Fuselage Structure Response to Boundary Layer, Tonal Sound, and Jet Noise

NASA Technical Reports Server (NTRS)

Maestrello, L.

2004-01-01

Experiments have been conducted to study the response of curved aluminum and graphite-epoxy fuselage structures to flow and sound loads from turbulent boundary layer, tonal sound, and jet noise. Both structures were the same size. The aluminum structure was reinforced with tear stoppers, while the graphite-epoxy structure was not. The graphite-epoxy structure weighed half as much as the aluminum structure. Spatiotemporal intermittence and chaotic behavior of the structural response was observed, as jet noise and tonal sound interacted with the turbulent boundary layer. The fundamental tone distributed energy to other components via wave interaction with the turbulent boundary layer. The added broadband sound from the jet, with or without a shock, influenced the responses over a wider range of frequencies. Instantaneous spatial correlation indicates small localized spatiotemporal regions of convected waves, while uncorrelated patterns dominate the larger portion of the space. By modifying the geometry of the tear stoppers between panels and frame, the transmitted and reflected waves of the aluminum panels were significantly reduced. The response level of the graphite-epoxy structure was higher, but the noise transmitted was nearly equal to that of the aluminum structure. The fundamental shock mode is between 80 deg and 150 deg and the first harmonic is between 20 deg and 80 deg for the underexpanded supersonic jet impinging on the turbulent boundary layer influencing the structural response. The response of the graphite-epoxy structure due to the fundamental mode of the shock impingement was stabilized by an externally fixed oscillator.

The double layers in the plasma sheet boundary layer during magnetic reconnection

NASA Astrophysics Data System (ADS)

Guo, J.; Yu, B.

2014-11-01

We studied the evolutions of double layers which appear after the magnetic reconnection through two-dimensional electromagnetic particle-in-cell simulation. The simulation results show that the double layers are formed in the plasma sheet boundary layer after magnetic reconnection. At first, the double layers which have unipolar structures are formed. And then the double layers turn into bipolar structures, which will couple with another new weak bipolar structure. Thus a new double layer or tripolar structure comes into being. The double layers found in our work are about several ten Debye lengths, which accords with the observation results. It is suggested that the electron beam formed during the magnetic reconnection is responsible for the production of the double layers.

An Experimental Study of a Separated/Reattached Flow Behind a Backward-Facing Step. Re(sub h) = 37,000

NASA Technical Reports Server (NTRS)

Jovic, Srba

1996-01-01

An experimental study was carried out to investigate turbulent structure of a two-dimensional incompressible separating/reattaching boundary layer behind a backward-facing step. Hot-wire measurement technique was used to measure three Reynolds stresses and higher-order mean products of velocity fluctuations. The Reynolds number, Re(sub h), based on the step height, h, and the reference velocity, U(sub 0), was 37,000. The upstream oncoming flow was fully developed turbulent boundary layer with the Re(sub theta) = 3600. All turbulent properties, such as Reynolds stresses, increase dramatically downstream of the step within an internally developing mixing layer. Distributions of dimensionless mean velocity, turbulent quantities and antisymmetric distribution of triple velocity products in the separated free shear layer suggest that the shear layer above the recirculating region strongly resembles free-shear mixing layer structure. In the reattachment region close to the wall, turbulent diffusion term balances the rate of dissipation since advection and production terms appear to be negligibly small. Further downstream, production and dissipation begin to dominate other transport processes near the wall indicating the growth of an internal turbulent boundary layer. In the outer region, however, the flow still has a memory of the upstream disturbance even at the last measuring station of 51 step-heights. The data show that the structure of the inner layer recovers at a much faster rate than the outer layer structure. The inner layer structure resembles the near-wall structure of a plane zero pressure-gradient turbulent boundary layer (plane TBL) by 25h to 30h, while the outer layer structure takes presumably over 100h.

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.

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.

Including fluid shear viscosity in a structural acoustic finite element model using a scalar fluid representation

PubMed Central

Cheng, Lei; Li, Yizeng; Grosh, Karl

2013-01-01

An approximate boundary condition is developed in this paper to model fluid shear viscosity at boundaries of coupled fluid-structure system. The effect of shear viscosity is approximated by a correction term to the inviscid boundary condition, written in terms of second order in-plane derivatives of pressure. Both thin and thick viscous boundary layer approximations are formulated; the latter subsumes the former. These approximations are used to develop a variational formation, upon which a viscous finite element method (FEM) model is based, requiring only minor modifications to the boundary integral contributions of an existing inviscid FEM model. Since this FEM formulation has only one degree of freedom for pressure, it holds a great computational advantage over the conventional viscous FEM formulation which requires discretization of the full set of linearized Navier-Stokes equations. The results from thick viscous boundary layer approximation are found to be in good agreement with the prediction from a Navier-Stokes model. When applicable, thin viscous boundary layer approximation also gives accurate results with computational simplicity compared to the thick boundary layer formulation. Direct comparison of simulation results using the boundary layer approximations and a full, linearized Navier-Stokes model are made and used to evaluate the accuracy of the approximate technique. Guidelines are given for the parameter ranges over which the accurate application of the thick and thin boundary approximations can be used for a fluid-structure interaction problem. PMID:23729844

Including fluid shear viscosity in a structural acoustic finite element model using a scalar fluid representation.

PubMed

Cheng, Lei; Li, Yizeng; Grosh, Karl

2013-08-15

An approximate boundary condition is developed in this paper to model fluid shear viscosity at boundaries of coupled fluid-structure system. The effect of shear viscosity is approximated by a correction term to the inviscid boundary condition, written in terms of second order in-plane derivatives of pressure. Both thin and thick viscous boundary layer approximations are formulated; the latter subsumes the former. These approximations are used to develop a variational formation, upon which a viscous finite element method (FEM) model is based, requiring only minor modifications to the boundary integral contributions of an existing inviscid FEM model. Since this FEM formulation has only one degree of freedom for pressure, it holds a great computational advantage over the conventional viscous FEM formulation which requires discretization of the full set of linearized Navier-Stokes equations. The results from thick viscous boundary layer approximation are found to be in good agreement with the prediction from a Navier-Stokes model. When applicable, thin viscous boundary layer approximation also gives accurate results with computational simplicity compared to the thick boundary layer formulation. Direct comparison of simulation results using the boundary layer approximations and a full, linearized Navier-Stokes model are made and used to evaluate the accuracy of the approximate technique. Guidelines are given for the parameter ranges over which the accurate application of the thick and thin boundary approximations can be used for a fluid-structure interaction problem.

Mach Number effects on turbulent superstructures in wall bounded flows

NASA Astrophysics Data System (ADS)

Kaehler, Christian J.; Bross, Matthew; Scharnowski, Sven

2017-11-01

Planer and three-dimensional flow field measurements along a flat plat boundary layer in the Trisonic Wind Tunnel Munich (TWM) are examined with the aim to characterize the scaling, spatial organization, and topology of large scale turbulent superstructures in compressible flow. This facility is ideal for this investigation as the ratio of boundary layer thickness to test section spanwise extent ratio is around 1/25, ensuring minimal sidewall and corner effects on turbulent structures in the center of the test section. A major difficulty in the experimental investigation of large scale features is the mutual size of the superstructures which can extend over many boundary layer thicknesses. Using multiple PIV systems, it was possible to capture the full spatial extent of large-scale structures over a range of Mach numbers from Ma = 0.3 - 3. To calculate the average large-scale structure length and spacing, the acquired vector fields were analyzed by statistical multi-point methods that show large scale structures with a correlation length of around 10 boundary layer thicknesses over the range of Mach numbers investigated. Furthermore, the average spacing between high and low momentum structures is on the order of a boundary layer thicknesses. This work is supported by the Priority Programme SPP 1881 Turbulent Superstructures of the Deutsche Forschungsgemeinschaft.

New Synthesis of Ocean Crust Velocity Structure From Two-Dimensional Profiles

NASA Astrophysics Data System (ADS)

Christeson, G. L.; Goff, J.; Carlson, R. L.; Reece, R.

2017-12-01

The velocity structure of typical oceanic crust consists of Layer 2, where velocities increase rapidly with depth from seafloor, and Layer 3, which is thicker and has a lower velocity gradient. Previous syntheses have found no correlation of velocity structure with spreading rate, even though we know that magmatic processes differ between slow-spreading and fast-spreading crust. We present a new synthesis of ocean crust velocity structure, compiling observations from two-dimensional studies in the Atlantic, Pacific, and Indian ocean basins. The Layer 2/3 boundary was picked from each publication at a change in gradient either on velocity-depth functions or contour plots (with at least 0.5 km/s contour interval), or from the appropriate layer boundary for layered models. We picked multiple locations at each seismic refraction profile if warranted by model variability. Preliminary results show statistically significant differences in average Layer 2 and Layer 3 thicknesses between slow-spreading and superfast-spreading crust, with Layer 2 thinner and Layer 3 thicker for the higher spreading rate crust. The thickness changes are about equivalent, resulting in no change in mean crustal thickness. The Layer 2/3 boundary is often interpreted as the top of the gabbros; however, a comparison with mapped magma lens depths at the ridge axis shows that the boundary is typically deeper than average axial melt lens depth at superfast-spreading crust, and shallower at intermediate-spreading crust.

Automated boundary detection of the optic disc and layer segmentation of the peripapillary retina in volumetric structural and angiographic optical coherence tomography.

PubMed

Zang, Pengxiao; Gao, Simon S; Hwang, Thomas S; Flaxel, Christina J; Wilson, David J; Morrison, John C; Huang, David; Li, Dengwang; Jia, Yali

2017-03-01

To improve optic disc boundary detection and peripapillary retinal layer segmentation, we propose an automated approach for structural and angiographic optical coherence tomography. The algorithm was performed on radial cross-sectional B-scans. The disc boundary was detected by searching for the position of Bruch's membrane opening, and retinal layer boundaries were detected using a dynamic programming-based graph search algorithm on each B-scan without the disc region. A comparison of the disc boundary using our method with that determined by manual delineation showed good accuracy, with an average Dice similarity coefficient ≥0.90 in healthy eyes and eyes with diabetic retinopathy and glaucoma. The layer segmentation accuracy in the same cases was on average less than one pixel (3.13 μm).

Automated boundary detection of the optic disc and layer segmentation of the peripapillary retina in volumetric structural and angiographic optical coherence tomography

PubMed Central

Zang, Pengxiao; Gao, Simon S.; Hwang, Thomas S.; Flaxel, Christina J.; Wilson, David J.; Morrison, John C.; Huang, David; Li, Dengwang; Jia, Yali

2017-01-01

To improve optic disc boundary detection and peripapillary retinal layer segmentation, we propose an automated approach for structural and angiographic optical coherence tomography. The algorithm was performed on radial cross-sectional B-scans. The disc boundary was detected by searching for the position of Bruch’s membrane opening, and retinal layer boundaries were detected using a dynamic programming-based graph search algorithm on each B-scan without the disc region. A comparison of the disc boundary using our method with that determined by manual delineation showed good accuracy, with an average Dice similarity coefficient ≥0.90 in healthy eyes and eyes with diabetic retinopathy and glaucoma. The layer segmentation accuracy in the same cases was on average less than one pixel (3.13 μm). PMID:28663830

Shock wave boundary layer interaction on suction side of compressor profile in single passage test section

NASA Astrophysics Data System (ADS)

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

2015-11-01

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). In order to investigate the flow structure on the suction side of a profile, a design of a generic test section in linear transonic wind tunnel was proposed. 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. Near the sidewalls the suction slots are applied for the corner flow structure control. It allows to control the Axial Velocity Density Ratio (AVDR), important parameter for compressor cascade investigations. Numerical results for Explicit Algebraic Reynolds Stress Model with transition modeling are compared with oil flow visualization, schlieren and Pressure Sensitive Paint. Boundary layer transition location is detected by Temperature Sensitive Paint.

Clear-air radar observations of the atmospheric boundary layer

NASA Astrophysics Data System (ADS)

Ince, Turker

2001-10-01

This dissertation presents the design and operation of a high-resolution frequency-modulated continuous-wave (FM- CW) radar system to study the structure and dynamics of clear-air turbulence in the atmospheric boundary layer (ABL). This sensitive radar can image the vertical structure of the ABL with both high spatial and temporal resolutions, and provide both qualitative information about the morphology of clear-air structures and quantitative information on the intensity of fluctuations in refractive-index of air. The principles of operation and the hardware and data acquisition characteristics of the radar are described in the dissertation. In October 1999, the radar participated in the Cooperative Atmosphere-Surface Exchange Study (CASES'99) Experiment to characterize the temporal structure and evolution of the boundary-layer features in both convective and stable conditions. The observed structures include clear-air convection, boundary layer evolution, gravity waves, Kelvin-Helmholtz instabilities, stably stratified layers, and clear-air turbulence. Many of the S-band radar images also show high- reflectivity returns from Rayleigh scatterers such as insects. An adaptive median filtering technique based on local statistics has, therefore, been developed to discriminate between Bragg and Rayleigh scattering in clear-air radar observations. The filter is tested on radar observations of clear air convection with comparison to two commonly used image processing techniques. The dissertation also examines the statistical mean of the radar-measured C2n for clear-air convection, and compares it with the theoretical predictions. The study also shows that the inversion height, local thickness of the inversion layer, and the height of the elevated atmospheric layers can be estimated from the radar reflectivity measurements. In addition, comparisons to the radiosonde-based height estimates are made. To examine the temporal and spatial structure of C2n , the dissertation presents two case studies with the measurements of remote (the FM-CW radar and Doppler lidar) and in-situ (research aircraft, kite, and radiosonde) sensors from the stable nighttime boundary layer. It also presents a unique observation of evolution of the convective and nocturnal boundary layers by the S-band radar, and provides description of the observed boundary layer characteristics with the aid of in-situ measurements by the 55m instrumented tower and radiosonde.

The flow separation delay in the boundary layer by induced vortices.

PubMed

Chaudhry, Ishtiaq A; Sultan, Tipu; Siddiqui, Farrukh A; Farhan, M; Asim, M

2017-01-01

A series of experiments involving the particle image velocimetry technique are carried out to analyse the quantitative effectiveness of the synthesized vortical structures towards actual flow separation control. The streamwise vortices are synthesized from the synthetic jet actuator and introduced into the attached and separating boundary layer developed on the flat plate surface. Two types of actuators with different geometrical set-ups are used to analyse the evolution of vortical structures in the near wall region and their impact towards achieving separation delay in the boundary layer. First, a single circular jet is synthesized by varying actuator operating parameters and issued into the boundary layer to evaluate the dynamics of the interaction between the vortical structures and the near wall low momentum fluid in the separated region. Second, an array of jets has been issued into the artificially separated region to assess the effectiveness of various vortical structures towards achieving the reattachment of the separated flow in the streamwise direction.

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.

Analysis of the electrolyte convection inside the concentration boundary layer during structured electrodeposition of copper in high magnetic gradient fields.

PubMed

König, Jörg; Tschulik, Kristina; Büttner, Lars; Uhlemann, Margitta; Czarske, Jürgen

2013-03-19

To experimentally reveal the correlation between electrodeposited structure and electrolyte convection induced inside the concentration boundary layer, a highly inhomogeneous magnetic field, generated by a magnetized Fe-wire, has been applied to an electrochemical system. The influence of Lorentz and magnetic field gradient force to the local transport phenomena of copper ions has been studied using a novel two-component laser Doppler velocity profile sensor. With this sensor, the electrolyte convection within 500 μm of a horizontally aligned cathode is presented. The electrode-normal two-component velocity profiles below the electrodeposited structure show that electrolyte convection is induced and directed toward the rim of the Fe-wire. The measured deposited structure directly correlates to the observed boundary layer flow. As the local concentration of Cu(2+) ions is enhanced due to the induced convection, maximum deposit thicknesses can be found at the rim of the Fe-wire. Furthermore, a complex boundary layer flow structure was determined, indicating that electrolyte convection of second order is induced. Moreover, the Lorentz force-driven convection rapidly vanishes, while the electrolyte convection induced by the magnetic field gradient force is preserved much longer. The progress for research is the first direct experimental proof of the electrolyte convection inside the concentration boundary layer that correlates to the deposited structure and reveals that the magnetic field gradient force is responsible for the observed structuring effect.

Lidar observations of the planetary boundary layer during FASINEX

NASA Technical Reports Server (NTRS)

Melfi, S. H.; Boers, R.; Palm, S. P.

1988-01-01

Data are presented on the planetary boundary layer (PBL) over the ocean acquired with an airborne downward-looking lidar during the Frontal Air-Sea Interaction Experiment (FASINEX) with the purpose of studying the impact of an ocean front on air-sea interactions. No changes in the PBL structure were detected by lidar. Lidar data were then used along with other readily available remotely-sensed data and a one-dimensional boundary-layer-growth model to infer the mean PBL moisture and temperature structure and to estimate the surface fluxes of heat and moisture.

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.

Electro-responsivity of ionic liquid boundary layers in a polar solvent revealed by neutron reflectance

NASA Astrophysics Data System (ADS)

Pilkington, Georgia A.; Harris, Kathryn; Bergendal, Erik; Reddy, Akepati Bhaskar; Palsson, Gunnar K.; Vorobiev, Alexei; Antzutkin, Oleg. N.; Glavatskih, Sergei; Rutland, Mark W.

2018-05-01

Using neutron reflectivity, the electro-responsive structuring of the non-halogenated ionic liquid (IL) trihexyl(tetradecyl)phosphonium-bis(mandelato)borate, [P6,6,6,14][BMB], has been studied at a gold electrode surface in a polar solvent. For a 20% w/w IL mixture, contrast matched to the gold surface, distinct Kiessig fringes were observed for all potentials studied, indicative of a boundary layer of different composition to that of the bulk IL-solvent mixture. With applied potential, the amplitudes of the fringes from the gold-boundary layer interface varied systematically. These changes are attributable to the differing ratios of cations and anions in the boundary layer, leading to a greater or diminished contrast with the gold electrode, depending on the individual ion scattering length densities. Such electro-responsive changes were also evident in the reflectivities measured for the pure IL and a less concentrated (5% w/w) IL-solvent mixture at the same applied potentials, but gave rise to less pronounced changes. These measurements, therefore, demonstrate the enhanced sensitivity achieved by contrast matching the bulk solution and that the structure of the IL boundary layers formed in mixtures is strongly influenced by the bulk concentration. Together these results represent an important step in characterising IL boundary layers in IL-solvent mixtures and provide clear evidence of electro-responsive structuring of IL ions in their solutions with applied potential.

Ultrastructural studies on the boundary tissue of the seminiferous tubules of different mammals.

PubMed

Cieciura, L; Jaszczuk-Jarosz, B; Pietrzkowska, K

1988-01-01

The aims of our studies were to compare the ultrastructure of the boundary tissue of seminiferous tubules of various mammals (rat, mouse, hamster, guinea pig, rabbit, ram, bull and man). Visual analysis of electron micrographs revealed the similarity of structure of all layers at investigated animals. The boundary tissue consists of 4 layers: 1) amorphous inner lamina, 2) cellular inner lamina, 3) amorphous outer lamina, 4) cellular outer lamina. The outer lamina of boundary tissue of rat, mouse and hamster revealed in histochemical reactions meshes resembling honey-combs. The wall of seminiferous canalicules of bull and ram consists of more bigger and different structure than one at the other laboratory animals. The most different structure of boundary tissue in man was observed. The capillary vessels penetrate in the myofibroblastic layer, when comparted to that found in other mammals on the surface of the wall.

UAV-borne coherent doppler lidar for marine atmospheric boundary layer observations

NASA Astrophysics Data System (ADS)

Wu, Songhua; Wang, Qichao; Liu, Bingyi; Liu, Jintao; Zhang, Kailin; Song, Xiaoquan

2018-04-01

A compact UAV-borne Coherent Doppler Lidar (UCDL) has been developed at the Ocean University of China for the observation of wind profile and boundary layer structure in Marine Atmospheric Boundary Layer (MABL). The design, specifications and motion-correction methodology of the UCDL are presented. Preliminary results of the first flight campaign in Hailing Island in December 2016 is discussed.

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

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.

Adaptive nonlinear polynomial neural networks for control of boundary layer/structural interaction

NASA Technical Reports Server (NTRS)

Parker, B. Eugene, Jr.; Cellucci, Richard L.; Abbott, Dean W.; Barron, Roger L.; Jordan, Paul R., III; Poor, H. Vincent

1993-01-01

The acoustic pressures developed in a boundary layer can interact with an aircraft panel to induce significant vibration in the panel. Such vibration is undesirable due to the aerodynamic drag and structure-borne cabin noises that result. The overall objective of this work is to develop effective and practical feedback control strategies for actively reducing this flow-induced structural vibration. This report describes the results of initial evaluations using polynomial, neural network-based, feedback control to reduce flow induced vibration in aircraft panels due to turbulent boundary layer/structural interaction. Computer simulations are used to develop and analyze feedback control strategies to reduce vibration in a beam as a first step. The key differences between this work and that going on elsewhere are as follows: that turbulent and transitional boundary layers represent broadband excitation and thus present a more complex stochastic control scenario than that of narrow band (e.g., laminar boundary layer) excitation; and secondly, that the proposed controller structures are adaptive nonlinear infinite impulse response (IIR) polynomial neural network, as opposed to the traditional adaptive linear finite impulse response (FIR) filters used in most studies to date. The controllers implemented in this study achieved vibration attenuation of 27 to 60 dB depending on the type of boundary layer established by laminar, turbulent, and intermittent laminar-to-turbulent transitional flows. Application of multi-input, multi-output, adaptive, nonlinear feedback control of vibration in aircraft panels based on polynomial neural networks appears to be feasible today. Plans are outlined for Phase 2 of this study, which will include extending the theoretical investigation conducted in Phase 2 and verifying the results in a series of laboratory experiments involving both bum and plate models.

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.

Transitional and turbulent flat-plate boundary layers with heat transfer

NASA Astrophysics Data System (ADS)

Wu, Xiaohua; Moin, Parviz

2010-11-01

We report on our direct numerical simulation of two incompressible, nominally zero-pressure-gradient flat-plate boundary layers from momentum thickness Reynolds number 80 to 1950. Heat transfer between the constant-temperature solid surface and the free-stream is also simulated with molecular Prandtl number=1. Throughout the entire flat-plate, the ratio of Stanton number and skin-friction St/Cfdeviates from the exact Reynolds analogy value of 0.5 by less than 1.5%. Turbulent Prandtl number t peaks at the wall. Preponderance of hairpin vortices is observed in both the transitional and turbulent regions of the boundary layers. In particular, the internal structure of merged turbulent spots is hairpin forest; the internal structure of infant turbulent spots is hairpin packet. Numerous hairpin vortices are readily detected in both the near-wall and outer regions of the boundary layers up to momentum thickness Reynolds number 1950. This suggests that the hairpin vortices in the turbulent region are not simply the aged hairpin forests convected from the upstream transitional region. Temperature iso-surfaces in the companion thermal boundary layers are found to be a useful tracer in identifying hairpin vortex structures.

The origin and structure of streak-like instabilities in laminar boundary layer flames

NASA Astrophysics Data System (ADS)

Gollner, Michael; Miller, Colin; Tang, Wei; Finney, Mark

2017-11-01

Streamwise streaks are consistently observed in wildland fires, at the base of pool fires, and in other heated flows within a boundary layer. This study examines both the origin of these structures and their role in influencing some of the macroscopic properties of the flow. Streaks were reproduced and characterized via experiments on stationary heated strips and liquid and gas-fueled burners in laminar boundary layer flows, providing a framework to develop theory based on both observed and measured physical phenomena. The incoming boundary layer was established as the controlling mechanism in forming streaks, which are generated by pre-existing coherent structures, while the amplification of streaks was determined to be compatible with quadratic growth of Rayleigh-Taylor Instabilities, providing credence to the idea that the downstream growth of streaks is strongly tied to buoyancy. These local instabilities were also found to affect macroscopic properties of the flow, including heat transfer to the surface, indicating that a two-dimensional assumption may fail to adequately describe heat and mass transfer during flame spread and other reacting boundary layer flows. This work was supported by NSF (CBET-1554026) and the USDA-FS (13-CS-11221637-124).

Contributions to the simulation of turbulence

NASA Technical Reports Server (NTRS)

Dutton, J. A.; Kerman, B. R.; Petersen, E. L.

1976-01-01

The simulation modeling of turbulence in the boundary layer in consolidated in terms of boundary layer similarity principles and empirical results. The modeling is extended for some aspects of the nonlinear and non-Gaussian structure of the turbulence. Properties of the discrete gust form structure of the modeled turbulence are identified.

SPATIAL VARIATION OF THE EVOLUTION AND STRUCTURE OF THE URBAN BOUNDARY LAYER

EPA Science Inventory

The spatial variation of the nocturnal urban boundary layer structure and the time variation of the mixing height, the nocturnal inversion top and strength after sunrise are presented for urban sites located upwind, downwind, and near the center of the heat island and for upwind ...

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.

Wall-pressure fluctuations beneath a spatially evolving turbulent boundary layer

NASA Astrophysics Data System (ADS)

Mahesh, Krishnan; Kumar, Praveen

2016-11-01

Wall-pressure fluctuations beneath a turbulent boundary layer are important in applications dealing with structural deformation and acoustics. Simulations are performed for flat plate and axisymmetric, spatially evolving zero-pressure-gradient turbulent boundary layers at inflow Reynolds number of 1400 and 2200 based on momentum thickness. The simulations generate their own inflow using the recycle-rescale method. The results for mean velocity and second-order statistics show excellent agreement with the data available in literature. The spectral characteristics of wall-pressure fluctuations and their relation to flow structure will be discussed. This work is supported by ONR.

Experimental investigation of the limits of ethanol combustion in the boundary layer behind an obstacle

NASA Astrophysics Data System (ADS)

Boyarshinov, B. F.

2018-01-01

Experimental data on the flow structure and mass transfer near the boundaries of the region existence of the laminar and turbulent boundary layers with combustion are considered. These data include the results of in-vestigation on reacting flow stability at mixed convection, mass transfer during ethanol evaporation "on the floor" and "on the ceiling", when the flame surface curves to form the large-scale cellular structures. It is shown with the help of the PIV equipment that when Rayleigh-Taylor instability manifests, the mushroom-like structures are formed, where the motion from the flame front to the wall and back alternates. The cellular flame exists in a narrow range of velocities from 0.55 to 0.65 m/s, and mass transfer is three times higher than its level in the standard laminar boundary layer.

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.

The turblent mixing layer - Geometry of large vortices

NASA Astrophysics Data System (ADS)

Browand, F. K.; Troutt, T. R.

1985-09-01

Large spanwide vortices in a mixing layer have been studied in numerous investigations. The present study represents an attempt to define the geometry of the large vortices. In the conducted experiments, the flow develops from a laminar boundary layer, or from an intentionally tripped turbulent boundary layer. However, no other forcing is provided. It is pointed out that in both cases the downstream structure becomes indistinguishable. The experimental apparatus and the employed techniques are discussed, taking into account details regarding the wind tunnel, the detection of the structure, and aspects of digitization. Attention is given to the mean growth of the mixing layer, the mean vortex spacing, the spanwise correlation of vortex structure, velocity-field visualizations, the transition criterion, and the permanence of structure.

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.

Sheared boundary layers in turbulent Rayleigh-Benard convection

NASA Astrophysics Data System (ADS)

Solomon, T. H.; Gollub, J. P.

1990-05-01

Thermal boundary layers in turbulent Rayleigh-Benard convection are studied experimentally using a novel system in which the convecting fluid is sheared from below with a flowing layer of mercury. Oscillatory shear substantially alters the spatial structure and frequency of the eruptions, with minimal effect on the heat flux (less than 5 percent). The temperature probability distribution function (PDF) just above the lower boundary layer changes from Gaussian to exponential without significant changes in the interior PDF. Implications for theories of 'hard' turbulence are discussed.

An Optimization Technique for the Development of Two-Dimensional Steady Turbulent Boundary Layer Models.

DTIC Science & Technology

1982-03-01

observed coherent structure of the wall layer flow and will now be briefly described. Over the past decade, it has been well documented (see, for example...D2, and x are all arbitrary constants. Equilibrium flows have been examined experimentally for a number of years and an equilibrium boundary layer...CP93, Paper No. 27, 6. Clauser, F.H. (1954). "Turbulent Boundary Layers in Adverse Pressure Gradients", J. Aeronaut. Sci., 21, pp. 91-108. 7. Clauser

Initial-boundary layer associated with the nonlinear Darcy-Brinkman-Oberbeck-Boussinesq system

NASA Astrophysics Data System (ADS)

Fei, Mingwen; Han, Daozhi; Wang, Xiaoming

2017-01-01

In this paper, we study the vanishing Darcy number limit of the nonlinear Darcy-Brinkman-Oberbeck-Boussinesq system (DBOB). This singular perturbation problem involves singular structures both in time and in space giving rise to initial layers, boundary layers and initial-boundary layers. We construct an approximate solution to the DBOB system by the method of multiple scale expansions. The convergence with optimal convergence rates in certain Sobolev norms is established rigorously via the energy method.

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

NASA Astrophysics Data System (ADS)

Wang, Chunbai; Mitra, Ambar K.

2016-01-01

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

Structure measurements in a synthetic turbulent boundary layer

NASA Astrophysics Data System (ADS)

Arakeri, Jaywant H.

Extensive hot-wire measurements were made to determine the structure of the large eddy in a synthetic turbulent boundary layer on a flat-plate model. The experiments were carried out in a wind tunnel at a nominal free-stream velocity of 12 m/s. The synthetic turbulent boundary layer had a hexagonal pattern of eddies and a ratio of streamwise scale to spanwise scale of 3.2:1. The measured celerity of the large eddy was 84.2 percent of the free-stream velocity. There was some loss of coherence, but very little distortion, as the eddies moved downstream. Several mean properties of the synthetic boundary layer were found to agree quite well with the mean properties of a natural turbulent boundary layer at the same Reynolds number. The large eddy is composed of a pair of primary counter-rotating vortices about five delta long in the steamwise direction and about one delta apart in the spanwise direction, where delta is the mean boundary-layer thickness. Definite signatures are obtained in terms of the mean skin-friction coefficient and the mean wake parameter averaged at constant phase. Velocities induced by the vortices are partly responsible for entrainment of irrotational fluid, for transport of momentum, for generation of Reynolds stresses, and for maintenance of streamwise and normal velocity in the outer flow.

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.

On the Unsteadiness of a Transitional Shock Wave-Boundary Layer Interaction Using Fast-Response Pressure-Sensitive Paint

NASA Astrophysics Data System (ADS)

Lash, E. Lara; Schmisseur, John

2017-11-01

Pressure-sensitive paint has been used to evaluate the unsteady dynamics of transitional and turbulent shock wave-boundary layer interactions generated by a vertical cylinder on a flat plate in a Mach 2 freestream. The resulting shock structure consists of an inviscid bow shock that bifurcates into a separation shock and trailing shock. The primary features of interest are the separation shock and an upstream influence shock that is intermittently present in transitional boundary layer interactions, but not observed in turbulent interactions. The power spectral densities, frequency peaks, and normalized wall pressures are analyzed as the incoming boundary layer state changes from transitional to fully turbulent, comparing both centerline and outboard regions of the interaction. The present study compares the scales and frequencies of the dynamics of the separation shock structure in different boundary layer regimes. Synchronized high-speed Schlieren imaging provides quantitative statistical analyses as well as qualitative comparisons to the fast-response pressure sensitive paint measurements. Materials based on research supported by the U.S. Office of Naval Research under Award Number N00014-15-1-2269.

Intercomparison of 7 Planetary Boundary-Layer/Surface-Layer Physics Schemes over Complex Terrain for Battlefield Situational Awareness

DTIC Science & Technology

This study considers the performance of 7 of the Weather Research and Forecast model boundary-layer (BL) parameterization schemes in a complex...schemes performed best. The surface parameters, planetary BL structure, and vertical profiles are important for US Army Research Laboratory

Effects of Land Surface Heterogeneity on Simulated Boundary-Layer Structures from the LES to the Mesoscale

NASA Astrophysics Data System (ADS)

Poll, Stefan; Shrestha, Prabhakar; Simmer, Clemens

2017-04-01

Land heterogeneity influences the atmospheric boundary layer (ABL) structure including organized (secondary) circulations which feed back on land-atmosphere exchange fluxes. Especially the latter effects cannot be incorporated explicitly in regional and climate models due to their coarse computational spatial grids, but must be parameterized. Current parameterizations lead, however, to uncertainties in modeled surface fluxes and boundary layer evolution, which feed back to cloud initiation and precipitation. This study analyzes the impact of different horizontal grid resolutions on the simulated boundary layer structures in terms of stability, height and induced secondary circulations. The ICON-LES (Icosahedral Nonhydrostatic in LES mode) developed by the MPI-M and the German weather service (DWD) and conducted within the framework of HD(CP)2 is used. ICON is dynamically downscaled through multiple scales of 20 km, 7 km, 2.8 km, 625 m, 312 m, and 156 m grid spacing for several days over Germany and partial neighboring countries for different synoptic conditions. We examined the entropy spectrum of the land surface heterogeneity at these grid resolutions for several locations close to measurement sites, such as Lindenberg, Jülich, Cabauw and Melpitz, and studied its influence on the surface fluxes and the evolution of the boundary layer profiles.

Simultaneous wall-shear-stress and wide-field PIV measurements in a turbulent boundary layer

NASA Astrophysics Data System (ADS)

Gomit, Guillaume; Fourrie, Gregoire; de Kat, Roeland; Ganapathisubramani, Bharathram

2015-11-01

Simultaneous particle image velocimetry (PIV) and hot-film shear stress sensor measurements were performed to study the large-scale structures associated with shear stress events in a flat plate turbulent boundary layer at a high Reynolds number (Reτ ~ 4000). The PIV measurement was performed in a streamwise-wall normal plane using an array of six high resolution cameras (4 ×16MP and 2 ×29MP). The resulting field of view covers 8 δ (where δ is the boundary layer thickness) in the streamwise direction and captures the entire boundary layer in the wall-normal direction. The spatial resolution of the measurement is approximately is approximately 70 wall units (1.8 mm) and sampled each 35 wall units (0.9 mm). In association with the PIV setup, a spanwise array of 10 skin-friction sensors (spanning one δ) was used to capture the footprint of the large-scale structures. This combination of measurements allowed the analysis of the three-dimensional conditional structures in the boundary layer. Particularly, from conditional averages, the 3D organisation of the wall normal and streamwise velocity components (u and v) and the Reynolds shear stress (-u'v') related to a low and high shear stress events can be extracted. European Research Council Grant No-277472-WBT.

Characterizing the structure of the atmospheric boundary layer under heavy pollution over urban area, Beijing, China

NASA Astrophysics Data System (ADS)

WANG, L.; Gao, Z.; Huang, M.; Fan, S.; Miao, S.

2017-12-01

A better understanding of the interactions between the occurrence of air pollution and the structure of the atmospheric boundary layer (ABL) is very important for the air-pollution-relevant investigations. In this study, the ABL structure was studied by using a Doppler lidar, a Depolarization lidar and the 325-m meteorological tower in Beijing during the winter 2016-2017, in particular during heavy polluted episodes. The planetary boundary layer (PBL) depth was estimated by using lidar data. The characteristics of wind, temperature and relative humidity at 15 levels, turbulence transport and radiation balance at three levels (47, 140 and 280 m) were analyzed by using the observational data collected on the 325-m meteorological tower.

On the Lagrangian description of unsteady boundary-layer separation. I - General theory

NASA Technical Reports Server (NTRS)

Van Dommelen, Leon L.; Cowley, Stephen J.

1990-01-01

Although unsteady, high-Reynolds number, laminar boundary layers have conventionally been studied in terms of Eulerian coordinates, a Lagrangian approach may have significant analytical and computational advantages. In Lagrangian coordinates the classical boundary layer equations decouple into a momentum equation for the motion parallel to the boundary, and a hyperbolic continuity equation (essentially a conserved Jacobian) for the motion normal to the boundary. The momentum equations, plus the energy equation if the flow is compressible, can be solved independently of the continuity equation. Unsteady separation occurs when the continuity equation becomes singular as a result of touching characteristics, the condition for which can be expressed in terms of the solution of the momentum equations. The solutions to the momentum and energy equations remain regular. Asymptotic structures for a number of unsteady 3-D separating flows follow and depend on the symmetry properties of the flow. In the absence of any symmetry, the singularity structure just prior to separation is found to be quasi 2-D with a displacement thickness in the form of a crescent shaped ridge. Physically the singularities can be understood in terms of the behavior of a fluid element inside the boundary layer which contracts in a direction parallel to the boundary and expands normal to it, thus forcing the fluid above it to be ejected from the boundary layer.

On the Lagrangian description of unsteady boundary layer separation. Part 1: General theory

NASA Technical Reports Server (NTRS)

Vandommelen, Leon L.; Cowley, Stephen J.

1989-01-01

Although unsteady, high-Reynolds number, laminar boundary layers have conventionally been studied in terms of Eulerian coordinates, a Lagrangian approach may have significant analytical and computational advantages. In Lagrangian coordinates the classical boundary layer equations decouple into a momentum equation for the motion parallel to the boundary, and a hyperbolic continuity equation (essentially a conserved Jacobian) for the motion normal to the boundary. The momentum equations, plus the energy equation if the flow is compressible, can be solved independently of the continuity equation. Unsteady separation occurs when the continuity equation becomes singular as a result of touching characteristics, the condition for which can be expressed in terms of the solution of the momentum equations. The solutions to the momentum and energy equations remain regular. Asymptotic structures for a number of unsteady 3-D separating flows follow and depend on the symmetry properties of the flow. In the absence of any symmetry, the singularity structure just prior to separation is found to be quasi 2-D with a displacement thickness in the form of a crescent shaped ridge. Physically the singularities can be understood in terms of the behavior of a fluid element inside the boundary layer which contracts in a direction parallel to the boundary and expands normal to it, thus forcing the fluid above it to be ejected from the boundary layer.

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.

Turbulent dusty boundary layer in an ANFO surface-burst explosion

NASA Astrophysics Data System (ADS)

Kuhl, A. L.; Ferguson, R. E.; Chien, K. Y.; Collins, J. P.

1992-01-01

This paper describes the results of numerical simulations of the dusty, turbulent boundary layer created by a surface burst explosion. The blast wave was generated by the detonation of a 600-T hemisphere of ANFO, similar to those used in large-scale field tests. The surface was assumed to be ideally noncratering but contained an initial loose layer of dust. The dust-air mixture in this fluidized bed was modeled as a dense gas (i.e., an equilibrium model, valid for very small-diameter dust particles). The evolution of the flow was calculated by a high-order Godunov code that solves the nonsteady conservation laws. Shock interactions with dense layer generated vorticity near the wall, a result that is similar to viscous, no-slip effects found in clean flows. The resulting wall shear layer was unstable, and rolled up into large-scale rotational structures. These structures entrained dense material from the wall layer and created a chaotically striated flow. The boundary layer grew due to merging of the large-scale structures and due to local entrainment of the dense material from the fluidized bed. The chaotic flow was averaged along similarity lines (i.e., lines of constant values of x = r/Rs and y = z/Rs where R(sub s) = ct(exp alpha)) to establish the mean-flow profiles and the r.m.s. fluctuating-flow profiles of the boundary layer.

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.

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.

Reynolds stress structures in a self-similar adverse pressure gradient turbulent boundary layer at the verge of separation.

NASA Astrophysics Data System (ADS)

Atkinson, C.; Sekimoto, A.; Jiménez, J.; Soria, J.

2018-04-01

Mean Reynolds stress profiles and instantaneous Reynolds stress structures are investigated in a self-similar adverse pressure gradient turbulent boundary layer (APG-TBL) at the verge of separation using data from direct numerical simulations. The use of a self-similar APG-TBL provides a flow domain in which the flow gradually approaches a constant non-dimensional pressure gradient, resulting in a flow in which the relative contribution of each term in the governing equations is independent of streamwise position over a domain larger than two boundary layer thickness. This allows the flow structures to undergo a development that is less dependent on the upstream flow history when compared to more rapidly decelerated boundary layers. This APG-TBL maintains an almost constant shape factor of H = 2.3 to 2.35 over a momentum thickness based Reynolds number range of Re δ 2 = 8420 to 12400. In the APG-TBL the production of turbulent kinetic energy is still mostly due to the correlation of streamwise and wall-normal fluctuations, 〈uv〉, however the contribution form the other components of the Reynolds stress tensor are no longer negligible. Statistical properties associated with the scale and location of sweeps and ejections in this APG-TBL are compared with those of a zero pressure gradient turbulent boundary layer developing from the same inlet profile, resulting in momentum thickness based range of Re δ 2 = 3400 to 3770. In the APG-TBL the peak in both the mean Reynolds stress and the production of turbulent kinetic energy move from the near wall region out to a point consistent with the displacement thickness height. This is associated with a narrower distribution of the Reynolds stress and a 1.6 times higher relative number of wall-detached negative uv structures. These structures occupy 5 times less of the boundary layer volume and show a similar reduction in their streamwise extent with respect to the boundary layer thickness. A significantly lower percentage of wall-attached structures is observed in the present case when compared with a similar investigation of a rapidly decelerating APG-TBL, suggesting that these wall-attached features could be the remanent from the lower pressure gradient domain upstream.

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.

Reconsideration of F-layer seismic model in the south polar region

NASA Astrophysics Data System (ADS)

Ohtaki, T.; Kaneshima, S.

2017-12-01

Previously, we analyzed the seismic structure near the inner core boundary beneath Antarctica (Ohtaki et al., 2012). In the study, we determined the velocity of the lowermost outer core (F-layer) using amplitude ratio observations between the inner-core phase (PKIKP) and the inner-core grazing/diffracted phase (PKPbc/c-diff). Because the observations are not so sensitive to the F-layer structure, a constant velocity is assumed in the layer to simplify the model. The obtained model (SPR) has a flat velocity zone with a 75 km thick on the inner core boundary. With this F-layer structure and using travel times of these phases as well as the phase that reflects at the boundary, we determined the seismic structure of the inner core in the south polar region. However, a constant velocity layer is unrealistic, although it is reasonable assumption.Recently, we determined F-layer velocity structures more accurately using the combined observations of PKiKP-PKPbc differential travel times and of PKPbc/c-diff dispersion (Ohtaki et al., 2015, 2016). The former observation is sensitive to average velocity in the F-layer; the latter to velocity gradient in the layer. By analyzing these two observations together, we can determine the detailed velocity structure in the F-layer. The surveyed areas are beneath the Northeast Pacific and Australia. The seismic velocity models obtained are quite different between the two regions. Thus our results require laterally heterogeneous F-layer, and show that F-layer is more complicated than we ever imagined.Then there is one question; which structure is that of the south polar region close to? Unfortunately, the seismic waveforms that we analyzed in the previous study may not have quality high enough to analyze the PKiKP-PKPbc or PKPbc dispersion. However, it would be meaningful to reanalyze the amplitude data and reconsider the F-layer velocity there. And we also estimate how large slope of velocity can be acceptable for the F-layer velocity structure in this region.

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).

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.

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.

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.

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.

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.

The thermodynamic evolution of the hurricane boundary layer during eyewall replacement cycles

NASA Astrophysics Data System (ADS)

Williams, Gabriel J.

2017-12-01

Eyewall replacement cycles (ERCs) are frequently observed during the lifecycle of mature tropical cyclones. Although the kinematic structure and intensity changes during an ERC have been well-documented, comparatively little research has been done to examine the evolution of the tropical cyclone boundary layer (TCBL) during an ERC. This study will examine how the inner core thermal structure of the TCBL is affected by the presence of multiple concentric eyewalls using a high-resolution moist, hydrostatic, multilayer diagnostic boundary layer model. Within the concentric eyewalls above the cloud base, latent heat release and vertical advection (due to the eyewall updrafts) dominate the heat and moisture budgets, whereas vertical advection (due to subsidence) and vertical diffusion dominate the heat and moisture budgets for the moat region. Furthermore, it is shown that the development of a moat region within the TCBL depends sensitively on the moat width in the overlying atmosphere and the relative strength of the gradient wind field in the overlying atmosphere. These results further indicate that the TCBL contributes to outer eyewall formation through a positive feedback process between the vorticity in the nascent outer eyewall, boundary layer convergence, and boundary layer moist convection.

The application of a shift theorem analysis technique to multipoint measurements

NASA Astrophysics Data System (ADS)

Dieckmann, M. E.; Chapman, S. C.

1999-03-01

A Fourier domain technique has been proposed previously which, in principle, quantifies the extent to which multipoint in-situ measurements can identify whether or not an observed structure is time stationary in its rest frame. Once a structure, sampled for example by four spacecraft, is shown to be quasi-stationary in its rest frame, the structure's velocity vector can be determined with respect to the sampling spacecraft. We investigate the properties of this technique, which we will refer to as a stationarity test, by applying it to two point measurements of a simulated boundary layer. The boundary layer was evolved using a PIC (particle in cell) electromagnetic code. Initial and boundary conditions were chosen such, that two cases could be considered, i.e. a spacecraft pair moving through (1) a time stationary boundary structure and (2) a boundary structure which is evolving (expanding) in time. The code also introduces noise in the simulated data time series which is uncorrelated between the two spacecraft. We demonstrate that, provided that the time series is Hanning windowed, the test is effective in determining the relative velocity between the boundary layer and spacecraft and in determining the range of frequencies over which the data can be treated as time stationary or time evolving. This work presents a first step towards understanding the effectiveness of this technique, as required in order for it to be applied to multispacecraft data.

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.

Numerical investigations of shock wave interaction with laminar boundary layer on compressor profile

NASA Astrophysics Data System (ADS)

Piotrowicz, M.; Flaszyński, P.

2016-10-01

The investigation of shockwave boundary layer interaction on suction side of transonic compressor blade is one of main objectives of TFAST project (Transition Location Effect on Shock Wave Boundary Layer Interaction). In order to look more closely into the flow structure on suction side of a profile, a design of generic test section in linear transonic wind tunnel was proposed. The experimental and numerical results of flow structure on a suction side of the compressor profile investigations are presented. The numerical simulations are carried out for EARSM (Explicit Algebraic Reynolds Stress Model) turbulence model with transition model. The result are compared with oil flow visualisation, schlieren pictures, Pressure Sensitive Paint (PSP) and static pressure.

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.

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.

Heat addition to a subsonic boundary layer: A preliminary analytical study

NASA Technical Reports Server (NTRS)

Macha, J. M.; Norton, D. J.

1971-01-01

A preliminary analytical study of the effects of heat addition to the subsonic boundary layer flow over a typical airfoil shape is presented. This phenomenon becomes of interest in the space shuttle mission since heat absorbed by the wing structure during re-entry will be rejected to the boundary layer during the subsequent low speed maneuvering and landing phase. A survey of existing literature and analytical solutions for both laminar and turbulent flow indicate that a heated surface generally destabilizes the boundary layer. Specifically, the boundary layer thickness is increased, the skin friction at the surface is decreased and the point of flow separation is moved forward. In addition, limited analytical results predict that the angle of attack at which a heated airfoil will stall is significantly less than the stall angle of an unheated wing. These effects could adversely affect the lift and drag, and thus the maneuvering capabilities of booster and orbiter shuttle vehicles.

An experimental investigation of the flow physics of high-lift systems

NASA Technical Reports Server (NTRS)

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

1995-01-01

This progress report is a series of overviews outlining experiments on the flow physics of confluent boundary layers for high-lift systems. The research objectives include establishing the role of confluent boundary layer flow physics in high-lift production; contrasting confluent boundary layer structures for optimum and non-optimum C(sub L) cases; forming a high quality, detailed archival data base for CFD/modelling; and examining the role of relaminarization and streamline curvature. Goals of this research include completing LDV study of an optimum C(sub L) case; performing detailed LDV confluent boundary layer surveys for multiple non-optimum C(sub L) cases; obtaining skin friction distributions for both optimum and non-optimum C(sub L) cases for scaling purposes; data analysis and inner and outer variable scaling; setting-up and performing relaminarization experiments; and a final report establishing the role of leading edge confluent boundary layer flow physics on high-lift performance.

Coordinated Parameterization Development and Large-Eddy Simulation for Marine and Arctic Cloud-Topped Boundary Layers

NASA Technical Reports Server (NTRS)

Bretherton, Christopher S.

2002-01-01

The goal of this project was to compare observations of marine and arctic boundary layers with: (1) parameterization systems used in climate and weather forecast models; and (2) two and three dimensional eddy resolving (LES) models for turbulent fluid flow. Based on this comparison, we hoped to better understand, predict, and parameterize the boundary layer structure and cloud amount, type, and thickness as functions of large scale conditions that are predicted by global climate models. The principal achievements of the project were as follows: (1) Development of a novel boundary layer parameterization for large-scale models that better represents the physical processes in marine boundary layer clouds; and (2) Comparison of column output from the ECMWF global forecast model with observations from the SHEBA experiment. Overall the forecast model did predict most of the major precipitation events and synoptic variability observed over the year of observation of the SHEBA ice camp.

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

NASA Technical Reports Server (NTRS)

Duck, Peter W.

1989-01-01

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

Measuring Plume Meander in the Nighttime Stable Boundary Layer with Lidar

NASA Astrophysics Data System (ADS)

Hiscox, A.; Miller, D. R.; Nappo, C. J.

2009-12-01

Complex dynamics of the stable planetary boundary layer (PBL), such as the effects of density currents, intermittent turbulence, surface-layer decoupling, internal gravity waves, cold air pooling, and katabatic flows affect plume transport and diffusion. A better understanding of these effects is needed for nighttime transport model development. The JORNADA (Joint Observational Research on Nocturnal Atmospheric Dispersion of Aerosols) field campaign, conducted in the New Mexico desert during April 2005, sought to address some of these issues The JORNADA data set includes simultaneous micrometeorological measurements of the boundary layer structure, turbulence, and wave activity along with continuous lidar measurement of aerosol plume releases. What makes JORNADA unique is the real-time monitoring of an elevated plume with a lidar. The quantification of plume meander will be presented in this paper. The application of these techniques to the JORNADA data allows for a more complete understanding of the nocturnal boundary layer (NBL). We will present an in-depth analysis of lidar measurements of plume meander and dispersion and their relationship to the complexities of NBL structure.

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.

Formation of nocturnal low-level jets and structure of the nocturnal boundary layer in the Southern Great Plains

NASA Astrophysics Data System (ADS)

Klein, P. M.; Bonin, T. A.; Newman, J. F.; Wainwright, C. E.; Blumberg, W. G.; Turner, D. D.; Chilson, P. B.; Wharton, S.

2014-12-01

The Lower Atmospheric Boundary Layer Experiment (LABLE) included two measurement campaigns at the Atmospheric Radiation Measurement (ARM) Southern Great Plains site in Oklahoma in 2012 and 2013. Its main objective was to study turbulent phenomena in the lowest 2-km of the atmosphere using a variety of novel atmospheric profiling techniques including a sodar, multiple Doppler wind lidars (DWL), a Raman lidar and an atmospheric emitted radiance interferometer (AERI). Several instruments from the University of Oklahoma and Lawrence Livermore National Laboratory were deployed to augment the suite of in-situ and remote sensing instruments at the ARM site. The complementary nature of the deployed instruments with respect to resolution and height coverage provides for a near-complete picture of the dynamic and thermodynamic structure of the atmospheric boundary layer. LABLE can be considered unique in that it was designed as a multi-phase, low-cost, and multi-agency collaboration. Graduate students served as principal investigators who took the lead in designing and conducting experiments aimed at examining boundary-layer processes. This presentation provides an overview of the LABLE experiments and a summary of important results. One focus area will be the dynamic and thermodynamic structure of the nocturnal boundary layer and the formation of nocturnal low-level jets. Such low-level jets were frequently observed during both LABLE campaigns and often interacted with mesoscale atmospheric disturbances such as frontal passages. The combination of high-resolution AERI temperature profiles with DWL mean wind and turbulence profiles provided new insights about the structure and evolution of low-level jets.

Turbulence structure of the marine stable boundary layer over the Baltic Sea

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

Smedman, A.S.; Hoegstroem, U.

For more than half of the year the land surfaces surrounding the Baltic Sea is warmer than the sea surface, and the marine boundary layer over the Baltic is stable. Observations, at various sites in the Baltic Sea area during the last decade. also indicate frequent occurrence of low-level jets at the top of the stable boundary layer. In many cases the marine jet can be considered as an analogy in space to the evolution of the nocturnal jet with time. The frictional decoupling occurs when warm air over the land is flowing out over the sea. Data from twomore » areas together with model simulations are used in this study to characterize turbulence structure in the marine boundary layer. The measurements include profiles of wind and temperature on towers situated at two isolated islands, together with turbulence recordings and aircraft measurements. Also wave height and water surface temperature have been measured. The model simulations are performed with a second-order closure model.« less

Structure of a reattaching supersonic shear flow

NASA Technical Reports Server (NTRS)

Samimy, M.; Abu-Hijleh, B. A. K.

1988-01-01

A Mach 1.83 fully developed turbulent boundary layer with boundary layer thickness, free stream velocity, and Reynolds number of 7.5 mm, 476 m/s, and 6.2 x 10 to the 7th/m, respectively, was separated at a 25.4-mm backward step and formed a shear layer. Fast-response pressure transducers, schlieren photography, and LDV were used to study the structure of this reattaching shear flow. The preliminary results show that large-scale relatively organized structures with limited spanwise extent form in the free shear layer. Some of these structures appear to survive the recompression and reattachment processes, while others break down into smaller scales and the flow becomes increasingly three-dimensional. The survived large-scale structures lose their organization through recompression/reattachment, but regain it after reattachment. The structures after reattachment form a 40-45-degree angle relative to the free stream and deteriorate gradually as they move downstream.

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.

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.

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.

The Perfectly Matched Layer absorbing boundary for fluid-structure interactions using the Immersed Finite Element Method.

PubMed

Yang, Jubiao; Yu, Feimi; Krane, Michael; Zhang, Lucy T

2018-01-01

In this work, a non-reflective boundary condition, the Perfectly Matched Layer (PML) technique, is adapted and implemented in a fluid-structure interaction numerical framework to demonstrate that proper boundary conditions are not only necessary to capture correct wave propagations in a flow field, but also its interacted solid behavior and responses. While most research on the topics of the non-reflective boundary conditions are focused on fluids, little effort has been done in a fluid-structure interaction setting. In this study, the effectiveness of the PML is closely examined in both pure fluid and fluid-structure interaction settings upon incorporating the PML algorithm in a fully-coupled fluid-structure interaction framework, the Immersed Finite Element Method. The performance of the PML boundary condition is evaluated and compared to reference solutions with a variety of benchmark test cases including known and expected solutions of aeroacoustic wave propagation as well as vortex shedding and advection. The application of the PML in numerical simulations of fluid-structure interaction is then investigated to demonstrate the efficacy and necessity of such boundary treatment in order to capture the correct solid deformation and flow field without the requirement of a significantly large computational domain.

Large-eddy simulations of unidirectional water flow over dunes

NASA Astrophysics Data System (ADS)

Grigoriadis, D. G. E.; Balaras, E.; Dimas, A. A.

2009-06-01

The unidirectional, subcritical flow over fixed dunes is studied numerically using large-eddy simulation, while the immersed boundary method is implemented to incorporate the bed geometry. Results are presented for a typical dune shape and two Reynolds numbers, Re = 17,500 and Re = 93,500, on the basis of bulk velocity and water depth. The numerical predictions of velocity statistics at the low Reynolds number are in very good agreement with available experimental data. A primary recirculation region develops downstream of the dune crest at both Reynolds numbers, while a secondary region develops at the toe of the dune crest only for the low Reynolds number. Downstream of the reattachment point, on the dune stoss, the turbulence intensity in the developing boundary layer is weaker than in comparable equilibrium boundary layers. Coherent vortical structures are identified using the fluctuating pressure field and the second invariant of the velocity gradient tensor. Vorticity is primarily generated at the dune crest in the form of spanwise "roller" structures. Roller structures dominate the flow dynamics near the crest, and are responsible for perturbing the boundary layer downstream of the reattachment point, which leads to the formation of "horseshoe" structures. Horseshoe structures dominate the near-wall dynamics after the reattachment point, do not rise to the free surface, and are distorted by the shear layer of the next crest. The occasional interaction between roller and horseshoe structures generates tube-like "kolk" structures, which rise to the free surface and persist for a long time before attenuating.

