

Optimal Control of Shock Wave Turbulent Boundary Layer Interactions Using Micro-Array Actuation

NASA Technical Reports Server (NTRS)

Anderson, Bernhard H.; Tinapple, Jon; Surber, Lewis

2006-01-01

The intent of this study on micro-array flow control is to demonstrate the viability and economy of Response Surface Methodology (RSM) to determine optimal designs of micro-array actuation for controlling the shock wave turbulent boundary layer interactions within supersonic inlets and compare these concepts to conventional bleed performance. The term micro-array refers to micro-actuator arrays which have heights of 25 to 40 percent of the undisturbed supersonic boundary layer thickness. This study covers optimal control of shock wave turbulent boundary layer interactions using standard micro-vane, tapered micro-vane, and standard micro-ramp arrays at a free stream Mach number of 2.0. The effectiveness of the three micro-array devices was tested using a shock pressure rise induced by the 10 shock generator, which was sufficiently strong as to separate the turbulent supersonic boundary layer. The overall design purpose of the micro-arrays was to alter the properties of the supersonic boundary layer by introducing a cascade of counter-rotating micro-vortices in the near wall region. In this manner, the impact of the shock wave boundary layer (SWBL) interaction on the main flow field was minimized without boundary bleed.

Generalization of Boundary-Layer Momentum-Integral Equations to Three-Dimensional Flows Including Those of Rotating System

NASA Technical Reports Server (NTRS)

Mager, Arthur

1952-01-01

The Navier-Stokes equations of motion and the equation of continuity are transformed so as to apply to an orthogonal curvilinear coordinate system rotating with a uniform angular velocity about an arbitrary axis in space. A usual simplification of these equations as consistent with the accepted boundary-layer theory and an integration of these equations through the boundary layer result in boundary-layer momentum-integral equations for three-dimensional flows that are applicable to either rotating or nonrotating fluid boundaries. These equations are simplified and an approximate solution in closed integral form is obtained for a generalized boundary-layer momentum-loss thickness and flow deflection at the wall in the turbulent case. A numerical evaluation of this solution carried out for data obtained in a curving nonrotating duct shows a fair quantitative agreement with the measures values. The form in which the equations are presented is readily adaptable to cases of steady, three-dimensional, incompressible boundary-layer flow like that over curved ducts or yawed wings; and it also may be used to describe the boundary-layer flow over various rotating surfaces, thus applying to turbomachinery, propellers, and helicopter blades.

Modeling marine boundary-layer clouds with a two-layer model: A one-dimensional simulation

NASA Technical Reports Server (NTRS)

Wang, Shouping

1993-01-01

A two-layer model of the marine boundary layer is described. The model is used to simulate both stratocumulus and shallow cumulus clouds in downstream simulations. Over cold sea surfaces, the model predicts a relatively uniform structure in the boundary layer with 90%-100% cloud fraction. Over warm sea surfaces, the model predicts a relatively strong decoupled and conditionally unstable structure with a cloud fraction between 30% and 60%. A strong large-scale divergence considerably limits the height of the boundary layer and decreases relative humidity in the upper part of the cloud layer; thus, a low cloud fraction results. The efffects of drizzle on the boundary-layer structure and cloud fraction are also studied with downstream simulations. It is found that drizzle dries and stabilizes the cloud layer and tends to decouple the cloud from the subcloud layer. Consequently, solid stratocumulus clouds may break up and the cloud fraction may decrease because of drizzle.

Calculation of sidewall boundary-layer parameters from rake measurements for the Langley 0.3-meter transonic cryogenic tunnel

NASA Technical Reports Server (NTRS)

Murthy, A. V.

1987-01-01

Correction of airfoil data for sidewall boundary-layer effects requires a knowledge of the boundary-layer displacement thickness and the shape factor with the tunnel empty. To facilitate calculation of these quantities under various test conditions for the Langley 0.3 m Transonic Cryogenic Tunnel, a computer program was written. This program reads the various tunnel parameters and the boundary-layer rake total head pressure measurements directly from the Engineering Unit tapes to calculate the required sidewall boundary-layer parameters. Details of the method along with the results for a sample case are presented.

Studies on the influence on flexural wall deformations on the development of the flow boundary layer

NASA Technical Reports Server (NTRS)

Schilz, W.

1978-01-01

Flexural wave-like deformations can be used to excite boundary layer waves which in turn lead to the onset of turbulence in the boundary layer. The investigations were performed with flow velocities between 5 m/s and 40 m/s. With four different flexural wave transmissions a frequency range from 0.2 kc/s to 1.5 kc/s and a phase velocity range from 3.5 m/s to 12 m/s was covered. The excitation of boundary layer waves becomes most effective if the phase velocity of the flexural wave coincides with the phase velocity region of unstable boundary layer waves.

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.

Effect of aspect ratio on sidewall boundary-layer influence in two-dimensional airfoil testing

NASA Technical Reports Server (NTRS)

Murthy, A. V.

1986-01-01

The effect of sidewall boundary layers in airfoil testing in two-dimensional wind tunnels is investigated. The non-linear crossflow velocity variation induced because of the changes in the sidewall boundary-layer thickness is represented by the flow between a wavy wall and a straight wall. Using this flow model, a correction for the sidewall boundary-layer effects is derived in terms of the undisturbed sidewall boundary-layer properties, the test Mach number and the airfoil aspect ratio. Application of the proposed correction to available experimental data showed good correlation for the shock location and pressure distribution on airfoils.

Boundary-field-driven control of discontinuous phase transitions on hyperbolic lattices

NASA Astrophysics Data System (ADS)

Lee, Yoju; Verstraete, Frank; Gendiar, Andrej

2016-08-01

The multistate Potts models on two-dimensional hyperbolic lattices are studied with respect to various boundary effects. The free energy is numerically calculated using the corner transfer matrix renormalization group method. We analyze phase transitions of the Potts models in the thermodynamic limit with respect to contracted boundary layers. A false phase transition is present even if a couple of the boundary layers are contracted. Its significance weakens, as the number of the contracted boundary layers increases, until the correct phase transition (deep inside the bulk) prevails over the false one. For this purpose, we derive a thermodynamic quantity, the so-called bulk excess free energy, which depends on the contracted boundary layers and memorizes additional boundary effects. In particular, the magnetic field is imposed on the outermost boundary layer. While the boundary magnetic field does not affect the second-order phase transition in the bulk if suppressing all the boundary effects on the hyperbolic lattices, the first-order (discontinuous) phase transition is significantly sensitive to the boundary magnetic field. Contrary to the phase transition on the Euclidean lattices, the discontinuous phase transition on the hyperbolic lattices can be continuously controlled (within a certain temperature coexistence region) by varying the boundary magnetic field.

The influence of free-stream turbulence on turbulent boundary layers with mild adverse pressure gradients

NASA Technical Reports Server (NTRS)

Hoffmann, Jon A.

1988-01-01

The influence of near isotropic free-stream turbulence on the shape factors and skin friction coefficients of turbulent bounday layers is presented for the cases of zero and mild adverse pressure gradients. With free-stream turbulence, improved fluid mixing occurs in boundary layers with adverse pressure gradients relative to the zero pressure gradient condition, with the same free-stream turbulence intensity and length scale. Stronger boundary layers with lower shape factors occur as a result of a lower ratio of the integral scale of turbulence to the boundary layer thickness, and to vortex stretching of the turbulent eddies in the free stream, both of which act to improve the transmission of momentum from the free stream to the boundary layers.

Observing the Vertical Extent of the Urban Boundary Layer Over Jersey City, NJ: A Diurnal and Seasonal Analysis

NASA Astrophysics Data System (ADS)

Dempsey, M. J.; Booth, J.; Arend, M.; Melecio-Vazquez, D.; Gonzalez, J.

2015-12-01

The atmospheric boundary remains one of the more difficult components of the climate system to classify. One of the most important characteristics is the boundary layer height, especially in urban settings. The current study examines the boundary layer height using the the New York City Meteorological Network or NYCMetNet. NYCMetNet is a network of weather stations, which report meteorological conditions in and around New York City, as part of the Optical Remote Sensing Laboratory of The City College of New York (ORSL). Of interest to this study is the data obtained from wind profiler station LSC01. The 915 MHz wind profiler is located 30m above the ground on the roof of the Liberty Science Center in Jersey City, NJ. It is a Vaisala Wind Profiler LAP 3000 with a wavelength of ~34cm, which means that the instrument responds primarily to Bragg backscattering. Can a seasonal urban boundary layer climatology be extrapolated from the data obtained from the wind profiler? What is the timing of boundary layer evolution and collapse over Jersey City? How effective is the profiler under cloudy skies and even in light rain or snow? This study examines the entire time period covered by the wind profile (2007 to present) and selects a series of clear days and a series of cloudy days. The top of the urban boundary layer is subjectively located from each half hour time stamp of signal to noise values. The urban boundary layer heights are recorded for clear and then cloudy days. Then the days are sorted seasonally (DJF, MAM, JJA, SON). A seasonal mean is calculated for every half hour time step. Finally a time series of seasonal urban boundary layer heights is constructed, and the timing of the urban boundary layer height maximum and time evolution and collapse of the boundary layer are generalized. A comparison is made against urban boundary layer heights obtained from Modern-Era Retrospective Analysis For Research And Applications (MERRA).

Foliar trichomes, boundary layers, and gas exchange in 12 species of epiphytic Tillandsia (Bromeliaceae).

PubMed

Benz, Brett W; Martin, Craig E

2006-04-01

We examined the relationships between H2O and CO2 gas exchange parameters and leaf trichome cover in 12 species of Tillandsia that exhibit a wide range in trichome size and trichome cover. Previous investigations have hypothesized that trichomes function to enhance boundary layers around Tillandsioid leaves thereby buffering the evaporative demand of the atmosphere and retarding transpirational water loss. Data presented herein suggest that trichome-enhanced boundary layers have negligible effects on Tillandsia gas exchange, as indicated by the lack of statistically significant relationships in regression analyses of gas exchange parameters and trichome cover. We calculated trichome and leaf boundary layer components, and their associated effects on H2O and CO2 gas exchange. The results further indicate trichome-enhanced boundary layers do not significantly reduce transpirational water loss. We conclude that although the trichomes undoubtedly increase the thickness of the boundary layer, the increase due to Tillandsioid trichomes is inconsequential in terms of whole leaf boundary layers, and any associated reduction in transpirational water loss is also negligible within the whole plant gas exchange pathway.

Hydrodynamic structure of the boundary layers in a rotating cylindrical cavity with radial inflow

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

Herrmann-Priesnitz, Benjamín, E-mail: bherrman@ing.uchile.cl; Torres, Diego A.; Advanced Mining Technology Center, Universidad de Chile, Av. Tupper 2007, Santiago

A flow model is formulated to investigate the hydrodynamic structure of the boundary layers of incompressible fluid in a rotating cylindrical cavity with steady radial inflow. The model considers mass and momentum transfer coupled between boundary layers and an inviscid core region. Dimensionless equations of motion are solved using integral methods and a space-marching technique. As the fluid moves radially inward, entraining boundary layers develop which can either meet or become non-entraining. Pressure and wall shear stress distributions, as well as velocity profiles predicted by the model, are compared to numerical simulations using the software OpenFOAM. Hydrodynamic structure of themore » boundary layers is governed by a Reynolds number, Re, a Rossby number, Ro, and the dimensionless radial velocity component at the periphery of the cavity, U{sub o}. Results show that boundary layers merge for Re < < 10 and Ro > > 0.1, and boundary layers become predominantly non-entraining for low Ro, low Re, and high U{sub o}. Results may contribute to improve the design of technology, such as heat exchange devices, and turbomachinery.« less

Control of boundary layer transition location and plate vibration in the presence of an external acoustic field

NASA Technical Reports Server (NTRS)

Maestrello, L.; Grosveld, F. W.

1991-01-01

The experiment is aimed at controlling the boundary layer transition location and the plate vibration when excited by a flow and an upstream sound source. Sound has been found to affect the flow at the leading edge and the response of a flexible plate in a boundary layer. Because the sound induces early transition, the panel vibration is acoustically coupled to the turbulent boundary layer by the upstream radiation. Localized surface heating at the leading edge delays the transition location downstream of the flexible plate. The response of the plate excited by a turbulent boundary layer (without sound) shows that the plate is forced to vibrate at different frequencies and with different amplitudes as the flow velocity changes indicating that the plate is driven by the convective waves of the boundary layer. The acoustic disturbances induced by the upstream sound dominate the response of the plate when the boundary layer is either turbulent or laminar. Active vibration control was used to reduce the sound induced displacement amplitude of the plate.

A Marine Boundary Layer Water Vapor Climatology Derived from Microwave and Near-Infrared Imagery

NASA Astrophysics Data System (ADS)

Millan Valle, L. F.; Lebsock, M. D.; Teixeira, J.

2017-12-01

The synergy of the collocated Advanced Microwave Scanning Radiometer (AMSR) and the Moderate Resolution Imaging Spectroradiometer (MODIS) provides daily global estimates of partial marine planetary boundary layer water vapor. AMSR microwave radiometry provides the total column water vapor, while MODIS near-infrared imagery provides the water vapor above the cloud layers. The difference between the two gives the vapor between the surface and the cloud top, which may be interpreted as the boundary layer water vapor. Comparisons against radiosondes, and GPS-Radio occultation data demonstrate the robustness of these boundary layer water vapor estimates. We exploit the 14 years of AMSR-MODIS synergy to investigate the spatial, seasonal, and inter-annual variations of the boundary layer water vapor. Last, it is shown that the measured AMSR-MODIS partial boundary layer water vapor can be generally prescribed using sea surface temperature, cloud top pressure and the lifting condensation level. The multi-sensor nature of the analysis demonstrates that there exists more information on boundary layer water vapor structure in the satellite observing system than is commonly assumed when considering the capabilities of single instruments. 2017 California Institute of Technology. U.S. Government sponsorship acknowledged.

Use of Vortex Generators to Reduce Distortion for Mach 1.6 Streamline-Traced Supersonic Inlets

NASA Technical Reports Server (NTRS)

Baydar, Ezgihan; Lu, Frank; Slater, John W.; Trefny, Chuck

2016-01-01

Reduce the total pressure distortion at the engine-fan face due to low-momentum flow caused by the interaction of an external terminal shock at the turbulent boundary layer along a streamline-traced external-compression (STEX) inlet for Mach 1.6.

Improved planetary boundary layer retrievals using a combination of direct and reflected bending angles from radio occultations

NASA Astrophysics Data System (ADS)

Wang, K. N.; Ao, C. O.; de la Torre Juarez, M.

2017-12-01

As a remote sensing technique, Global Positioning System (GPS) radio occultation (RO) is a suitable method to observe lower troposphere due to its high vertical resolution and cloud-penetrating capability. However, super-refraction (SR), or ducting, caused by large refractivity gradients usually associated with the top of the planetary boundary layer, can violate the uniqueness condition necessary for the traditional inverse Abel transform. Consequently, the retrieved refractivity, which is the minimum profile among an infinite number of potential solutions corresponding to the same bending angle profile, will be negatively biased under ducting layers. Previous research has shown that optimal estimation techniques that combine low altitude RO retrievals and the collocated precipitable water (PW) estimates can effectively reduce the negative RO bias and enhance the data quality under the ducting layer (Wang et al, 2017). Here we propose an improvement that uses the reflected RO bending angle observation information as a source for refractivity constraints. The RO signal reflected from the Earth surface profile can be reconstructed by solely using GPS-RO data without requiring external information such as PW. The radio holographic (RH) method is adapted here to calculate the reflected RO bending angle, and the forward model simulation is implemented to validate this preliminary concept. Our results suggest that this new approach can distinguish between different refractivity profiles when ducting occurs and theoretically this should reduce the negative bias. In addition, It also improves the RO observation in lower troposphere by capturing the sharpness and height of the critical layer separating the free troposphere from the boundary layer.

Aerosols attenuating the solar radiation collected by solar tower plants: The horizontal pathway at surface level

NASA Astrophysics Data System (ADS)

Elias, Thierry; Ramon, Didier; Dubus, Laurent; Bourdil, Charles; Cuevas-Agulló, Emilio; Zaidouni, Taoufik; Formenti, Paola

2016-05-01

Aerosols attenuate the solar radiation collected by solar tower plants (STP), along two pathways: 1) the atmospheric column pathway, between the top of the atmosphere and the heliostats, resulting in Direct Normal Irradiance (DNI) changes; 2) the grazing pathway close to surface level, between the heliostats and the optical receiver. The attenuation along the surface-level grazing pathway has been less studied than the aerosol impact on changes of DNI, while it becomes significant in STP of 100 MW or more. Indeed aerosols mostly lay within the surface atmospheric layer, called the boundary layer, and the attenuation increases with the distance covered by the solar radiation in the boundary layer. In STP of 100 MW or more, the distance between the heliostats and the optical receiver becomes large enough to produce a significant attenuation by aerosols. We used measured aerosol optical thickness and computed boundary layer height to estimate the attenuation of the solar radiation at surface level at Ouarzazate (Morocco). High variabilities in aerosol amount and in vertical layering generated a significant magnitude in the annual cycle and significant inter-annual changes. Indeed the annual mean of the attenuation caused by aerosols over a 1-km heliostat-receiver distance was 3.7% in 2013, and 5.4% in 2014 because of a longest desert dust season. The monthly minimum attenuation of less than 3% was observed in winter and the maximum of more than 7% was observed in summer.

Titan's lower troposphere: thermal structure and dynamics

NASA Astrophysics Data System (ADS)

Charnay, B.; Lebonnois, S.

2011-12-01

A new climate model for Titan's atmosphere has been developed, using the physics of the IPSL Titan 2-dimensional climate model with the current version of the LMDZ General Circulation Model's dynamical core. The GCM covers altitudes from the surface to 500 km with the diurnal cycle and the gravitational tides included. 1. Boundary layer and thermal structure The HASI profile of potential temperature shows a layer at 300 m, an other at 800 m and a slope change at 2 km ([5],[2]). Dune spacing on Titan is consistent with a 2-3 km boundary layer ([3]). We have reproduced this profile (see figure) and interpreted the layer at 300 m as a convective boundary layer, the layer at 800 m is a residual layer corresponding to the maximum diurnal vertical extension of the PBL. We interpret the slope change at 2 km as produced by the seasonal displacement of the ITCZ. This layer traps the circulation in the first two km and is responsible of the dune spacing. Finally we interpret the fog discovered in summer polar region ([1]) has clouds produced by the diurnal cycle of the PBL (as fair weather cumulus on Earth). 2. Surface winds 2.1 Effect of gravitational and thermal tides We analysed tropospheric winds and the influence of both the thermal and the gravitational tides. The impact of gravitational tides on the circulation is extremely small. Thermal tides have a visible effect, though quite tenuous. 2.2 Effect of topography We produced topography maps derived from spherical harmonic interpolation ([6]) on the reference ellipsoid ([4]). Surface temperatures at high altitude appear higher that the ambient air. Vertical air movements produce anabatic winds developing on smooth and long slopes. This could be one of the main causes controlling the direction of surface winds and the direction of dunes. References [1] Brown et al.: Discovery of fog at the south pole of Titan, Astrophys. J. 706 (2009), pp. L110-L113 [2] Griffith et al.: Titan's Tropical Storms in an Evolving Atmosphere, Astrophys. J. 687 (2008) L41-L44. [3] Lorenz et al.: A 3 km atmospheric boundary layer on Titan indiacted by dune spacing and Huygens data, Icarus 205, 719-721 (2010) [4] Luciano Iess et al.: Gravity Field, Shape, and Moment of Inertia of Titan, Science 327, 1367(2010) [5] Tokano et al.: Titan's planetary boundary layer structure at the Huygens landing site, J. Geophys. Res vol. 111 (2006) [6] HA. Zebker et al.: Size and Shape of Saturn's Moon TitanScience 324, 921(2009)

A novel investigation of a micropolar fluid characterized by nonlinear constitutive diffusion model in boundary layer flow and heat transfer.

PubMed

Sui, Jize; Zhao, Peng; Cheng, Zhengdong; Zheng, Liancun; Zhang, Xinxin

2017-02-01

The rheological and heat-conduction constitutive models of micropolar fluids (MFs), which are important non-Newtonian fluids, have been, until now, characterized by simple linear expressions, and as a consequence, the non-Newtonian performance of such fluids could not be effectively captured. Here, we establish the novel nonlinear constitutive models of a micropolar fluid and apply them to boundary layer flow and heat transfer problems. The nonlinear power law function of angular velocity is represented in the new models by employing generalized " n -diffusion theory," which has successfully described the characteristics of non-Newtonian fluids, such as shear-thinning and shear-thickening fluids. These novel models may offer a new approach to the theoretical understanding of shear-thinning behavior and anomalous heat transfer caused by the collective micro-rotation effects in a MF with shear flow according to recent experiments. The nonlinear similarity equations with a power law form are derived and the approximate analytical solutions are obtained by the homotopy analysis method, which is in good agreement with the numerical solutions. The results indicate that non-Newtonian behaviors involving a MF depend substantially on the power exponent n and the modified material parameter [Formula: see text] introduced by us. Furthermore, the relations of the engineering interest parameters, including local boundary layer thickness, local skin friction, and Nusselt number are found to be fitted by a quadratic polynomial to n with high precision, which enables the extraction of the rapid predictions from a complex nonlinear boundary-layer transport system.

Analysis of ferrite nanoparticles in the flow of ferromagnetic nanofluid

PubMed Central

Nadeem, Sohail; Mustafa, M. T.

2018-01-01

Theoretical analysis has been carried out to establish the heat transport phenomenon of six different ferromagnetic MnZnFe2O4—C2H6O2 (manganese zinc ferrite-ethylene glycol), NiZnFe2O4—C2H6O2 (Nickel zinc ferrite-ethylene glycol), Fe2O4—C2H6O2 (magnetite ferrite-ethylene glycol), NiZnFe2O4—H2O (Nickel zinc ferrite-water), MnZnFe2O4—H2O (manganese zinc ferrite-water), and Fe2O4—H2O (magnetite ferrite-water) nanofluids containing manganese zinc ferrite, Nickel zinc ferrite, and magnetite ferrite nanoparticles dispersed in a base fluid of ethylene glycol and water mixture. The performance of convective heat transfer is elevated in boundary layer flow region via nanoparticles. Magnetic dipole in presence of ferrites nanoparticles plays a vital role in controlling the thermal and momentum boundary layers. In perspective of this, the impacts of magnetic dipole on the nano boundary layer, steady, and laminar flow of incompressible ferromagnetic nanofluids are analyzed in the present study. Flow is caused by linear stretching of the surface. Fourier’s law of heat conduction is used in the evaluation of heat flux. Impacts of emerging parameters on the magneto—thermomechanical coupling are analyzed numerically. Further, it is evident that Newtonian heating has increasing behavior on the rate of heat transfer in the boundary layer. Comparison with available results for specific cases show an excellent agreement. PMID:29320488

A novel investigation of a micropolar fluid characterized by nonlinear constitutive diffusion model in boundary layer flow and heat transfer

PubMed Central

Zhao, Peng; Cheng, Zhengdong; Zheng, Liancun; Zhang, Xinxin

2017-01-01

The rheological and heat-conduction constitutive models of micropolar fluids (MFs), which are important non-Newtonian fluids, have been, until now, characterized by simple linear expressions, and as a consequence, the non-Newtonian performance of such fluids could not be effectively captured. Here, we establish the novel nonlinear constitutive models of a micropolar fluid and apply them to boundary layer flow and heat transfer problems. The nonlinear power law function of angular velocity is represented in the new models by employing generalized “n-diffusion theory,” which has successfully described the characteristics of non-Newtonian fluids, such as shear-thinning and shear-thickening fluids. These novel models may offer a new approach to the theoretical understanding of shear-thinning behavior and anomalous heat transfer caused by the collective micro-rotation effects in a MF with shear flow according to recent experiments. The nonlinear similarity equations with a power law form are derived and the approximate analytical solutions are obtained by the homotopy analysis method, which is in good agreement with the numerical solutions. The results indicate that non-Newtonian behaviors involving a MF depend substantially on the power exponent n and the modified material parameter K0 introduced by us. Furthermore, the relations of the engineering interest parameters, including local boundary layer thickness, local skin friction, and Nusselt number are found to be fitted by a quadratic polynomial to n with high precision, which enables the extraction of the rapid predictions from a complex nonlinear boundary-layer transport system. PMID:28344433

Effect of wakes on land-atmosphere fluxes

NASA Astrophysics Data System (ADS)

Markfort, C. D.; Zhang, W.; Porte-Agel, F.; Stefan, H. G.

2011-12-01

Wakes affect land-atmosphere fluxes of momentum and scalars, including water vapor and trace gases. Canopies and bluff bodies, including forests, buildings and topography, cause boundary layer flow separation, significantly extend flow recovery, and lead to a break down of standard Monin-Obukhov similarity relationships in the atmospheric boundary layer (ABL). Wakes generated by these land surface features persist for significant distances affecting a large fraction of the Earth's terrestrial surface. This effect is currently not accounted for in land-atmosphere modeling, and little is known about how heterogeneity of wake-generating features effect land surface fluxes. Additionally flux measurements, made in wake-affected regions, do not satisfy the homogeneous requirements for the standard eddy correlation (EC) method. This phenomenon often referred to as sheltering has been shown to affect momentum and kinetic energy fluxes into lakes from the atmosphere (Markfort et al. 2010). This presentation will highlight results from controlled wind tunnel experiments of neutral and thermally stratified boundary layers, using PIV and custom x-wire/cold-wire anemometry, designed to understand how the physical structure of upstream bluff bodies or porous canopies and thermal stability affect the separation zone, boundary layer recovery and surface fluxes. We also compare these results to field measurements taken with a Doppler LiDAR in the wake of a canopy and a building. We have found that there is a nonlinear relationship between porosity and flow separation behind a canopy to clearing transition. Results will provide the basis for new parameterizations to account for wake effects on land-atmosphere fluxes and corrections for EC measurements over open fields, lakes, and wetlands.

Medium fidelity modelling of loads in wind farms under non-neutral ABL stability conditions - a full-scale validation study

NASA Astrophysics Data System (ADS)

Larsen, G. C.; Larsen, T. J.; Chougule, A.

2017-05-01

The aim of the present paper is to demonstrate the capability of medium fidelity modelling of wind turbine component fatigue loading, when the wind turbines are subjected to wake affected non-stationary flow fields under non-neutral atmospheric stability conditions. To accomplish this we combine the classical Dynamic Wake Meandering model with a fundamental conjecture stating: Atmospheric boundary layer stability affects primary wake meandering dynamics driven by large turbulent scales, whereas wake expansion in the meandering frame of reference is hardly affected. Inclusion of stability (i.e. buoyancy) in description of both large- and small scale atmospheric boundary layer turbulence is facilitated by a generalization of the classical Mann spectral tensor, which consistently includes buoyancy effects. With non-stationary wind turbine inflow fields modelled as described above, fatigue loads are obtained using the state-of-the art aeroelastic model HAWC2. The Lillgrund offshore wind farm (WF) constitute an interesting case study for wind farm model validation, because the WT interspacing is small, which in turn means that wake effects are significant. A huge data set, comprising 5 years of blade and tower load recordings, is available for model validation. For a multitude of wake situations this data set displays a considerable scatter, which to a large degree seems to be caused by atmospheric boundary layer stability effects. Notable is also that rotating wind turbine components predominantly experience high fatigue loading for stable stratification with significant shear, whereas high fatigue loading of non-rotating wind turbine components are associated with unstable atmospheric boundary layer stratification.

Surface Roughness Measurement on a Wing Aircraft by Speckle Correlation

PubMed Central

Salazar, Félix; Barrientos, Alberto

2013-01-01

The study of the damage of aeronautical materials is important because it may change the microscopic surface structure profiles. The modification of geometrical surface properties can cause small instabilities and then a displacement of the boundary layer. One of the irregularities we can often find is surface roughness. Due to an increase of roughness and other effects, there may be extra momentum losses in the boundary layer and a modification in the parasite drag. In this paper we present a speckle method for measuring the surface roughness on an actual unmanned aircraft wing. The results show an inhomogeneous roughness distribution on the wing, as expected according to the anisotropic influence of the winds over the entire wing geometry. A calculation of the uncertainty of the technique is given. PMID:24013488

Surface roughness measurement on a wing aircraft by speckle correlation.

PubMed

Salazar, Félix; Barrientos, Alberto

2013-09-05

The study of the damage of aeronautical materials is important because it may change the microscopic surface structure profiles. The modification of geometrical surface properties can cause small instabilities and then a displacement of the boundary layer. One of the irregularities we can often find is surface roughness. Due to an increase of roughness and other effects, there may be extra momentum losses in the boundary layer and a modification in the parasite drag. In this paper we present a speckle method for measuring the surface roughness on an actual unmanned aircraft wing. The results show an inhomogeneous roughness distribution on the wing, as expected according to the anisotropic influence of the winds over the entire wing geometry. A calculation of the uncertainty of the technique is given.

The role of airfoil geometry in minimizing the effect of insect contamination of laminar flow sections

NASA Technical Reports Server (NTRS)

Maresh, J. L.; Bragg, M. B.

1984-01-01

A method has been developed to predict the contamination of an airfoil by insects and the resultant performance penalty. Insect aerodynamics have been modeled and the impingement of insects on an airfoil are solved by calculating their trajectories. Upon impact, insect rupture and the resulting height of the debris is determined based on experimental data. A boundary layer analysis is performed to determine which insects cause boundary layer transition and the resultant drag penalty. A contaminated airfoil figure of merit is presented to be used to compare airfoil susceptibility. Results show that the insect contamination effects depend on accretion conditions, airfoil angle of attack and Reynolds number. The importance of the stagnation region to designing airfoils for minimum drag penalties is discussed.

