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An experiment conducted in a small wind tunnel with a working space of 0. 305- by 0.230-meters in which a 1.52 meter-long plate was inserted revealed the automatic control of boundary layer shift. The location of shift was determined by pressure variations in the transition region. This in turn explained a signal, which was employed in the automatic control loop for stabilizing the location of shift about the given values.

Analysis of converging boundary layers near a plane of symmetry and their divergent solutions using three methods reveals that singularities with excessive boundary-layer thickness and vanishing skin friction occur for strong convergence of the overflow toward the plane of symmetry. The solutions are sensitive to choice of parameters. Boundary-layer assumptions are responsible for these singularities and complicate the solutions of three-dimensional boundary layers. Calculations using full Navier-Stokes equations exhibit no singularity.

Monin-Obukhov similarity applied to the real part of the refractive index variance n prime squared bar is discussed. It is shown that, because the observed correlation coefficient r(sub TQ) between temperature and humidity is less than unity, scaling by n(sub *) = n prime w prime bar/u(sub *) (where u(sub *) is the friction velocity) makes the dimensionless variance n prime squared/n(sub *) squared dependent on two dimensionless parameters, on dimensionless height z/L (where L is the Monin-Obukhov length), and on a parameter R, which is related to the Bowen ratio. As the Monin-Obukhov similarity framework is applied, a large scatter of the dimensionless refractive index variance is expected for certain values of the Bowen ratio. Such a scatter can be eliminated if a new scale N(sub *), defined as a combination of temperature and humidity scales, is employed.

An algebraic eddy viscosity model based on a new scale dependent on boundary layer flow is analyzed. Results show that the integral characteristics of the turbulent boundary layer including the location of transition, skin friction coefficient and velocity distribution across the boundary layer are in good agreement with available data. A logarithmic velocity law can likewise be modelled with equal success.

The effects of high-frequency traveling wave fluctuations on the disturbance amplitude of laminar boundary layers are studied. Unsteady incompressible laminar boundary-layer equations for conservation of mass are used to describe the boundary-layer dynamics under external freestream oscillation. Results show that traveling waves have considerable effects on the transition mode of boundary-layers.

A study was conducted to examine unsteady laminar free convection flow over a horizontal cylinder and a sphere embedded in a linearly stratified medium. The study assumes that a movement nearer the upper stagnation point conditions thicker boundary layers and invalidates curvature, streamwise effects and motion pressure in boundary layer analysis. Results show that increases in ambient thermal stratification increase average heat transfer.

Hypersonic experimental data for a series of three-dimensional shock wave/turbulent boundary-layer interaction is evaluated for possible applicationin the validation of turbulence models. The experiments were carried out in a hypersonic wind tunnel wherein a sharp plate having specific dimension is subjected to simulated turbulence under a speed of Mach 8.2. The evaluation reveals that that the experimental data are very useful in the analysis and documentation of three-dimensional flowfield.

Previous experimental data on the second-mode disturbances of laminar boundary layers at Mach numbers between four and ten are evaluated. Results obtained from recent hot-wire anemometry experiments involving a laminar boundary layer generated by a seven-degree half-angle cone at a local Mach number of 5.2 are used in the study. The flat plate model used in the experiments are found to be incapable of modeling the second-mode instabilitiesof the boundary layers.

The singular behavior of a dusty gas in steady boundary-layer flow is studied using an implicit finite element method. The method uses a boundary layer form of the governing equations to express the problem's important parameters, such as the particle phase tangential velocity and fluid phase kinematic viscosity. These equations are then simplified and solved using fluid phase reduction and numerical computations, respectively. However, experimental data are still needed to fully validate the reliability of the method.

Experiments were carried out in applying the concept of passive device called BLADEs (boundary-layer alteration devices) to fully developed pipe flow to assess its feasibility as a drag reduction device. The results of both the volumetric flow rate measurement and the pipe wall pressure distribution taken far downstream show that there is a net increase in drag with the device. With BLADES in tandem arrangement, there is a further net increase in drag which is contrary to its counterpart in boundary layer flow. Although the wall shear stress measurement following the device indicates some reduction in local drag, its magnitude of reduction is much smaller than that seen in the equivalent boundary flow. All these results suggest little possibility of any useful application of BLADEs to pipe flow.