Simultaneous measurement of aero-optical distortion and turbulent structure in a heated boundary layer

NASA Astrophysics Data System (ADS)

Saxton-Fox, Theresa; McKeon, Beverley; Smith, Adam; Gordeyev, Stanislav

2014-11-01

This study examines the relationship between turbulent structures and the aero-optical distortion of a laser beam passing through a turbulent boundary layer. Previous studies by Smith et al. (AIAA, 2014--2491) have found a bulk convection velocity of 0 . 8U∞ for aero-optical distortion in turbulent boundary layers, motivating a comparison of the distortion with the outer boundary layer. In this study, a turbulent boundary layer is developed over a flat plate with a moderately-heated section of length 25 δ . Density variation in the thermal boundary layer leads to aero-optical distortion, which is measured with a Malley probe (Smith et al., AIAA, 2013--3133). Simultaneously, 2D PIV measurements are recorded in a wall-normal, streamwise plane centered on the Malley probe location. Experiments are run at Reθ = 2100 and at a Mach number of 0.03, with the heated wall 10 to 20°C above the free stream temperature. Correlations and conditional averages are carried out between Malley probe distortion angles and flow features in the PIV vector fields. Aero-optical distortion in this study will be compared to distortion in higher Mach number flows studied by Gordeyev et al. (J. Fluid Mech., 2014), with the aim of extending conclusions into compressible flows. This research is made possible by the Department of Defense through the National Defense & Engineering Graduate Fellowship (NDSEG) Program and by the Air Force Office of Scientific Research Grant # FA9550-12-1-0060.

Dynamo Tests for Stratification Below the Core-Mantle Boundary

NASA Astrophysics Data System (ADS)

Olson, P.; Landeau, M.

2017-12-01

Evidence from seismology, mineral physics, and core dynamics points to a layer with an overall stable stratification in the Earth's outer core, possibly thermal in origin, extending below the core-mantle boundary (CMB) for several hundred kilometers. In contrast, energetic deep mantle convection with elevated heat flux implies locally unstable thermal stratification below the CMB in places, consistent with interpretations of non-dipole geomagnetic field behavior that favor upwelling flows below the CMB. Here, we model the structure of convection and magnetic fields in the core using numerical dynamos with laterally heterogeneous boundary heat flux in order to rationalize this conflicting evidence. Strongly heterogeneous boundary heat flux generates localized convection beneath the CMB that coexists with an overall stable stratification there. Partially stratified dynamos have distinctive time average magnetic field structures. Without stratification or with stratification confined to a thin layer, the octupole component is small and the CMB magnetic field structure includes polar intensity minima. With more extensive stratification, the octupole component is large and the magnetic field structure includes intense patches or high intensity lobes in the polar regions. Comparisons with the time-averaged geomagnetic field are generally favorable for partial stratification in a thin layer but unfavorable for stratification in a thick layer beneath the CMB.

Forced free-shear layer measurements

NASA Technical Reports Server (NTRS)

Leboeuf, Richard L.

1994-01-01

Detailed three-dimensional three-component phase averaged measurements of the spanwise and streamwise vorticity formation and evolution in acoustically forced plane free-shear flows have been obtained. For the first time, phase-averaged measurements of all three velocity components have been obtained in both a mixing layer and a wake on three-dimensional grids, yielding the spanwise and streamwise vorticity distributions without invoking Taylor's hypothesis. Initially, two-frequency forcing was used to phase-lock the roll-up and first pairing of the spanwise vortical structures in a plane mixing layer. The objective of this study was to measure the near-field vortical structure morphology in a mixing layer with 'natural' laminar initial boundary layers. For the second experiment the second and third subharmonics of the fundamental roll-up frequency were added to the previous two-frequency forcing in order to phase-lock the roll-up and first three pairings of the spanwise rollers in the mixing layer. The objective of this study was to determine the details of spanwise scale changes observed in previous time-averaged measurements and flow visualization of unforced mixing layers. For the final experiment, single-frequency forcing was used to phase-lock the Karman vortex street in a plane wake developing from nominally two-dimensional laminar initial boundary layers. The objective of this study was to compare measurements of the three-dimensional structure in a wake developing from 'natural' initial boundary layers to existing models of wake vortical structure.

Antiphase Boundaries in the Turbostratically Disordered Misfit Compound (BiSe)(1+δ)NbSe2.

PubMed

Mitchson, Gavin; Falmbigl, Matthias; Ditto, Jeffrey; Johnson, David C

2015-11-02

(BiSe)(1+δ)NbSe2 ferecrystals were synthesized in order to determine whether structural modulation in BiSe layers, characterized by periodic antiphase boundaries and Bi-Bi bonding, occurs. Specular X-ray diffraction revealed the formation of the desired compound with a c-axis lattice parameter of 1.21 nm from precursors with a range of initial compositions and initial periodicities. In-plane X-ray diffraction scans could be indexed as hk0 reflections of the constituents, with a rectangular basal BiSe lattice and a trigonal basal NbSe2 lattice. Electron micrographs showed extensive turbostratic disorder in the samples and the presence of periodic antiphase boundaries (approximately 1.5 nm periodicity) in BiSe layers oriented with the [110] direction parallel to the zone axis of the microscope. This indicates that the structural modulation in the BiSe layers is not due to coherency strain resulting from commensurate in-plane lattices. Electrical transport measurements indicate that holes are the dominant charge carrying species, that there is a weak decrease in resistivity as temperature decreases, and that minimal charge transfer occurs from the BiSe to NbSe2 layers. This is consistent with the lack of charge transfer from the BiX to the TX2 layers reported in misfit layer compounds where antiphase boundaries were observed. This suggests that electronic considerations, i.e., localization of electrons in the Bi-Bi pairs at the antiphase boundaries, play a dominant role in stabilizing the structural modulation.

Boundary Layer Characterization during Perdigão Field Campaign 2017

NASA Astrophysics Data System (ADS)

Leo, L. S.; Salvadore, J. J.; Belo-Pereira, M.; Menke, R.; Gomes, S.; Krishnamurthy, R.; Brown, W. O. J.; Creegan, E.; Klein, P. M.; Wildmann, N.; Oncley, S.; Fernando, J.; Mann, J.

2017-12-01

The depth and structure of the atmospheric boundary layer (ABL) significantly impact the performances of wind farms located in complex terrain environments, since low-level jets and other flow structures in the proximity of hills and mountains determine the weather extremes, such as shear layer instabilities, lee/internal wave breaking, etc. which in turn profoundly modify the turbulence profile at wind turbine relevant heights.A suite of instruments was deployed covering a double-ridge in central Portugal near the town of Perdigão in 2016-2017, and they are used here to characterize the ABL structure over complex terrain during the Intensive Observational Period (IOP, May 1- June 15, 2017) of the research field program dubbed "Perdigão". Firstly, the methodology adopted in this work to estimate the BL height will be discussed; secondly, an overview of the BL depth and characteristics during Perdigão-IOP campaign will be provided, with emphasis on case studies of interest for both the wind-power and boundary-layer communities.

INDIRECT ESTIMATION OF CONVECTIVE BOUNDARY LAYER STRUCTURE FOR USE IN ROUTINE DISPERSION MODELS

EPA Science Inventory

Dispersion models of the convectively driven atmospheric boundary layer (ABL) often require as input meteorological parameters that are not routinely measured. These parameters usually include (but are not limited to) the surface heat and momentum fluxes, the height of the cappin...

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.

Influence of Idealized Heterogeneity on Wet and Dry Planetary Boundary Layers Coupled to the Land Surface. 1; Instantaneous Fields and Statistics

NASA Technical Reports Server (NTRS)

Houser, Paul (Technical Monitor); Patton, Edward G.; Sullivan, Peter P.; Moeng, Chin-Hoh

2003-01-01

This is the first in a two-part series of manuscripts describing numerical experiments on the influence of 2-30 km striplike heterogeneity on wet and dry boundary layers coupled to the land surface. The strip-like heterogeneity is shown to dramatically alter the structure of the free-convective boundary layer by inducing significant organized circulations that modify turbulent statistics. The coupling with the land-surface modifies the circulations compared to previous studies using fixed surface forcing. Total boundary layer turbulence kinetic energy increases significantly for surface heterogeneity at scales between Lambda/z(sub i) = 4 and 9, however entrainment rates for all cases are largely unaffected by the strip-like heterogeneity.

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.

The effects of streamwise concave curvature on turbulent boundary layer structure

NASA Astrophysics Data System (ADS)

Jeans, A. H.; Johnston, J. P.

1982-06-01

Concave curvature has a relatively large, unpredictable effect on turbulent boundary layers. Some, but not all previous studies suggest that a large-scale, stationary array of counter-rotating vortices exists within the turbulent boundary layer on a concave wall. The objective of the present study was to obtain a qualitative model of the flow field in order to increase our understanding of the underlying physics. A large free-surface water channel was constructed in order to perform a visual study of the flow. Streamwise components of mean velocity and turbulence intensity were measured using a hot film anemometer. The upstream boundary was spanwise uniform with a momentum thickness to radius of curvature of 0.05. Compared to flat wall flow, large-scale, randomly distributed sweeps and ejections were seen in the boundary layer on the concave wall. The sweeps appear to suppress the normal mechanism for turbulence production near the wall by inhibiting the bursting process. The ejections appear to enhance turbulence production in the outer layers as the low speed fluid convected from regions near the wall interacts with the higher speed fluid farther out. The large-scale structures did not occur at fixed spanwise locations, and could not be called roll cells or vortices.

Comparison of turbulence in a transitional boundary layer to turbulence in a developed boundary layer*

NASA Astrophysics Data System (ADS)

Park, G. I.; Wallace, J.; Wu, X.; Moin, P.

2010-11-01

Using a recent DNS of a flat-plate boundary layer, statistics of turbulence in transition at Reθ= 500 where spots merge (distributions of the mean velocity, rms velocity and vorticity fluctuations, Reynolds shear stress, kinetic energy production and dissipation rates and enstrophy) have been compared to these statistics for the developed boundary layer turbulence at Reθ= 1850. When the distributions in the transitional region, determined in narrow planes 0.03 Reθ wide, exclude regions and times when the flow is not turbulent, they closely resemble those in the developed turbulent state at the higher Reynolds number, especially in the buffer and sublayers. The skin friction coefficient, determined in this conditional manner in the transitional flow is, of course, much larger than that obtained by including both turbulent and non-turbulent information there, and is consistent with a value obtained by extrapolating from the developed turbulent region. We are attempting to perform this data analysis even further upstream in the transitioning flow at Reθ= 300 where the turbulent spots are individuated. These results add further evidence to support the view that the structure of a developed turbulent boundary layer is little different from its structure in its embryonic form in turbulent spots. *CTR 2010 Summer Program research.

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.

EFFECTS OF VERTICAL-LAYER STRUCTURE AND BOUNDARY CONDITIONS ON CMAQ-V4.5 AND V4.6 MODELS

EPA Science Inventory

This work is aimed at determining whether the increased vertical layers in CMAQ provides substantially improved model performance and assess whether using the spatially and temporally varying boundary conditions from GEOS-CHEM offer improved model performance as compared to the d...

Detached eddy simulation for turbulent fluid-structure interaction of moving bodies using the constraint-based immersed boundary method

NASA Astrophysics Data System (ADS)

Nangia, Nishant; Bhalla, Amneet P. S.; Griffith, Boyce E.; Patankar, Neelesh A.

2016-11-01

Flows over bodies of industrial importance often contain both an attached boundary layer region near the structure and a region of massively separated flow near its trailing edge. When simulating these flows with turbulence modeling, the Reynolds-averaged Navier-Stokes (RANS) approach is more efficient in the former, whereas large-eddy simulation (LES) is more accurate in the latter. Detached-eddy simulation (DES), based on the Spalart-Allmaras model, is a hybrid method that switches from RANS mode of solution in attached boundary layers to LES in detached flow regions. Simulations of turbulent flows over moving structures on a body-fitted mesh incur an enormous remeshing cost every time step. The constraint-based immersed boundary (cIB) method eliminates this operation by placing the structure on a Cartesian mesh and enforcing a rigidity constraint as an additional forcing in the Navier-Stokes momentum equation. We outline the formulation and development of a parallel DES-cIB method using adaptive mesh refinement. We show preliminary validation results for flows past stationary bodies with both attached and separated boundary layers along with results for turbulent flows past moving bodies. This work is supported by the National Science Foundation Graduate Research Fellowship under Grant No. DGE-1324585.

Tracking atmospheric boundary layer in tehran using combined lidar remote sensing and ground base measurements

NASA Astrophysics Data System (ADS)

Panahifar, Hossein; Khalesifard, Hamid

2018-04-01

The vertical structure of the atmospheric boundary layer (ABL) has been studied by use of a depolarized LiDAR over Tehran, Iran. The boundary layer height (BLH) remains under 1km, and its retrieval from LiDAR have been compared with sonding measurements and meteorological model outputs. It is also shown that the wind speed and direction as well as topography lead to the persistence of air pollution in Tehran. The situation aggravate in fall and winter due to temperature inversion.

On the universality of inertial energy in the log layer of turbulent boundary layer and pipe flows

NASA Astrophysics Data System (ADS)

Chung, D.; Marusic, I.; Monty, J. P.; Vallikivi, M.; Smits, A. J.

2015-07-01

Recent experiments in high Reynolds number pipe flow have shown the apparent obfuscation of the behaviour in spectra of streamwise velocity fluctuations (Rosenberg et al. in J Fluid Mech 731:46-63, 2013). These data are further analysed here from the perspective of the behaviour in second-order structure functions, which have been suggested as a more robust diagnostic to assess scaling behaviour. A detailed comparison between pipe flows and boundary layers at friction Reynolds numbers of 5000-20,000 reveals subtle differences. In particular, the slope of the pipe flow structure function decreases with increasing wall distance, departing from the expected slope in a manner that is different to boundary layers. Here, , the slope of the log law in the streamwise turbulence intensity profile at high Reynolds numbers. Nevertheless, the structure functions for both flows recover the slope in the log layer sufficiently close to the wall, provided the Reynolds number is also high enough to remain in the log layer. This universality is further confirmed in very high Reynolds number data from measurements in the neutrally stratified atmospheric surface layer. A simple model that accounts for the `crowding' effect near the pipe axis is proposed in order to interpret the aforementioned differences.

Deleterious localized stress fields: the effects of boundaries and stiffness tailoring in anisotropic laminated plates

PubMed Central

Weaver, P. M.

2016-01-01

The safe design of primary load-bearing structures requires accurate prediction of stresses, especially in the vicinity of geometric discontinuities where deleterious three-dimensional stress fields can be induced. Even for thin-walled structures significant through-thickness stresses arise at edges and boundaries, and this is especially precarious for laminates of advanced fibre-reinforced composites because through-thickness stresses are the predominant drivers in delamination failure. Here, we use a higher-order equivalent single-layer model derived from the Hellinger–Reissner mixed variational principle to examine boundary layer effects in laminated plates comprising constant-stiffness and variable-stiffness laminae and deforming statically in cylindrical bending. The results show that zigzag deformations, which arise due to layerwise differences in the transverse shear moduli, drive boundary layers towards clamped edges and are therefore critically important in quantifying localized stress gradients. The relative significance of the boundary layer scales with the degree of layerwise anisotropy and the thickness to characteristic length ratio. Finally, we demonstrate that the phenomenon of alternating positive and negative transverse shearing deformation through the thickness of composite laminates, previously only observed at clamped boundaries, can also occur at other locations as a result of smoothly varying the material properties over the in-plane dimensions of the laminate. PMID:27843401

Hearing Protection - Needs, Technologies and Performance (Protection de l’ouie - besoins, technologies et resultats)

DTIC Science & Technology

2010-11-01

Human (AHAAH) which takes into account the whole signal transmission from the free sound field to the cochlear structures. Auditory Hazard Units...airflow around the aircraft canopy and the front structure of the aircraft (boundary layer flow noise), and the other is from internally generated noise...from the pressurisation and cockpit conditioning systems. The boundary layer flow noise is dependent upon the dynamic pressures on the aircraft and

Structural characteristics of the shock-induced boundary layer separation extended to the leading edge

NASA Astrophysics Data System (ADS)

Tao, Y.; Liu, W. D.; Fan, X. Q.; Zhao, Y. L.

2017-07-01

For a better understanding of the local unstart of supersonic/hypersonic inlet, a series of experiments has been conducted to investigate the shock-induced boundary layer separation extended to the leading edge. Using the nanoparticle-based planar laser scattering, we recorded the fine structures of these interactions under different conditions and paid more attention to their structural characteristics. According to their features, these interactions could be divided into four types. Specifically, Type A wave pattern is similar to the classic shock wave/turbulent boundary layer interaction, and Type B wave configuration consists of an overall Mach reflection above the large scale separation bubble. Due to the gradual decrease in the size of the separation bubble, the separation bubble was replaced by several vortices (Type C wave pattern). Besides, for Type D wave configuration which exists in the local unstart inlet, there appears to be some flow spillage around the leading edge.

Swept shock/boundary-layer interactions: Scaling laws, flowfield structure, and experimental methods

NASA Technical Reports Server (NTRS)

Settles, Gary S.

1993-01-01

A general review is given of several decades of research on the scaling laws and flowfield structures of swept shock wave/turbulent boundary layer interactions. Attention is further restricted to the experimental study and physical understanding of the steady-state aspects of these flows. The interaction produced by a sharp, upright fin mounted on a flat plate is taken as an archetype. An overall framework of quasiconical symmetry describing such interactions is first developed. Boundary-layer separation, the interaction footprint, Mach number scaling, and Reynolds number scaling are then considered, followed by a discussion of the quasiconical similarity of interactions produced by geometrically-dissimilar shock generators. The detailed structure of these interaction flowfields is next reviewed, and is illustrated by both qualitative visualizations and quantitative flow images in the quasiconical framework. Finally, the experimental techniques used to investigate such flows are reviewed, with emphasis on modern non-intrusive optical flow diagnostics.

Pressure Fluctuations Induced by a Hypersonic Turbulent Boundary Layer

NASA Technical Reports Server (NTRS)

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

2016-01-01

Direct numerical simulations (DNS) are used to examine the pressure fluctuations generated by a spatially-developed Mach 5.86 turbulent boundary layer. The unsteady pressure field is analyzed at multiple wall-normal locations, including those at the wall, within the boundary layer (including inner layer, the log layer, and the outer layer), and in the free stream. The statistical and structural variations of pressure fluctuations as a function of wall-normal distance are highlighted. Computational predictions for mean velocity pro les and surface pressure spectrum are in good agreement with experimental measurements, providing a first ever comparison of this type at hypersonic Mach numbers. The simulation shows that the dominant frequency of boundary-layer-induced pressure fluctuations shifts to lower frequencies as the location of interest moves away from the wall. The pressure wave propagates with a speed nearly equal to the local mean velocity within the boundary layer (except in the immediate vicinity of the wall) while the propagation speed deviates from the Taylor's hypothesis in the free stream. Compared with the surface pressure fluctuations, which are primarily vortical, the acoustic pressure fluctuations in the free stream exhibit a significantly lower dominant frequency, a greater spatial extent, and a smaller bulk propagation speed. The freestream pressure structures are found to have similar Lagrangian time and spatial scales as the acoustic sources near the wall. As the Mach number increases, the freestream acoustic fluctuations exhibit increased radiation intensity, enhanced energy content at high frequencies, shallower orientation of wave fronts with respect to the flow direction, and larger propagation velocity.

A new spatially scanning 2.7 µm laser hygrometer and new small-scale wind tunnel for direct analysis of the H2O boundary layer structure at single plant leaves

NASA Astrophysics Data System (ADS)

Wunderle, K.; Rascher, U.; Pieruschka, R.; Schurr, U.; Ebert, V.

2015-01-01

A new spatially scanning TDLAS in situ hygrometer based on a 2.7-µm DFB diode laser was constructed and used to analyse the water vapour concentration boundary layer structure at the surface of a single plant leaf. Using an absorption length of only 5.4 cm, the TDLAS hygrometer permits a H2O vapour concentration resolution of 31 ppmv. This corresponds to a normalized precision of 1.7 ppm m. In order to preserve and control the H2O boundary layer on an individual leaf and to study the boundary layer dependence on the wind speed to which the leaf might be exposed in nature, we also constructed a new, application specific, small-scale, wind tunnel for individual plant leaves. The rectangular, closed-loop tunnel has overall dimensions of 1.2 × 0.6 m and a measurement chamber dimension of 40 × 54 mm (H × W). It allows to generate a laminar flow with a precisely controlled wind speed at the plant leaf surface. Combining honeycombs and a miniaturized compression orifice, we could generate and control stable wind speeds from 0.1 to 0.9 m/s, and a highly laminar and homogeneous flow with an excellent relative spatial homogeneity of 0.969 ± 0.03. Combining the spectrometer and the wind tunnel, we analysed (for the first time) non-invasively the wind speed-dependent vertical structure of the H2O vapour distribution within the boundary layer of a single plant leaf. Using our time-lag-free data acquisition procedure for phase locked signal averaging, we achieved a temporal resolution of 0.2 s for an individual spatial point, while a complete vertical spatial scan at a spatial resolution of 0.18 mm took 77 s. The boundary layer thickness was found to decrease from 6.7 to 3.6 mm at increasing wind speeds of 0.1-0.9 m/s. According to our knowledge, this is the first experimental quantification of wind speed-dependent H2O vapour boundary layer concentration profiles of single plant leaves.

Modification of the Atmospheric Boundary Layer by a Small Island: Observations from Nauru

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

Matthews, Stuart; Hacker, Jorg M.; Cole, Jason N.

2007-03-01

Nauru, a small island in the tropical pacific, generates plumes of clouds that may grow to several hundred km length. This study uses observations to examine the mesoscale disturbance of the marine atmospheric boundary layer by the island that produces these cloud streets. Observations of the surface layer were made from two ships in the vicinity of Nauru and from instruments on the island. The structure of the atmospheric boundary layer over the island was investigated using aircraft flights. Cloud production over Nauru was examined using remote sensing instruments. During the day the island surface layer was warmer than themore » marine surface layer and wind speed was lower than over the ocean. Surface heating forced the growth of a thermal internal boundary layer, above which a street of cumulus clouds formed. The production of clouds resulted in reduced downwelling shortwave irradiance at the island surface. A plume of warm-dry air was observed over the island which extended 15 – 20 km downwind.« less

Coherent structures in bypass transition induced by a cylinder wake

NASA Astrophysics Data System (ADS)

Pan, Chong; Wang, Jin Jun; Zhang, Pan Feng; Feng, Li Hao

Flat-plate boundary layer transition induced by the wake vortex of a two-dimensional circular cylinder is experimentally investigated. Combined visualization and velocity measurements show a different transition route from the Klebanoff mode in free-stream turbulence-induced transition. This transition scenario is mainly characterized as: (i) generation of secondary transverse vortical structures near the flat plate surface in response to the von Kn vortex street of the cylinder; (ii) formation of hairpin vortices due to the secondary instability of secondary vortical structures; (iii) growth of hairpins which is accelerated by wake-vortex induction; (iv) formation of hairpin packets and the associated streaky structures. Detailed investigation shows that during transition the evolution dynamics and self-sustaining mechanisms of hairpins, hairpin packets and streaks are consistent with those in a turbulent boundary layer. The wake vortex mainly plays the role of generating and destabilizing secondary transverse vortices. After that, the internal mechanisms become dominant and lead to the setting up of a self-sustained turbulent boundary layer.

Influence of the angle between the wind and the isothermal surfaces on the boundary layer structures in turbulent thermal convection.

PubMed

Shishkina, Olga; Wagner, Sebastian; Horn, Susanne

2014-03-01

We derive the asymptotes for the ratio of the thermal to viscous boundary layer thicknesses for infinite and infinitesimal Prandtl numbers Pr as functions of the angle β between the large-scale circulation and an isothermal heated or cooled surface for the case of turbulent thermal convection with laminar-like boundary layers. For this purpose, we apply the Falkner-Skan ansatz, which is a generalization of the Prandtl-Blasius one to a nonhorizontal free-stream flow above the viscous boundary layer. Based on our direct numerical simulations (DNS) of turbulent Rayleigh-Bénard convection for Pr=0.1, 1, and 10 and moderate Rayleigh numbers up to 108 we evaluate the value of β that is found to be around 0.7π for all investigated cases. Our theoretical predictions for the boundary layer thicknesses for this β and the considered Pr are in good agreement with the DNS results.

Wall turbulence control

NASA Technical Reports Server (NTRS)

Wilkinson, Stephen P.; Lindemann, A. Margrethe; Beeler, George B.; Mcginley, Catherine B.; Goodman, Wesley L.; Balasubramanian, R.

1986-01-01

A variety of wall turbulence control devices which were experimentally investigated are discussed; these include devices for burst control, alteration of outer flow structures, large eddy substitution, increased heat transfer efficiency, and reduction of wall pressure fluctuations. Control of pre-burst flow was demonstrated with a single, traveling surface depression which is phase-locked to elements of the burst production process. Another approach to wall turbulence control is to interfere with the outer layer coherent structures. A device in the outer part of a boundary layer was shown to suppress turbulence and reduce drag by opposing both the mean and unsteady vorticity in the boundary layer. Large eddy substitution is a method in which streamline curvature is introduced into the boundary layer in the form of streamwise vortices. Riblets, which were already shown to reduce turbulent drag, were also shown to exhibit superior heat transfer characteristics. Heat transfer efficiency as measured by the Reynolds Analogy Factor was shown to be as much as 36 percent greater than a smooth flat plate in a turbulent boundary layer. Large Eddy Break-Up (LEBU) which are also known to reduce turbulent drag were shown to reduce turbulent wall pressure fluctuation.

A Vertically Resolved Planetary Boundary Layer

NASA Technical Reports Server (NTRS)

Helfand, H. M.

1984-01-01

Increase of the vertical resolution of the GLAS Fourth Order General Circulation Model (GCM) near the Earth's surface and installation of a new package of parameterization schemes for subgrid-scale physical processes were sought so that the GLAS Model GCM will predict the resolved vertical structure of the planetary boundary layer (PBL) for all grid points.

Interaction of viscous and inviscid instability modes in separation-bubble transition

NASA Astrophysics Data System (ADS)

Brinkerhoff, Joshua R.; Yaras, Metin I.

2011-12-01

This paper describes numerical simulations that are used to examine the interaction of viscous and inviscid instability modes in laminar-to-turbulent transition in a separation bubble. The results of a direct numerical simulation are presented in which separation of a laminar boundary-layer occurs in the presence of an adverse streamwise pressure gradient. The simulation is performed at low freestream-turbulence levels and at a flow Reynolds number and pressure distribution approximating those typically encountered on the suction side of low-pressure turbine blades in a gas-turbine engine. The simulation results reveal the development of a viscous instability upstream of the point of separation which produces streamwise-oriented vortices in the attached laminar boundary layer. These vortices remain embedded in the flow downstream of separation and are carried into the separated shear layer, where they are amplified by the local adverse pressure-gradient and contribute to the formation of coherent hairpin-like vortices. A strong interaction is observed between these vortices and the inviscid instability that typically dominates the shear layer in the separated zone. The interaction is noted to determine the spanwise extent of the vortical flow structures that periodically shed from the downstream end of the separated shear layer. The structure of the shed vortical flow structures is examined and compared with the coherent structures typically observed within turbulent boundary layers.

The Bottom Boundary Layer.

PubMed

Trowbridge, John H; Lentz, Steven J

2018-01-03

The oceanic bottom boundary layer extracts energy and momentum from the overlying flow, mediates the fate of near-bottom substances, and generates bedforms that retard the flow and affect benthic processes. The bottom boundary layer is forced by winds, waves, tides, and buoyancy and is influenced by surface waves, internal waves, and stratification by heat, salt, and suspended sediments. This review focuses on the coastal ocean. The main points are that (a) classical turbulence concepts and modern turbulence parameterizations provide accurate representations of the structure and turbulent fluxes under conditions in which the underlying assumptions hold, (b) modern sensors and analyses enable high-quality direct or near-direct measurements of the turbulent fluxes and dissipation rates, and (c) the remaining challenges include the interaction of waves and currents with the erodible seabed, the impact of layer-scale two- and three-dimensional instabilities, and the role of the bottom boundary layer in shelf-slope exchange.

The Bottom Boundary Layer

NASA Astrophysics Data System (ADS)

Trowbridge, John H.; Lentz, Steven J.

2018-01-01

The oceanic bottom boundary layer extracts energy and momentum from the overlying flow, mediates the fate of near-bottom substances, and generates bedforms that retard the flow and affect benthic processes. The bottom boundary layer is forced by winds, waves, tides, and buoyancy and is influenced by surface waves, internal waves, and stratification by heat, salt, and suspended sediments. This review focuses on the coastal ocean. The main points are that (a) classical turbulence concepts and modern turbulence parameterizations provide accurate representations of the structure and turbulent fluxes under conditions in which the underlying assumptions hold, (b) modern sensors and analyses enable high-quality direct or near-direct measurements of the turbulent fluxes and dissipation rates, and (c) the remaining challenges include the interaction of waves and currents with the erodible seabed, the impact of layer-scale two- and three-dimensional instabilities, and the role of the bottom boundary layer in shelf-slope exchange.

On hydromagnetic oscillations in a rotating cavity.

NASA Technical Reports Server (NTRS)

Gans, R. F.

1971-01-01

Time-dependent hydromagnetic phenomena in a rotating spherical cavity are investigated in the framework of an interior boundary-layer expansion. The first type of wave is a modification of the hydrodynamic inertial wave, the second is a pseudo-geostrophic wave and is involved in spinup, and the third is related to the MAC waves of Braginskii (1967). It is shown that the MAC waves must satisfy more than the usual normal boundary conditions, and that reference must be made to the boundary-layer solution to resolve the ambiguity regarding which conditions are to be taken. The boundary-layer structure is investigated in detail to display the interactions between applied field, viscosity, electrical conductivity, frequency and latitu de.

Forward and inverse models of electromagnetic scattering from layered media with rough interfaces

NASA Astrophysics Data System (ADS)

Tabatabaeenejad, Seyed Alireza

This work addresses the problem of electromagnetic scattering from layered dielectric structures with rough boundaries and the associated inverse problem of retrieving the subsurface parameters of the structure using the scattered field. To this end, a forward scattering model based on the Small Perturbation Method (SPM) is developed to calculate the first-order spectral-domain bistatic scattering coefficients of a two-layer rough surface structure. SPM requires the boundaries to be slightly rough compared to the wavelength, but to understand the range of applicability of this method in scattering from two-layer rough surfaces, its region of validity is investigated by comparing its output with that of a first principle solver that does not impose roughness restrictions. The Method of Moments (MoM) is used for this purpose. Finally, for retrieval of the model parameters of the layered structure using scattered field, an inversion scheme based on the Simulated Annealing method is investigated and a strategy is proposed to address convergence to local minimum.

Large scale structures in a turbulent boundary layer and their imprint on wall shear stress

NASA Astrophysics Data System (ADS)

Pabon, Rommel; Barnard, Casey; Ukeiley, Lawrence; Sheplak, Mark

2015-11-01

Experiments were performed on a turbulent boundary layer developing on a flat plate model under zero pressure gradient flow. A MEMS differential capacitive shear stress sensor with a 1 mm × 1 mm floating element was used to capture the fluctuating wall shear stress simultaneously with streamwise velocity measurements from a hot-wire anemometer traversed in the wall normal direction. Near the wall, the peak in the cross correlation corresponds to an organized motion inclined 45° from the wall. In the outer region, the peak diminishes in value, but is still significant at a distance greater than half the boundary layer thickness, and corresponds to a structure inclined 14° from the wall. High coherence between the two signals was found for the low-frequency content, reinforcing the belief that large scale structures have a vital impact on wall shear stress. Thus, estimation of the wall shear stress from the low-frequency velocity signal will be performed, and is expected to be statistically significant in the outer boundary layer. Additionally, conditionally averaged mean velocity profiles will be presented to assess the effects of high and low shear stress. This material is based upon work supported by the National Science Foundation Graduate Research Fellowship under Grant No. DGE-1315138.

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.

Dependence of air masses type on PBL vertical structure retrieved at the Mace Head station during EUCAARI campaign.

NASA Astrophysics Data System (ADS)

Milroy, Conor; Martucci, Giovanni; O'Dowd, Colin

2010-05-01

During the EUCAARI Intensive Observing Period held at the Mace Head GAW station from mid-May to mid-June, 2008, the PBL depth has been continuously measured by two ceilometers (Vaisala CL31 and Jenoptik CHM15K) and a microwave radiometer (RPG-HATPRO). The Lidar-Ceilometer, through the gradients in aerosol backscatter profiles, and the microwave profiler, through gradients in the specific humidity profiles, were used to remotely-sense the boundary layer structure. An automatic, newly developed Temporal Height-Tracking (THT) algorithm (Martucci et al., 2010) have been applied to both type of instruments data to retrieve the 2-layered structure of the local marine boundary layer. The two layers are defined as a lower, well mixed layer, i.e. the surface mixed layer, and the layer occupying the region below the free Troposphere inversion, i.e. the decoupled residual or convective layer. A categorization of the incoming air masses has been performed based on their origins and been used to asses the correlation with the PBL depths. The study confirmed the dependence of PBL vertical structure on different air masses and different type of advected aerosol.

Flow field predictions for a slab delta wing at incidence

NASA Technical Reports Server (NTRS)

Conti, R. J.; Thomas, P. D.; Chou, Y. S.

1972-01-01

Theoretical results are presented for the structure of the hypersonic flow field of a blunt slab delta wing at moderately high angle of attack. Special attention is devoted to the interaction between the boundary layer and the inviscid entropy layer. The results are compared with experimental data. The three-dimensional inviscid flow is computed numerically by a marching finite difference method. Attention is concentrated on the windward side of the delta wing, where detailed comparisons are made with the data for shock shape and surface pressure distributions. Surface streamlines are generated, and used in the boundary layer analysis. The three-dimensional laminar boundary layer is computed numerically using a specially-developed technique based on small cross-flow in streamline coordinates. In the rear sections of the wing the boundary layer decreases drastically in the spanwise direction, so that it is still submerged in the entropy layer at the centerline, but surpasses it near the leading edge. Predicted heat transfer distributions are compared with experimental data.

Marine boundary layer structure as observed by A-train satellites

DOE PAGES

Luo, Tao; Wang, Zhien; Zhang, Damao; ...

2016-05-13

The marine boundary layer (MBL) structure is important to the marine low cloud processes, and the exchange of heat, momentum, and moisture between oceans and the low atmosphere. This study examines the MBL structure over the eastern Pacific region and further explores the controlling factors of MBL structure over the global oceans with a new 4-year satellite-based data set. The MBL top (boundary layer height, BLH) and the mixing layer height (MLH) were identified using the MBL aerosol lidar backscattering from the CALIPSO (Cloud–Aerosol Lidar and Infrared Pathfinder Satellite Observations). Results showed that the MBL is generally decoupled with MLH ∕ BLHmore » ratio ranging from  ∼  0.5 to  ∼  0.8 over the eastern Pacific Ocean region. The MBL decoupling magnitude is mainly controlled by estimated inversion strength (EIS), which in turn controls the cloud top entrainment process. The systematic differences between drizzling and non-drizzling stratocumulus tops also show dependence on EIS. This may be related to the meso-scale circulations or gravity wave in the MBL. Further analysis indicates that the MBL shows a similar decoupled structure for clear-sky and cumulus-cloud-topped conditions, but is better mixed under stratiform cloud breakup and overcast conditions.« less

Experimental investigation of localized disturbances in the straight wing boundary layer, generated by finite surface vibrations

NASA Astrophysics Data System (ADS)

Kozlov, V. V.; Katasonov, M. M.; Pavlenko, A. M.

2017-10-01

Downstream development of artificial disturbances were investigated experimentally using hot-wire constant temperature anemometry. It is shown that vibrations with high-amplitude of a three-dimensional surface lead to formation of two types of perturbations in the straight wing boundary layer: streamwise oriented localized structures and wave packets. The amplitude of streamwise structure is decay downstream. The wave packets amplitude grows in adverse pressure gradient area. The flow separation is exponentially intensified of the wave packet amplitude.

Inference of the boundary layer structure over the oceans from satellite infrared measurements

NASA Technical Reports Server (NTRS)

Prabhakara, C.; Dalu, G.; Lo, R.; Nath, N. R.

1978-01-01

The characteristics of the boundary layer of the atmosphere over the global oceans between about 50 deg N to 40 deg S were remotely sensed for three different periods, about 3 months each, during the year 1970. The spectral measurements made by Nimbus 4 Infrared Interferometer Spectrometer were used for this purpose.

Interplanetary boundary layers at 1 AU. [magnetic field measurements from Explorer 34

NASA Technical Reports Server (NTRS)

Burlaga, L. F.; Lemaire, J. F.; Turner, J. M.

1976-01-01

The structure and nature of discontinuities in the interplanetary magnetic field at 1 AU in the period March 18, 1971 to April 9, 1971, is determined by using high-resolution magnetic field measurements from Explorer 34. The discontinuities that were selected for this analysis occurred under a variety of interplanetary conditions at an average rate of 0.5/hr. This set does not include all discontinuities that were present, but the sample is large and it is probably representative. Both tangential and rotational discontinuities were identified, the ratio of TD's to RD's being approximately 3 to 1. Tangential discontinuities were observed every day, even among Alfvenic fluctuations. The structure of most of the boundary layers was simple and ordered, i.e., the magnetic field usually changed smoothly and monotonically from one side of the boundary layer to the other.

Vortex structure and breakup mechanism of gaseous jet in supersonic crossflow with laminar boundary layer

NASA Astrophysics Data System (ADS)

Zhao, Yanhui; Liang, Jianhan; Zhao, Yuxin

2016-11-01

Employing nano-particle planar laser scattering and particle image velocimetry technology, underexpanded jet in supersonic crossflow with laminar boundary layer is experimental investigated in a low noise wind tunnel. Instantaneous flow structures and average velocity distribution of jet plume are captured in experimental images. Horseshoe vortex system is dominated by oscillating and coalescing regime, contributing to vortex generation of jet shear layer. The "tilting-stretching-tearing" mechanism dominating in near field raises average fractal dimension. But vortex structures generated on the windward side of jet plume scatter in jet plume and dissipate gradually, which makes the vortexes break up from outside in near field and break down into small turbulence completely in far field.

Understanding luminescence properties of grain boundaries in GaN thin films and their atomistic origin

NASA Astrophysics Data System (ADS)

Yoo, Hyobin; Yoon, Sangmoon; Chung, Kunook; Kang, Seoung-Hun; Kwon, Young-Kyun; Yi, Gyu-Chul; Kim, Miyoung

2018-03-01

We report our findings on the optical properties of grain boundaries in GaN films grown on graphene layers and discuss their atomistic origin. We combine electron backscatter diffraction with cathodoluminescence to directly correlate the structural defects with their optical properties, enabling the high-precision local luminescence measurement of the grain boundaries in GaN films. To further understand the atomistic origin of the luminescence properties, we carefully probed atomic core structures of the grain boundaries by exploiting aberration-corrected scanning transmission electron microscopy. The atomic core structures of grain boundaries show different ordering behaviors compared with those observed previously in threading dislocations. Energetics of the grain boundary core structures and their correlation with electronic structures were studied by first principles calculation.

Lubricated immersed boundary method in two dimensions

NASA Astrophysics Data System (ADS)

Fai, Thomas G.; Rycroft, Chris H.

2018-03-01

Many biological examples of fluid-structure interaction, including the transit of red blood cells through the narrow slits in the spleen and the intracellular trafficking of vesicles into dendritic spines, involve the near-contact of elastic structures separated by thin layers of fluid. Motivated by such problems, we introduce an immersed boundary method that uses elements of lubrication theory to resolve thin fluid layers between immersed boundaries. We demonstrate 2nd-order accurate convergence for simple two-dimensional flows with known exact solutions to showcase the increased accuracy of this method compared to the standard immersed boundary method. Motivated by the phenomenon of wall-induced migration, we apply the lubricated immersed boundary method to simulate an elastic vesicle near a wall in shear flow. We also simulate the dynamics of a vesicle traveling through a narrow channel and observe the ability of the lubricated method to capture the vesicle motion on relatively coarse fluid grids.

Inner-outer interactions in the convective atmospheric boundary layer

NASA Astrophysics Data System (ADS)

Salesky, S.

2017-12-01

Recently, observational and numerical studies have revealed the existence of so-called large scale motions (LSMs) that populate the logarithmic layer of wall-bounded turbulent shear flows and modulate the amplitude and frequency of turbulence dynamics near the ground. Properties of LSMs are well understood in neutrally stratified flows over smooth and rough walls. However, the implications of previous studies for the convective atmospheric boundary layer (CBL) are not entirely clear, since the morphology of both small-scale and large-scale turbulent structures is known to be strongly affected by buoyancy [e.g. Salesky et al., Bound.-Layer Meteorol. 163:41-68 (2017)]. In the present study, inner-outer interactions in the CBL are investigated using a suite of large eddy simulations spanning neutral to highly convective conditions. Simulation results reveal that, as the atmosphere becomes increasingly unstable, the inclination angle of structures near the ground increases from 12-15° to nearly 90°. Furthermore, the scale separation between the inner and outer peaks in the premultiplied velocity spectra decreases until only a single peak remains (comparable in magnitude to the boundary layer depth). The extent to which the amplitude modulation of surface layer turbulence by outer layer structures changes with increasing instability will be considered, following the decoupling procedure proposed by Mathis et al. [J. Fluid Mech., vol 628, 311-337 (2009)]. Frequency modulation of surface layer turbulence also will be examined, following the wavelet analysis approach of Baars et al. [Exp. Fluids, 56:188, (2015)].

Properties of the Equatorial Magnetotail Flanks ˜50-200 RE Downtail

NASA Astrophysics Data System (ADS)

Artemyev, A. V.; Angelopoulos, V.; Runov, A.; Wang, C.-P.; Zelenyi, L. M.

2017-12-01

In space, thin boundaries separating plasmas with different properties serve as a free energy source for various plasma instabilities and determine the global dynamics of large-scale systems. In planetary magnetopauses and shock waves, classical examples of such boundaries, the magnetic field makes a significant contribution to the pressure balance and plasma dynamics. The configuration and properties of such boundaries have been well investigated and modeled. However, much less is known about boundaries that form between demagnetized plasmas where the magnetic field is not important for pressure balance. The most accessible example of such a plasma boundary is the equatorial boundary layer of the Earth's distant magnetotail. Rather, limited measurements since its first encounter in the late 1970s by the International Sun-Earth Explorer-3 spacecraft revealed the basic properties of this boundary, but its statistical properties and structure have not been studied to date. In this study, we use Geotail and Acceleration, Reconnection, Turbulence and Electrodynamics of the Moon's Interaction with the Sun (ARTEMIS) missions to investigate the equatorial boundary layer from lunar orbit (˜55 Earth radii, RE, downtail) to as far downtail as ˜200 RE. Although the magnetic field has almost no effect on the structure of the boundary layer, the layer separates well the hot, rarefied plasma sheet from dense cold magnetosheath plasmas. We suggest that the most important role in plasma separation is played by polarization electric fields, which modify the efficiency of magnetosheath ion penetration into the plasma sheet. We also show that the total energies (bulk flow plus thermal) of plasma sheet ions and magnetosheath ions are very similar; that is, magnetosheath ion thermalization (e.g., via ion scattering by magnetic field fluctuations) is sufficient to produce hot plasma sheet ions without any additional acceleration.

Persistent Structures in the Turbulent Boundary Layer

NASA Technical Reports Server (NTRS)

Palumbo, Dan; Chabalko, Chris

2005-01-01

Persistent structures in the turbulent boundary layer are located and analyzed. The data are taken from flight experiments on large commercial aircraft. An interval correlation technique is introduced which is able to locate the structures. The Morlet continuous wavelet is shown to not only locates persistent structures but has the added benefit that the pressure data are decomposed in time and frequency. To better understand how power is apportioned among these structures, a discrete Coiflet wavelet is used to decompose the pressure data into orthogonal frequency bands. Results indicate that some structures persist a great deal longer in the TBL than would be expected. These structure contain significant power and may be a primary source of vibration energy in the airframe.

Measurement of corner separation zone response on a compression ramp to plasma actuation within the hypersonic boundary layer

NASA Astrophysics Data System (ADS)

Hedlund, Brock E.; Houpt, Alec W.; Gordeyev, Stanislav V.; Leonov, Sergey B.

2017-10-01

This study was performed to characterize the dominant frequencies present in the boundary layer uptsream of and in the corner separation zone of a compression surface in Mach 4.5 flow and to determine a control effect of transient plasma actuation on the boundary layer. Schlieren imaging was used to distinguish the corner separation zone for 20°, 25°, and 30° compression ramps mounted on flat plates. Spectra of the natural disturbances present in the boundary layer and separation zone were gathered using a high-speed Shack-Hartmann wavefront sensor and surface mounted PCBTM pressure sensors while varying flow parameters by adjusting total pressure, temperature, and ramp angle. Shallow cavity discharge plasma actuators were used as a high-frequency localized thermal forcing mechanism of the boundary layer. The plasma effect was negligible for forcing frequencies (50 kHz) below the natural dominant frequency (~55-80 kHz). High frequency perturbations that can promote the transition to turbulence were amplified when the plasma forcing frequency (100 kHz) was higher than the natural dominant frequency (~55-80 kHz). This technique can potentially be used for active control of hypersonic boundary layer transition and the supersonic flow structure on the compression surface.

Overview of Boundary Layer Transition Research in Support of Orbiter Return To Flight

NASA Technical Reports Server (NTRS)

Berry, Scott A.; Horvath, Thomas J.; Greene, Francis A.; Kinder, Gerald R.; Wang, K. C.

2006-01-01

A predictive tool for estimating the onset of boundary layer transition resulting from damage to and/or repair of the thermal protection system was developed in support of Shuttle Return to Flight. The boundary layer transition tool is part of a suite of tools that analyze the aerothermodynamic environment to the local thermal protection system to allow informed disposition of damage for making recommendations to fly as is or to repair. Using mission specific trajectory information and details of each damage site or repair, the expected time (and thus Mach number) at transition onset is predicted to help define the aerothermodynamic environment to use in the subsequent thermal and stress analysis of the local thermal protection system and structure. The boundary layer transition criteria utilized for the tool was developed from ground-based measurements to account for the effect of both protuberances and cavities and has been calibrated against select flight data. Computed local boundary layer edge conditions were used to correlate the results, specifically the momentum thickness Reynolds number over the edge Mach number and the boundary layer thickness. For the initial Return to Flight mission, STS-114, empirical curve coefficients of 27, 100, and 900 were selected to predict transition onset for protuberances based on height, and cavities based on depth and length, respectively.

Bending Boundary Layers in Laminated-Composite Circular Cylindrical Shells

NASA Technical Reports Server (NTRS)

Nemeth, Michael P.; Smeltzer, Stanley S., III

2000-01-01

A study of the attenuation of bending boundary layers in balanced and unbalanced, symmetrically and unsymmetrically laminated cylindrical shells is presented for nine contemporary material systems. The analysis is based on the linear Sanders-Koiter shell equations and specializations to the Love-Kirchhoff shell equations and Donnell's equations are included. Two nondimensional parameters are identified that characterize the effects of laminate orthotropy and anisotropy on the bending boundary-layer decay length in a very general manner. A substantial number of structural design technology results are presented for a wide range of laminated-composite cylinders. For all laminates considered, the results show that the differences between results obtained with the Sanders-Koiter shell equations, the Love-Kirchhoff shell equations, and Donnell's equations are negligible. The results also show that the effect of anisotropy in the form of coupling between pure bending and twisting has a negligible effect on the size of the bending boundary-layer decay length of the balanced, symmetrically laminated cylinders considered. Moreover, the results show that coupling between the various types of shell anisotropies has a negligible effect on the calculation of the bending boundary-layer decay length in most cases. The results also show that, in some cases, neglecting the shell anisotropy results in underestimating the bending boundary-layer decay length and, in other cases, results in an overestimation.

Characterization of the planetary boundary layer height and structure by Raman lidar: comparison of different approaches

NASA Astrophysics Data System (ADS)

Summa, D.; Di Girolamo, P.; Stelitano, D.; Cacciani, M.

2013-12-01

The planetary boundary layer (PBL) includes the portion of the atmosphere which is directly influenced by the presence of the earth's surface. Aerosol particles trapped within the PBL can be used as tracers to study the boundary-layer vertical structure and time variability. As a result of this, elastic backscatter signals collected by lidar systems can be used to determine the height and the internal structure of the PBL. The present analysis considers three different methods to estimate the PBL height. The first method is based on the determination of the first-order derivative of the logarithm of the range-corrected elastic lidar signals. Estimates of the PBL height for specific case studies obtained through this approach are compared with simultaneous estimates from the potential temperature profiles measured by radiosondes launched simultaneously to lidar operation. Additional estimates of the boundary layer height are based on the determination of the first-order derivative of the range-corrected rotational Raman lidar signals. This latter approach results to be successfully applicable also in the afternoon-evening decaying phase of the PBL, when the effectiveness of the approach based on the elastic lidar signals may be compromised or altered by the presence of the residual layer. Results from these different approaches are compared and discussed in the paper, with a specific focus on selected case studies collected by the University of Basilicata Raman lidar system BASIL during the Convective and Orographically-induced Precipitation Study (COPS).

Characterization of the planetary boundary layer height and structure by Raman lidar: comparison of different approaches

NASA Astrophysics Data System (ADS)

Summa, D.; Di Girolamo, P.; Stelitano, D.; Cacciani, M.

2013-06-01

The Planetary Boundary Layer (PBL) includes the portion of the atmosphere which is directly influenced by the presence of the Earth's surface. Aerosol particles trapped within the PBL can be used as tracers to study the boundary-layer vertical structure and time variability. As a result of this, elastic backscatter signals collected by lidar systems can be used to determine the height and the internal structure of the PBL. The present analysis considers three different methods to estimate the PBL height. A first method is based on the determination of the first order derivative of the logarithm of the range-corrected elastic lidar signals. Estimates of the PBL height for specific case studies obtained from this approach are compared with simultaneous estimates from the potential temperature profiles measured by radiosondes launched simultaneously to lidar operation. Additional estimates of the boundary layer height are based on the determination of the first order derivative of the range-corrected rotational Raman lidar signals. This latter approach results to be successfully applicable also in the afternoon-evening decaying phase of the PBL, when the effectiveness of the approach based on the elastic lidar signals may be compromised or altered by the presence of the residual layer. Results from these different approaches are compared and discussed in the paper, with a specific focus on selected case studies collected by the University of Basilicata Raman lidar system BASIL during the Convective and Orographically-induced Precipitation Study (COPS).

Outer-layer manipulators for turbulent drag reduction

NASA Technical Reports Server (NTRS)

Anders, J. B., Jr.

1990-01-01

The last ten years have yielded intriguing research results on aerodynamic boundary outer-layer manipulators as local skin friction reduction devices at low Reynolds numbers; net drag reduction device systems for entire aerodynamic configurations are nevertheless noted to remain elusive. Evidence has emerged for dramatic alterations of the structure of a turbulent boundary layer which persist for long distances downstream and reduce wall shear as a results of any one of several theoretically possible mechanisms. Reduced effectiveness at high Reynolds numbers may, however, limit the applicability of outer-layer manipulators to practical aircraft drag reduction.

Atomistic Modeling of the Fluid-Solid Interface in Simple Fluids

NASA Astrophysics Data System (ADS)

Hadjiconstantinou, Nicolas; Wang, Gerald

2017-11-01

Fluids can exhibit pronounced structuring effects near a solid boundary, typically manifested in a layered structure that has been extensively shown to directly affect transport across the interface. We present and discuss several results from molecular-mechanical modeling and molecular-dynamics (MD) simulations aimed at characterizing the structure of the first fluid layer directly adjacent to the solid. We identify a new dimensionless group - termed the Wall number - which characterizes the degree of fluid layering, by comparing the competing effects of wall-fluid interaction and thermal energy. We find that in the layering regime, several key features of the first layer layer - including its distance from the solid, its width, and its areal density - can be described using mean-field-energy arguments, as well as asymptotic analysis of the Nernst-Planck equation. For dense fluids, the areal density and the width of the first layer can be related to the bulk fluid density using a simple scaling relation. MD simulations show that these results are broadly applicable and robust to the presence of a second confining solid boundary, different choices of wall structure and thermalization, strengths of fluid-solid interaction, and wall geometries.

Diagnosis of boundary-layer circulations.

PubMed

Beare, Robert J; Cullen, Michael J P

2013-05-28

Diagnoses of circulations in the vertical plane provide valuable insights into aspects of the dynamics of the climate system. Dynamical theories based on geostrophic balance have proved useful in deriving diagnostic equations for these circulations. For example, semi-geostrophic theory gives rise to the Sawyer-Eliassen equation (SEE) that predicts, among other things, circulations around mid-latitude fronts. A limitation of the SEE is the absence of a realistic boundary layer. However, the coupling provided by the boundary layer between the atmosphere and the surface is fundamental to the climate system. Here, we use a theory based on Ekman momentum balance to derive an SEE that includes a boundary layer (SEEBL). We consider a case study of a baroclinic low-level jet. The SEEBL solution shows significant benefits over Ekman pumping, including accommodating a boundary-layer depth that varies in space and structure, which accounts for buoyancy and momentum advection. The diagnosed low-level jet is stronger than that determined by Ekman balance. This is due to the inclusion of momentum advection. Momentum advection provides an additional mechanism for enhancement of the low-level jet that is distinct from inertial oscillations.

Nonlinear Transient Growth and Boundary Layer Transition

NASA Technical Reports Server (NTRS)

Paredes, Pedro; Choudhari, Meelan M.; Li, Fei

2016-01-01

Parabolized stability equations (PSE) are used in a variational approach to study the optimal, non-modal disturbance growth in a Mach 3 at plate boundary layer and a Mach 6 circular cone boundary layer. As noted in previous works, the optimal initial disturbances correspond to steady counter-rotating streamwise vortices, which subsequently lead to the formation of streamwise-elongated structures, i.e., streaks, via a lift-up effect. The nonlinear evolution of the linearly optimal stationary perturbations is computed using the nonlinear plane-marching PSE for stationary perturbations. A fully implicit marching technique is used to facilitate the computation of nonlinear streaks with large amplitudes. To assess the effect of the finite-amplitude streaks on transition, the linear form of plane- marching PSE is used to investigate the instability of the boundary layer flow modified by spanwise periodic streaks. The onset of bypass transition is estimated by using an N- factor criterion based on the amplification of the streak instabilities. Results show that, for both flow configurations of interest, streaks of sufficiently large amplitude can lead to significantly earlier onset of transition than that in an unperturbed boundary layer without any streaks.

Physics of magnetospheric boundary layers

NASA Technical Reports Server (NTRS)

Cairns, I. H.

1993-01-01

The central ideas of this grant are that the magnetospheric boundary layers link disparate regions of the magnetosphere together, and the global behavior of the magnetosphere can be understood only by understanding the linking mechanisms. Accordingly the present grant includes simultaneous research on the global, meso-, and micro-scale physics of the magnetosphere and its boundary layers. These boundary layers include the bow shock, magnetosheath, the plasma sheet boundary layer, and the ionosphere. Analytic, numerical and simulation projects have been performed on these subjects, as well as comparison of theoretical results with observational data. Very good progress has been made, with four papers published or in press and two additional papers submitted for publication during the six month period 1 June - 30 November 1993. At least two projects are currently being written up. In addition, members of the group have given papers at scientific meetings. The further structure of this report is as follows: section two contains brief accounts of research completed during the last six months, while section three describes the research projects intended for the grant's final period.

An Experimental Investigation of Forced Mixing of a Turbulent Boundary Layer in an Annular Diffuser. Ph.D. Thesis - Ohio State Univ.; [for boundary layer control

NASA Technical Reports Server (NTRS)

Shaw, R. J.

1979-01-01

The forced mixing process of a turbulent boundary layer in an axisymmetric annular diffuser using conventional wing-like vortex generators was studied. Flow field measurements were made at four axial locations downstream of the vortex generators. At each axial location, a total of 25 equally spaced profiles were measured behind three consecutive vortex generators which formed two pairs of vortex generators. Hot film anemometry probes measured the boundary layer turbulence structure at the same locations where pressure measurements were made. Both single and cross film probes were used. The diffuser turbulence data was teken only for a nominal inlet Mach number of 0.3. Three vortex generator configurations were tested. The differences between configurations involved changes in size and relative vortex generator positions. All three vortex generator configurations tested provided increases in diffuser performance. Distinct differences in the boundary layer integral properties and skin friction levels were noted between configurations. The axial turbulence intensity and Reynolds stress profiles measured displayed similarities in trends but differences in levels for the three configurations.