Boundary layers in cataclysmic variables: The HEAO-1 X-ray constraints

NASA Technical Reports Server (NTRS)

Jensen, K. A.

1983-01-01

The predictions of the boundary layer model for the X-ray emission from novae are summarized. A discrepancy between observations and theory in the X-ray observations is found. Constraints on the nature of the boundary layers in novae, based on the lack of detections of novae in the HEAO-1 soft X-ray survey are provided. Temperature and column densities for optically thick boundary layers in novae are estimated.

Turbulent boundary layers with secondary flow

NASA Technical Reports Server (NTRS)

Grushwitz, E.

1984-01-01

An experimental analysis of the boundary layer on a plane wall, along which the flow occurs, whose potential flow lines are curved in plane parallel to the wall is discussed. According to the equation frequently applied to boundary layers in a plane flow, which is usually obtained by using the pulse law, a generalization is derived which is valid for boundary layers with spatial flow. The wall shear stresses were calculated with this equation.

Investigation of blown boundary layers with an improved wall jet system. Ph.D. Thesis. Final Technical Report, 1 Jul. 1978 - Dec. 1979; [to prevent turbulent boundary layer separation

NASA Technical Reports Server (NTRS)

Saripalli, K. R.; Simpson, R. L.

1979-01-01

The behavior of two dimensional incompressible turbulent wall jets submerged in a boundary layer when they are used to prevent boundary layer separation on plane surfaces is investigated. The experimental set-up and instrumentation are described. Experimental results of zero pressure gradient flow and adverse pressure gradient flow are presented. Conclusions are given and discussed.

Three-dimensional boundary layers approaching separation

NASA Technical Reports Server (NTRS)

Williams, J. C., III

1976-01-01

The theory of semi-similar solutions of the laminar boundary layer equations is applied to several flows in which the boundary layer approaches a three-dimensional separation line. The solutions obtained are used to deduce the nature of three-dimensional separation. It is shown that in these cases separation is of the "ordinary" type. A solution is also presented for a case in which a vortex is embedded within the three-dimensional boundary layer.

Inventory of File gfs.t06z.smartguam24.tm00.grib2

Science.gov Websites

boundary layer WDIR 24 hour fcst Wind Direction (from which blowing) [degtrue] 016 planetary boundary layer WIND 24 hour fcst Wind Speed [m/s] 017 planetary boundary layer RH 24 hour fcst Relative Humidity [%] 018 planetary boundary layer DIST 24 hour fcst Geometric Height [m] 019 surface 4LFTX 24 hour fcst

Destiny of earthward streaming plasma in the plasmasheet boundary layer

NASA Technical Reports Server (NTRS)

Green, J. L.; Horwitz, J. L.

1986-01-01

The dynamics of the earth's magnetotail have been investigated, and it has become clear that the plasmasheet boundary layer field lines map into the Region I Field-Aligned Currents (FAC) of the auroral zone. It is pointed out that the role of earthward streaming ions in the plasmasheet boundary layer may be of fundamental importance in the understanding of magnetotail dynamics, auroral zone physics, and especially for ionospheric-magnetospheric interactions. The present paper has the objective to evaluate propagation characteristics for the earthward streaming ions observed in the plasmasheet boundary layer. An investigation is conducted of the propagation characteristics of protons in the plasmasheet boundary layer using independent single particle dynamics, and conclusions are discussed. The density of earthward streaming ions found in the plasmasheet boundary layer should include the ring current as well as the auroral zone precipitaiton and inner plasmasheet regions of the magnetosphere.

Application of the E - Turbulence Closure Model to the Neutral and Stable Atmospheric Boundary Layer.

NASA Astrophysics Data System (ADS)

Duynkerke, P. G.

1988-03-01

In the E - turbulence model an eddy-exchange coefficient is evaluated from the turbulent kinetic energy E and viscous dissipation . In this study we will apply the E - model to the stable and neutral atmospheric boundary layer. A discussion is given on the equation for , which terms should be included and how we have evaluated the constants. Constant cooling rate results for the stable atmospheric boundary layer are compared with a second-order closure study. For the neutral atmospheric boundary layer a comparison is made with observations, large-eddy simulations and a second-order closure study. It is shown that a small stability effect can change the neutral atmospheric boundary layer quite drastically, and therefore, it will be difficult to observe a neutral boundary layer in the atmosphere.

a Fractal Permeability Model Coupling Boundary-Layer Effect for Tight Oil Reservoirs

NASA Astrophysics Data System (ADS)

Wang, Fuyong; Liu, Zhichao; Jiao, Liang; Wang, Congle; Guo, Hu

A fractal permeability model coupling non-flowing boundary-layer effect for tight oil reservoirs was proposed. Firstly, pore structures of tight formations were characterized with fractal theory. Then, with the empirical equation of boundary-layer thickness, Hagen-Poiseuille equation and fractal theory, a fractal torturous capillary tube model coupled with boundary-layer effect was developed, and verified with experimental data. Finally, the parameters influencing effective liquid permeability were quantitatively investigated. The research results show that effective liquid permeability of tight formations is not only decided by pore structures, but also affected by boundary-layer distributions, and effective liquid permeability is the function of fluid type, fluid viscosity, pressure gradient, fractal dimension, tortuosity fractal dimension, minimum pore radius and maximum pore radius. For the tight formations dominated with nanoscale pores, boundary-layer effect can significantly reduce effective liquid permeability, especially under low pressure gradient.

A review of turbulent-boundary-layer heat transfer research at Stanford, 1958-1983

NASA Technical Reports Server (NTRS)

Moffat, R. J.; Kays, W. M.

1984-01-01

For the past 25 years, there has existed in the Thermosciences Laboratory of the Mechanical Engineering Department of Stanford University a research program, primarily experimental, concerned with heat transfer through turbulent boundary layers. In the early phases of the program, the topics considered were the simple zero-pressure-gradient turbulent boundary layer with constant and with varying surface temperature, and the accelerated boundary layer. Later equilibrium boundary layers were considered along with factors affecting the boundary layer, taking into account transpired flows, flows with axial pressure gradients, transpiration, acceleration, deceleration, roughness, full-coverage film cooling, surface curvature, free convection, and mixed convection. A description is provided of the apparatus and techniques used, giving attention to the smooth plate rig, the rough plate rig, the full-coverage film cooling rig, the curvature rig, the concave wall rig, the mixed convection tunnel, and aspects of data reduction and uncertainty analysis.

Interaction of solar wind with the magnetopause-boundary layer and generation of magnetic impulse events

NASA Technical Reports Server (NTRS)

Lee, L. C.; Wei, C. Q.

1993-01-01

The transport of mass, momentum, energy and waves from the solar wind to the Earth's magnetosphere takes place in the magnetopause-boundary layer region. Various plasma processes that may occur in this region have been proposed and studied. In this paper, we present a brief review of the plasma processes in the dayside magnetopause-boundary layer. These processes include (1) flux transfer events at the dayside magnetopause, (2) formation of plasma vortices in the low-latitude boundary layer by the Kelvin-Helmholtz instability and coupling to the polar ionosphere, (3) the response of the magnetopause to the solar wind dynamic pressure pulses, and (4) the impulsive penetration of solar wind plasma filaments through the dayside magnetopause into the magnetospheric boundary layer. Through the coupling of the magnetopause-boundary layer to the polar ionosphere, those above processes may lead to occurrence of magnetic impulse events observed in the high-latitude stations.

Three Dimensional Viscous Flow Field in an Axial Flow Turbine Nozzle Passage

NASA Technical Reports Server (NTRS)

Ristic, D.; Lakshminarayana, B.

1997-01-01

The objective of this investigation is experimental and computational study of three dimensional viscous flow field in the nozzle passage of an axial flow turbine stage. The nozzle passage flow field has been measured using a two sensor hot-wire probe at various axial and radial stations. In addition, two component LDV measurements at one axial station (x/c(sum m) = 0.56) were performed to measure the velocity field. Static pressure measurements and flow visualization, using a fluorescent oil technique, were also performed to obtain the location of transition and the endwall limiting streamlines. A three dimensional boundary layer code, with a simple intermittency transition model, was used to predict the viscous layers along the blade and endwall surfaces. The boundary layers on the blade surface were found to be very thin and mostly laminar, except on the suction surface downstream of 70% axial chord. Strong radial pressure gradient, especially close to the suction surface, induces strong cross flow components in the trailing edge regions of the blade. On the end-walls the boundary layers were much thicker, especially near the suction corner of the casing surface, caused by secondary flow. The secondary flow region near the suction-casing surface corner indicates the presence of the passage vortex detached from the blade surface. The corner vortex is found to be very weak. The presence of a closely spaced rotor downstream (20% of the nozzle vane chord) introduces unsteadiness in the blade passage. The measured instantaneous velocity signal was filtered using FFT square window to remove the periodic unsteadiness introduced by the downstream rotor and fans. The filtering decreased the free stream turbulence level from 2.1% to 0.9% but had no influence on the computed turbulence length scale. The computation of the three dimensional boundary layers is found to be accurate on the nozzle passage blade surfaces, away from the end-walls and the secondary flow region. On the nozzle passage endwall surfaces the presence of strong pressure gradients and secondary flow limit the validity of the boundary layer code.

F-16XL ship #1 - CAWAP boundary layer rakes and hot film on left wing

NASA Technical Reports Server (NTRS)

1996-01-01

This photo shows the boundary layer hot film and the boundary layer rakes on the left wing of NASA's single-seat F-16XL (ship #1) used for the Cranked-Arrow Wing Aerodynamic Project (CAWAP) at Dryden Flight Research Center, Edwards, California. The modified airplane features a delta 'cranked-arrow' wing with strips of tubing along the leading edge to the trailing edge to sense static on the wing and obtain pressure distribution data. The right wing receives data on pressure distribution and the left wing has three types of instrumentation - preston tubes to measure local skin friction, boundary layer rakes to measure boundary layer profiles (the layer where the air interacts with the surfaces of a moving aircraft), and hot films to determine boundary layer transition locations. The program also gathered aero data on two wing planforms for NASA's High Speed Research Program. The first flight of CAWAP occurred on November 21, 1995, and the test program ended in April 1996.

Boundary-Layer Characteristics Over a Coastal Megacity

NASA Astrophysics Data System (ADS)

Melecio-Vazquez, D.; Ramamurthy, P.; Arend, M.; Moshary, F.; Gonzalez, J.

2017-12-01

Boundary-layer characteristics over New York City are analyzed for various local and synoptic conditions over several seasons. An array of vertical profilers, including a Doppler LiDAR, a micro-pulse LiDAR and a microwave radiometer are used to observe the structure and evolution of the boundary-layer. Additionally, an urbanized Weather Research and Forecasting (uWRF) model coupled to a high resolution landcover/land-use database is used to study the spatial variability in boundary layer characteristics. The summer daytime averaged potential temperature profile from the microwave radiometer shows the presence of a thermal internal boundary layer wherein a superadiabatic layer lies underneath a stable layer instead of a mixed-layer. Both the winter daytime and nighttime seasonal averages show that the atmosphere remains unstable near the surface and does not reach stable conditions during the nighttime. The mixing ratio seasonal averages show peaks in humidity near 200-m and 1100-m, above instrument level, which could result from sea breeze and anthropogenic sources. Ceilometer measurements show a high degree of variability in boundary layer height depending on wind direction. Comparison with uWRF results show that the model tends to overestimate convective efficiency for selected summer and winter cases and therefore shows a much deeper thermal boundary layer than the observed profiles. The model estimates a less humid atmosphere than seen in observations.

Vorticity interaction effects on blunt bodies. [hypersonic viscous shock layers

NASA Technical Reports Server (NTRS)

Anderson, E. C.; Wilcox, D. C.

1977-01-01

Numerical solutions of the viscous shock layer equations governing laminar and turbulent flows of a perfect gas and radiating and nonradiating mixtures of perfect gases in chemical equilibrium are presented for hypersonic flow over spherically blunted cones and hyperboloids. Turbulent properties are described in terms of the classical mixing length. Results are compared with boundary layer and inviscid flowfield solutions; agreement with inviscid flowfield data is satisfactory. Agreement with boundary layer solutions is good except in regions of strong vorticity interaction; in these flow regions, the viscous shock layer solutions appear to be more satisfactory than the boundary layer solutions. Boundary conditions suitable for hypersonic viscous shock layers are devised for an advanced turbulence theory.

The Atmospheric Boundary Layer

ERIC Educational Resources Information Center

Tennekes, Hendrik

1974-01-01

Discusses some important parameters of the boundary layer and effects of turbulence on the circulation and energy dissipation of the atmosphere. Indicates that boundary-layer research plays an important role in long-term forecasting and the study of air-pollution meteorology. (CC)

Internal and external 2-d boundary layer flows

NASA Technical Reports Server (NTRS)

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

1978-01-01

Computer program computes general two dimensional turbulent boundary-layer flow using finite-difference techniques. Structure allows for user modification to accommodate unique problems. Program should prove useful in many applications where accurate boundary-layer flow calculations are required.

The turbulent plasmasphere boundary layer and the outer radiation belt boundary

NASA Astrophysics Data System (ADS)

Mishin, Evgeny; Sotnikov, Vladimir

2017-12-01

We report on observations of enhanced plasma turbulence and hot particle distributions in the plasmasphere boundary layer formed by reconnection-injected hot plasma jets entering the plasmasphere. The data confirm that the electron pressure peak is formed just outward of the plasmapause in the premidnight sector. Free energy for plasma wave excitation comes from diamagnetic ion currents near the inner edge of the boundary layer due to the ion pressure gradient, electron diamagnetic currents in the entry layer near the electron plasma sheet boundary, and anisotropic (sometimes ring-like) ion distributions revealed inside, and further inward of, the inner boundary. We also show that nonlinear parametric coupling between lower oblique resonance and fast magnetosonic waves significantly contributes to the VLF whistler wave spectrum in the plasmasphere boundary layer. These emissions represent a distinctive subset of substorm/storm-related VLF activity in the region devoid of substorm injected tens keV electrons and could be responsible for the alteration of the outer radiation belt boundary during (sub)storms.

Study of the Effect of Free-Stream Turbulence upon Disturbances in the Pre-Transitional Laminar Boundary Layer. Part I. Laminar Boundary Layer Distortion by Surface Roughness; Effect upon Stability. Part II.

DTIC Science & Technology

1982-04-01

Boundary Layer Near a Plate." NACA Rept. 562, 1936. 5) A. A. Hall and G. S. Hislop , "Experiments on the Transition of the Laminar Boundary Layer on a...Cylinder." Proc. 5th Inter. Congr. Appl. Math, 1938. 7) G. S. Hislop , "The Transition of a Laminar Boundary Layer in a Wind Tunnel." Ph.D. Thesis...Small Vertical Cylinder Attached to a Flat Plate", h Fa- Elul"s, Vol. 23, Part 1, pp. 221-223, Jan. 1980 . 9. A. Von Doenhoff and E. A. Horton, "A Low

Electron distributions in the plasma sheet boundary layer - Time-of-flight effects

NASA Technical Reports Server (NTRS)

Onsager, T. G.; Thomsen, M. F.; Gosling, J. T.; Bame, S. J.

1990-01-01

The electron edge of the plasma sheet boundary layer lies lobeward of the ion edge. Measurements obtained near the electron edge of the boundary layer reveal low-speed cutoffs for earthward and tailward-flowing electrons. These cutoffs progress to lower speeds with deeper penetration into the boundary layer, and are consistently lower for the earthward-directed electrons than for the tailward-direction electrons. The cutoffs and their variation with distance from the edge of the boundary layer can be consistently interpreted in terms of a time-of-flight effect on recently reconnected magnetic field lines. The observed cutoff speeds are used to estimate the downtail location of the reconnection site.

Goertler instability in compressible boundary layers along curved surfaces with suction and cooling

NASA Technical Reports Server (NTRS)

El-Hady, N.; Verma, A. K.

1982-01-01

The Goertler instability of the laminar compressible boundary layer flows along concave surfaces is investigated. The linearized disturbance equations for the three-dimensional, counter-rotating streamwise vortices in two-dimensional boundary layers are presented in an orthogonal curvilinear coordinate. The basic approximation of the disturbance equations, that includes the effect of the growth of the boundary layer, is considered and solved numerically. The effect of compressibility on critical stability limits, growth rates, and amplitude ratios of the vortices is evaluated for a range of Mach numbers for 0 to 5. The effect of wall cooling and suction of the boundary layer on the development of Goertler vortices is investigated for different Mach numbers.

A review of quasi-coherent structures in a numerically simulated turbulent boundary layer

NASA Technical Reports Server (NTRS)

Robinson, S. K.; Kline, S. J.; Spalart, P. R.

1989-01-01

Preliminary results of a comprehensive study of the structural aspects of a numerically simulated number turbulent boundary layer are presented. A direct Navier-Stokes simulation of a flat-plate, zero pressure gradient boundary layer at Re0 = 670 was used. Most of the known nonrandom, coherent features of turbulent boundary layers are confirmed in the simulation, and several new aspects of their spatial character are reported. The spatial relationships between many of the various structures are described, forming the basis for a more complete kinematical picture of boundary layer physics than has been previously known. In particular, the importance of vortex structures of various forms to the generation of Reynolds shear stress is investigated.

Computer graphic visualization of orbiter lower surface boundary-layer transition

NASA Technical Reports Server (NTRS)

Throckmorton, D. A.; Hartung, L. C.

1984-01-01

Computer graphic techniques are applied to the processing of Shuttle Orbiter flight data in order to create a visual presentation of the extent and movement of the boundary-layer transition front over the orbiter lower surface during entry. Flight-measured surface temperature-time histories define the onset and completion of the boundary-layer transition process at any measurement location. The locus of points which define the spatial position of the boundary-layer transition front on the orbiter planform is plotted at each discrete time for which flight data are available. Displaying these images sequentially in real-time results in an animated simulation of the in-flight boundary-layer transition process.

Sublayer of Prandtl Boundary Layers

NASA Astrophysics Data System (ADS)

Grenier, Emmanuel; Nguyen, Toan T.

2018-03-01

The aim of this paper is to investigate the stability of Prandtl boundary layers in the vanishing viscosity limit {ν \\to 0} . In Grenier (Commun Pure Appl Math 53(9):1067-1091, 2000), one of the authors proved that there exists no asymptotic expansion involving one of Prandtl's boundary layer, with thickness of order {√{ν}} , which describes the inviscid limit of Navier-Stokes equations. The instability gives rise to a viscous boundary sublayer whose thickness is of order {ν^{3/4}} . In this paper, we point out how the stability of the classical Prandtl's layer is linked to the stability of this sublayer. In particular, we prove that the two layers cannot both be nonlinearly stable in L^∞. That is, either the Prandtl's layer or the boundary sublayer is nonlinearly unstable in the sup norm.

The lagRST Model: A Turbulence Model for Non-Equilibrium Flows

NASA Technical Reports Server (NTRS)

Lillard, Randolph P.; Oliver, A. Brandon; Olsen, Michael E.; Blaisdell, Gregory A.; Lyrintzis, Anastasios S.

2011-01-01

This study presents a new class of turbulence model designed for wall bounded, high Reynolds number flows with separation. The model addresses deficiencies seen in the modeling of nonequilibrium turbulent flows. These flows generally have variable adverse pressure gradients which cause the turbulent quantities to react at a finite rate to changes in the mean flow quantities. This "lag" in the response of the turbulent quantities can t be modeled by most standard turbulence models, which are designed to model equilibrium turbulent boundary layers. The model presented uses a standard 2-equation model as the baseline for turbulent equilibrium calculations, but adds transport equations to account directly for non-equilibrium effects in the Reynolds Stress Tensor (RST) that are seen in large pressure gradients involving shock waves and separation. Comparisons are made to several standard turbulence modeling validation cases, including an incompressible boundary layer (both neutral and adverse pressure gradients), an incompressible mixing layer and a transonic bump flow. In addition, a hypersonic Shock Wave Turbulent Boundary Layer Interaction with separation is assessed along with a transonic capsule flow. Results show a substantial improvement over the baseline models for transonic separated flows. The results are mixed for the SWTBLI flows assessed. Separation predictions are not as good as the baseline models, but the over prediction of the peak heat flux downstream of the reattachment shock that plagues many models is reduced.

Methods and results of boundary layer measurements on a glider

NASA Technical Reports Server (NTRS)

Nes, W. V.

1978-01-01

Boundary layer measurements were carried out on a glider under natural conditions. Two effects are investigated: the effect of inconstancy of the development of static pressure within the boundary layer and the effect of the negative pressure difference in a sublaminar boundary layer. The results obtained by means of an ion probe in parallel connection confirm those results obtained by means of a pressure probe. Additional effects which have occurred during these measurements are briefly dealt with.

A study of juncture flow in the NASA Langley 0.3-meter transonic cryogenic tunnel

NASA Technical Reports Server (NTRS)

Chokani, Ndaona

1992-01-01

A numerical investigation of the interaction between a wind tunnel sidewall boundary layer and a thin low-aspect-ratio wing has been performed for transonic speeds and flight Reynolds numbers. A three-dimensional Navier-Stokes code was applied to calculate the flow field. The first portion of the investigation examined the capability of the code to calculate the flow around the wing, with no sidewall boundary layer present. The second part of the research examined the effect of modeling the sidewall boundary layer. The results indicated that the sidewall boundary layer had a strong influence on the flow field around the wing. The viscous sidewall computations accurately predicted the leading edge suction peaks, and the strong adverse pressure gradients immediately downstream of the leading edge. This was in contrast to the consistent underpredictions of the free-air computations. The low momentum of the sidewall boundary layer resulted in higher pressures in the juncture region, which decreased the favorable spanwise pressure gradient. This significantly decreased the spanwise migration of the wing boundary layer. The computations indicated that the sidewall boundary layer remained attached for all cases examined. Weak vortices were predicted in both the upper and lower surface juncture regions. These vortices are believed to have been generated by lateral skewing of the streamlines in the approaching boundary layer.

Approach to Modeling Boundary Layer Ingestion Using a Fully Coupled Propulsion-RANS Model

NASA Technical Reports Server (NTRS)

Gray, Justin S.; Mader, Charles A.; Kenway, Gaetan K. W.; Martins, Joaquim R. R. A.

2017-01-01

Airframe-propulsion integration concepts that use boundary layer ingestion have the potential to reduce aircraft fuel burn. One concept that has been recently explored is NASA's Starc-ABL aircraft configuration, which offers the potential for 12% mission fuel burn reduction by using a turbo-electric propulsion system with an aft-mounted electrically driven boundary layer ingestion propulsor. This large potential for improved performance motivates a more detailed study of the boundary layer ingestion propulsor design, but to date, analyses of boundary layer ingestion have used uncoupled methods. These methods account for only aerodynamic effects on the propulsion system or propulsion system effects on the aerodynamics, but not both simultaneously. This work presents a new approach for building fully coupled propulsive-aerodynamic models of boundary layer ingestion propulsion systems. A 1D thermodynamic cycle analysis is coupled to a RANS simulation to model the Starc-ABL aft propulsor at a cruise condition and the effects variation in propulsor design on performance are examined. The results indicates that both propulsion and aerodynamic effects contribute equally toward the overall performance and that the fully coupled model yields substantially different results compared to uncoupled. The most significant finding is that boundary layer ingestion, while offering substantial fuel burn savings, introduces throttle dependent aerodynamics effects that need to be accounted for. This work represents a first step toward the multidisciplinary design optimization of boundary layer ingestion propulsion systems.

Effect of Protuberance Shape and Orientation on Space Shuttle Orbiter Boundary-Layer Transition

NASA Technical Reports Server (NTRS)

King, RUdolph A.; Berry, Scott A.; Kegerise, Michael A.

2008-01-01

This document describes an experimental study conducted to examine the effects of protuberances on hypersonic boundary-layer transition. The experiment was conducted in the Langley 20-Inch Mach 6 Tunnel on a series of 0.9%-scale Shuttle Orbiter models. The data were acquired to complement the existing ground-based boundary-layer transition database that was used to develop Version 1.0 of the boundary-layer transition RTF (return-to-flight) tool. The existing ground-based data were all acquired on 0.75%-scale Orbiter models using diamond-shaped ( pizza-box ) trips. The larger model scale facilitated in manufacturing higher fidelity protuberances. The end use of this experimental database will be to develop a technical basis (in the form of a boundary-layer transition correlation) to assess representative protrusion shapes, e.g., gap fillers and protrusions resulting from possible tile repair concepts. The primary objective of this study is to investigate the effects of protuberance-trip location and geometry on Shuttle Orbiter boundary-layer transition. Secondary goals are to assess the effects of gap-filler orientation and other protrusion shapes on boundary-layer transition. Global heat-transfer images using phosphor thermography of the Orbiter windward surface and the corresponding streamwise and spanwise heating distributions were used to infer the state of the boundary layer, i.e., laminar, transitional, or turbulent.

Boundary-layer exchange by bubble: A novel method for generating transient nanofluidic layers

NASA Astrophysics Data System (ADS)

Jennissen, Herbert P.

2005-10-01

Unstirred layers (i.e., Nernst boundary layers) occur on every dynamic solid-liquid interface, constituting a diffusion barrier, since the velocity of a moving liquid approaches zero at the surface (no slip). If a macromolecule-surface reaction rate is higher than the diffusion rate, the Nernst layer is solute depleted and the reaction rate becomes mass-transport limited. The thickness of a Nernst boundary layer (δN) generally lies between 5 and 50μm. In an evanescent wave rheometer, measuring fibrinogen adsorption to fused silica, we made the fundamental observation that an air bubble preceding the sample through the flow cell abolishes the mass-transport limitation of the Nernst diffusion layer. Instead exponential kinetics are found. Experimental and simulation studies strongly indicate that these results are due to the elimination of the Nernst diffusion layer and its replacement by a dynamic nanofluidic layer (δν) maximally 200-300nm thick. It is suggested that the air bubble leads to a transient boundary-layer separation into a novel nanoboundary layer on the surface and the bulk fluid velocity profile separated by a vortex sheet with an estimated lifetime of 30-60s. A bubble-induced boundary-layer exchange from the Nernst to the nanoboundary layer and back is obtained, giving sufficient time for the measurement of unbiased exponential surface kinetics. Noteworthy is that the nanolayer can exist at all and displays properties such as (i) a long persistence and resistance to dissipation by the bulk liquid (boundary-layer-exchange-hysteresis) and (ii) a lack of solute depletion in spite of boundary-layer separation. The boundary-layer-exchange by bubble (BLEB) method therefore appears ideal for enhancing the rates of all types of diffusion-limited macromolecular reactions on surfaces with contact angles between 0° and 90° and only appears limited by slippage due to nanobubbles or an air gap beneath the nanofluidic layer on very hydrophobic surfaces. The possibility of producing nanoboundary layers without any nanostructuring or nanomachining should also be useful for fundamental physical studies in nanofluidics.

Structure of the low-latitude boundary layer. [in magnetopause

NASA Technical Reports Server (NTRS)

Sckopke, N.; Paschmann, G.; Haerendel, G.; Sonnerup, B. U. OE.; Bame, S. J.; Forbes, T. G.; Hones, E. W., Jr.; Russell, C. T.

1981-01-01

High temporal resolution observations of the frontside magnetopause and plasma boundary layer made with the fast plasma analyzer aboard the ISEE 1 and 2 spacecraft are reported. The data are found to be compatible with a boundary layer that is always attached to the magnetopause but where the layer thickness has a large-scale spatial modulation pattern which travels tailward past the spacecraft. Periods are included when the thickness is essentially zero and others when it is of the order of 1 earth radius. The duration of these periods is highly variable but is typically in the range of 2-5 min corresponding to a distance along the magnetopuase of approximately 3-8 earth radii. The observed boundary layer features include a steep density gradient at the magnetopause with an approximately constant boundary layer plasma density amounting to about 25% of the magnetosheath density, and a second abrupt density decrease at the inner edge of the layer.

Computation of the shock-wave boundary layer interaction with flow separation

NASA Technical Reports Server (NTRS)

Ardonceau, P.; Alziary, T.; Aymer, D.

1980-01-01

The boundary layer concept is used to describe the flow near the wall. The external flow is approximated by a pressure displacement relationship (tangent wedge in linearized supersonic flow). The boundary layer equations are solved in finite difference form and the question of the presence and unicity of the solution is considered for the direct problem (assumed pressure) or converse problem (assumed displacement thickness, friction ratio). The coupling algorithm presented implicitly processes the downstream boundary condition necessary to correctly define the interacting boundary layer problem. The algorithm uses a Newton linearization technique to provide a fast convergence.

A Physical Mechanism for the Asymmetry in Top-Down and Bottom-Up Diffusion.

NASA Astrophysics Data System (ADS)

Wyngaard, J. C.

1987-04-01

Recent large-eddy simulations of the vertical diffusion of a passive, conservative scalar through the convective boundary layer (CBL) show strikingly different eddy diffusivity profiles in the `top-down' and `bottom-up' cases. These results indicate that for a given turbulent velocity field and associated scalar flux, the mean change in scalar mixing ratio across the CBL is several times larger if the flux originates at the top of the boundary layer (i.e., in top-down diffusion) rather than at the bottom. The large-eddy simulation (LES) data show that this asymmetry is due to a breakdown of the eddy-diffusion concept.A simple updraft-downdraft model of the CBL reveals a physical mechanism that could cause this unexpected behavior. The large, positive skewness of the convectively driven vertical velocity gives an appreciably higher probability of downdrafts than updrafts; this excess probability of downdrafts, interacting with the time changes of the mean mixing ratio caused by the nonstationarity of the bottom-up and top-down diffusion processes, decreases the equilibrium value of mean mixing-ratio jump across the mixed layer in the bottom-up case and increases it in the top-down case. The resulting diffusion asymmetry agrees qualitatively with that found through LES.