A study was conducted to evaluate the implementation of Vigneron's streamwise pressure gradient approximation in parabolized Navier-Stokes equations occurring in a supersonic flat-plate flowfield. Results show that significant errors in the skin-friction coefficient and the maximum temperature exist in the numerical solutions of supersonic flow. A finite volume procedure is implemented to overcome the errors by rewriting the parabolized Navier-Stokes equations with the full streamwise flux and an additional term is included. This additional term is the product of omega and a derivative.

The study analyzes a new turbulence model geared for backflow regions. The model is based on the facts that backflow regions are characterized by negligible turbulence production and the region of turbulence energy balance. An ordinary differential equation for the eddy viscosity is derived analytically from the original turbulence kinetic energy equation. The eddy-viscosity formula is used inside backflow regions. This model still has to be tested further.

Boundary-layer transition-detection studies using an infrared (IR) imaging system were carried out in the 0.3-meter Transonic Cryogenic Tunnel. The purpose is to determine the minimum flow temperature where IR imaging systems operating in the 8-12 microwave band can still detect transition on models in high Reynolds numbers identical to those encountered in flight. The results show that 170 Kelvin is the lowest temperature limit where transition detection is possible with such IR systems. Testing at high Reynolds number may require IR imaging systems operating at longer wavelengths.

The characteristics of turbulent boundary-layers formed over a flat-plate/wedge at high Mach number regimes are studied through experimental procedures. Tests are conducted in a Mach 6 wind tunnel wherein a smooth flat-plate/wedge structure is subjected to simulated turbulent flows. Temperature and pressure measurements are then obtained using several pressure probes and thermocouples. Results reveal the presence of multiple peaks in the mass-flux turbulence intensity profiles.

Molecular dynamics simulations of atomically thin, fluid films confined between two solid plates are described. For a broad range of parameters, a generic stick-slip motion is observed, consistent with the [...]

Heat transfer characteristics around a low aspect ratio cylindrical protuberance placed in a turbulent boundary layer were investigated. The results revealed that the overall heat transfer for the cylindrical protuberance reaches a maximum value when H /delta=0.24.

Ludwig Prandtl, a professor at the Technische Hoschschule in Hanover has presented a new boundary-layer concept, which helps in understanding and analyzing the fluid dynamics phenomenon more effectively and accurately. His suggested notion that the effects of friction are experienced only near an object moving through a fluid has revolutionized fluid dynamics and has made him a monumental figure in the modern aerodynamics.

The amount of seasoning retained by a fried tortilla chip when exposed to air at different flow rates and angles of inclination was measured in a wind tunnel experiment. The inferred adhesion force of seasoning particle and chip surface using boundary layer theory increased with seasoning particle size, oil content of tortilla chip, viscosity, and surface tension of oil.

Sintering temperature and time affect density, microstructure, electrical properties and porosity of the internal boundary layer capacitors (IBLCs) and it is assumed that the porosity affects the thickness of the grain boundary region and grain size of the IBLCs of Y(sub 2)O(sub 3)-doped SrTiO(Sub 3). The results indicate that electrical properties decrease with an increase in porosity and there exists a correlation between effective dielectric constant and conductivity.

Numerical results are reported for very strong fully separated three-dimensional crossing shock-wave/turbulent-boundary-layer interactions at Mach 5. The flowfield is generated by two sharp fins mounted at angle of attack on a flat plate in a manner closely resembling a portion of a scramjet inlet. Two symmetric configurations with fin angles of attack of 18 and 23 deg are considered. The flowfield is determined through solution of the full three-dimensional mean compressible Navier-Stokes equations using a sophisticated [kappa]-[epsilon] closure model. The computations are validated by comparison with available experimental data. The close similarity between the simulated and experimental surface oil flow patterns--particularly in the strong 23 x 23 case in which new topological patterns appear--indicate that the computations are successful in obtaining the mean flowfield. These additional features include not only new critical points but also phenomena associated with secondary separation. Ramifications of the new surface features on the off-surface flow are examined in great detail by probing the computed flowfield. Previous models of the flowfield evolution with interaction strength are updated to include these new features.