Characterization of structural response to hypersonic boundary-layer transition

DOE PAGES

Riley, Zachary B.; Deshmukh, Rohit; Miller, Brent A.; ...

2016-05-24

The inherent relationship between boundary-layer stability, aerodynamic heating, and surface conditions makes the potential for interaction between the structural response and boundary-layer transition an important and challenging area of study in high-speed flows. This paper phenomenologically explores this interaction using a fundamental two-dimensional aerothermoelastic model under the assumption of an aluminum panel with simple supports. Specifically, an existing model is extended to examine the impact of transition onset location, transition length, and transitional overshoot in heat flux and fluctuating pressure on the structural response of surface panels. Transitional flow conditions are found to yield significantly increased thermal gradients, and theymore » can result in higher maximum panel temperatures compared to turbulent flow. Results indicate that overshoot in heat flux and fluctuating pressure reduces the flutter onset time and increases the strain energy accumulated in the panel. Furthermore, overshoot occurring near the midchord can yield average temperatures and peak displacements exceeding those experienced by the panel subject to turbulent flow. Lastly, these results suggest that fully turbulent flow does not always conservatively predict the thermo-structural response of surface panels.« less

Mineralogy of Cretaceous/Tertiary boundary clays in the Chicxulub structure in northern Yucatan

NASA Technical Reports Server (NTRS)

Ming, D. W.; Sharpton, Virgil L.; Schuraytz, B. C.

1991-01-01

The Cretaceous/Tertiary (K/T) boundary clay layer is thought to be derived from ejecta material from meteorite impact, based on the anomalous concentrations of noble metals in the layer. Because of recent findings of a half-meter thick ejecta deposit at the K/T boundary in Haiti, efforts have focused on locating a large impact feature in the Caribbean and the Gulf of Mexico. One of the leading candidates for the site of a large impact is the Chicxulub structure located on the northern Yucatan Peninsula in Mexico. The Chicxulub structure is a subsurface zone of upper Cretaceous igneous rocks, carbonates, and breccias. The structure has been interpreted to be a 200 km diameter; however, there is some question to the size of the structure or to the fact that it even is an impact feature. Little is known about the mineralogy of this structure; the objective of this study was to determine the clay mineralogy of core samples from within the Chicxulub structure.

Effects of local and global mechanical distortions to hypervelocity boundary layers

NASA Astrophysics Data System (ADS)

Flaherty, William P.

The response of hypervelocity boundary layers to global mechanical distortions due to concave surface curvature is examined. Surface heat transfer, visual boundary layer thickness, and pressure sensitive paint (PSP) data are obtained for a suite of models with different concave surface geometries. Results are compared to predictions using existing approximate methods. Near the leading edge, good agreement is observed, but at larger pressure gradients, predictions diverge significantly from the experimental data. Up to a factor of five underprediction is reported in regions with greatest distortion. Curve fits to the experimental data are compared with surface equations. It is demonstrated that reasonable estimates of the laminar heat flux augmentation may be obtained as a function of the local turning angle for all model geometries, even at the conditions of greatest distortion. As a means of introducing additional local distortions, vortex generators are used to impose streamwise structures into the boundary layer. The response of the large scale vortical structures to an adverse pressure gradient is investigated. For a flat plate baseline case, heat transfer augmentation at similar levels to turbulent flow is measured. For the concave geometries, increases in heat transfer by factors up to 2.6 are measured over the laminar values, though for higher turning angle cases, a relaxation to below undisturbed values is reported at turning angles between 10 and 15 degrees. The scaling of heat transfer with turning angle that is identified for the laminar boundary layer response is found to be robust even in the presence of the imposed vortex structures. PSP measurements indicated that natural streaks form over concave models even when imposed vorticity is present. Correlations found between the heat transfer and natural streak formation are discussed and indicate possible vortex interactions.

Vertical structure of aeolian turbulence in a boundary layer with sand transport

NASA Astrophysics Data System (ADS)

Lee, Zoe S.; Baas, Andreas C. W.

2016-04-01

Recently we have found that Reynolds shear stress shows a significant variability with measurement height (Lee and Baas, 2016), and so an alternative parameter for boundary layer turbulence may help to explain the relationship between wind forcing and sediment transport. We present data that were collected during a field study of boundary layer turbulence conducted on a North Atlantic beach. High-frequency (50 Hz) 3D wind velocity measurements were collected using ultrasonic anemometry at thirteen different measurement heights in a tight vertical array between 0.11 and 1.62 metres above the surface. Thanks to the high density installation of sensors a detailed analysis of the boundary layer flow can be conducted using methods more typically used in studies where data is only available from one or just a few measurement heights. We use quadrant analysis to explore the vertical structure of turbulence and track the changes in quadrant signatures with measurement elevation and over time. Results of quadrant analysis, at the 'raw' 50 Hz timescale, demonstrates the tendency for event clustering across all four quadrants, which implies that at-a-point quadrant events are part of larger-scale turbulent structures. Using an HSV colour model, applied to the quadrant analysis data and plotted in series, we create colour maps of turbulence, which can provide a clear visualisation of the clustering of event activity at each height and illustrate the shape of the larger coherent flow structures that are present within the boundary layer. By including a saturation component to the colour model, the most significant stress producing sections of the data are emphasised. This results in a 'banded' colour map, which relates to clustering of quadrant I (Outward Interaction) and quadrant IV (Sweep) activity, separate from clustering of quadrant II (Burst) and quadrant III (Inward Interaction). Both 'sweep-type' and 'burst-type' sequences are shown to have a diagonal structure originating from the top of the boundary layer, indicating a downwards direction of eddy motion. While directionality of turbulence cannot be definitively determined, our results indicate that the top-down turbulence model is a suitable explanation, further supported by the presence of 'incomplete' eddies which originate at higher elevations but fail to extend to the surface. This provides the first evidence in support of a top down turbulence model as observed in aeolian geomorphology, and we present preliminary findings on its relationship to sand transport activity. Lee, Z.S., Baas, A.C.W. (2016) Variable and conflicting shear stress estimates inside a boundary layer with sediment transport. Earth Surface Processes and Landforms; DOI: 10.1002/esp.3829

Global stability analysis of axisymmetric boundary layer over a circular cylinder

NASA Astrophysics Data System (ADS)

Bhoraniya, Ramesh; Vinod, Narayanan

2018-05-01

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

A boundary condition for layer to level ocean model interaction

NASA Astrophysics Data System (ADS)

Mask, A.; O'Brien, J.; Preller, R.

2003-04-01

A radiation boundary condition based on vertical normal modes is introduced to allow a physical transition between nested/coupled ocean models that are of differing vertical structure and/or differing physics. In this particular study, a fine resolution regional/coastal sigma-coordinate Naval Coastal Ocean Model (NCOM) has been successfully nested to a coarse resolution (in the horizontal and vertical) basin scale NCOM and a coarse resolution basin scale Navy Layered Ocean Model (NLOM). Both of these models were developed at the Naval Research Laboratory (NRL) at Stennis Space Center, Mississippi, USA. This new method, which decomposes the vertical structure of the models into barotropic and baroclinic modes, gives improved results in the coastal domain over Orlanski radiation boundary conditions for the test cases. The principle reason for the improvement is that each mode has the radiation boundary condition applied individually; therefore, the packet of information passing through the boundary is allowed to have multiple phase speeds instead of a single-phase speed. Allowing multiple phase speeds reduces boundary reflections, thus improving results.

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.

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.

Impact of interfacial imperfection on transverse wave in a functionally graded piezoelectric material structure with corrugated boundaries

NASA Astrophysics Data System (ADS)

Kumar Singh, Abhishek; Kumar, Santan; Kumari, Richa

2018-03-01

The propagation behavior of Love-type wave in a corrugated functionally graded piezoelectric material layered structure has been taken into account. Concretely, the layered structure incorporates a corrugated functionally graded piezoelectric material layer imperfectly bonded to a functionally graded piezoelectric material half-space. An analytical treatment has been employed to determine the dispersion relation for both cases of electrically open condition and electrically short condition. The phase velocity of the Love-type wave has been computed numerically and its dependence on the wave number has been depicted graphically for a specific type of corrugated boundary surfaces for both said conditions. The crux of the study lies in the fact that the imperfect bonding of the interface, the corrugated boundaries present in the layer, and the material properties of the layer and the half-space strongly influence the phase velocity of the Love-type wave. It can be remarkably noted that the imperfect bonding of the interface reduces the phase velocity of the Love-type wave significantly. As a special case of the problem, it is noticed that the procured dispersion relation for both cases of electrically open and electrically short conditions is in accordance with the classical Love wave equation.

Si-Doping Effects in Cu(In,Ga)Se2 Thin Films and Applications for Simplified Structure High-Efficiency Solar Cells.

PubMed

Ishizuka, Shogo; Koida, Takashi; Taguchi, Noboru; Tanaka, Shingo; Fons, Paul; Shibata, Hajime

2017-09-13

We found that elemental Si-doped Cu(In,Ga)Se 2 (CIGS) polycrystalline thin films exhibit a distinctive morphology due to the formation of grain boundary layers several tens of nanometers thick. The use of Si-doped CIGS films as the photoabsorber layer in simplified structure buffer-free solar cell devices is found to be effective in enhancing energy conversion efficiency. The grain boundary layers formed in Si-doped CIGS films are expected to play an important role in passivating CIGS grain interfaces and improving carrier transport. The simplified structure solar cells, which nominally consist of only a CIGS photoabsorber layer and a front transparent and a back metal electrode layer, demonstrate practical application level solar cell efficiencies exceeding 15%. To date, the cell efficiencies demonstrated from this type of device have remained relatively low, with values of about 10%. Also, Si-doped CIGS solar cell devices exhibit similar properties to those of CIGS devices fabricated with post deposition alkali halide treatments such as KF or RbF, techniques known to boost CIGS device performance. The results obtained offer a new approach based on a new concept to control grain boundaries in polycrystalline CIGS and other polycrystalline chalcogenide materials for better device performance.

Nonlinear stability of non-stationary cross-flow vortices in compressible boundary layers

NASA Technical Reports Server (NTRS)

Gajjar, J. S. B.

1995-01-01

The nonlinear evolution of long wavelength non-stationary cross-flow vortices in a compressible boundary layer is investigated and the work extends that of Gajjar (1994) to flows involving multiple critical layers. The basic flow profile considered in this paper is that appropriate for a fully three-dimensional boundary layer with O(1) Mach number and with wall heating or cooling. The governing equations for the evolution of the cross-flow vortex are obtained and some special cases are discussed. One special case includes linear theory where exact analytic expressions for the growth rate of the vortices are obtained. Another special case is a generalization of the Bassom & Gajjar (1988) results for neutral waves to compressible flows. The viscous correction to the growth rate is derived and it is shown how the unsteady nonlinear critical layer structure merges with that for a Haberman type of viscous critical layer.

Flow-around modes for a rhomboid wing with a stall vortex in the shock layer

NASA Astrophysics Data System (ADS)

Zubin, M. A.; Maximov, F. A.; Ostapenko, N. A.

2017-12-01

The results of theoretical and experimental investigation of an asymmetrical hypersonic flow around a V-shaped wing with the opening angle larger than π on the modes with attached shockwaves on forward edges, when the stall flow is implemented on the leeward wing cantilever behind the kink point of the cross contour. In this case, a vortex of nonviscous nature is formed in which the velocities on the sphere exceeding the speed of sound and resulting in the occurrence of pressure shocks with an intensity sufficient for the separation of the turbulent boundary layer take place in the reverse flow according to the calculations within the framework of the ideal gas. It is experimentally established that a separation boundary layer can exist in the reverse flow, and its structure is subject to the laws inherent to the reverse flow in the separation region of the turbulent boundary layer arising in the supersonic conic flow under the action of a shockwave incident to the boundary layer.

Smooth- and rough-wall boundary layer structure from high spatial range particle image velocimetry

NASA Astrophysics Data System (ADS)

Squire, D. T.; Morrill-Winter, C.; Hutchins, N.; Marusic, I.; Schultz, M. P.; Klewicki, J. C.

2016-10-01

Two particle image velocimetry arrangements are used to make true spatial comparisons between smooth- and rough-wall boundary layers at high Reynolds numbers across a very wide range of streamwise scales. Together, the arrangements resolve scales ranging from motions on the order of the Kolmogorov microscale to those longer than twice the boundary layer thickness. The rough-wall experiments were obtained above a continuous sandpaper sheet, identical to that used by Squire et al. [J. Fluid Mech. 795, 210 (2016), 10.1017/jfm.2016.196], and cover a range of friction and equivalent sand-grain roughness Reynolds numbers (12 000 ≲δ+≲ 18000, 62 ≲ks+≲104 ). The smooth-wall experiments comprise new and previously published data spanning 6500 ≲δ+≲17 000 . Flow statistics from all experiments show similar Reynolds number trends and behaviors to recent, well-resolved hot-wire anemometry measurements above the same rough surface. Comparisons, at matched δ+, between smooth- and rough-wall two-point correlation maps and two-point magnitude-squared coherence maps demonstrate that spatially the outer region of the boundary layer is the same between the two flows. This is apparently true even at wall-normal locations where the total (inner-normalized) energy differs between the smooth and rough wall. Generally, the present results provide strong support for Townsend's [The Structure of Turbulent Shear Flow (Cambridge University Press, Cambridge, 1956), Vol. 1] wall-similarity hypothesis in high Reynolds number fully rough boundary layer flows.

Spectral structure and linear mechanisms in a 'rapidly' distorted boundary layer

NASA Astrophysics Data System (ADS)

Diwan, Sourabh; Morrison, Jonathan

2016-11-01

A characteristic feature of a turbulent boundary layer (TBL) at high Reynolds numbers is the presence of coherent motions such as the 'large scale motions' and 'superstructures'. In this work we attempt to mimic such coherent motions and their spectral structure using a simplified experimental arrangement of a boundary layer flow over a flat plate subjected to grid-generated turbulence and/or localized patch of surface roughness. The velocity measurements done downstream of a grit roughness patch (in absence of grid turbulence) show that over a certain distance the energy spectrum of streamwise velocity fluctuations shows a bi-modal shape which resembles that found in a high-Re TBL. We also carry out experiments with both grid turbulence and grit roughness present and show that it is possible to 'synthesize' the structure of a TBL in the wall-normal direction, in the limited context of streamwise coherent motions, using the present experimental design. These results indicate that the predictions of the Rapid Distortion Theory (RDT) can be applied to the present case in a region close to the plate leading edge, and we examine the linearized effects of 'blocking' and 'shear' on turbulent fluctuations near the edge of the boundary layer and close to the wall in the framework of the RDT. We acknowledge financial support from EPSRC (Grant No. EP/1037938).

Mantle plumes - A boundary layer approach for Newtonian and non-Newtonian temperature-dependent rheologies. [modeling for island chains and oceanic aseismic ridges

NASA Technical Reports Server (NTRS)

Yuen, D. A.; Schubert, G.

1976-01-01

Stress is placed on the temperature dependence of both a linear Newtonian rheology and a nonlinear olivine rheology in accounting for narrow mantle flow structures. The boundary-layer theory developed incorporates an arbitrary temperature-dependent power-law rheology for the medium, in order to facilitate the study of mantle plume dynamics under real conditions. Thermal, kinematic, and dynamic structures of mantle plumes are modelled by a two-dimensional natural-convection boundary layer rising in a fluid with a temperature-dependent power-law relationship between shear stress and strain rate. An analytic similarity solution is arrived at for upwelling adjacent to a vertical isothermal stress-free plane. Newtonian creep as a deformation mechanism, thermal anomalies resulting from chemical heterogeneity, the behavior of plumes in non-Newtonian (olivine) mantles, and differences in the dynamics of wet and dry olivine are discussed.

The relationship between surface topography, gravity anomalies, and temperature structure of convection

NASA Technical Reports Server (NTRS)

Parsons, B.; Daly, S.

1983-01-01

Consideration is given to the relationship between the temperature structure of mantle convection and the resulting surface topography and gravity anomalies, which are used in its investigation. Integral expressions relating the three variables as a function of wavelength are obtained with the use of Green's function solutions to the equations of motion for the case of constant-viscosity convection in a plane layer subject to a uniform gravitational field. The influence of the boundary conditions, particularly at large wavelengths, is pointed out, and surface topographies and gravity produced by convection are illustrated for a number of simple temperature distributions. It is shown that the upper thermal boundary layer plays an important role in determining the surface observables, while temperatures near the bottom of the layer affect mainly that boundary. This result is consistent with an explanation of geoid anomalies over mid-ocean swells in terms of convection beneath the lithosphere.

Stably Stratified Atmospheric Boundary Layers

NASA Astrophysics Data System (ADS)

Mahrt, L.

2014-01-01

Atmospheric boundary layers with weak stratification are relatively well described by similarity theory and numerical models for stationary horizontally homogeneous conditions. With common strong stratification, similarity theory becomes unreliable. The turbulence structure and interactions with the mean flow and small-scale nonturbulent motions assume a variety of scenarios. The turbulence is intermittent and may no longer fully satisfy the usual conditions for the definition of turbulence. Nonturbulent motions include wave-like motions and solitary modes, two-dimensional vortical modes, microfronts, intermittent drainage flows, and a host of more complex structures. The main source of turbulence may not be at the surface, but rather may result from shear above the surface inversion. The turbulence is typically not in equilibrium with the nonturbulent motions, sometimes preventing the formation of an inertial subrange. New observational and analysis techniques are expected to advance our understanding of the very stable boundary layer.

Predicting boundary shear stress and sediment transport over bed forms

USGS Publications Warehouse

McLean, S.R.; Wolfe, S.R.; Nelson, J.M.

1999-01-01

To estimate bed-load sediment transport rates in flows over bed forms such as ripples and dunes, spatially averaged velocity profiles are frequently used to predict mean boundary shear stress. However, such averaging obscures the complex, nonlinear interaction of wake decay, boundary-layer development, and topographically induced acceleration downstream of flow separation and often leads to inaccurate estimates of boundary stress, particularly skin friction, which is critically important in predicting bed-load transport rates. This paper presents an alternative methodology for predicting skin friction over 2D bed forms. The approach is based on combining the equations describing the mechanics of the internal boundary layer with semiempirical structure functions to predict the velocity at the crest of a bedform, where the flow is most similar to a uniform boundary layer. Significantly, the methodology is directed toward making specific predictions only at the bed-form crest, and as a result it avoids the difficulty and questionable validity of spatial averaging. The model provides an accurate estimate of the skin friction at the crest where transport rates are highest. Simple geometric constraints can be used to derive the mean transport rates as long as bed load is dominant.To estimate bed-load sediment transport rates in flows over bed forms such as ripples and dunes, spatially averaged velocity profiles are frequently used to predict mean boundary shear stress. However, such averaging obscures the complex, nonlinear interaction of wake decay, boundary-layer development, and topographically induced acceleration downstream of flow separation and often leads to inaccurate estimates of boundary stress, particularly skin friction, which is critically important in predicting bed-load transport rates. This paper presents an alternative methodology for predicting skin friction over 2D bed forms. The approach is based on combining the equations describing the mechanics of the internal boundary layer with semiempirical structure functions to predict the velocity at the crest of a bedform, where the flow is most similar to a uniform boundary layer. Significantly, the methodology is directed toward making specific predictions only at the bed-form crest, and as a result it avoids the difficulty and questionable validity of spatial averaging. The model provides an accurate estimate of the skin friction at the crest where transport rates are highest. Simple geometric constraints can be used to derive the mean transport rates as long as bed load is dominant.

Magnetopause structure from satellite observations

NASA Technical Reports Server (NTRS)

Sonnerup, B. U. O.

1979-01-01

Observations on magnetopause structure are reported. Major topics covered include: classical reconnection, transport mechanisms, magnetospheric boundary layers, tearing modes, and Jupiter's magnetopause.

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

PubMed

Widmann, Alexander; Tropea, Cameron

2017-02-06

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

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

PubMed Central

Tropea, Cameron

2017-01-01

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

Localized rotating convection with no-slip boundary conditions

NASA Astrophysics Data System (ADS)

Beaume, Cédric; Kao, Hsien-Ching; Knobloch, Edgar; Bergeon, Alain

2013-12-01

Localized patches of stationary convection embedded in a background conduction state are called convectons. Multiple states of this type have recently been found in two-dimensional Boussinesq convection in a horizontal fluid layer with stress-free boundary conditions at top and bottom, and rotating about the vertical. The convectons differ in their lengths and in the strength of the self-generated shear within which they are embedded, and exhibit slanted snaking. We use homotopic continuation of the boundary conditions to show that similar structures exist in the presence of no-slip boundary conditions at the top and bottom of the layer and show that such structures exhibit standard snaking. The homotopic continuation allows us to study the transformation from slanted snaking characteristic of systems with a conserved quantity, here the zonal momentum, to standard snaking characteristic of systems with no conserved quantity.

Effects of air pollution on thermal structure and dispersion in an urban planetary boundary layer

NASA Technical Reports Server (NTRS)

Viskanta, R.; Johnson, R. O.; Bergstrom, R. W.

1977-01-01

The short-term effects of urbanization and air pollution on the transport processes in the urban planetary boundary layer (PBL) are studied. The investigation makes use of an unsteady two-dimensional transport model which has been developed by Viskanta et al., (1976). The model predicts pollutant concentrations and temperature in the PBL. The potential effects of urbanization and air pollution on the thermal structure in the urban PBL are considered, taking into account the results of numerical simulations modeling the St. Louis, Missouri metropolitan area.

Fluid-membrane tethers: minimal surfaces and elastic boundary layers.

PubMed

Powers, Thomas R; Huber, Greg; Goldstein, Raymond E

2002-04-01

Thin cylindrical tethers are common lipid bilayer membrane structures, arising in situations ranging from micromanipulation experiments on artificial vesicles to the dynamic structure of the Golgi apparatus. We study the shape and formation of a tether in terms of the classical soap-film problem, which is applied to the case of a membrane disk under tension subject to a point force. A tether forms from the elastic boundary layer near the point of application of the force, for sufficiently large displacement. Analytic results for various aspects of the membrane shape are given.

Boundary Layer Structure and Its Relation to Precipitation Over the St. Louis Area.

DTIC Science & Technology

1980-10-01

of METEORO LOGY SECTION 0i{1J ( 0I~) AT THE mp UNI VERSITY OV ILLINOIS0 SMISContract Report 241 T - BOUNDARY LAYER STRUCTURE AND ITS RELATION TO...PRECIPITATION OVER THE ST. LOUIS AREA Gary L. Achtemeier Meteorology Section Ill1inois State Water &uIvey, DTII CLeELEC T E C.> JAN 15 1981( Technical...in f r ’TNil PA&F rlhImm Does Rnteredl 𔄃. -. , .’.-..,. -.- -/" . ECumITYv CLASSFICATIOW Of TH t PAGE(Wfhn Date Entr,.e) 15529. 4-GS ?0. ABSTRACT

Observations of the Early Evening Boundary-Layer Transition Using a Small Unmanned Aerial System

NASA Astrophysics Data System (ADS)

Bonin, Timothy; Chilson, Phillip; Zielke, Brett; Fedorovich, Evgeni

2013-01-01

The evolution of the lower portion of the planetary boundary layer is investigated using the Small Multifunction Research and Teaching Sonde (SMARTSonde), an unmanned aerial vehicle developed at the University of Oklahoma. The study focuses on the lowest 200 m of the atmosphere, where the most noticeable thermodynamic changes occur during the day. Between October 2010 and February 2011, a series of flights was conducted during the evening hours on several days to examine the vertical structure of the lower boundary layer. Data from a nearby Oklahoma Mesonet tower was used to supplement the vertical profiles of temperature, humidity, and pressure, which were collected approximately every 30 min, starting 2 h before sunset and continuing until dusk. From the profiles, sensible and latent heat fluxes were estimated. These fluxes were used to diagnose the portion of the boundary layer that was most affected by the early evening transition. During the transition period, a shallow cool and moist layer near the ground was formed, and as the evening progressed the cooling affected an increasingly shallower layer just above the surface.

FIRE aircraft observations of horizontal and vertical transport in marine stratocumulus

NASA Technical Reports Server (NTRS)

Paluch, Ilga R.; Lenschow, Donald H.

1990-01-01

A major goal of research on marine stratocumulus is to try to understand the processes that generate and dissipate them. One approach to studying this problem is to investigate the boundary layer structure in the vicinity of a transition from a cloudy to a cloud-free region to document the differences in structure on each side of the transition. Since stratiform clouds have a major impact on the radiation divergence in the boundary layer, the transition from a cloudy to a clear boundary layer is a region of large horizontal inhomogeneity in air temperature and turbulence intensity. This leads to a considerable difference in horizontal and vertical transports between the cloudy and cloud-free regions. Measurements are used from the NCAR Electra aircraft during flights 5 (7 July 1987) and 10 (18 July 1987) of FIRE for this purpose. Flight 5 coincided with a LANDSAT overflight, and was designed to investigate the transition across a well-defined N-S cloud boundary, since the LANDSAT image can document the cloud cover in considerable detail. Turbulence legs were flown about 60 km on both sides of the cloud boundary. Flight 10 was flown at night in an area of scattered small cumuli and broken cloud patches.

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.

Atomic migration of carbon in hard turned layers of carburized bearing steel

DOE PAGES

Bedekar, Vikram; Poplawsky, Jonathan D.; Guo, Wei; ...

2016-01-01

In grain finement and non-equilibrium there is carbon segregation within grain boundaries alters the mechanical performance of hard turning layers in carburized bearing steel. Moreover, an atom probe tomography (APT) study on the nanostructured hard turning layers reveals carbon migration to grain boundaries as a result of carbide decomposition during severe plastic deformation. In addition, samples exposed to different cutting speeds show that the carbon migration rate increases with the cutting speed. For these two effects lead to an ultrafine carbon network structure resulting in increased hardness and thermal stability in the severely deformed surface layer.

Bending Boundary Layers in Laminated-Composite Circular Cylindrical Shells

NASA Technical Reports Server (NTRS)

Nemeth, Michael P.; Smeltzer, Stanley S., III

2000-01-01

An analytical, parametric study of the attenuation of bending boundary layers or edge effects in balanced and unbalanced, symmetrically and unsymmetrically laminated thin cylindrical shells is presented for nine contemporary material systems. The analysis is based on the linear Sanders-Koiter shell equations and specializations to the Love-Kirchhoff shell equations and Donnell's equations are included. Two nondimensional parameters are identified that characterize and quantify the effects of laminate orthotropy and laminate anisotropy on the bending boundary-layer decay length in a very general and encompassing manner. A substantial number of structural design technology results are presented for a wide range of laminated-composite cylinders. For all the laminate constructions considered, the results show that the differences between results that were obtained with the Sanders-Koiter shell equations, the Love-Kirchhoff shell equations, and Donnell's equations are negligible. The results also show that the effect of anisotropy in the form of coupling between pure bending and twisting has a negligible effect on the size of the bending boundary-layer decay length of the balanced, symmetrically laminated cylinders considered. Moreover, the results show that coupling between the various types of shell anisotropies has a negligible effect on the calculation of the bending boundary-layer decay length in most cases. The results also show that in some cases neglecting the shell anisotropy results in underestimating the bending boundary-layer decay length and in other cases it results in an overestimation.

Further studies of turbulence structure resulting from interactions between embedded vortices and wall jets at high blowing ratios

NASA Astrophysics Data System (ADS)

Doner, William D.

1989-12-01

Interactions of wall jets and vortices embedded in turbulent layers commonly occur near gas turbine blades and endwalls where film cooling is employed. These interactions frequently result in undesirable heat transfer effects at blade and endwall surfaces. In this thesis, a crossed hot-wire probe is used to measure the turbulence structure resulting from this type of interaction. The vortex is generated using a half delta-wing vortex generator mounted 12 deg with respect to a 10 m/s mean velocity flow over a flat plate. A single injection hole, 0.95 cm in diameter, inclined 30 deg to the horizontal, is positioned 59.3 cm downstream of the vortex generator. The vortex generator is positioned so that vortex upwash and downwash could be located over the injection hole. Streamwise development of the turbulent boundary layer was investigated for the following cases: (1) boundary layer with jet only (m = 1.5), and (2) boundary layer with vortex only. Measurement of interaction between the boundary layer, vortex upwash, and the wall jet was made at one station with various blowing ratios. At low blowing ratios (m = 0.5 and 1.5) the vortex dominates the flow. Significant alterations to the turbulent structure are seen in the Reynolds stress components, vorticity distributions and mean velocities. At higher blowing ratios (m = 2.5 and 3.5) the jet dominates the flow, the vortex is blown away from the wall, and its turbulence effects are dispersed over a larger area.

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.

Experimental investigation of the micro-ramp based shock wave and turbulent boundary layer interaction control

NASA Astrophysics Data System (ADS)

Bo, Wang; Weidong, Liu; Yuxin, Zhao; Xiaoqiang, Fan; Chao, Wang

2012-05-01

Using a nanoparticle-based planar laser-scattering technique and supersonic particle image velocimetry, we investigated the effects of micro-ramp control on incident shockwave and boundary-layer interaction (SWBLI) in a low-noise supersonic wind-tunnel with Mach number 2.7 and Reynolds number Rθ = 5845. High spatiotemporal resolution wake structures downstream of the micro-ramps were detected, while a complex evolution process containing a streamwise counter-rotating vortex pair and large-scale hairpin-like vortices with Strouhal number Stδ of about 0.5-0.65 was revealed. The large-scale structures could survive while passing through the SWBLI region. Reflected shockwaves are clearly seen to be distorted accompanied by high-frequency fluctuations. Micro-ramp applications have a distinct influence on flow patterns of the SWBLI field that vary depending on spanwise locations. Both the shock foot and separation line exhibit undulations corresponding with modifications of the velocity distribution of the incoming boundary layer. Moreover, by energizing parts of the boundary flow, the micro-ramp is able to dampen the separation.

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.

Tectonic plates, D (double prime) thermal structure, and the nature of mantle plumes

NASA Technical Reports Server (NTRS)

Lenardic, A.; Kaula, W. M.

1994-01-01

It is proposed that subducting tectonic plates can affect the nature of thermal mantle plumes by determining the temperature drop across a plume source layer. The temperature drop affects source layer stability and the morphology of plumes emitted from it. Numerical models are presented to demonstrate how introduction of platelike behavior in a convecting temperature dependent medium, driven by a combination of internal and basal heating, can increase the temperature drop across the lower boundary layer. The temperature drop increases dramatically following introduction of platelike behavior due to formation of a cold temperature inversion above the lower boundary layer. This thermal inversion, induced by deposition of upper boundary layer material to the system base, decays in time, but the temperature drop across the lower boundary layer always remains considerably higher than in models lacking platelike behavior. On the basis of model-inferred boundary layer temperature drops and previous studies of plume dynamics, we argue that generally accepted notions as to the nature of mantle plumes on Earth may hinge on the presence of plates. The implication for Mars and Venus, planets apparently lacking plate tectonics, is that mantle plumes of these planets may differ morphologically from those of Earth. A corollary model-based argument is that as a result of slab-induced thermal inversions above the core mantle boundary the lower most mantle may be subadiabatic, on average (in space and time), if major plate reorganization timescales are less than those acquired to diffuse newly deposited slab material.

Modelling of surface fluxes and Urban Boundary Layer over an old mediterannean city core

NASA Astrophysics Data System (ADS)

Lemonsu, A.; Masson, V.; Grimmond, Cs. B.

2003-04-01

In the frameworks of the UBL(Urban Boundary Layer)-ESCOMPTE campaign, the Town Energy Balance (TEB) model was run in off-line mode for Marseille. TEB's performance is evaluated with observations of surface temperatures and surface energy balance fluxes collected during the campaign. Parameterization improvements allow to better represent the energy exchanges between the air inside the canyon and the atmosphere above the roof level. Then, high resolution Méso-NH simulations are done to study the 3-D structure and the evolution of the Urban Boundary Layer (UBL) over Marseille. Will will give a special attention to the impact of the seabord effects (sea-breeze circulation) on the UBL.

An experimental investigation of the flow physics of high-lift systems

NASA Technical Reports Server (NTRS)

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

1995-01-01

This progress report, a series of viewgraphs, outlines experiments on the flow physics of confluent boundary layers for high lift systems. The design objective is to design high lift systems with improved C(sub Lmax) for landing approach and improved take-off L/D and simultaneously reduce acquisition and maintenance costs. In effect, achieve improved performance with simpler designs. The research objectives include: establish the role of confluent boundary layer flow physics in high-lift production; contrast confluent boundary layer structure for optimum and non-optimum C(sub L) cases; formation of a high quality, detailed archival data base for CFD/modeling; and examination of the role of relaminarization and streamline curvature.

Benthic boundary layer processes in the Lower Florida Keys

USGS Publications Warehouse

Lavoie, D.L.; Richardson, M.D.; Holmes, C.

1997-01-01

This special issue of Geo-Marine Letters, "Benthic Boundary Layer Processes in the Lower Florida Keys," includes 12 papers that present preliminary results from the Key West Campaign. The Dry Tortugas and Marquesas Keys test sites were selected by a group of 115 scientists and technicians to study benthic boundary layer processes in a carbonate environment controlled by bioturbation and biogeochemical processes. Major activities included remote sediment classification; high-frequency acoustic scattering experiments; sediment sampling for radiological, geotechnical, biological, biogeochemical, physical, and geoacoustic studies; and hydrodynamic studies using an instrumented tetrapod. All these data are being used to improve our understanding of the effects of environmental processes on sediment structure and behavior.

Study of the Structure of Turbulence in Accelerating Transitional Boundary Layers.

DTIC Science & Technology

1987-12-23

be sufficient to relaminarize even fully turbulent boundary layers. Since local heat transfer rates are very sensitive to the state of the boundary...was calibrated for velocity and angular sensitivity in a low- .’ turbulence 1 1/2-in. dia. jet flow for approximately twenty jet flow speeds "-’ ranging...intersection of the wires of the x. The angular sensitivity of the wires was assumed to conform to Champagne’s k2 law (Ref. 20), UE2 (0) = U2(0 = 0) (cos 2

Raman lidar characterization of PBL structure during COPS

NASA Astrophysics Data System (ADS)

Summa, D.; Di Girolamo, P.; Stelitano, D.; Di Iorio, T.

2012-04-01

The planetary boundary layer includes the portion of the atmosphere which is directly influenced by the presence of the Earth's surface. Aerosol particles trapped within the PBL can be used as tracers to study boundary-layer vertical structure and time variability. Aerosols can be dispersed out of the PBL during strong convection or temporary breaks of the capping temperature inversion. As a result of this, elastic backscatter signals collected by lidar systems can be used to determine the height and the internal structure of the PBL. Our analysis considers a method based on the first order derivative of the range-corrected elastic signal (RCS), which is a modified version of the method defined by Seibert et al. (2000) and Sicard et al. (2006). The analysis is focused on selected case studies collected by the Raman lidar system BASIL during the Convective and Orographically-induced Precipitation Study (COPS), held in Southern Germany and Eastern France in the period 01 June - 31 August 2007. Measurements were performed by the Raman lidar system BASIL, which was operational in Achern (Black Forest, Lat: 48.64 ° N, Long: 8.06 ° E, Elev.: 140 m). During COPS, BASIL collected more than 500 hours of measurements, distributed over 58 measurement days and 34 intensive observation periods (IOPs), covering both night-time and daytime and the transitions between the two. Therefore BASIL data during COPS represent a unique source of information for the study of the boundary layer structure and evolution. Potential temperature profiles obtained from the radiosonde data were used to get an additional estimate of the boundary layer height. Estimates of the PBL height and structure for specific case studies obtained from the lidar data and their comparison with estimates obtained from the radiosonde data will be illustrated and discussed at the Conference.

Spatiotemporal Variability in Observations of Urban Mixed-Layer Heights from Surface-based Lidar Systems during DISCOVER-AQ 2011

NASA Astrophysics Data System (ADS)

Lewis, J. R.; Banks, R. F.; Berkoff, T.; Welton, E. J.; Joseph, E.; Thompson, A. M.; Decola, P.; Hegarty, J. D.

2015-12-01

Accurate characterization of the planetary boundary layer height is crucial for numerical weather prediction, estimating pollution emissions and modeling air quality. More so, given the increasing trend in global urban populations, there is a growing need to improve our understanding of the urban boundary layer structure and development. The Deriving Information on Surface conditions from COlumn and VERtically resolved observations relevant to Air Quality (DISCOVER-AQ) 2011 field campaign, which took place in the Baltimore-Washington DC region, offered a unique opportunity to study boundary layer processes in an urban area using a geographically dense collection of surface-based lidar systems (see figure). Lidars use aerosols as tracers for atmospheric boundary layer dynamics with high vertical and temporal resolutions. In this study, we use data from two permanent Micropulse Lidar Network (MPLNET) sites and five field deployed Micropulse lidar (MPL) systems in order to observe spatiotemporal variations in the daytime mixed layer height. We present and compare lidar-derived retrievals of the mixed layer height using two different methods. The first method uses the wavelet covariance transform and a "fuzzy logic" attribution scheme in order to determine the mixed layer height. The second method uses an objective approach utilizing a time-adaptive extended Kalman filter. Independent measurements of the boundary layer height are obtained using profiles from ozonesonde launches at the Beltsville and Edgewood sites for comparison with lidar observations.

Ultra-Parameterized CAM: Progress Towards Low-Cloud Permitting Superparameterization

NASA Astrophysics Data System (ADS)

Parishani, H.; Pritchard, M. S.; Bretherton, C. S.; Khairoutdinov, M.; Wyant, M. C.; Singh, B.

2016-12-01

A leading source of uncertainty in climate feedback arises from the representation of low clouds, which are not resolved but depend on small-scale physical processes (e.g. entrainment, boundary layer turbulence) that are heavily parameterized. We show results from recent attempts to achieve an explicit representation of low clouds by pushing the computational limits of cloud superparameterization to resolve boundary-layer eddy scales relevant to marine stratocumulus (250m horizontal and 20m vertical length scales). This extreme configuration is called "ultraparameterization". Effects of varying horizontal vs. vertical resolution are analyzed in the context of altered constraints on the turbulent kinetic energy statistics of the marine boundary layer. We show that 250m embedded horizontal resolution leads to a more realistic boundary layer vertical structure, but also to an unrealistic cloud pulsation that cannibalizes time mean LWP. We explore the hypothesis that feedbacks involving horizontal advection (not typically encountered in offline LES that neglect this degree of freedom) may conspire to produce such effects and present strategies to compensate. The results are relevant to understanding the emergent behavior of quasi-resolved low cloud decks in a multi-scale modeling framework within a previously unencountered grey zone of better resolved boundary-layer turbulence.

Prediction of mean flow data for adiabatic 2-D compressible turbulent boundary layers

NASA Astrophysics Data System (ADS)

Motallebi, Fariborz

1995-02-01

This report presents a method for the prediction of mean flow data (i.e. , skin friction, velocity profile, and shape parameter) for adiabatic two-dimensional compressible turbulent boundary layers at zero pressure gradient. The transformed law of the wall, law of the wake, the van Driest model for the complete inner region, and a correlation between the Reynolds number based on the boundary layer integral length scale (Re(sub Delta*)) and the Reynolds number based on the boundary layer momentum thickness (Re(sub theta)) were used to predict the mean flow quantities. The results for skin friction coefficient show good agreement with a number of existing theories including those of van Driest and Huang et al. Comparison with a large number of experimental data suggests that at least for transonic and supersonic flows, the velocity profile as described by van Driest and Coles is Reynolds number dependent and should not be presumed universal. Extra information or perhaps a better physical approach to the formulation of the mean structure of compressible turbulent boundary layers, even in zero pressure gradient and adiabatic condition, is required in order to achieve complete (physical and mathematical) convergence when it is applied in any prediction methods.

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.

Shear-layer structures in near-wall turbulence

NASA Technical Reports Server (NTRS)

Johansson, A. V.; Alfredsson, P. H.; Kim, J.

1987-01-01

The structure of internal shear layer observed in the near-wall region of turbulent flows is investigated by analyzing flow fields obtained from numerical simulations of channel and boundary-layer flows. It is found that the shear layer is an important contributor to the turbulence production. The conditionally averaged production at the center of the structure was almost twice as large as the long-time mean value. The shear-layer structure is also found to retain its coherence over streamwise distances on the order of a thousand viscous length units, and propagates with a constant velocity of about 10.6 u sub rho throughout the near wall region.

Turbulent Transfer Between Street Canyons and the Overlying Atmospheric Boundary Layer

NASA Astrophysics Data System (ADS)

Salizzoni, Pietro; Marro, Massimo; Soulhac, Lionel; Grosjean, Nathalie; Perkins, Richard J.

2011-12-01

The turbulent exchange of momentum between a two-dimensional cavity and the overlying boundary layer has been studied experimentally, using hot-wire anemometry and particle image velocimetry (PIV). Conditions within the boundary layer were varied by changing the width of the canyons upstream of the test canyon, whilst maintaining the square geometry of the test canyon. The results show that turbulent transfer is due to the coupling between the instabilities generated in the shear layer above the canyons and the turbulent structures in the oncoming boundary layer. As a result, there is no single, unique velocity scale that correctly characterizes all the processes involved in the turbulent exchange of momentum across the boundary layer. Similarly, there is no single velocity scale that can characterize the different properties of the turbulent flow within the canyon, which depends strongly on the way in which turbulence from the outer flow is entrained into the cavity and carried round by the mean flow. The results from this study will be useful in developing simple parametrizations for momentum exchange in the urban canopy, in situations where the street geometry consists principally of relatively long, uniform streets arranged in grid-like patterns; they are unlikely to be applicable to sparse geometries composed of isolated three-dimensional obstacles.

Comparison of WRF local and nonlocal boundary layer Physics in Greater Kuala Lumpur, Malaysia

NASA Astrophysics Data System (ADS)

Ooi, M. C. G.; Chan, A.; Kumarenthiran, S.; Morris, K. I.; Oozeer, M. Y.; Islam, M. A.; Salleh, S. A.

2018-02-01

The urban boundary layer (UBL) is the internal advection layer of atmosphere above urban region which determines the exchanges of momentum, water and other atmospheric constituents between the urban land surface and the free troposphere. This paper tested the performance of three planetary boundary layer (PBL) physics schemes of Weather Research and Forecast (WRF) software to ensure the appropriate representation of vertical structure of UBL in Greater Kuala Lumpur (GKL). Comparison was conducted on the performance of respective PBL schemes to generate vertical and near-surface weather profile and rainfall. Mellor-Yamada- Janjíc (MYJ) local PBL scheme coupled with Eta MM5 surface layer scheme was found to predict the near-surface temperature and wind profile and mixing height better than the nonlocal schemes during the intermonsoonal period with least influences of the synoptic background weather.

Characteristics of Boundary Layer Structure during a Persistent Haze Event in the Central Liaoning City Cluster, Northeast China

NASA Astrophysics Data System (ADS)

Li, Xiaolan; Wang, Yangfeng; Shen, Lidu; Zhang, Hongsheng; Zhao, Hujia; Zhang, Yunhai; Ma, Yanjun

2018-04-01

The characteristics of boundary layer structure during a persistent regional haze event over the central Liaoning city cluster of Northeast China from 16 to 21 December 2016 were investigated based on the measurements of particulate matter (PM) concentration and the meteorological data within the atmospheric boundary layer (ABL). During the observational period, the maximum hourly mean PM2.5 and PM10 concentrations in Shenyang, Anshan, Fushun, and Benxi ranged from 276 to 355 μg m-3 and from 378 to 442 μg m-3, respectively, and the lowest hourly mean atmospheric visibility (VIS) in different cities ranged from 0.14 to 0.64 km. The central Liaoning city cluster was located in the front of a slowly moving high pressure and was mainly controlled by southerly winds. Wind speed (WS) within the ABL (< 2 km) decreased significantly and WS at 10-m height mostly remained below 2 m s-1 during the hazy episodes, which was favorable for the accumulation of air pollutants. A potential temperature inversion layer existed throughout the entire ABL during the earlier hazy episode [from 0500 Local Time (LT) 18 December to 1100 LT 19 December], and then a potential temperature inversion layer developed with the bottom gradually decreased from 900 m to 300 m. Such a stable atmospheric stratification further weakened pollutant dispersion. The atmospheric boundary layer height (ABLH) estimated based on potential temperature profiles was mostly lower than 400 m and varied oppositely with PM2.5 in Shenyang. In summary, weak winds due to calm synoptic conditions, strong thermal inversion layer, and shallow atmospheric boundary layer contributed to the formation and development of this haze event. The backward trajectory analysis revealed the sources of air masses and explained the different characteristics of the haze episodes in the four cities.

Continuous modeling of a grain boundary in MgO and its disclination induced grain-boundary migration mechanism

NASA Astrophysics Data System (ADS)

Cordier, P.; Sun, X.; Taupin, V.; Fressengeas, C.

2016-12-01

Grain boundaries (GBs) are thin material layers where the lattice rotates from one orientation to the next one within a few nanometers. Because they treat these layers as infinitely thin interfaces, large-scale polycrystalline representations fail to describe their structure. Conversely, atomistic representations provide a detailed description of the GBs, but their character remains discrete and not prone to coarse-graining procedures. Continuum descriptions based on kinematic and crystal defect fields defined at interatomic scale are appealing because they can provide smooth and thorough descriptions of GBs, recovering in some sense the atomistic description and potentially serving as a basis for coarse-grained polycrystalline representations. In this work, a crossover between atomistic description and continuous representation of a MgO tilt boundary in polycrystals is set-up to model the periodic arrays of structural units by using dislocation and disclination dipole arrays along GBs. The strain, rotation, curvature, disclination and dislocation density fields are determined in the boundary area by using the discrete atomic positions generated by molecular dynamics simulations. Then, this continuous disclination/dislocation model is used as part of the initial conditions in elasto-plastic continuum mechanics simulations to investigate the shear-coupled boundary migration of tilt boundaries. The present study leads to better understanding of the structure and mechanical architecture of grain boundaries.

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

NASA Astrophysics Data System (ADS)

Chong, Tze Pei; Vathylakis, Alexandros

2015-10-01

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

Segregation and Migration of the Oxygen Vacancies in the 3 (111) Tilt Grain Boundaries of Ceria

DOE PAGES

Yuan, Fenglin; Liu, Bin; Zhang, Yanwen; ...

2016-03-01

In nanocrystalline materials, defect-grain boundary (GB) interaction plays a key role in determining the structure stability, as well as size-dependent ionic, electronic, magnetic and chemical properties. In this study, we systematically investigated using density functional theory segregation and migration of oxygen vacancies at the Σ3 [110] / (111) grain boundary of ceria. Three oxygen layers near the GB are predicted to be segregation sites for oxygen vacancies. Moreover, the presence of oxygen vacancies stabilizes this tilt GB at a low Fermi level and/or oxygen poor conditions. An atomic strain model was proposed to rationalize layer dependency of the relaxation energymore » for +2 charged oxygen vacancy. The structural origin of large relaxation energies at layers 1 and 2 was determined to be free-volume space that induces ion relaxation towards the GB. Our results not only pave the way for improving the oxygen transport near GBs of ceria, but also provide important insights into engineering the GB structure for better ionic, magnetic and chemical properties of nanocrystalline ceria.« less

Hairpin vortices in the outer and near wall regions of the canonical turbulent boundary layer

NASA Astrophysics Data System (ADS)

Wallace, James; Wu, Xiaohua; Moin, Parviz

2016-11-01

While the dominance of hairpin vortices and their significance for transport processes in the transitional and early turbulent regions of the canonical turbulent boundary layer has been widely accepted, opinion is divided about the developed flow downstream. Here we investigate the representative vortical structures in the outer and near wall regions for the momentum thickness Reynolds number, Reθ , of up to 3000 using the DNS database described in. This boundary layer grows spatially from a laminar state at Reθ = 80 beneath a freestream of continuous and nearly isotropic turbulence decaying from an intensity of 3 to 0.8%. The vortical structures are visualized with the swirling strength, λci. In the outer region hairpin vortices appear and are advected over distances corresponding to about 300 - 400 in Reθ within the fully turbulent region, demonstrating that they are not remnants of transitional structures. The near wall vortical structures are more difficult to visualize and require careful tuning of the swirling strength and making invisible the flow above the near wall region of the flow. The hairpins in this region occur in intermittent clusters that have features remarkably similar to transitional turbulent spots.

Optimized capping layers for EUV multilayers

DOEpatents

Bajt, Sasa [Livermore, CA; Folta, James A [Livermore, CA; Spiller, Eberhard A [Livermore, CA

2004-08-24

A new capping multilayer structure for EUV-reflective Mo/Si multilayers consists of two layers: A top layer that protects the multilayer structure from the environment and a bottom layer that acts as a diffusion barrier between the top layer and the structure beneath. One embodiment combines a first layer of Ru with a second layer of B.sub.4 C. Another embodiment combines a first layer of Ru with a second layer of Mo. These embodiments have the additional advantage that the reflectivity is also enhanced. Ru has the best oxidation resistance of all materials investigated so far. B.sub.4 C is an excellent barrier against silicide formation while the silicide layer formed at the Si boundary is well controlled.

Natural convection heat transfer in water near its density maximum

NASA Astrophysics Data System (ADS)

Yen, Yin-Chao

1990-12-01

This monograph reviews and summarizes to date the experimental and analytical results on the effect of water density near its maximum convection, transient flow and temperature structure characteristics: (1) in a vertical enclosure; (2) in a vertical annulus; (3) between horizontal concentric cylinders; (4) in a square enclosure; (5) in a rectangular enclosure; (6) in a horizontal layer; (7) in a circular confined melt layer; and (8) in bulk water during melting. In a layer of water containing a maximum density temperature of 4 C, the onset of convection (the critical number) is found not to be a constant value as in the classical normal fluid but one that varies with the imposed thermal and hydrodynamic boundaries. In horizontal layers, a nearly constant temperature zone forms and continuously expands between the warm and cold boundaries. A minimum heat transfer exists in most of the geometries studied and, in most cases, can be expressed in terms of a density distribution parameter. The effect of this parameter on a cells formation, disappearance and transient structure is discussed, and the effect of split boundary flow on heat transfer is presented.

Cloud System Evolution in the Trades—CSET

NASA Astrophysics Data System (ADS)

Albrecht, B. A.; Zuidema, P.; Bretherton, C. S.; Wood, R.; Ghate, V. P.

2015-12-01

The Cloud System Evolution in the Trades (CSET) study was designed to describe and explain the evolution of the boundary layer aerosol, cloud, and thermodynamic structures along trajectories within the north-Pacific trade-winds. The observational component of this study centered on 7 round-trips made by the NSF NCAR Gulfstream V (GV) between Sacramento, CA and Kona, Hawaii between 1 July and 15 August 2015. The CSET observing strategy used a Lagrangian approach to sample aerosol, cloud, and boundary layer properties upwind from the transition zone over the North Pacific and to resample these areas two days later. GFS forecast trajectories were used to plan the outbound flight to Hawaii and then updated forecast trajectories helped set the return flight plan two days later. Two key elements of the CSET observing system were the newly developed HIAPER Cloud Radar (HCR) and the HIAPER Spectral Resolution Lidar (HSRL). Together they provided unprecedented characterizations of aerosol, cloud and precipitation structures. A full suite of probes on the aircraft were used for in situ measurements of aerosol, cloud, precipitation, and turbulence properties during the low-level aircraft profiling portions of the flights. A wide range of boundary layer structures and aerosol, cloud, and precipitation conditions were observed during CSET. The cloud systems sampled included solid stratocumulus infused with smoke from Canadian wildfires, mesoscale (100-200 km) cloud-precipitation complexes, and patches of shallow cumuli in environments with accumulation mode aerosol concentrations of less than 50 cm-3. Ultra clean layers (UCLs with accumulation mode concentrations of less than 10 cm-3) were observed frequently near the top of the boundary layer and were often associated with shallow, gray (optically thin) layered clouds—features that are the subject of focused investigations by the CSET science team. The extent of aerosol, cloud, drizzle and boundary layer sampling that was made over open areas of the North Pacific along 2-day trajectories during CSET is unprecedented and will enable focused modeling studies of cloud system evolution and the role of aerosol-cloud-precipitation interactions in that evolution.

Scaling of heat transfer augmentation due to mechanical distortions in hypervelocity boundary layers

NASA Astrophysics Data System (ADS)

Flaherty, W.; Austin, J. M.

2013-10-01

We examine the response of hypervelocity boundary layers to global mechanical distortions due to concave surface curvature. Surface heat transfer and visual boundary layer thickness data are obtained for a suite of models with different concave surface geometries. Results are compared to predictions using existing approximate methods. Near the leading edge, good agreement is observed, but at larger pressure gradients, predictions diverge significantly from the experimental data. Up to a factor of five underprediction is reported in regions with greatest distortion. Curve fits to the experimental data are compared with surface equations. We demonstrate that reasonable estimates of the laminar heat flux augmentation may be obtained as a function of the local turning angle for all model geometries, even at the conditions of greatest distortion. This scaling may be explained by the application of Lees similarity. As a means of introducing additional local distortions, vortex generators are used to impose streamwise structures into the boundary layer. The response of the large scale vortices to an adverse pressure gradient is investigated. Surface streak evolution is visualized over the different surface geometries using fast response pressure sensitive paint. For a flat plate baseline case, heat transfer augmentation at similar levels to turbulent flow is measured. For the concave geometries, increases in heat transfer by factors up to 2.6 are measured over the laminar values. The scaling of heat transfer with turning angle that is identified for the laminar boundary layer response is found to be robust even in the presence of the imposed vortex structures.

LABLE: A Multi-Institutional, Student-Led, Atmospheric Boundary Layer Experiment

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

Klein, P.; Bonin, T. A.; Newman, J. F.

This paper presents an overview of the Lower Atmospheric Boundary Layer Experiment (LABLE), which included two measurement campaigns conducted at the Atmospheric Radiation Measurement (ARM) Southern Great Plains site in Oklahoma during 2012 and 2013. LABLE was conducted as a collaborative effort between the University of Oklahoma (OU), the National Severe Storms Laboratory, Lawrence Livermore National Laboratory (LLNL), and the ARM program. LABLE can be considered unique in that it was designed as a multi-phase, low-cost, multi-agency collaboration. Graduate students served as principal investigators and took the lead in designing and conducting experiments aimed at examining boundary-layer processes. The mainmore » objective of LABLE was to study turbulent phenomena in the lowest 2 km of the atmosphere over heterogeneous terrain using a variety of novel atmospheric profiling techniques. Several instruments from OU and LLNL were deployed to augment the suite of in-situ and remote sensing instruments at the ARM site. The complementary nature of the deployed instruments with respect to resolution and height coverage provides a near-complete picture of the dynamic and thermodynamic structure of the atmospheric boundary layer. This paper provides an overview of the experiment including i) instruments deployed, ii) sampling strategies, iii) parameters observed, and iv) student involvement. To illustrate these components, the presented results focus on one particular aspect of LABLE, namely the study of the nocturnal boundary layer and the formation and structure of nocturnal low-level jets. During LABLE, low-level jets were frequently observed and they often interacted with mesoscale atmospheric disturbances such as frontal passages.« less

Advances and challenges in periodic forcing of the turbulent boundary layer on a body of revolution

NASA Astrophysics Data System (ADS)

Kornilov, V. I.; Boiko, A. V.

2018-04-01

The effectiveness of local forcing by periodic blowing/suction through a thin transverse slot to alter the properties of an incompressible turbulent boundary layer is considered. In the first part of the review the effectiveness of the forcing through a single slot is discussed. Analysis of approaches for experimental modeling of the forcing, including those on flat plate, is given. Some ambiguities in simulating such flows are reviewed. The main factors affecting the structure of the forced flow are analyzed. In the second part the effectiveness of the forcing on a body of revolution by periodic blowing/suction through a series of transverse annular slots is discussed. The focus is the structure, properties, and main regularities of the forced flows in a wide range of variable conditions and basic parameters such as the Reynolds number, the dimensionless amplitude of the forced signal, and the frequency of the forced signal. The effect of the forcing on skin-friction in the turbulent boundary layer is clearly revealed. A phase synchronism of blowing/suction using an independent control of the forcing through the slots provides an additional skin friction reduction at distances up to 5-6 boundary layer displacement thicknesses upstream of an annular slot. The local skin friction reduction under the effect of periodic blowing/suction is stipulated by a dominating influence of an unsteady coherent vortex formed in the boundary layer, the vortex propagating downstream promoting a shift of low-velocity fluid further from the wall, a formation of a retarded region at the wall, and hence, a thickening of the viscous sublayer.