The behavior of a compressible turbulent boundary layer in a shock-wave-induced adverse pressure gradient. Ph.D. Thesis - Washington Univ., Seattle, Aug. 1972

NASA Technical Reports Server (NTRS)

Rose, W. C.

1973-01-01

The results of an experimental investigation of the mean- and fluctuating-flow properties of a compressible turbulent boundary layer in a shock-wave-induced adverse pressure gradient are presented. The turbulent boundary layer developed on the wall of an axially symmetric nozzle and test section whose nominal free-stream Mach number and boundary-layer thickness Reynolds number were 4 and 100,000, respectively. The adverse pressure gradient was induced by an externally generated conical shock wave. Mean and time-averaged fluctuating-flow data, including the complete experimental Reynolds stress tensor and experimental turbulent mass- and heat-transfer rates are presented for the boundary layer and external flow, upstream, within and downstream of the pressure gradient. The mean-flow data include distributions of total temperature throughout the region of interest. The turbulent mixing properties of the flow were determined experimentally with a hot-wire anemometer. The calibration of the wires and the interpretation of the data are discussed. From the results of the investigation, it is concluded that the shock-wave - boundary-layer interaction significantly alters the turbulent mixing characteristics of the boundary layer.

Response of a hypersonic boundary layer to freestream pulse acoustic disturbance.

PubMed

Wang, Zhenqing; Tang, Xiaojun; Lv, Hongqing

2014-01-01

The response of hypersonic boundary layer over a blunt wedge to freestream pulse acoustic disturbance was investigated. The stability characteristics of boundary layer for freestream pulse wave and continuous wave were analyzed comparatively. Results show that freestream pulse disturbance changes the thermal conductivity characteristics of boundary layer. For pulse wave, the number of main disturbance clusters decreases and the frequency band narrows along streamwise. There are competition and disturbance energy transfer among different modes in boundary layer. The dominant mode of boundary layer has an inhibitory action on other modes. Under continuous wave, the disturbance modes are mainly distributed near fundamental and harmonic frequencies, while under pulse wave, the disturbance modes are widely distributed in different modes. For both pulse and continuous waves, most of disturbance modes slide into a lower-growth or decay state in downstream, which is tending towards stability. The amplitude of disturbance modes in boundary layer under continuous wave is considerably larger than pulse wave. The growth rate for the former is also considerably larger than the later the disturbance modes with higher growth are mainly distributed near fundamental and harmonic frequencies for the former, while the disturbance modes are widely distributed in different frequencies for the latter.

Response of a Hypersonic Boundary Layer to Freestream Pulse Acoustic Disturbance

PubMed Central

Wang, Zhenqing; Tang, Xiaojun; Lv, Hongqing

2014-01-01

The response of hypersonic boundary layer over a blunt wedge to freestream pulse acoustic disturbance was investigated. The stability characteristics of boundary layer for freestream pulse wave and continuous wave were analyzed comparatively. Results show that freestream pulse disturbance changes the thermal conductivity characteristics of boundary layer. For pulse wave, the number of main disturbance clusters decreases and the frequency band narrows along streamwise. There are competition and disturbance energy transfer among different modes in boundary layer. The dominant mode of boundary layer has an inhibitory action on other modes. Under continuous wave, the disturbance modes are mainly distributed near fundamental and harmonic frequencies, while under pulse wave, the disturbance modes are widely distributed in different modes. For both pulse and continuous waves, most of disturbance modes slide into a lower-growth or decay state in downstream, which is tending towards stability. The amplitude of disturbance modes in boundary layer under continuous wave is considerably larger than pulse wave. The growth rate for the former is also considerably larger than the later the disturbance modes with higher growth are mainly distributed near fundamental and harmonic frequencies for the former, while the disturbance modes are widely distributed in different frequencies for the latter. PMID:24737993

Wind turbine wakes in forest and neutral plane wall boundary layer large-eddy simulations

NASA Astrophysics Data System (ADS)

Schröttle, Josef; Piotrowski, Zbigniew; Gerz, Thomas; Englberger, Antonia; Dörnbrack, Andreas

2016-09-01

Wind turbine wake flow characteristics are studied in a strongly sheared and turbulent forest boundary layer and a neutral plane wall boundary layer flow. The reference simulations without wind turbine yield similar results as earlier large-eddy simulations by Shaw and Schumann (1992) and Porte-Agel et al. (2000). To use the fields from the homogeneous turbulent boundary layers on the fly as inflow fields for the wind turbine wake simulations, a new and efficient methodology was developed for the multiscale geophysical flow solver EULAG. With this method fully developed turbulent flow fields can be achieved upstream of the wind turbine which are independent of the wake flow. The large-eddy simulations reproduce known boundary-layer statistics as mean wind profile, momentum flux profile, and eddy dissipation rate of the plane wall and the forest boundary layer. The wake velocity deficit is more asymmetric above the forest and recovers faster downstream compared to the velocity deficit in the plane wall boundary layer. This is due to the inflection point in the mean streamwise velocity profile with corresponding turbulent coherent structures of high turbulence intensity in the strong shear flow above the forest.

Inventory of File nam.t00z.smartpr00.tm00.grib2

Science.gov Websites

layer WDIR analysis Wind Direction (from which blowing) [degtrue] 016 planetary boundary layer WIND analysis Wind Speed [m/s] 017 planetary boundary layer RH analysis Relative Humidity [%] 018 planetary boundary layer DIST analysis Geometric Height [m] 019 surface 4LFTX analysis Best (4 layer) Lifted Index [K

Inventory of File nam.t00z.smartak00.tm00.grib2

Science.gov Websites

layer WDIR analysis Wind Direction (from which blowing) [degtrue] 016 planetary boundary layer WIND analysis Wind Speed [m/s] 017 planetary boundary layer RH analysis Relative Humidity [%] 018 planetary boundary layer DIST analysis Geometric Height [m] 019 surface 4LFTX analysis Best (4 layer) Lifted Index [K

Inventory of File nam.t00z.smarthi00.tm00.grib2

Science.gov Websites

layer WDIR analysis Wind Direction (from which blowing) [degtrue] 016 planetary boundary layer WIND analysis Wind Speed [m/s] 017 planetary boundary layer RH analysis Relative Humidity [%] 018 planetary boundary layer DIST analysis Geometric Height [m] 019 surface 4LFTX analysis Best (4 layer) Lifted Index [K

Current Issues in Unsteady Turbomachinery Flows (Images)

NASA Technical Reports Server (NTRS)

Povinelli, Louis

2004-01-01

Among the numerous causes for unsteadiness in turbo machinery flows are turbulence and flow environment, wakes from stationary and rotating vanes, boundary layer separation, boundary layer/shear layer instabilities, presence of shock waves and deliberate unsteadiness for flow control purposes. These unsteady phenomena may lead to flow-structure interactions such as flutter and forced vibration as well as system instabilities such as stall and surge. A major issue of unsteadiness relates to the fact that a fundamental understanding of unsteady flow physics is lacking and requires continued attention. Accurate simulations and sufficient high fidelity experimental data are not available. The Glenn Research Center plan for Engine Component Flow Physics Modeling is part of the NASA 21st Century Aircraft Program. The main components of the plan include Low Pressure Turbine National Combustor Code. The goals, technical output and benefits/impacts of each element are described in the presentation. The specific areas selected for discussion in this presentation are blade wake interactions, flow control, and combustor exit turbulence and modeling.

Matrix operator theory of radiative transfer. 2: scattering from maritime haze.

PubMed

Kattawar, G W; Plass, G N; Catchings, F E

1973-05-01

Matrix operator theory is used to calculate the reflected and transmitted radiance of photons that have interacted with plane-parallel maritime haze layers. The results are presented for three solar zenith angles, three values of the surface albedo, and a range of optical thicknesses from very thin to very thick. The diffuse flux at the lower boundary and the cloud albedo are tabulated. The forward peak and other features in the single scattered phase function cause the radiance in many cases to be very different from that for Rayleigh scattering. In particular the variation of the radiance with both the zenith or nadir angle and the azimuthal angle is more marked and the relative limb darkening under very thick layers is greater for haze M than for Rayleigh scattering. The downward diffuse flux at the lower boundary for A = 0 is always greater and the cloud albedo is always less for haze M than for Rayleigh layers.

Effects of Sweep Angle on the Boundary-Layer Stability Characteristics of an Untapered Wing at Low Speeds

NASA Technical Reports Server (NTRS)

Boltz, Frederick W.; Kenyon, George C.; Allen, Clyde Q.

1960-01-01

An investigation was conducted in the Ames 12-Foot Low-Turbulence Pressure Tunnel to determine the effects of sweep on the boundary-layer stability characteristics of an untapered variable-sweep wing having an NACA 64(2)A015 section normal to the leading edge. Pressure distribution and transition were measured on the wing at low speeds at sweep angles of 0, 10, 20, 30, 40, and 50 deg. and at angles of attack from -3 to 3 deg. The investigation also included flow-visualization studies on the surface at sweep angles from 0 to 50 deg. and total pressure surveys in the boundary layer at a sweep angle of 30 deg. for angles of attack from -12 to 0 deg. It was found that sweep caused premature transition on the wing under certain conditions. This effect resulted from the formation of vortices in the boundary layer when a critical combination of sweep angle, pressure gradient, and stream Reynolds number was attained. A useful parameter in indicating the combined effect of these flow variables on vortex formation and on beginning transition is the crossflow Reynolds number. The critical values of crossflow Reynolds number for vortex formation found in this investigation range from about 135 to 190 and are in good agreement with those reported in previous investigations. The values of crossflow Reynolds number for beginning transitions were found to be between 190 and 260. For each condition (i.e., development of vortices and initiation of transition at a given location) the lower values in the specified ranges were obtained with a light coating of flow-visualization material on the surface. A method is presented for the rapid computation of crossflow Reynolds number on any swept surface for which the pressure distribution is known. From calculations based on this method, it was found that the maximum values of crossflow Reynolds number are attained under conditions of a strong pressure gradient and at a sweep angle of about 50 deg. Due to the primary dependence on pressure gradient, effects of sweep in causing premature transition are generally first encountered on the lower surfaces of wings operating at positive angles of attack.

On the tectonics of Venus

NASA Astrophysics Data System (ADS)

Arkani-Hamed, Jafar

1993-02-01

The thermal evolution and mechanical properties of a mechanical boundary layer of mantle convection are calculated for three Venus models—cold, Earth-like, and hot—with temperatures of 1300°C, 1400°C, and 1500°C, respectively at the base of their thermal boundary layers. The mechanical boundary layers consist of a basaltic crust with thicknesses of 3 km, 9 km, and 18 km, and depleted periodotitic mantle with thicknesses of 37 km, 65 km, and 90 km, respectively. The thin crust of the cold Venus model couples tightly to the underlying mantle and produces a single competent layer, whereas the thicker crust of the other models has a weak lower part that decouples the crust from the mantle. The characteristic wavelengths (10-20 km) of the banded terrains of tesserae surrounding Ishtar Terra can be explained by the buckling of the crusts of all three Venus models as long as their mechanical boundary layers are older than approximately 150 m.a., implying that the observed wavelengths provide no constraint on the thickness and age of the Venusian crust that is older than approximately 150 m.a. Shortening of the basaltic crust, however, cannot produce surface elevations higher than about 2 km on Venus, because basalt in the lower crust transforms to high-density eclogite, which sinks into the mantle. Therefore, Lakshmi Planum and the surrounding mountains probably contain lower-density material and are analogous to continental masses on the Earth. The ridge spacings of the northern ridge belt can be interpreted as being caused by faulting of the depleted mantle of the cold and Earth-like Venus models if the mechanical boundary layer is older than about 100 m.a. and 200 m.a., respectively. The hot model, however, cannot account for the formation of the ridge belt. Besides the characteristic wavelengths of the banded terrains and spacings of the ridge belts, the cold Venus model seems to account for many other features on Venus. The dynamic support of the surface topography of tesserae requires a convergence velocity of less than 0.1 cm year -1 for the mechanical boundary layer of the cold Venus model. This very low velocity is supported by the spatially random distribution of craters on Venus. Furthermore, the lack of pervasive volcanism on Venus in approximately the last 500 m.y., the lack of an internal magnetic field of Venus, and the lack of an oceanic type ridge system on Venus support the cold Venus model.

Modeling large wind farms in conventionally neutral atmospheric boundary layers under varying initial conditions

NASA Astrophysics Data System (ADS)

Allaerts, Dries; Meyers, Johan

2014-05-01

Atmospheric boundary layers (ABL) are frequently capped by an inversion layer limiting the entrainment rate and boundary layer growth. Commonly used analytical models state that the entrainment rate is inversely proportional to the inversion strength. The height of the inversion turns out to be a second important parameter. Conventionally neutral atmospheric boundary layers (CNBL) are ABLs with zero surface heat flux developing against a stratified free atmosphere. In this regime the inversion-filling process is merely driven by the downward heat flux at the inversion base. As a result, CNBLs are strongly dependent on the heating history of the boundary layer and strong inversions will fail to erode during the course of the day. In case of large wind farms, the power output of the farm inside a CNBL will depend on the height and strength of the inversion above the boundary layer. On the other hand, increased turbulence levels induced by wind farms may partially undermine the rigid lid effect of the capping inversion, enhance vertical entrainment of air into the farm, and increase boundary layer growth. A suite of large eddy simulations (LES) is performed to investigate the effect of the capping inversion on the conventionally neutral atmospheric boundary layer and on the wind farm performance under varying initial conditions. For these simulations our in-house pseudo-spectral LES code SP-Wind is used. The wind turbines are modelled using a non-rotating actuator disk method. In the absence of wind farms, we find that a decrease in inversion strength corresponds to a decrease in the geostrophic angle and an increase in entrainment rate and geostrophic drag. Placing the initial inversion base at higher altitudes further reduces the effect of the capping inversion on the boundary layer. The inversion can be fully neglected once it is situated above the equilibrium height that a truly neutral boundary layer would attain under the same external conditions such as geostrophic wind speed and surface roughness. Wind farm simulations show the expected increase in boundary layer height and growth rate with respect to the case without wind farms. Raising the initial strength of the capping inversion in these simulations dampens the turbulent growth of the boundary layer above the farm, decreasing the farms energy extraction. The authors acknowledge support from the European Research Council (FP7-Ideas, grant no. 306471). Simulations were performed on the computing infrastructure of the VSC Flemish Supercomputer Center, funded by the Hercules Foundation and the Flemish Government.

Numerical investigation of the boundary layer separation in chemical oxygen iodine laser

NASA Astrophysics Data System (ADS)

Huai, Ying; Jia, Shuqin; Wu, Kenan; Jin, Yuqi; Sang, Fengting

2017-11-01

Large eddy simulation is carried out to model the flow process in a supersonic chemical oxygen iodine laser. Unlike the common approaches relying on the tensor representation theory only, the model in the present work is an explicit anisotropy-resolving algebraic Subgrid-scale scalar flux formulation. With an accuracy in capturing the unsteady flow behaviours in the laser. Boundary layer separation initiated by the adverse pressure gradient is identified using Large Eddy Simulation. To quantify the influences of flow boundary layer on the laser performance, the fluid computations coupled with a physical optics loaded cavity model is developed. It has been found that boundary layer separation has a profound effect on the laser outputs due to the introduced shock waves. The F factor of the output beam decreases to 10% of the original one when the boundary transit into turbulence for the setup depicted in the paper. Because the pressure is always greater on the downstream of the boundary layer, there will always be a tendency of boundary separation in the laser. The results inspire designs of the laser to apply positive/passive control methods avoiding the boundary layer perturbation.

Understanding Micro-Ramp Control for Shock Boundary Layer Interactions

DTIC Science & Technology

2008-02-07

micro-ramps on a supersonic boundary layer at M=3.0 was investigated using monotone integrated Large Eddy Simulations (MILES) and Reynolds Averaged Navier... Supersonic boundary layer flow with micro-ramp and no shock wave 3.2 SBLI with no micro-ramp 3.3 SBLI with micro-ramp 3.4 Micro-ramp size and location IV . C...ramps on a supersonic boundary layer at M=3.0 was investigated using monotone integrated Large Eddy Simulations (MILES) and Reynolds Averaged Navier

The Effects of Rotation on Boundary Layers in Turbomachine Rotors

NASA Technical Reports Server (NTRS)

Johnston, J. P.

1974-01-01

The boundary layers in turbomachine rotors are subject to Coriolis forces which can (1) contribute directly to the development of secondary flows and (2) indirectly influence the behavior of boundary layers by augmentation and/or suppression of turbulence production in the boundary layers on blades. Both these rotation-induced phenomena are particularly important in the development of understanding of flow and loss mechanisms in centrifugal and mixed flow machines. The primary objective of this paper is to review the information available on these effects.

Boundary layers in cataclysmic variables - The HEAO 1 X-ray constraints

NASA Technical Reports Server (NTRS)

Jensen, K. A.

1984-01-01

The predictions of the boundary layer model for the X-ray emission from novae are summarized. A discrepancy between observations and theory in the X-ray observations is found. Constraints on the nature of the boundary layers in novae, based on the lack of detections of novae in the HEAO-1 soft X-ray survey are provided. Temperature and column densities for optically thick boundary layers in novae are estimated. Previously announced in STAR as N84-13046

Some Features of Artificially Thickened Fully Developed Turbulent Boundary Layers with Zero Pressure Gradient

NASA Technical Reports Server (NTRS)

Klebanoff, P S; Diehl, Z W

1952-01-01

Report gives an account of an investigation conducted to determine the feasibility of artificially thickening a turbulent boundary layer on a flat plate. A description is given of several methods used to thicken artificially the boundary layer. It is shown that it is possible to do substantial thickening and obtain a fully developed turbulent boundary layer, which is free from any distortions introduced by the thickening process, and, as such, is a suitable medium for fundamental research.

Measurements in a synthetic turbulent boundary layer

NASA Astrophysics Data System (ADS)

Arakeri, J. H.; Coles, D. E.

Some measurements in a synthetic turbulent boundary layer (SBL) are reported. The main diagnostic tool is an X-wire probe. The velocity of the large eddies is determined to be 0.842 times the freestream velocity. The mean properties of the SBL are reasonably close to those of a natural turbulent boundary layer. The large eddy in the SBL appears to be a pair of counterrotating eddies in the stream direction, inclined at a shallow angle and occupying much of the boundary-layer thickness.

Boundary layer transition observations on a body of revolution with surface heating and cooling in water

NASA Astrophysics Data System (ADS)

Arakeri, V. H.

1980-04-01

Boundary layer flow visualization in water with surface heat transfer was carried out on a body of revolution which had the predicted possibility of laminar separation under isothermal conditions. Flow visualization was by in-line holographic technique. Boundary layer stabilization, including elimination of laminar separation, was observed to take place on surface heating. Conversely, boundary layer destabilization was observed on surface cooling. These findings are consistent with the theoretical predictions of Wazzan et al. (1970).

A solar escalator on Mars: Self-lifting of dust layers by radiative heating

NASA Astrophysics Data System (ADS)

Daerden, F.; Whiteway, J. A.; Neary, L.; Komguem, L.; Lemmon, M. T.; Heavens, N. G.; Cantor, B. A.; Hébrard, E.; Smith, M. D.

2015-09-01

Dust layers detected in the atmosphere of Mars by the light detection and ranging (LIDAR) instrument on the Phoenix Mars mission are explained using an atmospheric general circulation model. The layers were traced back to observed dust storm activity near the edge of the north polar ice cap where simulated surface winds exceeded the threshold for dust lifting by saltation. Heating of the atmospheric dust by solar radiation caused buoyant instability and mixing across the top of the planetary boundary layer (PBL). Differential advection by wind shear created detached dust layers above the PBL that ascended due to radiative heating and arrived at the Phoenix site at heights corresponding to the LIDAR observations. The self-lifting of the dust layers is similar to the "solar escalator" mechanism for aerosol layers in the Earth's stratosphere.

Re-Innovating Recycling for Turbulent Boundary Layer Simulations

NASA Astrophysics Data System (ADS)

Ruan, Joseph; Blanquart, Guillaume

2017-11-01

Historically, turbulent boundary layers along a flat plate have been expensive to simulate numerically, in part due to the difficulty of initializing the inflow with ``realistic'' turbulence, but also due to boundary layer growth. The former has been resolved in several ways, primarily dedicating a region of at least 10 boundary layer thicknesses in width to rescale and recycle flow or by extending the region far enough downstream to allow a laminar flow to develop into turbulence. Both of these methods are relatively costly. We propose a new method to remove the need for an inflow region, thus reducing computational costs significantly. Leveraging the scale similarity of the mean flow profiles, we introduce a coordinate transformation so that the boundary layer problem can be solved as a parallel flow problem with additional source terms. The solutions in the new coordinate system are statistically homogeneous in the downstream direction and so the problem can be solved with periodic boundary conditions. The present study shows the stability of this method, its implementation and its validation for a few laminar and turbulent boundary layer cases.

The effect of hydrocarbons on the microstructural evolution in rock salt: a case study on hydrocarbon bearing Ara salt from the South Oman Salt Basin

NASA Astrophysics Data System (ADS)

Schmatz, Joyce; Urai, Janos L.; Wübbeler, Franziska M. M.; Sadler, Marc

2014-05-01

It has been shown that dilatant deformation promotes the incorporation of hydrocarbons into typically low permeable rock salt (Schoenherr et al., 2007). However, there is not much knowledge on subsequent mechanisms related to recrystallization processes, which cause morphological and chemical changes of the carbonic inclusions. This work aims to contribute to an increased understanding of fluid inclusion dynamics related to grain boundary migration recrystallization and hence to facilitate the interpretation of complex microstructures in recrystallized, multiphase salt rocks. In this case study we investigate hydrocarbon-impregnated salt from the Cambrian Ara Group in the South Oman Salt Basin. The samples were cored from cm-m thick anhydrite-salt sequences overlying hydrocarbon bearing carbonate stringers in 3300 m depth. The anhydrite layers consist mainly of fine-grained anhydrite, which contains calcite, dolomite, and olivine inclusions. Solid bitumen and lighter hydrocarbon phases are observed in between the anhydrite grains and along cracks. Anhydrite layers host salt veins, which contain fragments of anhydrite. These fragments do not differ in composition or structure from the host material and the related vein microstructures indicate crack-seal mechanisms. Halite in the salt layers is almost entirely recrystallized with solid inclusions consisting of anhydrite, calcite, dolomite and olivine with hydrocarbon-coatings present inside grains and along grain boundaries. Solid inclusions cause pinning indicated by a decreased recrystallized grain size and by the presence of grains with preserved substructures representing earlier deformation phases. We observe two types of carbonic inclusions: I) solid bitumen coatings along grain boundaries and microcracks, interpreted to be incorporated into the salt in an overpressure state that allowed dilatancy of the salt, and II) less degraded, liquid hydrocarbons along grain boundaries in the vicinity of the anhydrite, interpreted to be incorporated into the salt in a subsequent deformation phase. Type II inclusions usually form arrays of isolated inclusions (liquid hydrocarbons, vapor, and aqueous phases in minor proportions) along grain boundaries of the recrystallized grains, presumably formed in a surface-energy controlled shrinking process from thin fluid films. Here, the contact with mobile grain boundaries promoted necking down and decomposition of multiphase inclusions. We present a model, which describes the dynamic behavior of liquid hydrocarbons in mobile grain boundaries after their enclosure into the salt layers. The model is based on numerous microanalytical methods, such as optical microscopy, fluorescence microscopy, cryo-SEM, and EDX. Schoenherr, J., et al. (2007), Limits to the sealing capacity of rock salt: A case study of the infra-Cambrian Ara Salt from the South Oman salt basin, AAPG Bulletin, 91(11), 1541-1557

Observations of Strong Surface Radar Ducts over the Persian Gulf.

NASA Astrophysics Data System (ADS)

Brooks, Ian M.; Goroch, Andreas K.; Rogers, David P.

1999-09-01

Ducting of microwave radiation is a common phenomenon over the oceans. The height and strength of the duct are controlling factors for radar propagation and must be determined accurately to assess propagation ranges. A surface evaporation duct commonly forms due to the large gradient in specific humidity just above the sea surface; a deeper surface-based or elevated duct frequently is associated with the sudden change in temperature and humidity across the boundary layer inversion.In April 1996 the U.K. Meteorological Office C-130 Hercules research aircraft took part in the U.S. Navy Ship Antisubmarine Warfare Readiness/Effectiveness Measuring exercise (SHAREM-115) in the Persian Gulf by providing meteorological support and making measurements for the study of electromagnetic and electro-optical propagation. The boundary layer structure over the Gulf is influenced strongly by the surrounding desert landmass. Warm dry air flows from the desert over the cooler waters of the Gulf. Heat loss to the surface results in the formation of a stable internal boundary layer. The layer evolves continuously along wind, eventually forming a new marine atmospheric boundary layer. The stable stratification suppresses vertical mixing, trapping moisture within the layer and leading to an increase in refractive index and the formation of a strong boundary layer duct. A surface evaporation duct coexists with the boundary layer duct.In this paper the authors present aircraft- and ship-based observations of both the surface evaporation and boundary layer ducts. A series of sawtooth aircraft profiles map the boundary layer structure and provide spatially distributed estimates of the duct depth. The boundary layer duct is found to have considerable spatial variability in both depth and strength, and to evolve along wind over distances significant to naval operations (100 km). The depth of the evaporation duct is derived from a bulk parameterization based on Monin-Obukhov similarity theory using near-surface data taken by the C-130 during low-level (30 m) flight legs and by ship-based instrumentation. Good agreement is found between the two datasets. The estimated evaporation ducts are found to be generally uniform in depth; however, localized regions of greatly increased depth are observed on one day, and a marked change in boundary layer structure resulting in merging of the surface evaporation duct with the deeper boundary layer duct was observed on another. Both of these cases occurred within exceptionally shallow boundary layers (100 m), where the mean evaporation duct depths were estimated to be between 12 and 17 m. On the remaining three days the boundary layer depth was between 200 and 300 m, and evaporation duct depths were estimated to be between 20 and 35 m, varying by just a few meters over ranges of up to 200 km.The one-way radar propagation factor is modeled for a case with a pronounced change in duct depth. The case is modeled first with a series of measured profiles to define as accurately as possible the refractivity structure of the boundary layer, then with a single profile collocated with the radar antenna and assuming homogeneity. The results reveal large errors in the propagation factor when derived from a single profile.

Effects of resolved boundary layer turbulence on near-ground rotation in simulated quasi-linear convective systems (QLCSs)

NASA Astrophysics Data System (ADS)

Nowotarski, C. J.

2017-12-01

Though most strong to violent tornadoes are associated with supercell thunderstorms, quasi-linear convective systems (QLCSs) pose a risk of tornadoes, often at times and locations where supercell tornadoes are less common. Because QLCS low-level mesocyclones and tornado signatures tend to be less coherent, forecasting such tornadoes remains particularly difficult. The majority of simulations of such storms rely on horizontally homogeneous base states lacking resolved boundary layer turbulence and surface fluxes. Previous work has suggested that heterogeneities associated with boundary layer turbulence in the form of horizontal convective rolls can influence the evolution and characteristics of low-level mesocyclones in supercell thunderstorms. This study extends methods for generating boundary layer convection to idealized simulations of QLCSs. QLCS simulations with resolved boundary layer turbulence will be compared against a control simulation with a laminar boundary layer. Effects of turbulence, the resultant heterogeneity in the near-storm environment, and surface friction on bulk storm characteristics and the intensity, morphology, and evolution of low-level rotation will be presented. Although maximum surface vertical vorticity values are similar, when boundary layer turbulence is included, a greater number of miso- and meso-scale vortices develop along the QLCS gust front. The source of this vorticity is analyzed using Eulerian decomposition of vorticity tendency terms and trajectory analysis to delineate the relative importance of surface friction and baroclinicity in generating QLCS vortices. The role of anvil shading in suppressing boundary layer turbulence in the near-storm environment and subsequent effects on QLCS vortices will also be presented. Finally, implications of the results regarding inclusion of more realistic boundary layers in future idealized simulations of deep convection will be discussed.

Impact of the Diurnal Cycle of the Atmospheric Boundary Layer on Wind-Turbine Wakes: A Numerical Modelling Study

NASA Astrophysics Data System (ADS)

Englberger, Antonia; Dörnbrack, Andreas

2018-03-01

The wake characteristics of a wind turbine for different regimes occurring throughout the diurnal cycle are investigated systematically by means of large-eddy simulation. Idealized diurnal cycle simulations of the atmospheric boundary layer are performed with the geophysical flow solver EULAG over both homogeneous and heterogeneous terrain. Under homogeneous conditions, the diurnal cycle significantly affects the low-level wind shear and atmospheric turbulence. A strong vertical wind shear and veering with height occur in the nocturnal stable boundary layer and in the morning boundary layer, whereas atmospheric turbulence is much larger in the convective boundary layer and in the evening boundary layer. The increased shear under heterogeneous conditions changes these wind characteristics, counteracting the formation of the night-time Ekman spiral. The convective, stable, evening, and morning regimes of the atmospheric boundary layer over a homogeneous surface as well as the convective and stable regimes over a heterogeneous surface are used to study the flow in a wind-turbine wake. Synchronized turbulent inflow data from the idealized atmospheric boundary-layer simulations with periodic horizontal boundary conditions are applied to the wind-turbine simulations with open streamwise boundary conditions. The resulting wake is strongly influenced by the stability of the atmosphere. In both cases, the flow in the wake recovers more rapidly under convective conditions during the day than under stable conditions at night. The simulated wakes produced for the night-time situation completely differ between heterogeneous and homogeneous surface conditions. The wake characteristics of the transitional periods are influenced by the flow regime prior to the transition. Furthermore, there are different wake deflections over the height of the rotor, which reflect the incoming wind direction.