A modified [kappa]--[epsilon] model is proposed for calculation of transitional boundary-layer flows. To develop the eddy viscosity model for the problem, the flow is divided into three regions: the pretransition region, transition region, and fully turbulent region. In the pretransition region, because the turbulence does not yet attain its equilibrium state in which the eddy viscosity is proportional to the distance from the wall, it is postulated that a viscous sublayer structure prevails across the boundary layer so that the eddy viscosity is proportional to the cube of the wall distance. Further it is assumed that as the turbulent spots which have appeared at the onset of transition grow with the downstream distance in the transition region, dependence of the eddy viscosity on the wall distance changes gradually from that in the pretransition region to that in the fully turbulent state. A universal downstream variation of intermittency factor in the transition region is employed to represent such a transition eddy viscosity in the transition region. In addition, the model constant [C.sub.[epsilon]1] in the standard [kappa]--[epsilon] model is modified to take into account the particular characteristics of turbulence in the transition region. In the present test calculations, because the governing equations are integrated from a point close to the leading edge in the pretransition region, the initial and boundary conditions of [kappa] and [epsilon] at the onset of transition are automatically supplied. The proposed model is applied to calculate three benchmark cases of the transitional boundary-layer flows with different freestream turbulent intensity (1-6%) under zero-pressure gradient. It was found that the profiles of mean velocity and turbulent intensity, local maximum of velocity fluctuations, their locations as well as the streamwise variation of integral properties such as skin friction, shape factor, and maximum velocity fluctuations are very satisfactorily predicted throughout the flow regions.

The development of time-domain impedance boundary condition (TDIBC) for prediction of aeroacoustics in wall bounded flows is explored. The presence of a flow and its boundary layer over a wave-absorbing surface complicates the modeling and implementation of TDIBC. Considered here are three different approaches to account for the effects of wave refraction, absorption, reflection, and convection at a wave-absorbing wall. They are the effective plane-wave impedance in a slip flow, convection-modified impedance in a slip flow, and wave reflection in a mean shear-layer flow. Their validity, effectiveness, stability, and implementation in time-domain finite-difference schemes will be discussed. The schemes and methods developed here are benchmarked and compared with experiment and other methods.

The interactions between shock waves and turbulent boundary layers in a Mach 2.5 wind tunnel have been visualized by a megahertz-rate imaging system. The shock waves were produced by two-dimensional compression corners having angles of 14 and 24 deg, and the flows were, respectively, attached and separated. At the compression comer, the sequential images clearly indicate the correlation between the shock motion and the incoming turbulent boundary layer. Some large eddies in the boundary layer cause the shock to move in the streamwise direction for distances as large as the boundary-layer thickness at a frequency as high as large-eddy frequency ([U.sub.e]/[Delta]), but other eddies seem to have minor effect on the shock wave. The images also indicate how the shock waves influence the boundary-layer structures.

An experimental study was undertaken to investigate the characteristics of turbulent boundary layers developing on smooth flat plate in an open channel flow at moderately high Froude numbers (0.25 [is less than] Fr [is less than] 1.1) and low momentum thickness Reynolds numbers (800 [is less than] [Re.sub.[Theta]] [is less than] 2900). The low range of Reynolds numbers and the high Froude number range make the study important, as most other studies of this type have been conducted at high Reynolds numbers and lower Froude numbers (~0.1). Velocity measurements were carried out using a laser-Doppler anemometer equipped with a beam expansion device to enable measurements close to the wall region. The shear velocities were computed using the near-wall measurements in the viscous subregion. The variables of interest include the longitudinal mean velocity, the turbulence intensity, and the velocity skewness and flatness distributions across the boundary layer. The applicability of a constant Coles' wake parameter ([Pi]=0.55) to open channel flows has been discounted. The effect of the Froude number on the above parameters was also examined. [DOI: 10.1115/1.1366321]