Estimate of Boundary-Layer Depth Over Beijing, China, Using Doppler Lidar Data During SURF-2015

NASA Astrophysics Data System (ADS)

Huang, Meng; Gao, Zhiqiu; Miao, Shiguang; Chen, Fei; LeMone, Margaret A.; Li, Ju; Hu, Fei; Wang, Linlin

2017-03-01

Planetary boundary-layer (PBL) structure was investigated using observations from a Doppler lidar and the 325-m Institute of Atmospheric Physics (IAP) meteorological tower in the centre of Beijing during the summer 2015 Study of Urban-impacts on Rainfall and Fog/haze (SURF-2015) field campaign. Using six fair-weather days of lidar and tower data under clear to cloudy skies, we evaluate the ability of the Doppler lidar to probe the urban boundary-layer structure, and then propose a composite method for estimating the diurnal cycle of the PBL depth using the Doppler lidar. For the convective boundary layer (CBL), a threshold method using vertical velocity variance (σ _w^2 >0.1 m2s^{-2}) is used, since it provides more reliable CBL depths than a conventional maximum wind-shear method. The nocturnal boundary-layer (NBL) depth is defined as the height at which σ _w^2 decreases to 10 % of its near-surface maximum minus a background variance. The PBL depths determined by combining these methods have average values ranging from ≈ 270 to ≈ 1500 m for the six days, with the greatest maximum depths associated with clear skies. Release of stored and anthropogenic heat contributes to the maintenance of turbulence until late evening, keeping the NBL near-neutral and deeper at night than would be expected over a natural surface. The NBL typically becomes more shallow with time, but grows in the presence of low-level nocturnal jets. While current results are promising, data over a broader range of conditions are needed to fully develop our PBL-depth algorithms.

Vertical structure of atmospheric boundary layer over Ranchi during the summer monsoon season

NASA Astrophysics Data System (ADS)

Chandra, Sagarika; Srivastava, Nishi; Kumar, Manoj

2018-04-01

Thermodynamic structure and variability in the atmospheric boundary layer have been investigated with the help of balloon-borne GPS radiosonde over a monsoon trough station Ranchi (Lat. 23°45'N, Long. 85°43'E, India) during the summer monsoon season (June-September) for a period of 2011-2013. Virtual potential temperature gradient method is used for the determination of mixed layer height (MLH). The MLH has been found to vary in the range of 1000-1300 m during the onset, 600-900 m during the active and 1400-1750 m during the break phase of monsoon over this region. Inter-annual variations noticed in MLH could be associated with inter-annual variability in convection and rainfall prevailing over the region. Along with the MLH, the cloud layer heights are also derived from the thermodynamic profiles for the onset, active and break phases of monsoon. Cloud layer height varied a lot during different phases of the monsoon. For the determination of boundary-layer convection, thermodynamic parameter difference (δθ = θ es- θ e) between saturated equivalent potential temperature (θ es ) and equivalent potential temperature (θ e) is used. It is a good indicator of convection and indicates the intense and suppressed convection during different phases of monsoon.

European Science Notes. Volume 41, Number 10,

DTIC Science & Technology

1987-10-01

the following topics: laminar/turbulent transition in boundary layers; coherent structures in the modeling of turbulent boundary layers, wakes, and jets...of the labeling of a model protein, human immu- indicator. The amount of oxygen produced noglobulin (hIgG), with acridinium ester, can easily be...has concerned cations, and Computer Science. Research model reduction of large-scale systems in the controls area is conducted in the and state and

Hair Receptor Sensitivity to Changes in Laminar Boundary Layer Shape (Postprint)

DTIC Science & Technology

2010-02-01

copyright owner. Biologists have shown that bat wings contain distributed arrays of flow -sensitive hair receptors. The hair receptors are hypothesized...specialization of hair-like structures for the detection of changes in boundary layer velocity profiles (shapes). A quasi-steady model that relates the flow ...Mechanoreceptor, Artificial Hair Sensor, Medium Flow Sensor UNCLAS UNCLAS UNCLAS UL 11 Benjamin T. Dickinson 850-883-2645 Reset IOP PUBLISHING

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.

Cross-sectional scanning tunneling microscopy of antiphase boundaries in epitaxially grown GaP layers on Si(001)

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

Prohl, Christopher; Lenz, Andrea, E-mail: alenz@physik.tu-berlin.de; Döscher, Henning

2016-05-15

In a fundamental cross-sectional scanning tunneling microscopy investigation on epitaxially grown GaP layers on a Si(001) substrate, differently oriented antiphase boundaries are studied. They can be identified by a specific contrast and by surface step edges starting/ending at the position of an antiphase boundary. Moreover, a change in the atomic position of P and Ga atoms along the direction of growth is observed in agreement with the structure model of antiphase boundaries in the GaP lattice. This investigation opens the perspective to reveal the orientation and position of the antiphase boundaries at the atomic scale due to the excellent surfacemore » sensitivity of this method.« less

Convective Cold Pool Structure and Boundary Layer Recovery in DYNAMO

NASA Astrophysics Data System (ADS)

Savarin, A.; Chen, S. S.; Kerns, B. W.; Lee, C.; Jorgensen, D. P.

2012-12-01

One of the key factors controlling convective cloud systems in the Madden-Julian Oscillation (MJO) over the tropical Indian Ocean is the property of the atmospheric boundary layer. Convective downdrafts and precipitation from the cloud systems produce cold pools in the boundary layer, which can inhibit subsequent development of convection. The recovery time is the time it takes for the boundary layer to return to pre convective conditions. It may affect the variability of the convection on various time scales during the initiation of MJO. This study examines the convective cold pool structure and boundary layer recovery using the NOAA WP-3D aircraft observations, include the flight-level, Doppler radar, and GPS dropsonde data, collected during the Dynamics of MJO (DYNAMO) field campaign from November-December 2011. The depth and strength of convective cold pools are defined by the negative buoyancy, which can be computed from the dropsonde data. Convective downdraft can be affected by environmental water vapor due to entrainment. Mid-level dry air observed during the convectively suppressed phase of MJO seems to enhance convective downdraft, making the cold pools stronger and deeper. Recovery of the cold pools in the boundary layer is determined by the strength and depth of the cold pools and also the air-sea heat and moisture fluxes. Given that the water vapor and surface winds are distinct for the convectively active and suppressed phases of MJO over the Indian Ocean, the aircraft data are stratified by the two different large-scale regimes of MJO. Preliminary results show that the strength and depth of the cold pools are inversely correlated with the surrounding mid-level moisture. During the convectively suppressed phase, the recovery time is ~5-20 hours in relative weak wind condition with small air-sea fluxes. The recovery time is generally less than 6 hours during the active phase of MJO with moist mid-levels and stronger surface wind and air-sea fluxes.

Vortical structures and development of laminar flow over convergent-divergent riblets

NASA Astrophysics Data System (ADS)

Xu, Fang; Zhong, Shan; Zhang, Shanying

2018-05-01

In this work, the development of a laminar boundary layer over a rectangular convergent-divergent riblet section with a finite streamwise length is studied experimentally using dye visualization and particle image velocimetry in a water flume. The flow topology over this highly directional spanwise roughness is established from this study. It is shown that convergent-divergent riblets generate a spanwise flow above the riblets from the diverging line toward the adjacent converging line. This consequently leads to the formation of a weak recirculating secondary flow in cross-stream planes across the boundary layer that creates a downwash motion over the diverging line and an upwash motion over the converging line. It is found that the fluid inside the riblet valley follows a helicoidal path and it also interacts with the crossflow boundary layer hence playing a key role in determining the structure of the secondary flow across the boundary layer. The impact of riblet wavelength on vortical structures is also revealed for the first time. A larger riblet wavelength is seen to produce a stronger upwash/downwash and hence a more intense secondary flow as well as a stronger deceleration effect on the crossflow. Furthermore, the streamwise development of the flow over the riblet section can be divided into a developing stage followed by a developed stage. In the developing stage, the magnitude of induced streamwise velocity and vorticity over the converging line continues to increase, whereas in the developed stage the values of these parameters remain essentially unchanged.

Structure of high and low shear-stress events in a turbulent boundary layer

NASA Astrophysics Data System (ADS)

Gomit, G.; de Kat, R.; Ganapathisubramani, B.

2018-01-01

Simultaneous particle image velocimetry (PIV) and wall-shear-stress sensor measurements were performed to study structures associated with shear-stress events in a flat plate turbulent boundary layer at a Reynolds number Reτ≈4000 . The PIV field of view covers 8 δ (where δ is the boundary layer thickness) along the streamwise direction and captures the entire boundary layer in the wall-normal direction. Simultaneously, wall-shear-stress measurements that capture the large-scale fluctuations were taken using a spanwise array of hot-film skin-friction sensors (spanning 2 δ ). Based on this combination of measurements, the organization of the conditional wall-normal and streamwise velocity fluctuations (u and v ) and of the Reynolds shear stress (-u v ) can be extracted. Conditional averages of the velocity field are computed by dividing the histogram of the large-scale wall-shear-stress fluctuations into four quartiles, each containing 25% of the occurrences. The conditional events corresponding to the extreme quartiles of the histogram (positive and negative) predominantly contribute to a change of velocity profile associated with the large structures and in the modulation of the small scales. A detailed examination of the Reynolds shear-stress contribution related to each of the four quartiles shows that the flow above a low wall-shear-stress event carries a larger amount of Reynolds shear stress than the other quartiles. The contribution of the small and large scales to this observation is discussed based on a scale decomposition of the velocity field.

Routes to turbulence in the rotating disk boundary-layer of a rotor-stator cavity

NASA Astrophysics Data System (ADS)

Yim, Eunok; Serre, Eric; Martinand, Denis; Chomaz, Jean-Marc

2016-11-01

The rotating disk is an important classical problem, due to the similarities between the 3D boundary layers on a disk and a swept aircraft wing. It is nowadays admitted that a direct transition to turbulence may exist through a steep-fronted nonlinear global mode located at the boundary between the locally connectively and absolutely unstable regions (Pier 2003; Viaud et al. 2008, 2011; Imayama et al. 2014 and others). However, recent studies (Healey 2010; Harris et al. 2012; Imayama et al. 2013) suggest that there may be an alternative route starting at lower critical Reynolds number, based on convective travelling waves but this scenario is still not fully validated and proven. To better characterize such transition, direct numerical simulations are performed in a closed cylindrical rotor-stator cavity (without hub) up to Re = O (105) . All boundaries are no slip and for the stable region around the rotation axis prevents the disturbances coming from the very unstable stator boundary to disturb the rotor boundary layer. Different transition scenarii to turbulence are investigated when the rotor boundary layer is forced at different positions and forcing amplitude. The associated dynamics of coherent structures in various flow regions are also investigated when increasing Re .

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

Bedekar, Vikram; Poplawsky, Jonathan D.; Guo, Wei

In grain finement and non-equilibrium there is carbon segregation within grain boundaries alters the mechanical performance of hard turning layers in carburized bearing steel. Moreover, an atom probe tomography (APT) study on the nanostructured hard turning layers reveals carbon migration to grain boundaries as a result of carbide decomposition during severe plastic deformation. In addition, samples exposed to different cutting speeds show that the carbon migration rate increases with the cutting speed. For these two effects lead to an ultrafine carbon network structure resulting in increased hardness and thermal stability in the severely deformed surface layer.

Investigation of the fluid flow dynamic parameters for Newtonian and non-Newtonian materials: an approach to understanding the fluid flow-like structures within fault zones

NASA Astrophysics Data System (ADS)

Tanaka, H.; Shiomi, Y.; Ma, K.-F.

2017-11-01

To understand the fault zone fluid flow-like structure, namely the ductile deformation structure, often observed in the geological field (e.g., Ramsay and Huber The techniques of modern structure geology, vol. 1: strain analysis, Academia Press, London, 1983; Hobbs and Ord Structure geology: the mechanics of deforming metamorphic rocks, Vol. I: principles, Elsevier, Amsterdam, 2015), we applied a theoretical approach to estimate the rate of deformation, the shear stress and the time to form a streak-line pattern in the boundary layer of viscous fluids. We model the dynamics of streak lines in laminar boundary layers for Newtonian and pseudoplastic fluids and compare the results to those obtained via laboratory experiments. The structure of deformed streak lines obtained using our model is consistent with experimental observations, indicating that our model is appropriate for understanding the shear rate, flow time and shear stress based on the profile of deformed streak lines in the boundary layer in Newtonian and pseudoplastic viscous materials. This study improves our understanding of the transportation processes in fluids and of the transformation processes in fluid-like materials. Further application of this model could facilitate understanding the shear stress and time history of the fluid flow-like structure of fault zones observed in the field.[Figure not available: see fulltext.

Formation of nano-laminated structures in a dry sliding wear-induced layer under different wear mechanisms of 20CrNi2Mo steel

NASA Astrophysics Data System (ADS)

Yin, Cun-hong; Liang, Yi-long; Jiang, Yun; Yang, Ming; Long, Shao-lei

2017-11-01

The microstructures of 20CrNi2Mo steel underneath the contact surface were examined after dry sliding. Scanning Electronic Microscopy (SEM), Transmission Electron Microscopy (TEM), Electron Backscattered Diffraction (EBSD) and an ultra-micro-hardness tester were used to characterize the worn surface and dry sliding wear-induced layer. Martensite laths were ultra-refined due to cumulative strains and a large strain gradient that occurred during cyclic loading in wear near the surface. The microstructure evolution in dominant abrasive wear differs from that in adhesive wear. In dominant abrasive wear, only bent martensite laths with high-density deformation dislocations were observed. In contrast, in dominant adhesive wear, gradient structures were formed along the depth from the wear surface. Cross-sectional TEM foils were prepared in a focused ion beam (FIB) to observe the gradient structures in a dry sliding wear-induced layer at depths of approximately 1-5 μm and 5-20 μm. The gradient structures contained nano-laminated structures with an average thickness of 30-50 nm and bent martensite laths. We found that the original martensite laths coordinated with the strain energy and provided origin boundaries for the formation of gradient structures. Geometrically necessary boundaries (GNBs) and isolated dislocation boundaries (IDBs) play important roles in forming the nano-laminated structures.

Wind-US Code Contributions to the First AIAA Shock Boundary Layer Interaction Prediction Workshop

NASA Technical Reports Server (NTRS)

Georgiadis, Nicholas J.; Vyas, Manan A.; Yoder, Dennis A.

2013-01-01

This report discusses the computations of a set of shock wave/turbulent boundary layer interaction (SWTBLI) test cases using the Wind-US code, as part of the 2010 American Institute of Aeronautics and Astronautics (AIAA) shock/boundary layer interaction workshop. The experiments involve supersonic flows in wind tunnels with a shock generator that directs an oblique shock wave toward the boundary layer along one of the walls of the wind tunnel. The Wind-US calculations utilized structured grid computations performed in Reynolds-averaged Navier-Stokes mode. Four turbulence models were investigated: the Spalart-Allmaras one-equation model, the Menter Baseline and Shear Stress Transport k-omega two-equation models, and an explicit algebraic stress k-omega formulation. Effects of grid resolution and upwinding scheme were also considered. The results from the CFD calculations are compared to particle image velocimetry (PIV) data from the experiments. As expected, turbulence model effects dominated the accuracy of the solutions with upwinding scheme selection indicating minimal effects.

Analytical and Experimental Evaluation of the Heat Transfer Distribution over the Surfaces of Turbine Vanes

NASA Technical Reports Server (NTRS)

Hylton, L. D.; Mihelc, M. S.; Turner, E. R.; Nealy, D. A.; York, R. E.

1983-01-01

Three airfoil data sets were selected for use in evaluating currently available analytical models for predicting airfoil surface heat transfer distributions in a 2-D flow field. Two additional airfoils, representative of highly loaded, low solidity airfoils currently being designed, were selected for cascade testing at simulated engine conditions. Some 2-D analytical methods were examined and a version of the STAN5 boundary layer code was chosen for modification. The final form of the method utilized a time dependent, transonic inviscid cascade code coupled to a modified version of the STAN5 boundary layer code featuring zero order turbulence modeling. The boundary layer code is structured to accommodate a full spectrum of empirical correlations addressing the coupled influences of pressure gradient, airfoil curvature, and free-stream turbulence on airfoil surface heat transfer distribution and boundary layer transitional behavior. Comparison of pedictions made with the model to the data base indicates a significant improvement in predictive capability.

Analytical and experimental evaluation of the heat transfer distribution over the surfaces of turbine vanes

NASA Astrophysics Data System (ADS)

Hylton, L. D.; Mihelc, M. S.; Turner, E. R.; Nealy, D. A.; York, R. E.

1983-05-01

Three airfoil data sets were selected for use in evaluating currently available analytical models for predicting airfoil surface heat transfer distributions in a 2-D flow field. Two additional airfoils, representative of highly loaded, low solidity airfoils currently being designed, were selected for cascade testing at simulated engine conditions. Some 2-D analytical methods were examined and a version of the STAN5 boundary layer code was chosen for modification. The final form of the method utilized a time dependent, transonic inviscid cascade code coupled to a modified version of the STAN5 boundary layer code featuring zero order turbulence modeling. The boundary layer code is structured to accommodate a full spectrum of empirical correlations addressing the coupled influences of pressure gradient, airfoil curvature, and free-stream turbulence on airfoil surface heat transfer distribution and boundary layer transitional behavior. Comparison of pedictions made with the model to the data base indicates a significant improvement in predictive capability.

Flow prediction over a transport multi-element high-lift system and comparison with flight measurements

NASA Technical Reports Server (NTRS)

Vijgen, P. M. H. W.; Hardin, J. D.; Yip, L. P.

1992-01-01

Accurate prediction of surface-pressure distributions, merging boundary-layers, and separated-flow regions over multi-element high-lift airfoils is required to design advanced high-lift systems for efficient subsonic transport aircraft. The availability of detailed measurements of pressure distributions and both averaged and time-dependent boundary-layer flow parameters at flight Reynolds numbers is critical to evaluate computational methods and to model the turbulence structure for closure of the flow equations. Several detailed wind-tunnel measurements at subscale Reynolds numbers were conducted to obtain detailed flow information including the Reynolds-stress component. As part of a subsonic-transport high-lift research program, flight experiments are conducted using the NASA-Langley B737-100 research aircraft to obtain detailed flow characteristics for support of computational and wind-tunnel efforts. Planned flight measurements include pressure distributions at several spanwise locations, boundary-layer transition and separation locations, surface skin friction, as well as boundary-layer profiles and Reynolds stresses in adverse pressure-gradient flow.

Linking Sediment Transport to Coherent Flow Structures: First Results Using 2-Phase PIV and Considerations of the Origin of Large-Scale Turbulence

NASA Astrophysics Data System (ADS)

Best, J.

2004-05-01

The origin and scaling of large-scale coherent flow structures has been of central interest in furthering understanding of the nature of turbulent boundary layers, and recent work has shown the presence of large-scale turbulent flow structures that may extend through the whole flow depth. Such structures may dominate the entrainment of bedload sediment and advection of fine sediment in suspension. However, we still know remarkably little of the interactions between the dynamics of coherent flow structures and sediment transport, and its implications for ecosystem dynamics. This paper will discuss the first results of two-phase particle imaging velocimetry (PIV) that has been used to visualize large-scale turbulent flow structures moving over a flat bed in a water channel, and the motion of sand particles within these flows. The talk will outline the methodology, involving the fluorescent tagging of sediment and its discrimination from the fluid phase, and show results that illustrate the key role of these large-scale structures in the transport of sediment. Additionally, the presence of these structures will be discussed in relation to the origin of vorticity within flat-bed boundary layers and recent models that envisage these large-scale motions as being linked to whole-flow field structures. Discussion will focus on if these recent models simply reflect the organization of turbulent boundary layer structure and vortex packets, some of which are amply visualised at the laminar-turbulent transition.

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.

Effect of real-time boundary wind conditions on the air flow and pollutant dispersion in an urban street canyon—Large eddy simulations

NASA Astrophysics Data System (ADS)

Zhang, Yun-Wei; Gu, Zhao-Lin; Cheng, Yan; Lee, Shun-Cheng

2011-07-01

Air flow and pollutant dispersion characteristics in an urban street canyon are studied under the real-time boundary conditions. A new scheme for realizing real-time boundary conditions in simulations is proposed, to keep the upper boundary wind conditions consistent with the measured time series of wind data. The air flow structure and its evolution under real-time boundary wind conditions are simulated by using this new scheme. The induced effect of time series of ambient wind conditions on the flow structures inside and above the street canyon is investigated. The flow shows an obvious intermittent feature in the street canyon and the flapping of the shear layer forms near the roof layer under real-time wind conditions, resulting in the expansion or compression of the air mass in the canyon. The simulations of pollutant dispersion show that the pollutants inside and above the street canyon are transported by different dispersion mechanisms, relying on the time series of air flow structures. Large scale air movements in the processes of the air mass expansion or compression in the canyon exhibit obvious effects on pollutant dispersion. The simulations of pollutant dispersion also show that the transport of pollutants from the canyon to the upper air flow is dominated by the shear layer turbulence near the roof level and the expansion or compression of the air mass in street canyon under real-time boundary wind conditions. Especially, the expansion of the air mass, which features the large scale air movement of the air mass, makes more contribution to the pollutant dispersion in this study. Comparisons of simulated results under different boundary wind conditions indicate that real-time boundary wind conditions produces better condition for pollutant dispersion than the artificially-designed steady boundary wind conditions.

A study of the vortex structures around circular cylinder mounted on vertical heated plate

NASA Astrophysics Data System (ADS)

Malah, Hamid; Chumakov, Yurii S.; Levchenya, Alexander M.

2018-05-01

In recent years, studies of natural convection boundary layer interacting with obstacles draw much of attention, because of its practical applications. Pressure gradient resulting from this interaction leads to separation of the boundary layer. The formation of vortex structure around obstacle is characteristic to any kind of convection flow. In this paper, we describe the formation of three-dimensional vortex structure for the case of natural convection flow around the circular cylinder mounted on vertical heated plate. Navier-Stokes equations were used for numerical computations. The results proved the presence of a horseshoe vortex system in the case of natural convection flow as in the forced convection flow.

Asymptotic structure and similarity solutions for three-dimensional turbulent boundary layers

NASA Technical Reports Server (NTRS)

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

1989-01-01

The asymptotic structure of the three-dimensional turbulent boundary layer is investigated in the limit of large Reynolds numbers. A self-consistent, but relatively complex, two-layer structure exists and the simplest situation, corresponding to a plane of symmetry, is considered in this paper as a first step. The adjustment of the streamwise velocity to relative rest, through an outer defect layer and then an inner wall layer, is similar to that in two-dimensional flow. The adjustment of the cross-streamwise velocity is more complicated and it is shown that two terms in the expansion are required to obtain useful results, and in particular to obtain the velocity skew angle at the wall near the symmetry plane. The conditions under which self-similarity is achieved near a plane of symmetry are investigated. A set of ordinary differential equations is developed which describe the streamwise and cross-streamwise velocities near a plane of symmetry in a self-similar flow through two orders of magnitude. Calculated numerical solutions of these equations yield trends which are consistent with experimental observations.

First Atmospheric Science Results from the Mars Exploration Rovers Mini-TES

NASA Technical Reports Server (NTRS)

Smith, Michael D.; Wolff, Michael J.; Lemmon, Mark T.; Spanovich, Nicole; Banfield, Don; Budney, Charles J.; Clancy, R. Todd; Ghosh, Amitabha; Landis, Geoffrey A.; Smith, Peter;

First Atmospheric Science Results from the Mars Exploration Rovers Mini-TES.

PubMed

Smith, Michael D; Wolff, Michael J; Lemmon, Mark T; Spanovich, Nicole; Banfield, Don; Budney, Charles J; Clancy, R Todd; Ghosh, Amitabha; Landis, Geoffrey A; Smith, Peter; Whitney, Barbara; Christensen, Philip R; Squyres, Steven W

2004-12-03

Thermal infrared spectra of the martian atmosphere taken by the Miniature Thermal Emission Spectrometer (Mini-TES) were used to determine the atmospheric temperatures in the planetary boundary layer and the column-integrated optical depth of aerosols. Mini-TES observations show the diurnal variation of the martian boundary layer thermal structure, including a near-surface superadiabatic layer during the afternoon and an inversion layer at night. Upward-looking Mini-TES observations show warm and cool parcels of air moving through the Mini-TES field of view on a time scale of 30 seconds. The retrieved dust optical depth shows a downward trend at both sites.

Attached flow structure and streamwise energy spectra in a turbulent boundary layer

NASA Astrophysics Data System (ADS)

Srinath, S.; Vassilicos, J. C.; Cuvier, C.; Laval, J.-P.; Stanislas, M.; Foucaut, J.-M.

2018-05-01

On the basis of (i) particle image velocimetry data of a turbulent boundary layer with large field of view and good spatial resolution and (ii) a mathematical relation between the energy spectrum and specifically modeled flow structures, we show that the scalings of the streamwise energy spectrum E11(kx) in a wave-number range directly affected by the wall are determined by wall-attached eddies but are not given by the Townsend-Perry attached eddy model's prediction of these spectra, at least at the Reynolds numbers Reτ considered here which are between 103 and 104. Instead, we find E11(kx) ˜kx-1 -p where p varies smoothly with distance to the wall from negative values in the buffer layer to positive values in the inertial layer. The exponent p characterizes the turbulence levels inside wall-attached streaky structures conditional on the length of these structures. A particular consequence is that the skin friction velocity is not sufficient to scale E11(kx) for wave numbers directly affected by the wall.

The inner core thermodynamics of the tropical cyclone boundary layer

NASA Astrophysics Data System (ADS)

Williams, Gabriel J.

2016-10-01

Although considerable progress has been made in understanding the inner-core dynamics of the tropical cyclone boundary layer (TCBL), our knowledge of the inner-core thermodynamics of the TCBL remains limited. In this study, the inner-core budgets of potential temperature (θ), specific humidity ( q), and reversible equivalent potential temperature (θ _e) are examined using a high-resolution multilevel boundary layer model. The potential temperature budgets show that the heat energy is dominated by latent heat release in the eyewall, evaporative cooling along the outer edge of the eyewall, and upward surface fluxes of sensible and latent heat from the underlying warm ocean. It is shown that the vertical θ advection overcompensates the sum of radial advective warming from the boundary layer outflow jet and latent heating for the development of cooling in the eyewall within the TCBL. The moisture budgets show the dominant upward transport of moisture in the eyewall updrafts, partly by the boundary-layer outflow jet from the bottom eye region, so that the eyewall remains nearly saturated. The θ _e budgets reveal that the TCBL is maintained thermodynamically by the upward surface flux of higher-θ _e air from the underlying warm ocean, the radial transport of low-θ _e air from the outer regions of the TCBL, and the dry adiabatic cooling associated by eyewall updrafts. These results underscore the significance of vertical motion and the location of the boundary layer outflow jet in maintaining the inner core thermal structure of the TCBL.

Lidar observations of vertically organized convection in the planetary boundary layer over the ocean

NASA Technical Reports Server (NTRS)

Melfi, S. H.; Spinhirne, J. D.; Chou, S.-H.; Palm, S. P.

1985-01-01

Observations of a convective planetary boundary layer (PBL) were made with an airborne, downward-looking lidar system over the Atlantic Ocean during a cold air outbreak. The lidar data revealed well-organized, regularly spaced cellular convection with dominant spacial scales between two and four times the height of the boundary layer. It is demonstrated that the lidar can accurately measure the structure of the PBL with high vertical and horizontal resolution. Parameters important for PBL modeling such as entrainment zone thickness, entrainment rate, PBL height and relative heat flux can be inferred from the lidar data. It is suggested that wind shear at the PBL top may influence both entrainment and convective cell size.

Physics and control of wall turbulence for drag reduction.

PubMed

Kim, John

2011-04-13

Turbulence physics responsible for high skin-friction drag in turbulent boundary layers is first reviewed. A self-sustaining process of near-wall turbulence structures is then discussed from the perspective of controlling this process for the purpose of skin-friction drag reduction. After recognizing that key parts of this self-sustaining process are linear, a linear systems approach to boundary-layer control is discussed. It is shown that singular-value decomposition analysis of the linear system allows us to examine different approaches to boundary-layer control without carrying out the expensive nonlinear simulations. Results from the linear analysis are consistent with those observed in full nonlinear simulations, thus demonstrating the validity of the linear analysis. Finally, fundamental performance limit expected of optimal control input is discussed.

Effect of inlet conditions for numerical modelling of the urban boundary layer

NASA Astrophysics Data System (ADS)

Gnatowska, Renata

2018-01-01

The paper presents the numerical results obtained with the use of the ANSYS FLUENT commercial code for analysing the flow structure around two rectangular inline surface-mounted bluff bodies immersed in a boundary layer. The effects of the inflow boundary layer for the accuracy of the numerical modelling of the flow field around a simple system of objects are described. The analysis was performed for two concepts. In the former case, the inlet velocity profile was defined using the power law, whereas the kinetic and dissipation energy was defined from the equations according to Richards and Hoxey [1]. In the latter case, the inlet conditions were calculated for the flow over the rough area composed of the rectangular components.

Atomic structure and electronic properties of MgO grain boundaries in tunnelling magnetoresistive devices

PubMed Central

Bean, Jonathan J.; Saito, Mitsuhiro; Fukami, Shunsuke; Sato, Hideo; Ikeda, Shoji; Ohno, Hideo; Ikuhara, Yuichi; McKenna, Keith P.

2017-01-01

Polycrystalline metal oxides find diverse applications in areas such as nanoelectronics, photovoltaics and catalysis. Although grain boundary defects are ubiquitous their structure and electronic properties are very poorly understood since it is extremely challenging to probe the structure of buried interfaces directly. In this paper we combine novel plan-view high-resolution transmission electron microscopy and first principles calculations to provide atomic level understanding of the structure and properties of grain boundaries in the barrier layer of a magnetic tunnel junction. We show that the highly [001] textured MgO films contain numerous tilt grain boundaries. First principles calculations reveal how these grain boundaries are associated with locally reduced band gaps (by up to 3 eV). Using a simple model we show how shunting a proportion of the tunnelling current through grain boundaries imposes limits on the maximum magnetoresistance that can be achieved in devices. PMID:28374755

Compressibility effect on thermal coherent structures in spatially-developing turbulent boundary layers via DNS

NASA Astrophysics Data System (ADS)

Araya, Guillermo; Jansen, Kenneth

2017-11-01

DNS of compressible spatially-developing turbulent boundary layers is performed at a Mach number of 2.5 over an isothermal flat plate. Turbulent inflow information is generated by following the concept of the rescaling-recycling approach introduced by Lund et al. (J. Comp. Phys. 140, 233-258, 1998); although, the proposed methodology is extended to compressible flows. Furthermore, a dynamic approach is employed to connect the friction velocities at the inlet and recycle stations (i.e., there is no need of an empirical correlation as in Lund et al.). Additionally, the Morkovin's Strong Reynolds Analogy (SRA) is used in the rescaling process of the thermal fluctuations from the recycle plane. Low/high order flow statistics is compared with direct simulations of an incompressible isothermal ZPG boundary layer at similar Reynolds numbers and temperature regarded as a passive scalar. Focus is given to the effect assessment of flow compressibility on the dynamics of thermal coherent structures. AFOSR #FA9550-17-1-0051.

The vertical structure of the circulation and dynamics in Hudson Shelf Valley

USGS Publications Warehouse

Lentz, Steven J.; Butman, Bradford; Harris, Courtney K.

2014-01-01

Hudson Shelf Valley is a 20–30 m deep, 5–10 km wide v-shaped submarine valley that extends across the Middle Atlantic Bight continental shelf. The valley provides a conduit for cross-shelf exchange via along-valley currents of 0.5 m s−1 or more. Current profile, pressure, and density observations collected during the winter of 1999–2000 are used to examine the vertical structure and dynamics of the flow. Near-bottom along-valley currents having times scales of a few days are driven by cross-shelf pressure gradients setup by wind stresses, with eastward (westward) winds driving onshore (offshore) flow within the valley. The along-valley momentum balance in the bottom boundary layer is predominantly between the pressure gradient and bottom stress because the valley bathymetry limits current veering. Above the bottom boundary layer, the flow veers toward an along-shelf (cross-valley) orientation and a geostrophic balance with some contribution from the wind stress (surface Ekman layer). The vertical structure and strength of the along-valley current depends on the magnitude and direction of the wind stress. During offshore flows driven by westward winds, the near-bottom stratification within the valley increases resulting in a thinner bottom boundary layer and weaker offshore currents. Conversely, during onshore flows driven by eastward winds the near-bottom stratification decreases resulting in a thicker bottom boundary layer and stronger onshore currents. Consequently, for wind stress magnitudes exceeding 0.1 N m−2, onshore along-valley transport associated with eastward wind stress exceeds the offshore transport associated with westward wind stress of the same magnitude.

The structure of the stably stratified internal boundary layer in offshore flow over the sea

NASA Astrophysics Data System (ADS)

Garratt, J. R.; Ryan, B. F.

1989-04-01

Observations obtained mainly from a research aircraft are presented of the mean and turbulent structure of the stably stratified internal boundary layer (IBL) over the sea formed by warm air advection from land to sea. The potential temperature and humidity fields reveal the vertical extent of the IBL, for fetches out to several hundred of kilometres, geostrophic winds of 20 25 m s-1, and potential temperature differences between undisturbed continental air and the sea surface of 7 to 17 K. The dependence of IBL depth on these external parameters is discussed in the context of the numerical results of Garratt (1987), and some discrepancies are noted. Wind observations show the development of a low-level wind maximum (wind component normal to the coast) and rotation of the wind to smaller cross-isobar flow angles. Potential temperature (θ) profiles within the IBL reveal quite a different structure to that found in the nocturnal boundary layer (NBL) over land. Over the sea, θ profiles have large positive curvature with vertical gradients increasing monotonically with height; this reflects the dominance of turbulent cooling within the layer. The behaviour is consistent with known behaviour in the NBL over land where curvature becomes negative (vertical gradients of θ decreasing with height) as radiative cooling becomes dominant. Turbulent properties are discussed in terms of non-dimensional quantities, normalised by the surface friction velocity, as functions of normalised height using the IBL depth. Vertical profiles of these and the normalised wavelength of the spectral maximum agree well with known results for the stable boundary layer over land (Caughey et al., 1979).

Large-scale coherent structures of suspended dust concentration in the neutral atmospheric surface layer: A large-eddy simulation study

NASA Astrophysics Data System (ADS)

Zhang, Yangyue; Hu, Ruifeng; Zheng, Xiaojing

2018-04-01

Dust particles can remain suspended in the atmospheric boundary layer, motions of which are primarily determined by turbulent diffusion and gravitational settling. Little is known about the spatial organizations of suspended dust concentration and how turbulent coherent motions contribute to the vertical transport of dust particles. Numerous studies in recent years have revealed that large- and very-large-scale motions in the logarithmic region of laboratory-scale turbulent boundary layers also exist in the high Reynolds number atmospheric boundary layer, but their influence on dust transport is still unclear. In this study, numerical simulations of dust transport in a neutral atmospheric boundary layer based on an Eulerian modeling approach and large-eddy simulation technique are performed to investigate the coherent structures of dust concentration. The instantaneous fields confirm the existence of very long meandering streaks of dust concentration, with alternating high- and low-concentration regions. A strong negative correlation between the streamwise velocity and concentration and a mild positive correlation between the vertical velocity and concentration are observed. The spatial length scales and inclination angles of concentration structures are determined, compared with their flow counterparts. The conditionally averaged fields vividly depict that high- and low-concentration events are accompanied by a pair of counter-rotating quasi-streamwise vortices, with a downwash inside the low-concentration region and an upwash inside the high-concentration region. Through the quadrant analysis, it is indicated that the vertical dust transport is closely related to the large-scale roll modes, and ejections in high-concentration regions are the major mechanisms for the upward motions of dust particles.

Three-Dimensional Structure of Boundary Layers in Transition to Turbulence

DTIC Science & Technology

1989-03-01

step-by-step Orr- Sommerfeld solution and integration. What is needed is an initial condition and initial wavenumber. These data can be obtained from a ...general than unsteady boundary-layer equations and Orr- Sommerfeld equation which are special cases. There- fore, the PSE will be a valuable tool for...spectra (discrete, continuous) result in a given problem is discussed in monographs and journal articles. Here, we try to find solutions to the

Similarity Scaling for the Inner Region of the Turbulent Boundary Layer

DTIC Science & Technology

2009-11-20

Turan , O., Anderson, C, and Castillo, L., "Outer Scaling in Turbulent Boundary Layers," AIAA 2005-4814 (2005). 25 [28] Townsend, A ., The Structure of...for failing to comply with a collection of information if it does not display a currently valid OMB control number. PLEASE DO NOT RETURN YOUR FORM TO...2010-0012 12. DISTRIBUTION / AVAILABILITY STATEMENT DISTRIBUTION A : APPROVED FOR PUBLIC RELEASE: DISTRIBUTION UNLIMITED 13. SUPPLEMENTARY NOTES

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

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.

Dynamic characteristics of specialty composite structures with embedded damping layers

NASA Technical Reports Server (NTRS)

Saravanos, D. A.; Chamis, C. C.

1993-01-01

Damping mechanics for simulating the damped dynamic characteristics in specialty composite structures with compliant interlaminar damping layers are presented. Finite-element based mechanics incorporating a discrete layer (or layer-wise) laminate damping theory are utilized to represent general laminate configurations in terms of lay-up and fiber orientation angles, cross-sectional thickness, shape, and boundary conditions. Evaluations of the method with exact solutions and experimental data illustrate the accuracy of the method. Additional applications investigate the potential for significant damping enhancement in angle-ply composite laminates with cocured interlaminar damping layers.

Application of dynamic slip wall modeling to a turbine nozzle guide vane

NASA Astrophysics Data System (ADS)

Bose, Sanjeeb; Talnikar, Chaitanya; Blonigan, Patrick; Wang, Qiqi

2015-11-01

Resolution of near-wall turbulent structures is computational prohibitive necessitating the need for wall-modeled large-eddy simulation approaches. Standard wall models are often based on assumptions of equilibrium boundary layers, which do not necessarily account for the dissimilarity of the momentum and thermal boundary layers. We investigate the use of the dynamic slip wall boundary condition (Bose and Moin, 2014) for the prediction of surface heat transfer on a turbine nozzle guide vane (Arts and de Rouvroit, 1992). The heat transfer coefficient is well predicted by the slip wall model, including capturing the transition to turbulence. The sensitivity of the heat transfer coefficient to the incident turbulence intensity will additionally be discussed. Lastly, the behavior of the thermal and momentum slip lengths will be contrasted between regions where the strong Reynolds analogy is invalid (near transition on the suction side) and an isothermal, zero pressure gradient flat plate boundary layer (Wu and Moin, 2010).

Structure and properties of the subsolar magnetopause for northward interplanetary magnetic field - Multiple-instrument particle observations

NASA Technical Reports Server (NTRS)

Song, P.; Russell, C. T.; Fitzenreiter, R. J.; Gosling, J. T.; Thomsen, M. F.; Mitchell, D. G.; Fuselier, S. A.; Parks, G. K.; Anderson, R. R.; Hubert, D.

1993-01-01

The paper examines the structure and properties of the subsolar magnetopause for northward IMF on the basis of measurements from 10 different instrument for three ISEE crossings. It is shown that the overall structure and properties are similar for the three crossings, indicating that the magnetopause is relatively well determined in the subsolar region for strongly northward IMF. The combined data set suggests that the magnetopause region is best organized by defining a sheath transition layer and steplike boundary layers. The electron flux enhancements in the lowest energies in the boundary layers and magnetosphere are found to be ionospheric electrons and not photoelectrons from the spacecraft. For northward IMF, they are photoelectrons, but for southward IMF they may be secondary electrons. The density measurements from differential and integral techniques are similar, leaving no room for a significant 'invisible' population.

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)

Plasma-based actuators for turbulent boundary layer control in transonic flow

NASA Astrophysics Data System (ADS)

Budovsky, A. D.; Polivanov, P. A.; Vishnyakov, O. I.; Sidorenko, A. A.

2017-10-01

The study is devoted to development of methods for active control of flow structure typical for the aircraft wings in transonic flow with turbulent boundary layer. The control strategy accepted in the study was based on using of the effects of plasma discharges interaction with miniature geometrical obstacles of various shapes. The conceptions were studied computationally using 3D RANS, URANS approaches. The results of the computations have shown that energy deposition can significantly change the flow pattern over the obstacles increasing their influence on the flow in boundary layer region. Namely, one of the most interesting and promising data were obtained for actuators basing on combination of vertical wedge with asymmetrical plasma discharge. The wedge considered is aligned with the local streamlines and protruding in the flow by 0.4-0.8 of local boundary layer thickness. The actuator produces negligible distortion of the flow at the absence of energy deposition. Energy deposition along the one side of the wedge results in longitudinal vortex formation in the wake of the actuator providing momentum exchange in the boundary layer. The actuator was manufactured and tested in wind tunnel experiments at Mach number 1.5 using the model of flat plate. The experimental data obtained by PIV proved the availability of the actuator.

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

NASA Technical Reports Server (NTRS)

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

2012-01-01

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

Transitional boundary layer in low-Prandtl-number convection at high Rayleigh number

NASA Astrophysics Data System (ADS)

Schumacher, Joerg; Bandaru, Vinodh; Pandey, Ambrish; Scheel, Janet

2016-11-01

The boundary layer structure of the velocity and temperature fields in turbulent Rayleigh-Bénard flows in closed cylindrical cells of unit aspect ratio is revisited from a transitional and turbulent viscous boundary layer perspective. When the Rayleigh number is large enough the boundary layer dynamics at the bottom and top plates can be separated into an impact region of downwelling plumes, an ejection region of upwelling plumes and an interior region (away from side walls) that is dominated by a shear flow of varying orientation. This interior plate region is compared here to classical wall-bounded shear flows. The working fluid is liquid mercury or liquid gallium at a Prandtl number of Pr = 0 . 021 for a range of Rayleigh numbers of 3 ×105 <= Ra <= 4 ×108 . The momentum transfer response to these system parameters generates a fluid flow in the closed cell with a macroscopic flow Reynolds number that takes values in the range of 1 . 8 ×103 <= Re <= 4 . 6 ×104 . It is shown that particularly the viscous boundary layers for the largest Ra are highly transitional and obey some properties that are directly comparable to transitional channel flows at friction Reynolds numbers below 100. This work is supported by the Deutsche Forschungsgemeinschaft.

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.

Wind-tunnel experiments of turbulent flow over a surface-mounted 2-D block in a thermally-stratified boundary layer

NASA Astrophysics Data System (ADS)

Zhang, Wei; Markfort, Corey; Porté-Agel, Fernando

2014-11-01

Turbulent flows over complex surface topography have been of great interest in the atmospheric science and wind engineering communities. The geometry of the topography, surface roughness and temperature characteristics as well as the atmospheric thermal stability play important roles in determining momentum and scalar flux distribution. Studies of turbulent flow over simplified topography models, under neutrally stratified boundary-layer conditions, have provided insights into fluid dynamics. However, atmospheric thermal stability has rarely been considered in laboratory experiments, e.g., wind-tunnel experiments. Series of wind-tunnel experiments of thermally-stratified boundary-layer flow over a surface-mounted 2-D block, in a well-controlled boundary-layer wind tunnel, will be presented. Measurements using high-resolution PIV, x-wire/cold-wire anemometry and surface heat flux sensors were conducted to quantify the turbulent flow properties, including the size of the recirculation zone, coherent vortex structures and the subsequent boundary layer recovery. Results will be shown to address thermal stability effects on momentum and scalar flux distribution in the wake, as well as dominant mechanism of turbulent kinetic energy generation and consumption. The authors gratefully acknowledge funding from the Swiss National Foundation (Grant 200021-132122), the National Science Foundation (Grant ATM-0854766) and NASA (Grant NNG06GE256).

Orbiter Boundary Layer Transition Prediction Tool Enhancements

NASA Technical Reports Server (NTRS)

Berry, Scott A.; King, Rudolph A.; Kegerise, Michael A.; Wood, William A.; McGinley, Catherine B.; Berger, Karen T.; Anderson, Brian P.

2010-01-01

Updates to an analytic tool developed for Shuttle support to predict the onset of boundary layer transition resulting from thermal protection system damage or repair are presented. The boundary layer transition tool is part of a suite of tools that analyze the local aerothermodynamic environment to enable informed disposition of damage for making recommendations to fly as is or to repair. Using mission specific trajectory information and details of each d agmea site or repair, the expected time (and thus Mach number) of transition onset is predicted to help define proper environments for use in subsequent thermal and stress analysis of the thermal protection system and structure. The boundary layer transition criteria utilized within the tool were updated based on new local boundary layer properties obtained from high fidelity computational solutions. Also, new ground-based measurements were obtained to allow for a wider parametric variation with both protuberances and cavities and then the resulting correlations were calibrated against updated flight data. The end result is to provide correlations that allow increased confidence with the resulting transition predictions. Recently, a new approach was adopted to remove conservatism in terms of sustained turbulence along the wing leading edge. Finally, some of the newer flight data are also discussed in terms of how these results reflect back on the updated correlations.

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

Numerical studies of porous airfoils in transonic flow. Ph.D. Thesis. Final Report, 1 Jun. 1985 - 31 Aug. 1986

NASA Technical Reports Server (NTRS)

Chow, C. Y.

1986-01-01

A numerical tool is constructed to examine the effects of a porous surface on transonic airfoil performance and to help understand the flow structure of passive shockwave/boundary layer interactions. The porous region is located near the shock with a cavity underneath it. This study is composed of two parts. Solved in the first part, with an inviscid-flow approach, is the transonic full-potential equation associated with transpiration boundary conditions which are obtained from porosity modeling. The numerical results indicate that a porous airfoil has a wave drag lower than that of a solid airfoil. The observed lambda-shock structure in the wind-tunnel testing can be predicted. Furthermore, the lift could be increased with an appropriate porosity distribution. In the second part of this work, the modified version of either an interactive boundary layer (IBL) algorithm or a thin-layer Navier-Stokes (TLNS) algorithm is used to study the outer flow, while a stream-function formulation is used to model the inner flow in the shallow cavity. The coupling procedure at the porous surface is based on Darcy's law and the assumption of a constant total pressure in the cavity. In addition, a modified Baldwin-Lomax turbulence model is used to describe the transpired turbulent boundary layer in the TLNS approach, while the Cebeci turbulence model is used in the IBL approach. According to the present analysis, a porous surface can reduce the wave drag appreciably, but can also increase the viscous losses. As has been observed experimentally, the numerical results indicate that the total drag is reduced at higher Mach numbers and increased at lower Mach numbers when the angles of attack are small. Furthermore, the streamline pattern of passive shock/boundary layer interaction are revealed.

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.

Mean turbulence statistics in boundary layers over high-porosity foams

NASA Astrophysics Data System (ADS)

Efstathiou, Christoph; Luhar, Mitul

2018-04-01

This paper reports turbulent boundary layer measurements made over open-cell reticulated foams with varying pore size and thickness, but constant porosity ($\\epsilon \\approx 0.97$). The foams were flush-mounted into a cutout on a flat plate. A Laser Doppler Velocimeter (LDV) was used to measure mean streamwise velocity and turbulence intensity immediately upstream of the porous section, and at multiple measurement stations along the porous substrate. The friction Reynolds number upstream of the porous section was $Re_\\tau \\approx 1690$. For all but the thickest foam tested, the internal boundary layer was fully developed by $<10 \\delta$ downstream from the porous transition, where $\\delta$ is the boundary layer thickness. Fully developed mean velocity profiles showed the presence of a substantial slip velocity at the porous interface ($>30\\%$ of the free stream velocity) and a mean velocity deficit relative to the canonical smooth-wall profile further from the wall. While the magnitude of the mean velocity deficit increased with average pore size, the slip velocity remained approximately constant. Fits to the mean velocity profile suggest that the logarithmic region is shifted relative to a smooth wall, and that this shift increases with pore size until it becomes comparable to substrate thickness $h$. For all foams, the turbulence intensity was found to be elevated further into the boundary layer to $y/ \\delta \\approx 0.2$. An outer peak in intensity was also evident for the largest pore sizes. Velocity spectra indicate that this outer peak is associated with large-scale structures resembling Kelvin-Helmholtz vortices that have streamwise length scale $2\\delta-4\\delta$. Skewness profiles suggest that these large-scale structures may have an amplitude-modulating effect on the interfacial turbulence.

Transport velocity transformation - A convenient method for performance analysis of multilayer solar cell structure

NASA Technical Reports Server (NTRS)

Wolf, M.

1981-01-01

It is noted that in the case of low-level injection, space-charge quasi-neutrality, and spatially constant material parameters (including an electrostatic field), the individual layer can be treated analytically and the basic solar cell performance parameters can be evaluated from three equations. The first equation represents the transformation of the transport velocity across the layer from the other layer boundary. The second establishes the light-generated current output from the layer interface, under the influence of the transport velocities and minority-carrier density at both layer boundaries and of bulk recombination. The third equation describes the flow of these carriers across other layers. The power of the approach is considered to lie in its facility for analysis of the solar cell's performance layer by layer, giving a clear picture of the individual layer's influence on cell efficiency.

Direct numerical simulation of supersonic turbulent boundary layer subjected to a curved compression ramp

NASA Astrophysics Data System (ADS)

Tong, Fulin; Li, Xinliang; Duan, Yanhui; Yu, Changping

2017-12-01

Numerical investigations on a supersonic turbulent boundary layer over a longitudinal curved compression ramp are conducted using direct numerical simulation for a free stream Mach number M∞ = 2.9 and Reynolds number Reθ = 2300. The total turning angle is 24°, and the concave curvature radius is 15 times the thickness of the incoming turbulent boundary layer. Under the selected conditions, the shock foot is transferred to a fan of the compression wave because of the weaker adverse pressure gradient. The time-averaged flow-field in the curved ramp is statistically attached where the instantaneous flow-field is close to the intermittent transitory detachment state. Studies on coherent vortex structures have shown that large-scale vortex packets are enhanced significantly when the concave curvature is aligned in the spanwise direction. Consistent with findings of previous experiments, the effect of the concave curvature on the logarithmic region of the mean velocity profiles is found to be small. The intensity of the turbulent fluctuations is amplified across the curved ramp. Based on the analysis of the Reynolds stress anisotropy tensor, the evolutions of the turbulence state in the inner and outer layers of the boundary layer are considerably different. The curvature effect on the transport mechanism of the turbulent kinetic energy is studied using the balance analysis of the contributing terms in the transport equation. Furthermore, the Görtler instability in the curved ramp is quantitatively analyzed using a stability criterion. The instantaneous streamwise vorticity confirms the existence of the Görtler-like structures. These structures are characterized by an unsteady motion. In addition, the dynamic mode decomposition analysis of the instantaneous flow field at the spanwise/wall-normal plane reveals that four dynamical relevant modes with performance loss of 16% provide an optimal low-order representation of the essential characteristics of the numerical data. The spatial structures of the dominated low-frequency dynamic modes are found to be similar to that of the Görtler-like vortices.

Non-local Second Order Closure Scheme for Boundary Layer Turbulence and Convection

NASA Astrophysics Data System (ADS)

Meyer, Bettina; Schneider, Tapio

2017-04-01

There has been scientific consensus that the uncertainty in the cloud feedback remains the largest source of uncertainty in the prediction of climate parameters like climate sensitivity. To narrow down this uncertainty, not only a better physical understanding of cloud and boundary layer processes is required, but specifically the representation of boundary layer processes in models has to be improved. General climate models use separate parameterisation schemes to model the different boundary layer processes like small-scale turbulence, shallow and deep convection. Small scale turbulence is usually modelled by local diffusive parameterisation schemes, which truncate the hierarchy of moment equations at first order and use second-order equations only to estimate closure parameters. In contrast, the representation of convection requires higher order statistical moments to capture their more complex structure, such as narrow updrafts in a quasi-steady environment. Truncations of moment equations at second order may lead to more accurate parameterizations. At the same time, they offer an opportunity to take spatially correlated structures (e.g., plumes) into account, which are known to be important for convective dynamics. In this project, we study the potential and limits of local and non-local second order closure schemes. A truncation of the momentum equations at second order represents the same dynamics as a quasi-linear version of the equations of motion. We study the three-dimensional quasi-linear dynamics in dry and moist convection by implementing it in a LES model (PyCLES) and compare it to a fully non-linear LES. In the quasi-linear LES, interactions among turbulent eddies are suppressed but nonlinear eddy—mean flow interactions are retained, as they are in the second order closure. In physical terms, suppressing eddy—eddy interactions amounts to suppressing, e.g., interactions among convective plumes, while retaining interactions between plumes and the environment (e.g., entrainment and detrainment). In a second part, we employ the possibility to include non-local statistical correlations in a second-order closure scheme. Such non-local correlations allow to directly incorporate the spatially coherent structures that occur in the form of convective updrafts penetrating the boundary layer. This allows us to extend the work that has been done using assumed-PDF schemes for parameterising boundary layer turbulence and shallow convection in a non-local sense.

Flutter Sensitivity to Boundary Layer Thickness, Structural Damping, and Static Pressure Differential for a Shuttle Tile Overlay Repair Concept

NASA Technical Reports Server (NTRS)

Scott, Robert C.; Bartels, Robert E.

2009-01-01

This paper examines the aeroelastic stability of an on-orbit installable Space Shuttle patch panel. CFD flutter solutions were obtained for thick and thin boundary layers at a free stream Mach number of 2.0 and several Mach numbers near sonic speed. The effect of structural damping on these flutter solutions was also examined, and the effect of structural nonlinearities associated with in-plane forces in the panel was considered on the worst case linear flutter solution. The results of the study indicated that adequate flutter margins exist for the panel at the Mach numbers examined. The addition of structural damping improved flutter margins as did the inclusion of nonlinear effects associated with a static pressure difference across the panel.

Structure measurements in a synthetic turbulent boundary layer

NASA Astrophysics Data System (ADS)

Arakeri, Jaywant H.

1987-09-01

Extensive hot-wire measurements have been made to determine the structure of the large eddy in a synthejc turbulent boundary layer on a flat-plate model. The experiments were carried out in a wind tunnel at a nominal free-stream velocity of 12 m/s. The synthetic turbulent boundary layer had a hexagonal pattern of eddies and a ratio of streamwise scale to spanwise scale of 3.2:1. The measured celerity of the large eddy was 84.2 percent of the free-stream velocity. There was some loss of coherence, but very little distortion, as the eddies moved downstream. Several mean properties of the synthetic boundary layer were found to agree quite well with the mean properties of a natural turbulent boundary layer at the same Reynolds number. The large eddy is composed of a pair of primary counter-rotating vortices about five [...] long in the streamwise direction and about one [...] apart in the spanwise direction, where [...] is the mean boundary-layer thickness. The sense of the primary pair is such as to pump fluid away from the wall in the region between the vortices. A secondary pair of counter-rotating streamwise vortices, having a sense opposite to that of the primary pair, is observed outside of and slightly downstream from the primary vortices. Both pairs of vortices extend across the full thickness of the boundary layer and are inclined at a shallow angle to the surface of the flat plate. The data show that the mean vorticity vectors are not tangential to the large-eddy vortices. In fact, the streamwise and normal vorticity components that signal the presence of the eddy are of the same order of magnitude. Definite signatures are obtained in terms of the mean skin-friction coefficient and the mean wake parameter averaged at constant phase. Velocities induced by the vortices are partly responsible for entrainment of irrotational fluid, for transport of momentum, for generation of Reynolds stresses, and for maintenance of streamwise and normal vorticity in the outer flow. A stretching mechanism is important in matching spanwise vorticity close to the wall to variations in turbulent shearing stress. Regions where the stretching term is large coincide with regions of large wall shearing stress and large turbulence production.

Remote sensing of the boundary layer over the oceans. [by IRIS measurements

NASA Technical Reports Server (NTRS)

Prabhakara, C.; Dalu, G.; Nath, N. R.; Lo, R.

1978-01-01

The paper explores the possibility of remotely sensing the boundary layer structure over the oceans by means of the Nimbus 4 IR Interferometric Spectrometer (IRIS) measurements in the water vapor bands. It is found from theoretical considerations that the moderately strong spectral lines in the 9-micron water vapor window region contain useful information about the lowest layers in the atmosphere. The difference between the observed line strength and the theoretically predicted line strength provides information about the departure in the atmospheric temperature and water vapor profiles from standard conditions. The observations of METEOR oceanographic expedition over the North and South Atlantic, and the Indian Ocean expedition make it possible to model the inversion conditions. It is concluded that significant characteristics of the temperature and water vapor profiles in the boundary layer of the atmosphere can be remotely sensed using the water vapor spectral measurements over the oceans.

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.