Bristled shark skin: a microgeometry for boundary layer control?

PubMed

Lang, A W; Motta, P; Hidalgo, P; Westcott, M

2008-12-01

There exists evidence that some fast-swimming shark species may have the ability to bristle their scales during fast swimming. Experimental work using a water tunnel facility has been performed to investigate the flow field over and within a bristled shark skin model submerged within a boundary layer to deduce the possible boundary layer control mechanisms being used by these fast-swimming sharks. Fluorescent dye flow visualization provides evidence of the formation of embedded cavity vortices within the scales. Digital particle image velocimetry (DPIV) data, used to evaluate the cavity vortex formation and boundary layer characteristics close to the surface, indicate increased momentum in the slip layer forming above the scales. This increase in flow velocity close to the shark's skin is indicative of boundary layer control mechanisms leading to separation control and possibly transition delay for the bristled shark skin microgeometry.

Experimental study of the separating confluent boundary-layer. Volume 2: Experimental data

NASA Technical Reports Server (NTRS)

Braden, J. A.; Whipkey, R. R.; Jones, G. S.; Lilley, D. E.

1983-01-01

An experimental low speed study of the separating confluent boundary layer on a NASA GAW-1 high lift airfoil is described. The airfoil was tested in a variety of high lift configurations comprised of leading edge slat and trailing edge flap combinations. The primary test instrumentation was a two dimensional laser velocimeter (LV) system operating in a backscatter mode. Surface pressures and corresponding LV derived boundary layer profiles are given in terms of velocity components, turbulence intensities and Reynolds shear stresses as characterizing confluent boundary layer behavior up to and beyond stall. LV derived profiles and associated boundary layer parameters and those obtained from more conventional instrumentation such as pitot static transverse, Preston tube measurements and hot-wire surveys are compared.

Boundary-layer transition and displacement thickness effects on zero-lift drag of a series of power-law bodies at Mach 6

NASA Technical Reports Server (NTRS)

Ashby, G. C., Jr.; Harris, J. E.

1974-01-01

Wave and skin-friction drag have been numerically calculated for a series of power-law bodies at a Mach number of 6 and Reynolds numbers, based on body length, from 1.5 million to 9.5 million. Pressure distributions were computed on the nose by the inverse method and on the body by the method of characteristics. These pressure distributions and the measured locations of boundary-layer transition were used in a nonsimilar-boundary-layer program to determine viscous effects. A coupled iterative approach between the boundary-layer and pressure-distribution programs was used to account for boundary-layer displacement-thickness effects. The calculated-drag coefficients compared well with previously obtained experimental data.

Stability characteristics of compressible boundary layers over thermo-mechanically compliant walls

NASA Astrophysics Data System (ADS)

Dettenrieder, Fabian; Bodony, Daniel

2017-11-01

Transition prediction at hypersonic flight conditions continues to be a challenge and results in conservative safety factors that increase vehicle weight. The weight and thus cost reduction of the outer skin panels promises significant impact; however, fluid-structure interaction due to unsteady perturbations in the laminar boundary layer regime has not been systematically studied at conditions relevant for reusable, hypersonic flight. In this talk, we develop and apply convective and global stability analyses for compressible boundary layers over thermo-mechanically compliant panels. This compliance is shown to change the convective stability of the boundary layer modes, with both stabilization and destabilization observed. Finite panel lengths are shown to affect the global stability properties of the boundary layer.

Boundary Layer Flow Over a Moving Wavy Surface

NASA Astrophysics Data System (ADS)

Hendin, Gali; Toledo, Yaron

2016-04-01

Boundary Layer Flow Over a Moving Wavy Surface Gali Hendin(1), Yaron Toledo(1) January 13, 2016 (1)School of Mechanical Engineering, Tel-Aviv University, Israel Understanding the boundary layer flow over surface gravity waves is of great importance as various atmosphere-ocean processes are essentially coupled through these waves. Nevertheless, there are still significant gaps in our understanding of this complex flow behaviour. The present work investigates the fundamentals of the boundary layer air flow over progressive, small-amplitude waves. It aims to extend the well-known Blasius solution for a boundary layer over a flat plate to one over a moving wavy surface. The current analysis pro- claims the importance of the small curvature and the time-dependency as second order effects, with a meaningful impact on the similarity pattern in the first order. The air flow over the ocean surface is modelled using an outer, inviscid half-infinite flow, overlaying the viscous boundary layer above the wavy surface. The assumption of a uniform flow in the outer layer, used in former studies, is now replaced with a precise analytical solution of the potential flow over a moving wavy surface with a known celerity, wavelength and amplitude. This results in a conceptual change from former models as it shows that the pressure variations within the boundary layer cannot be neglected. In the boundary layer, time-dependent Navier-Stokes equations are formulated in a curvilinear, orthogonal coordinate system. The formulation is done in an elaborate way that presents additional, formerly neglected first-order effects, resulting from the time-varying coordinate system. The suggested time-dependent curvilinear orthogonal coordinate system introduces a platform that can also support the formulation of turbulent problems for any surface shape. In order to produce a self-similar Blasius-type solution, a small wave-steepness is assumed and a perturbation method is applied. Consequently, a novel self-similar solution is obtained from the first order set of equations. A second order solution is also obtained, stressing the role of small curvature on the boundary layer flow. The proposed model and solution for the boundary layer problem overlaying a moving wavy surface can also be used as a base flow for stability problems that can develop in a boundary layer, including phases of transitional states.

Seismic imaging of slab metamorphism and genesis of intermediate-depth intraslab earthquakes

NASA Astrophysics Data System (ADS)

Hasegawa, Akira; Nakajima, Junichi

2017-12-01

We review studies of intermediate-depth seismicity and seismic imaging of the interior of subducting slabs in relation to slab metamorphism and their implications for the genesis of intermediate-depth earthquakes. Intermediate-depth events form a double seismic zone in the depth range of c. 40-180 km, which occur only at locations where hydrous minerals are present, and are particularly concentrated along dehydration reaction boundaries. Recent studies have revealed detailed spatial distributions of these events and a close relationship with slab metamorphism. Pressure-temperature paths of the crust for cold slabs encounter facies boundaries with large H2O production rates and positive total volume change, which are expected to cause highly active seismicity near the facies boundaries. A belt of upper-plane seismicity in the crust nearly parallel to 80-90 km depth contours of the slab surface has been detected in the cold Pacific slab beneath eastern Japan, and is probably caused by slab crust dehydration with a large H2O production rate. A seismic low-velocity layer in the slab crust persists down to the depth of this upper-plane seismic belt, which provides evidence for phase transformation of dehydration at this depth. Similar low-velocity subducting crust closely related with intraslab seismicity has been detected in several other subduction zones. Seismic tomography studies in NE Japan and northern Chile also revealed the presence of a P-wave low-velocity layer along the lower plane of a double seismic zone. However, in contrast to predictions based on the serpentinized mantle, S-wave velocity along this layer is not low. Seismic anisotropy and pore aspect ratio may play a role in generating this unique structure. Although further validation is required, observations of these distinct low P-wave velocities along the lower seismic plane suggest the presence of hydrated rocks or fluids within that layer. These observations support the hypothesis that dehydration-derived H2O causes intermediate-depth intraslab earthquakes. However, it is possible that dual mechanisms generate these earthquakes; the initiation of earthquake rupture may be caused by local excess pore pressure from H2O, and subsequent ruptures may propagate through thermal shear instability. In either case, slab-derived H2O plays an important role in generating intermediate-depth events.

A perspective on coherent structures and conceptual models for turbulent boundary layer physics

NASA Technical Reports Server (NTRS)

Robinson, Stephen K.

1990-01-01

Direct numerical simulations of turbulent boundary layers have been analyzed to develop a unified conceptual model for the kinematics of coherent motions in low Reynolds number canonical turbulent boundary layers. All classes of coherent motions are considered in the model, including low-speed streaks, ejections and sweeps, vortical structures, near-wall and outer-region shear layers, sublayer pockets, and large-scale outer-region eddies. The model reflects the conclusions from the study of the simulated boundary layer that vortical structures are directly associated with the production of turbulent shear stresses, entrainment, dissipation of turbulence kinetic energy, and the fluctuating pressure field. These results, when viewed from the perspective of the large body of published work on the subject of coherent motions, confirm that vortical structures may be considered the central dynamic element in the maintenance of turbulence in the canonical boundary layer. Vortical structures serve as a framework on which to construct a unified picture of boundary layer structure, providing a means to relate the many known structural elements in a consistent way.

An experimental investigation of turbulent boundary layers along curved surfaces

NASA Technical Reports Server (NTRS)

So, R. M. C.; Mellor, G. L.

1972-01-01

A curved wall tunnel was designed, and an equilibrium turbulent boundary layer was set up on the straight section preceding the curved test section. Turbulent boundary layer flows with uniform and adverse pressure distributions along convex and concave walls were investigated. Hot-wire measurements along the convex surface indicated that turbulent mixing between fluid layers was very much reduced. However, the law of the wall held and the skin friction, thus determined, correlated well with other measurements. Hot-wire measurements along the concave test wall revealed a system of longitudinal vortices inside the boundary layer and confirmed that concave curvature enhances mixing. A self-consistent set of turbulent boundary layer equations for flows along curved surfaces was derived together with a modified eddy viscosity. Solution of these equations together with the modified eddy viscosity gave results that correlated well with the present data on flows along the convex surface with arbitrary pressure distribution. However, it could only be used to predict the mean characteristics of the flow along concave walls because of the existence of the system of longitudinal vortices inside the boundary layer.

Instabilities encountered during heat transfer to a supercritical fluid

NASA Technical Reports Server (NTRS)

Cornelius, A. J.

1969-01-01

Investigation was made of the unstable behavior of a heat-transfer loop operating at a supercritical pressure. Natural convection operation of the loop, with observations on acoustic and slow oscillatory behavior, was emphasized during testing. The basic cause of both types of behavior appeared to originate in the heated boundary layer.

Smoothed Two-Dimensional Edges for Laminar Flow

NASA Technical Reports Server (NTRS)

Holmes, B. J.; Liu, C. H.; Martin, G. L.; Domack, C. S.; Obara, C. J.; Hassan, A.; Gunzburger, M. D.; Nicolaides, R. A.

1986-01-01

New concept allows passive method for installing flaps, slats, iceprotection equipment, and other leading-edge devices on natural-laminar-flow (NLF) wings without causing loss of laminar flow. Two-dimensional roughness elements in laminar boundary layers strategically shaped to increase critical (allowable) height of roughness. Facilitates installation of leading-edge devices by practical manufacturing methods.

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.

Influence of bulk turbulence and entrance boundary layer thickness on the curved duct flow field

NASA Technical Reports Server (NTRS)

Crawford, R. A.

1988-01-01

The influence of bulk turbulence and boundary layer thickness on the secondary flow development in a square, 90 degree turning duct was investigated. A three-dimensional laser velocimetry system was utilized to measure the mean and fluctuating components of velocity at six cross-planes in the duct. The results from this investigation, with entrance boundary layer thickness of 20 percent, were compared with the thin boundary layer results documented in NASA CR-174811. The axial velocity profiles, cross-flow velocities, and turbulence intensities were compared and evaluated with regard to the influence of bulk turbulence intensity and boundary layer thickness, and the influence was significant. The results of this investigation expand the 90 degree curved duct experimental data base to higher turbulence levels and thicker entrance boundary layers. The experimental results provide a challenging benchmark data base for computational fluid dynamics code development and validation. The variation of inlet bulk turbulence intensity provides additional information to aid in turbulence model evaluation.

Exact Calculation of Laminar Boundary Layer in Longitudinal Flow over a Flat Plate with Homogeneous Suction

NASA Technical Reports Server (NTRS)

Iglisch, Rudolf

1949-01-01

Lately it has been proposed to reduce the friction drag of a body in a flow for the technically important large Reynolds numbers by the following expedient: the boundary layer, normally turbulent, is artificially kept laminar up to high Reynolds numbers by suction. The reduction in friction drag thus obtained is of the order of magnitude of 60 to 80 percent of the turbulent friction drag, since the latter, for large Reynolds numbers, is several times the laminar friction drag. In considering the idea mentioned one has first to consider whether suction is a possible means of keeping the boundary layer laminar. This question can be answered by a theoretical investigation of the stability of the laminar boundary layer with suction. A knowledge, as accurate as possible, of the velocity distribution in the laminar boundary layer with suction forms the starting point for the stability investigation. E. Schlichting recently gave a survey of the present state of calculation of the laminar boundary layer with suction.

Dynamic behavior of an unsteady trubulent boundary layer

NASA Technical Reports Server (NTRS)

Parikh, P. G.; Reynolds, W. C.; Jayaramen, R.; Carr, L. W.

1981-01-01

Experiments on an unsteady turbulent boundary layer are reported in which the upstream portion of the flow is steady (in the mean) and in the downstream region, the boundary layer sees a linearly decreasing free stream velocity. This velocity gradient oscillates in time, at frequencies ranging from zero to approximately the bursting frequency. For the small amplitude, the mean velocity and mean turbulence intensity profiles are unaffected by the oscillations. The amplitude of the periodic velocity component, although as much as 70% greater than that in the free stream for very low frequencies, becomes equal to that in the free stream at higher frequencies. At high frequencies, both the boundary layer thickness and the Reynolds stress distribution across the boundary layer become frozen. The behavior at higher amplitude is quite similar. At sufficiently high frequencies, the boundary layer thickness remains frozen at the mean value over the oscillation cycle, even though flow reverses near the wall during a part of the cycle.

The Western North American Cretaceous-Tertiary (K-T) boundary interval and its content of shock-metamorphosed minerals: Implications concerning the K-T boundary impact-extinction theory

NASA Technical Reports Server (NTRS)

Izett, G. A.

1988-01-01

At 20 sites in the Raton Basin of Colorado and New Mexico, and at several other sites in Wyoming, Montana, and Canada, a pair of claystone units, an Ir abundance anomaly, and a concentration of shock-metamorphosed minerals mark the palynological K-T boundary. The K-T boundary claystone, which is composed of kaolinite and small amounts of illite/smectite mixed-layer clay, is similar in most respects to kaolinite tonstein layers in coal beds. At some, but not all, K-T boundary localities, the boundary claystone contains solid kaolinite and hollow and solid goyazite spherules, 0.05 to 1.2 mm in diameter. The upper unit, the K-T boundary impact layer, consists chiefly of kaolinite and various amounts of illite/smectite mixed-layer clay. The impact layer and boundary claystone are similar chemically, except that the former has slightly more Fe, K, Ba, Cr, Cu, Li, V, and Zn than the latter. The facts that the boundary claystone and impact layer contain anomalous amounts of Ir, comprise a stratigraphic couplet at Western North American sites, and form thin, discrete layers, similar to air-fall units (volcanic or impact), suggest that the claystone units are of impact origin. Significantly, the impact layer contains as much as 2 percent clastic mineral grains, about 30 percent of which contain multiple sets of shock lamellae. Only one such concentration of shocked minerals has been found near the K-T boundary. The type of K-T boundary shock-metamorphosed materials (quartzite and metaquartzite) in the impact layer and the lack of shock lamellae in quartz and feldspar of pumice lapilli and granitic xenoliths in air-fall pumice units of silicic tuffs, such as the Bishop Tuff, eliminate the possibility that the shock-metamorphosed minerals in the K-T impact layer are of volcanic origin. The global size distribution and abundance of shock-metamorphosed mineral grains suggest that the K-T impact occurred in North America.

Analysis and Modeling of Boundary Layer Separation Method (BLSM).

PubMed

Pethő, Dóra; Horváth, Géza; Liszi, János; Tóth, Imre; Paor, Dávid

2010-09-01

Nowadays rules of environmental protection strictly regulate pollution material emission into environment. To keep the environmental protection laws recycling is one of the useful methods of waste material treatment. We have developed a new method for the treatment of industrial waste water and named it boundary layer separation method (BLSM). We apply the phenomena that ions can be enriched in the boundary layer of the electrically charged electrode surface compared to the bulk liquid phase. The main point of the method is that the boundary layer at correctly chosen movement velocity can be taken out of the waste water without being damaged, and the ion-enriched boundary layer can be recycled. Electrosorption is a surface phenomenon. It can be used with high efficiency in case of large electrochemically active surface of electrodes. During our research work two high surface area nickel electrodes have been prepared. The value of electrochemically active surface area of electrodes has been estimated. The existence of diffusion part of the double layer has been experimentally approved. The electrical double layer capacity has been determined. Ion transport by boundary layer separation has been introduced. Finally we have tried to estimate the relative significance of physical adsorption and electrosorption.

Dynamic Turbulence Modelling in Large-eddy Simulations of the Cloud-topped Atmospheric Boundary Layer

NASA Technical Reports Server (NTRS)

Kirkpatrick, M. P.; Mansour, N. N.; Ackerman, A. S.; Stevens, D. E.

2003-01-01

The use of large eddy simulation, or LES, to study the atmospheric boundary layer dates back to the early 1970s when Deardor (1972) used a three-dimensional simulation to determine velocity and temperature scales in the convective boundary layer. In 1974 he applied LES to the problem of mixing layer entrainment (Deardor 1974) and in 1980 to the cloud-topped boundary layer (Deardor 1980b). Since that time the LES approach has been applied to atmospheric boundary layer problems by numerous authors. While LES has been shown to be relatively robust for simple cases such as a clear, convective boundary layer (Mason 1989), simulation of the cloud-topped boundary layer has proved more of a challenge. The combination of small length scales and anisotropic turbulence coupled with cloud microphysics and radiation effects places a heavy burden on the turbulence model, especially in the cloud-top region. Consequently, over the past few decades considerable effort has been devoted to developing turbulence models that are better able to parameterize these processes. Much of this work has involved taking parameterizations developed for neutral boundary layers and deriving corrections to account for buoyancy effects associated with the background stratification and local buoyancy sources due to radiative and latent heat transfer within the cloud (see Lilly 1962; Deardor 1980a; Mason 1989; MacVean & Mason 1990, for example). In this paper we hope to contribute to this effort by presenting a number of turbulence models in which the model coefficients are calculated dynamically during the simulation rather than being prescribed a priori.

Modeling the urban boundary layer

NASA Technical Reports Server (NTRS)

Bergstrom, R. W., Jr.

1976-01-01

A summary and evaluation is given of the Workshop on Modeling the Urban Boundary Layer; held in Las Vegas on May 5, 1975. Edited summaries from each of the session chairpersons are also given. The sessions were: (1) formulation and solution techniques, (2) K-theory versus higher order closure, (3) surface heat and moisture balance, (4) initialization and boundary problems, (5) nocturnal boundary layer, and (6) verification of models.

The Interactions of a Flame and Its Self-Induced Boundary Layer

NASA Technical Reports Server (NTRS)

Ott, James D.; Oran, Elaine S.; Anderson, John D.

1999-01-01

The interaction of a laminar flame with its self-generated boundary layer in a rectangular channel was numerically simulated using the two-dimensional, reacting, Navier-Stokes equations. A two species chemistry model was implemented which simulates the stoichiometric reaction of acetylene and air. Calculations were performed to investigate the effects of altering the boundary condition of the wall temperature, the Lewis number, the dynamic viscosity, and the ignition method. The purpose of this study was to examine the fundamental physics of the formation of the boundary layer and the interaction of the flame as it propagates into the boundary layer that its own motion has created.

Influence of the characteristics of atmospheric boundary layer on the vertical distribution of air pollutant in China's Yangtze River Delta

NASA Astrophysics Data System (ADS)

Wang, Chenggang; Cao, Le

2016-04-01

Air pollution occurring in the atmospheric boundary layer is a kind of weather phenomenon which decreases the visibility of the atmosphere and results in poor air quality. Recently, the occurrence of the heavy air pollution events has become more frequent all over Asia, especially in Mid-Eastern China. In December 2015, the most severe air pollution in recorded history of China occurred in the regions of Yangtze River Delta and Beijing-Tianjin-Hebei. More than 10 days of severe air pollution (Air Quality Index, AQI>200) appeared in many large cities of China such as Beijing, Tianjin, Shijiazhuang and Baoding. Thus, the research and the management of the air pollution has attracted most attentions in China. In order to investigate the formation, development and dissipation of the air pollutions in China, a field campaign has been conducted between January 1, 2015 and January 28, 2015 in Yangtze River Delta of China, aiming at a intensive observation of the vertical structure of the air pollutants in the atmospheric boundary layer during the time period with heavy pollution. In this study, the observation data obtained in the field campaign mentioned above is analyzed. The characteristics of the atmospheric boundary layer and the vertical distribution of air pollutants in the city Dongshan located in the center of Lake Taihu are shown and discussed in great detail. It is indicated that the stability of the boundary layer is the strongest during the nighttime and the early morning of Dongshan. Meanwhile, the major air pollutants, PM2.5 and PM10 in the boundary layer, reach their maximum values, 177.1μg m-3 and 285μg m-3 respectively. The convective boundary layer height in the observations ranges from approximately 700m to 1100m. It is found that the major air pollutants tend to be confined in a relatively shallow boundary layer, which represents that the boundary layer height is the dominant factor for controlling the vertical distribution of the air pollutants. In the observations, several strong temperature inversion layers are also found in the surface layer and the middle part of the boundary layer, which lead to the suppression of the vertical mixing of the air pollutants. The jet stream occurring in the boundary layer also contributes to the prevention of the vertical dissipation of the air pollutants. It is also observed that the temporal and spatial evolution of the air pollutants and the hygroscopic growth of the aerosols in the boundary layer are heavily dependent on the humidity of the air.

Lear jet boundary layer/shear layer laser propagation experiments

NASA Technical Reports Server (NTRS)

Gilbert, K.

1980-01-01

Optical degradations of aircraft turbulent boundary layers with shear layers generated by aerodynamic fences are analyzed. A collimated 2.5 cm diameter helium-neon laser (0.63 microns) traversed the approximate 5 cm thick natural aircraft boundary layer in double pass via a reflective airfoil. In addition, several flights examined shear layer-induced optical degradation. Flight altitudes ranged from 1.5 to 12 km, while Mach numbers were varied from 0.3 to 0.8. Average line spread function (LSF) and Modulation Transfer Function (MTF) data were obtained by averaging a large number of tilt-removed curves. Fourier transforming the resulting average MTF yields an LSF, thus affording a direct comparison of the two optical measurements. Agreement was good for the aerodynamic fence arrangement, but only fair in the case of a turbulent boundary layer. Values of phase variance inferred from the LSF instrument for a single pass through the random flow and corrected for a large aperture ranged from 0.08 to 0.11 waves (lambda = .63 microns) for the boundary layer. Corresponding values for the fence vary from 0.08 to 0.16 waves. Extrapolation of these values to 10.6 microns suggests negligible degradation for a CO2 laser transmitted through a 5 cm thick, subsonic turbulent boundary layer.

Airship measurements of aerosol size distributions, cloud droplet spectra, and trace gas concentrations in the marine boundary layers

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

Frick, G.M.; Hoppel, W.A.

1993-11-01

The use of an airship as a platform to conduct atmospheric chemistry, aerosol, and cloud microphysical research is described, and results from demonstration flights made off the Oregon coast are presented. The slow speed of the airship makes it an ideal platform to do high-spatial resolution profiling both vertically and horizontally, and to measure large aerosol and cloud droplet distributions without the difficulties caused by high-speed aircraft sampling. A unique set of data obtained during the demonstration flights show the effect that processing marine boundary layer aerosol through stratus clouds has on the aerosol size distribution. Evidence of new particlemore » formation (nucleation of particles) was also observed on about half the days on which flights were made. 11 refs., 9 figs., 1 tab.« less

Model of formation of droplets during electric arc surfacing of functional coatings

NASA Astrophysics Data System (ADS)

Sarychev, Vladimir D.; Granovskii, Alexei Yu; Nevskii, Sergey A.; Gromov, Victor E.

2016-01-01

The mathematical model was developed for the initial stage of formation of an electrode metal droplet in the process of arc welding. Its essence lies in the fact that the presence of a temperature gradient in the boundary layer of the molten metal causes thermo-capillary instability, which leads to the formation of electrode metal droplets. A system of equations including Navier-Stokes equations, heat conduction and Maxwell's equations was solved as well as the boundary conditions for the system electrodes-plasma. Dispersion equation for thermo-capillary waves in the linear approximation for the plane layer was received and analyzed. The values of critical wavelengths, at which thermo-capillary instability appears in the nanometer wavelength range, were found. The parameters at which the mode of a fine-droplet transfer of the material takes place were theoretically defined.

A discussion of cone and flat-plate Reynolds numbers for equal ratios of the laminar shear to the shear caused by small velocity fluctuations in a laminar boundary layer

NASA Technical Reports Server (NTRS)

Tetervin, Neal

1957-01-01

By use of the linear theory of boundary-layer stability and Schlichting's formula for the maximum amplification of a disturbance, an approximate relation is derived between the Reynolds number on a cone and the Reynolds number on a flat plate for equal closeness to transition. The indication is that the ratio of the cone Reynolds number for transition, based on the distance to the cone apex, to the plate Reynolds number for transition, based on the distance to the leading edge, is not in general equal to 3, as has been suggested by other investigators, but varies from 3 when transition occurs at the minimum critical Reynolds number to unity when transition occurs at a large multiple of the critical Reynolds number.

Improvement of Subsonic Basic Research Tunnel Flow Quality as Applied to Wall Mounted Testing

NASA Technical Reports Server (NTRS)

Howerton, Brian M.

1995-01-01

A survey to determine the characteristics of a boundary layer that forms on the wall of the Subsonic Basic Research Tunnel has been performed. Early results showed significant differences in the velocity profiles as measured spanwise across the wall. An investigation of the flow in the upstream contraction revealed the presence of a separation bubble at the beginning of the contraction which caused much of the observed unsteadiness. Vortex generators were successfully applied to the contraction inlet to alleviate the separation. A final survey of the wall boundary layer revealed variations in the displacement and momentum thicknesses to be less than +/- 5% for all but the most upper portion of the wall. The flow quality was deemed adequate to continue the planned follow-on tests to help develop the semi-span test technique.

The Effect of Internal Gravity Waves on Fluctuations in Meteorological Parameters of the Atmospheric Boundary Layer

NASA Astrophysics Data System (ADS)

Zaitseva, D. V.; Kallistratova, M. A.; Lyulyukin, V. S.; Kouznetsov, R. D.; Kuznetsov, D. D.

2018-03-01

Variations in the intensity of turbulence during wave activity in the stable atmospheric boundary layer over a homogeneous steppe surface have been analyzed. Eight wave activity episodes recorded with a Doppler sodar in August 2015 at the Tsimlyansk Scientific Station of the Obukhov Institute of Atmospheric Physics have been studied. These episodes include seven trains of Kelvin-Helmholtz waves and one train of buoyancy waves. Variations in the rms deviation of the vertical wind-velocity component, the temperature structure parameter, and vertical heat and momentum fluxes have been estimated for each episode of wave activity. It has been found that Kelvin-Helmholtz waves slightly affect the intensity of turbulence, while buoyancy waves cause the temperature structure parameter and the vertical fluxes to increase by more than an order of magnitude.

Numerical Investigation of a Heated, Sheared Planetary Boundary Layer

NASA Astrophysics Data System (ADS)

Liou, Yu-Chieng

1996-01-01

A planetary boundary layer (PBL) developed on 11 July, 1987 during the First International Satellites Land Surface Climatology Project (ISLSCP) Field Experiment (FIFE) is investigated numerically by a two dimensional and a three dimensional large eddy simulation (LES) model. Most of the simulated mean and statistical properties are utilized to compare or verify against the observational results extracted from single Doppler lidar scans conducted by Gal-Chen et al. (1992) on the same day. Through the methods of field measurements and numerical simulations, it is found that this PBL, in contrast to the well-known convective boundary layer (CBL), is driven by not only buoyancy but also wind shear. Large eddies produced by the surface heating, as well as internal gravity waves excited by the convection, are both present in the boundary layer. The most unique feature is that in the stable layer, the momentum flux ({overlinerm u^' w^'}), transported by the gravity waves, is counter-gradient. The occurrence of this phenomenon is interpreted by Gal-Chen et al. (1992) using the theory of critical layer singularity, and is confirmed by the numerical simulations in this study. Qualitative agreements are achieved between the model-generated and lidar-derived results. However, quantitative comparisons are less satisfactory. The most serious discrepancy is that in the stable layer the magnitudes of the observed momentum flux ({overlinerm u^ ' w^'}) and vertical velocity variance ({overlinerm w^'^2}) are much larger than their simulated counterparts. Nevertheless, through the technique of numerical simulation, evidence is collected to show inconsistencies among the observations. Thus, the lidar measurements of {overline rm u^' w^'} and {overlinerm w^ '^2} seem to be doubtful. A Four Dimensional Data Assimilation (FDDA) experiment is performed in order to connect the evolution of the model integration with the observations. The results indicate that the dynamical relaxation (nudging) scheme appears to be an appropriate method by which the observed mean quantities such as mean wind ({overline u}) and potential temperature ({ overlinetheta}) can be assimilated into the model without causing data rejection.

An experimental investigation of the effect of boundary layer refraction on the noise from a high-speed propeller

NASA Technical Reports Server (NTRS)

Dittmar, J. H.; Burns, R. J.; Leciejewski, D. J.