Grain Boundary Engineering and Air Oxidation Behavior of Alloy 690

NASA Astrophysics Data System (ADS)

Xu, Peng; Zhao, Liang Y.; Sridharan, Kumar; Allen, Todd R.

Grain boundary engineering (GBE) was performed on nickel-based alloy 690 by thermomechanical processing (TMP) to alter the grain boundary character distribution (GBCD). It was found that 5% and 35% thickness reduction in single and multiple steps followed by solution annealing and water quench yielded a high fraction of special boundaries. The total length fraction of the low ∑ CSL (coincidence site lattice) was as high as 87.2%. The grain boundary network was disrupted after the TMP treatment, and the average grain size calculated after exclusion of special twin boundaries can be as much as 5 times larger than the as-received (AR) sample. The GBE sample showed better oxidation resistance compared to the AR sample during the long term air oxidation. In the cyclic oxidation test, both AR and GBE samples showed a mass gain at the beginning of the test which was then followed by a mass loss. The mass change of GBE samples oscillated after the first couple cycles, while the AR sample became relatively stable. The oxide film most likely consists of duplex structures with one stable layer that was formed inside and one unstable layer that was formed outside. The stable inner layer was the protective layer and prevented alloy 690 from further oxidation.

Photovoltaic devices comprising zinc stannate buffer layer and method for making

DOEpatents

Wu, Xuanzhi; Sheldon, Peter; Coutts, Timothy J.

2001-01-01

A photovoltaic device has a buffer layer zinc stannate Zn.sub.2 SnO.sub.4 disposed between the semiconductor junction structure and the transparent conducting oxide (TCO) layer to prevent formation of localized junctions with the TCO through a thin window semiconductor layer, to prevent shunting through etched grain boundaries of semiconductors, and to relieve stresses and improve adhesion between these layers.

Inner Plasma Structure of the Low-Latitude Reconnection Layer

NASA Technical Reports Server (NTRS)

Zhang, Q.-H.; Dunlop, M. W.; Lockwood, M.; Lavraud, B.; Bogdanova, Y. V.; Hasegawa, H.; Yang, H. -G.; Liu, R. -Y.; Hu, H. -Q.; Zhang, B. -C.;

Flow Visualization in Supersonic Turbulent Boundary Layers.

NASA Astrophysics Data System (ADS)

Smith, Michael Wayne

This thesis is a collection of novel flow visualizations of two different flat-plate, zero pressure gradient, supersonic, turbulent boundary layers (M = 2.8, Re _theta ~ 82,000, and M = 2.5, Re_ theta ~ 25,000, respectively). The physics of supersonic shear flows has recently drawn increasing attention with the renewed interest in flight at super and hypersonic speeds. This work was driven by the belief that the study of organized, Reynolds -stress producing turbulence structures will lead to improved techniques for the modelling and control of high-speed boundary layers. Although flow-visualization is often thought of as a tool for providing qualitative information about complex flow fields, in this thesis an emphasis is placed on deriving quantitative results from image data whenever possible. Three visualization techniques were applied--'selective cut-off' schlieren, droplet seeding, and Rayleigh scattering. Two experiments employed 'selective cut-off' schlieren. In the first, high-speed movies (40,000 fps) were made of strong density gradient fronts leaning downstream at between 30^circ and 60^ circ and travelling at about 0.9U _infty. In the second experiment, the same fronts were detected with hot-wires and imaged in real time, thus allowing the examination of the density gradient fronts and their associated single-point mass -flux signals. Two experiments employed droplet seeding. In both experiments, the boundary layer was seeded by injecting a stream of acetone through a single point in the wall. The acetone is atomized by the high shear at the wall into a 'fog' of tiny (~3.5mu m) droplets. In the first droplet experiment, the fog was illuminated with copper-vapor laser sheets of various orientations. The copper vapor laser pulses 'froze' the fog motion, revealing a variety of organized turbulence structures, some with characteristic downstream inclinations, others with large-scale roll-up on the scale of delta. In the second droplet experiment, high-speed movies were made of the fog under general illumination, thus providing information about the streamwise evolution of the structures seen in the planar stills. Rayleigh scattering from a laser sheet was used to create instantaneous density cross-sections in the M = 2.5 boundary layer. The Rayleigh scattering experiment represents the first measurement of the instantaneous 2-D field of an intrinsic fluid property in any boundary layer. Imaged by an intensified UV camera, scattering from the Argon-Fluoride laser (193 nm) revealed density structures with sharp interfaces between high and low-density fluid. These pictures were also used to generated quantitative turbulence information. Density pdf profiles, intermittency values, density correlations, and structure shape data were derived with standard digital image-processing techniques.

CDUCT-LaRC Status - Shear Layer Refraction and Noise Radiation

NASA Technical Reports Server (NTRS)

Nark, Douglas M.; Farassat, F.

2006-01-01

A proposed boundary condition accounting for shear layer effects within the Ffowcs Williams-Hawkings radiation module of the CDUCT-LaRC code is investigated. The development and numerical justification of the boundary condition formulation are reviewed. An initial assessment of the effectiveness of the shear layer correction is conducted through comparison with experimental data. Preliminary results indicate that the correction provides physically meaningful modifications of the baseline predicted directivity patterns. Trends of peak directivity steepening and shifting that appeared in predicted patterns were found to follow similar structures in measured data, particularly at higher radiation angles.

Adaptive wing and flow control technology

NASA Astrophysics Data System (ADS)

Stanewsky, E.

2001-10-01

The development of the boundary layer and the interaction of the boundary layer with the outer “inviscid” flow field, exacerbated at high speed by the occurrence of shock waves, essentially determine the performance boundaries of high-speed flight. Furthermore, flight and freestream conditions may change considerably during an aircraft mission while the aircraft itself is only designed for multiple but fixed design points thus impairing overall performance. Consequently, flow and boundary layer control and adaptive wing technology may have revolutionary new benefits for take-off, landing and cruise operating conditions for many aircraft by enabling real-time effective geometry optimization relative to the flight conditions. In this paper we will consider various conventional and novel means of boundary layer and flow control applied to moderate-to-large aspect ratio wings, delta wings and bodies with the specific objectives of drag reduction, lift enhancement, separation suppression and the improvement of air-vehicle control effectiveness. In addition, adaptive wing concepts of varying complexity and corresponding aerodynamic performance gains will be discussed, also giving some examples of possible structural realizations. Furthermore, penalties associated with the implementation of control and adaptation mechanisms into actual aircraft will be addressed. Note that the present contribution is rather application oriented.

Simulation of hypersonic shock wave - laminar boundary layer interactions

NASA Astrophysics Data System (ADS)

Kianvashrad, N.; Knight, D.

2017-06-01

The capability of the Navier-Stokes equations with a perfect gas model for simulation of hypersonic shock wave - laminar boundary layer interactions is assessed. The configuration is a hollow cylinder flare. The experimental data were obtained by Calspan-University of Buffalo (CUBRC) for total enthalpies ranging from 5.07 to 21.85 MJ/kg. Comparison of the computed and experimental surface pressure and heat transfer is performed and the computed §ow¦eld structure is analyzed.

Numerical study of 3D flow structure near a cylinder piercing turbulent free-convection boundary layer on a vertical plate

NASA Astrophysics Data System (ADS)

Levchenya, A. M.; Smirnov, E. M.; Zhukovskaya, V. D.

2018-05-01

The present contribution covers RANS-based simulation of 3D flow near a cylinder introduced into turbulent vertical-plate free-convection boundary layer. Numerical solutions were obtained with a finite-volume Navier-Stokes code of second-order accuracy using refined grids. Peculiarities of the flow disturbed by the obstacle are analyzed. Cylinder-diameter effect on the horseshoe vortex size and its position is evaluated.

Quantifying the Stable Boundary Layer Structure and Evolution during T-REX 2006

DTIC Science & Technology

2014-09-30

integrating surface observations, data from in-situ measurements, and a nested numerical model with two related topics was conducted in this project. the WRF ...as well as quantify differences at a fine scale model output using the different turbulent mixing/diffusion options in the WRF -ARW model; and (2... WRF model planetary boundary layer schemes were also conducted to study a downslope windstorm and rotors in Las Vegas valley. Two events (March 20

Application of renormalization group theory to the large-eddy simulation of transitional boundary layers

NASA Technical Reports Server (NTRS)

Piomelli, Ugo; Zang, Thomas A.; Speziale, Charles G.; Lund, Thomas S.

1990-01-01

An eddy viscosity model based on the renormalization group theory of Yakhot and Orszag (1986) is applied to the large-eddy simulation of transition in a flat-plate boundary layer. The simulation predicts with satisfactory accuracy the mean velocity and Reynolds stress profiles, as well as the development of the important scales of motion. The evolution of the structures characteristic of the nonlinear stages of transition is also predicted reasonably well.

Modeling interface shear behavior of granular materials using micro-polar continuum approach

NASA Astrophysics Data System (ADS)

Ebrahimian, Babak; Noorzad, Ali; Alsaleh, Mustafa I.

2018-01-01

Recently, the authors have focused on the shear behavior of interface between granular soil body and very rough surface of moving bounding structure. For this purpose, they have used finite element method and a micro-polar elasto-plastic continuum model. They have shown that the boundary conditions assumed along the interface have strong influences on the soil behavior. While in the previous studies, only very rough bounding interfaces have been taken into account, the present investigation focuses on the rough, medium rough and relatively smooth interfaces. In this regard, plane monotonic shearing of an infinite extended narrow granular soil layer is simulated under constant vertical pressure and free dilatancy. The soil layer is located between two parallel rigid boundaries of different surface roughness values. Particular attention is paid to the effect of surface roughness of top and bottom boundaries on the shear behavior of granular soil layer. It is shown that the interaction between roughness of bounding structure surface and the rotation resistance of bounding grains can be modeled in a reasonable manner through considered Cosserat boundary conditions. The influence of surface roughness is investigated on the soil shear strength mobilized along the interface as well as on the location and evolution of shear localization formed within the layer. The obtained numerical results have been qualitatively compared with experimental observations as well as DEM simulations, and acceptable agreement is shown.

Developing a framework for integrating turbulence measurements and modeling of ecosystem-atmosphere interactions

NASA Astrophysics Data System (ADS)

Markfort, C. D.

2017-12-01

Aquatic ecosystems are integrators of nutrient and carbon from their watersheds. The effects of climate change in many cases will enhance the rate of these inputs and change the thermodynamics within aquatic environments. It is unclear the extent these changes will have on water quality and carbon assimilation, but the drivers of these processes will be determined by the complex interactions at the land-water and air-water interfaces. For example, flow over and beneath wind-driven surface waves generate turbulence that plays an important role in aquatic ecology and biogeochemistry, exchange of gases such as oxygen and carbon dioxide, and it is important for the transfer of energy and controlling evaporation. Energy transferred from the atmosphere promotes the generation and maintenance of waves. A fraction of the energy is transferred to the surface mixed layer through the generation of turbulence. Energy is also transferred back to the atmosphere by waves. There is a need to quantify the details of the coupled boundary layers of the air-water system to better understand how turbulence plays a role in the interactions. We have developed capabilities to conduct field and laboratory experiments using eddy covariance on tall-towers and rafts, UAS platforms integrated with remote sensing, and detailed wind-wave measurements with time-resolved PIV in a new boundary layer wind-wave tunnel. We will show measurements of the detailed structure of the air and water boundary layers under varying wind and wave conditions in the newly developed IIHR Boundary-Layer Wind-Wave Tunnel. The facility combines a 30-m long recirculating water channel with an open-return boundary layer wind tunnel. A thick turbulent boundary layer is developed in the 1 m high air channel, over the water surface, allowing for the study of boundary layer turbulence interacting with a wind-driven wave field. Results will help interpret remote sensing, energy budget measurements, and turbulence transport models for sheltered lakes influenced by terrain and tall trees.

The control effect in a detached laminar boundary layer of an array of normal synthetic jets

NASA Astrophysics Data System (ADS)

Valenzuela Calva, Fernando; Avila Rodriguez, Ruben

2016-11-01

In this work, 3D numerical simulations of an array of three normal circular synthetic jets embedded in an attached laminar boundary layer that separates under the influence of an inclined flap are performed for flow separation control. At the beginning of the present study, three cases are used to validate the numerical simulation with data obtained from experiments. The experimental data is chosen based on the cases which presented higher repeatability and reliability. Simulations showed reasonable agreement when compared with experiments. The simulations are undertaken at three synthetic jet operating conditions, i.e. Case A: L = 2, VR = 0.32; Case B: L = 4, VR = 0.64 and Case C: L = 6, VR = 0.96. The vortical structures produced for each synthetic jet operating condition are hairpin vortices for Case A and tilted vortices for Case B and C, respectively. By examining the spatial wall shear stress variations, the effect on the boundary layer prior to separation of the middle synthetic jet is evaluated. For effective flow control, produced at a relatively low the finding from this study suggests that hairpin vortical structures are more desirable structures. Universidad Nacional Autonoma de Mexico.

Characteristic Lifelength of Coherent Structure in the Turbulent Boundary Layer

NASA Technical Reports Server (NTRS)

Palumbo, Daniel L.

2006-01-01

A characteristic lifelength is defined by which a Gaussian distribution is fit to data correlated over a 3 sensor array sampling streamwise sidewall pressure. The data were acquired at subsonic, transonic and supersonic speeds aboard a Tu-144. Lifelengths are estimated using the cross spectrum and are shown to compare favorably with Efimtsov's prediction of correlation space scales. Lifelength distributions are computed in the time/frequency domain using an interval correlation technique on the continuous wavelet transform of the original time data. The median values of the lifelength distributions are found to be very close to the frequency averaged result. The interval correlation technique is shown to allow the retrieval and inspection of the original time data of each event in the lifelength distribution, thus providing a means to locate and study the nature of the coherent structure in the turbulent boundary layer. The lifelength data can be converted to lifetimes using the convection velocity. The lifetime of events in the time/frequency domain are displayed in Lifetime Maps. The primary purpose of the paper is to validate these new analysis techniques so that they can be used with confidence to further characterize coherent structure in the turbulent boundary layer.

Supersonic compressor

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

Roberts, II, William Byron; Lawlor, Shawn P.; Breidenthal, Robert E.

A supersonic compressor including a rotor to deliver a gas at supersonic conditions to a diffuser. The diffuser includes a plurality of aerodynamic ducts that have converging and diverging portions, for deceleration of gas to subsonic conditions and then for expansion of subsonic gas, to change kinetic energy of the gas to static pressure. The aerodynamic ducts include vortex generating structures for controlling boundary layer, and structures for changing the effective contraction ratio to enable starting even when the aerodynamic ducts are designed for high pressure ratios, and structures for boundary layer control. In an embodiment, aerodynamic ducts are providedmore » having an aspect ratio of in excess of two to one, when viewed in cross-section orthogonal to flow direction at an entrance to the aerodynamic duct.« less

Parallelization of the Flow Field Dependent Variation Scheme for Solving the Triple Shock/Boundary Layer Interaction Problem

NASA Technical Reports Server (NTRS)

Schunk, Richard Gregory; Chung, T. J.

2001-01-01

A parallelized version of the Flowfield Dependent Variation (FDV) Method is developed to analyze a problem of current research interest, the flowfield resulting from a triple shock/boundary layer interaction. Such flowfields are often encountered in the inlets of high speed air-breathing vehicles including the NASA Hyper-X research vehicle. In order to resolve the complex shock structure and to provide adequate resolution for boundary layer computations of the convective heat transfer from surfaces inside the inlet, models containing over 500,000 nodes are needed. Efficient parallelization of the computation is essential to achieving results in a timely manner. Results from a parallelization scheme, based upon multi-threading, as implemented on multiple processor supercomputers and workstations is presented.

Boundary-Layer Stability Analysis of the Mean Flows Obtained Using Unstructured Grids

NASA Technical Reports Server (NTRS)

Liao, Wei; Malik, Mujeeb R.; Lee-Rausch, Elizabeth M.; Li, Fei; Nielsen, Eric J.; Buning, Pieter G.; Chang, Chau-Lyan; Choudhari, Meelan M.

2012-01-01

Boundary-layer stability analyses of mean flows extracted from unstructured-grid Navier- Stokes solutions have been performed. A procedure has been developed to extract mean flow profiles from the FUN3D unstructured-grid solutions. Extensive code-to-code validations have been performed by comparing the extracted mean ows as well as the corresponding stability characteristics to the predictions based on structured-grid solutions. Comparisons are made on a range of problems from a simple at plate to a full aircraft configuration-a modified Gulfstream-III with a natural laminar flow glove. The future aim of the project is to extend the adjoint-based design capability in FUN3D to include natural laminar flow and laminar flow control by integrating it with boundary-layer stability analysis codes, such as LASTRAC.

Large-eddy simulation of the urban boundary layer in the MEGAPOLI Paris Plume experiment

NASA Astrophysics Data System (ADS)

Esau, Igor

2010-05-01

This study presents results from the specific large-eddy simulation study of the urban boundary layer in the MEGAPOLI Paris Plume field campaign. We used LESNIC and PALM codes, MEGAPOLI city morphology database, nudging to the observed meteorological conditions during the Paris Plume campaign and some concentration measurements from that campaign to simulate and better understand the nature of the urban boundary layer on scales larger then the street canyon scales. The primary attention was paid to turbulence self-organization and structure-to-surface interaction. The study has been aimed to demonstrate feasibility and estimate required resources for such research. Therefore, at this stage we do not compare the simulation with other relevant studies as well as we do not formulate the theoretical conclusions.

Convective Differentiation of the Earth's Mantle

NASA Astrophysics Data System (ADS)

Hansen, U.; Schmalzl, J.; Stemmer, K.

2007-05-01

The differentiation of the Earth is likely to be influenced by convective motions within the early mantle. Double- diffusive convection (d.d.c), driven by thermally and compositionally induced density differences is considered as a vital mechanism behind the dynamic differentiation of the early mantle.. We demonstrate that d.d.c can lead to layer formation on a planetary scale in the diffusive regime where composition stabilizes the system whil heat provides the destabilizing force. Choosing initial conditions in which a stable compositional gradient overlies a hot reservoir we mimic the situation of a planet in a phase after core formation. Differently from earlier studies we fixed the temperature rather than the heat flux at the lower boundary, resembling a more realistic condition for the core-mantle boundary. We have carried out extended series of numerical experiments, ranging from 2D calculations in constant viscosity fluids to fully 3D experiments in spherical geometry with strongly temperature dependent viscosity. The buoyancy ratio R and the Lewis number Le are the important dynamical parameters. In all scenarios we could identify a parameter regime where the non-layered initial structure developed into a state consisting of several, mostly two layers. Initially plumes from the bottom boundary homogenize a first layer which subsequently thickens. The bottom layer heats up and then convection is initiated in the top layer. This creates dynamically (i.e. without jump in the material behavior) a stack of separately convecting layers. The bottom layer is significantly thicker than the top layer. Strongly temperature dependent viscosity leads to a more complex evolution The formation of the bottom layer is followed by the generation of several layers on top. Finally the uppermost layer starts to convect. In general, the multilayer structure collapses into a two layer system. We employed a numerical technique, allowing for a diffusion free treatment of the compositional field. In each case a similar evolution has been observed. This indicates that a temporary formation of layered structures in planetary interiors is a typical phenomenon. Moreover, in this scenario, plate tectonics appears only in later stages of the evolution.

THE EFFECT OF RECONNECTION ON THE STRUCTURE OF THE SUN’S OPEN–CLOSED FLUX BOUNDARY

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

Pontin, D. I.; Wyper, P. F., E-mail: dpontin@maths.dundee.ac.uk, E-mail: peter.f.wyper@nasa.gov

2015-05-20

Global magnetic field extrapolations are now revealing the huge complexity of the Sun's corona, and in particular the structure of the boundary between open and closed magnetic flux. Moreover, recent developments indicate that magnetic reconnection in the corona likely occurs in highly fragmented current layers, and that this typically leads to a dramatic increase in the topological complexity beyond that of the equilibrium field. In this paper we use static models to investigate the consequences of reconnection at the open–closed flux boundary (“interchange reconnection”) in a fragmented current layer. We demonstrate that it leads to efficient mixing of magnetic fluxmore » (and therefore plasma) from open and closed field regions. This corresponds to an increase in the length and complexity of the open–closed boundary. Thus, whenever reconnection occurs at a null point or separator of this open–closed boundary, the associated separatrix arc of the so-called S-web in the high corona becomes not a single line but a band of finite thickness within which the open–closed boundary is highly structured. This has significant implications for the acceleration of the slow solar wind, for which the interaction of open and closed field is thought to be important, and may also explain the coronal origins of certain solar energetic particles. The topological structures examined contain magnetic null points, separatrices and separators, and include a model for a pseudo-streamer. The potential for understanding both the large scale morphology and fine structure observed in flare ribbons associated with coronal nulls is also discussed.« less

Boundary layer structure and scavenging effect during a typical winter haze-fog episode in a core city of BTH region, China

NASA Astrophysics Data System (ADS)

Han, Suqin; Liu, Jingle; Hao, Tianyi; Zhang, Yufen; Li, Peiyan; Yang, Jianbo; Wang, Qinliang; Cai, Ziying; Yao, Qing; Zhang, Min; Wang, Xiujun

2018-04-01

The vertical distribution of PM2.5 and meteorological parameters from ground to upper levels were observed simultaneously using meteorological tower, tethered balloons and aerosol laser radar in Dec of 2016 in the urban area of Tianjin and its southern district, Jinghai. The influence of the vertical structure of boundary layer on a typical haze-fog episode was analyzed. There existed long distance transport of PM in the high layers before the haze formed in Tianjin and the downward airflows brought the PM from the high layer to the ground. In the early stages of this episode, periodic temperature inversions occurred, leading to conspicuous diurnal variations in the vertical profile of the PM2.5. In the middle and late stages of this episode, strong inversion and thick humidity layer were sustained below 400 m, and there were no big daily changes in the vertical profiles of the PM2.5. During the rapid formation period of the fog, the inversion layer was damaged and turbulence was strengthened. During the stationary phase of the fog process, wind and turbulence in the boundary layer became weak again. Rime was the main weather-related, wet cleaning mechanism that lowered pollutants concentration during this fog episode. High concentrations of water soluble ions in the rime samples and the concentrations of those ions in ambient PM2.5 appeared significant decrease during the rime period, which illustrated the scavenging effect of rime.

Active constrained layer damping treatments for shell structures: a deep-shell theory, some intuitive results, and an energy analysis

NASA Astrophysics Data System (ADS)

Shen, I. Y.

1997-02-01

This paper studies vibration control of a shell structure through use of an active constrained layer (ACL) damping treatment. A deep-shell theory that assumes arbitrary Lamé parameters 0964-1726/6/1/011/img1 and 0964-1726/6/1/011/img2 is first developed. Application of Hamilton's principle leads to the governing Love equations, the charge equation of electrostatics, and the associated boundary conditions. The Love equations and boundary conditions imply that the control action of the ACL for shell treatments consists of two components: free-end boundary actuation and membrane actuation. The free-end boundary actuation is identical to that of beam and plate ACL treatments, while the membrane actuation is unique to shell treatments as a result of the curvatures of the shells. In particular, the membrane actuation may reinforce or counteract the boundary actuation, depending on the location of the ACL treatment. Finally, an energy analysis is developed to determine the proper control law that guarantees the stability of ACL shell treatments. Moreover, the energy analysis results in a simple rule predicting whether or not the membrane actuation reinforces the boundary actuation.

Highly mobile type II twin boundary in Ni-Mn-Ga five-layered martensite

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

Sozinov, A.; Lanska, N.; Soroka, A.

2011-09-19

Twin relationships and stress-induced reorientation were studied in Ni{sub 2}Mn{sub 1.14}Ga{sub 0.86} single crystal with five-layered modulated martensite crystal structure. Very low twinning stress of about 0.1 MPa was found for twin boundaries which deviated a few degrees from the (011) crystallographic plane. However, twin boundaries oriented exactly parallel to the (011) plane exhibited considerably higher level of twinning stress, above 1 MPa. X-ray diffraction experiments and calculations based on approximation of the martensite crystal lattice as a tetragonal lattice with a slight monoclinic distortion identified the two different kinds of twin interfaces as type II and type I twinmore » boundaries.« less

Large Eddy Simulations of Continental Boundary Layer Clouds Observed during the RACORO Field Campaign

NASA Astrophysics Data System (ADS)

Endo, S.; Fridlind, A. M.; Lin, W.; Vogelmann, A. M.; Toto, T.; Liu, Y.

2013-12-01

Three cases of boundary layer clouds are analyzed in the FAst-physics System TEstbed and Research (FASTER) project, based on continental boundary-layer-cloud observations during the RACORO Campaign [Routine Atmospheric Radiation Measurement (ARM) Aerial Facility (AAF) Clouds with Low Optical Water Depths (CLOWD) Optical Radiative Observations] at the ARM Climate Research Facility's Southern Great Plains (SGP) site. The three 60-hour case study periods are selected to capture the temporal evolution of cumulus, stratiform, and drizzling boundary-layer cloud systems under a range of conditions, intentionally including those that are relatively more mixed or transitional in nature versus being of a purely canonical type. Multi-modal and temporally varying aerosol number size distribution profiles are derived from aircraft observations. Large eddy simulations (LESs) are performed for the three case study periods using the GISS Distributed Hydrodynamic Aerosol and Radiative Modeling Application (DHARMA) model and the WRF-FASTER model, which is the Weather Research and Forecasting (WRF) model implemented with forcing ingestion and other functions to constitute a flexible LES. The two LES models commonly capture the significant transitions of cloud-topped boundary layers in the three periods: diurnal evolution of cumulus layers repeating over multiple days, nighttime evolution/daytime diminution of thick stratus, and daytime breakup of stratus and stratocumulus clouds. Simulated transitions of thermodynamic structures of the cloud-topped boundary layers are examined by balloon-borne soundings and ground-based remote sensors. Aircraft observations are then used to statistically evaluate the predicted cloud droplet number size distributions under varying aerosol and cloud conditions. An ensemble approach is used to refine the model configuration for the combined use of observations with parallel LES and single-column model simulations. See Lin et al. poster for single-column model investigation.

On the impact of adverse pressure gradient on the supersonic turbulent boundary layer

NASA Astrophysics Data System (ADS)

Wang, Qian-Cheng; Wang, Zhen-Guo; Zhao, Yu-Xin

2016-11-01

By employing the particle image velocimetry, the mean and turbulent characteristics of a Mach 2.95 turbulent boundary layer are experimentally investigated without the impact of curvature. The physical mechanism with which the streamwise adverse pressure gradient affects the supersonic boundary layer is revealed. The data are compared to that of the concave boundary layer with similar streamwise distributions of wall static pressure to clarify the separate impacts of the adverse pressure gradient and the concave curvature. The logarithmic law is observed to be well preserved for both of the cases. The dip below the logarithmic law is not observed in present investigation. Theoretical analysis indicates that it could be the result of compromise between the opposite impacts of the compression wave and the increased turbulent intensity. Compared to the zero pressure gradient boundary layer, the principal strain rate and the turbulent intensities are increased by the adverse pressure gradient. The shear layer formed due the hairpin packets could be sharpened by the compression wave, which leads to higher principal strain rate and the associated turbulent level. Due to the additional impact of the centrifugal instability brought by the concave wall, even higher turbulent intensities than that of the adverse pressure gradient case are introduced. The existence of velocity modes within the zero pressure gradient boundary layer suggests that the large scale motions are statistically well organized. The generation of new velocity modes due to the adverse pressure gradient indicates that the turbulent structure is changed by the adverse pressure gradient, through which more turbulence production that cannot be effectively predicted by the Reynolds-stress transport equations could be brought.

Influence of Idealized Heterogeneity on Wet and Dry Planetary Boundary Layers Coupled to the Land Surface. 2; Phase-Averages

NASA Technical Reports Server (NTRS)

Houser, Paul (Technical Monitor); Patton, Edward G.; Sullivan, Peter P.; Moeng, Chin-Hoh

2003-01-01

We examine the influence of surface heterogeneity on boundary layers using a large-eddy simulation coupled to a land-surface model. Heterogeneity, imposed in strips varying from 2-30 km (1 less than lambda/z(sub i) less than 18), is found to dramatically alter the structure of the free convective boundary layer by inducing significant organized circulations. A conditional sampling technique, based on the scale of the surface heterogeneity (phase averaging), is used to identify and quantify the organized surface fluxes and motions in the atmospheric boundary layer. The impact of the organized motions on turbulent transport depends critically on the scale of the heterogeneity lambda, the boundary layer height zi and the initial moisture state of the boundary layer. Dynamical and scalar fields respond differently as the scale of the heterogeneity varies. Surface heterogeneity of scale 4 less than lamba/z(sub i) less than 9 induces the strongest organized flow fields (up, wp) while heterogeneity with smaller or larger lambda/z(sub i) induces little organized motion. However, the organized components of the scalar fields (virtual potential temperature and mixing ratio) grow continuously in magnitude and horizontal scale, as lambda/z(sub i) increases. For some cases, the organized motions can contribute nearly 100% of the total vertical moisture flux. Patch-induced fluxes are shown to dramatically impact point measurements that assume the time-average vertical velocity to be zero. The magnitude and sign of this impact depends on the location of the measurement within the region of heterogeneity.

Transient Growth Analysis of Compressible Boundary Layers with Parabolized Stability Equations

NASA Technical Reports Server (NTRS)

Paredes, Pedro; Choudhari, Meelan M.; Li, Fei; Chang, Chau-Lyan

2016-01-01

The linear form of parabolized linear stability equations (PSE) is used in a variational approach to extend the previous body of results for the optimal, non-modal disturbance growth in boundary layer flows. This methodology includes the non-parallel effects associated with the spatial development of boundary layer flows. As noted in literature, the optimal initial disturbances correspond to steady counter-rotating stream-wise vortices, which subsequently lead to the formation of stream-wise-elongated structures, i.e., streaks, via a lift-up effect. The parameter space for optimal growth is extended to the hypersonic Mach number regime without any high enthalpy effects, and the effect of wall cooling is studied with particular emphasis on the role of the initial disturbance location and the value of the span-wise wavenumber that leads to the maximum energy growth up to a specified location. Unlike previous predictions that used a basic state obtained from a self-similar solution to the boundary layer equations, mean flow solutions based on the full Navier-Stokes (NS) equations are used in select cases to help account for the viscous-inviscid interaction near the leading edge of the plate and also for the weak shock wave emanating from that region. These differences in the base flow lead to an increasing reduction with Mach number in the magnitude of optimal growth relative to the predictions based on self-similar mean-flow approximation. Finally, the maximum optimal energy gain for the favorable pressure gradient boundary layer near a planar stagnation point is found to be substantially weaker than that in a zero pressure gradient Blasius boundary layer.

The dependence of the strength and thickness of field-aligned currents on solar wind and ionospheric parameters

PubMed Central

Johnson, Jay R.; Wing, Simon

2017-01-01

Sheared plasma flows at the low-latitude boundary layer (LLBL) correlate well with early afternoon auroral arcs and upward field-aligned currents. We present a simple analytic model that relates solar wind and ionospheric parameters to the strength and thickness of field-aligned currents (Λ) in a region of sheared velocity, such as the LLBL. We compare the predictions of the model with DMSP observations and find remarkably good scaling of the upward region 1 currents with solar wind and ionospheric parameters in region located at the boundary layer or open field lines at 1100–1700 magnetic local time. We demonstrate that Λ~nsw−0.5 and Λ ~ L when Λ/L < 5 where L is the auroral electrostatic scale length. The sheared boundary layer thickness (Δm) is inferred to be around 3000 km, which appears to have weak dependence on Vsw. J‖ has dependencies on Δm, Σp, nsw, and Vsw. The analytic model provides a simple way to organize data and to infer boundary layer structures from ionospheric data. PMID:29057194

Electromagnetic fluctuations generated in the boundary layer of laboratory-created ionospheric depletions

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

Liu, Yu; Lei, Jiuhou, E-mail: leijh@ustc.edu.cn; Collaborative Innovation Center of Astronautical Science and Technology, Harbin 150001

Ionospheric depletions, produced by release of attachment chemicals into the ionosphere, were widely investigated and taken as a potential technique for the artificial modification of space weather. In this work, we reported the experimental evidence of spontaneously generated electromagnetic fluctuations in the boundary layer of laboratory-created ionospheric depletions. These depletions were produced by releasing attachment chemicals into the ambient plasmas. Electron density gradients and sheared flows arose in the boundary layer between the ambient and the negative ions plasmas. These generated electromagnetic fluctuations with fundamental frequency f{sub 0} = 70 kHz lie in the lower hybrid frequency range, and the mode propagates withmore » angles smaller than 90° (0.3π–0.4π) relative to the magnetic field. Our results revealed that these observed structures were most likely due to electromagnetic components of the electron-ion hybrid instability. This research demonstrates that electromagnetic fluctuations also can be excited during active release experiments, which should be considered as an essential ingredient in the boundary layer processes of ionospheric depletions.« less

The effect of non-Newtonian viscosity on the stability of the Blasius boundary layer

NASA Astrophysics Data System (ADS)

Griffiths, P. T.; Gallagher, M. T.; Stephen, S. O.

2016-07-01

We consider, for the first time, the stability of the non-Newtonian boundary layer flow over a flat plate. Shear-thinning and shear-thickening flows are modelled using a Carreau constitutive viscosity relationship. The boundary layer equations are solved in a self-similar fashion. A linear asymptotic stability analysis, that concerns the lower-branch structure of the neutral curve, is presented in the limit of large Reynolds number. It is shown that the lower-branch mode is destabilised and stabilised for shear-thinning and shear-thickening fluids, respectively. Favourable agreement is obtained between these asymptotic predictions and numerical results obtained from an equivalent Orr-Sommerfeld type analysis. Our results indicate that an increase in shear-thinning has the effect of significantly reducing the value of the critical Reynolds number, this suggests that the onset of instability will be significantly advanced in this case. This postulation, that shear-thinning destabilises the boundary layer flow, is further supported by our calculations regarding the development of the streamwise eigenfunctions and the relative magnitude of the temporal growth rates.

Changes in the turbulent boundary layer structure associated with net drag reduction by outer layer manipulators

NASA Technical Reports Server (NTRS)

Rashidnia, N.; Falco, R. E.

1987-01-01

A specially designed wind tunnel was used to examine the effects of tandemly arranged parallel plate manipulators (TAPPMs) on a turbulent boundary-layer structure and the associated drag. Momentum balances, as well as measurements of the local shear stress from the velocity gradient near the wall, were used to obtain the net drag and local skin friction changes. Two TAPPMs, identical except for the thickness of their plates, were used in the study. Results with .003 inch plates were a maximum net drag reduction of 10 percent at 58 beta sub o (using a momentum balance). At 20 beta sub o, simultaneous laser sheet flow visualization and hot-wire anemometry data showed that the Reynolds stress in the large eddies was significantly reduced, as were the streamwise and normal velocity components. Using space-time correlations the reductions were again identified. Furthermore, quantitative flow visualization showed that the outward normal velocity of the inner region was also significantly decreased in the region around 20 beta sub o. However, throughout the first 130 beta sub o, the measured sublayer thickness with the TAPPMs in place was 15 to 20 percent greater. The data showed that the skin friction, as well as the structure of the turbulence, was strongly modified in the first 35 beta sub o, but that they both significantly relaxed toward unmanipulated boundary layer values by 50 beta sub o.

Characterization of the multilayered shell of a limpet, Lottia kogamogai (Mollusca: Patellogastropoda), using SEM-EBSD and FIB-TEM techniques.

PubMed

Suzuki, Michio; Kameda, Jun; Sasaki, Takenori; Saruwatari, Kazuko; Nagasawa, Hiromichi; Kogure, Toshihiro

2010-08-01

The microstructure and its crystallographic aspect of the shell of a limpet, Lottiakogamogai, have been investigated, as the first step to clarify the mechanism of shell formation in limpet. The shell consists of five distinct layers stacked along the shell thickness direction. Transmission electron microscopy (TEM) with the focused ion beam (FIB) sample preparation technique was primarily adopted, as well as scanning electron microscopy (SEM) with electron back-scattered diffraction (EBSD). The five layers were termed as M+3, M+2, M+1, M, M-1 from the outside to the inside in previous works, where M means myostracum. The outmost M+3 layer consists of calcite with a "mosaic" structure; granular submicron sub-grains with small-angle grain boundaries often accompanying dislocation arrays. M+2 layer consists of flat prismatic aragonite crystals with a leaf-like cross section, stacked obliquely to the shell surface. It looks that the prismatic crystals are surrounded by organic sheets, forming a compartment structure. M+1 and M-1 layers adopt a crossed lamellar structure consisting of aragonite flat prisms with rectangular cross section. M layer has a prismatic structure of aragonite perpendicular to the shell surface and with irregular shaped cross sections. Distinct organic sheets were not observed between the crystals in M+1, M and M-1 layers. The {110} twins are common in all aragonite M+2, M+1, M and M-1 layers, with the twin boundaries parallel to the prisms. These results for the microstructure of each layer should be considered in the discussion of the formation mechanism of the limpet shell structure. Copyright 2010 Elsevier Inc. All rights reserved.

Effects of complex internal structures on rheology of multiple emulsions particles in 2D from a boundary integral method.

PubMed

Wang, Jingtao; Liu, Jinxia; Han, Junjie; Guan, Jing

2013-02-08

A boundary integral method is developed to investigate the effects of inner droplets and asymmetry of internal structures on rheology of two-dimensional multiple emulsion particles with arbitrary numbers of layers and droplets within each layer. Under a modest extensional flow, the number increment of layers and inner droplets, and the collision among inner droplets subject the particle to stronger shears. In addition, the coalescence or release of inner droplets changes the internal structure of the multiple emulsion particles. Since the rheology of such particles is sensitive to internal structures and their change, modeling them as the core-shell particles to obtain the viscosity equation of a single particle should be modified by introducing the time-dependable volume fraction Φ(t) of the core instead of the fixed Φ. An asymmetric internal structure induces an oriented contact and merging of the outer and inner interface. The start time of the interface merging is controlled by adjusting the viscosity ratio and enhancing the asymmetry, which is promising in the controlled release of inner droplets through hydrodynamics for targeted drug delivery.

Flow characteristics and scaling past highly porous wall-mounted fences

NASA Astrophysics Data System (ADS)

Rodríguez-López, Eduardo; Bruce, Paul J. K.; Buxton, Oliver R. H.

2017-07-01

An extensive characterization of the flow past wall-mounted highly porous fences based on single- and multi-scale geometries has been performed using hot-wire anemometry in a low-speed wind tunnel. Whilst drag properties (estimated from the time-averaged momentum equation) seem to be mostly dependent on the grids' blockage ratio; wakes of different size and orientation bars seem to generate distinct behaviours regarding turbulence properties. Far from the near-grid region, the flow is dominated by the presence of two well-differentiated layers: one close to the wall dominated by the near-wall behaviour and another one corresponding to the grid's wake and shear layer, originating from between this and the freestream. It is proposed that the effective thickness of the wall layer can be inferred from the wall-normal profile of root-mean-square streamwise velocity or, alternatively, from the wall-normal profile of streamwise velocity correlation. Using these definitions of wall-layer thickness enables us to collapse different trends of the turbulence behaviour inside this layer. In particular, the root-mean-square level of the wall shear stress fluctuations, longitudinal integral length scale, and spanwise turbulent structure is shown to display a satisfactory scaling with this thickness rather than with the whole thickness of the grid's wake. Moreover, it is shown that certain grids destroy the spanwise arrangement of large turbulence structures in the logarithmic region, which are then re-formed after a particular streamwise extent. It is finally shown that for fences subject to a boundary layer of thickness comparable to their height, the effective thickness of the wall layer scales with the incoming boundary layer thickness. Analogously, it is hypothesized that the growth rate of the internal layer is also partly dependent on the incoming boundary layer thickness.

Dynamical Generation of the Transition Zone in the Earth's Mantle

NASA Astrophysics Data System (ADS)

Hansen, U.; Stemmer, K.

2005-12-01

The internal structure of the Earth is made up by a series of layers, though it is unclear how many layers exist and if there are layers invisible to remote sensing techniques. The transition zone is likely to be a boundary layer separating the convective systems in the lower and upper mantle. It seems likely that currently there is some mass exchange across this boundary, rather than the two systems beeing strictly separated.a Double-diffusive convection(d.d.c) is a vital mechanism which can generate layered structure and may thus be an important mmical machinery behind the formation of the transition zone. Double-diffusive convection determines the dynamics of systems whose density is influenced by at least two components with different molecular diffusivities.In the mantle, composition and temperature play the role of those two components. By means of numerical experiments we demonstrate that under mantle relevant conditions d.d.c typically leads to the formation of a transition zone. The calculations encompass two- and three dimensional Cartesian geometries as well as fully 3D spherical domains. We have further included strongly temperature dependent viscosity and find that this leads to even more pronounced layering. In most cases a layered flow pattern emerges, where two layers with a transition zone in between resembles a quasistationary state. Thus, the transition zone can be the result of a self organization process of the convective flow in the mantle. The presence of a phase transition further helps to stabilize the boundary against overturning, even on a time scale on the order of the age of the Earth.

An Analysis of the Observed Low-level Structure of Rapidly Intensifying and Mature Hurricane Earl (2010)

DTIC Science & Technology

2014-01-01

characteristics of the boundary layer The studies by Braun and Tao (2000) and Smith and Thomsen (2010) have elevated awareness of an important problem ...estimates also of forecast uncertainty which follow from the uncertainty in not knowing the optimum boundary-layer scheme to use. In an effort to address this...Quarterly Journal of the Royal Meteorological Society Q. J. R. Meteorol. Soc. (2014) DOI:10.1002/qj.2283 An analysis of the observed low-level

Progress in modeling hypersonic turbulent boundary layers

NASA Technical Reports Server (NTRS)

Zeman, Otto

1993-01-01

A good knowledge of the turbulence structure, wall heat transfer, and friction in turbulent boundary layers (TBL) at high speeds is required for the design of hypersonic air breathing airplanes and reentry space vehicles. This work reports on recent progress in the modeling of high speed TBL flows. The specific research goal described here is the development of a second order closure model for zero pressure gradient TBL's for the range of Mach numbers up to hypersonic speeds with arbitrary wall cooling requirements.

Shed vortex structure and phase-averaged velocity statistics in symmetric/asymmetric turbulent flat plate wakes

NASA Astrophysics Data System (ADS)

Rai, Man Mohan

2018-05-01

The near wake of a flat plate is investigated via direct numerical simulations. Many earlier experimental investigations have used thin plates with sharp trailing edges and turbulent boundary layers to create the wake. This results in large θ/DTE values (θ is the boundary layer momentum thickness toward the end of the plate and DTE is the trailing edge thickness). In the present study, the emphasis is on relatively thick plates with circular trailing edges (CTEs) resulting in θ/D values less than one (D is the plate thickness and the diameter of the CTE) and vigorous vortex shedding. The Reynolds numbers based on the plate length and D are 1.255 × 106 and 10 000, respectively. Two cases are computed: one with turbulent boundary layers on both the upper and lower surfaces of the plate (statistically the same, symmetric wake, Case TT) and the other with turbulent and laminar boundary layers on the upper and lower surfaces, respectively (asymmetric case, Case TL). The data and understanding obtained are of considerable engineering interest, particularly in turbomachinery where the pressure side of an airfoil can remain laminar or transitional because of a favorable pressure gradient and the suction side is turbulent. Shed-vortex structure and phase-averaged velocity statistics obtained in the two cases are compared here. The upper negative shed vortices in Case TL (turbulent separating boundary layer) are weaker than the lower positive ones (laminar separating boundary layer) at inception (a factor of 1.27 weaker in terms of peak phase-averaged spanwise vorticity at the first appearance of a peak). The upper vortices weaken rapidly as they travel downstream. A second feature of interest in Case TL is a considerable increase in the peak phase-averaged, streamwise normal intensity (random component) with increasing streamwise distance (x/D) that occurs near the positive vortex cores. This behavior is observed for a few diameters in the near wake. This is counter to Case TT where the peak value essentially decreases with increasing x/D. Both these effects are examined in detail, and the important contributors are identified.

Electrical sensing of the dynamical structure of the planetary boundary layer

NASA Astrophysics Data System (ADS)

Nicoll, K. A.; Harrison, R. G.; Silva, H. G.; Salgado, R.; Melgâo, M.; Bortoli, D.

2018-04-01

Turbulent and convective processes within the planetary boundary layer are responsible for the transport of moisture, momentum and particulate matter, but are also important in determining the electrical charge transport of the lower atmosphere. This paper presents the first high resolution vertical charge profiles during fair weather conditions, obtained with instrumented radiosonde balloons over Alqueva, Portugal during the summer of 2014. The short intervals (4 h) between balloon flights enabled the diurnal variation in the vertical profile of charge within the boundary layer to be examined in detail, with much smaller charges (up to 20 pC m- 3) observed during stable night time periods than during the day. Following sunrise, the evolution of the charge profile was complex, demonstrating charged ultrafine aerosol, lofted upwards by daytime convection. This produced charge up to 92 pC m- 3 up to 500 m above the surface. The diurnal variation in the integrated column of charge above the site tracked closely with the diurnal variation in near surface charge as derived from a nearby electric field sensor, confirming the importance of the link between surface charge generation processes and aloft. The local aerosol vertical profiles were estimated using backscatter measurements from a collocated ceilometer. These were utilised in a simple model to calculate the charge expected due to vertical conduction current flow in the global electric circuit through aerosol layers. The analysis presented here demonstrates that charge can provide detailed information about boundary layer transport, particularly in regard to the ultrafine aerosol structure, that conventional thermodynamic and ceilometer measurements do not.

Parameterization of turbulence and the planetary boundary layer in the GLA Fourth Order GCM

NASA Technical Reports Server (NTRS)

Helfand, H. M.

1985-01-01

A new scheme has been developed to model the planetary boundary layer in the GLAS Fourth Order GCM through explicit resolution of its vertical structure into two or more vertical layers. This involves packing the lowest layers of the GCM close to the ground and developing new parameterization schemes that can express the turbulent vertical fluxes of heat, momentum and moisture at the earth's surface and between the layers that are contained with the PBL region. Offline experiments indicate that the combination of the modified level 2.5 second-order turbulent closure scheme and the 'extended surface layer' similarity scheme should work well to simulate the behavior of the turbulent PBL even at the coarsest vertical resolution with which such schemes will conceivably be used in the GLA Fourth Order GCM.

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.

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

Experimental Investigation of the Near Wall Flow Structure of a Low Reynolds Number 3-D Turbulent Boundary Layer

NASA Technical Reports Server (NTRS)

Fleming, J. L.; Simpson, R. L.

1997-01-01

Laser Doppler velocimetry (LDV) measurements and hydrogen bubble flow visualization techniques were used to examine the near-wall flow structure of 2D and 3D turbulent boundary layers (TBLs) over a range of low Reynolds numbers. The goals of this research were (1) an increased understanding of the flow physics in the near wall region of turbulent boundary layers,(2) to observe and quantify differences between 2D and 3D TBL flow structures, and (3) to document Reynolds number effects for 3D TBLs. The LDV data have provided results detailing the turbulence structure of the 2D and 3D TBLs. These results include mean Reynolds stress distributions, flow skewing results, and U and V spectra. Effects of Reynolds number for the 3D flow were also examined. Comparison to results with the same 3D flow geometry but at a significantly higher Reynolds number provided unique insight into the structure of 3D TBLs. While the 3D mean and fluctuating velocities were found to be highly dependent on Reynolds number, a previously defined shear stress parameter was discovered to be invariant with Reynolds number. The hydrogen bubble technique was used as a flow visualization tool to examine the near-wall flow structure of 2D and 3D TBLs. Both the quantitative and qualitative results displayed larger turbulent fluctuations with more highly concentrated vorticity regions for the 2D flow.

On the mechanism of flow evolution in shock-tube experiments

NASA Astrophysics Data System (ADS)

Kiverin, Alexey; Yakovenko, Ivan

2018-02-01

The paper studies numerically the flow development behind the shock wave propagating inside the tube. The detailed analysis of the flow patterns behind the shock wave allows determination of the gas-dynamical origins of the temperature non-uniformities responsible for the subsequent localized start of chemical reactions in the test mixture. In particular, it is shown that the temperature field structure is determined mainly by the mechanisms of boundary layer instability development. The kinetic energy dissipation related to the flow deceleration inside boundary layer results in local heating of the test gas. At the same time, the heat losses to the tube wall lead to the cooling of the gas. Therefore the temperature stratification takes place on the scales of the boundary layer. As soon as the shock wave reflected from the end-wall of the tube interacts with the developed boundary layer the localized hot regions arise at a certain distance from the end wall. The position of these hot regions is associated with the zones of shock wave interaction with roller vortices at the margin between the boundary layer and the bulk flow. Formulated mechanism of the temperature field evolution can be used to explain the peculiarities of non-steady shock-induced ignition of combustible mixtures with moderate ignition delay times, where the ignition starts inside localized kernels at distance from the end wall.

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 Lattice Boltzmann Study of the 2d Boundary Layer Created by AN Oscillating Plate

NASA Astrophysics Data System (ADS)

Cappietti, L.; Chopard, B.

We study the applicability of the Lattice Boltzmann Method (LBM) to simulate the 2D laminar boundary layer induced by an oscillating flat plate. We also investigate the transition to the disturbed laminar regime that occurs with a rough oscillating plate. The simulations were performed in two cases: first with a fluid otherwise at rest and second in presence of superimposed current. The generation of coherent vortex structures and their evolution are commented. The accuracy of the method was checked by comparisons with the exact analytical solution of the Navier-Stokes equations for the so-called Stokes' Second Problem. The comparisons show that LBM reproduces this time varying flow with first order accuracy. In the case of the wavy-plate, the results show that a mechanism of vortex-jet formations, low speed-streak and shear instability sustain a systems of stationary vortices outside the boundary layer. The vortex-jet takes place at the end of the decelerating phase whereas the boundary layer turns out to be laminar when the plate accelerates. In the presence of the superimposed current, the vortex-jet mechanism is still effective but the vortices outside the boundary layer are only present during part of the oscillating period. During the remaining part, the flow turns out to be laminar although a wave perturbation in the velocity field is present.

An analysis of the crossover between local and massive separation on airfoils

NASA Technical Reports Server (NTRS)

Barnett, M.; Carter, J. E.

1987-01-01

Massive separation on airfoils operating at high Reynolds number is an important problem to the aerodynamicist, since its onset generally determines the limiting performance of an airfoil, and it can lead to serious problems related to aircraft control as well as turbomachinery operation. The phenomenon of crossover between local separation and massive separation on realistic airfoil geometries induced by airfoil thickness is investigated for low speed (incompressible) flow. The problem is studied both for the asymptotic limit of infinite Reynolds number using triple-deck theory, and for finite Reynolds number using interacting boundary-layer theory. Numerical results are presented which follow the evolution of the flow as it develops from a mildly separated state to one dominated by the massively separated flow structure as the thickness of the airfoil geometry is systematically increased. The effect of turbulence upon the evolution of the flow is considered, and the impact is significant, with the principal effect being the suppression of the onset of separation. Finally, the effect of surface suction and injection for boundary-layer control is considered. The approach which was developed provides a valuable tool for the analysis of boundary-layer separation up to and beyond stall. Another important conclusion is that interacting boundary-layer theory provides an efficient tool for the analysis of the effect of turbulence and boundary-layer control upon separated vicsous flow.

Three-Dimensional Navier-Stokes Simulations with Two-Equation Turbulence Models of Intersecting Shock-Waves/Turbulent Boundary Layer at Mach 8.3

NASA Technical Reports Server (NTRS)

Bardina, J. E.; Coakley, T. J.

1994-01-01

An investigation of the numerical simulation with two-equation turbulence models of a three-dimensional hypersonic intersecting (SWTBL) shock-wave/turbulent boundary layer interaction flow is presented. The flows are solved with an efficient implicit upwind flux-difference split Reynolds-averaged Navier-Stokes code. Numerical results are compared with experimental data for a flow at Mach 8.28 and Reynolds number 5.3x10(exp 6) with crossing shock-waves and expansion fans generated by two lateral 15 fins located on top of a cold-wall plate. This experiment belongs to the hypersonic database for modeling validation. Simulations show the development of two primary counter-rotating cross-flow vortices and secondary turbulent structures under the main vortices and in each corner singularity inside the turbulent boundary layer. A significant loss of total pressure is produced by the complex interaction between the main vortices and the uplifted jet stream of the boundary layer. The overall agreement between computational and experimental data is generally good. The turbulence modeling corrections show improvements in the predictions of surface heat transfer distribution and an increase in the strength of the cross-flow vortices. Accurate predictions of the outflow flowfield is found to require accurate modeling of the laminar/turbulent boundary layers on the fin walls.

Experimental studies on flow visualization and velocity field of compression ramp with different incoming boundary layers

NASA Astrophysics Data System (ADS)

Wu, Yu; Yi, Shi-He; He, Lin; Chen, Zhi; Zhu, Yang-Zhu

2014-11-01

Experimental studies which focus on flow visualization and the velocity field of a supersonic laminar/turbulent flow over a compression ramp were carried out in a Mach 3.0 wind tunnel. Fine flow structures and velocity field structures were obtained via NPLS (nanoparticle-tracer planar laser scattering) and PIV (particle image velocimetry) techniques, time-averaged flow structures were researched, and spatiotemporal evolutions of transient flow structures were analyzed. The flow visualization results indicated that when the ramp angles were 25°, a typical separation occurred in the laminar flow, some typical flow structures such as shock induced by the boundary layer, separation shock, reversed flow and reattachment shock were visible clearly. While a certain extent separation occurred in turbulent flow, the separation region was much smaller. When the ramp angles were 28°, laminar flow separated further, and the separation region expanded evidently, flow structures in the separation region were complex. While a typical separation occurred in turbulent flow, reversed flow structures were significant, flow structures in the separation region were relatively simple. The experimental results of velocity field were corresponding to flow visualization, and the velocity field structures of both compression ramp flows agreed with the flow structures well. There were three layered structures in the U component velocity, and the V component velocity appeared like an oblique “v”. Some differences between these two compression ramp flows can be observed in the velocity profiles of the shear layer and the shearing intensity.

The relation between skin friction fluctuations and turbulent fluctuating velocities in turbulent boundary layers

NASA Astrophysics Data System (ADS)

Diaz Daniel, Carlos; Laizet, Sylvain; Vassilicos, John Christos

2015-11-01

The Townsend-Perry hypothesis of wall-attached eddies relates the friction velocity uτ at the wall to velocity fluctuations at a position y from the wall, resulting in a wavenumber range where the streamwise fluctuating velocity spectrum scales as E (k) ~k-1 and the corresponding structure function scales as uτ2 in the corresponding length-scale range. However, this model does not take in account the fluctuations of the skin friction velocity, which are in fact strongly intermittent. A DNS of zero-pressure gradient turbulent boundary layer suggests a 10 to 15 degree angle from the lag of the peak in the cross-correlations between the fluctuations of the shear stress and streamwise fluctuating velocities at different heights in the boundary layer. Using this result, it is possible to refine the definition of the attached eddy range of scales, and our DNS suggests that, in this range, the second order structure function depends on filtered skin friction fluctuations in a way which is about the same at different distances from the wall and different local Reynolds numbers.

Convection of Plasmaspheric Plasma into the Outer Magnetosphere and Boundary Layer Region: Initial Results

NASA Technical Reports Server (NTRS)

Ober, Daniel M.; Horwitz, J. L.

1998-01-01

We present initial results on the modeling of the circulation of plasmaspheric-origin plasma into the outer magnetosphere and low-latitude boundary layer (LLBL), using a dynamic global core plasma model (DGCPM). The DGCPM includes the influences of spatially and temporally varying convection and refilling processes to calculate the equatorial core plasma density distribution throughout the magnetosphere. We have developed an initial description of the electric and magnetic field structures in the outer magnetosphere region. The purpose of this paper is to examine both the losses of plasmaspheric-origin plasma into the magnetopause boundary layer and the convection of this plasma that remains trapped on closed magnetic field lines. For the LLBL electric and magnetic structures we have adopted here, the plasmaspheric plasma reaching the outer magnetosphere is diverted anti-sunward primarily along the dusk flank. These plasmas reach X= -15 R(sub E) in the LLBL approximately 3.2 hours after the initial enhancement of convection and continues to populate the LLBL for 12 hours as the convection electric field diminishes.

Sound Transmission through Cylindrical Shell Structures Excited by Boundary Layer Pressure Fluctuations

NASA Technical Reports Server (NTRS)

Tang, Yvette Y.; Silcox, Richard J.; Robinson, Jay H.