1984-01-01

Models of supersonic propellers were previously tested for acoustics in the Lewis 8- by 6-Foot Wind Tunnel using pressure transducers mounted in the tunnel ceiling. The boundary layer on the tunnel ceiling is believed to refract some of the propeller noise away from the measurement transducers. Measurements were made on a plate installed in the wind tunnel which had a thinner boundary layer than the ceiling boundary layer. The plate was installed in two locations for comparison with tunnel ceiling noise data and with fuselage data taken on the NASA Dryden Jetstar airplane. Analysis of the data indicates that the refraction increases with: increasing boundary layer thickness; increasing free stream Mach number; increasing frequency; and decreasing sound radiation angle (toward the inlet axis). At aft radiation angles greater than about 100 deg there was little or no refraction. Comparisons with the airplane data indicated that not only is the boundary layer thickness important but also the shape of the velocity profile. Comparisons with an existing two-dimensional theory, using an idealized shear layer to approximate the boundary layer, showed that the theory and data had the same trends. Analysis of the data taken in the tunnel at two different distances from the propeller indicates a decay with distance in the wind tunnel at high Mach numbers but the decay at low Mach numbers is not as clear.

Convection Cells in the Atmospheric Boundary Layer

NASA Astrophysics Data System (ADS)

Fodor, Katherine; Mellado, Juan-Pedro

2017-04-01

In dry, shear-free convective boundary layers (CBLs), the turbulent flow of air is known to organise itself on large scales into coherent, cellular patterns, or superstructures, consisting of fast, narrow updraughts and slow, wide downdraughts which together form circulations. Superstructures act as transport mechanisms from the surface to the top of the boundary layer and vice-versa, as opposed to small-scale turbulence, which only modifies conditions locally. This suggests that a thorough investigation into superstructure properties may help us better understand transport across the atmospheric boundary layer as a whole. Whilst their existence has been noted, detailed studies into superstructures in the CBL have been scarce. By applying methods which are known to successfully isolate similar large-scale patterns in turbulent Rayleigh-Bénard convection, we can assess the efficacy of those detection techniques in the CBL. In addition, through non-dimensional analysis, we can systematically compare superstructures in various convective regimes. We use direct numerical simulation of four different cases for intercomparison: Rayleigh-Bénard convection (steady), Rayleigh-Bénard convection with an adiabatic top lid (quasi-steady), a stably-stratified CBL (quasi-steady) and a neutrally-stratified CBL (unsteady). The first two are non-penetrative and the latter two penetrative. We find that although superstructures clearly emerge from the time-mean flow in the non-penetrative cases, they become obscured by temporal averaging in the CBL. This is because a rigid lid acts to direct the flow into counter-rotating circulation cells whose axis of rotation remains stationary, whereas a boundary layer that grows in time and is able to entrain fluid from above causes the circulations to not only grow in vertical extent, but also to move horizontally and merge with neighbouring circulations. Spatial filtering is a useful comparative technique as it can be performed on boundary layers of the same depth, defined from the surface to the height at which the turbulent kinetic energy (TKE) is zero (in non-penetrative cases) or less than 10% of its maximum value (in penetrative cases). We find that with increasing filter width, the contribution of the filtered flow to the total TKE in the middle of the boundary layer decreases much more rapidly in the penetrative cases than in the non-penetrative cases. In particular, around 20-25% of the TKE at this height comes from small-scale turbulence with a length scale less than or equal to 15% of the boundary layer depth in the CBL, whereas in Rayleigh-Bénard convection, it is just 6-7%. This is consistent with visualisations, which show that entrainment creates additional small-scale mixing within the large-scale circulations in the CBL. Without entrainment, large-scale organisation predominates. Neither spatial nor temporal filtering are as successful at extracting superstructures in the penetrative cases as in the non-penetrative cases. Hence, these techniques depend not on the steadiness of the system, but rather on the presence of entrainment. We therefore intend to try other detection techniques, such as proper orthogonal decomposition, in order to make a rigorous assessment of which is most effective for isolating superstructures in all four cases.

F-16XL ship #1 wing close-up showing boundary layer detection Preston tubes

NASA Technical Reports Server (NTRS)

1995-01-01

This photo shows the boundary layer Preston tubes mounted on the left wing of NASA's single-seat F-16XL (ship #1) used for the Cranked-Arrow Wing Aerodynamic Project (CAWAP) at Dryden Flight Research Center, Edwards, California. The modified airplane features a delta 'cranked-arrow' wing with strips of tubing along the leading edge to the trailing edge to sense static on the wing and obtain pressure distribution data. The right wing receives data on pressure distribution and the left wing has three types of instrumentation - preston tubes to measure local skin friction, boundary layer rakes to measure boundary layer profiles (the layer where the air interacts with the surfaces of a moving aircraft), and hot films to determine boundary layer transition locations. The first flight of CAWAP occurred on November 21, 1995, and the test program ended in April 1996.

On the Existence of the Logarithmic Surface Layer in the Inner Core of Hurricanes

DTIC Science & Technology

2012-01-01

characteristics of eyewall boundary layer of Hurricane Hugo (1989). Mon. Wea. Rev., 139, 1447-1462. Zhang, JA, Montgomery MT. 2012 Observational...the inner core of hurricanes Roger K. Smitha ∗and Michael T. Montgomeryb a Meteorological Institute, University of Munich, Munich, Germany b Dept. of...logarithmic surface layer”, or log layer, in the boundary layer of the rapidly-rotating core of a hurricane . One such study argues that boundary-layer

Stereoscopic Imaging in Hypersonics Boundary Layers using Planar Laser-Induced Fluorescence

NASA Technical Reports Server (NTRS)

Danehy, Paul M.; Bathel, Brett; Inman, Jennifer A.; Alderfer, David W.; Jones, Stephen B.

2008-01-01

Stereoscopic time-resolved visualization of three-dimensional structures in a hypersonic flow has been performed for the first time. Nitric Oxide (NO) was seeded into hypersonic boundary layer flows that were designed to transition from laminar to turbulent. A thick laser sheet illuminated and excited the NO, causing spatially-varying fluorescence. Two cameras in a stereoscopic configuration were used to image the fluorescence. The images were processed in a computer visualization environment to provide stereoscopic image pairs. Two methods were used to display these image pairs: a cross-eyed viewing method which can be viewed by naked eyes, and red/blue anaglyphs, which require viewing through red/blue glasses. The images visualized three-dimensional information that would be lost if conventional planar laser-induced fluorescence imaging had been used. Two model configurations were studied in NASA Langley Research Center's 31-Inch Mach 10 Air Wind tunnel. One model was a 10 degree half-angle wedge containing a small protuberance to force the flow to transition. The other model was a 1/3-scale, truncated Hyper-X forebody model with blowing through a series of holes to force the boundary layer flow to transition to turbulence. In the former case, low flowrates of pure NO seeded and marked the boundary layer fluid. In the latter, a trace concentration of NO was seeded into the injected N2 gas. The three-dimensional visualizations have an effective time resolution of about 500 ns, which is fast enough to freeze this hypersonic flow. The 512x512 resolution of the resulting images is much higher than high-speed laser-sheet scanning systems with similar time response, which typically measure 10-20 planes.

The impact of a large boreal wildfire on boundary-layer conditions and carbon cycling in adjacent unburned areas: case study of the 2011 Utikuma Complex fire, Alberta, Canada

NASA Astrophysics Data System (ADS)

Petrone, R. M.; Thompson, D. K.; Chasmer, L.; Kljun, N.; Flannigan, M.; Devito, K. J.; Waddington, J. M.

2016-12-01

Boreal wildfire conflagrations have increased in frequency in the western boreal forest of Canada, with notable events in 2011, 2015, and 2016. Significant advances have been made in recent years in understanding fire-atmosphere interactions, with similar gains in the knowledge of carbon emissions and post-fire carbon cycling in forests. However, the focus of such studies is routinely on the burned stands themselves, with little attention to the adjacent forest whose boundary layer meteorology and carbon cycling may be impacted by smoke plume. We capitalize here on opportunistic eddy covariance observations of boundary-layer conditions and carbon cycling taken over a long-term monitoring site adjacent to an active wildfire in Alberta, Canada in 2011. Over a one-week period while the wildfire was burning near the footprint of the tower the turbulent structure of the boundary layer near the tower was altered with significant changes in friction velocity, air temperature, and vapour pressure deficit. Moreover, growing season net ecosystem productivity (NEP) decreased to almost zero largely due to reduced photosynthesis likely due to smoke-related reductions in photosynthetically active radiation (PAR). While the `smoke event' caused a reduction in forest CO2 sequestration by 7 g CO2 m-2 given that the smoked affected area was 120 times greater than the area burned this carbon reduction was equivalent to 30% of gross fire emissions from the fire. Consequently, we argue that smoke related inhibition of photosynthesis via reduced light should be considered when investigating the net radiative forcing of boreal forest wildfires.

Modeling the Relationships Between Aerosol Properties and the Direct and Indirect Effects of Aerosols on Climate

NASA Technical Reports Server (NTRS)

Toon, Owen B.

1994-01-01

Aerosols may affect climate directly by scattering and absorbing visible and infrared energy, They may also affect climate indirectly by modifying the properties of clouds through microphysical processes, and by altering abundances of radiatively important gases through heterogeneous chemistry. Researchers understand which aerosol properties control the direct effect of aerosols on the radiation budget. Unfortunately, despite an abundance of data on certain types of aerosols, much work remains to be done to determine the values of these properties. For instance we have little idea about the global distribution, seasonal variation, or interannual variability of the aerosol optical depth. Also we do not know the visible light absorption properties of tropical aerosols which may contain much debris from slash and burn agriculture. A positive correlation between aerosol concentrations and albedos of marine stratus clouds is observed, and the causative microphysics is understood. However, models suggest that it is difficult to produce new particles in the marine boundary layer. Some modelers have suggested that the particles in the marine boundary layer may originate in the free troposphere and be transported into the boundary layer. Others argue that the aerosols are created in the marine boundary layer. There are no data linking aerosol concentration and cirrus cloud albedo, and models suggest cirrus properties may not be very sensitive to aerosol abundance. There is clear evidence of a radiatively significant change in the global lower stratospheric ozone abundance during the past few decades. These changes are caused by heterogeneous chemical reactions occurring on the surfaces of particles. The rates of these reactions depend upon the chemical composition of the particles. Although rapid advances in understanding heterogeneous chemistry have been made, much remains to be done.

Bottom-boundary-layer measurements on the continental shelf off the Ebro River, Spain

USGS Publications Warehouse

Cacchione, D.A.; Drake, D.E.; Losada, M.A.; Medina, R.

1990-01-01

Measurements of currents, waves and light transmission obtained with an instrumented bottom tripod (GEOPROBE) were used in conjunction with a theoretical bottom-boundary-layer model for waves and currents to investigate sediment transport on the continental shelf south of the Ebro River Delta, Spain. The current data show that over a 48-day period during the fall of 1984, the average transport at 1 m above the seabed was alongshelf and slightly offshore toward the south-southwest at about 2 cm/s. A weak storm passed through the region during this period and caused elevated wave and current speeds near the bed. The bottom-boundary-layer model predicted correspondingly higher combined wave and current bottom shear velocities at this time, but the GEOPROBE optical data indicate that little to no resuspension occurred. This result suggests that the fine-grained bottom sediment, which has a clay component of 80%, behaves cohesively and is more difficult to resuspend than noncohesive materials of similar size. Model computations also indicate that noncohesive very fine sand in shallow water (20 m deep) was resuspended and transported mainly as bedload during this storm. Fine-grained materials in shallow water that are resuspended and transported as suspended load into deeper water probably account for the slight increase in sediment concentration at the GEOPROBE sensors during the waning stages of the storm. The bottom-boundary-layer data suggest that the belt of fine-grained bottom sediment that extends along the shelf toward the southwest is deposited during prolonged periods of low energy and southwestward bottom flow. This pattern is augmented by enhanced resuspension and transport toward the southwest during storms. ?? 1990.

Toward the optimization of control of unsteady separation

NASA Technical Reports Server (NTRS)

Shen, S. F.; Xiao, Zheng-Hua

1992-01-01

Regardless of our understanding of the complicated physical process, means can always be found to alter the occurrence and development of unsteady separation. To be able to optimize the control of separation, however, requires the identification of the critical aspects to which the intervention may be focused and achieve the desired result with minimum waste of effort. The Lagrangian analysis of unsteady boundary-layer traces the trajectories of individual fluid particles and reveals the 'bad seeds' that, through extreme deformation in the direction normal to the wall, eventually develop into a virtual barrier and cause the ejection of boundary-layer material into the main stream. It follows logically that separation can be triggered or delayed most effectively by targeting these 'bad seeds.' Since they are normally interior points of the boundary layer, attempts to influence them through the boundary conditions are necessarily indirect. Furthermore, as the strategy has to be the modification of the growing process of the 'bad seeds,' whatever may be the intervention scheme, it needs to be strong enough and early enough. In Shen and Wu, examples of how acceleration/deceleration of the two dimensional body, as well as the moving wall of a rotating cylinder, may affect the development of the bad seed toward separation are shown. In fact it was mentioned therein that the results might be the first step for a feasibility study of the control of unsteady separation. Presented are additional results of applying suction to an impulsively started circular cylinder.

Application of a transonic similarity rule to correct the effects of sidewall boundary layers in two-dimensional transonic wind tunnels. M.S. Thesis - George Washington Univ.

NASA Technical Reports Server (NTRS)

Sewall, W. G.

1982-01-01

A transonic similarity rule which accounts for the effects of attached sidewall boundary layers is presented and evaluated by comparison with the characteristics of airfoils tested in a two dimensional transonic tunnel with different sidewall boundary layer thicknesses. The rule appears valid provided the sidewall boundary layer both remains attached in the vicinity of the model and occupies a small enough fraction of the tunnel width to preserve sufficient two dimensionality in the tunnel.

Comparative Measurements of Total Temperature in a Supersonic Turbulent Boundary Layer Using a Conical Equilibrium and Combined Temperature-Pressure Probe

DTIC Science & Technology

1974-07-01

AD/A-002 982 COMPARATIVE MEASUREMENTS CF TOTAL TEMPERATURE IN A SUPERSONIC TURBULENT BOUNDARY LAYER USING A CONICAL EQUILIB- RIUM AND COMBINED...SUPERSONIC TURBULENT BOUNDARY LAYER USING A CONICAL EQUILIORIUM AND COMBINED TEMPERATURE-PRESSURE PROBE H.L.P. Vowt R.E. L" 0H.U. M.i July 1974 NAVAL...1 ~~o iotaPRO eig ature In A Supersonic Turbulent Boundary ____________ Layer Using A Conical Equilibrium and 6. 111111ORWING OR. 0111001117,~t

Vortex/boundary layer interactions

NASA Technical Reports Server (NTRS)

Cutler, A. D.; Bradshaw, P.

1989-01-01

Detailed and high quality measurements with hot-wires and pressure probes are presented for two different interactions between a vortex pair with common flow down and a turbulent boundary layer. The interactions studied have larger values of the vortex circulation parameter than those studied previously. The results indicate that the boundary layer under the vortex pair is thinned by lateral divergence and that boundary layer fluid is entrained into the vortex. The effect of the interaction on the vortex core (other than the inviscid effect of the image vortices behind the surface) is small.

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.

Structure of turbulence in three-dimensional boundary layers

NASA Technical Reports Server (NTRS)

Subramanian, Chelakara S.

1993-01-01

This report provides an overview of the three dimensional turbulent boundary layer concepts and of the currently available experimental information for their turbulence modeling. It is found that more reliable turbulence data, especially of the Reynolds stress transport terms, is needed to improve the existing modeling capabilities. An experiment is proposed to study the three dimensional boundary layer formed by a 'sink flow' in a fully developed two dimensional turbulent boundary layer. Also, the mean and turbulence field measurement procedure using a three component laser Doppler velocimeter is described.

An Estimation of Turbulent Kinetic Energy and Energy Dissipation Rate Based on Atmospheric Boundary Layer Similarity Theory

NASA Technical Reports Server (NTRS)

Han, Jongil; Arya, S. Pal; Shaohua, Shen; Lin, Yuh-Lang; Proctor, Fred H. (Technical Monitor)

2000-01-01

Algorithms are developed to extract atmospheric boundary layer profiles for turbulence kinetic energy (TKE) and energy dissipation rate (EDR), with data from a meteorological tower as input. The profiles are based on similarity theory and scalings for the atmospheric boundary layer. The calculated profiles of EDR and TKE are required to match the observed values at 5 and 40 m. The algorithms are coded for operational use and yield plausible profiles over the diurnal variation of the atmospheric boundary layer.

A novel concept for subsonic inlet boundary-layer control

NASA Technical Reports Server (NTRS)

Miller, B. A.

1977-01-01

A self-bleeding method for boundary layer control is described and tested for a subsonic inlet designed to operate in the flowfield generated by high angles of attack. Naturally occurring surface static pressure gradients are used to remove the boundary layer from a separation-prone region of the inlet and to reinject it at a less critical location with a net performance gain. The results suggest that this self-bleeding method for boundary-layer control might be successfully applied to other inlets operating at extreme aerodynamic conditions.

The atmospheric boundary layer — advances in knowledge and application

NASA Astrophysics Data System (ADS)

Garratt, J. R.; Hess, G. D.; Physick, W. L.; Bougeault, P.

1996-02-01

We summarise major activities and advances in boundary-layer knowledge in the 25 years since 1970, with emphasis on the application of this knowledge to surface and boundary-layer parametrisation schemes in numerical models of the atmosphere. Progress in three areas is discussed: (i) the mesoscale modelling of selected phenomena; (ii) numerical weather prediction; and (iii) climate simulations. Future trends are identified, including the incorporation into models of advanced cloud schemes and interactive canopy schemes, and the nesting of high resolution boundary-layer schemes in global climate models.

Boundary-layer cumulus over land: Some observations and conceptual models

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

Stull, R.B.

1993-09-01

Starting in 1980, the Boundary Layer Research Team at the University of Wisconsin has been systematically studying the formation and evolution of nonprecipitating boundary-layer cumulus clouds (BLCu) in regions of fair weather (anticyclones) over land (Stull, 1980). Our approach is to quantify the average statistical characteristics of the surface, thermals, boundary layer, and clouds over horizontal regions of roughly 20 km in diameter. Within such a region over land, there is typically quite a variation in land use, and associated variations in surface albedo and moisture.

An investigation of the effects of the propeller slipstream of a laminar wing boundary layer

NASA Technical Reports Server (NTRS)

Howard, R. M.; Miley, S. J.; Holmes, B. J.

1985-01-01

A research program is in progress to study the effects of the propeller slipstream on natural laminar flow. Flight and wind tunnel measurements of the wing boundary layer have been made using hot-film velocity sensor probes. The results show the boundary layer, at any given point, to alternate between laminar and turbulent states. This cyclic behavior is due to periodic external flow turbulence originating from the viscous wake of the propeller blades. Analytic studies show the cyclic laminar/turbulent boundary layer to result in a significantly lower wing section drag than a fully turbulent boundary layer. The application of natural laminar flow design philosophy yields drag reduction benefits in the slipstream affected regions of the airframe, as well as the unaffected regions.

Calculations of unsteady turbulent boundary layers with flow reversal

NASA Technical Reports Server (NTRS)

Nash, J. F.; Patel, V. C.

1975-01-01

The results are presented of a series of computational experiments aimed at studying the characteristics of time-dependent turbulent boundary layers with embedded reversed-flow regions. A calculation method developed earlier was extended to boundary layers with reversed flows for this purpose. The calculations were performed for an idealized family of external velocity distributions, and covered a range of degrees of unsteadiness. The results confirmed those of previous studies in demonstrating that the point of flow reversal is nonsingular in a time-dependent boundary layer. A singularity was observed to develop downstream of reversal, under certain conditions, accompanied by the breakdown of the boundary-layer approximations. A tentative hypothesis was advanced in an attempt to predict the appearance of the singularity, and is shown to be consistent with the calculated results.

Energy efficient engine, low-pressure turbine boundary layer program

NASA Technical Reports Server (NTRS)

Gardner, W. B.

1981-01-01

A study was conducted to investigate development of boundary layers under the influence of velocity distributions simulating the suction side of two state-of-the-art turbine airfoils: a forward loaded airfoil (squared-off design) and an aft loaded airfoil (aft-loaded design). These velocity distributions were simulated in a boundary layer wind tunnel. Detailed measurements of boundary layer mean velocity and turbulence intensity profiles were obtained for an inlet turbulence level of 2.4 percent and an exit Reynolds number of 800,000. Flush-mounted hot film probes identified the boundary layer transition regimes in the adverse pressure gradient regions for both velocity distributions. Wall intermittency data showed good agreement with the correlations of Dhawan and Narasimha for the intermittency factor distribution in transitional flow regimes.

Experimental measurements of unsteady turbulent boundary layers near separation

NASA Technical Reports Server (NTRS)

Simpson, R. L.

1982-01-01

Investigations conducted to document the behavior of turbulent boundary layers on flat surfaces that separate due to adverse pressure gradients are reported. Laser and hot wire anemometers measured turbulence and flow structure of a steady free stream separating turbulent boundary layer produced on the flow of a wind tunnel section. The effects of sinusoidal and unsteadiness of the free stream velocity on this separating turbulent boundary layer at a reduced frequency were determined. A friction gage and a thermal tuft were developed and used to measure the surface skin friction and the near wall fraction of time the flow moves downstream for several cases. Abstracts are provided of several articles which discuss the effects of the periodic free stream unsteadiness on the structure or separating turbulent boundary layers.

Computation of turbulent boundary layers on curved surfaces, 1 June 1975 - 31 January 1976

NASA Technical Reports Server (NTRS)

Wilcox, D. C.; Chambers, T. L.

1976-01-01

An accurate method was developed for predicting effects of streamline curvature and coordinate system rotation on turbulent boundary layers. A new two-equation model of turbulence was developed which serves as the basis of the study. In developing the new model, physical reasoning is combined with singular perturbation methods to develop a rational, physically-based set of equations which are, on the one hand, as accurate as mixing-length theory for equilibrium boundary layers and, on the other hand, suitable for computing effects of curvature and rotation. The equations are solved numerically for several boundary layer flows over plane and curved surfaces. For incompressible boundary layers, results of the computations are generally within 10% of corresponding experimental data. Somewhat larger discrepancies are noted for compressible applications.

Effect of Sub-Boundary Layer Vortex Generations on Incident Turbulence

NASA Technical Reports Server (NTRS)

Casper, J.; Lin, J. C.; Yao, C. S.

2003-01-01

Sub-boundary layer vortex generators were tested in a wind tunnel to assess their effect on the velocity field within the wake region of a turbulent boundary layer. Both mean flow quantities and turbulence statistics were measured. Although very small relative to the boundary layer thickness, these so-called micro vortex generators were found to have a measurable effect on the power spectra and integral length scales of the turbulence at a distance many times the height of the devices themselves. In addition, the potential acoustic impact of these devices is also discussed. Measured turbulence spectra are used as input to an acoustic formulation in a manner that compares predicted sound pressure levels that result from the incident boundary-layer turbulence, with and without the vortex generators in the flow.

Hypersonic three-dimensional nonequilibrium boundary-layer equations in generalized curvilinear coordinates

NASA Technical Reports Server (NTRS)

Lee, Jong-Hun

1993-01-01

The basic governing equations for the second-order three-dimensional hypersonic thermal and chemical nonequilibrium boundary layer are derived by means of an order-of-magnitude analysis. A two-temperature concept is implemented into the system of boundary-layer equations by simplifying the rather complicated general three-temperature thermal gas model. The equations are written in a surface-oriented non-orthogonal curvilinear coordinate system, where two curvilinear coordinates are non-orthogonial and a third coordinate is normal to the surface. The equations are described with minimum use of tensor expressions arising from the coordinate transformation, to avoid unnecessary confusion for readers. The set of equations obtained will be suitable for the development of a three-dimensional nonequilibrium boundary-layer code. Such a code could be used to determine economically the aerodynamic/aerothermodynamic loads to the surfaces of hypersonic vehicles with general configurations. In addition, the basic equations for three-dimensional stagnation flow, of which solution is required as an initial value for space-marching integration of the boundary-layer equations, are given along with the boundary conditions, the boundary-layer parameters, and the inner-outer layer matching procedure. Expressions for the chemical reaction rates and the thermodynamic and transport properties in the thermal nonequilibrium environment are explicitly given.

Boundary layer effects on liners for aircraft engines

NASA Astrophysics Data System (ADS)

Gabard, Gwénaël

2016-10-01

The performance of acoustic treatments installed on aircraft engines is strongly influenced by the boundary layer of the grazing flow on the surface of the liner. The parametric study presented in this paper illustrates the extent of this effect and identifies when it is significant. The acoustic modes of a circular duct with flow are calculated using a finite difference method. The parameters are representative of the flow conditions, liners and sound fields found in current turbofan engines. Both the intake and bypass ducts are considered. Results show that there is a complex interplay between the boundary layer thickness, the direction of propagation and the liner impedance and that the boundary layer can have a strong impact on liner performance for typical configurations (including changes of the order of 30 dB on the attenuation of modes associated with tonal fan noise). A modified impedance condition including the effect of a small but finite boundary layer thickness is considered and compared to the standard Myers condition based on an infinitely thin boundary layer. We show how this impedance condition can be implemented in a mode calculation method by introducing auxiliary variables. This condition is able to capture the trends associated with the boundary layer effects and in most cases provides improved predictions of liner performance.

Effects of Periodic Unsteady Wake Flow and Pressure Gradient on Boundary Layer Transition Along the Concave Surface of a Curved Plate. Part 3

NASA Technical Reports Server (NTRS)

Schobeiri, M. T.; Radke, R. E.

1996-01-01

Boundary layer transition and development on a turbomachinery blade is subjected to highly periodic unsteady turbulent flow, pressure gradient in longitudinal as well as lateral direction, and surface curvature. To study the effects of periodic unsteady wakes on the concave surface of a turbine blade, a curved plate was utilized. On the concave surface of this plate, detailed experimental investigations were carried out under zero and negative pressure gradient. The measurements were performed in an unsteady flow research facility using a rotating cascade of rods positioned upstream of the curved plate. Boundary layer measurements using a hot-wire probe were analyzed by the ensemble-averaging technique. The results presented in the temporal-spatial domain display the transition and further development of the boundary layer, specifically the ensemble-averaged velocity and turbulence intensity. As the results show, the turbulent patches generated by the wakes have different leading and trailing edge velocities and merge with the boundary layer resulting in a strong deformation and generation of a high turbulence intensity core. After the turbulent patch has totally penetrated into the boundary layer, pronounced becalmed regions were formed behind the turbulent patch and were extended far beyond the point they would occur in the corresponding undisturbed steady boundary layer.

An experimental study of the turbulent boundary layer on a transport wing in subsonic and transonic flow

NASA Technical Reports Server (NTRS)

Spaid, Frank W.; Roos, Frederick W.; Hicks, Raymond M.

1990-01-01

The upper surface boundary layer on a transport wing model was extensively surveyed with miniature yaw probes at a subsonic and a transonic cruise condition. Additional data were obtained at a second transonic test condition, for which a separated region was present at mid-semispan, aft of mid-chord. Significant variation in flow direction with distance from the surface was observed near the trailing edge except at the wing root and tip. The data collected at the transonic cruise condition show boundary layer growth associated with shock wave/boundary layer interaction, followed by recovery of the boundary layer downstream of the shock. Measurements of fluctuating surface pressure and wingtip acceleration were also obtained. The influence of flow field unsteadiness on the boundary layer data is discussed. Comparisons among the data and predictions from a variety of computational methods are presented. The computed predictions are in reasonable agreement with the experimental data in the outboard regions where 3-D effects are moderate and adverse pressure gradients are mild. In the more highly loaded mid-span region near the trailing edge, displacement thickness growth was significantly underpredicted, except when unrealistically severe adverse pressure gradients associated with inviscid calculations were used to perform boundary layer calculations.

Measurements of tropospheric nitric acid over the Western United States and Northeastern Pacific Ocean

NASA Technical Reports Server (NTRS)

Lebel, P. J.; Huebert, B. J.; Schiff, H. I.; Vay, S. A.; Vanbramer, S. E.; Hastie, D. R.

1990-01-01

Over 240 measurements of nitric acid (HNO3) were made in the free troposphere as well as in the boundary layer. Marine HNO3 measurement results were strikingly similar to results from GAMETAG and other past atmospheric field experiments. The marine boundary layer HNO3 average, 62 parts-per-trillion by volume (pptv), was 1/3 lower than the marine free tropospheric average, 108 pptv, suggesting that the boundary layer is a sink for tropospheric nitric acid, probably by dry deposition. Nitric acid measurements on a nighttime continental flight gave a free tropospheric average of 218 pptv, substantially greater than the daytime continental free tropospheric 5-flight average of 61 pptv. However, the nighttime results may be influenced by highly convective conditions that existed from thunderstorms in the vicinity during that night flight. The continental boundary layer HNO3 average of 767 pptv is an order of magnitude greater than the free tropospheric average, indicating that the boundary layer is a source of free tropospheric HNO3. The distribution of continental boundary layer HNO3 data, from averages of 123 over rural Nevada and Utah to 1057 pptv in the polluted San Joaquin Valley of California suggest a close tie between boundary layer HNO3 and anthropogenic activity.

Steady Boundary Layer Disturbances Created By Two-Dimensional Surface Ripples

NASA Astrophysics Data System (ADS)

Kuester, Matthew

2017-11-01

Multiple experiments have shown that surface roughness can enhance the growth of Tollmien-Schlichting (T-S) waves in a laminar boundary layer. One of the common observations from these studies is a ``wall displacement'' effect, where the boundary layer profile shape remains relatively unchanged, but the origin of the profile pushes away from the wall. The objective of this work is to calculate the steady velocity field (including this wall displacement) of a laminar boundary layer over a surface with small, 2D surface ripples. The velocity field is a combination of a Blasius boundary layer and multiple disturbance modes, calculated using the linearized Navier-Stokes equations. The method of multiple scales is used to include non-parallel boundary layer effects of O (Rδ- 1) ; the non-parallel terms are necessary, because a wall displacement is mathematically inconsistent with a parallel boundary layer assumption. This technique is used to calculate the steady velocity field over ripples of varying height and wavelength, including cases where a separation bubble forms on the leeward side of the ripple. In future work, the steady velocity field will be the input for stability calculations, which will quantify the growth of T-S waves over rough surfaces. The author would like to acknowledge the support of the Kevin T. Crofton Aerospace & Ocean Engineering Department at Virginia Tech.

PLIF Visualization of Active Control of Hypersonic Boundary Layers Using Blowing

NASA Technical Reports Server (NTRS)

Bathel, Brett F.; Danehy, Paul M.; Inman, Jennifer A.; Alderfer, David W.; Berry, Scott A.

2008-01-01

Planar laser-induced fluorescence (PLIF) imaging was used to visualize the boundary layer flow on a 1/3-scale Hyper-X forebody model. The boundary layer was perturbed by blowing out of orifices normal to the model surface. Two blowing orifice configurations were used: a spanwise row of 17-holes spaced at 1/8 inch, with diameters of 0.020 inches and a single-hole orifice with a diameter of 0.010 inches. The purpose of the study was to visualize and identify laminar and turbulent structures in the boundary layer and to make comparisons with previous phosphor thermography measurements of surface heating. Jet penetration and its influence on the boundary layer development was also examined as was the effect of a compression corner on downstream boundary layer transition. Based upon the acquired PLIF images, it was determined that global surface heating measurements obtained using the phosphor thermography technique provide an incomplete indicator of transitional and turbulent behavior of the corresponding boundary layer flow. Additionally, the PLIF images show a significant contribution towards transition from instabilities originating from the underexpanded jets. For this experiment, a nitric oxide/nitrogen mixture was seeded through the orifices, with nitric oxide (NO) serving as the fluorescing gas. The experiment was performed in the 31-inch Mach 10 Air Tunnel at NASA Langley Research Center.

Reduced thermal conductivity of nanotwinned random layer structures: a promising nanostructuring towards efficient Si and Si/Ge thermoelectric materials

NASA Astrophysics Data System (ADS)

Samaraweera, Nalaka; Chan, Kin L.; Mithraratne, Kumar

2018-05-01

Si and Si/Ge based nanostructures of reduced lattice thermal conductivity are widely attractive for developing efficient thermoelectric materials. In this study, we demonstrate the reduced thermal conductivity of Si nanotwinned random layer (NTRL) structures over corresponding superlattice and twin-free counterparts. The participation ratio analysis of vibrational modes shows that a possible cause of thermal conductivity reduction is phonon localization due to the random arrangement of twin boundaries. Via non-equilibrium molecular dynamic simulations, it is shown that ~23 and ~27% reductions over superlattice counterparts and ~55 and 53% over twin-free counterparts can be attained for the structures of total lengths of 90 and 170 nm, respectively. Furthermore, a random twin boundary distribution is applied for Si/Ge random layer structures seeking further reduction of thermal conductivity. A significant reduction in thermal conductivity of Si/Ge structures exceeding the thermal insulating performance of the corresponding amorphous Si structure by ~31% for a total length of 90 nm can be achieved. This reduction is as high as ~98% compared to the twin-free Si counterpart. It is demonstrated that application of randomly organised nanoscale twin boundaries is a promising nanostructuring strategy towards developing efficient Si and Si/Ge based thermoelectric materials in the future.

F-111 natural laminar flow glove flight test data analysis and boundary layer stability analysis

NASA Technical Reports Server (NTRS)

Runyan, L. J.; Navran, B. H.; Rozendaal, R. A.

1984-01-01

An analysis of 34 selected flight test data cases from a NASA flight program incorporating a natural laminar flow airfoil into partial wing gloves on the F-111 TACT airplane is given. This analysis determined the measured location of transition from laminar to turbulent flow. The report also contains the results of a boundary layer stability analysis of 25 of the selected cases in which the crossflow (C-F) and Tollmien-Schlichting (T-S) disturbance amplification factors are correlated with the measured transition location. The chord Reynolds numbers for these cases ranges from about 23 million to 29 million, the Mach numbers ranged from 0.80 to 0.85, and the glove leading-edge sweep angles ranged from 9 deg to 25 deg. Results indicate that the maximum extent of laminar flow varies from 56% chord to 9-deg sweep on the upper surface, and from 51% chord at 16-deg sweep to 6% chord at 25-deg sweep on the lower. The results of the boundary layer stability analysis indicate that when both C-F and T-S disturbances are amplified, an interaction takes place which reduces the maximum amplification factor of either type of disturbance that can be tolerated without causing transition.

The Summertime Arctic Atmosphere: Meteorological Measurements during the Arctic Ocean Experiment 2001.

NASA Astrophysics Data System (ADS)

Tjernström, Michael; Leck, Caroline; Persson, P. Ola G.; Jensen, Michael L.; Oncley, Steven P.; Targino, Admir

2004-09-01

An atmospheric boundary layer experiment into the high Arctic was carried out on the Swedish ice-breaker Oden during the summer of 2001, with the primary boundary layer observations obtained while the icebreaker drifted with the ice near 89°N during 3 weeks in August. The purposes of the experiment were to gain an understanding of atmospheric boundary layer structure and transient mixing mechanisms, in addition to their relationships to boundary layer clouds and aerosol production. Using a combination of in situ and remote sensing instruments, with temporal and spatial resolutions previously not deployed in the Arctic, continuous measurements of the lower-troposphere structure and boundary layer turbulence were taken concurrently with atmospheric gas and particulate chemistry, and marine biology measurements.The boundary layer was strongly controlled by ice thermodynamics and local turbulent mixing. Near-surface temperatures mostly remained between near the melting points of the sea- and freshwater, and near-surface relative humidity was high. Low clouds prevailed and fog appeared frequently. Visibility outside of fog was surprisingly good even with very low clouds, probably due to a lack of aerosol particles preventing the formation of haze. The boundary layer was shallow but remained well mixed, capped by an occasionally very strong inversion. Specific humidity often increased with height across the capping inversion.In contrast to the boundary layer, the free troposphere often retained its characteristics from well beyond the Arctic. Elevated intrusions of warm, moist air from open seas to the south were frequent. The picture that the Arctic atmosphere is less affected by transport from lower latitudes in summer than the winter may, thus, be an artifact of analyzing only surface measurements. The transport of air from lower latitudes at heights above the boundary layer has a major impact on the Arctic boundary layer, even very close to the North Pole. During a few week-long periods synoptic-scale weather systems appeared, while weaker and shallower mesoscale fronts were frequent. While frontal passages changed the properties of the free troposphere, changes in the boundary layer were more determined by local effects that often led to changes contrary to those aloft. For example, increasing winds associated with a cold front often led to a warming of the near-surface air by mixing and entrainment.

Predictions and Verification of an Isotope Marine Boundary Layer Model

NASA Astrophysics Data System (ADS)

Feng, X.; Posmentier, E. S.; Sonder, L. J.; Fan, N.

2017-12-01

A one-dimensional (1D), steady state isotope marine boundary layer (IMBL) model is constructed. The model includes meteorologically important features absent in Craig and Gordon type models, namely height-dependent diffusion/mixing and convergence of subsiding external air. Kinetic isotopic fractionation results from this height-dependent diffusion which starts as pure molecular diffusion at the air-water interface and increases linearly with height due to turbulent mixing. The convergence permits dry, isotopically depleted air subsiding adjacent to the model column to mix into ambient air. In δD-δ18O space, the model results fill a quadrilateral, of which three sides represent 1) vapor in equilibrium with various sea surface temperatures (SSTs) (high d18O boundary of quadrilateral); 2) mixture of vapor in equilibrium with seawater and vapor in the subsiding air (lower boundary depleted in both D and 18O); and 3) vapor that has experienced the maximum possible kinetic fractionation (high δD upper boundary). The results can be plotted in d-excess vs. δ18O space, indicating that these processes all cause variations in d-excess of MBL vapor. In particular, due to relatively high d-excess in the descending air, mixing of this air into the MBL causes an increase in d-excess, even without kinetic isotope fractionation. The model is tested by comparison with seven datasets of marine vapor isotopic ratios, with excellent correspondence; >95% of observational data fall within the quadrilateral area predicted by the model. The distribution of observations also highlights the significant influence of vapor from the nearby converging descending air on isotopic variations in the MBL. At least three factors may explain the <5% of observations that fall slightly outside of the predicted region in both δD-δ18O and d-excess - δ18O space: 1) variations in seawater isotopic ratios, 2) variations in isotopic composition of subsiding air, and 3) influence of sea spray. The model can be used for understanding the effects of boundary layer processes and meteorological conditions on isotopic composition of vapor within, and vapor fluxes through the MBL, and how changes in moisture source regions affect the isotopic composition of precipitation. The model can be applied to modern as well as paleo- climate conditions.

The effect of heat generation on mixed convection flow in nano fluids over a horizontal circular cylinder

NASA Astrophysics Data System (ADS)

Juliyanto, Bagus; Widodo, Basuki; Imron, Chairul

2018-04-01

The purpose of this research is to study the effect of heat generation on mixed convection flow on Nano fluids over a horizontal circular cylinder of a heated in two dimension form. A stream of fluids are steady and incompressible, a stream flowing vertically upwards for circular cylinder and the boundary layer at the stagnation point. Three different types of nanoparticles considered are Cu, Al2O3, and TiO2. Mixed convection flow in Nano fluids on the surface of a circular cylinder will cause the boundary layer. The governing boundary layer equations are transformed into a non-dimensional form, and then the non-dimensional forms are transformed into a similar boundary equations by using stream function. Furthermore, an implicit finite-difference scheme known as the Keller-box method is applied to solve numerically the resulting similar boundary layer equations. The result of the research by varying the non-dimensional parameters are mixed convection, Prandtl number, nanoparticle volume fraction, heat generation, and radius of a cylinder are as follows. First, the velocity profile increase and temperature profile decrease when mixed convection parameter increase. Second, the velocity and temperature profiles decrease when Prandtl number parameter increase. Third, the velocity profile with the variation of nanoparticle volume fraction (χ) is increased when the value of χ is 0,1 ≤ χ ≤ 0,15 and the velocity profile decreases when the value of χ is 0,19 ≤ χ ≤ 0,5 while the temperature profile is increasing when the value of χ is 0,1 ≤ χ ≤ 0,5. Fourth, the velocity and temperature profiles increase when heat generation and the radius of the cylinder increase. The last, Cu, Al 2 O 3, and TiO 2 nanoparticles produce the same velocity and temperature profiles, but the three types of nanoparticles are different at the velocity and temperature values.

Linking Dynamics of the Near-surface Flow to Deeper Boundary Layer Forcing in the Nocturnal Boundary Layer

DTIC Science & Technology

2012-06-01

Kaimal and Finnigan (1994), modified) Figure 2.2 illustrates the evolution from unstable CBL to a nocturnal Stable Bound- ary Layer ( SBL ) in the absence...mixed layer acts as a cap for the SBL . The SBL persists through the night until sunrise when surface heating resumes and a new unstable layer begins...to form at the surface, gradually returning to a CBL. 7 2.2.1 Dynamics of the stable boundary layer Because the SBL is stably stratified, buoyancy

Boundary-layer effects in droplet splashing

NASA Astrophysics Data System (ADS)

Riboux, Guillaume; Gordillo, Jose Manuel

2017-11-01

A drop falling onto a solid substrate will disintegrate into smaller parts when its impact velocity exceeds the so called critical velocity for splashing. Under these circumstances, the very thin liquid sheet ejected tangentially to the solid after the drop touches the substrate, lifts off as a consequence of the aerodynamic forces exerted on it and finally breaks into smaller droplets, violently ejected radially outwards, provoking the splash. Here, the tangential deceleration experienced by the fluid entering the thin liquid sheet is investigated making use of boundary layer theory. The velocity component tangent to the solid, computed using potential flow theory provides the far field boundary condition as well as the pressure gradient for the boundary layer equations. The structure of the flow permits to find a self similar solution of the boundary layer equations. This solution is then used to calculate the boundary layer thickness at the root of the lamella as well as the shear stress at the wall. The splash model presented in, which is slightly modified to account for the results obtained from the boundary layer analysis, provides a very good agreement between the measurements and the predicted values of the critical velocity for the splash.

Boundary layer and fundamental problems of hydrodynamics (compatibility of a logarithmic velocity profile in a turbulent boundary layer with the experience values)

NASA Astrophysics Data System (ADS)

Zaryankin, A. E.

2017-11-01

The compatibility of the semiempirical turbulence theory of L. Prandtl with the actual flow pattern in a turbulent boundary layer is considered in this article, and the final calculation results of the boundary layer is analyzed based on the mentioned theory. It shows that accepted additional conditions and relationships, which integrate the differential equation of L. Prandtl, associating the turbulent stresses in the boundary layer with the transverse velocity gradient, are fulfilled only in the near-wall region where the mentioned equation loses meaning and are inconsistent with the physical meaning on the main part of integration. It is noted that an introduced concept about the presence of a laminar sublayer between the wall and the turbulent boundary layer is the way of making of a physical meaning to the logarithmic velocity profile, and can be defined as adjustment of the actual flow to the formula that is inconsistent with the actual boundary conditions. It shows that coincidence of the experimental data with the actual logarithmic profile is obtained as a result of the use of not particular physical value, as an argument, but function of this value.

Semi-discrete Galerkin solution of the compressible boundary-layer equations with viscous-inviscid interaction

NASA Technical Reports Server (NTRS)

Day, Brad A.; Meade, Andrew J., Jr.

1993-01-01

A semi-discrete Galerkin (SDG) method is under development to model attached, turbulent, and compressible boundary layers for transonic airfoil analysis problems. For the boundary-layer formulation the method models the spatial variable normal to the surface with linear finite elements and the time-like variable with finite differences. A Dorodnitsyn transformed system of equations is used to bound the infinite spatial domain thereby providing high resolution near the wall and permitting the use of a uniform finite element grid which automatically follows boundary-layer growth. The second-order accurate Crank-Nicholson scheme is applied along with a linearization method to take advantage of the parabolic nature of the boundary-layer equations and generate a non-iterative marching routine. The SDG code can be applied to any smoothly-connected airfoil shape without modification and can be coupled to any inviscid flow solver. In this analysis, a direct viscous-inviscid interaction is accomplished between the Euler and boundary-layer codes through the application of a transpiration velocity boundary condition. Results are presented for compressible turbulent flow past RAE 2822 and NACA 0012 airfoils at various freestream Mach numbers, Reynolds numbers, and angles of attack.

High Enthalpy Effects on Two Boundary Layer Disturbances in Supersonic and Hypersonic Flow

NASA Astrophysics Data System (ADS)

Wagnild, Ross Martin

The fluid flow phenomenon of boundary layer transition is a complicated and difficult process to model and predict. The importance of the state of the boundary layer with regard to vehicle design cannot be understated. The high enthalpy environment in which high speed vehicles operate in further complicates the transition process by adding several more degrees of freedom. In this environment, the internal properties of the gas can stabilize or destabilize the boundary layer as well as modify the disturbances that cause transition. In the current work, the interaction of two types of disturbances with the high enthalpy flow environment are analyzed. The first is known as a second mode disturbance, which is acoustic in nature. The second type is known as a transient growth disturbance and is associated with flows behind roughness elements. Theoretical analyses, linear stability analyses, and computation fluid dynamics (CFD) are used to determine the ways in which these disturbances interact with the high enthalpy environment as well as the consequences of these interactions. First, acoustic wave are directly studied in order to gain a basic understanding of the response of second mode disturbances in the high enthalpy boundary layer. Next, this understanding is used in interpreting the results of several computations attempting to simulate the flow through a high enthalpy flow facility as well as experiments attempting to take advantage of the acoustic interaction with the high enthalpy environment. Because of the difficulty in modeling these experiments, direct simulations of acoustic waves in a hypersonic flow of a gas with molecular vibration are performed. Lastly, compressible transient growth disturbances are simulated using a linear optimal disturbance solver as well as a CFD solver. The effect of an internal molecular process on this type of disturbance is tested through the use of a vibrational mode. It is the goal of the current work to reinforce the critical importance of accurately capturing the physics of the "real" gas effects in the high enthalpy flow environment in order to understand and predict transition on high speed vehicles.

A computer program for calculating laminar and turbulent boundary layers for two-dimensional time-dependent flows

NASA Technical Reports Server (NTRS)

Cebeci, T.; Carr, L. W.

1978-01-01

A computer program is described which provides solutions of two dimensional equations appropriate to laminar and turbulent boundary layers for boundary conditions with an external flow which fluctuates in magnitude. The program is based on the numerical solution of the governing boundary layer equations by an efficient two point finite difference method. An eddy viscosity formulation was used to model the Reynolds shear stress term. The main features of the method are briefly described and instructions for the computer program with a listing are provided. Sample calculations to demonstrate its usage and capabilities for laminar and turbulent unsteady boundary layers with an external flow which fluctuated in magnitude are presented.

Rotor boundary layer development with inlet guide vane (IGV) wake impingement

NASA Astrophysics Data System (ADS)

Jia, Lichao; Zou, Tengda; Zhu, Yiding; Lee, Cunbiao

2018-04-01

This paper examines the transition process in a boundary layer on a rotor blade under the impingement of an inlet guide vane wake. The effects of wake strengths and the reduced frequency on the unsteady boundary layer development on a low-speed axial compressor were investigated using particle image velocimetry. The measurements were carried out at two reduced frequencies (fr = fIGVS0/U2i, fr = 1.35, and fr = 0.675) with the Reynolds number, based on the blade chord and the isentropic inlet velocity, being 97 500. At fr = 1.35, the flow separated at the trailing edge when the wake strength was weak. However, the separation was almost totally suppressed as the wake strength increased. For the stronger wake, both the wake's high turbulence and the negative jet behavior of the wake dominated the interaction between the unsteady wake and the separated boundary layer on the suction surface of the airfoil. The boundary layer displacement thickened first due to the negative jet effect. Then, as the disturbances developed underneath the wake, the boundary layer thickness reduced gradually. The high disturbance region convected downstream at a fraction of the free-stream velocity and spread in the streamwise direction. The separation on the suction surface was suppressed until the next wake's arrival. Because of the long recovery time at fr = 0.675, the boundary layer thickened gradually as the wake convected further downstream and finally separated due to the adverse pressure gradient. The different boundary layer states in turn affected the development of disturbances.

Evaluation of Flush-Mounted, S-Duct Inlets With Large Amounts of Boundary Layer Ingestion

NASA Technical Reports Server (NTRS)

Berrier, Bobby L.; Morehouse, Melissa B.

2003-01-01

A new high Reynolds number test capability for boundary layer ingesting inlets has been developed for the NASA Langley Research Center 0.3-Meter Transonic Cryogenic Tunnel. Using this new capability, an experimental investigation of four S-duct inlet configurations with large amounts of boundary layer ingestion (nominal boundary layer thickness of about 40% of inlet height) was conducted at realistic operating conditions (high subsonic Mach numbers and full-scale Reynolds numbers). The objectives of this investigation were to 1) develop a new high Reynolds number, boundary-layer ingesting inlet test capability, 2) evaluate the performance of several boundary layer ingesting S-duct inlets, 3) provide a database for CFD tool validation, and 4) provide a baseline inlet for future inlet flow-control studies. Tests were conducted at Mach numbers from 0.25 to 0.83, Reynolds numbers (based on duct exit diameter) from 5.1 million to a fullscale value of 13.9 million, and inlet mass-flow ratios from 0.39 to 1.58 depending on Mach number. Results of this investigation indicate that inlet pressure recovery generally decreased and inlet distortion generally increased with increasing Mach number. Except at low Mach numbers, increasing inlet mass-flow increased pressure recovery and increased distortion. Increasing the amount of boundary layer ingestion (by decreasing inlet throat height and increasing inlet throat width) or ingesting a boundary layer with a distorted profile decreased pressure recovery and increased distortion. Finally, increasing Reynolds number had almost no effect on inlet distortion but increased inlet recovery by about one-half percent at a Mach number near cruise.

Trade cumulus clouds embedded in a deep regional haze: Results from Indian Ocean CARDEX experiment

NASA Astrophysics Data System (ADS)

Wilcox, E. M.; Thomas, R. M.; Praveen, P. S.; Pistone, K.; Bender, F.; Feng, Y.; Ramanathan, V.

2013-12-01

During the winter monsoon, trade cumulus clouds over the North Indian Ocean are embedded within a deep regional haze described as an atmospheric brown cloud. While the trade-cu clouds are largely confined to the marine boundary layer, the sooty brown cloud extends from the boundary layer to as high as 3 km; well above the tops of the cumulus. The boundary layer pollution is persistent and limits drizzle in the cumulus over a period of greater than a month at the Maldives Climate Observatory located at Hanimaadhoo Island. The elevated haze from 1 to 3 km altitude is episodic and strongly modulated by synoptic variability in the 700 hPa flow. The elevated plume enhances heating above the marine boundary layer through daytime absorption of sunlight by the haze particles. The interplay between the microphysical modification of clouds by boundary layer pollution and the episodic elevated heating by the atmospheric brown cloud are explored in in-situ observations from UAVs and surface remote sensing during the CARDEX field campaign of winter 2012 and supported by multi-year analysis of satellite remote sensing observations. These observations document the variability in pollution at the surface and above the marine boundary layer and the effects of pollution on the microphysics of the trade-cu clouds, the depth of the marine boundary layer, the liquid water path of trade-cu clouds, and the profile of turbulent moisture flux through the boundary layer. The consequences of these effects for the radiative forcing of regional climate will be discussed.

The Azimuthally Averaged Boundary Layer Structure of a Numerically Simulated Major Hurricane

DTIC Science & Technology

2015-08-14

layer in which the effects of sur- face friction are associated with significant departures from gradient wind balance. The boundary layer in the... effects of surface friction are associated with significant departures from gradient wind balance. More specifically, we follow Key Points: The...comprises a balance between three horizontal forces: Coriolis , pressure gradient, and friction. The boundary layer flow is characterized by a large Reynolds

Large-Eddy Simulation in Planetary Boundary-Layer Research

NASA Technical Reports Server (NTRS)

Wyngaard, J. C.

1985-01-01

The structure and dynamics of the convective boundary layer are discussed. The vertical transport of a conservative, passive scalar was simulated. Also studied were the statistics by top-down and bottom-up scalar fields. Substantial differences were found between them due, presumably, to the asymmetry in the convective boundary layer. A generalization of mixed-layer scaling was developed which allows one to include the effects of top-down diffusion.

Towards Natural Transition in Compressible Boundary Layers

DTIC Science & Technology

2016-06-29

Behaviour of a natural laminar flow aerofoil in flight through atmospheric turbulence. Journal of Fluid Mechanics, 767:394–429, 003 2015. [70] O...DISTRIBUTION STATEMENT A. Approved for public release; distribution is unlimited See report Wave packet, compressible boundary layer, subsonic flow ...Base flow generation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 3.1.1 Boundary layer profiles

Numerical study of shock-wave/boundary layer interactions in premixed hydrogen-air hypersonic flows

NASA Technical Reports Server (NTRS)

Yungster, Shaye

1991-01-01

A computational study of shock wave/boundary layer interactions involving premixed combustible gases, and the resulting combustion processes is presented. The analysis is carried out using a new fully implicit, total variation diminishing (TVD) code developed for solving the fully coupled Reynolds-averaged Navier-Stokes equations and species continuity equations in an efficient manner. To accelerate the convergence of the basic iterative procedure, this code is combined with vector extrapolation methods. The chemical nonequilibrium processes are simulated by means of a finite-rate chemistry model for hydrogen-air combustion. Several validation test cases are presented and the results compared with experimental data or with other computational results. The code is then applied to study shock wave/boundary layer interactions in a ram accelerator configuration. Results indicate a new combustion mechanism in which a shock wave induces combustion in the boundary layer, which then propagates outwards and downstream. At higher Mach numbers, spontaneous ignition in part of the boundary layer is observed, which eventually extends along the entire boundary layer at still higher values of the Mach number.

Space-Time Correlations and Spectra of Wall Pressure in a Turbulent Boundary Layer

NASA Technical Reports Server (NTRS)

Willmarth, W. W.

1959-01-01

Measurements of the statistical properties of the fluctuating wall pressure produced by a subsonic turbulent boundary layer are described. The measurements provide additional information about the structure of the turbulent boundary layer; they are applicable to the problems of boundary-layer induced noise inside an airplane fuselage and to the generation of waves-on water. The spectrum of the wall pressure is presented in dimensionless form. The ratio of the root-mean-square wall pressure to the free-stream dynamic pressure is found to be a constant square root of bar P(sup 2)/q(sub infinity) = 0.006 independent of Mach number and Reynolds number. In addition, space- time correlation measurements in the stream direction show that pressure fluctuations whose scale is greater than or equal to 0.3 times the boundary-layer thickness are convected with the convection speed U(sub c) = 0.82U(sub infinity) where U(infinity) is the free-stream velocity and have lost their identity in a distance approximately equal to 10 boundary-layer thicknesses.

Hypersonic Boundary Layer Stability over a Flared Cone in a Quiet Tunnel

NASA Technical Reports Server (NTRS)

Lachowicz, Jason T.; Chokani, Ndaona; Wilkinson, Stephen P.

1996-01-01

Hypersonic boundary layer measurements were conducted over a flared cone in a quiet wind tunnel. The flared cone was tested at a freestream unit Reynolds number of 2.82x106/ft in a Mach 6 flow. This Reynolds number provided laminar-to-transitional flow over the model in a low-disturbance environment. Point measurements with a single hot wire using a novel constant voltage anemometry system were used to measure the boundary layer disturbances. Surface temperature and schlieren measurements were also conducted to characterize the laminar-to-transitional state of the boundary layer and to identify instability modes. Results suggest that the second mode disturbances were the most unstable and scaled with the boundary layer thickness. The integrated growth rates of the second mode compared well with linear stability theory in the linear stability regime. The second mode is responsible for transition onset despite the existence of a second mode sub-harmonic. The sub-harmonic wavelength also scales with the boundary layer thickness. Furthermore, the existence of higher harmonics of the fundamental suggests that non-linear disturbances are not associated with high free stream disturbance levels.

High enthalpy hypersonic boundary layer flow

NASA Technical Reports Server (NTRS)

Yanow, G.

1972-01-01

A theoretical and experimental study of an ionizing laminar boundary layer formed by a very high enthalpy flow (in excess of 12 eV per atom or 7000 cal/gm) with allowance for the presence of helium driver gas is described. The theoretical investigation has shown that the use of variable transport properties and their respective derivatives is very important in the solution of equilibrium boundary layer equations of high enthalpy flow. The effect of low level helium contamination on the surface heat transfer rate is minimal. The variation of ionization is much smaller in a chemically frozen boundary layer solution than in an equilibrium boundary layer calculation and consequently, the variation of the transport properties in the case of the former was not essential in the integration. The experiments have been conducted in a free piston shock tunnel, and a detailed study of its nozzle operation, including the effects of low levels of helium driver gas contamination has been made. Neither the extreme solutions of an equilibrium nor of a frozen boundary layer will adequately predict surface heat transfer rate in very high enthalpy flows.

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.

Simulations of laminar boundary-layer flow encountering large-scale surface indentions

NASA Astrophysics Data System (ADS)

Beratlis, N.; Balaras, E.; Squires, K.; Vizard, A.

2016-03-01

The transition from laminar to turbulent flow over dimples and grooves has been investigated through a series of direct numerical simulations. Emphasis has been given to the mechanism of transition and the momentum transport in the post-dimple boundary layer. It has been found that the dimple geometry plays an important role in the evolution of the turbulent boundary layer downstream. The mechanism of transition in all cases is that of the reorientation of the spanwise vorticity into streamwise oriented structures resembling hairpin vortices commonly encountered in wall bounded turbulent flows. Although qualitatively the transition mechanism amongst the three different cases is similar, important quantitative differences exist. It was shown that two-dimensional geometries like a groove are more stable than three-dimensional geometries like a dimple. In addition, it was found that the cavity geometry controls the initial thickness of the boundary layer and practically results in a shift of the virtual origin of the turbulent boundary layer. Important differences in the momentum transport downstream of the dimples exist but in all cases the boundary layer grows in a self-similar manner.

A Real-Time Method for Estimating Viscous Forebody Drag Coefficients

NASA Technical Reports Server (NTRS)

Whitmore, Stephen A.; Hurtado, Marco; Rivera, Jose; Naughton, Jonathan W.

2000-01-01

This paper develops a real-time method based on the law of the wake for estimating forebody skin-friction coefficients. The incompressible law-of-the-wake equations are numerically integrated across the boundary layer depth to develop an engineering model that relates longitudinally averaged skin-friction coefficients to local boundary layer thickness. Solutions applicable to smooth surfaces with pressure gradients and rough surfaces with negligible pressure gradients are presented. Model accuracy is evaluated by comparing model predictions with previously measured flight data. This integral law procedure is beneficial in that skin-friction coefficients can be indirectly evaluated in real-time using a single boundary layer height measurement. In this concept a reference pitot probe is inserted into the flow, well above the anticipated maximum thickness of the local boundary layer. Another probe is servomechanism-driven and floats within the boundary layer. A controller regulates the position of the floating probe. The measured servomechanism position of this second probe provides an indirect measurement of both local and longitudinally averaged skin friction. Simulation results showing the performance of the control law for a noisy boundary layer are then presented.