1996-01-01

This paper examines sound transmission into two concentric cylindrical sandwich shells subject to turbulent flow on the exterior surface of the outer shell. The interior of the shells is filled with fluid medium and there is an airgap between the shells in the annular space. The description of the pressure field is based on the cross-spectral density formulation of Corcos, Maestrello, and Efimtsov models of the turbulent boundary layer. The classical thin shell theory and the first-order shear deformation theory are applied for the inner and outer shells, respectively. Modal expansion and the Galerkin approach are used to obtain closed-form solutions for the shell displacements and the radiation and transmission pressures in the cavities including both the annular space and the interior. The average spectral density of the structural responses and the transmitted interior pressures are expressed explicitly in terms of the summation of the cross-spectral density of generalized force induced by the boundary layer turbulence. The effects of acoustic and hydrodynamic coincidences on the spectral density are observed. Numerical examples are presented to illustrate the method for both subsonic and supersonic flows.

Small-scale behavior in distorted turbulent boundary layers at low Reynolds number

NASA Technical Reports Server (NTRS)

Saddoughi, Seyed G.

1994-01-01

During the last three years we have conducted high- and low-Reynolds-number experiments, including hot-wire measurements of the velocity fluctuations, in the test-section-ceiling boundary layer of the 80- by 120-foot Full-Scale Aerodynamics Facility at NASA Ames Research Center, to test the local-isotropy predictions of Kolmogorov's universal equilibrium theory. This hypothesis, which states that at sufficiently high Reynolds numbers the small-scale structures of turbulent motions are independent of large-scale structures and mean deformations, has been used in theoretical studies of turbulence and computational methods such as large-eddy simulation; however, its range of validity in shear flows has been a subject of controversy. The present experiments were planned to enhance our understanding of the local-isotropy hypothesis. Our experiments were divided into two sets. First, measurements were taken at different Reynolds numbers in a plane boundary layer, which is a 'simple' shear flow. Second, experiments were designed to address this question: will our criteria for the existence of local isotropy hold for 'complex' nonequilibrium flows in which extra rates of mean strain are added to the basic mean shear?

Zinc enhanced hard disk media

DOEpatents

Zou, Jie; Lambeth, David N.; Laughlin, David E.

2002-01-01

The present invention provides a magnetic recording media incorporating Zn containing layers in close proximity to a magnetic layer to provide media having increased coercivity and lower noise. The Zn containing layer can be incorporated in a rotating, translating or stationary recording media to operate in conjunction with magnetic transducing heads for recording and reading of magnetic data, as well as other applications. The magnetic recording medium of the invention preferably includes a Co or Co alloy film magnetic layer, underlayer structures to promote epitaxial crystalline structure in the magnetic layer, and a Zn containing layer to promote isolation between the magnetic grains. The medium can further include seed layers, underlayers, intermediate layers, and overlayers. The process of manufacture includes promoting diffusion of Zn to the magnetic layer grain boundaries.

Constraints on Mercury's Core-Mantle Boundary Region

NASA Astrophysics Data System (ADS)

Hauck, S. A., II; Chabot, N. L.; Sun, P.; Jing, Z.; Johnson, C. L.; Margot, J. L.; Padovan, S.; Peale, S. J.; Phillips, R. J.; Solomon, S. C.

2014-12-01

Understanding the boundary between a planet's metallic core and silicate mantle is important for constraining processes that dominate on either side of this boundary. Geophysical measurements of the planet Mercury by the MESSENGER spacecraft have provided evidence of a core larger than earlier, less-constrained estimates. Further, these results, taken in concert with measurements of the elemental composition of the surface by MESSENGER, have led to the suggestion that the uppermost layer of the outer core may be highly enriched in sulfur, and the top of the core may consist of a solid sulfide layer. The low iron and relatively large sulfur contents of the surface indicate highly reducing conditions during planet formation, placing constraints on the potential composition of Mercury's core. Recent metal-silicate partitioning experiments have developed new limits on the amount of sulfur and silicon that may partition into the core as a function of sulfur abundance at the surface. Models for the planet's internal structure constrained by the current best estimates of the bulk density, normalized polar moment of inertia, and fraction of the polar moment of inertia of the solid layer that extends from the surface to the top of the liquid outer core provide an important view of the layering and bulk composition of Mercury. By combining the results of these internal structure models with the experimental relationship between core and mantle composition we place new limits on core composition and structure. Further, imposing measured compositional constraints on the miscibility of iron-sulfur-silicon alloys yields important limits on the presence or absence of an immiscible sulfur-rich liquid layer or a solid sulfide layer at the top of the core.

The Effects of Land Surface Heating And Roughness Elements on the Structure and Scaling Laws of Atmospheric Boundary Layer Turbulence

NASA Astrophysics Data System (ADS)

Ghannam, Khaled

The atmospheric boundary-layer is the lowest 500-2000 m of the Earth's atmosphere where much of human life and ecosystem services reside. This layer responds to land surface (e.g. buoyancy and roughness elements) and slowly evolving free tropospheric (e.g. temperature and humidity lapse rates) conditions that arguably mediate and modulate biosphere-atmosphere interactions. Such response often results in spatially- and temporally-rich turbulence scales that continue to be the subject of inquiry given their significance to a plethora of applications in environmental sciences and engineering. The work here addresses key aspects of boundary layer turbulence with a focus on the role of roughness elements (vegetation canopies) and buoyancy (surface heating) in modifying the well-studied picture of shear-dominated wall-bounded turbulence. A combination of laboratory channel experiments, field experiments, and numerical simulations are used to explore three distinct aspects of boundary layer turbulence. These are: • The concept of ergodicity in turbulence statistics within canopies: It has been long-recognized that homogeneous and stationary turbulence is ergodic, but less is known about the effects of inhomogeneity introduced by the presence of canopies on the turbulence statistics. A high resolution (temporal and spatial) flume experiment is used here to test the convergence of the time statistics of turbulent scalar concentrations to their ensemble (spatio-temporal) counterpart. The findings indicate that within-canopy scalar statistics have a tendency to be ergodic, mostly in shallow layers (close to canopy top) where the sweeping flow events appear to randomize the statistics. Deeper layers within the canopy are dominated by low-dimensional (quasi-deterministic) von Karman vortices that tend to break ergodicity. • Scaling laws of turbulent velocity spectra and structure functions in near-surface atmospheric turbulence: the existence of a logarithmic scaling in the structure function of the longitudinal and vertical velocity components is examined using five experimental data sets that span the roughness sub-layer above vegetation canopies, the atmospheric surface-layer above a lake and a grass field, and an open channel experiment. The results indicate that close to the wall/surface, this scaling exists in the longitudinal velocity structure function only, with the vertical velocity counterpart exhibiting a much narrower extent of this range due to smaller separation of scales. Phenomenological aspects of the large-scale eddies show that the length scale formed by the friction velocity and energy dissipation acts as a dominant similarity length scale in collapsing experimental data at different heights, mainly due to the imbalance between local production and dissipation of turbulence kinetic energy. • Nonlocal heat transport in the convective atmospheric boundary-layer: Failure of the mean gradient-diffusion (K-theory) in the convective boundary-layer is explored. Using large eddy simulation runs for the atmospheric boundary layer spanning weakly to strongly convective conditions, a generic diagnostic framework that encodes the role of third-order moments in nonlocal heat transport is developed and tested. The premise is that these nonlocal effects are responsible for the inherent asymmetry in vertical transport, and hence the necessary non-Gaussian nature of the joint probability density function (JPDF) of vertical velocity and potential temperature must account for these effects. Conditional sampling (quadrant analysis) of this function and the imbalance between the flow mechanisms of ejections and sweeps are used to characterize this asymmetry, which is then linked to the third-order moments using a cumulant-discard method for the Gram-Charlier expansion of the JPDF. The connection between the ejection-sweep events and the third-order moments shows that the concepts of bottom-up/top-down diffusion, or updraft/downdraft models, are accounted for by various quadrants of this joint probability density function. To this end, future research directions that build upon this work are also discussed.

Low-dimensional representation of near-wall dynamics in shear flows, with implications to wall-models.

PubMed

Schmid, P J; Sayadi, T

2017-03-13

The dynamics of coherent structures near the wall of a turbulent boundary layer is investigated with the aim of a low-dimensional representation of its essential features. Based on a triple decomposition into mean, coherent and incoherent motion and a dynamic mode decomposition to recover statistical information about the incoherent part of the flow field, a driven linear system coupling first- and second-order moments of the coherent structures is derived and analysed. The transfer function for this system, evaluated for a wall-parallel plane, confirms a strong bias towards streamwise elongated structures, and is proposed as an 'impedance' boundary condition which replaces the bulk of the transport between the coherent velocity field and the coherent Reynolds stresses, thus acting as a wall model for large-eddy simulations (LES). It is interesting to note that the boundary condition is non-local in space and time. The extracted model is capable of reproducing the principal Reynolds stress components for the pretransitional, transitional and fully turbulent boundary layer.This article is part of the themed issue 'Toward the development of high-fidelity models of wall turbulence at large Reynolds number'. © 2017 The Author(s).

Flux estimation of the FIFE planetary boundary layer (PBL) with 10.6 micron Doppler lidar

NASA Technical Reports Server (NTRS)

Gal-Chen, Tzvi; Xu, Mei; Eberhard, Wynn

1990-01-01

A method is devised for calculating wind, momentum, and other flux parameters that characterize the planetary boundary layer (PBL) and thereby facilitate the calibration of spaceborne vs. in situ flux estimates. Single Doppler lidar data are used to estimate the variance of the mean wind and the covariance related to the vertically pointing fluxes of horizontal momentum. The skewness of the vertical velocity and the range of kinetic energy dissipation are also estimated, and the surface heat flux is determined by means of a statistical Navier-Stokes equation. The conclusion shows that the PBL structure combines both 'bottom-up' and 'top-down' processes suggesting that the relevant parameters for the atmospheric boundary layer be revised. The conclusions are of significant interest to the modeling techniques used in General Circulation Models as well as to flux estimation.

Atmospheric surface and boundary layers of the Amazon Basin

NASA Technical Reports Server (NTRS)

Garstang, Michael

1987-01-01

Three phases of work were performed: design of and preparation for the Amazon Boundary Layer Experiment (ABLE 2-A); execution of the ABLE 2-A field program; and analysis of the ABLE 2-A data. Three areas of experiment design were dealt with: surface based meteorological measurements; aircraft missions; and project meteorological support. The primary goal was to obtain a good description of the structure of the atmosphere immediately above the rain forest canopy (top of canopy to a few thousand meters), to describe this region during the growing daytime phase of the boundary layer; and to examine the nighttime stratified state. A secondary objective was to examine the role that deep convective storms play in the vertical transport of heat, water vapor, and other trace gases. While significant progress was made, much of the analysis remains to be done.

On the Coupling Between a Supersonic Turbulent Boundary Layer and a Flexible Structure

NASA Technical Reports Server (NTRS)

Frendi, Abdelkader

1996-01-01

A mathematical model and a computer code have been developed to fully couple the vibration of an aircraft fuselage panel to the surrounding flow field, turbulent boundary layer and acoustic fluid. The turbulent boundary layer model is derived using a triple decomposition of the flow variables and applying a conditional averaging to the resulting equations. Linearized panel and acoustic equations are used. Results from this model are in good agreement with existing experimental and numerical data. It is shown that in the supersonic regime, full coupling of the flexible panel leads to lower response and radiation from the panel. This is believed to be due to an increase in acoustic damping on the panel in this regime. Increasing the Mach number increases the acoustic damping, which is in agreement with earlier work.

An experimental study of fluctuating pressure loads beneath swept shock/boundary-layer interactions

NASA Technical Reports Server (NTRS)

Settles, Gary S.

1991-01-01

A database is established on the fluctuating pressure loads produced on aerodynamic surfaces beneath 3-D shock wave/boundary layer interactions. Such loads constitute a fundamental problem of critical concern to future supersonic and hypersonic flight vehicles. A turbulent boundary layer on a flat plate is subjected to interactions with swept planar shock waves generated by sharp fins. Fin angles from 5 to 25 deg at freestream Mach numbers between 2.5 and 4 produce a variety of interaction strengths from weak to very strong. Miniature Kulite pressure transducers mounted in the flat plate were used to measure interaction-induced wall pressure fluctuations. These data will be correlated with proposed new optical data on the fluctuations of the interaction structure, especially that of the lambda-shock system and its associated high-speed jet impingement.

Characteristics of biogenic calcite in the prismatic layer of a pearl oyster, Pinctada fucata.

PubMed

Okumura, Taiga; Suzuki, Michio; Nagasawa, Hiromichi; Kogure, Toshihiro

2010-10-01

The fine structure of the calcite prism in the outer layer of a pearl oyster, Pinctada fucata, has been investigated using various electron beam techniques, in order to understand its characteristics and growth mechanism including the role of intracrystalline organic substances. As the calcite prismatic layer grows thicker, sinuous boundaries develop to divide the prism into a number of domains. The crystal misorientation between the adjacent domains is several to more than ten degrees. The component of the misorientation is mainly the rotation about the c-axis. There is no continuous organic membrane at the boundaries. Furthermore, the crystal orientation inside the domains changes gradually, as indicated by the electron back-scattered diffraction (EBSD) in a scanning electron microscope (SEM). Transmission electron microscopy (TEM) examination revealed that the domain consists of sub-grains of a few hundred nanometers divided by small-angle grain boundaries, which are probably the origin of the gradual change of the crystal orientation inside the domains. Spherular Fresnel contrasts were often observed at the small-angle grain boundaries, in defocused TEM images. Electron energy-loss spectroscopy (EELS) indicated the spherules are organic macromolecules, suggesting that incorporation of organic macromolecules during the crystal growth forms the sub-grain structure of the calcite prism.

A study of field-aligned currents observed at high and low altitudes in the nightside magnetosphere

NASA Technical Reports Server (NTRS)

Elphic, R. C.; Craven, J. D.; Frank, L. A.; Sugiura, M.

1988-01-01

Field-aligned current structures on auroral field lines observed at low and high altitudes using DE 1 and ISEE 2 magnetometer, and particle data observed when the spacecraft are in magnetic conjunction in the near-midnight magnetosphere, are investigated. To minimize latitudinal ambiguity, the plasma-sheet boundary layer observed with ISEE 2 and the discrete aurora at the poleward edge of the auroral oval with DE 1 are studied. The overall current observed at highest latitudes is flowing into the ionosphere, and is likely to be carried by ionospheric electrons flowing upward. There are, however, smaller-scale current structures within this region. The sense and magnitude of the field-aligned currents agree at the two sites. The ISEE 2 data suggests that the high-latitude downward current corresponds to the high-latitude boundary of the plasma-sheet boundary layer, and may be associated with the ion beams observed there.

Optimization of bump and blowing to control the flow through a transonic compressor blade cascade

NASA Astrophysics Data System (ADS)

Mazaheri, K.; Khatibirad, S.

2018-03-01

Shock control bump (SCB) and blowing are two flow control methods, used here to improve the aerodynamic performance of transonic compressors. Both methods are applied to a NASA rotor 67 blade section and are optimized to minimize the total pressure loss. A continuous adjoint algorithm is used for multi-point optimization of a SCB to improve the aerodynamic performance of the rotor blade section, for a range of operational conditions around its design point. A multi-point and two single-point optimizations are performed in the design and off-design conditions. It is shown that the single-point optimized shapes have the best performance for their respective operating conditions, but the multi-point one has an overall better performance over the whole operating range. An analysis is given regarding how similarly both single- and multi-point optimized SCBs change the wave structure between blade sections resulting in a more favorable flow pattern. Interactions of the SCB with the boundary layer and the wave structure, and its effects on the separation regions are also studied. We have also introduced the concept of blowing for control of shock wave and boundary-layer interaction. A geometrical model is introduced, and the geometrical and physical parameters of blowing are optimized at the design point. The performance improvements of blowing are compared with the SCB. The physical interactions of SCB with the boundary layer and the shock wave are analyzed. The effects of SCB on the wave structure in the flow domain outside the boundary-layer region are investigated. It is shown that the effects of the blowing mechanism are very similar to the SCB.

Vortex dynamics of in-line twin synthetic jets in a laminar boundary layer

NASA Astrophysics Data System (ADS)

Wen, Xin; Tang, Hui; Duan, Fei

2015-08-01

An experimental investigation is conducted on the vortices induced by twin synthetic jets (SJs) in line with a laminar boundary layer flow over a flat plate. The twin SJs operating at four different phase differences, i.e., Δϕ = 0°, 90°, 180°, and 270°, are visualized using a stereoscopic color dye visualization system and measured using a two-dimensional particle image velocimetry (PIV) system. It is found that depending on the phase difference of twin SJs, three types of vortex structures are produced. At Δϕ = 90°, the two hairpin vortices interact in a very constructive way in terms of the vortex size, strength, and celerity, forming one combined vortex. At Δϕ = 270°, the two individual hairpin vortices do not have much interaction, forming two completely separated hairpin vortices that behave like doubling the frequency of the single SJ case. At Δϕ = 0° and 180°, the two hairpin vortices produced by the twin SJ actuators are close enough, with the head of one hairpin vortex coupled with the legs of the other, forming partially interacting vortex structures. Quantitative analysis of the twin SJs is conducted, including the time histories of vortex circulation in the mid-span plane as well as a selected spanwise-wall-normal plane, and the influence of the twin SJs on the boundary layer flow filed. In addition, dynamic mode decomposition analysis of the PIV data is conducted to extract representative coherent structures. Through this study, a better understanding in the vortex dynamics associated with the interaction of in-line twin SJs in laminar boundary layers is achieved, which provides useful information for future SJ-array applications.

Plasmonic detection of possible defects in multilayer nanohole array consisting of essential materials in simplified STT-RAM cell

NASA Astrophysics Data System (ADS)

Sadri-Moshkenani, Parinaz; Khan, Mohammad Wahiduzzaman; Zhao, Qiancheng; Krivorotov, Ilya; Nilsson, Mikael; Bagherzadeh, Nader; Boyraz, Ozdal

2017-08-01

Plasmonic nanostructures are highly used for sensing purposes since they support plasmonic modes which make them highly sensitive to the refractive index change of their surrounding medium. Therefore, they can also be used to detect changes in optical properties of ultrathin layer films in a multilayer plasmonic structure. Here, we investigate the changes in optical properties of ultrathin films of macro structures consisting of STT-RAM layers. Among the highest sensitive plasmonic structures, nanohole array has attracted many research interest because of its ease of fabrication, small footprint, and simplified optical alignment. Hence it is more suitable for defect detection in STT-RAM geometries. Moreover, the periodic nanohole pattern in the nanohole array structure makes it possible to couple the light to the surface plasmon polariton (SPP) mode supported by the structure. To assess the radiation damages and defects in STT-RAM cells we have designed a multilayer nanohole array based on the layers used in STT-RAM structure, consisting 4nm- Ta/1.5nm-CoFeB/2nm-MgO/1.5nm-CoFeB/4nm-Ta layers, all on a 300nm silver layer on top of a PEC boundary. The nanoholes go through all the layers and become closed by the PEC boundary on one side. The dimensions of the designed nanoholes are 313nm depth, 350nm diameter, and 700nm period. Here, we consider the normal incidence of light and investigate zeroth-order reflection coefficient to observe the resonance. Our simulation results show that a 10% change in refractive index of the 2nm-thick MgO layer leads to about 122GHz shift in SPP resonance in reflection pattern.

The Impact of Model Uncertainty on Spatial Compensation in Active Structural Acoustic Control

NASA Technical Reports Server (NTRS)

Cabell, Randolph H.; Gibbs, Gary P.; Sprofera, Joseph D.; Clark, Robert L.

2004-01-01

Turbulent boundary layer (TBL) noise is considered a primary factor in the interior noise experienced by passengers aboard commercial airliners. There have been numerous investigations of interior noise control devoted to aircraft panels; however, practical realization is a challenge since the physical boundary conditions are uncertain at best. In most prior studies, pinned or clamped boundary conditions have been assumed; however, realistic panels likely display a range of varying boundary conditions between these two limits. Uncertainty in boundary conditions is a challenge for control system designers, both in terms of the compensator implemented and the location of actuators and sensors required to achieve the desired control. The impact of model uncertainties, uncertain boundary conditions in particular, on the selection of actuator and sensor locations for structural acoustic control are considered herein. Results from this research effort indicate that it is possible to optimize the design of actuator and sensor location and aperture, which minimizes the impact of boundary conditions on the desired structural acoustic control.

Meteorological Simulations of Ozone Episode Case Days during the 1996 Paso del Norte Ozone Study

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

Brown, M.J.; Costigan, K.; Muller, C.

1999-02-01

Meteorological simulations centered around the border cities of El Paso and Ciudad Juarez have been performed during an ozone episode that occurred on Aug. 13,1996 during the 1996 Paso del Norte Ozone Study field campaign. Simulations were petiormed using the HOTMAC mesoscale meteorological model using a 1,2,4, and 8 km horizontal grid size nested mesh system. Investigation of the vertical structure and evolution of the atmospheric boundary layer for the Aug. 11-13 time period is emphasized in this paper. Comparison of model-produced wind speed profiles to rawirisonde and radar profiler measurements shows reasonable agreement. A persistent upper-level jet was capturedmore » in the model simulations through data assimilation. In the evening hours, the model was not able to produce the strong wind direction shear seen in the radar wind profiles. Based on virtual potential temperature profile comparisons, the model appears to correctly simulate the daytime growth of the convective mixed layer. However, the model underestimates the cooling of the surface layer at night. We found that the upper-level jet significantly impacted the turbulence structure of the boundary layer, leading to relatively high turbulent kinetic energy (tke) values aloft at night. The model indicates that these high tke values aloft enhance the mid-morning growth of the boundary layer. No upper-level turbulence measurements were available to verify this finding, however. Radar profiler-derived mixing heights do indicate relatively rapid morning growth of the mixed layer.« less

Separated and Recovering Turbulent Boundary Layer Flow Behind a Backward Facing Step For Different Reynolds Numbers

NASA Technical Reports Server (NTRS)

Jovic, Srba; Kutler, Paul F. (Technical Monitor)

1994-01-01

Experimental results for a two-dimensional separated turbulent boundary layer behind a backward facing step for five different Reynolds numbers are reported. Results are presented in the form of tables, graphs and a floppy disk for an easy access of the data. Reynolds number based on the step height was varied by changing the reference velocity upstream of the step, U(sub o), and the step height, h. Hot-wire measurement techniques were used to measure three Reynolds stresses and four triple-velocity correlations. In addition, surface pressure and skin friction coefficients were measured. All hot-wire measurements were acquired in a measuring domain which excluded recirculating flow region due to the directional insensitivity of hot-wires. The downstream extent of the domain from the step was 51 h for the largest and I 14h for the smallest step height. This significant downstream length permitted extensive study of the flow recovery. Prediction of perturbed flows and their recovery is particularly attractive for popular turbulence models since variations of turbulence length and time scales and flow interactions in different regions are generally inadequately predicted. The data indicate that the flow in the free shear layer region behaves like the plane mixing layer up to about 2/3 of the mean reattachment length when the flow interaction with the wall commences the flow recovery to that of an ordinary turbulent boundary layer structure. These changes of the flow do not occur abruptly with the change of boundary conditions. A reattachment region represents a transitional region where the flow undergoes the most dramatic adjustments to the new boundary conditions. Large eddies, created in the upstream free-shear layer region, are being torn, recirculated, reentrained back into the main stream interacting with the incoming flow structure. It is foreseeable that it is quite difficult to describe the physics of this region in a rational and quantitative manner other than statistical. Downstream of the reattachment point the flow recovers at different rates near the wall, in the newly developing internal boundary layer, and in the outer part of the flow. It appears that Reynolds stresses do not fully recover up to the longest recovery length of 114 h.

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.

The urban boundary-layer field campaign in marseille (ubl/clu-escompte): set-up and first results

NASA Astrophysics Data System (ADS)

Mestayer, P.G.; Durand, P.; Augustin, P.; Bastin, S.; Bonnefond, J.-M.; Benech, B.; Campistron, B.; Coppalle, A.; Delbarre, H.; Dousset, B.; Drobinski, P.; Druilhet, A.; Frejafon, E.; Grimmond, C.S.B.; Groleau, D.; Irvine, M.; Kergomard, C.; Kermadi, S.; Lagouarde, J.-P.; Lemonsu, A.; Lohou, F.; Long, N.; Masson, V.; Moppert, C.; Noilhan, J.; Offerle, B.; Oke, T.R.; Pigeon, G.; Puygrenier, V.; Roberts, S.; Rosant, J.-M.; Sanid, F.; Salmond, J.; Talbaut, M.; Voogt, J.

The UBL/CLU (urban boundary layer/couche limite urbaine) observation and modelling campaign is a side-project of the regional photochemistry campaign ESCOMPTE. UBL/CLU focuses on the dynamics and thermodynamics of the urban boundary layer of Marseille, on the Mediterranean coast of France. The objective of UBL/CLU is to document the four-dimensional structure of the urban boundary layer and its relation to the heat and moisture exchanges between the urban canopy and the atmosphere during periods of low wind conditions, from June 4 to July 16, 2001. The project took advantage of the comprehensive observational set-up of the ESCOMPTE campaign over the Berre-Marseille area, especially the ground-based remote sensing, airborne measurements, and the intensive documentation of the regional meteorology. Additional instrumentation was installed as part of UBL/CLU. Analysis objectives focus on (i) validation of several energy balance computational schemes such as LUMPS, TEB and SM2-U, (ii) ground truth and urban canopy signatures suitable for the estimation of urban albedos and aerodynamic surface temperatures from satellite data, (iii) high resolution mapping of urban land cover, land-use and aerodynamic parameters used in UBL models, and (iv) testing the ability of high resolution atmospheric models to simulate the structure of the UBL during land and sea breezes, and the related transport and diffusion of pollutants over different districts of the city. This paper presents initial results from such analyses and details of the overall experimental set-up.

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.

Aerosol and ozone distributions over the western North Atlantic during WATOX-86

NASA Astrophysics Data System (ADS)

Bridgman, H. A.; Schnell, Russell C.; Bodhaine, B. A.; Oltmans, S. J.

1988-03-01

On January 4, 6, 8, and 9, 1986, a series of National Oceanic and Atmospheric Administration WP-3D research flights was conducted over the western Atlantic Ocean 200-300 km off the coast of North America from Nova Scotia to Georgia as part of the Western Atlantic Ocean Experiment (WATOX). Rights were made perpendicular to NW airflow to establish the flux of gas and aerosol emissions off the North American continent to the ocean. Representative condensation nucleus (CN) concentrations averaged 150-250 cm-3 in the free troposphere in clean conditions, but in atmospheric layers containing anthropogenic air pollution transported from long distances, CN concentrations reached 6500 cm-3. In the marine boundary layer, CN concentrations averaged 500 to 750 cm-3 under relatively clean conditions, and 1500 to 3000 cm-3 in polluted air. Aerosol scattering extinction (bsp) ranged from 70 × 10-6 m-1 in the marine boundary layer to 20 × 10-6 m-1 in the free troposphere. Aerosol bsp was not as responsive to changes in atmospheric structure as CN although factor-of-2 changes across the marine boundary layer were observed. Aerosol size spectra in the marine boundary layer were an order of magnitude greater than those in the free troposphere. Consistent peaks in the volume spectra between 8 and 10 μm diameter established the importance of sea salt as a major aerosol component. Ozone profiles in the free troposphere, normally in the 30-40 ppb range, exhibited laminae of enhanced concentrations (up to 70 ppb) at moisture boundaries, suggesting that active ozone production was occurring at these levels. Ozone concentrations within the marine boundary layer were generally lower than in the free troposphere.

Drag reduction using wrinkled surfaces in high Reynolds number laminar boundary layer flows

NASA Astrophysics Data System (ADS)

Raayai-Ardakani, Shabnam; McKinley, Gareth H.

2017-09-01

Inspired by the design of the ribbed structure of shark skin, passive drag reduction methods using stream-wise riblet surfaces have previously been developed and tested over a wide range of flow conditions. Such textures aligned in the flow direction have been shown to be able to reduce skin friction drag by 4%-8%. Here, we explore the effects of periodic sinusoidal riblet surfaces aligned in the flow direction (also known as a "wrinkled" texture) on the evolution of a laminar boundary layer flow. Using numerical analysis with the open source Computational Fluid Dynamics solver OpenFOAM, boundary layer flow over sinusoidal wrinkled plates with a range of wavelength to plate length ratios ( λ / L ), aspect ratios ( 2 A / λ ), and inlet velocities are examined. It is shown that in the laminar boundary layer regime, the riblets are able to retard the viscous flow inside the grooves creating a cushion of stagnant fluid that the high-speed fluid above can partially slide over, thus reducing the shear stress inside the grooves and the total integrated viscous drag force on the plate. Additionally, we explore how the boundary layer thickness, local average shear stress distribution, and total drag force on the wrinkled plate vary with the aspect ratio of the riblets as well as the length of the plate. We show that riblets with an aspect ratio of close to unity lead to the highest reduction in the total drag, and that because of the interplay between the local stress distribution on the plate and stream-wise evolution of the boundary layer the plate has to exceed a critical length to give a net decrease in the total drag force.

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

NASA Technical Reports Server (NTRS)

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

2012-01-01

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

Gas flow in the near-surface porous boundary layer of the 67P/Churyumov-Gerasimenko using micro-CT images

NASA Astrophysics Data System (ADS)

Christou, Chariton; Kokou Dadzie, S.; Thomas, Nicolas; Hartogh, Paul; Jorda, Laurent; Kührt, Ekkehard; Whitby, James; Wright, Ian; Zarnecki, John

2017-04-01

While ESA's Rosetta mission has formally been completed, the data analysis and interpretation continues. Here, we address the physics of the gas flow at the surface of the comet. Understanding the sublimation of ice at the surface of the nucleus provides the initial boundary condition for studying the inner coma. The gas flow at the surface of the comet 67P/Churyumov-Gerasimenko can be in the rarefaction regime and a non-Maxwellian velocity distribution may be present. In these cases, continuum methods like Navier-Stokes-Fourier (NSF) set of equations are rarely applicable. Discrete particle methods such as Direct Simulation Monte Carlo (DSMC) method are usually adopted. DSMC is currently the dominant numerical method to study rarefied gas flows. It has been widely used to study cometary outflow over past years .1,2. In the present study, we investigate numerically, gas transport near the surface of the nucleus using DSMC. We focus on the outgassing from the near surface boundary layer into the vacuum (˜20 cm above the nucleus surface). Simulations are performed using the open source code dsmcFoam on an unstructured grid. Until now, artificially generated random porous media formed by packed spheres have been used to represent the comet surface boundary layer structure .3. In the present work, we used instead Micro-computerized-tomography (micro-CT) scanned images to provide geologically realistic 3D representations of the boundary layer porous structure. The images are from earth basins. The resolution is relatively high - in the range of some μm. Simulations from different rock samples with high porosity (and comparable to those expected at 67P) are compared. Gas properties near the surface boundary layer are presented and characterized. We have identified effects of the various porous structure properties on the gas flow fields. Temperature, density and velocity profiles have also been analyzed. .1. J.-F. Crifo, G. Loukianov, A. Rodionov and V. Zakharov, Icarus 176 (1), 192-219 (2005). 2. Y. Liao, C. Su, R. Marschall, J. Wu, M. Rubin, I. Lai, W. Ip, H. Keller, J. Knollenberg and E. Kührt, Earth, Moon, and Planets 117 (1), 41-64 (2016). 3. Y. V. Skorov, R. Van Lieshout, J. Blum and H. U. Keller, Icarus 212 (2), 867-876 (2011).

Inclined cross-stream stereo particle image velocimetry measurements in turbulent boundary layers

NASA Astrophysics Data System (ADS)

Hutchins, N.; Hambleton, W. T.; Marusic, Ivan

2005-10-01

This work can be viewed as a reprise of Head & Bandyopadhyay's (J. Fluid Mech. vol. 107, p. 297) original boundary-layer visualization study although in this instance we make use of stereo particle image velocimetry (PIV), techniques to obtain a quantitative view of the turbulent structure. By arranging the laser light-sheet and image plane of a stereo PIV system in inclined spanwise/wall-normal planes (inclined at both 45(°) and 135(°) to the streamwise axis) a unique quantitative view of the turbulent boundary layer is obtained. Experiments are repeated across a range of Reynolds numbers, Re_{tau} {≈} 690-2800. Despite numerous experimental challenges (due to the large out-of-plane velocity components), mean flow and Reynolds stress profiles indicate that the salient features of the turbulent flow have been well resolved. The data are analysed with specific attention to a proposed hairpin eddy model. In-plane two-dimensional swirl is used to identify vortical eddy structures piercing the inclined planes. The vast majority of this activity occurs in the 135(°) plane, indicating an inclined eddy structure, and Biot-Savart law calculations are carried out to aid in the discussion. Conditional averaging and linear stochastic estimation results also support the presence of inclined eddies, arranged about low-speed regions. In the 135(°) plane, instantaneous swirl patterns exhibit a predisposition for counter-rotating vortex pairs (arranged with an ejection at their confluence). Such arrangements are consistent with the hairpin packet model. Correlation and scaling results show outer-scaling to be the correct way to quantify the characteristic spanwise length scale across the log and wake regions of the boundary layers (for the range of Reynolds numbers tested). A closer investigation of two-point velocity correlation contours indicates the occurrence of a distinct two-regime behaviour, in which contours (and hence streamwise velocity fluctuations) either appear to be ‘attached’ to the buffer region, or ‘detaching’ from it. The demarcation between these two regimes is found to scale well with outer variables. The results are consistent with a coherent structure that becomes increasingly uncoupled (or decorrelated) from the wall as it grows beyond the logarithmic region, providing additional support for a wall awake description of turbulent boundary layers.

Deriving Lifetime Maps in the Time/Frequency Domain of Coherent Structures in the Turbulent Boundary Layer

NASA Technical Reports Server (NTRS)

Palumbo, Dan

2008-01-01

The lifetimes of coherent structures are derived from data correlated over a 3 sensor array sampling streamwise sidewall pressure at high Reynolds number (> 10(exp 8)). The data were acquired at subsonic, transonic and supersonic speeds aboard a Tupolev Tu-144. The lifetimes are computed from a variant of the correlation length termed the lifelength. Characteristic lifelengths are estimated by fitting a Gaussian distribution to the sensors cross spectra and are shown to compare favorably with Efimtsov s prediction of correlation space scales. Lifelength distributions are computed in the time/frequency domain using an interval correlation technique on the continuous wavelet transform of the original time data. The median values of the lifelength distributions are found to be very close to the frequency averaged result. The interval correlation technique is shown to allow the retrieval and inspection of the original time data of each event in the lifelength distributions, thus providing a means to locate and study the nature of the coherent structure in the turbulent boundary layer. The lifelength data are converted to lifetimes using the convection velocity. The lifetime of events in the time/frequency domain are displayed in Lifetime Maps. The primary purpose of the paper is to validate these new analysis techniques so that they can be used with confidence to further characterize the behavior of coherent structures in the turbulent boundary layer.

The Physics of Turbulence in the Boundary Layer

NASA Technical Reports Server (NTRS)

Kline, Stephen; Cantwell, Brian

1995-01-01

The geometry of the velocity field in a numerically simulated incompressible turbulent boundary layer over a flat plate at Re theta=670 has been studied using the invariants of the velocity gradient tensor. These invariants are computed at every grid point in the flow and used to form the discriminant. Of primary interest are those regions in the flow where the discriminant is positive; regions where, according to the characteristic equation, the eigenvalues of the velocity gradient tensor are complex. An observer moving with a frame of reference which is attached to a fluid particle lying within such a region would see a local flow pattern of the type stable-focus-stretching or unstable-focus-compressing. When the flow is visualized this way, continuous, connected, large-scale structures are revealed that extend from the point just below the buffer layer out to the beginning of the wake region. These structures are aligned with the mean shear close to the wall and arch in the cross-stream direction away from the wall. In some cases the structures observed are very similar to to the hairpin eddy vision of boundary layer structure proposed by Theodorsen. That the structure of the flow is revealed more effectively by the discriminant rather than by the vorticity is important and adds support to recent observations of the discriminant in a channel flow simulation. Of particular importance is the fact that the procedure does not require the use of an arbitrary threshold in the discriminant. Further analysis using computer flow visualization shows a high degree of spatial correlation between regions of positive discriminant, extreme negative pressure fluctuations and large instantaneous values of Reynolds shear stress.

Building and Modification of the Continental Lithosphere: the History of the Contiguous U.S. as told by MLDs and LABs

NASA Astrophysics Data System (ADS)

Hopper, E.; Fischer, K. M.

2016-12-01

The lithosphere preserves a record of past and present tectonic processes in its internal structures and its boundary with the underlying asthenosphere. We use common conversion point stacked Sp converted waves recorded by EarthScope's Transportable Array, as well as other available permanent and temporary broadband stations, to image such structures in the lithospheric mantle of the contiguous U.S. In the tectonically youngest western U.S., a shallow, sharp velocity gradient at the base of the lithosphere suggests a boundary defined by ponded melt. The lithosphere thickens with age of volcanism, implying the lithosphere is a melt-mitigated, conductively cooling thermal boundary layer. Beneath older, colder lithosphere where melt fractions are likely much lower, the velocity gradient at the base of such a layer should be a more diffuse, primarily thermal boundary. This is consistent with observations in the eastern U.S. where the lithosphere-asthenosphere boundary (LAB) is locally sharp and shallower only in areas of inferred enhanced upwelling - such as ancient hot spot tracks and areas of inferred delamination. In the cratonic interior, the LAB is even more gradual in depth, and is transparent to Sp waves with dominant periods of 10 s. Although seismic imaging only provides a snapshot of the lithosphere as it is today, preserved internal structures extend the utility of this imaging back into deep geological time. Ancient accretion within the cratonic lithospheric mantle is preserved as dipping structures associated with relict subducted slabs from Paleoproterozoic continental accretion, suggesting that lateral accretion was integral to the cratonic mantle root formation process. Metasomatism, melt migration and ponding below a carbonated peridotite solidus explain a sub-horizontal mid-lithospheric discontinuity (MLD) commonly observed at 70-100 km depth. This type of MLD is strongest in Mesoproterozoic and older lithosphere, suggesting that it formed more vigorously in the deep past, that a billion years or more are required to build up an observable volatile-rich layer, or that strong, ancient lithosphere is required to support an inherently weak, volatilized layer.

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.

Vortex Interactions from a Finite Span Cylinder with a Laminar Boundary Layer for Varied Parameters

NASA Astrophysics Data System (ADS)

Gildersleeve, Samantha; Amitay, Michael

2017-11-01

Flow structures around a stationary, wall-mounted, finite-span cylindrical pin were investigated experimentally over a flat plate to explore the effects of varied aspect ratio and pin mean height with respect to the local boundary layer. Nine static pin configurations were tested where the pin's mean height to the local boundary layer thickness were 0.5, 1, and 1.5 for a range of aspect ratios between 0.125 and 1.125. The freestream velocity was fixed at 11 m/s, corresponding to ReD 2800, 5600, and 8400, respectively. Three-dimensional flowfields were reconstructed and analyzed from SPIV measurements where data were collected along cross-stream planes in the wake of the pin. This study focuses on three dominant vortical patterns associated with a finite span cylinder: the arch-type vortex horseshoe vortex, and the tip vortices Results indicate that both the aspect ratio and mean height play an important role in the behavior and interactions of these vortex structures which alter the wake characteristics significantly. Understanding the mechanisms by which the vortical structures may be strengthened while reducing adverse local pressure drag are key for developing more efficient means of passive and/or active flow control through finite span cylindrical pins and will be discussed in further detail. NDSEG Fellowship for Samantha Gildersleeve.

Flow boundary conditions for chain-end adsorbing polymer blends.

PubMed

Zhou, Xin; Andrienko, Denis; Delle Site, Luigi; Kremer, Kurt

2005-09-08

Using the phenol-terminated polycarbonate blend as an example, we demonstrate that the hydrodynamic boundary conditions for a flow of an adsorbing polymer melt are extremely sensitive to the structure of the epitaxial layer. Under shear, the adsorbed parts (chain ends) of the polymer melt move along the equipotential lines of the surface potential whereas the adsorbed additives serve as the surface defects. In response to the increase of the number of the adsorbed additives the surface layer becomes thinner and solidifies. This results in a gradual transition from the slip to the no-slip boundary condition for the melt flow, with a nonmonotonic dependence of the slip length on the surface concentration of the adsorbed ends.

Schlieren and OH* chemiluminescence imaging of combustion in a turbulent boundary layer over a solid fuel

NASA Astrophysics Data System (ADS)

Jens, Elizabeth T.; Miller, Victor A.; Cantwell, Brian J.

2016-03-01

Combustion in a turbulent boundary layer over a solid fuel is studied using simultaneous schlieren and OH* chemiluminescence imaging. The flow configuration is representative of a hybrid rocket motor combustor. Six different hydrocarbon fuels, including both classical hybrid rocket fuels and a high regression rate fuel (paraffin wax), are burned in an undiluted oxygen free-stream at pressures ranging from atmospheric to 1524.2 kPa (221.1 psi). A detailed explanation of methods for registering the schlieren and OH* chemiluminescence images to one another is presented, and additionally, details of the routines used to extract flow features of interest (like the boundary layer height and flame location) are provided. At atmospheric pressure, the boundary layer location is consistent between all fuels; however, the flame location varies for each fuel. The flame zone appears to be smoothly distributed over the fuel surface at atmospheric pressure. At elevated pressures and correspondingly increased Dahmköhler number (but at constant Reynolds number), flame morphology is markedly different, exhibiting large rollers in a shear layer above the fuel grain and finer structures in the flame. The chemiluminescence intensity is found to be roughly proportional to the fuel burn rate at both atmospheric and elevated chamber pressures.

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.

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.

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.

Effects of variable thermal diffusivity on the structure of convection

NASA Astrophysics Data System (ADS)

Shcheritsa, O. V.; Getling, A. V.; Mazhorova, O. S.

2018-03-01

The structure of multiscale convection in a thermally stratified plane horizontal fluid layer is investigated by means of numerical simulations. The thermal diffusivity is assumed to produce a thin boundary sublayer convectively much more unstable than the bulk of the layer. The simulated flow is a superposition of cellular structures with three different characteristic scales. In contrast to the largest convection cells, the smaller ones are localised in the upper portion of the layer. The smallest cells are advected by the larger-scale convective flows. The simulated flow pattern qualitatively resembles that observed on the Sun.

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.

STEM and APT characterization of scale formation on a La,Hf,Ti-doped NiCrAl model alloy.

PubMed

Unocic, Kinga A; Chen, Yimeng; Shin, Dongwon; Pint, Bruce A; Marquis, Emmanuelle A

2018-06-01

A thermally grown scale formed on a cast NiCrAl model alloy doped with lanthanum, hafnium, and titanium was examined after isothermal exposure at 1100 °C for 100 h in dry flowing O 2 to understand the dopant segregation along scale grain boundaries. The complex scale formed on the alloy surface was composed of two types of substrates: phase-dependent, thin (<250 nm) outer layers and a columnar-grained ∼3.5 μm inner alumina layer. Two types of oxides formed between the inner and outer scale layers: small (3-15 nm) La 2 O 3 and larger (≤50 nm) HfO 2 oxide precipitates. Nonuniform distributions of the hafnium, lanthanum, and titanium dopants were observed along the inner scale grain boundaries, with hafnium dominating in most of the grain boundaries of α-Al 2 O 3. The concentration of reactive elements (RE) seemed to strongly depend on the grain boundary structure. The level of titanium grain boundary segregation in the inner scale decreased toward the model alloy (substrate), confirming the fast outward diffusion of titanium. Hafnium was also observed at the metal-scale interface and in the γ' (Ni 3 Al) phase of the alloy. High-resolution scanning transmission electron microscopy (STEM) confirmed the substitution of REs for aluminum atoms at the scale grain boundaries, consistent with both the semiconducting band structure and the site-blocking models. Both STEM and atom probe tomography allowed quantification of REs along the scale grain boundaries across the scale thickness. Analysis of the scale morphology after isothermal exposure in flowing oxygen revealed a myriad of new precipitate phases, RE segregation dependence on grain boundary type, and atomic arrangement along scale grain boundaries, which is expected to influence the scale growth rate, stability, and mechanical properties. Copyright © 2018 Elsevier Ltd. All rights reserved.

Initial investigations of microscale cellular convection in an equatorial marine atmospheric boundary layer revealed by lidar

NASA Astrophysics Data System (ADS)

Cooper, D. I.; Eichinger, W. E.; Ecke, R. E.; Kao, J. C. Y.; Reisner, J. M.; Tellier, L. L.

During the Combined Sensor Program (CSP) in March of 1996, the Los Alamos National Laboratory (LANL) fielded an advanced scanning Raman lidar. The lidar was part of a larger suite of micrometeorological sensors to quantify processes associated with the ocean-atmosphere interface, including intermittency and coherent atmospheric features in the “warm pool” of the Tropical Western Pacific (TWP) near Manus Island (2° S. lat, 147° E. long). Initial inspection of the data has revealed excellent information on the microscale vertical and horizontal spatial and temporal structure of the equatorial Marine Atmospheric Boundary Layer (MABL). The data from this experiment have added to the increasing body of measurements on surface layer convection and intermittency including, for the first time, the observation of microscale cellular convective structures such as hexagonal patterns associated with Rayleigh-Bénard cells.

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.

Observations of the atmospheric boundary layer height over Abu Dhabi, United Arab Emirates: Investigating boundary layer climatology in arid regions

NASA Astrophysics Data System (ADS)

Marzooqi, Mohamed Al; Basha, Ghouse; Ouarda, Taha B. M. J.; Armstrong, Peter; Molini, Annalisa

2014-05-01

Strong sensible heat fluxes and deep turbulent mixing - together with marked dustiness and a low substrate water content - represent a characteristic signature in the boundary layer over hot deserts, resulting in "thicker" mixing layers and peculiar optical properties. Beside these main features however, desert ABLs present extremely complex local structures that have been scarcely addressed in the literature, and whose understanding is essential in modeling processes such as the transport of dust and pollutants, and turbulent fluxes of momentum, heat and water vapor in hyper-arid regions. In this study, we analyze a continuous record of observations of the atmospheric boundary layer (ABL) height from a single lens LiDAR ceilometer operated at Masdar Institute Field Station (24.4oN, 54.6o E, Abu Dhabi, United Arab Emirates), starting March 2013. We compare different methods for the estimation of the ABL height from Ceilometer data such as, classic variance-, gradient-, log gradient- and second derivation-methods as well as recently developed techniques such as the Bayesian Method and Wavelet covariance transform. Our goal is to select the most suited technique for describing the climatology of the ABL in desert environments. Comparison of our results with radiosonde observations collected at the nearby airport of Abu Dhabi indicate that the WCT and the Bayesian method are the most suitable tools to accurately identify the ABL height in all weather conditions. These two methods are used for the definition of diurnal and seasonal climatologies of the boundary layer conditional to different atmospheric stability classes.

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.

Enhanced viscous flow drag reduction using acoustic excitation

NASA Technical Reports Server (NTRS)

Nagel, R. T.

1988-01-01

Large eddy break up devices (LEBUs) constitute a promising method of obtaining drag reduction in a turbulent boundary layer. Enhancement of the LEBU effectiveness by exciting its trailing edge with acoustic waves phase locked to the large scale structure influencing the momentum transfer to the wall is sought. An initial estimate of the required sound pressure level for an effective pulse was obtained by considering the magnitude of the pressure perturbations at the near wake of a thin plate in inviscid flow. Detailed skin friction measurments were obtained in the flow region downstream of a LEBU excited with acoustic waves. The data are compared with skin friction measurements of a simply manipulated flow, without acoustic excitation and with a plain flow configuration. The properties and the scales of motion in the flow regime downstream of the acoustically excited LEBU are studied. A parametric study based upon the characteristics of the acoustic input was pursued in addition to the careful mapping of the drag reduction phenomenon within the acoustically manipulated boundary layer. This study of boundary layer manipulation has lead to improved skin friction drag reduction and further understanding of the turbulent boundary layer.

Structure and Optical Properties of the Atmospheric Boundary Layer over Dusty Hot Deserts

NASA Astrophysics Data System (ADS)

Chalermthai, B.; Al Marzooqi, M.; Basha, G.; Ouarda, T.; Armstrong, P.; Molini, A.

2014-12-01

Strong sensible heat fluxes and deep turbulent mixing - together with marked dustiness and a low substrate water content - represent a characteristic signature of the atmospheric boundary layer (ABL) over hot deserts, resulting in "thicker" mixing layers and peculiar optical properties. Beside these main common features however, desert boundary layers present extremely complex local structures that have been scarcely addressed in the literature, and whose understanding is essential in modeling processes such as transport and deposition of dust and pollutants, local wind fields, turbulent fluxes and their impacts on the sustainable development, human health and solar energy harvesting in these regions. In this study, we explore the potential of the joint usage of Lidar Ceilometer backscattering profiles and sun-photometer optical depth retrievals to quantitatively determine the vertical aerosol profile over dusty hot desert regions. Toward this goal, we analyze a continuous record of observations of the atmospheric boundary layer height from a single lens LiDAR ceilometer operated at Masdar Institute Field Station (24.4425N 54.6163E, Abu Dhabi, United Arab Emirates), starting March 2013, and the concurrent measurements of aerosol optical depth derived independently from the Masdar Institute AERONET sun-photometer. The main features of the desert ABL are obtained from the ceilometer range corrected backscattering profiles through bi-dimensional clustering technique we developed as a modification of the recently proposed single-profile clustering method, and therefore "directly" and "indirectly" calibrated to obtain a full diurnal cycle climatology of the aerosol optical depth and aerosol profiles. The challenges and the advantages of applying a similar methodology to the monitoring of aerosols and dust over hyper-arid regions are also discussed, together with the issues related to the sensitivity of commercial ceilometers to changes in the solar background.

Fluid Mechanics and Heat Transfer in Transitional Boundary Layers

NASA Technical Reports Server (NTRS)

Wang, Ting

2007-01-01

Experiments have been performed to investigate the effects of elevated free-stream turbulence and streamwise acceleration on flow and thermal structures in transitional boundary layers. The free-stream turbulence ranges from 0.5 to 6.4% and the streamwise acceleration ranges from K = 0 to 0.8 x 10(exp -6). The onset of transition, transition length and the turbulent spot formation rate are determined. The statistical results and conditionally sampled results of th streamwise and cross-stream velocity fluctuations, temperature fluctuations, Reynolds stress and Reynolds heat fluxes are presented.

Application of Lidar and other profiling techniques to study the impact that Severe weather hazards have on the New York City built environment

NASA Astrophysics Data System (ADS)

Arend, Mark; Campmier, Mark; Fernandez, Aris; Moshary, Fred

2018-04-01

The complexity of urban boundary layer dynamics poses challenges to those responsible for the design and regulation of buildings and structures in the urban environment. Lidar systems in the New York City Metropolitan region have been used extensively to study urban boundary layer dynamics. These systems, in conjunction with other sensing platforms can provide an observatory to perform research and analysis of turbulent and inclement weather patterns of interest to developers and agencies.

Review: the atmospheric boundary layer

NASA Astrophysics Data System (ADS)

Garratt, J. R.

1994-10-01

An overview is given of the atmospheric boundary layer (ABL) over both continental and ocean surfaces, mainly from observational and modelling perspectives. Much is known about ABL structure over homogeneous land surfaces, but relatively little so far as the following are concerned, (i) the cloud-topped ABL (over the sea predominantly); (ii) the strongly nonhomogeneous and nonstationary ABL; (iii) the ABL over complex terrain. These three categories present exciting challenges so far as improved understanding of ABL behaviour and improved representation of the ABL in numerical models of the atmosphere are concerned.

Rod-shaped cavitation bubble structure in ultrasonic field.

PubMed

Bai, Lixin; Wu, Pengfei; Liu, Huiyu; Yan, Jiuchun; Su, Chang; Li, Chao

2018-06-01

Rod-shaped cavitation bubble structure in thin liquid layers in ultrasonic field is investigated experimentally. It is found that cavitation structure successively experiences several stages with the change of the thickness of the thin liquid layer. Rod-shaped structure is a stable structure of the boundary between the cavitation cloud region and the non-cavitation liquid region, which can be formed in two different ways. Cavitation bubbles in a thin liquid layer have a distribution in the thickness direction. The rod-shaped structures tend to crosslink with each other to form stable Y-branch structures. The angle of the Y-branch structure is Gauss distribution with mathematical expectation μ = 119.93. A special rod-shaped cavitation structure with source is also investigated in detail. Due to the pressure gradient in the normal direction, the primary Bjerknes force causes the bubbles in the rod-shaped structure on both sides to converge to the axis. The secondary Bjerknes forces between the bubbles also make the cluster converge, so the large bubbles which are attached to the radiating surface tend to align themselves along the central line. According to the formula deduced in this paper, the variation of curvature of curved rod-shaped structure is qualitatively analyzed. The Y-branch structure of cavitation cloud and Plateau boundary of soap bubbles are compared. Copyright © 2018 Elsevier B.V. All rights reserved.

Segregation and trapping of oxygen vacancies near the SrTiO 3Σ3 (112) [110] tilt grain boundary

DOE PAGES

Liu, Bin; Cooper, Valentino R.; Zhang, Yanwen; ...

2015-03-21

In nanocrystalline materials, structural discontinuities at grain boundaries (GBs) and the segregation of point defects to these GBs play a key role in defining the structural stability of a material, as well as its macroscopic electrical/mechanical properties. In this study, the segregation of oxygen vacancies near the Σ3 (1 1 2) [¯110] tilt GB in SrTiO 3 is explored using density functional theory. We find that oxygen vacancies segregate toward the GB, preferring to reside within the next nearest-neighbor layer. This oxygen vacancy segregation is found to be crucial for stabilizing this tilt GB. Furthermore, we find that the migrationmore » barriers of oxygen vacancies diffusing toward the first nearest-neighbor layer of the GB are low, while those away from this layer are very high. Furthermore, the segregation and trapping of the oxygen vacancies in the first nearest-neighbor layer of GBs are attributed to the large local distortions, which can now accommodate the preferred sixfold coordination of Ti. These results suggest that the electronic, transport, and capacitive properties of SrTiO 3 can be engineered through the control of GB structure and grain size or layer thickness.« less

A computer program for the calculation of the flow field including boundary layer effects for mixed-compression inlets at angle of attack

NASA Technical Reports Server (NTRS)

Vadyak, J.; Hoffman, J. D.

1982-01-01

A computer program was developed which is capable of calculating the flow field in the supersonic portion of a mixed compression aircraft inlet operating at angle of attack. The supersonic core flow is computed using a second-order three dimensional method-of-characteristics algorithm. The bow shock and the internal shock train are treated discretely using a three dimensional shock fitting procedure. The boundary layer flows are computed using a second-order implicit finite difference method. The shock wave-boundary layer interaction is computed using an integral formulation. The general structure of the computer program is discussed, and a brief description of each subroutine is given. All program input parameters are defined, and a brief discussion on interpretation of the output is provided. A number of sample cases, complete with data listings, are provided.

Equilibrium structure of the plasma sheet boundary layer-lobe interface

NASA Technical Reports Server (NTRS)

Romero, H.; Ganguli, G.; Palmadesso, P.; Dusenbery, P. B.

1990-01-01

Observations are presented which show that plasma parameters vary on a scale length smaller than the ion gyroradius at the interface between the plasma sheet boundary layer and the lobe. The Vlasov equation is used to investigate the properties of such a boundary layer. The existence, at the interface, of a density gradient whose scale length is smaller than the ion gyroradius implies that an electrostatic potential is established in order to maintain quasi-neutrality. Strongly sheared (scale lengths smaller than the ion gyroradius) perpendicular and parallel (to the ambient magnetic field) electron flows develop whose peak velocities are on the order of the electron thermal speed and which carry a net current. The free energy of the sheared flows can give rise to a broadband spectrum of electrostatic instabilities starting near the electron plasma frequency and extending below the lower hybrid frequency.

A nonlinear investigation of the stationary modes of instability of the three-dimensional compressible boundary layer due to a rotating disc

NASA Technical Reports Server (NTRS)

Seddougui, Sharon O.

1989-01-01

The effects of compressibility on a stationary mode of instability of the 3-D boundary layer due to a rotating disc are investigated. The aim is to determine whether this mode will be important in the finite amplitude destabilization of the boundary layer. This stationary mode is characterized by the effective velocity profile having zero shear stress at the wall. Triple-deck solutions are presented for an adiabatic wall and an isothermal wall. It is found that this stationary mode is only possible over a finite range of Mach numbers. Asymptotic solutions are obtained which describe the structure of the wavenumber and the orientation of these modes as functions of the local Mach number. The effects of nonlinearity are investigated allowing the finite amplitude growth of a disturbance close to the neutral location to be described.