A numerical method for the prediction of high-speed boundary-layer transition using linear theory

NASA Technical Reports Server (NTRS)

Mack, L. M.

1975-01-01

A method is described of estimating the location of transition in an arbitrary laminar boundary layer on the basis of linear stability theory. After an examination of experimental evidence for the relation between linear stability theory and transition, a discussion is given of the three essential elements of a transition calculation: (1) the interaction of the external disturbances with the boundary layer; (2) the growth of the disturbances in the boundary layer; and (3) a transition criterion. The computer program which carried out these three calculations is described. The program is first tested by calculating the effect of free-stream turbulence on the transition of the Blasius boundary layer, and is then applied to the problem of transition in a supersonic wind tunnel. The effects of unit Reynolds number and Mach number on the transition of an insulated flat-plate boundary layer are calculated on the basis of experimental data on the intensity and spectrum of free-stream disturbances. Reasonable agreement with experiment is obtained in the Mach number range from 2 to 4.5.

Sensored Field Oriented Control of a Robust Induction Motor Drive Using a Novel Boundary Layer Fuzzy Controller

PubMed Central

Saghafinia, Ali; Ping, Hew Wooi; Uddin, Mohammad Nasir

2013-01-01

Physical sensors have a key role in implementation of real-time vector control for an induction motor (IM) drive. This paper presents a novel boundary layer fuzzy controller (NBLFC) based on the boundary layer approach for speed control of an indirect field-oriented control (IFOC) of an induction motor (IM) drive using physical sensors. The boundary layer approach leads to a trade-off between control performances and chattering elimination. For the NBLFC, a fuzzy system is used to adjust the boundary layer thickness to improve the tracking performance and eliminate the chattering problem under small uncertainties. Also, to eliminate the chattering under the possibility of large uncertainties, the integral filter is proposed inside the variable boundary layer. In addition, the stability of the system is analyzed through the Lyapunov stability theorem. The proposed NBLFC based IM drive is implemented in real-time using digital signal processor (DSP) board TI TMS320F28335. The experimental and simulation results show the effectiveness of the proposed NBLFC based IM drive at different operating conditions.

An experimental study of the compressor rotor blade boundary layer

NASA Technical Reports Server (NTRS)

Pouagare, M.; Lakshminarayana, B.; Galmes, J. M.

1984-01-01

The three-dimensional turbulent boundary layer developing on a rotor blade of an axial flow compressor was measured using a miniature 'x' configuration hot-wire probe. The measurements were carried out at nine radial locations on both surfaces of the blade at various chordwise locations. The data derived includes streamwise and radial mean velocities and turbulence intensities. The validity of conventional velocity profiles such as the 'power law profile' for the streamwise profile, and Mager and Eichelbrenner's for the radial profile, is examined. A modification to Mager's crossflow profile is proposed. Away from the blade tip, the streamwise component of the blade boundary layer seems to be mainly influenced by the streamwise pressure gradient. Near the tip of the blade, the behavior of the blade boundary layer is affected by the tip leakage flow and the annulus wall boundary layer. The 'tangential blockage' due to the blade boundary layer is derived from the data. The profile losses are found to be less than that of an equivalent cascade, except in the tip region of the blade.

An experimental study of low Re cavity vortex formation embedded in a laminar boundary layer

NASA Astrophysics Data System (ADS)

Gautam, Sashank; Lang, Amy; Wilroy, Jacob

2016-11-01

Laminar boundary layer flow across a grooved surface leads to the formation of vortices inside rectangular cavities. The nature and stability of the vortex inside any single cavity is determined by the Re and cavity geometry. According to the hypothesis, under low Re and stable vortex conditions a single cavity vortex leads to a roller-bearing effect which results in a decrease in drag as quantified by velocity profiles measured within the boundary layer. At higher Re once the vortex becomes unstable, drag should increase due to the mixing of low-momentum fluid within the cavity and the outer boundary layer flow. The primary objective of this experiment is to document the phenomenon using DPIV in a tow tank facility. This study focuses on the transition of the cavity flow from a steady to an unsteady state as the Re is increased above a critical value. The change in boundary layer momentum and cavity vortex characteristics are documented as a function of Re and boundary layer thickness. Funding from NSF CBET fluid dynamics Grant 1335848 is gratefully acknowledged.

Laser transit anemometer and Pitot probe comparative measurements in a sharp cone boundary layer at Mach 4

NASA Technical Reports Server (NTRS)

Hunter, W. W., Jr.; Ocheltree, S. L.; Russ, C. E., Jr.

1991-01-01

Laser transit anemometer (LTA) measurements of a 7 degree sharp cone boundary layer were conducted in the Air Force/AEDC Supersonic Tunnel A Mach 4 flow field. These measurements are compared with Pitot probe measurements and tricone theory provided by AEDC staff. Measurements were made both in laminar and turbulent boundary layers of the model. Comparison of LTA measurements with theory showed agreement to better than 1 percent for the laminar boundary layer cases. This level of agreement was obtained after small position corrections, 0.01 to 0.6 mm, were applied to the experimental data sets. Pitot probe data when compared with theory also showed small positioning errors. The Pitot data value was also limited due to probe interference with the flow near the model. The LTA turbulent boundary layer data indicated a power law dependence of 6.3 to 6.9. The LTA data was analyzed in the time (Tau) domain in which it was obtained and in the velocity domain. No significant differences were noted between Tau and velocity domain results except in one turbulent boundary layer case.

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.

Pressure-sensing performance of upright cylinders in a Mach 10 boundary-layer

NASA Technical Reports Server (NTRS)

Johnson, Steven; Murphy, Kelly

1994-01-01

An experimental research program to provide basic knowledge of the pressure-sensing performance of upright, flushported cylinders in a hypersonic boundary layer is described. Three upright cylinders of 0.25-, 0.5- and l.0-in. diameters and a conventional rake were placed in the test section sidewall boundary layer of the 31 Inch Mach 10 Wind Tunnel at NASA Langley Research Center, Hampton, Virginia. Boundary-layer pressures from these cylinders were compared to those measured with a conventional rake. A boundary-layer thickness-to-cylinder-diameter ratio of 8 proved sufficient to accurately measure an overall pressure profile and ascertain the boundary-layer thickness. Effects of Reynolds number, flow angularity, and shock wave impingement on pressure measurement were also investigated. Although Reynolds number effects were negligible at the conditions studied, flow angularity above 10 deg significantly affects the measured pressures. Shock wave impingement was used to investigate orifice-to-orifice pressure crosstalk. No crosstalk was measured. The lower pressure measured above the oblique shock wave impingement showed no influence of the higher pressure generated at the lower port locations.

Investigation of boundary layer and turbulence characteristics inside the passages of an axial flow inducer

NASA Technical Reports Server (NTRS)

Anand, A.; Gorton, C.; Lakshminarayana, B.; Yamaoka, H.

1973-01-01

A study of the boundary layer and turbulence characteristics inside the passages of an axial flow inducer is reported. The first part deals with the analytical and experimental investigation of the boundary layer characteristics in a four bladed flat plate inducer passage operated with no throttle. An approximate analysis for the prediction of radial and chordwise velocity profiles across the passage is carried out. The momentum integral technique is used to predict the gross properties of the boundary layer. Equations are given for the exact analysis of the turbulent boundary layer characteristics using the turbulent field method. Detailed measurement of boundary layer profiles, limiting streamline angle and skin friction stress on the rotating blade is also reported. Part two of this report deals with the prediction of the flow as well as blade static pressure measurements in a three bladed inducer with cambered blades operated at a flow coefficient of 0.065. In addition, the mean velocity and turbulence measurements carried out inside the passage using a rotating triaxial probe is reported.

Numerical study of shock-wave/boundary layer interactions in premixed hydrogen-air hypersonic flows

NASA Technical Reports Server (NTRS)

Yungster, Shaye

1990-01-01

A computational study of shock wave/boundary layer interactions involving premixed combustible gases, and the resulting combustion processes is presented. The analysis is carried out using a new fully implicit, total variation diminishing (TVD) code developed for solving the fully coupled Reynolds-averaged Navier-Stokes equations and species continuity equations in an efficient manner. To accelerate the convergence of the basic iterative procedure, this code is combined with vector extrapolation methods. The chemical nonequilibrium processes are simulated by means of a finite-rate chemistry model for hydrogen-air combustion. Several validation test cases are presented and the results compared with experimental data or with other computational results. The code is then applied to study shock wave/boundary layer interactions in a ram accelerator configuration. Results indicate a new combustion mechanism in which a shock wave induces combustion in the boundary layer, which then propagates outwards and downstream. At higher Mach numbers, spontaneous ignition in part of the boundary layer is observed, which eventually extends along the entire boundary layer at still higher values of the Mach number.

Premixed Turbulent Combustion in High Reynolds Number Regimes of Thickened Flamelets and Distributed Reactions

DTIC Science & Technology

2016-03-24

thickened preheat (TP) regime that is bounded by the Klimov-Williams limit, (b) the broken reaction layers (BR) boundary and the partially-distributed...b) the broken reaction layers (BR) boundary that is bounded by Norbert Peters predicted limit, and the partially-distributed reactions (PDR...Nomenclature BR = broken reaction layer boundary DR = distributed reaction zone boundary Ka = Karlovitz number of Peters (Eq. 1) equal to (δF,L

Distinct roles of the cortical layers of area V1 in figure-ground segregation.

PubMed

Self, Matthew W; van Kerkoerle, Timo; Supèr, Hans; Roelfsema, Pieter R

2013-11-04

What roles do the different cortical layers play in visual processing? We recorded simultaneously from all layers of the primary visual cortex while monkeys performed a figure-ground segregation task. This task can be divided into different subprocesses that are thought to engage feedforward, horizontal, and feedback processes at different time points. These different connection types have different patterns of laminar terminations in V1 and can therefore be distinguished with laminar recordings. We found that the visual response started 40 ms after stimulus presentation in layers 4 and 6, which are targets of feedforward connections from the lateral geniculate nucleus and distribute activity to the other layers. Boundary detection started shortly after the visual response. In this phase, boundaries of the figure induced synaptic currents and stronger neuronal responses in upper layer 4 and the superficial layers ~70 ms after stimulus onset, consistent with the hypothesis that they are detected by horizontal connections. In the next phase, ~30 ms later, synaptic inputs arrived in layers 1, 2, and 5 that receive feedback from higher visual areas, which caused the filling in of the representation of the entire figure with enhanced neuronal activity. The present results reveal unique contributions of the different cortical layers to the formation of a visual percept. This new blueprint of laminar processing may generalize to other tasks and to other areas of the cerebral cortex, where the layers are likely to have roles similar to those in area V1. Copyright © 2013 Elsevier Ltd. All rights reserved.

Impacts of synoptic condition and planetary boundary layer structure on the trans-boundary aerosol transport from Beijing-Tianjin-Hebei region to northeast China

NASA Astrophysics Data System (ADS)

Miao, Yucong; Guo, Jianping; Liu, Shuhua; Zhao, Chun; Li, Xiaolan; Zhang, Gen; Wei, Wei; Ma, Yanjun

2018-05-01

The northeastern China frequently experiences severe aerosol pollution in winter under unfavorable meteorological conditions. How and to what extent the meteorological factors affect the air quality there are not yet clearly understood. Thus, this study investigated the impacts of synoptic patterns on the aerosol transport and planetary boundary layer (PBL) structure in Shenyang from 1 to 3 December 2016, using surface observations, sounding measurements, satellite data, and three-dimensional simulations. Results showed that the aerosol pollution occurred in Shenyang was not only related to the local emissions, but also contributed by trans-boundary transport of aerosols from the Beiijng-Tianjin-Hebei (BTH) region. In the presence of the westerly and southwesterly synoptic winds, the aerosols emitted from BTH could be brought to Shenyang. From December 2 to 3, the aerosols emitted from BTH accounted for ∼20% of near-surface PM2.5 in Shenyang. In addition, the large-scale synoptic forcings could affect the vertical mixing of pollutants through modulating the PBL structure in Shenyang. The westerly and southwesterly synoptic winds not only brought the aerosols but also the warmer air masses from the southwest regions to Shenyang. The strong warm advections above PBL could enhance the already existing thermal inversion layers capping over PBL in Shenyang, leading to the suppressions of PBL. Both the trans-boundary transport of aerosols and the suppressions of PBL caused by the large-scale synoptic forcings should be partly responsible for the poor air quality in Shenyang, in addition to the high pollutant emissions. The present study revealed the physical mechanisms underlying the aerosol pollution in Shenyang, which has important implications for better forecasting and controlling the aerosols pollution.

A Study of the Physical Processes of an Advection Fog Boundary Layer

NASA Astrophysics Data System (ADS)

Liu, Duan Yang; Yan, Wen Lian; Yang, Jun; Pu, Mei Juan; Niu, Sheng Jie; Li, Zi Hua

2016-01-01

A large quantity of advection fog appeared in the Yangtze River delta region between 1 and 2 December 2009. Here, we detail the fog formation and dissipation processes and the background weather conditions. The fog boundary layer and its formation and dissipation mechanisms have also been analyzed using field data recorded in a northern suburb of Nanjing. The results showed the following: (1) This advection fog was generated by interaction between advection of a north-east cold ground layer and a south-east warm upper layer. The double-inversion structure generated by this interaction between the cold and warm advections and steady south-east vapour transport was the main cause of this long-lasting fog. The double-inversion structure provided good thermal conditions for the thick fog, and the south-east vapour transport was not only conducive to maintaining the thickness of the fog but also sustained its long duration. (2) The fog-top altitude was over 600 m for most of the time, and the fog reduced visibility to less than 100 m for approximately 12 h. (3) The low-level jet near the lower inversion layer also played a role in maintaining the thick fog system by promoting heat, momentum and south-east vapour transport.

Non-local sub-characteristic zones of influence in unsteady interactive boundary-layers

NASA Technical Reports Server (NTRS)

Rothmayer, A. P.

1992-01-01

The properties of incompressible, unsteady, interactive, boundary layers are examined for a model hypersonic boundary layer and internal flow past humps or, equivalently, external flow past short-scaled humps. Using a linear high frequency analysis, it is shown that the domains of dependence within the viscous sublayer may be a strong function of position within the sublayer and may be strongly influenced by the pressure displacement interaction, or the prescribed displacement condition. Detailed calculations are presented for the hypersonic boundary layer. This effect is found to carry over directly to the fully viscous problem as well as the nonlinear problem. In the fully viscous problem, the non-local character of the domains of dependence manifests itself in the sub-characteristics. Potential implications of the domain of dependence structure on finite difference computations of unsteady boundary layers are briefly discussed.

Representation of Clear and Cloudy Boundary Layers in Climate Models. Chapter 14

NASA Technical Reports Server (NTRS)

Randall, D. A.; Shao, Q.; Branson, M.

1997-01-01

The atmospheric general circulation models which are being used as components of climate models rely on their boundary layer parameterizations to produce realistic simulations of the surface turbulent fluxes of sensible heat. moisture. and momentum: of the boundary-layer depth over which these fluxes converge: of boundary layer cloudiness: and of the interactions of the boundary layer with the deep convective clouds that grow upwards from it. Two current atmospheric general circulation models are used as examples to show how these requirements are being addressed: these are version 3 of the Community Climate Model. which has been developed at the U.S. National Center for Atmospheric Research. and the Colorado State University atmospheric general circulation model. The formulations and results of both models are discussed. Finally, areas for future research are suggested.

Effects of Riblets on Skin Friction in High-Speed Turbulent Boundary Layers

NASA Technical Reports Server (NTRS)

Duan, Lian; Choudhari, Meelan M.

2012-01-01

Direct numerical simulations of spatially developing turbulent boundary layers over riblets are conducted to examine the effects of riblets on skin friction at supersonic speeds. Zero-pressure gradient boundary layers with an adiabatic wall, a Mach number of M1 = 2.5, and a Reynolds number based on momentum thickness of Re = 1720 are considered. Simulations are conducted for boundary-layer flows over a clean surface and symmetric V- groove riblets with nominal spacings of 20 and 40 wall units. The DNS results confirm the few existing experimental observations and show that a drag reduction of approximately 7% is achieved for riblets with proper spacing. The influence of riblets on turbulence statistics is analyzed in detail with an emphasis on identifying the differences, if any, between the drag reduction mechanisms for incompressible and high-speed boundary layers.

Friction and Wear Management Using Solvent Partitioning of Hydrophilic-Surface-Interactive Chemicals Contained in Boundary Layer-Targeted Emulsions

NASA Technical Reports Server (NTRS)

Richmond, Robert Chaffee (Inventor); Schramm, Jr., Harry F. (Inventor); Defalco, Francis G. (Inventor)

2015-01-01

Lubrication additives of the current invention require formation of emulsions in base lubricants, created with an aqueous salt solution plus a single-phase compound such that partitioning within the resulting emulsion provides thermodynamically targeted compounds for boundary layer organization thus establishing anti-friction and/or anti-wear. The single-phase compound is termed "boundary layer organizer", abbreviated BLO. These emulsion-contained compounds energetically favor association with tribologic surfaces in accord with the Second Law of Thermodynamics, and will organize boundary layers on those surfaces in ways specific to the chemistry of the salt and BLO additives. In this way friction modifications may be provided by BLOs targeted to boundary layers via emulsions within lubricating fluids, wherein those lubricating fluids may be water-based or oil-based.

Impurity distribution and microstructure of Ga-doped ZnO films grown by molecular beam epitaxy

NASA Astrophysics Data System (ADS)

Kvit, A. V.; Yankovich, A. B.; Avrutin, V.; Liu, H.; Izyumskaya, N.; Özgür, Ü.; Morkoç, H.; Voyles, P. M.

2012-12-01

We report microstructural characterization of heavily Ga-doped ZnO (GZO) thin films on GaN and sapphire by aberration-corrected scanning transmission electron microscopy. Growth under oxygen-rich and metal-rich growth conditions leads to changes in the GZO polarity and different extended defects. For GZO layers on sapphire, the primary extended defects are voids, inversion domain boundaries, and low-angle grain boundaries. Ga doping of ZnO grown under metal-rich conditions causes a switch from pure oxygen polarity to mixed oxygen and zinc polarity in small domains. Electron energy loss spectroscopy and energy dispersive spectroscopy spectrum imaging show that Ga is homogeneous, but other residual impurities tend to accumulate at the GZO surface and at extended defects. GZO grown on GaN on c-plane sapphire has Zn polarity and no voids. There are misfit dislocations at the interfaces between GZO and an undoped ZnO buffer layer and at the buffer/GaN interface. Low-angle grain boundaries are the only threading microstructural defects. The potential effects of different extended defects and impurity distributions on free carrier scattering are discussed.

Plume effects on the flow around a blunted cone at hypersonic speeds

NASA Technical Reports Server (NTRS)

Atcliffe, P.; Kumar, D.; Stollery, J. L.

1992-01-01

Tests at M = 8.2 show that a simulated rocket plume at the base of a blunted cone can cause large areas of separated flow, with dramatic effects on the heat transfer rate distribution. The plume was simulated by solid discs of varying sizes or by an annular jet of gas. Flow over the cone without a plume is fully laminar and attached. Using a large disc, the boundary layer is laminar at separation at the test Reynolds number. Transition occurs along the separated shear layer and the boundary layer quickly becomes turbulent. The reduction in heat transfer associated with a laminar separated region is followed by rising values as transition occurs and the heat transfer rates towards the rear of the cone substantially exceed the values obtained without a plume. With the annular jet or a small disc, separation occurs much further aft, so that heat transfer rates at the front of the cone are comparable with those found without a plume. Downstream of separation the shear layer now remains laminar and the heat transfer rates to the surface are significantly lower than the attached flow values.

Hairpin vortices in turbulent boundary layers

NASA Astrophysics Data System (ADS)

Eitel-Amor, G.; Örlü, R.; Schlatter, P.; Flores, O.

2015-02-01

The present work presents a number of parallel and spatially developing simulations of boundary layers to address the question of whether hairpin vortices are a dominant feature of near-wall turbulence, and which role they play during transition. In the first part, the parent-offspring regeneration mechanism is investigated in parallel (temporal) simulations of a single hairpin vortex introduced in a mean shear flow corresponding to either turbulent channels or boundary layers (Reτ ≲ 590). The effect of a turbulent background superimposed on the mean flow is considered by using an eddy viscosity computed from resolved simulations. Tracking the vortical structure downstream, it is found that secondary hairpins are only created shortly after initialization, with all rotational structures decaying for later times. For hairpins in a clean (laminar) environment, the decay is relatively slow, while hairpins in weak turbulent environments (10% of νt) dissipate after a couple of eddy turnover times. In the second part, the role of hairpin vortices in laminar-turbulent transition is studied using simulations of spatial boundary layers tripped by hairpin vortices. These vortices are generated by means of specific volumetric forces representing an ejection event, creating a synthetic turbulent boundary layer initially dominated by hairpin-like vortices. These hairpins are advected towards the wake region of the boundary layer, while a sinusoidal instability of the streaks near the wall results in rapid development of a turbulent boundary layer. For Reθ > 400, the boundary layer is fully developed, with no evidence of hairpin vortices reaching into the wall region. The results from both the parallel and spatial simulations strongly suggest that the regeneration process is rather short-lived and may not sustain once a turbulent background is developed. From the transitional flow simulations, it is conjectured that the forest of hairpins reported in former direct numerical simulation studies is reminiscent of the transitional boundary layer and may not be connected to some aspects of the dynamics of the fully developed wall-bounded turbulence.

Influence of trans-boundary air pollution from China on multi-day high PM10 episodes in Seoul, Korea

NASA Astrophysics Data System (ADS)

Oh, H. R.; Ho, C. H.; Kim, J.; Chen, D.; Lee, S.; Choi, Y. S.; Chang, L. S.; Song, C. K.

2014-12-01

Air quality problems have become a serious global issue as it causes over 3 million deaths per year all over the world. With generations of massive air pollutants in China, the effects of trans-boundary transports of air pollutants on human health have become a serious international concern in East Asia. However, only a limited number of studies are available for providing scientific evidences for quantifying the sources and transports of air pollutants over major countries in East Asia. Here, it is shown that particulate matters originated from China played major role in the occurrence of multi-day (≥ 4 days) severe air pollution episodes in Seoul, Korea, in which the concentration of particulate matter of diameters ≤ 10 μm exceeds 100 μg m-3. Observations show that these multi-day severe air quality episodes occur when a strong high-pressure system resides over the eastern China - Korea region. Such a weather condition confines air pollutants within the atmospheric boundary layer and spread them by slow westerlies within the boundary layer from China into the neighboring countries. Understanding such dynamical processes is a key for advancing the predictability of trans-boundary air pollutants and their health impacts in East Asia as well as developing international measures to improve air quality for the region.

Interferometric data for a shock-wave/boundary-layer interaction

NASA Technical Reports Server (NTRS)

Dunagan, Stephen E.; Brown, James L.; Miles, John B.

1986-01-01

An experimental study of the axisymmetric shock-wave / boundary-layer strong interaction flow generated in the vicinity of a cylinder-cone intersection was conducted. The study data are useful in the documentation and understanding of compressible turbulent strong interaction flows, and are part of a more general effort to improve turbulence modeling for compressible two- and three-dimensional strong viscous/inviscid interactions. The nominal free stream Mach number was 2.85. Tunnel total pressures of 1.7 and 3.4 atm provided Reynolds number values of 18 x 10(6) and 36 x 10(6) based on model length. Three cone angles were studied giving negligible, incipient, and large scale flow separation. The initial cylinder boundary layer upstream of the interaction had a thickness of 1.0 cm. The subsonic layer of the cylinder boundary layer was quite thin, and in all cases, the shock wave penetrated a significant portion of the boundary layer. Owing to the thickness of the cylinder boundary layer, considerable structural detail was resolved for the three shock-wave / boundary-layer interaction cases considered. The primary emphasis was on the application of the holographic interferometry technique. The density field was deduced from an interferometric analysis based on the Able transform. Supporting data were obtained using a 2-D laser velocimeter, as well as mean wall pressure and oil flow measurements. The attached flow case was observed to be steady, while the separated cases exhibited shock unsteadiness. Comparisons with Navier-Stokes computations using a two-equation turbulence model are presented.

Interaction between a normal shock wave and a turbulent boundary layer at high transonic speeds. I - Pressure distribution

NASA Technical Reports Server (NTRS)

Messiter, A. F.

1980-01-01

Asymptotic solutions are derived for the pressure distribution in the interaction of a weak normal shock wave with a turbulent boundary layer. The undisturbed boundary layer is characterized by the law of the wall and the law of the wake for compressible flow. In the limiting case considered, for 'high' transonic speeds, the sonic line is very close to the wall. Comparisons with experiment are shown, with corrections included for the effect of longitudinal wall curvature and for the boundary-layer displacement effect in a circular pipe.

Experimental studies on the stability and transition of 3-dimensional boundary layers

NASA Technical Reports Server (NTRS)

Nitschke-Kowsky, P.

1987-01-01

Three-dimensional unstable boundary layers were investigated as to their characteristic instabilities, leading to turbulence. Standing cross-flow instabilities and traveling waves preceding the transition were visualized with the hydrogen bubble technique in the boundary layer above the wall of a swept cylinder. With the sublimation method and hot film technique, a model consisting of a swept flat plate with a pressure-inducing displacement body in the 1 m wind tunnel was studied. Standing waves and traveling waves in a broad frequency are observed. The boundary layer of this model is close to the assumptions of the theory.

Evaluation of a technique to generate artificially thickened boundary layers in supersonic and hypersonic flows

NASA Technical Reports Server (NTRS)

Porro, A. R.; Hingst, W. R.; Davis, D. O.; Blair, A. B., Jr.

1991-01-01

The feasibility of using a contoured honeycomb model to generate a thick boundary layer in high-speed, compressible flow was investigated. The contour of the honeycomb was tailored to selectively remove momentum in a minimum of streamwise distance to create an artificially thickened turbulent boundary layer. Three wind tunnel experiments were conducted to verify the concept. Results indicate that this technique is a viable concept, especially for high-speed inlet testing applications. In addition, the compactness of the honeycomb boundary layer simulator allows relatively easy integration into existing wind tunnel model hardware.

Exact solution for the layered convection of a viscous incompressible fluid at specified temperature gradients and tangential forces on the free boundary

NASA Astrophysics Data System (ADS)

Burmasheva, N. V.; Prosviryakov, E. Yu.

2017-12-01

A new exact analytical solution of a system of thermal convection equations in the Boussinesq approximation describing layered flows in an incompressible viscous fluid is obtained. A fluid flow in an infinite layer is considered. Convection in the fluid is induced by tangential stresses specified on the upper non-deformable boundary. At the fixed lower boundary, the no-slip condition is satisfied. Temperature corrections are given on the both boundaries of the fluid layer. The possibility of physical field stratification is investigated.

An experimental investigation of wall boundary layer transition Reynolds numbers in an expansion tube

NASA Technical Reports Server (NTRS)

Weilmuenster, K. J.

1974-01-01

Experimental measurements of boundary-layer transition in an expansion-tube test-gas flow are presented along with radial distributions of pitot pressure. An integral method for calculating constant Reynolds number lines for an expansion-tube flow is introduced. Comparison of experimental data and constant Reynolds number calculations has shown that for given conditions, wall boundary-layer transition occurs at a constant Reynolds number in an expansion-tube flow. Operating conditions in the expansion tube were chosen so that the effects of test-gas nonequilibrium on boundary-layer transition could be studied.

Forward-facing steps induced transition in a subsonic boundary layer

NASA Astrophysics Data System (ADS)

Zh, Hui; Fu, Song

2017-10-01

A forward-facing step (FFS) immersed in a subsonic boundary layer is studied through a high-order flux reconstruction (FR) method to highlight the flow transition induced by the step. The step height is a third of the local boundary-layer thickness. The Reynolds number based on the step height is 720. Inlet disturbances are introduced giving rise to streamwise vortices upstream of the step. It is observed that these small-scale streamwise structures interact with the step and hairpin vortices are quickly developed after the step leading to flow transition in the boundary layer.

Computer program for design of two-dimensional supersonic turbine rotor blades with boundary-layer correction

NASA Technical Reports Server (NTRS)

Goldman, L. J.; Scullin, V. J.

1971-01-01

A FORTRAN 4 computer program for the design of two-dimensional supersonic rotor blade sections corrected for boundary-layer displacement thickness is presented. The ideal rotor is designed by the method of characteristics to produce vortex flow within the blade passage. The boundary-layer parameters are calculated by Cohen and Reshotoko's method for laminar flow and Sasman and Cresci's method for turbulent flow. The program input consists essentially of the blade surface Mach number distribution and total flow conditions. The primary output is the corrected blade profile and the boundary-layer parameters.

Correlations for Boundary-Layer Transition on Mars Science Laboratory Entry Vehicle Due to Heat-Shield Cavities

NASA Technical Reports Server (NTRS)

Hollis, Brian R.; Liechty, Derek S.

2008-01-01

The influence of cavities (for attachment bolts) on the heat-shield of the proposed Mars Science Laboratory entry vehicle has been investigated experimentally and computationally in order to develop a criterion for assessing whether the boundary layer becomes turbulent downstream of the cavity. Wind tunnel tests were conducted on the 70-deg sphere-cone vehicle geometry with various cavity sizes and locations in order to assess their influence on convective heating and boundary layer transition. Heat-transfer coefficients and boundary-layer states (laminar, transitional, or turbulent) were determined using global phosphor thermography.

Ozone Laminae and Their Entrainment Into a Valley Boundary Layer, as Observed From a Mountaintop Monitoring Station, Ozonesondes, and Aircraft Over California's San Joaquin Valley

NASA Astrophysics Data System (ADS)

Faloona, I. C.; Conley, S. A.; Caputi, D.; Trousdell, J.; Chiao, S.; Eiserloh, A. J., Jr.; Clark, J.; Iraci, L. T.; Yates, E. L.; Marrero, J. E.; Ryoo, J. M.; McNamara, M. E.

2016-12-01

The San Joaquin Valley of California is wide ( 75 km) and long ( 400 km), and is situated under strong atmospheric subsidence due, in part, to the proximity of the midlatitude anticyclone of the Pacific High. The capping effect of this subsidence is especially prominent during the warm season when ground level ozone is a serious air quality concern across the region. While relatively clean marine boundary layer air is primarily funneled into the valley below the strong subsidence inversion at significant gaps in the upwind Coast Range mountains, airflow aloft also spills over these barriers and mixes into the valley from above. Because this transmountain flow occurs under the influence of synoptic subsidence it tends to present discrete, laminar sheets of differing air composition above the valley boundary layer. Meanwhile, although the boundary layers tend to remain shallow due to the prevailing subsidence, orographic and anabatic venting of valley boundary layer air around the basin whips up a complex admixture of regional air masses into a "buffer layer" just above the boundary layer (zi) and below the lower free troposphere. We present scalar data of widely varying lifetimes including ozone, methane, NOx, and thermodynamic observations from upwind and within the San Joaquin Valley to better explain this layering and its subsequent erosion into the valley boundary layer via entrainment. Data collected at a mountaintop monitoring station on Chews Ridge in the Coast Range, by coastal ozonesondes, and aircraft are analyzed to document the dynamic layering processes around the complex terrain surrounding the valley. Particular emphasis will be made on observational methods whereby distal ozone can be distinguished from the regional ozone to better understand the influence of exogenous sources on air quality in the valley.

Characteristics of the nocturnal boundary layer inferred from ozone measurements onboard a Zeppelin airship

NASA Astrophysics Data System (ADS)

Rohrer, Franz; Li, Xin; Hofzumahaus, Andreas; Ehlers, Christian; Holland, Frank; Klemp, Dieter; Lu, Keding; Mentel, Thomas F.; Kiendler-Scharr, Astrid; Wahner, Andreas

2014-05-01

The nocturnal boundary layer (NBL) is a sublayer within the planetary boundary layer (PBL) which evolves above solid land each day in the late afternoon due to radiation cooling of the surface. It is a region of several hundred meters thickness which inhibits vertical mixing. A residual and a surface layer remain above and below the NBL. Inside the surface layer, almost all direct emissions of atmospheric constituents take place during this time. This stratification lasts until the next morning after sunrise. Then, the heating of the surface generates a new convectionally mixed layer which successively eats up the NBL from below. This process lasts until shortly before noon when the NBL disappears completely and the PBL is mixed convectionally. Ozone measurements onboard a Zeppelin airship in The Netherlands, in Italy, and in Finland are used to analyse this behaviour with respect to atmospheric constituents and consequences for the diurnal cycles observed in the surface layer, the nocturnal boundary layer, and the residual layer are discussed.

The influence of free-stream turbulence on separation of turbulent boundary layers in incompressible, two-dimensional flow

NASA Technical Reports Server (NTRS)

Potter, J. Leith; Barnett, R. Joel; Fisher, Carl E.; Koukousakis, Costas E.

1986-01-01

Experiments were conducted to determine if free-stream turbulence scale affects separation of turbulent boundary layers. In consideration of possible interrelation between scale and intensity of turbulence, the latter characteristic also was varied and its role was evaluated. Flow over a 2-dimensional airfoil in a subsonic wind tunnel was studied with the aid of hot-wire anemometry, liquid-film flow visualization, a Preston tube, and static pressure measurements. Profiles of velocity, relative turbulence intensity, and integral scale in the boundary layer were measured. Detachment boundary was determined for various angles of attack and free-stream turbulence. The free-stream turbulence intensity and scale were found to spread into the entire turbulent boundary layer, but the effect decreased as the airfoil surface was approached. When the changes in stream turbulence were such that the boundary layer velocity profiles were unchanged, detachment location was not significantly affected by the variations of intensity and scale. Pressure distribution remained the key factor in determining detachment location.

The Role of Wave Cyclones in Transporting Boundary Layer Air to the Free Troposphere During the Spring 2001 NASA / TRACE-P Experiment

NASA Technical Reports Server (NTRS)

Fuelberg, Henry E.; Hannan, J. R.; Crawford, J. H.; Sachse, G. W.; Blake, D. R.

2003-01-01

Transport of boundary layer air to the free troposphere by cyclones during NASA's Transport and Chemical Evolution over the Pacific (TRACE-P) experiment is investigated. Airstreams responsible for boundary layer venting are diagnosed using results from a high-resolution meteorological model (MM5) together with in situ and remotely sensed chemical data. Hourly wind data from the MM5 are used to calculate three-dimensional grids of backward air trajectories. A reverse domain filling (RDF) technique then is employed to examine the characteristics of airstreams over the computational domain, and to isolate airstreams ascending from the boundary layer to the free troposphere during the previous 36 hours. Two cases are examined in detail. Results show that airstreams responsible for venting the boundary layer differ considerably from those described by classic conceptual models and in the recent literature. In addition, airstreams sampled by the TRACE-P aircraft are found to exhibit large variability in chemical concentrations. This variability is due to differences in the boundary layer histories of individual airstreams with respect to anthropogenic sources over continental Asia and Japan. Complex interactions between successive wave cyclones also are found to be important in determining the chemical composition of the airstreams. Particularly important is the process of post-cold frontal boundary layer air being rapidly transported offshore and recirculated into ascending airstreams of upstream cyclones.

Development of a Boundary Layer Property Interpolation Tool in Support of Orbiter Return To Flight

NASA Technical Reports Server (NTRS)

Greene, Francis A.; Hamilton, H. Harris

2006-01-01

A new tool was developed to predict the boundary layer quantities required by several physics-based predictive/analytic methods that assess damaged Orbiter tile. This new tool, the Boundary Layer Property Prediction (BLPROP) tool, supplies boundary layer values used in correlations that determine boundary layer transition onset and surface heating-rate augmentation/attenuation factors inside tile gouges (i.e. cavities). BLPROP interpolates through a database of computed solutions and provides boundary layer and wall data (delta, theta, Re(sub theta)/M(sub e), Re(sub theta)/M(sub e), Re(sub theta), P(sub w), and q(sub w)) based on user input surface location and free stream conditions. Surface locations are limited to the Orbiter s windward surface. Constructed using predictions from an inviscid w/boundary-layer method and benchmark viscous CFD, the computed database covers the hypersonic continuum flight regime based on two reference flight trajectories. First-order one-dimensional Lagrange interpolation accounts for Mach number and angle-of-attack variations, whereas non-dimensional normalization accounts for differences between the reference and input Reynolds number. Employing the same computational methods used to construct the database, solutions at other trajectory points taken from previous STS flights were computed: these results validate the BLPROP algorithm. Percentage differences between interpolated and computed values are presented and are used to establish the level of uncertainty of the new tool.

On the turbulent friction layer for rising pressure

NASA Technical Reports Server (NTRS)

Wieghardt, K; Tillmann, W

1951-01-01

Among the information presented are included displacement, momentum, and kinetic energy thicknesses, shearing stress distributions across boundary layer, and surface friction coefficients. The Gruschwitz method and its modifications are examined and tested. An energy theorem for the turbulent boundary layer is introduced and discussed but does not lead to a method for the prediction of the behavior of the turbulent boundary layer because relations for the shearing stress and the surface friction are lacking.

Boundary streaming with Navier boundary condition.

PubMed

Xie, Jin-Han; Vanneste, Jacques

2014-06-01

In microfluidic applications involving high-frequency acoustic waves over a solid boundary, the Stokes boundary-layer thickness δ is so small that some non-negligible slip may occur at the fluid-solid interface. This paper assesses the impact of this slip by revisiting the classical problem of steady acoustic streaming over a flat boundary, replacing the no-slip boundary condition with the Navier condition u|_{y=0}=L_{s}∂_{y}u|_{y=0}, where u is the velocity tangent to the boundary y=0, and the parameter L_{s} is the slip length. A general expression is obtained for the streaming velocity across the boundary layer as a function of the dimensionless parameter L_{s}/δ. The limit outside the boundary layer provides an effective slip velocity satisfied by the interior mean flow. Particularizing to traveling and standing waves shows that the boundary slip respectively increases and decreases the streaming velocity.

Adaptive step-size algorithm for Fourier beam-propagation method with absorbing boundary layer of auto-determined width.

PubMed

Learn, R; Feigenbaum, E

2016-06-01

Two algorithms that enhance the utility of the absorbing boundary layer are presented, mainly in the framework of the Fourier beam-propagation method. One is an automated boundary layer width selector that chooses a near-optimal boundary size based on the initial beam shape. The second algorithm adjusts the propagation step sizes based on the beam shape at the beginning of each step in order to reduce aliasing artifacts.

On an Asymptotically Consistent Unsteady Interacting Boundary Layer

NASA Technical Reports Server (NTRS)

Bartels, Robert E.

2007-01-01

This paper develops the asymptotic matching of an unsteady compressible boundary layer to an inviscid flow. Of particular importance is the velocity injection or transpiration boundary condition derived by this theory. It is found that in general the transpiration will contain a slope of the displacement thickness and a time derivative of a density integral. The conditions under which the second term may be neglected, and its consistency with the established results of interacting boundary layer are discussed.

Adaptive step-size algorithm for Fourier beam-propagation method with absorbing boundary layer of auto-determined width

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

Learn, R.; Feigenbaum, E.

Two algorithms that enhance the utility of the absorbing boundary layer are presented, mainly in the framework of the Fourier beam-propagation method. One is an automated boundary layer width selector that chooses a near-optimal boundary size based on the initial beam shape. Furthermore, the second algorithm adjusts the propagation step sizes based on the beam shape at the beginning of each step in order to reduce aliasing artifacts.

Adaptive step-size algorithm for Fourier beam-propagation method with absorbing boundary layer of auto-determined width

DOE PAGES

Learn, R.; Feigenbaum, E.

2016-05-27

Two algorithms that enhance the utility of the absorbing boundary layer are presented, mainly in the framework of the Fourier beam-propagation method. One is an automated boundary layer width selector that chooses a near-optimal boundary size based on the initial beam shape. Furthermore, the second algorithm adjusts the propagation step sizes based on the beam shape at the beginning of each step in order to reduce aliasing artifacts.

Shooting method for solution of boundary-layer flows with massive blowing

NASA Technical Reports Server (NTRS)

Liu, T.-M.; Nachtsheim, P. R.

1973-01-01

A modified, bidirectional shooting method is presented for solving boundary-layer equations under conditions of massive blowing. Unlike the conventional shooting method, which is unstable when the blowing rate increases, the proposed method avoids the unstable direction and is capable of solving complex boundary-layer problems involving mass and energy balance on the surface.

Solution of the surface Euler equations for accurate three-dimensional boundary-layer analysis of aerodynamic configurations

NASA Technical Reports Server (NTRS)

Iyer, V.; Harris, J. E.

1987-01-01

The three-dimensional boundary-layer equations in the limit as the normal coordinate tends to infinity are called the surface Euler equations. The present paper describes an accurate method for generating edge conditions for three-dimensional boundary-layer codes using these equations. The inviscid pressure distribution is first interpolated to the boundary-layer grid. The surface Euler equations are then solved with this pressure field and a prescribed set of initial and boundary conditions to yield the velocities along the two surface coordinate directions. Results for typical wing and fuselage geometries are presented. The smoothness and accuracy of the edge conditions obtained are found to be superior to the conventional interpolation procedures.

An investigation of turbulence structure in a low-Reynolds-number incompressible turbulent boundary

NASA Technical Reports Server (NTRS)

White, B. R.; Strataridakis, C. J.

1987-01-01

An existing high turbulence intensity level (5%) atmospheric boundary-layer wind tunnel has been successfully converted to a relatively low level turbulence (0.3%) wind tunnel through extensive modification, testing, and calibration. A splitter plate was designed, built, and installed into the wind-tunnel facility to create thick, mature, two-dimensional turbulent boundary layer flow at zero pressure gradient. Single and cross hot-wire measurements show turbulent boundary layer characteristics of good quality with unusually large physical size, i.e., viscous sublayer of the order of 1 mm high. These confirm the potential ability of the tunnel to be utilized for future high-quality near-wall turbulent boundary layer measurements. It compares very favorably with many low turbulence research tunnels.

Amendment to "Analytical Solution for the Convectively-Mixed Atmospheric Boundary Layer": Inclusion of Subsidence

NASA Astrophysics Data System (ADS)

Ouwersloot, H. G.; de Arellano, J. Vilà-Guerau

2013-09-01

In Ouwersloot and Vilà-Guerau de Arellano (Boundary-Layer Meteorol. doi: 10.1007/s10546-013-9816-z , 2013, this issue), the analytical solutions for the boundary-layer height and scalar evolutions are derived for the convective boundary layer, based on the prognostic equations of mixed-layer slab models without taking subsidence into account. Here, we include and quantify the added effect of subsidence if the subsidence velocity scales linearly with height throughout the atmosphere. This enables analytical analyses for a wider range of observational cases. As a demonstration, the sensitivity of the boundary-layer height and the potential temperature jump to subsidence and the free tropospheric stability is graphically presented. The new relations show the importance of the temporal distribution of the surface buoyancy flux in determining the evolution if there is subsidence.

F-16XL ship #1 - CAWAP boundary layer hot film, left wing

NASA Technical Reports Server (NTRS)

1996-01-01

This photo shows the boundary layer hot film on the left wing of NASA's single-seat F-16XL (ship #1) used for the Cranked-Arrow Wing Aerodynamic Project (CAWAP) at Dryden Flight Research Center, Edwards, California. Hot film is used to measure temperature changes on a surface. The modified airplane features a delta 'cranked-arrow' wing with strips of tubing along the leading edge to the trailing edge to sense static on the wing and obtain pressure distribution data. The right wing receives data on pressure distribution and the left wing has three types of instrumentation - preston tubes to measure local skin friction, boundary layer rakes to measure boundary layer profiles (the layer where the air interacts with the surfaces of a moving aircraft), and hot films to determine boundary layer transition locations. The program also gathered aero data on two wing planforms for NASA's High Speed Research Program. The first flight of CAWAP occurred on November 21, 1995, and the test program ended in April 1996.

Boundary layer thermal stresses in angle-ply composite laminates, part 1. [graphite-epoxy composites

NASA Technical Reports Server (NTRS)

Wang, S. S.; Choi, I.

1981-01-01

Thermal boundary-layer stresses (near free edges) and displacements were determined by a an eigenfunction expansion technique and the establishment of an appropriate particular solution. Current solutions in the region away from the singular domain (free edge) are found to be excellent agreement with existing approximate numerical results. As the edge is approached, the singular term controls the near field behavior of the boundary layer. Results are presented for cases of various angle-ply graphite/epoxy laminates with (theta/-theta/theta/theta) configurations. These results show high interlaminar (through-the-thickness) stresses. Thermal boundary-layer thicknesses of different composite systems are determined by examining the strain energy density distribution in composites. It is shown that the boundary-layer thickness depends on the degree of anisotropy of each individual lamina, thermomechanical properties of each ply, and the relative thickness of adjacent layers. The interlaminar thermal stresses are compressive with increasing temperature. The corresponding residual stresses are tensile and may enhance interply delaminations.

Method for transition prediction in high-speed boundary layers, phase 2

NASA Astrophysics Data System (ADS)

Herbert, T.; Stuckert, G. K.; Lin, N.

1993-09-01

The parabolized stability equations (PSE) are a new and more reliable approach to analyzing the stability of streamwise varying flows such as boundary layers. This approach has been previously validated for idealized incompressible flows. Here, the PSE are formulated for highly compressible flows in general curvilinear coordinates to permit the analysis of high-speed boundary-layer flows over fairly general bodies. Vigorous numerical studies are carried out to study convergence and accuracy of the linear-stability code LSH and the linear/nonlinear PSE code PSH. Physical interfaces are set up to analyze the M = 8 boundary layer over a blunt cone calculated by using a thin-layer Navier Stokes (TNLS) code and the flow over a sharp cone at angle of attack calculated using the AFWAL parabolized Navier-Stokes (PNS) code. While stability and transition studies at high speeds are far from routine, the method developed here is the best tool available to research the physical processes in high-speed boundary layers.

Large Eddy Simulations of a Bottom Boundary Layer Under a Shallow Geostrophic Front

NASA Astrophysics Data System (ADS)

Bateman, S. P.; Simeonov, J.; Calantoni, J.

2017-12-01

The unstratified surf zone and the stratified shelf waters are often separated by dynamic fronts that can strongly impact the character of the Ekman bottom boundary layer. Here, we use large eddy simulations to study the turbulent bottom boundary layer associated with a geostrophic current on a stratified shelf of uniform depth. The simulations are initialized with a spatially uniform vertical shear that is in geostrophic balance with a pressure gradient due to a linear horizontal temperature variation. Superposed on the temperature front is a stable vertical temperature gradient. As turbulence develops near the bottom, the turbulence-induced mixing gradually erodes the initial uniform temperature stratification and a well-mixed layer grows in height until the turbulence becomes fully developed. The simulations provide the spatial distribution of the turbulent dissipation and the Reynolds stresses in the fully developed boundary layer. We vary the initial linear stratification and investigate its effect on the height of the bottom boundary layer and the turbulence statistics. The results are compared to previous models and simulations of stratified bottom Ekman layers.

A New View on Origin, Role and Manipulation of Large Scales in Turbulent Boundary Layers

NASA Technical Reports Server (NTRS)

Corke, T. C.; Nagib, H. M.; Guezennec, Y. G.

1982-01-01

The potential of passive 'manipulators' for altering the large scale turbulent structures in boundary layers was investigated. Utilizing smoke wire visualization and multisensor probes, the experiment verified that the outer scales could be suppressed by simple arrangements of parallel plates. As a result of suppressing the outer scales in turbulent layers, a decrease in the streamwise growth of the boundary layer thickness was achieved and was coupled with a 30 percent decrease in the local wall friction coefficient. After accounting for the drag on the manipulator plates, the net drag reduction reached a value of 20 percent within 55 boundary layer thicknesses downstream of the device. No evidence for the reoccurrence of the outer scales was present at this streamwise distance thereby suggesting that further reductions in the net drag are attainable. The frequency of occurrence of the wall events is simultaneously dependent on the two parameters, Re2 delta sub 2 and Re sub x. As a result of being able to independently control the inner and outer boundary layer characteristics with these manipulators, a different view of these layers emerged.

Rapid Changes in Water Properties on a Shallow Reef in the Chesapeake Bay due to a Wind Driven Internal Seiche

NASA Astrophysics Data System (ADS)

Kilbourne, B.

2016-12-01

The Chesapeake Bay Interpretive Buoy System has collected oceanographic and meteorological observations in Chesapeake Bay from 2007 to the present. The relatively long and well resolved time series of wind, current, and salinity data provided by this array creates an opportunity to better understand the many finescale circulation pathways in Chesapeake Bay. The mean vertical structure of Chesapeake Bay is approximated by a three layer system: a well-mixed surface boundary layer from 1 to 8 m depth, a stratified transition layer from 8 to 15 m depth, and a well-mixed bottom boundary layer from 15 m to the bottom (typically < 30 m). The conditions in the surface and bottom boundary layers can be strikingly different with the bottom layer being saltier, lower in pH, and lower in dissolved oxygen than the surface layer. The Gooses Reef station of this array is located on `Gooses Reef', a shallow bar just 10 m in depth, dividing the Choptank River basin from the main channel of the Chesapeake Bay. This shallow bar provides habitat for oysters, a keystone species in the Chesapeake Bay, and is both commercially and ecologically critical to the region. These shallow habitats are threatened when anoxic (< 0.5 mg l-1 O2) conditions exist in the upper 10 m of the water column. The Gooses Reef station is unique in the array due to the addition of a bottom mounted sensor package; data from August 2012 show rapid changes in the salinity (11 to 17 PSU), dissolved oxygen (6 to 0.05 mg l-1) , and pH (8.3 to 7.7) at the bottom. Investigations of wind and current data before these rapid changes show along channel wind stress oscillations near the M2 tidal frequency. Current profiles from the buoy ADCP show low-frequency along-channel baroclinic oscillations. Observed currents appear to be an internal seiche, forced by resonance between the along-channel wind and diurnal tide. At the Gooses Reef bar, this internal seiche forced the bottom boundary layer up and over the bar, causing the sudden shift in water properties. These observations highlight the strong physical controls on local water conditions in the Chesapeake Bay and similar estuaries.

Damage Tolerance and Mechanics of Interfaces in Nanostructured Metals

NASA Astrophysics Data System (ADS)

Foley, Daniel J.

The concept of interface driven properties in crystalline metals has been one of the most intensely discussed topics in materials science for decades. Since the 1980s researchers have been exploring the concept of grain boundary engineering as route for tuning properties such as fracture toughness and irradiation resistance. This is especially true in ultra-fine grained and nanocrystalline materials where grain boundary mediated properties become dominant. More recently, materials composed of hierarchical nanostructures, such as amorphous-crystalline nanolaminates, have attracted considerable attention due to their favorable properties, ease of manufacture and highly tunable microstructure. While both grain boundary engineering and hierarchical nanostructures have shown promise there are still questions remaining regarding the role of specific attributes of the microstructure (such as grain boundaries, grain/layer size and inter/intralayer morphology) in determining material properties. This thesis attempts to address these questions by using atomistic simulations to perform deformation and damage loading studies on a series of nanolaminate and bicrystalline structures. During the course of this thesis the roles of layer thickness, interlayer structure and interlayer chemistry on the mechanical properties of Ni-NiX amorphous-crystalline nanolaminates were explored using atomistic simulations. This thesis found that layer thickness/thickness ratio and amorphous layer chemistry play a crucial role in yield strength and Young's modulus. Analysis of the deformation mechanisms at the atomic scale revealed that structures containing single crystalline, crystalline layers undergo plastic deformation when shear transformation zones form in the amorphous layer and impinge on the amorphous-crystalline interface, leading to dislocation emission. However, structures containing nanocrystalline, crystalline layers (both equiaxed and columnar nanocrystalline) undergo plastic deformation through a combination of grain boundary sliding and grain boundary mediated dislocation nucleation. Since grain boundaries were found to play a critical role as sources and sinks for dislocations in amorphous-crystalline nanolaminates a follow-up study on the effect of grain boundary character on damage accumulation/accommodation in copper symmetric tilt grain boundaries was performed. This study found that grain boundaries will become saturated with damage, a state where grain boundary energy and grain boundary free volume oscillate about a plateau during continuous defect loading (vacancy, interstitial and frenkel pair loading were all considered). Further, grain boundary character (specifically equilibrium grain boundary energy) was strongly correlated to the damage accommodation behavior of grain boundaries in copper. Finally, a study that attempted to link grain boundary damage saturation behavior to variations in grain boundary mechanical properties was performed. This study found no direct relationships between grain boundary damage saturation behavior and variations in grain boundary properties. The results of this thesis provide researchers with several strategies for tuning the properties of amorphous-crystalline nanolaminates. These strategies include manipulated bulk attributes such as layer thickness and morphology as well as manipulation of microscale attributes such as grain boundary engineering. Finally, this thesis provides valuable insight into the damage loading/accommodation behavior of FCC symmetric tilt grain boundaries.

Wind Turbine Gust Prediction Using Remote Sensing Data

NASA Astrophysics Data System (ADS)

Towers, Paul; Jones, Bryn

2013-11-01

Offshore wind energy is a growing energy source as governments around the world look for environmentally friendly solutions to potential future energy shortages. In order to capture more energy from the wind, larger turbines are being designed, leading to the structures becoming increasingly vulnerable to damage caused by violent gusts of wind. Advance knowledge of such gusts will enable turbine control systems to take preventative action, reducing turbine maintenance costs. We present a system which can accurately forecast the velocity profile of an oncoming wind, given only limited spatial measurements from light detection and ranging (LiDAR) units, which are currently operational in industry. Our method combines nonlinear state estimation techniques with low-order models of atmospheric boundary-layer flows to generate flow-field estimates. We discuss the accuracy of our velocity profile predictions by direct comparison to data derived from large eddy simulations of the atmospheric boundary layer.

Effect of truncated cone roughness element density on hydrodynamic drag

NASA Astrophysics Data System (ADS)

Womack, Kristofer; Schultz, Michael; Meneveau, Charles

2017-11-01

An experimental study was conducted on rough-wall, turbulent boundary layer flow with roughness elements whose idealized shape model barnacles that cause hydrodynamic drag in many applications. Varying planform densities of truncated cone roughness elements were investigated. Element densities studied ranged from 10% to 79%. Detailed turbulent boundary layer velocity statistics were recorded with a two-component LDV system on a three-axis traverse. Hydrodynamic roughness length (z0) and skin-friction coefficient (Cf) were determined and compared with the estimates from existing roughness element drag prediction models including Macdonald et al. (1998) and other recent models. The roughness elements used in this work model idealized barnacles, so implications of this data set for ship powering are considered. This research was supported by the Office of Naval Research and by the Department of Defense (DoD) through the National Defense Science & Engineering Graduate Fellowship (NDSEG) Program.

Convective response of a wall-mounted hot-film sensor in a shock tube

NASA Technical Reports Server (NTRS)

Roberts, A. Sidney, Jr.; Ortgies, Kelly R.; Gartenberg, Ehud; Carraway, Debra L.

1991-01-01

Shock tube experiments were performed in order to determine the response of a single hot-film element of a sensor array to transiently induced flow behind weak normal shock waves. The experiments attempt to isolate the response due only to the change in convective heat transfer at the hot-film surface mounted on the wall of the shock tube. The experiments are described, the results being correlated with transient boundary layer theory and compared with an independent set of experimental results. One of the findings indicates that the change in the air properties (temperature and pressure) precedes the air mass transport, causing an ambiguity in the sensor response to the development of the velocity boundary layer. Also, a transient, local heat transfer coefficient is formulated to be used as a forcing function in an hot-film instrument model and simulation which remains under investigation.

Computation of turbulent flow in a thin liquid layer of fluid involving a hydraulic jump

NASA Technical Reports Server (NTRS)

Rahman, M. M.; Faghri, A.; Hankey, W. L.

1991-01-01

Numerically computed flow fields and free surface height distributions are presented for the flow of a thin layer of liquid adjacent to a solid horizontal surface that encounters a hydraulic jump. Two kinds of flow configurations are considered: two-dimensional plane flow and axisymmetric radial flow. The computations used a boundary-fitted moving grid method with a k-epsilon model for the closure of turbulence. The free surface height was determined by an optimization procedure which minimized the error in the pressure distribution on the free surface. It was also checked against an approximate procedure involving integration of the governing equations and use of the MacCormack predictor-corrector method. The computed film height also compared reasonably well with previous experiments. A region of recirculating flow was found to be present adjacent to the solid boundary near the location of the jump, which was caused by a rapid deceleration of the flow.

Control of flow separation in a turbulent boundary layer

NASA Astrophysics Data System (ADS)

Cho, Minjeong; Choi, Sangho; Choi, Haecheon

2015-11-01

Towards the development of successful control methods for separation delay in a turbulent boundary layer, we adopt a model flow field, in which a turbulent separation occurs above a flat plate (Na and Moin 1998 JFM), and apply controls to this flow for reducing the size of the separation bubble and investigating the interaction between the forcing and flow near the separation bubble. We provide a single-frequency forcing with zero net mass flow rate at the upstream of the separation bubble. At low forcing frequencies, spanwise vortices are generated and travel downstream, bringing high momentum toward the wall and reducing the size of the separation bubble. Also, these vortices cause the separation and reattachment points to travel downstream. On the other hand, at high forcing frequencies, the size of the separation bubble becomes smaller and larger in time, respectively, due to the pressure gradient alternating favorably and adversely in time. Supported by NRF-2011-0028032 and 2014048162.

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.

Effects of surface poisons on the oxidation of binary alloys

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

Hagan, P.S.; Polizzotti, R.S.; Luckman, G.

1985-10-01

A system of reaction-diffusion equations describing the oxidation of binary alloys in environments containing small amounts of surface poisons is analyzed. These poisons reduce the oxygen flux into the alloy, which causes the alloy to oxidize in two stages.During the initial stage, the oxidation reaction occurs in a stationary boundary layer at the alloy surface. Consequently, a thin zone containing a very high concentration of the metal oxide is created at the alloy surface. During the second stage, the oxidation reaction occurs in a moving boundary layer. This leads to a Stefan problem, which is analyzed by using asymptotic andmore » numerical techniques. By comparing the solutions to those of alloys in unpoisoned environments, it is concluded that surface poisons can lead to the formation of protective external oxide scales in alloys which would not normally form such scales. 11 references.« less

Development of an experimental setup for analyzing the influence of Magnus effect on the performance of airfoil

NASA Astrophysics Data System (ADS)

Aktharuzzaman, Md; Sarker, Md. Samad; Safa, Wasiul; Sharah, Nahreen; Salam, Md. Abdus

2017-12-01

Magnus effect is a phenomenon where pressure difference is created according to Bernoulli's effect due to induced velocity changes caused by a rotating object in a fluid. Using this concept, the idea of delaying boundary layer separation on airfoil by providing moving surface boundary layer control has been developed. In order to analyze the influence of Magnus effect on the aerodynamic performance of an airfoil, there is no alternative of developing an experimental setup. This paper aims to develop such an experimental setup which will be capable of analyzing the influence of Magnus effect on both symmetric and asymmetric airfoils by placing a cylinder at the leading edge. To provide arrangements for a rotating cylinder at the leading edge of airfoil, necessary modifications and additions have been done in the test section of an AF100 subsonic wind tunnel.