Evaluation of thermal stability in spectrally selective few-layer metallo-dielectric structures for solar thermophotovoltaics

NASA Astrophysics Data System (ADS)

Shimizu, Makoto; Kohiyama, Asaka; Yugami, Hiroo

2018-06-01

The thermal stability of spectrally selective few-layer metallo-dielectric structures is evaluated to analyze their potential as absorber and emitter materials in solar thermophotovoltaic (STPV) systems. High-efficiency (e.g., STPV) systems require materials with spectrally selective properties, especially at high temperatures (>1273 K). Aiming to develop such materials for high-temperature applications, we propose a few-layer structure composed of a refractory metal (i.e., Mo) nanometric film sandwiched between the layers of a dielectric material (i.e., hafnium oxide, HfO2) deposited on a Mo bulk substrate. In vacuum conditions (<5 × 10-2 Pa), the few-layer structure shows thermal stability at 1423 K for at least 1 h. At 1473 K, the spectral selectivity was degraded. This could have been caused by the oxidation of the Mo thin film by the residual oxygen through the grain boundaries of the upper HfO2 layer. This experiment showed the potential stability of few-layer structures for applications working at temperatures greater than 1273 K as well as the degradation mechanism of the few-layer structure. This characteristic is expected to help improve the thermal stability in few-layer structures further.

Boundary Layer Transition Results From STS-114

NASA Technical Reports Server (NTRS)

Berry, Scott A.; Horvath, Thomas J.; Cassady, Amy M.; Kirk, Benjamin S.; Wang, K. C.; Hyatt, Andrew J.

2006-01-01

The tool for predicting the onset of boundary layer transition from damage to and/or repair of the thermal protection system developed in support of Shuttle Return to Flight is compared to the STS-114 flight results. The Boundary Layer Transition (BLT) Tool is part of a suite of tools that analyze the aerothermodynamic environment of the local thermal protection system to allow informed disposition of damage for making recommendations to fly as is or to repair. Using mission specific trajectory information and details of each damage site or repair, the expected time of transition onset is predicted to help determine the proper aerothermodynamic environment to use in the subsequent thermal and stress analysis of the local structure. The boundary layer transition criteria utilized for the tool was developed from ground-based measurements to account for the effect of both protuberances and cavities and has been calibrated against flight data. Computed local boundary layer edge conditions provided the means to correlate the experimental results and then to extrapolate to flight. During STS-114, the BLT Tool was utilized and was part of the decision making process to perform an extravehicular activity to remove the large gap fillers. The role of the BLT Tool during this mission, along with the supporting information that was acquired for the on-orbit analysis, is reviewed. Once the large gap fillers were removed, all remaining damage sites were cleared for reentry as is. Post-flight analysis of the transition onset time revealed excellent agreement with BLT Tool predictions.

Secondary eyewall formation as a progressive boundary layer response

NASA Astrophysics Data System (ADS)

Abarca, S. F.; Montgomery, M. T.; Bell, M. M.

2012-12-01

The robust observational (satellite based) evidence that secondary eyewalls are common features in major hurricanes contrasts with the scarce in situ observations of the phenomena and its life cycle. This lack of observations has resulted in an incomplete understanding of the dynamics of secondary eyewall formation (SEF). A wide variety of physical processes have been invoked to explain SEF, but only the recently proposed theory of a progressive boundary layer control in SEF has been supported by a variety of full physics mesoscale numerical integrations. The RAINEX field project provided unique observations of the secondary eyewall of Hurricane Rita (2005) both before and during the time Rita exhibited a clear secondary eyewall structure. These observations have contributed to the advancement of the understanding of the secondary eyewall phenomenon. However, in the RAINEX experiment, there was limited data sampling during the development of the secondary wind maxima, thereby precluding a complete observational investigation of the dynamics of SEF. In this presentation we adopt an azimuthally-averaged perspective of the flow dynamics and we test the newly proposed theory of a progressive boundary layer control on SEF. Specifically, we use both RAINEX data as well as data from high resolution, full physics mesoscale numerical simulations to initialize and force an axisymmetric slab boundary layer model with radial diffusion included. The objective is to investigate whether such a reduced boundary layer model can generate secondary wind maxima as a response to environments like those that result in SEF in nature and in full physics simulations.

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.

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 kinetic energy equation and free mixing

NASA Technical Reports Server (NTRS)

Morel, T.; Torda, T. P.; Bradshaw, P.

1973-01-01

Calculation of free shear flows was carried out to investigate the usefulness of several concepts which were previously successfully applied to wall flows. The method belongs to the class of differential approaches. The turbulence is taken into account by the introduction of one additional partial differential equation, the transport equation for the turbulent shear stress. The structure of turbulence is modeled after Bradshaw et al. This model was used successfully in boundary layers and its applicability to other flows is demonstrated. The work reported differs substantially from that of an earlier attempt to use this approach for calculation of free flows. The most important difference is that the region around the center line is treated by invoking the interaction hypothesis (concerning the structure of turbulence in the regions separated by the velocity extrema). The compressibility effects on shear layer spreading at low and moderate Mach numbers were investigated. In the absence of detailed experiments in free flows, the evidence from boundary layers that at low Mach numbers the structure of turbulence is unaffected by the compressibility was relied on. The present model was tested over a range of self-preserving and developing flows including pressure gradients using identical empirical input. The dependence of the structure of turbulence on the spreading rate of the shear layer was established.

Evaluation of WRF PBL parameterization schemes against direct observations during a dry event over the Ganges valley

NASA Astrophysics Data System (ADS)

Sathyanadh, Anusha; Prabha, Thara V.; Balaji, B.; Resmi, E. A.; Karipot, Anandakumar

2017-09-01

Accurate representations of the planetary boundary layer (PBL) are important in all weather forecast systems, especially in simulations of turbulence, wind and air quality in the lower atmosphere. In the present study, detailed observations from the Cloud Aerosol Interaction and Precipitation Enhancement Experiment - Integrated Ground based Observational Campaign (CAIPEEX-IGOC) 2014 comprising of the complete surface energy budget and detailed boundary layer observations are used to validate Advanced Research Weather Research and Forecasting (WRF) model simulations over a diverse terrain over the Ganges valley region, Uttar Pradesh, India. A drying event in June 2014 associated with a heat wave is selected for validation.Six local and nonlocal PBL schemes from WRF at 1 km resolution are compared with hourly observations during the diurnal cycle. Near-surface observations of weather parameters, radiation components and eddy covariance fluxes from micrometeorological tower, and profiles of variables from microwave radiometer, and radiosonde observations are used for model evaluations. Models produce a warmer, drier surface layer with higher wind speed, sensible heat flux and temperature than observations. Layered boundary layer dynamics, including the residual layer structure as illustrated in the observations over the Ganges valley are missed in the model, which lead to deeper mixed layers and excessive drying.Although it is difficult to identify any single scheme as the best, the qualitative and quantitative analyses for the entire study period and overall reproducibility of the observations indicate that the MYNN2 simulations describe lower errors and more realistic simulation of spatio-temporal variations in the boundary layer height.

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

Direct Determination of Atomic Structure and Magnetic Coupling of Magnetite Twin Boundaries.

PubMed

Chen, Chunlin; Li, Hongping; Seki, Takehito; Yin, Deqiang; Sanchez-Santolino, Gabriel; Inoue, Kazutoshi; Shibata, Naoya; Ikuhara, Yuichi

2018-03-27

Clarifying how the atomic structure of interfaces/boundaries in materials affects the magnetic coupling nature across them is of significant academic value and will facilitate the development of state-of-the-art magnetic devices. Here, by combining atomic-resolution transmission electron microscopy, atomistic spin-polarized first-principles calculations, and differential phase contrast imaging, we conduct a systematic investigation of the atomic and electronic structures of individual Fe 3 O 4 twin boundaries (TBs) and determine their concomitant magnetic couplings. We demonstrate that the magnetic coupling across the Fe 3 O 4 TBs can be either antiferromagnetic or ferromagnetic, which directly depends on the TB atomic core structures and resultant electronic structures within a few atomic layers. Revealing the one-to-one correspondence between local atomic structures and magnetic properties of individual grain boundaries will shed light on in-depth understanding of many interesting magnetic behaviors of widely used polycrystalline magnetic materials, which will surely promote the development of advanced magnetic materials and devices.

Nonlinear electric field structures in the inner magnetosphere

DOE PAGES

Malaspina, D. M.; Andersson, L.; Ergun, R. E.; ...

2014-08-28

Recent observations by the Van Allen Probes spacecraft have demonstrated that a variety of electric field structures and nonlinear waves frequently occur in the inner terrestrial magnetosphere, including phase space holes, kinetic field-line resonances, nonlinear whistler-mode waves, and several types of double layer. However, it is nuclear whether such structures and waves have a significant impact on the dynamics of the inner magnetosphere, including the radiation belts and ring current. To make progress toward quantifying their importance, this study statistically evaluates the correlation of such structures and waves with plasma boundaries. A strong correlation is found. These statistical results, combinedmore » with observations of electric field activity at propagating plasma boundaries, are consistent with the identification of these boundaries as the source of free energy responsible for generating the electric field structures and nonlinear waves of interest. Therefore, the ability of these structures and waves to influence plasma in the inner magnetosphere is governed by the spatial extent and dynamics of macroscopic plasma boundaries in that region.« less

Feather roughness reduces flow separation during low Reynolds number glides of swifts.

PubMed

van Bokhorst, Evelien; de Kat, Roeland; Elsinga, Gerrit E; Lentink, David

2015-10-01

Swifts are aerodynamically sophisticated birds with a small arm and large hand wing that provides them with exquisite control over their glide performance. However, their hand wings have a seemingly unsophisticated surface roughness that is poised to disturb flow. This roughness of about 2% chord length is formed by the valleys and ridges of overlapping primary feathers with thick protruding rachides, which make the wing stiffer. An earlier flow study of laminar-turbulent boundary layer transition over prepared swift wings suggested that swifts can attain laminar flow at a low angle of attack. In contrast, aerodynamic design theory suggests that airfoils must be extremely smooth to attain such laminar flow. In hummingbirds, which have similarly rough wings, flow measurements on a 3D printed model suggest that the flow separates at the leading edge and becomes turbulent well above the rachis bumps in a detached shear layer. The aerodynamic function of wing roughness in small birds is, therefore, not fully understood. Here, we performed particle image velocimetry and force measurements to compare smooth versus rough 3D-printed models of the swift hand wing. The high-resolution boundary layer measurements show that the flow over rough wings is indeed laminar at a low angle of attack and a low Reynolds number, but becomes turbulent at higher values. In contrast, the boundary layer over the smooth wing forms open laminar separation bubbles that extend beyond the trailing edge. The boundary layer dynamics of the smooth surface varies non-linearly as a function of angle of attack and Reynolds number, whereas the rough surface boasts more consistent turbulent boundary layer dynamics. Comparison of the corresponding drag values, lift values and glide ratios suggests, however, that glide performance is equivalent. The increased structural performance, boundary layer robustness and equivalent aerodynamic performance of rough wings might have provided small (proto) birds with an evolutionary window to high glide performance. © 2015. Published by The Company of Biologists Ltd.

Large-Eddy Simulation of the Flat-plate Turbulent Boundary Layer at High Reynolds numbers

NASA Astrophysics Data System (ADS)

Inoue, Michio

The near-wall, subgrid-scale (SGS) model [Chung and Pullin, "Large-eddy simulation and wall-modeling of turbulent channel flow'', J. Fluid Mech. 631, 281--309 (2009)] is used to perform large-eddy simulations (LES) of the incompressible developing, smooth-wall, flat-plate turbulent boundary layer. In this model, the stretched-vortex, SGS closure is utilized in conjunction with a tailored, near-wall model designed to incorporate anisotropic vorticity scales in the presence of the wall. The composite SGS-wall model is presently incorporated into a computer code suitable for the LES of developing flat-plate boundary layers. This is then used to study several aspects of zero- and adverse-pressure gradient turbulent boundary layers. First, LES of the zero-pressure gradient turbulent boundary layer are performed at Reynolds numbers Retheta based on the free-stream velocity and the momentum thickness in the range Retheta = 103-1012. Results include the inverse skin friction coefficient, 2/Cf , velocity profiles, the shape factor H, the Karman "constant", and the Coles wake factor as functions of Re theta. Comparisons with some direct numerical simulation (DNS) and experiment are made, including turbulent intensity data from atmospheric-layer measurements at Retheta = O (106). At extremely large Retheta , the empirical Coles-Fernholz relation for skin-friction coefficient provides a reasonable representation of the LES predictions. While the present LES methodology cannot of itself probe the structure of the near-wall region, the present results show turbulence intensities that scale on the wall-friction velocity and on the Clauser length scale over almost all of the outer boundary layer. It is argued that the LES is suggestive of the asymptotic, infinite Reynolds-number limit for the smooth-wall turbulent boundary layer and different ways in which this limit can be approached are discussed. The maximum Retheta of the present simulations appears to be limited by machine precision and it is speculated, but not demonstrated, that even larger Retheta could be achieved with quad- or higher-precision arithmetic. Second, the time series velocity signals obtained from LES within the logarithmic region of the zero-pressure gradient turbulent boundary layer are used in combination with an empirical, predictive inner--outer wall model [Marusic et al., "Predictive model for wall-bounded turbulent flow'', Science 329, 193 (2010)] to calculate the statistics of the fluctuating streamwise velocity in the inner region of the zero-pressure gradient turbulent boundary layer. Results, including spectra and moments up to fourth order, are compared with equivalent predictions using experimental time series, as well as with direct experimental measurements at Reynolds numbers Retau based on the friction velocity and the boundary layer thickness, Retau = 7,300, 13,600 and 19,000. LES combined with the wall model are then used to extend the inner-layer predictions to Reynolds numbers Retau = 62,000, 100,000 and 200,000 that lie within a gap in log(Retau) space between laboratory measurements and surface-layer, atmospheric experiments. The present results support a log-like increase in the near-wall peak of the streamwise turbulence intensities with Retau and also provide a means of extending LES results at large Reynolds numbers to the near-wall region of wall-bounded turbulent flows. Finally, we apply the wall model to LES of a turbulent boundary layer subject to an adverse pressure gradient. Computed statistics are found to be consistent with recent experiments and some Reynolds number similarity is observed over a range of two orders of magnitude.

Cross-flow vortex structure and transition measurements using multi-element hot films

NASA Technical Reports Server (NTRS)

Agarwal, Naval K.; Mangalam, Siva M.; Maddalon, Dal V.; Collier, Fayette S., Jr.

1991-01-01

An experiment on a 45-degree swept wing was conducted to study three-dimensional boundary-layer characteristics using surface-mounted, micro-thin, multi-element hot-film sensors. Cross-flow vortex structure and boundary-layer transition were measured from the simultaneously acquired signals of the hot films. Spanwise variation of the root-mean-square (RMS) hot-film signal show a local minima and maxima. The distance between two minima corresponds to the stationary cross-flow vortex wavelength and agrees with naphthalene flow-visualization results. The chordwise and spanwise variation of amplified traveling (nonstationary) cross-flow disturbance characteristics were measured as Reynolds number was varied. The frequency of the most amplified cross-flow disturbances agrees with linear stability theory.

Study of Near-Surface Models in Large-Eddy Simulations of a Neutrally Stratified Atmospheric Boundary Layer

NASA Technical Reports Server (NTRS)

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

2004-01-01

Large-eddy simulation (LES) is a widely used technique in armospheric modeling research. In LES, large, unsteady, three dimensional structures are resolved and small structures that are not resolved on the computational grid are modeled. A filtering operation is applied to distinguish between resolved and unresolved scales. We present two near-surface models that have found use in atmospheric modeling. We also suggest a simpler eddy viscosity model that adopts Prandtl's mixing length model (Prandtl 1925) in the vicinity of the surface and blends with the dynamic Smagotinsky model (Germano et al, 1991) away from the surface. We evaluate the performance of these surface models by simulating a neutraly stratified atmospheric boundary layer.

Lunar and Planetary Science XXXV: Effects of Impacts: Shock and Awe

NASA Technical Reports Server (NTRS)

Kyte, F. T.; Koeberl, C.

2004-01-01

This document discusses the following topics: Zircon as a Shock Indicator in Impactites of Drill Core Yaxcopoil-1, Chicxulub Impact Structure, Mexico; Experimental Investigation of Shock Effects in a Metapelitic Granulite; Experimental Reproduction of Shock Veins in Single-Crystal Minerals; Post-Shock Crystal-Plastic Processes in Quartz from Crystalline Target Rocks of the Charlevoix Impact Structure; Shock Reequilibration of Fluid Inclusions; How Does Tektite Glass Lose Its Water?; Assessing the Role of Anhydrite in the KT Mass Extinction: Hints from Shock-loading Experiments; A Mineralogical and Geochemical Study of the Nonmarine Permian/Triassic Boundary in the Southern Karoo Basin, South Africa; Extraterrestrial Chromium in the Permian-Triassic Boundary at Graphite Peak, Antarctica; Magnetic Fe,Si,Al-rich Impact Spherules from the P-T Boundary Layer at Graphite Peak, Antarctica; A Newly Recognized Late Archean Impact Spherule Layer in the Reivilo Formation, Griqualand West Basin, South Africa; Initial Cr-Isotopic and Iridium Measurements of Concentrates from Late Eocene Cpx-Spherule Deposits; An Ordinary Chondrite Impactor Composition for the Bosumtwi Impact Structure, Ghana, West Africa: Discussion of Siderophile Element Contents and Os and Cr Isotope Data.

A sharp and flat section of the core-mantle boundary

USGS Publications Warehouse

Vidale, J.E.; Benz, H.M.

1992-01-01

THE transition zone between the Earth's core and mantle plays an important role as a boundary layer for mantle and core convection1. This zone conducts a large amount of heat from the core to the mantle, and contains at least one thermal boundary layer2,3; the proximity of reactive silicates and molten iron leads to the possibility of zones of intermediate composition4. Here we investigate one region of the core-mantle boundary using seismic waves that are converted from shear to compressional waves by reflection at the boundary. The use of this phase (known as ScP), the large number of receiving stations, and the large aperture of our array all provide higher resolution than has previously been possible5-7. For the 350-km-long section of the core-mantle boundary under the northeast Pacific sampled by the reflections, the local boundary topography has an amplitude of less than 500 m, no sharp radial gradients exist in the 400 km above the boundary, and the mantle-lo-core transition occurs over less than 1 km. The simplicity of the structure near and above the core-mantle boundary argues against chemical heterogeneity at the base of the mantle in this location.

Influence of incoherent twin boundaries on the electrical properties of β-Ga2O3 layers homoepitaxially grown by metal-organic vapor phase epitaxy

NASA Astrophysics Data System (ADS)

Fiedler, A.; Schewski, R.; Baldini, M.; Galazka, Z.; Wagner, G.; Albrecht, M.; Irmscher, K.

2017-10-01

We present a quantitative model that addresses the influence of incoherent twin boundaries on the electrical properties in β-Ga2O3. This model can explain the mobility collapse below a threshold electron concentration of 1 × 1018 cm-3 as well as partly the low doping efficiency in β-Ga2O3 layers grown homoepitaxially by metal-organic vapor phase epitaxy on (100) substrates of only slight off-orientation. A structural analysis by transmission electron microscopy (TEM) reveals a high density of twin lamellae in these layers. In contrast to the coherent twin boundaries parallel to the (100) plane, the lateral incoherent twin boundaries exhibit one dangling bond per unit cell that acts as an acceptor-like electron trap. Since the twin lamellae are thin, we consider the incoherent twin boundaries to be line defects with a density of 1011-1012 cm-2 as determined by TEM. We estimate the influence of the incoherent twin boundaries on the electrical transport properties by adapting Read's model of charged dislocations. Our calculations quantitatively confirm that the mobility reduction and collapse as well as partly the compensation are due to the presence of twin lamellae.

Synchroneity of the K-T oceanic mass extinction and meteorite impact: Blake Nose, western North Atlantic

USGS Publications Warehouse

Norris, R.D.; Huber, B.T.; Self-Trail, J.

1999-01-01

A 10-cm-thick layer of green spherules occurs precisely at the biostratigraphic boundary between the Cretaceous and Paleogene (K-T boundary) at Ocean Drilling Program Site 1049 (lat 30??08???N, long 76??06???W). The spherulitic layer contains abundant rock fragments (chalk, limestone, dolomite, chert, mica books, and schist) as well as shocked quartz, abundant large Cretaceous planktic foraminifera, and rounded clasts of clay as long as 4 mm interpreted as altered tektite glass probably derived from the Chicxulub impact structure. Most of the Cretaceous foraminifera present above the spherule layer are not survivors since small specimens are conspicuously rare compared to large individuals. Instead, the Cretaceous taxa in Paleocene sediments are thought to be reworked. The first Paleocene planktic foraminifera and calcareous nannofossil species are recorded immediately above the spherule bed, the upper part of which contains an iridium anomaly. Hence, deposition of the impact ejecta exactly coincided with the biostratigraphic K-T boundary and demonstrates that the impact event was synchronous with the evolutionary turnover in the oceans. These results are consistent with a reanalysis of the biostratigraphy of the K-T boundary stratotype, which argues that shallow-marine K-T boundary sections are not biostratigraphically more complete than deep-sea K-T boundary sites.

Wideband Low-Reflection Inhomogeneous Dielectric Structures

NASA Astrophysics Data System (ADS)

Denisova, N. A.; Rezvov, A. V.

2017-08-01

We consider reflection of electromagnetic waves from two-layer dielectric films with finite thickness, whose refractive indices vary in the direction of wave propagation, which is perpendicular to the substrate boundary. The profiles of the refractive indices of the structures having low reflection coefficients in a wide frequency range are found. The obtained results are based on exact analytical solutions of the Helmholtz equation for one type of the layered inhomogeneous dielectric medium. The possibility of creating new low-reflection wideband inhomogeneous dielectric structures is demonstrated.

Influence of a density increase on the evolution of the Kelvin-Helmholtz instability and vortices

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

Amerstorfer, U. V.; Erkaev, N. V.; Institute of Computational Modelling, 660036 Krasnoyarsk

2010-07-15

Results of two-dimensional nonlinear numerical simulations of the magnetohydrodynamic Kelvin-Helmholtz instability are presented. A boundary layer of a certain width is assumed, which separates the plasma in the upper layer from the plasma in the lower layer. A special focus is given on the influence of a density increase toward the lower layer. The evolution of the Kelvin-Helmholtz instability can be divided into three different phases, namely, a linear growth phase at the beginning, followed by a nonlinear phase with regular structures of the vortices, and finally, a turbulent phase with nonregular structures. The spatial scales of the vortices aremore » about five times the initial width of the boundary layer. The considered configuration is similar to the situation around unmagnetized planets, where the solar wind (upper plasma layer) streams past the ionosphere (lower plasma layer), and thus the plasma density increases toward the planet. The evolving vortices might detach around the terminator of the planet and eventually so-called plasma clouds might be formed, through which ionospheric material can be lost. For the special case of a Venus-like planet, loss rates are estimated, which are of the order of estimated loss rates from observations at Venus.« less

Mass Conservation in Modeling Moisture Diffusion in Multi-Layer Carbon Composite Structures

NASA Technical Reports Server (NTRS)

Nurge, Mark A.; Youngquist, Robert C.; Starr, Stanley O.

2009-01-01

Moisture diffusion in multi-layer carbon composite structures is difficult to model using finite difference methods due to the discontinuity in concentrations between adjacent layers of differing materials. Applying a mass conserving approach at these boundaries proved to be effective at accurately predicting moisture uptake for a sample exposed to a fixed temperature and relative humidity. Details of the model developed are presented and compared with actual moisture uptake data gathered over 130 days from a graphite epoxy composite sandwich coupon with a Rohacell foam core.

Unsteady Flow in Different Atmospheric Boundary Layer Regimes and Its Impact on Wind-Turbine Performance

NASA Astrophysics Data System (ADS)

Gohari, Iman; Korobenko, Artem; Yan, Jinhui; Bazilevs, Yuri; Sarkar, Sutanu

2016-11-01

Wind is a renewable energy resource that offers several advantages including low pollutant emission and inexpensive construction. Wind turbines operate in conditions dictated by the Atmospheric Boundary Layer (ABL) and that motivates the study of coupling ABL simulations with wind turbine dynamics. The ABL simulations can be used for realistic modeling of the environment which, with the use of fluid-structure interaction, can give realistic predictions of extracted power, rotor loading, and blade structural response. The ABL simulations provide inflow boundary conditions to the wind-turbine simulator which uses arbitrary Lagrangian-Eulerian variational multiscale formulation. In the present work, ABL simulations are performed to examine two different scenarios: (i) A neutral ABL with zero heat-flux and inversion layer at 350m, in which the wind turbine experiences maximum mean shear; (2) A shallow ABL with the surface cooling-rate of -1 K/hr, in which the wind turbine experiences maximum mean velocity at the low-level-jet nose height. We will discuss differences in the unsteady flow between the two different ABL conditions and their impact on the performance of the wind turbine cluster in the coupled ABL-wind turbine simulations.

A viscous flow study of shock-boundary layer interaction, radial transport, and wake development in a transonic compressor

NASA Technical Reports Server (NTRS)

Hah, Chunill; Reid, Lonnie

1991-01-01

A numerical study based on the 3D Reynolds-averaged Navier-Stokes equation has been conducted to investigate the detailed flow physics inside a transonic compressor. 3D shock structure, shock-boundary layer interaction, flow separation, radial mixing, and wake development are all investigated at design and off-design conditions. Experimental data based on laser anemometer measurements are used to assess the overall quality of the numerical solution. An additional experimental study to investigate end-wall flow with a hot-film was conducted, and these results are compared with the numerical results. Detailed comparison with experimental data indicates that the overall features of the 3D shock structure, the shock-boundary layer interaction, and the wake development are all calculated very well in the numerical solution. The numerical results are further analyzed to examine the radial mixing phenomena in the transonic compressor. A thin sheet of particles is injected in the numerical solution upstream of the compressor. The movement of particles is traced with a 3D plotting package. This numerical survey of tracer concentration reveals the fundamental mechanisms of radial transport in this transonic compressor.

Shed Vortex Structure and Phase-Averaged Velocity Statistics in Symmetric/Asymmetric Turbulent Flat Plate Wakes

NASA Technical Reports Server (NTRS)

Rai, Man Mohan

2017-01-01

The near wake of a flat plate is investigated via direct numerical simulations (DNS). Many earlier experimental investigations have used thin plates with sharp trailing edges and turbulent boundary layers to create the wake. This results in large theta divided by D (sub TE) values (theta is the boundary layer momentum thickness towards the end of the plate and D (sub TE) is the trailing edge thickness). In the present study the emphasis is on relatively thick plates with circular trailing edges (CTE) resulting in theta divided by D values less than one (D is the plate thickness and the diameter of the CTE), and vigorous vortex shedding. The Reynolds numbers based on the plate length and D are 1.255 x 10 (sup 6) and 10,000, respectively. Two cases are computed; one with turbulent boundary layers on both the upper and lower surfaces of the plate (statistically the same, symmetric wake, Case TT) and, a second with turbulent and laminar boundary layers on the upper and lower surfaces, respectively (asymmetric case, Case TL). The data and understanding obtained is of considerable engineering interest, particularly in turbomachinery where the pressure side of an airfoil can remain laminar or transitional because of a favorable pressure gradient and the suction side is turbulent. Shed-vortex structure and phase-averaged velocity statistics obtained in the two cases are compared here. The upper negative shed vortices in Case TL (turbulent separating boundary layer) are weaker than the lower positive ones (laminar separating boundary layer) at inception (a factor 1.27 weaker in terms of peak phase-averaged spanwise vorticity at first appearance of a peak). The upper vortices weaken rapidly as they travel downstream. A second feature of interest in Case TL is a considerable increase in the peak phase-averaged, streamwise normal intensity (random component) with increasing streamwise distance (x divided by D) that occurs nears the positive vortex cores. This behavior is observed for a few diameters in the near wake. This is counter to Case TT where the peak value essentially decreases with increasing x divided by D. Both these effects are examined in detail and the important contributors are identified.

New links between the Chicxulub impact structure and the Cretaceous/Tertiary boundary

USGS Publications Warehouse

Sharpton, V.L.; Dalrymple, G.B.; Marin, L.E.; Ryder, G.; Schuraytz, B.C.; Urrutia-Fucugauchi, J.

1992-01-01

THE 200-km-diameter Chicxulub structure1-3 in northern Yucatan, Mexico has emerged as the prime candidate for the Cretaceous/Tertiary (K/T) boundary impact crater3-6. Concentric geophysical anomalies associated with enigmatic occurrences of Upper Cretaceous breccias and andesitic rocks led Penfield and Camargo1 to suspect that this structure was a buried impact basin. More recently, the discovery of shocked quartz grains in a Chicxulub breccia3, and chemical similarities between Chicxulub rocks and K/T tektite-like glasses3-6 have been advanced as evidence that the Chicxulub structure is a K/T impact site. Here we present evidence from core samples that Chicxulub is indeed a K/T source crater, and can apparently account for all the evidence of impact distributed globally at the K/T boundary without the need for simultaneous multiple impacts or comet showers. Shocked breccia clasts found in the cores are similar to shocked lithic fragments found worldwide in the K/T boundary ejecta layer7,8. The Chicxulub melt rocks that we studied contain anomalously high levels of iridium (up to 13.5 parts per 109), also consistent with the indium-enriched K/T boundary layer9. Our best estimate of the crystallization age of these melt rocks, as determined by 40Ar/39Ar analyses, is 65.2??0.4 (1??) Myr, in good agreement with the mean plateau age of 64.98 ?? 0.05 Myr recently reported10. Furthermore, these melt rocks acquired a remanent magnetization indicating that they cooled during an episode of reversed geomagnetic polarity. The only such episode consistent with 40Ar/39Ar constraints is chron 29R, which includes the K/T boundary.

Subduction and Restratification Along an Eddy Edge: The Role of Ekman Dynamics and Submesoscale Processes

NASA Astrophysics Data System (ADS)

Lucas, A.; Sengupta, D.; D'Asaro, E. A.; Nash, J. D.; Shroyer, E.; Mahadevan, A.; Tandon, A.; MacKinnon, J. A.; Pinkel, R.

2016-02-01

The exchange of heat between the atmosphere and ocean depends sensitively on the structure and extent of the oceanic boundary layer. Heat fluxes into and out of the ocean in turn influence atmospheric processes, and, in the northern Indian Ocean, impact the dominant regional weather pattern (the southwest Monsoon). In late 2015, measurements of the physical structure of the oceanic boundary layer were collected from a pair of research vessels and an array of autonomous assets in the Bay of Bengal as part of an India-U.S. scientific collaboration. Repeated CTD casts by a specialized shipboard system to 200m with a repeat rate of <3 min and a lateral spacing of < 200m, as well as near-surface sampling acoustic current profilers, showed how on the edge of an oceanic mesoscale eddy, the interaction of the mesoscale strain field, Ekman dynamics, and nonlinear submesoscale processes acted to subduct relative saline water under a very thin layer of fresher water derived from riverine sources. Our detailed surveys of the front between the overriding thin, fresh layer, and subducting adjacent more saline water demonstrated the important of small-scale physical dynamics to frontal slumping and the resulting re-stratification processes. These processes were strongly 3-dimensional and time-dependent. Such dynamics ultimately influence air-sea interactions by creating strongly stratified and very thin oceanic boundary layers in the Bay of Bengal, and allow the development of strong, persistent subsurface temperature maxima.

On the instability of hypersonic flow past a flat plate

NASA Technical Reports Server (NTRS)

Blackaby, Nicholas; Cowley, Stephen; Hall, Philip

1990-01-01

The instability of hypersonic boundary-layer flows over flat plates is considered. The viscosity of the fluid is taken to be governed by Sutherland's law, which gives a much more accurate representation of the temperature dependence of fluid viscosity at hypersonic speeds than Chapman's approximate linear law; although at lower speeds the temperature variation of the mean state is less pronounced so that the Chapman law can be used with some confidence. Attention is focussed on the so-called (vorticity) mode of instability of the viscous hypersonic boundary layer. This is thought to be the fastest growing inviscid disturbance at hypersonic speeds; it is also believed to have an asymptotically larger growth rate than any viscous or centrifugal instability. As a starting point the instability of the hypersonic boundary layer which exists far downstream from the leading edge of the plate is investigated. In this regime the shock that is attached to the leading edge of the plate plays no role, so that the basic boundary layer is non-interactive. It is shown that the vorticity mode of instability of this flow operates on a significantly different lengthscale than that obtained if a Chapman viscosity law is assumed. In particular, it is found that the growth rate predicted by a linear viscosity law overestimates the size of the growth rate by O(M(exp 2). Next, the development of the vorticity mode as the wavenumber decreases is described, and it is shown that acoustic modes emerge when the wavenumber has decreased from it's O(1) initial value to O(M (exp -3/2). Finally, the inviscid instability of the boundary layer near the leading edge in the interaction zone is discussed and particular attention is focussed on the strong interaction region which occurs sufficiently close to the leading edge. It is found that the vorticity mode in this regime is again unstable, and that it is concentrated in the transition layer at the edge of the boundary layer where the temperature adjusts from its large, O(M(exp 2), value in the viscous boundary layer, to its O(1) free stream value. The existence of the shock indirectly, but significantly, influences the instability problem by modifying the basic flow structure in this layer.

Electrophoretic deposition of bi-layered LSM/LSM-YSZ cathodes for solid oxide fuel cell

NASA Astrophysics Data System (ADS)

Itagaki, Yoshiteru; Watanabe, Shinji; Yamaji, Tsuyoshi; Asamoto, Makiko; Yahiro, Hidenori; Sadaoka, Yoshihiko

2012-09-01

Bi-layered cathodes with the LSM/LSM-YSZ structure for solid oxide fuel cells were successfully formed on the carbon-sputtered surface of a YSZ sheet by electrophoretic deposition (EPD). The thicknesses of the first layer of LSM-YSZ (LY) and the second layer of La0.8Sr0.2MnO3 (LSM) could be controlled by adjusting the deposition time in the EPD process. The cathodic properties of the bi-layered structures were superior to those of the mono-layered structures, and were dependent on the thickness of each layer. Decreasing the thickness of the first layer and increasing that of the second layer tended to reduce both polarization and ohmic resistances. The optimal thickness of the first layer at the operating temperature of 600 °C was 4 μm, suggesting that an effective three-phase boundary was extended from the interface between the electrolyte and cathode film to around 4 μm thickness.

Edge plasma boundary layer generated by kink modes in tokamaks

NASA Astrophysics Data System (ADS)

Zakharov, Leonid E.

2011-06-01

This paper describes the structure of the electric current generated by external wall touching and free boundary kink modes at the plasma edge using the ideally conducting plasma model. Both kinds of modes generate δ-functional surface current at the plasma edge. Free boundary kink modes also perturb the core plasma current, which in the plasma edge compensates the difference between the δ-functional surface currents of free boundary and wall touching kink modes. In addition, the resolution of an apparent paradox with the pressure balance across the plasma boundary in the presence of the surface currents is provided.

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.

The atmospheric boundary layer in the CSIRO global climate model: simulations versus observations

NASA Astrophysics Data System (ADS)

Garratt, J. R.; Rotstayn, L. D.; Krummel, P. B.

2002-07-01

A 5-year simulation of the atmospheric boundary layer in the CSIRO global climate model (GCM) is compared with detailed boundary-layer observations at six locations, two over the ocean and four over land. Field observations, in the form of surface fluxes and vertical profiles of wind, temperature and humidity, are generally available for each hour over periods of one month or more in a single year. GCM simulations are for specific months corresponding to the field observations, for each of five years. At three of the four land sites (two in Australia, one in south-eastern France), modelled rainfall was close to the observed climatological values, but was significantly in deficit at the fourth (Kansas, USA). Observed rainfall during the field expeditions was close to climatology at all four sites. At the Kansas site, modelled screen temperatures (Tsc), diurnal temperature amplitude and sensible heat flux (H) were significantly higher than observed, with modelled evaporation (E) much lower. At the other three land sites, there is excellent correspondence between the diurnal amplitude and phase and absolute values of each variable (Tsc, H, E). Mean monthly vertical profiles for specific times of the day show strong similarities: over land and ocean in vertical shape and absolute values of variables, and in the mixed-layer and nocturnal-inversion depths (over land) and the height of the elevated inversion or height of the cloud layer (over the sea). Of special interest is the presence climatologically of early morning humidity inversions related to dewfall and of nocturnal low-level jets; such features are found in the GCM simulations. The observed day-to-day variability in vertical structure is captured well in the model for most sites, including, over a whole month, the temperature range at all levels in the boundary layer, and the mix of shallow and deep mixed layers. Weaknesses or unrealistic structure include the following, (a) unrealistic model mixed-layer temperature profiles over land in clear skies, related to use of a simple local first-order turbulence closure, (b) a tendency to overpredict cloud liquid water near the surface.

Application of Bayesian Inversion for Multilayer Reservoir Mapping while Drilling Measurements

NASA Astrophysics Data System (ADS)

Wang, J.; Chen, H.; Wang, X.

2017-12-01

Real-time geosteering technology plays a key role in horizontal well development, which keeps the wellbore trajectories within target zones to maximize reservoir contact. The new generation logging while drilling (LWD) resistivity tools have longer spacing and deeper investigation depth, but meanwhile bring a new challenge to inversion of logging data that is formation model not be restricted to few possible numbers of layer such as typical three layers model. If the inappropriate starting models of deterministic and gradient-based methods are adopted may mislead geophysicists in interpretation of subsurface structure. For this purpose, to take advantage of richness of the measurements and deep depth of investigation across multiple formation boundaries, a trans-dimensional Markov chain Monte Carlo(MCMC) inversion algorithm has been developed that combines phase and attenuation measurements at various frequencies and spacings. Unlike conventional gradient-based inversion approaches, MCMC algorithm does not introduce bias from prior information and require any subjective choice of regularization parameter. A synthetic three layers model example demonstrates how the algorithm can be used to image the subsurface using the LWD data. When the tool is far from top boundary, the inversion clearly resolves the boundary position; that is where the boundary histogram shows a large peak. But the measurements cannot resolve the bottom boundary; the large spread between quantiles reflects the uncertainty associated with the bed resolution. As the tool moves closer to the top boundary, the middle layer and bottom layer are resolved and retained models are more similar, the uncertainty associated with these two beds decreases. From the spread observed between models, we can evaluate actual depth of investigation, uncertainty, and sensitivity, which is more useful then just a single best model.

Impact of vertical wind shear on roll structure in idealized hurricane boundary layers

NASA Astrophysics Data System (ADS)

Wang, Shouping; Jiang, Qingfang

2017-03-01

Quasi-two-dimensional roll vortices are frequently observed in hurricane boundary layers. It is believed that this highly coherent structure, likely caused by the inflection-point instability, plays an important role in organizing turbulent transport. Large-eddy simulations are conducted to investigate the impact of wind shear characteristics, such as the shear strength and inflection-point level, on the roll structure in terms of its spectral characteristics and turbulence organization. A mean wind nudging approach is used in the simulations to maintain the specified mean wind shear without directly affecting turbulent motions. Enhancing the radial wind shear expands the roll horizontal scale and strengthens the roll's kinetic energy. Increasing the inflection-point level tends to produce a narrow and sharp peak in the power spectrum at the wavelength consistent with the roll spacing indicated by the instantaneous turbulent fields. The spectral tangential momentum flux, in particular, reaches a strong peak value at the roll wavelength. In contrast, the spectral radial momentum flux obtains its maximum at the wavelength that is usually shorter than the roll's, suggesting that the roll radial momentum transport is less efficient than the tangential because of the quasi-two-dimensionality of the roll structure. The most robust rolls are produced in a simulation with the highest inflection-point level and relatively strong radial wind shear. Based on the spectral analysis, the roll-scale contribution to the turbulent momentum flux can reach 40 % in the middle of the boundary layer.

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.

Studies on the structure of the boundary tissue of the white rat seminiferous tubules.

PubMed

Cieciura, L

1988-01-01

The studies on boundary tissue of the white rat seminiferous tubules with light and electron microscopy were carried out. The wall of the tubules consists of four layers: two cellular and two amorphous ones. In cellular external sheath the characteristic intercellular fissures a network of hexagonal meshes were seen resembling the honey-combs.

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.

Three-dimensional structure of dominant instabilities in turbulent flow over smooth and rough boundaries

NASA Astrophysics Data System (ADS)

Grass, A. J.; Stuart, R. J.; Mansour-Tehrani, M.

1991-01-01

The current status of knowledge regarding coherent vortical structures in turbulent boundary layers and their role in turbulence generation are reviewed. The investigations reported in the study concentrate attention on rough-wall flows prevailing in the geophysical environment and include an experiment determining the three-dimensional form of the turbulence structures linked to the ejection and inrush events observed over rough walls and an experiment concerned with measuring the actual spanwise scale of the near-wall structures for boundary conditions ranging from hydrodynamically smooth to fully rough. It is demonstrated that horseshoe vortical structures are present and play an important role in rough-wall flows and they increase in scale with increasing wall distance, while a dominant spanwise wavelength occurs in the instantaneous cross-flow distribution of streamwise velocity close to the rough wall.

Modeling Electrothermal Plasma with Boundary Layer Effects

NASA Astrophysics Data System (ADS)

AlMousa, Nouf Mousa A.

Electrothermal plasma sources produce high-density (1023-10 28 /m3) and high temperature (1-5 eV) plasmas that are of interest for a variety of applications such as hypervelocity launch devices, fusion reactor pellet injectors, and pulsed thrusters for small satellites. Also, the high heat flux (up to 100 GW/m2) and high pressure (100s MPa) of electrothermal (ET) plasmas allow for the use of such facilities as a source of high heat flux to simulate off-normal events in Tokamak fusion reactors. Off-normal events like disruptions, thermal and current quenches, are the perfect recipes for damage of plasma facing components (PFC). Successful operation of a fusion reactor requires comprehensive understanding of material erosion behavior. The extremely high heat fluxes deposited in PFCs melt and evaporate or directly sublime the exposed surfaces, which results in a thick vapor/melt boundary layer adjacent to the solid wall structure. The accumulating boundary layers provide a self-protecting nature by attenuating the radiant energy transport to the PFCs. The ultimate goal of this study is to develop a reliable tool to adequately simulate the effect of the boundary layers on the formation and flow of the energetic ET plasma and its impact on exposed surfaces erosion under disruption like conditions. This dissertation is a series of published journals/conferences papers. The first paper verified the existence of the vapor shield that evolved at the boundary layer under the typical operational conditions of the NC State University ET plasma facilities PIPE and SIRENS. Upon the verification of the vapor shield, the second paper proposed novel model to simulate the evolution of the boundary layer and its effectiveness in providing a self-protecting nature for the exposed plasma facing surfaces. The developed models simulate the radiant heat flux attenuation through an optically thick boundary layer. The models were validated by comparing the simulation results to experimental data taken from the ET plasma facilities. Upon validation of the boundary layer models, computational experiments were conducted with the purpose of evaluation the PFCs' erosion during plasma disruption in Tokamak fusion reactors. Erosion of a set of selected low-Z and high-Z materials were analyzed and discussed. For metallic plasma facing materials under the impact of hard and long time-scale disruption events, melting and melt-layer splashing become dominate erosion mechanisms during plasma-material interaction. In order to realistically assess the erosion of the metallic fusion reactor components, the fourth paper accounts for the various mechanisms by which material evolved from PFCs due to melting and vaporization, with a developed melting and splattering/splashing model incorporated in the ET plasma code. Also, the shielding effect associated with melt-layer and vapor-layer is investigated. The quantitative results of material erosion with the boundary layer effects including a vapor layer, melt layer and splashing effects is a new model and an important step towards achieving a better understanding of plasma-material interactions under exposure to such high heat flux conditions.

Toward a Self-Consistent Dynamical Model of the NSSL

NASA Astrophysics Data System (ADS)

Matilsky, Loren

2018-01-01

The advent of helioseismology has revealed in detail the internal differential rotation profile of the Sun. In particular, the presence of two boundary layers, the tachocline at the bottom of the convection zone (CZ) and the Near Surface Shear Layer (NSSL) at the top of the CZ, has remained a mystery. These two boundary layers may have significant consequences for the internal dynamo that operates the Sun's magnetic field, and so understanding their dynamics is an important step in solar physics and in the theory of solar-like stellar structure in general. In this talk, we analyze three numerical models of hydrodynamic convection in rotating spherical shells with varying degrees of stratification in order to understand the dynamical balance of the solar near-surface shear layer (NSSL). We find that with sufficient stratification, a boundary layer with some characteristics of the NSSL develops at high latitudes, and it is maintained purely an inertial balance of torques in which the viscosity is negligible. An inward radial flux of angular momentum from the Reynold's stress (as has been predicted by theory) is balanced by the poleward latitudinal flux of angular momentum due to the meridional circulation. We analyze the similarities of the near surface shear in our models to that of the Sun, and find that the solar NSSL is most likely maintained by the inertial balance our simulations display at high latitudes, but with a modified upper boundary condition.

Strain solitons and topological defects in bilayer graphene

PubMed Central

Alden, Jonathan S.; Tsen, Adam W.; Huang, Pinshane Y.; Hovden, Robert; Brown, Lola; Park, Jiwoong; Muller, David A.; McEuen, Paul L.

2013-01-01

Bilayer graphene has been a subject of intense study in recent years. The interlayer registry between the layers can have dramatic effects on the electronic properties: for example, in the presence of a perpendicular electric field, a band gap appears in the electronic spectrum of so-called Bernal-stacked graphene [Oostinga JB, et al. (2007) Nature Materials 7:151–157]. This band gap is intimately tied to a structural spontaneous symmetry breaking in bilayer graphene, where one of the graphene layers shifts by an atomic spacing with respect to the other. This shift can happen in multiple directions, resulting in multiple stacking domains with soliton-like structural boundaries between them. Theorists have recently proposed that novel electronic states exist at these boundaries [Vaezi A, et al. (2013) arXiv:1301.1690; Zhang F, et al. (2013) arXiv:1301.4205], but very little is known about their structural properties. Here we use electron microscopy to measure with nanoscale and atomic resolution the widths, motion, and topological structure of soliton boundaries and related topological defects in bilayer graphene. We find that each soliton consists of an atomic-scale registry shift between the two graphene layers occurring over 6–11 nm. We infer the minimal energy barrier to interlayer translation and observe soliton motion during in situ heating above 1,000 °C. The abundance of these structures across a variety of samples, as well as their unusual properties, suggests that they will have substantial effects on the electronic and mechanical properties of bilayer graphene. PMID:23798395

Mathematical modeling of sustainability of porous Al2O3 growth during two-stage anodization process

NASA Astrophysics Data System (ADS)

Aryslanova, Elizaveta M.; Alfimov, Anton V.; Chivilikhin, Sergey A.

2015-06-01

Currently, due to the development of nanotechnology and metamaterials, it has become important to obtain regular nanoporous structures with different parameters, such as porous anodic alumina films that are used for synthesis of various nanocomposites. In this work we consider the motion of the interfaces between electrolyte and alumina layers, and between alumina and aluminum layers. We also took into account the dynamics of moving boundaries and the change of small perturbations of these boundaries. Each area under Laplace's equation is solved for the potential of the electric field. The growth of porous alumina is described with the theory of small perturbations. Small perturbations of the interface are considered, which lead to small changes in potential and current in the boundaries. As a result of the developed model we obtained the minimum distance between centers of aluminum oxide pores in the beginning of anodizing process and the wavelength of porous structure irregularities.

Evolution of vortex-surface fields in transitional boundary layers

NASA Astrophysics Data System (ADS)

Yang, Yue; Zhao, Yaomin; Xiong, Shiying

2016-11-01

We apply the vortex-surface field (VSF), a Lagrangian-based structure-identification method, to the DNS database of transitional boundary layers. The VSFs are constructed from the vorticity fields within a sliding window at different times and locations using a recently developed boundary-constraint method. The isosurfaces of VSF, representing vortex surfaces consisting of vortex lines with different wall distances in the laminar stage, show different evolutionary geometries in transition. We observe that the vortex surfaces with significant deformation evolve from wall-parallel planar sheets through hairpin-like structures and packets into a turbulent spot with regeneration of small-scale hairpins. From quantitative analysis, we show that a small number of representative or influential vortex surfaces can contribute significantly to the increase of the drag coefficient in transition, which implies a reduced-order model based on VSF. This work has been supported in part by the National Natural Science Foundation of China (Grant Nos. 11472015, 11522215 and 11521091), and the Thousand Young Talents Program of China.

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

Doppler lidar characterization of the boundary layer for aircraft mass-balance estimates of greenhouse gas emissions

NASA Astrophysics Data System (ADS)

Hardesty, R.; Brewer, A.; Banta, R. M.; Senff, C. J.; Sandberg, S. P.; Alvarez, R. J.; Weickmann, A. M.; Sweeney, C.; Karion, A.; Petron, G.; Frost, G. J.; Trainer, M.

2012-12-01

Aircraft-based mass balance approaches are often used to estimate greenhouse gas emissions from distributed sources such as urban areas and oil and gas fields. A scanning Doppler lidar, which measures range-resolved wind and aerosol backscatter information, can provide important information on mixing and transport processes in the planetary boundary layer for these studies. As part of the Uintah Basin Winter Ozone Study, we deployed a high resolution Doppler lidar to characterize winds and turbulence, atmospheric mixing, and mixing layer depth in the oil and gas fields near Vernal, Utah. The lidar observations showed evolution of the horizontal wind field, vertical mixing and aerosol structure for each day during the 5-week deployment. This information was used in conjunction with airborne in situ observations of methane and carbon dioxide to compute methane fluxes and estimate basin-wide methane emissions. A similar experiment incorporating a lidar along with a radar wind profiler and instrumented aircraft was subsequently carried out in the vicinity of the Denver-Julesburg Basin in Colorado. Using examples from these two studies we discuss the use of Doppler lidar in conjunction with other sources of wind information and boundary layer structure for mass-balance type studies. Plans for a one-year deployment of a Doppler lidar as part of the Indianapolis Flux experiment to estimate urban-scale greenhouse gas emissions near are also presented.

Wintertime Boundary Layer Structure in the Grand Canyon.

NASA Astrophysics Data System (ADS)

Whiteman, C. David; Zhong, Shiyuan; Bian, Xindi

1999-08-01

Wintertime temperature profiles in the Grand Canyon exhibit a neutral to isothermal stratification during both daytime and nighttime, with only rare instances of actual temperature inversions. The canyon warms during daytime and cools during nighttime more or less uniformly through the canyon's entire depth. This weak stability and temperature structure evolution differ from other Rocky Mountain valleys, which develop strong nocturnal inversions and exhibit convective and stable boundary layers that grow upward from the valley floor. Mechanisms that may be responsible for the different behavior of the Grand Canyon are discussed, including the possibility that the canyon atmosphere is frequently mixed to near-neutral stratification when cold air drains into the top of the canyon from the nearby snow-covered Kaibab Plateau. Another feature of canyon temperature profiles is the sharp inversions that often form near the canyon rims. These are generally produced when warm air is advected over the canyon in advance of passing synoptic-scale ridges.Wintertime winds in the main canyon are not classical diurnal along-valley wind systems. Rather, they are driven along the canyon axis by the horizontal synoptic-scale pressure gradient that is superimposed along the canyon's axis by passing synoptic-scale weather disturbances. They may thus bring winds into the canyon from either end at any time of day.The implications of the observed canyon boundary layer structure for air pollution dispersion are discussed.

3D fold growth rates in transpressional tectonic settings

NASA Astrophysics Data System (ADS)

Frehner, Marcel

2015-04-01

Geological folds are inherently three-dimensional (3D) structures; hence, they also grow in 3D. In this study, fold growth in all three dimensions is quantified numerically using a finite-element algorithm for simulating deformation of Newtonian media in 3D. The presented study is an extension and generalization of the work presented in Frehner (2014), which only considered unidirectional layer-parallel compression. In contrast, the full range from strike slip settings (i.e., simple shear) to unidirectional layer-parallel compression is considered here by varying the convergence angle of the boundary conditions; hence the results are applicable to general transpressional tectonic settings. Only upright symmetrical single-layer fold structures are considered. The horizontal higher-viscous layer exhibits an initial point-like perturbation. Due to the mixed pure- and simple shear boundary conditions a mechanical buckling instability grows from this perturbation in all three dimensions, described by: Fold amplification (vertical growth): Fold amplification describes the growth from a fold shape with low limb-dip angle to a shape with higher limb-dip angle. Fold elongation (growth parallel to fold axis): Fold elongation describes the growth from a dome-shaped (3D) structure to a more cylindrical fold (2D). Sequential fold growth (growth perpendicular to fold axial plane): Sequential fold growth describes the growth of secondary (and further) folds adjacent to the initial isolated fold. The term 'lateral fold growth' is used as an umbrella term for both fold elongation and sequential fold growth. In addition, the orientation of the fold axis is tracked as a function of the convergence angle. Even though the absolute values of all three growth rates are markedly reduced with increasing simple-shear component at the boundaries, the general pattern of the quantified fold growth under the studied general-shear boundary conditions is surprisingly similar to the end-member case of unidirectional layer-parallel compression (Frehner, 2014). Fold growth rates in the two lateral directions are almost identical resulting in bulk fold structures with aspect ratios in map view close to 1. Fold elongation is continuous with increasing bulk deformation, while sequential fold growth exhibits jumps whenever a new sequential fold appears. Compared with the two lateral growth directions, fold amplification exhibits a slightly higher growth rate. The orientation of the fold axis has an angle equal to 1 2 of 90° minus the convergence angle; and this orientation is stable with increasing bulk deformation, i.e. the fold axis does not rotate with increasing general-shear deformation. For example, for simple-shear boundary conditions (convergence angle 0°) the fold axis is stable at an angle of 45° to the boundaries; for a convergence angle of 45° the fold axis is stable at an angle of 22.5° to the boundaries. REFERENCE: Frehner M., 2014: 3D fold growth rates, Terra Nova 26, 417-424, doi:10.1111/ter.12116.

Extremely high wall-shear stress events in a turbulent boundary layer

NASA Astrophysics Data System (ADS)

Pan, Chong; Kwon, Yongseok

2018-04-01

The present work studies the fluctuating characteristics of the streamwise wall-shear stress in a DNS of a turbulent boundary layer at Re τ =1500 from a structural view. The two-dimensional field of the fluctuating friction velocity u‧ τ (x,z) is decomposed into the large- and small-scale components via a recently proposed scale separation algorithm, Quasi-bivariate Variational Mode Decomposition (QB-VMD). Both components are found to be dominated by streak-like structures, which can be regarded as the wall signature of the inner-layer streaks and the outer-layer LSMs, respectively. Extreme positive/negative wall-shear stress fluctuation events are detected in the large-scale component. The former’s occurrence frequency is nearly one order of magnitude higher than the latter; therefore, they contribute a significant portion of the long tail of the wall-shear stress distribution. Both two-point correlations and conditional averages show that these extreme positive wall-shear stress events are embedded in the large-scale positive u‧ τ streaks. They seem to be formed by near-wall ‘splatting’ process, which are related to strong finger-like sweeping (Q4) events originated from the outer-layer positive LSMs.

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.

Scale growth of structures in the turbulent boundary layer with a rod-roughened wall

NASA Astrophysics Data System (ADS)

Lee, Jin; Kim, Jung Hoon; Lee, Jae Hwa

2016-01-01

Direct numerical simulation of a turbulent boundary layer over a rod-roughened wall is performed with a long streamwise domain to examine the streamwise-scale growth mechanism of streamwise velocity fluctuating structures in the presence of two-dimensional (2-D) surface roughness. An instantaneous analysis shows that there is a slightly larger population of long structures with a small helix angle (spanwise inclinations relative to streamwise) and a large spanwise width over the rough-wall compared to that over a smooth-wall. Further inspection of time-evolving instantaneous fields clearly exhibits that adjacent long structures combine to form a longer structure through a spanwise merging process over the rough-wall; moreover, spanwise merging for streamwise scale growth is expected to occur frequently over the rough-wall due to the large spanwise scales generated by the 2-D roughness. Finally, we examine the influence of a large width and a small helix angle of the structures over the rough-wall with regard to spatial two-point correlation. The results show that these factors can increase the streamwise coherence of the structures in a statistical sense.

The drive for Aircraft Energy Efficiency

NASA Technical Reports Server (NTRS)

James, R. L., Jr.; Maddalon, D. V.

1984-01-01

NASA's Aircraft Energy Efficiency (ACEE) program, which began in 1976, has mounted a development effort in four major transport aircraft technology fields: laminar flow systems, advanced aerodynamics, flight controls, and composite structures. ACEE has explored two basic methods for achieving drag-reducing boundary layer laminarization: the use of suction through the wing structure (via slots or perforations) to remove boundary layer turbulence, and the encouragement of natural laminar flow maintenance through refined design practices. Wind tunnel tests have been conducted for wide bodied aircraft equipped with high aspect ratio supercritical wings and winglets. Maneuver load control and pitch-active stability augmentation control systems reduce fuel consumption by reducing the drag associated with high aircraft stability margins. Composite structures yield lighter airframes that in turn call for smaller wing and empennage areas, reducing induced drag for a given payload. In combination, all four areas of development are expected to yield a fuel consumption reduction of 40 percent.

Mixing Heights and Three-Dimensional Ozone Structure Observed by Airborne Lidar During the 2006 Texas Air Quality Study

NASA Astrophysics Data System (ADS)

Hardesty, R. M.; Senff, C. J.; Alvarez, R. J.; Banta, R. M.; Sandberg, S. P.; Weickmann, A. M.; Darby, L. S.

2007-12-01

A new all solid state ozone lidar was deployed on a NOAA Twin Otter to study boundary layer ozone and aerosol, mostly around Houston, during the 2006 Texas Air Quality Study. The new instrument transmits high pulse-rate, low pulse-energy light at 3 wavelengths in the ultraviolet to obtain ozone profiles with 500 m horizontal resolution and 90 m vertical resolution. During the Texas field study, 20 research flights resulted in nearly 70 hours of ozone measurements during the period from August 1 to September 15. Science objectives included characterization of background ozone levels over rural areas near Houston and Dallas and variability and structure of the boundary layer over different surface types, including urban, wooded, and agricultural land surface areas as well as over Galveston Bay and the Gulf of Mexico. A histogram of all boundary layer ozone concentration measurements showed a bimodal distribution with modes at 45 ppb and 70 ppb. The lower mode correlated with southerly flow, when relatively clean air was transported onshore into the Houston area. Segmenting the observations during southerly flow by region, including the Gulf of Mexico, land within about 55 km from the coast, and further inland indicated that background levels increased by about 10 ppb as air was transported onshore. During the latter part of the experiment, as more pollution was imported into the Houston region, background levels rose to nearly 80 ppb in regions N of Houston. Two flights aimed at observing import of ozone into Texas from the east showed that ozone concentrations increased and boundary layer depths deepened upwind of Houston between September 4 and September 8. Background levels rose by more than 10 ppb over this period. In addition to ozone measurements, we also estimated boundary layer height based on maximum gradient in observed backscatter. The technique worked well when the layer topped by the strongest gradient extends down to the surface. Investigation of the correlation between ozone levels and mixing layer heights both within and external to the Houston urban plume showed a variety of relationships, depending on, e.g., wind direction and occurrence of a bay/gulf breeze. On a day-to-day basis, higher ozone levels were weakly correlated with deeper mixing levels - this was likely due to advection of the urban heat island downwind with the high-ozone urban plume.

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.

Altered vocal fold kinematics in synthetic self-oscillating models that employ adipose tissue as a lateral boundary condition.

NASA Astrophysics Data System (ADS)

Saidi, Hiba; Erath, Byron D.

2015-11-01

The vocal folds play a major role in human communication by initiating voiced sound production. During voiced speech, the vocal folds are set into sustained vibrations. Synthetic self-oscillating vocal fold models are regularly employed to gain insight into flow-structure interactions governing the phonation process. Commonly, a fixed boundary condition is applied to the lateral, anterior, and posterior sides of the synthetic vocal fold models. However, physiological observations reveal the presence of adipose tissue on the lateral surface between the thyroid cartilage and the vocal folds. The goal of this study is to investigate the influence of including this substrate layer of adipose tissue on the dynamics of phonation. For a more realistic representation of the human vocal folds, synthetic multi-layer vocal fold models have been fabricated and tested while including a soft lateral layer representative of adipose tissue. Phonation parameters have been collected and are compared to those of the standard vocal fold models. Results show that vocal fold kinematics are affected by adding the adipose tissue layer as a new boundary condition.

Ozone budgets from the Dynamics and Chemistry of Marine Stratocumulus experiment

NASA Technical Reports Server (NTRS)

Kawa, S. R.; Pearson, R., Jr.

1989-01-01

Measurements from the Dynamics and Chemistry of marine Stratocumulus experiment have been used to study components of the regional ozone budget. The surface destruction rate is determined by eddy correlation of ozone and vertical velocity measured by a low-flying aircraft. Significant variability is found in the measured surface resistance; it is partially correlated with friction velocity but appears to have other controlling influences as well. The mean resistance is 4190 s/m which is higher (slower destruction) than most previous estimates for seawater. Flux and mean measurements throughout the marine boundary layer are used to estimate the net rate of in situ photochemical production/destruction of ozone. Averaged over the flights, ozone concentration is found to be near steady state, and a net of photochemical destruction of 0.02-0.07 ng/cu m per sec is diagnosed. This is an important confirmation of photochemical model results for the remote marine boundary layer. Ozone vertical distributions above the boundary layer show a strongly layered structure with very sharp gradients. These distributions are possibly related to the stratospheric ozone source.

Boundary Layer Thermodynamics and Cloud Microphysics for a Mixed Stratocumulus and Cumulus Cloud Field Observed during ACE-ENA

NASA Astrophysics Data System (ADS)

Jensen, M. P.; Miller, M. A.; Wang, J.

2017-12-01

The first Intensive Observation Period of the DOE Aerosol and Cloud Experiments in the Eastern North Atlantic (ACE-ENA) took place from 21 June through 20 July 2017 involving the deployment of the ARM Gulfstream-159 (G-1) aircraft with a suite of in situ cloud and aerosol instrumentation in the vicinity of the ARM Climate Research Facility Eastern North Atlantic (ENA) site on Graciosa Island, Azores. Here we present preliminary analysis of the thermodynamic characteristics of the marine boundary layer and the variability of cloud properties for a mixed cloud field including both stratiform cloud layers and deeper cumulus elements. Analysis combines in situ atmospheric state observations from the G-1 with radiosonde profiles and surface meteorology from the ENA site in order to characterize the thermodynamic structure of the marine boundary layer including the coupling state and stability. Cloud/drizzle droplet size distributions measured in situ are combined with remote sensing observations from a scanning cloud radar, and vertically pointing cloud radar and lidar provide quantification of the macrophysical and microphysical properties of the mixed cloud field.

Longitudinal curvature and displacement speed effects on incompressible laminar boundary layers.

NASA Technical Reports Server (NTRS)

Werle, M. J.; Wornom, S. F.

1972-01-01

The title problem is considered for the case of flow past a circular cylinder placed normal to a uniform mainstream with Reynolds numbers from 40 to 200. Implicit finite difference numerical solutions are obtained for a set of boundary-layer equations that account for the second order effects associated with surface curvature and displacement speed. It was found that both of these contributors have a significant influence on the internal structure of the viscous region and that an accurate estimate of the surface pressure distribution is essential for estimating the surface shear stress.

Wind-tunnel measurements in the wakes of structures

NASA Technical Reports Server (NTRS)

Woo, H. G. C.; Peterka, J. A.; Cermak, J. E.

1977-01-01

Detailed measurements of longitudinal mean velocity, turbulence intensity, space correlations, and spectra made in the wake of two rectangular scaled models in simulated atmospheric boundary-layer winds are presented. The model buildings were 1:50 scale models of two trailers. Results of a flow visualization study of the wake geometry are analyzed with some singular point theorems. Two hypothetical flow patterns of the detailed wake geometry are proposed. Some preliminary studies of the vortex wake, effects of the model size, model aspect ratios, and boundary layer characteristics on the decay rate and extent of the wake are also presented and discussed.

The "Grey Zone" cold air outbreak global model intercomparison: A cross evaluation using large-eddy simulations

NASA Astrophysics Data System (ADS)

Tomassini, Lorenzo; Field, Paul R.; Honnert, Rachel; Malardel, Sylvie; McTaggart-Cowan, Ron; Saitou, Kei; Noda, Akira T.; Seifert, Axel

2017-03-01

A stratocumulus-to-cumulus transition as observed in a cold air outbreak over the North Atlantic Ocean is compared in global climate and numerical weather prediction models and a large-eddy simulation model as part of the Working Group on Numerical Experimentation "Grey Zone" project. The focus of the project is to investigate to what degree current convection and boundary layer parameterizations behave in a scale-adaptive manner in situations where the model resolution approaches the scale of convection. Global model simulations were performed at a wide range of resolutions, with convective parameterizations turned on and off. The models successfully simulate the transition between the observed boundary layer structures, from a well-mixed stratocumulus to a deeper, partly decoupled cumulus boundary layer. There are indications that surface fluxes are generally underestimated. The amount of both cloud liquid water and cloud ice, and likely precipitation, are under-predicted, suggesting deficiencies in the strength of vertical mixing in shear-dominated boundary layers. But also regulation by precipitation and mixed-phase cloud microphysical processes play an important role in the case. With convection parameterizations switched on, the profiles of atmospheric liquid water and cloud ice are essentially resolution-insensitive. This, however, does not imply that convection parameterizations are scale-aware. Even at the highest resolutions considered here, simulations with convective parameterizations do not converge toward the results of convection-off experiments. Convection and boundary layer parameterizations strongly interact, suggesting the need for a unified treatment of convective and turbulent mixing when addressing scale-adaptivity.

Impact of different parameterization schemes on simulation of mesoscale convective system over south-east India

NASA Astrophysics Data System (ADS)

Madhulatha, A.; Rajeevan, M.

2018-02-01

Main objective of the present paper is to examine the role of various parameterization schemes in simulating the evolution of mesoscale convective system (MCS) occurred over south-east India. Using the Weather Research and Forecasting (WRF) model, numerical experiments are conducted by considering various planetary boundary layer, microphysics, and cumulus parameterization schemes. Performances of different schemes are evaluated by examining boundary layer, reflectivity, and precipitation features of MCS using ground-based and satellite observations. Among various physical parameterization schemes, Mellor-Yamada-Janjic (MYJ) boundary layer scheme is able to produce deep boundary layer height by simulating warm temperatures necessary for storm initiation; Thompson (THM) microphysics scheme is capable to simulate the reflectivity by reasonable distribution of different hydrometeors during various stages of system; Betts-Miller-Janjic (BMJ) cumulus scheme is able to capture the precipitation by proper representation of convective instability associated with MCS. Present analysis suggests that MYJ, a local turbulent kinetic energy boundary layer scheme, which accounts strong vertical mixing; THM, a six-class hybrid moment microphysics scheme, which considers number concentration along with mixing ratio of rain hydrometeors; and BMJ, a closure cumulus scheme, which adjusts thermodynamic profiles based on climatological profiles might have contributed for better performance of respective model simulations. Numerical simulation carried out using the above combination of schemes is able to capture storm initiation, propagation, surface variations, thermodynamic structure, and precipitation features reasonably well. This study clearly demonstrates that the simulation of MCS characteristics is highly sensitive to the choice of parameterization schemes.

Turbulent Helicity in the Atmospheric Boundary Layer

NASA Astrophysics Data System (ADS)

Chkhetiani, Otto G.; Kurgansky, Michael V.; Vazaeva, Natalia V.

2018-05-01

We consider the assumption postulated by Deusebio and Lindborg (J Fluid Mech 755:654-671, 2014) that the helicity injected into the Ekman boundary layer undergoes a cascade, with preservation of its sign (right- or alternatively left-handedness), which is a signature of the system rotation, from large to small scales, down to the Kolmogorov microscale of turbulence. At the same time, recent direct field measurements of turbulent helicity in the steppe region of southern Russia near Tsimlyansk Reservoir show the opposite sign of helicity from that expected. A possible explanation for this phenomenon may be the joint action of different scales of atmospheric flows within the boundary layer, including the sea-breeze circulation over the test site. In this regard, we consider a superposition of the classic Ekman spiral solution and Prandtl's jet-like slope-wind profile to describe the planetary boundary-layer wind structure. The latter solution mimics a hydrostatic shallow breeze circulation over a non-uniformly heated surface. A 180°-wide sector on the hodograph plane exists, within which the relative orientation of the Ekman and Prandtl velocity profiles favours the left rotation with height of the resulting wind velocity vector in the lowermost part of the boundary layer. This explains the negative (left-handed) helicity cascade toward small-scale turbulent motions, which agrees with the direct field measurements of turbulent helicity in Tsimlyansk. A simple turbulent relaxation model is proposed that explains the measured positive values of the relatively minor contribution to turbulent helicity from the vertical components of velocity and vorticity.

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

An experimental investigation of a two and a three-dimensional low speed turbulent boundary layer

NASA Technical Reports Server (NTRS)

Winkelmann, A. E.; Melnik, W. L.

1976-01-01

Experimental studies of a two and a three-dimensional low speed turbulent boundary layer were conducted on the side wall of a boundary layer wind tunnel. The 20 ft. long test section, with a rectangular cross section measuring 17.5 in. x 46 in., produced a 3.5 in. thick turbulent boundary layer at a free stream Reynolds number. The three-dimensional turbulent boundary layer was produced by a 30 deg swept wing-like model faired into the side wall of the test section. Preliminary studies in the two-dimensional boundary layer indicated that the flow was nonuniform on the 46 in. wide test wall. The nonuniform boundary layer is characterized by transverse variations in the wall shear stress and is primarily caused by nonuniformities in the inlet damping screens.

Response of the Atmospheric Boundary Layer and Soil Layer to a High Altitude, Dense Aerosol Cover.

NASA Astrophysics Data System (ADS)

Garratt, J. R.; Pittock, A. B.; Walsh, K.

1990-01-01

The response of the atmospheric boundary layer to the appearance of a high-altitude smoke layer has been investigated in a mesoscale numerical model of the atmosphere. Emphasis is placed on the changes in mean boundary-layer structure and near-surface temperatures when smoke of absorption optical depth (AOD) in the, range 0 to 1 is introduced. Calculations have been made at 30°S, for different soil thermal properties and degrees of surface wetness, over a time period of several days during which major smoke-induced cooling occurs. The presence of smoke reduces the daytime mixed-layer depth and, for large enough values of AOD, results in a daytime surface inversion with large cooling confined to heights of less than a few hundred meters. Smoke-induced reductions in daytime soil and air temperatures of several degrees are typical, dependent critically upon soil wetness and smoke AOD. Locations near the coast experience reduced cooling whenever there is a significant onshore flow related to a sea breeze (this would also be the case with a large-scale onshore flow). The sea breeze itself disappears for large enough smoke AOD and, over sloping coastal terrain, a smoke-induced, offshore drainage flow may exist throughout the diurnal cycle.

Propagation of SH waves in an infinite/semi-infinite piezoelectric/piezomagnetic periodically layered structure.

PubMed

Pang, Yu; Liu, Yu-Shan; Liu, Jin-Xi; Feng, Wen-Jie

2016-04-01

In this paper, SH bulk/surface waves propagating in the corresponding infinite/semi-infinite piezoelectric (PE)/piezomagnetic (PM) and PM/PE periodically layered composites are investigated by two methods, the stiffness matrix method and the transfer matrix method. For a semi-infinite PE/PM or PM/PE medium, the free surface is parallel to the layer interface. Both PE and PM materials are assumed to be transversely isotropic solids. Dispersion equations are derived by the stiffness/transfer matrix methods, respectively. The effects of electric-magnetic (ME) boundary conditions at the free surface and the layer thickness ratios on dispersion curves are considered in detail. Numerical examples show that the results calculated by the two methods are the same. The dispersion curves of SH surface waves are below the bulk bands or inside the frequency gaps. The ratio of the layer thickness has an important effect not only on the bulk bands but also on the dispersion curves of SH surface waves. Electric and magnetic boundary conditions, respectively, determine the dispersion curves of SH surface waves for the PE/PM and PM/PE semi-infinite structures. The band structures of SH bulk waves are consistent for the PE/PM and PM/PE structures, however, the dispersive behaviors of SH surface waves are indeed different for the two composites. The realization of the above-mentioned characteristics of SH waves will make it possible to design PE/PM acoustic wave devices with periodical structures and achieve the better performance. Copyright © 2016 Elsevier B.V. All rights reserved.

Formation of the Dayside Magnetopause and Its Boundary Layers Under the Radial IMF

NASA Astrophysics Data System (ADS)

Pi, Gilbert; Němeček, Zdeněk.; Å afránková, Jana; Grygorov, Kostiantyn; Shue, Jih-Hong

2018-05-01

The global structure of magnetopause boundary layers under the radial interplanetary magnetic field (IMF) conditions is studied by a comparison of experimental and simulation results. In magnetohydrodynamic simulations, the hemispherical asymmetry of the reconnection locations was found. The draped field adjacent to the magnetopause points northward in the Northern Hemisphere, but it is oriented southward in the Southern Hemisphere at the beginning of the simulation for negative IMF Bx. The magnetopause region affected by the positive IMF Bz component enlarges over time, and the density profile exhibit a north-south asymmetry near the magnetopause. The experimental part of the study uses the Time History of Events and Macroscale Interactions during Substorm data. We analyze profiles of the plasma parameters and magnetic field as well as the ion pitch-angle distributions. The nonsimultaneous appearance of parallel and antiparallel aligned flows suggests two spatially separated sources of these flows. We have identified (1) the inner part of the low-latitude boundary layer (LLBL) on closed magnetic field lines; (2) the outer LLBL on open field lines; (3) the inner part of the magnetosheath boundary layer (MSBL) formed by dayside reconnection in the Southern Hemisphere; and (4) the outer MSBL resulting from lobe reconnection in the Northern Hemisphere.

Mesh Dependence on Shear Driven Boundary Layers in Stable Stratification Generated by Large Eddy-Simulation

NASA Astrophysics Data System (ADS)

Berg, Jacob; Patton, Edward G.; Sullivan, Peter S.

2017-11-01

The effect of mesh resolution and size on shear driven atmospheric boundary layers in a stable stratified environment is investigated with the NCAR pseudo-spectral LES model (J. Atmos. Sci. v68, p2395, 2011 and J. Atmos. Sci. v73, p1815, 2016). The model applies FFT in the two horizontal directions and finite differencing in the vertical direction. With vanishing heat flux at the surface and a capping inversion entraining potential temperature into the boundary layer the situation is often called the conditional neutral atmospheric boundary layer (ABL). Due to its relevance in high wind applications such as wind power meteorology, we emphasize on second order statistics important for wind turbines including spectral information. The simulations range from mesh sizes of 643 to 10243 grid points. Due to the non-stationarity of the problem, different simulations are compared at equal eddy-turnover times. Whereas grid convergence is mostly achieved in the middle portion of the ABL, statistics close to the surface of the ABL, where the presence of the ground limits the growth of the energy containing eddies, second order statistics are not converged on the studies meshes. Higher order structure functions also reveal non-Gaussian statistics highly dependent on the resolution.

Coupled wake boundary layer model of windfarms

NASA Astrophysics Data System (ADS)

Stevens, Richard; Gayme, Dennice; Meneveau, Charles

2014-11-01

We present a coupled wake boundary layer (CWBL) model that describes the distribution of the power output in a windfarm. The model couples the traditional, industry-standard wake expansion/superposition approach with a top-down model for the overall windfarm boundary layer structure. Wake models capture the effect of turbine positioning, while the top-down approach represents the interaction between the windturbine wakes and the atmospheric boundary layer. Each portion of the CWBL model requires specification of a parameter that is unknown a-priori. The wake model requires the wake expansion rate, whereas the top-down model requires the effective spanwise turbine spacing within which the model's momentum balance is relevant. The wake expansion rate is obtained by matching the mean velocity at the turbine from both approaches, while the effective spanwise turbine spacing is determined from the wake model. Coupling of the constitutive components of the CWBL model is achieved by iterating these parameters until convergence is reached. We show that the CWBL model predictions compare more favorably with large eddy simulation results than those made with either the wake or top-down model in isolation and that the model can be applied successfully to the Horns Rev and Nysted windfarms. The `Fellowships for Young Energy Scientists' (YES!) of the Foundation for Fundamental Research on Matter supported by NWO, and NSF Grant #1243482.

Modeling of composite coupling technology for oil-gas pipeline section resource-saving repair

NASA Astrophysics Data System (ADS)

Donkova, Irina; Yakubovskiy, Yuriy; Kruglov, Mikhail

2017-10-01

The article presents a variant of modeling and calculation of a main pipeline repair section with a composite coupling installation. This section is presented in a shape of a composite cylindrical shell. The aim of this work is mathematical modeling and study of main pipeline reconstruction section stress-strain state (SSS). There has been given a description of a structure deformation mathematical model. Based on physical relations of elasticity, integral characteristics of rigidity for each layer of a two-layer pipe section have been obtained. With the help of the systems of forces and moments which affect the layers differential equations for the first and second layer (pipeline and coupling) have been obtained. The study of the SSS has been conducted using the statements and hypotheses of the composite structures deformation theory with consideration of interlayer joint stresses. The relations to describe the work of the joint have been stated. Boundary conditions for each layer have been formulated. To describe the deformation of the composite coupling with consideration of the composite cylindrical shells theory a mathematical model in the form of a system of differential equations in displacements and boundary conditions has been obtained. Calculation of a two-layer cylindrical shell under the action of an axisymmetric load has been accomplished.

Turbulent Flow Over Large Roughness Elements: Effect of Frontal and Plan Solidity on Turbulence Statistics and Structure

NASA Astrophysics Data System (ADS)

Placidi, M.; Ganapathisubramani, B.

2018-04-01

Wind-tunnel experiments were carried out on fully-rough boundary layers with large roughness (δ /h ≈ 10, where h is the height of the roughness elements and δ is the boundary-layer thickness). Twelve different surface conditions were created by using LEGO™ bricks of uniform height. Six cases are tested for a fixed plan solidity (λ _P) with variations in frontal density (λ _F), while the other six cases have varying λ _P for fixed λ _F. Particle image velocimetry and floating-element drag-balance measurements were performed. The current results complement those contained in Placidi and Ganapathisubramani (J Fluid Mech 782:541-566, 2015), extending the previous analysis to the turbulence statistics and spatial structure. Results indicate that mean velocity profiles in defect form agree with Townsend's similarity hypothesis with varying λ _F, however, the agreement is worse for cases with varying λ _P. The streamwise and wall-normal turbulent stresses, as well as the Reynolds shear stresses, show a lack of similarity across most examined cases. This suggests that the critical height of the roughness for which outer-layer similarity holds depends not only on the height of the roughness, but also on the local wall morphology. A new criterion based on shelter solidity, defined as the sheltered plan area per unit wall-parallel area, which is similar to the `effective shelter area' in Raupach and Shaw (Boundary-Layer Meteorol 22:79-90, 1982), is found to capture the departure of the turbulence statistics from outer-layer similarity. Despite this lack of similarity reported in the turbulence statistics, proper orthogonal decomposition analysis, as well as two-point spatial correlations, show that some form of universal flow structure is present, as all cases exhibit virtually identical proper orthogonal decomposition mode shapes and correlation fields. Finally, reduced models based on proper orthogonal decomposition reveal that the small scales of the turbulence play a significant role in assessing outer-layer similarity.

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.

Vertical Transport by Coastal Mesoscale Convective Systems

NASA Astrophysics Data System (ADS)

Lombardo, K.; Kading, T.

2016-12-01

This work is part of an ongoing investigation of coastal mesoscale convective systems (MCSs), including changes in vertical transport of boundary layer air by storms moving from inland to offshore. The density of a storm's cold pool versus that of the offshore marine atmospheric boundary layer (MABL), in part, determines the ability of the storm to successfully cross the coast, the mechanism driving storm propagation, and the ability of the storm to lift air from the boundary layer aloft. The ability of an MCS to overturn boundary layer air can be especially important over the eastern US seaboard, where warm season coastal MCSs are relatively common and where large coastal population centers generate concentrated regions of pollution. Recent work numerically simulating idealized MCSs in a coastal environment has provided some insight into the physical mechanisms governing MCS coastal crossing success and the impact on vertical transport of boundary layer air. Storms are simulated using a cloud resolving model initialized with atmospheric conditions representative of a Mid-Atlantic environment. Simulations are run in 2-D at 250 m horizontal resolution with a vertical resolution stretched from 100 m in the boundary layer to 250 m aloft. The left half of the 800 km domain is configured to represent land, while the right half is assigned as water. Sensitivity experiments are conducted to quantify the influence of varying MABL structure on MCS coastal crossing success and air transport, with MABL values representative of those observed over the western Mid-Atlantic during warm season. Preliminary results indicate that when the density of the cold pool is much greater than the MABL, the storm successfully crosses the coastline, with lifting of surface parcels, which ascend through the troposphere. When the density of the cold pool is similar to that of the MABL, parcels within the MABL remain at low levels, though parcels above the MABL ascend through the troposphere.

Aeroelastic Analysis Of Versatile Thermal Insulation Panels For Launchers Applications

NASA Astrophysics Data System (ADS)

Carrera, E.; Zappino, E.; Augello, G.; Ferrarese, A.; Montabone, M.

2011-05-01

The aeroelastic behavior of a Versatile Thermal Insulation (VTI) has been investigated. Among the various loadings acting on the panels in this work the attention is payed to fluid structure interaction. e.g. panel flutter phenomena. Known available results from open literature, related to similar problems, permit to analyze the effect of various Mach regimes, including boundary layers thickness effects, in-plane mechanical and thermal loadings, nonlinear effect and amplitude of so called limit cycle oscillations. Dedicated finite element model is developed for the supersonic regime. The model used for coupling orthotropic layered structural model with to Piston Theory aerodynamic models allows the calculations of flutter conditions in case of curved panels supported in a dis- crete number of points. Through this approach the flutter boundaries of the VTI-panel have been investigated.

Phase portrait analysis of super solitary waves and flat top solutions

NASA Astrophysics Data System (ADS)

Steffy, S. V.; Ghosh, S. S.

2018-06-01

The phase portrait analysis of super solitary waves has revealed a new kind of intermediate solution which defines the boundary between the two types of super solitary waves, viz., Type I and Type II. A Type I super solitary wave is known to be associated with an intermediate double layer while a Type II solution has no such association. The intermediate solution at the boundary has a flat top structure and is called a flat top solitary wave. Its characteristics resemble an amalgamation of a solitary wave and a double layer. It was found that, mathematically, such kinds of structures may emerge due to the presence of an extra nonlinearity. Although they are relatively unfamiliar in the realm of plasma physics, they have much wider applications in other physical systems.

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.

Electrical structure in two thunderstorm anvil clouds

NASA Technical Reports Server (NTRS)

Marshall, Thomas C.; Rust, W. David; Winn, William P.; Gilbert, Kenneth E.

1989-01-01

Electrical structures in two thunderstorm anvil clouds (or 'anvils'), one in New Mexico, the other in Oklahoma, were investigated, using measurements of electric field by balloon-carried instruments and a one-dimensional model to calculate the time and spatial variations of electrical parameters in the clear air below the anvil. The electric field soundings through the two thunderstorm anvils showed similar charge structures; namely, negatively charged screening layers on the top and the bottom surfaces, a layer of positive charge in the interior, and one or two layers of zero charge. It is suggested that the positive charge originated in the main positive charge region normally found at high altitudes in the core of thunderclouds, and the negatively charged layers probably formed as screening layers, resulting from the discontinuity in the electrical conductivity at the cloud boundaries.

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.

Numerical Modeling Studies of Wake Vortex Transport and Evolution Within the Planetary Boundary Layer

NASA Technical Reports Server (NTRS)

Lin, Yuh-Lang; Arya, S. Pal; Kaplan, Michael L.; Shen, Shaohua

1998-01-01

In support of the wake vortex effect of the Terminal Area Productivity program, we have put forward four tasks to be accomplished in our proposal. The first task is validation of two-dimensional wake vortex-turbulence interaction. The second task is investigation of three-dimensional interaction between wake vortices and atmospheric boundary layer (ABL) turbulence. The third task is ABL studies. The, fourth task is addition of a Klemp-Durran condition at the top boundary for TASS model. The accomplishment of these tasks will increase our understanding of the dynamics of wake vortex and improve forecasting systems responsible for air safety and efficiency. The first two tasks include following three parts: (a) Determine significant length scale for vortex decay and transport, especially the length scales associated with the onset of Crow instability (Crow, 1970); (b) Study the effects of atmospheric turbulence on the decay of the wake vortices; and (c) Determine the relationships between decay rate, transport properties and atmospheric parameters based on large eddy simulation (LES) results and the observational data. These parameters may include turbulence kinetic energy, dissipation rate, wind shear and atmospheric stratification. The ABL studies cover LES modeling of turbulence structure within planetary boundary layer under transition and stable stratification conditions. Evidences have shown that the turbulence in the stable boundary layer can be highly intermittent and the length scales of eddies are very small compared to those in convective case. We proposed to develop a nesting grid mesh scheme and a modified Klemp-Durran conditions (Klemp and Wilhelmson, 1978) at the top boundary for TASS model to simulate planetary boundary layer under stable stratification conditions. During the past year, our group has made great efforts to carry out the above mentioned four tasks simultaneously. The work accomplished in the last year will be described in the next section.

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.

Electroneutral models for dynamic Poisson-Nernst-Planck systems

NASA Astrophysics Data System (ADS)

Song, Zilong; Cao, Xiulei; Huang, Huaxiong

2018-01-01

The Poisson-Nernst-Planck (PNP) system is a standard model for describing ion transport. In many applications, e.g., ions in biological tissues, the presence of thin boundary layers poses both modeling and computational challenges. In this paper, we derive simplified electroneutral (EN) models where the thin boundary layers are replaced by effective boundary conditions. There are two major advantages of EN models. First, it is much cheaper to solve them numerically. Second, EN models are easier to deal with compared to the original PNP system; therefore, it would also be easier to derive macroscopic models for cellular structures using EN models. Even though the approach used here is applicable to higher-dimensional cases, this paper mainly focuses on the one-dimensional system, including the general multi-ion case. Using systematic asymptotic analysis, we derive a variety of effective boundary conditions directly applicable to the EN system for the bulk region. This EN system can be solved directly and efficiently without computing the solution in the boundary layer. The derivation is based on matched asymptotics, and the key idea is to bring back higher-order contributions into the effective boundary conditions. For Dirichlet boundary conditions, the higher-order terms can be neglected and the classical results (continuity of electrochemical potential) are recovered. For flux boundary conditions, higher-order terms account for the accumulation of ions in boundary layer and neglecting them leads to physically incorrect solutions. To validate the EN model, numerical computations are carried out for several examples. Our results show that solving the EN model is much more efficient than the original PNP system. Implemented with the Hodgkin-Huxley model, the computational time for solving the EN model is significantly reduced without sacrificing the accuracy of the solution due to the fact that it allows for relatively large mesh and time-step sizes.

Molecular statics simulation of CdTe grain boundary structures and energetics using a bond-order potential

NASA Astrophysics Data System (ADS)

Stechmann, Guillaume; Zaefferer, Stefan; Raabe, Dierk

2018-06-01

The structure and energetics of coincidence site lattice grain boundaries (GB) in CdTe are investigated by mean of molecular statics simulations, using the Cd–Zn–Te bond-order potential (second iteration) developed by Ward et al (2012 Phys. Rev. B 86 245203; 2013 J. Mol. Modelling 19 5469–77). The effects of misorientation (Σ value) and interface plane are treated separately, complying with the critical need for full five-parameter characterization of GB. In addition, stoichiometric shifts, occurring between the inner interfaces and their adjacent atomic layers, are also predicted, revealing the energetic preference of Te-rich boundaries, opening opportunities for crystallography-based intrinsic interface doping. Our results also suggest that the intuitive assumption that Σ3 boundaries with low-indexed planes are more energetically favorable is often unfounded, except for coherent twins developing on {111} boundary planes. Therefore, Σ5, 7 or 9 boundaries, with lower interface energy than that of twin boundaries lying on different facets, are frequently encountered.

On the use of colour reflectivity plots to monitor the structure of the troposphere and stratosphere

NASA Technical Reports Server (NTRS)

Rottger, J.; Fu, I. J.; Kuo, F. S.; Liu, C. H.; Chao, J. K.

1986-01-01

The radar reflectivity, defined as the range squared corrected power of VHF radar echoes, can be used to monitor and study the temporal development of inversion layer, frontal boundaries and convective turbulence. From typical featurs of upward or downward motion of reflectivity structures, the advection/convection of cold and warm air can be predicted. High resolution color plots appear to be useful to trace and to study the life history of these structures, particularly their persistency, descent and ascent. These displays allow an immediate determination of the tropopause height as well as the determination of the tropopause structure. The life history of warm fronts, cold fronts, and occlusions can be traced, and these reflectivity plots allow detection of even very weak events which cannot be seen in the traditional meteorological data sets. The life history of convective turbulence, particular evolving from the planetary boundary layer, can be tracked quite easily. Its development into strong convection reaching the middle troposphere can be followed and predicted.

Helical circulations in the typhoon boundary layer

NASA Astrophysics Data System (ADS)

Ellis, Ryan; Businger, Steven

2010-03-01

Low-level wind data from the WSR-88D in Guam obtained in Typhoon Dale (1996) and Typhoon Keith (1997) are analyzed for coherent structures. Consistent with the results of previous studies of Atlantic hurricanes, velocity anomalies associated with coherent structures were found in the boundary layer of both storms. A total of 99 cases of coherent structures, also known as roll vortices, were documented during a 6 h evaluation period for each storm. Storm-relative roll location, roll vorticity, asymmetries in the upward and downward momentum fluxes, and signatures of circulations transverse to the mean flow associated with roll circulations were explored. The effects of terrain and convective precipitation systems, such as rainbands, on the occurrence of rolls were investigated. The results support and extend prior findings of roll observations, and can be used to help validate theoretical and numerical models of coherent structures within tropical cyclones. Moreover, the wind variations documented in this study may have application for wave runup and wind damage potential in tropical cyclones.

Velocity-vorticity correlation structures (VVCS) in spatially developing compressible turbulent boundary layer

NASA Astrophysics Data System (ADS)

Li, Shi-Yao; She, Zhen-Su; Chen, Jun

2017-11-01

A velocity-vorticity correlation structure (VVCS) analysis is applied to the direct numerical simulation (DNS) of compressible turbulent boundary layer (CTBL) at Mach numbers, Ma = 2.25 , 4.50 and 6.0 . It is shown that the VVCS analysis captures the geometry variation in the streamwise direction during the transition and in the wall-normal direction in the fully developed regime. Specifically, before transition, the VVCS captures the instability wave number, while in the transition region it displays a distinct scaling change of the dimensions. The fully developed turbulence regime is characterized by a nearly constant spatial extension of the VVCS. Particularly, after turbulence is well developed, a multi-layer structure in the wall normal direction is observed in the maximum correlation coefficient and in the length scales of the VVCS, as expected from a recent symmetry-based theory, the ensemble structure dynamics (SED). The most interesting outcome is an observed linear dependence of the length scale of the VVCS from y+ 50 to 200, which is a direct support to Townsend's attached-eddy theory. In conclusion, the VVCS analysis quantifies the geometrical characteristics of the coherent structures in turbulent compressible shear flows throughout the whole domain. Supported by NSFC (11172006, 11221062, 11452002) and by MOST (China) 973 project (2009CB724100).

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.

An Algorithm for the Vertical Structure of Aerosol Extinction in the Lowest Kilometer of the Atmosphere: Rev. 1

DTIC Science & Technology

2017-11-01

inversion layer, or the well-mixed boundary layer. In such cases a low cloud ceiling is not present. In all instances the atmospheric extinction profiles...height, radiation fog depth, or the inversion layer height. The visibility regions and several representative vertical profiles of extinction are...the coefficient B can be found by B = ln(D/A) . (2) The coefficient B is sometimes a function of the cloud ceiling height, the inversion layer height

Theoretical model for VITA-educed coherent structures in the wall region of a turbulent boundary layer

NASA Technical Reports Server (NTRS)

Landahl, Marten T.

1988-01-01

Experiments on wall-bounded shear flows (channel flows and boundary layers) have indicated that the turbulence in the region close to the wall exhibits a characteristic intermittently formed pattern of coherent structures. For a quantitative study of coherent structures it is necessary to make use of conditional sampling. One particularly successful sampling technique is the Variable Integration Time Averaging technique (VITA) first explored by Blackwelder and Kaplan (1976). In this, an event is assumed to occur when the short time variance exceeds a certain threshold multiple of the mean square signal. The analysis presented removes some assumptions in the earlier models in that the effects of pressure and viscosity are taken into account in an approximation based on the assumption that the near-wall structures are highly elongated in the streamwise direction. The appropriateness of this is suggested by the observations but is also self consistent with the results of the model which show that the streamwise dimension of the structure grows with time, so that the approximation should improve with the age of the structure.

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.

Structure and properties of parts produced by electron-beam additive manufacturing

NASA Astrophysics Data System (ADS)

Klimenov, Vasilii; Klopotov, Anatolii; Fedorov, Vasilii; Abzaev, Yurii; Batranin, Andrey; Kurgan, Kirill; Kairalapov, Daniyar

2017-12-01

The paper deals with the study of structure, microstructure, composition and microhardness of a tube processed by electron-beam additive manufacturing using optical and scanning electron microscopy. The structure and macrodefects of a tube made of Grade2 titanium alloy is studied using the X-ray computed tomography. The principles of layer-by-layer assembly and boundaries after powder sintering are set out in this paper. It is found that the titanium alloy has two phases. Future work will involve methods to improve properties of created parts.

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.

Task reports on developing techniques for scattering by 3D composite structures and to generate new solutions in diffraction theory using higher order boundary conditions

NASA Technical Reports Server (NTRS)

Volakis, John L.

1990-01-01

There are two tasks described in this report. First, an extension of a two dimensional formulation is presented for a three dimensional body of revolution. With the introduction of a Fourier expansion of the vector electric and magnetic fields, a coupled two dimensional system is generated and solved via the finite element method. An exact boundary condition is employed to terminate the mesh and the fast fourier transformation is used to evaluate the boundary integrals for low O(n) memory demand when an iterative solution algorithm is used. Second, the diffraction by a material discontinuity in a thick dielectric/ferrite layer is considered by modeling the layer as a distributed current sheet obeying generalized sheet transition conditions (GSTC's).

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.

Nonlocal Poisson-Fermi double-layer models: Effects of nonuniform ion sizes on double-layer structure

NASA Astrophysics Data System (ADS)

Xie, Dexuan; Jiang, Yi

2018-05-01

This paper reports a nonuniform ionic size nonlocal Poisson-Fermi double-layer model (nuNPF) and a uniform ionic size nonlocal Poisson-Fermi double-layer model (uNPF) for an electrolyte mixture of multiple ionic species, variable voltages on electrodes, and variable induced charges on boundary segments. The finite element solvers of nuNPF and uNPF are developed and applied to typical double-layer tests defined on a rectangular box, a hollow sphere, and a hollow rectangle with a charged post. Numerical results show that nuNPF can significantly improve the quality of the ionic concentrations and electric fields generated from uNPF, implying that the effect of nonuniform ion sizes is a key consideration in modeling the double-layer structure.

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.

The role of boundary variability in polycrystalline grain-boundary diffusion

NASA Astrophysics Data System (ADS)

Moghadam, M. M.; Rickman, J. M.; Harmer, M. P.; Chan, H. M.

2015-01-01

We investigate the impact of grain-boundary variability on mass transport in a polycrystal. More specifically, we perform both numerical and analytical studies of steady-state diffusion in prototypical microstructures in which there is either a discrete spectrum of grain-boundary activation energies or else a complex distribution of grain-boundary character, and hence a continuous spectrum of boundary activation energies. An effective diffusivity is calculated for these structures using simplified multi-state models and, for the case of a continuous spectrum, employing experimentally obtained grain-boundary energy data. We identify different diffusive regimes for these cases and quantify deviations from Arrhenius behavior using effective medium theory. Finally, we examine the diffusion kinetics of a simplified model of an interfacial layering (i.e., complexion) transition.

Vertical thermodynamic structure of the troposphere during the Norwegian young sea ICE expedition (N-ICE2015)

NASA Astrophysics Data System (ADS)

Kayser, Markus; Maturilli, Marion; Graham, Robert M.; Hudson, Stephen R.; Rinke, Annette; Cohen, Lana; Kim, Joo-Hong; Park, Sang-Jong; Moon, Woosok; Granskog, Mats A.

2017-10-01

The Norwegian young sea ICE (N-ICE2015) expedition was designed to investigate the atmosphere-snow-ice-ocean interactions in the young and thin sea ice regime north of Svalbard. Radiosondes were launched twice daily during the expedition from January to June 2015. Here we use these upper air measurements to study the multiple cyclonic events observed during N-ICE2015 with respect to changes in the vertical thermodynamic structure, moisture content, and boundary layer characteristics. We provide statistics of temperature inversion characteristics, static stability, and boundary layer extent. During winter, when radiative cooling is most effective, we find the strongest impact of synoptic cyclones. Changes to thermodynamic characteristics of the boundary layer are associated with transitions between the radiatively "clear" and "opaque" atmospheric states. In spring, radiative fluxes warm the surface leading to lifted temperature inversions and a statically unstable boundary layer. Further, we compare the N-ICE2015 static stability distributions to corresponding profiles from ERA-Interim reanalysis, from the closest land station in the Arctic North Atlantic sector, Ny-Ålesund, and to soundings from the SHEBA expedition (1997/1998). We find similar stability characteristics for N-ICE2015 and SHEBA throughout the troposphere, despite differences in location, sea ice thickness, and snow cover. For Ny-Ålesund, we observe similar characteristics above 1000 m, while the topography and ice-free fjord surrounding Ny-Ålesund generate great differences below. The long-term radiosonde record (1993-2014) from Ny-Ålesund indicates that during the N-ICE2015 spring period, temperatures were close to the climatological mean, while the lowest 3000 m were 1-3°C warmer than the climatology during winter.

Overview of Boundary Layer Clouds Using Satellite and Ground-Based Measurements

NASA Astrophysics Data System (ADS)

Xi, B.; Dong, X.; Wu, P.; Qiu, S.

2017-12-01

A comprehensive summary of boundary layer clouds properties based on our few recently studies will be presented. The analyses include the global cloud fractions and cloud macro/micro- physical properties based on satellite measurements using both CERES-MODIS and CloudSat/Caliposo data products,; the annual/seasonal/diurnal variations of stratocumulus clouds over different climate regions (mid-latitude land, mid-latitude ocean, and Arctic region) using DOE ARM ground-based measurements over Southern great plain (SGP), Azores (GRW), and North slope of Alaska (NSA) sites; the impact of environmental conditions to the formation and dissipation process of marine boundary layer clouds over Azores site; characterizing Arctice mixed-phase cloud structure and favorable environmental conditions for the formation/maintainess of mixed-phase clouds over NSA site. Though the presentation has widely spread topics, we will focus on the representation of the ground-based measurements over different climate regions; evaluation of satellite retrieved cloud properties using these ground-based measurements, and understanding the uncertainties of both satellite and ground-based retrievals and measurements.

Vortex Generators in a Two-Dimensional, External-Compression Supersonic Inlet

NASA Technical Reports Server (NTRS)

Baydar, Ezgihan; Lu, Frank K.; Slater, John W.

2016-01-01

Vortex generators within a two-dimensional, external-compression supersonic inlet for Mach 1.6 were investigated to determine their ability to increase total pressure recovery, reduce total pressure distortion, and improve the boundary layer. The vortex generators studied included vanes and ramps. The geometric factors of the vortex generators studied included height, length, spacing, and positions upstream and downstream of the inlet terminal shock. The flow through the inlet was simulated through the computational solution of the steady-state Reynolds-averaged Navier-Stokes equations on multi-block, structured grids. The vortex generators were simulated by either gridding the geometry of the vortex generators or modeling the vortices generated by the vortex generators. The inlet performance was characterized by the inlet total pressure recovery, total pressure distortion, and incompressible shape factor of the boundary-layer at the engine face. The results suggested that downstream vanes reduced the distortion and improved the boundary layer. The height of the vortex generators had the greatest effect of the geometric factors.

Global isostatic geoid anomalies for plate and boundary layer models of the lithosphere

NASA Technical Reports Server (NTRS)

Hager, B. H.

1981-01-01

Commonly used one dimensional geoid models predict that the isostatic geoid anomaly over old ocean basins for the boundary layer thermal model of the lithosphere is a factor of two greater than that for the plate model. Calculations presented, using the spherical analogues of the plate and boundary layer thermal models, show that for the actual global distribution of plate ages, one dimensional models are not accurate and a spherical, fully three dimensional treatment is necessary. The maximum difference in geoid heights predicted for the two models is only about two meters. The thermal structure of old lithosphere is unlikely to be resolvable using global geoid anomalies. Stripping the effects of plate aging and a hypothetical uniform, 35 km, isostatically-compensated continental crust from the observed geoid emphasizes that the largest-amplitude geoid anomaly is the geoid low of almost 120 m over West Antarctica, a factor of two greater than the low of 60 m over Ceylon.

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.

Experimental research on crossing shock wave boundary layer interactions

NASA Astrophysics Data System (ADS)

Settles, G. S.; Garrison, T. J.

1994-10-01

An experimental research effort of the Penn State Gas Dynamics Laboratory on the subject of crossing shock wave boundary layer interactions is reported. This three year study was supported by AFOSR Grant 89-0315. A variety of experimental techniques were employed to study the above phenomena including planar laser scattering flowfield visualization, kerosene lampblack surface flow visualization, laser-interferometer skin friction surveys, wall static pressure measurements, and flowfield five-hole probe surveys. For a model configuration producing two intersecting shock waves, measurements were made for a range of oblique shock strengths at freestream Mach numbers of 3.0 and 3.85. Additionally, measurements were made at Mach 3.85 for a configuration producing three intersecting waves. The combined experimental dataset was used to formulate the first detailed flowfield models of the crossing-shock and triple-shock wave/boundary layer interactions. The structure of these interactions was found to be similar over a broad range of interaction strengths and is dominated by a large, separated, viscous flow region.

Single-Column Model Simulations of Subtropical Marine Boundary-Layer Cloud Transitions Under Weakening Inversions

NASA Astrophysics Data System (ADS)

Neggers, R. A. J.; Ackerman, A. S.; Angevine, W. M.; Bazile, E.; Beau, I.; Blossey, P. N.; Boutle, I. A.; de Bruijn, C.; Cheng, A.; van der Dussen, J.; Fletcher, J.; Dal Gesso, S.; Jam, A.; Kawai, H.; Cheedela, S. K.; Larson, V. E.; Lefebvre, M.-P.; Lock, A. P.; Meyer, N. R.; de Roode, S. R.; de Rooy, W.; Sandu, I.; Xiao, H.; Xu, K.-M.

2017-10-01

Results are presented of the GASS/EUCLIPSE single-column model intercomparison study on the subtropical marine low-level cloud transition. A central goal is to establish the performance of state-of-the-art boundary-layer schemes for weather and climate models for this cloud regime, using large-eddy simulations of the same scenes as a reference. A novelty is that the comparison covers four different cases instead of one, in order to broaden the covered parameter space. Three cases are situated in the North-Eastern Pacific, while one reflects conditions in the North-Eastern Atlantic. A set of variables is considered that reflects key aspects of the transition process, making use of simple metrics to establish the model performance. Using this method, some longstanding problems in low-level cloud representation are identified. Considerable spread exists among models concerning the cloud amount, its vertical structure, and the associated impact on radiative transfer. The sign and amplitude of these biases differ somewhat per case, depending on how far the transition has progressed. After cloud breakup the ensemble median exhibits the well-known "too few too bright" problem. The boundary-layer deepening rate and its state of decoupling are both underestimated, while the representation of the thin capping cloud layer appears complicated by a lack of vertical resolution. Encouragingly, some models are successful in representing the full set of variables, in particular, the vertical structure and diurnal cycle of the cloud layer in transition. An intriguing result is that the median of the model ensemble performs best, inspiring a new approach in subgrid parameterization.

Transport of chemical tracers from the boundary layer to stratosphere associated with the dynamics of the Asian summer monsoon

NASA Astrophysics Data System (ADS)

Pan, Laura L.; Honomichl, Shawn B.; Kinnison, Douglas E.; Abalos, Marta; Randel, William J.; Bergman, John W.; Bian, Jianchun

2016-12-01

Chemical transport associated with the dynamics of the Asian summer monsoon (ASM) system is investigated using model output from the National Center for Atmospheric Research (NCAR) Whole Atmosphere Community Climate Model run in specified dynamics mode. The 3-D day-to-day behavior of modeled carbon monoxide is analyzed together with dynamical fields and transport boundaries to identify preferred locations of uplifting from the boundary layer, the role of subseasonal-scale dynamics in the upper troposphere and lower stratosphere (UTLS), and the relationship of ASM transport and the stratospheric residual circulation. The model simulation of CO shows the intraseasonal east-west oscillation of the anticyclone may play an essential role in transporting convectively pumped boundary layer pollutants in the UTLS. A statistical analysis of 11 year CO also shows that the southern flank of the Tibetan plateau is a preferred location for boundary layer tracers to be lofted to the tropopause region. The vertical structure of a model tracer (E90) further shows that the rapid ASM vertical transport is only effective up to the tropopause level (around 400 K). The efficiency of continued vertical transport into the deep stratosphere is limited by the slow ascent associated with the zonal-mean residual circulation in the lower stratosphere during northern summer. Quasi-isentropic transport near the 400 K potential temperature level is likely the most effective process for ASM anticyclone air to enter the stratosphere.

Numerical study of the effects of Planetary Boundary Layer structure on the pollutant dispersion within built-up areas.

PubMed

Miao, Yucong; Liu, Shuhua; Zheng, Yijia; Wang, Shu; Liu, Zhenxin; Zhang, Bihui

2015-06-01

The effects of different Planetary Boundary Layer (PBL) structures on pollutant dispersion processes within two idealized street canyon configurations and a realistic urban area were numerically examined by a Computational Fluid Dynamics (CFD) model. The boundary conditions of different PBL structures/conditions were provided by simulations of the Weather Researching and Forecasting model. The simulated results of the idealized 2D and 3D street canyon experiments showed that the increment of PBL instability favored the downward transport of momentum from the upper flow above the roof to the pedestrian level within the street canyon. As a result, the flow and turbulent fields within the street canyon under the more unstable PBL condition are stronger. Therefore, more pollutants within the street canyon would be removed by the stronger advection and turbulent diffusion processes under the unstable PBL condition. On the contrary, more pollutants would be concentrated in the street canyon under the stable PBL condition. In addition, the simulations of the realistic building cluster experiments showed that the density of buildings was a crucial factor determining the dynamic effects of the PBL structure on the flow patterns. The momentum field within a denser building configuration was mostly transported from the upper flow, and was more sensitive to the PBL structures than that of the sparser building configuration. Finally, it was recommended to use the Mellor-Yamada-Nakanishi-Niino (MYNN) PBL scheme, which can explicitly output the needed turbulent variables, to provide the boundary conditions to the CFD simulation. Copyright © 2015. Published by Elsevier B.V.

A Coupled Model of Langmuir Circulations and Ramp-like Structures in the Upper Ocean Turbulent Boundary Layer

NASA Astrophysics Data System (ADS)

Soloviev, A.; Dean, C.; Lukas, R.; Donelan, M. A.; Terray, E. A.

2016-12-01

Surface-wave breaking is a powerful mechanism producing significant energy flux to small scale turbulence. Most of the turbulent energy produced by breaking waves dissipates within one significant wave height, while the turbulent diffusion layer extends to approximately ten significant wave heights. Notably, the near-surface shear may practically vanish within the wave-stirred layer due to small-scale turbulent mixing. The surface ocean temperature-salinity structure, circulation, and mass exchanges (including greenhouse gases and pollutants) substantially depend on turbulent mixing and non-local transport in the near-surface layer of the ocean. Spatially coherent organized motions have been recognized as an important part of non-local transport. Langmuir circulation (LC) and ramp-like structures are believed to vertically transfer an appreciable portion of the momentum, heat, gases, pollutants (e.g., oil), and other substances in the upper layer of the ocean. Free surface significantly complicates the analysis of turbulent exchanges at the air-sea interface and the coherent structures are not yet completely understood. In particular, there is growing observational evidence that in the case of developing seas when the wind direction may not coincide with the direction of the energy containing waves, the Langmuir lines are oriented in the wind rather than the wave direction. In addition, the vortex force due to Stokes drift in traditional models is altered in the breaking-wave-stirred layer. Another complication is that the ramp-like structures in the upper ocean turbulent boundary layer have axes perpendicular to the axes of LC. The ramp-like structures are not considered in the traditional model. We have developed a new model, which treats the LC and ramp-like structures in the near-surface layer of the ocean as a coupled system. Using computational fluid dynamics tools (LES), we have been able to reproduce both LC and ramp-like structures coexisting in space though intermittent in time. In the model, helicity isosurfaces appear to be tilted and, in general, coordinated with the tilted velocity isosurfaces produced by ramp-like structures. This is an indication of coupling between the LC and ramp-like structures. Remarkably, the new model is able to explain observations of LC under developing seas.

Structure and formation of convection of secondary rainbands in a simulated typhoon Jangmi (2008)

NASA Astrophysics Data System (ADS)

Xiao, Jing; Tan, Zhe-Min; Chow, Kim-Chiu

2018-04-01

Secondary rainbands in tropical cyclone are relatively transient compared with the quasi-stationary principle rainbands. To have a better understanding on their convective structure, a cloud-resolving scale numerical simulation of the super typhoon Jangmi (2008) was performed. The results suggest that the convections in secondary rainbands have some distinctive features that may not be seen in other types of rainbands in tropical cyclone. First, they have a front-like structure and are triggered to form above the boundary layer by the convergence of the above-boundary outflow from the inner side (warmer) and the descending inflow (colder) from the outer side. These elevated convections can be further confirmed by the three-dimensional backward trajectory calculations. Second, due to the release in baroclinic energy, the lower portion of the mid-level inflow from outside may penetrate into the bottom of the convection tower and may help accelerate the boundary layer inflow in the inner side. Third, the local maximum tangential wind is concentrated in the updraft region, with a lower portion which is dipping inward. Tangential wind budget analysis also suggests that the maxima are mainly contributed by the updraft advection, and can be advected cyclonically downstream by the tangential advection.

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...

Investigation of Vortical Flow Patterns in the Near Field of a Dynamic Low-Aspect-Ratio Cylinder

NASA Astrophysics Data System (ADS)

Gildersleeve, Samantha; Amitay, Michael

2016-11-01

The flowfield and associated flow structures of a low-aspect-ratio cylindrical pin were investigated experimentally in the near-field as the pin underwent wall-normal periodic oscillations. Under dynamic conditions, the pin is driven at the natural wake shedding frequency with an amplitude of 33% of its mean height. Additionally, a static pin was also tested at various mean heights of 0.5, 1.0, and 1.5 times the local boundary layer thickness to explore the effect of the mean height on the flowfield. Three-dimensional flowfields were reconstructed and analyzed from SPIV measurements where data were collected along streamwise planes for several spanwise locations under static and dynamic conditions. The study focuses on the incoming boundary layer as it interacts with the pin, as well as two main vortical formations: the arch-type vortex and the horseshoe vortex. Under dynamic conditions, the upstream boundary layer is thinner, relative to the baseline, and the downwash in the wake increases, resulting in a reduced wake deficit. These results indicate enhanced strength of the aforementioned vortical flow patterns under dynamic conditions. The flow structures in the near-field of the static/dynamic cylinder will be discussed in further detail. Supported by The Boeing Company.

Robust boundary treatment for open-channel flows in divergence-free incompressible SPH

NASA Astrophysics Data System (ADS)

Pahar, Gourabananda; Dhar, Anirban

2017-03-01

A robust Incompressible Smoothed Particle Hydrodynamics (ISPH) framework is developed to simulate specified inflow and outflow boundary conditions for open-channel flow. Being purely divergence-free, the framework offers smoothed and structured pressure distribution. An implicit treatment of Pressure Poison Equation and Dirichlet boundary condition is applied on free-surface to minimize error in velocity-divergence. Beyond inflow and outflow threshold, multiple layers of dummy particles are created according to specified boundary condition. Inflow boundary acts as a soluble wave-maker. Fluid particles beyond outflow threshold are removed and replaced with dummy particles with specified boundary velocity. The framework is validated against different cases of open channel flow with different boundary conditions. The model can efficiently capture flow evolution and vortex generation for random geometry and variable boundary conditions.

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