This paper discusses the boundary stabilization of a beam in free transverse vibration. The dynamics of the beam is presented by a nonlinear partial differential equation (PDE). Based on this model a nonlinear control law is constructed to stabilize the system. The control law is a nonlinear function of the slopes and velocity at the boundary of the beam. The novelty of this article is that it has been possible to exponentially stabilize a free transversely vibrating beam via boundary control without restoring to truncation of the model. This result is achieved while the coupling between longitudinal and transversal displacements has been taken into account. [DOI: 10.1115/1.1369111]

In the middle of the convective boundary layer, also known as the mixed layer, is a relatively thick region where wind speed and potential temperature are nearly uniform with height. Below this uniform layer (UL), wind speed decreases to zero at the ground, and potential temperature increases to the surface skin value. This whole region below the UL is called the radix layer (RxL), and is of order hundreds of meters thick. Within the bottom of the RxL lies the classical surface layer (order of tens of meters thick) that obeys traditional Monin-Obukhov similarity theory. The RxL depth is shown to depend on friction velocity, Deardorff velocity, and boundary layer depth. The wind RxL is usually thicker than the temperature RxL. Using RxL depth, UL wind speed, and UL potential temperature as length, velocity, and temperature scales, respectively, one can form dimensionless heights, velocities, and temperatures. When observations obtained within the RxL are plotted in this dimensionless framework, the data collapse into similarity curves. This data collapse is tightly packed for data collected over single-location homogeneous surfaces, and shows more scatter for data collected along 72-km flight tracks over heterogeneous surfaces. Empirical profile equations are proposed to describe this RxL similarity. When these profile equations are combined with the flux equations from convective transport theory, the results are new flux-profile equations for a deep region within the bottom of the convective boundary layer. These RxL profile similarity equations are calibrated using data from four sites with different roughnesses: Minnesota, BLX96-Lamont, BLX96-Meeker, and BLX96-Winfield. The empirical parameters are found to be invariant from site to site, except for the profile shape parameter for wind speed. This parameter is found to depend on standard deviation of terrain elevation, rather than on the aerodynamic roughness length. The resulting parameter values are compared with independent data from a forested fifth site, Koorin, and it is found that displacement height must be subtracted from all the heights in the RxL profile equations. The resulting profile equations could be useful for calculating wind loading on bridges, wind turbine power estimation, air pollutant transport, or other applications where wind speeds or temperatures are needed over the bottom hundreds of meters of the convective boundary layer.

The formation and evolution of nocturnal boundary layer clouds over land are studied using a simple well-mixed boundary layer theory. By analyzing the deepening rate of the mixed layer depth based on the turbulent kinetic energy budget of the whole boundary layer, the authors studied how the formation of idealized nocturnal boundary layer clouds is related to the physical processes associated with the land surface and the boundary layer. Preliminary analysis indicates that for a range of surface moisture and heat fluxes, wind shear can be an important factor in triggering the formation of nocturnal stratus. The relative importance of different physical processes responsible for cloud formation can be evaluated by the ratio between the lifting condensation level and a critical level, which is proportional to the Monin-Obukhov length scale. In this study, data collected from the Atmospheric Radiation Measurement site in the southern Great Plains are used to examine the results of the theoretical analysis. The analyses of the two nocturnal stratus cloud cases observed on 25 October 1996 and 6 November 1997 indicate that the turbulent mixing induced by the wind shear plays a pivotal role in the cloud formation during these two cases.

Results are presented from a large eddy simulation (LES) and wind tunnel study of the turbulence regime in a horizontally evolving sheared atmospheric convective boundary layer (CBL) capped by a temperature inversion. The wind tunnel part of the study has been conducted in the thermally stratified tunnel of the University of Karlsruhe. For the numerical part a modified LES procedure that was originally designed for simulation of the horizontally homogeneous atmospheric CBL has been employed. The study focuses on the transition between the neutrally buoyant boundary layer in the initial portion of the wind tunnel flow and a quasi-homogeneous convectively mixed layer developing downwind. The character of the transition between the two boundary layers and the associated changes in the turbulence structure are found to be strongly dependent on the magnitude and distribution of disturbances in the flow at the entrance of the wind tunnel test section. For all simulated inflow conditions, the transition is preceded by accumulation of potential energy in the premixed CBL. The eventual energy release in the transition zone leads to turbulence enhancement that has a form of turbulence outbreak for particular flow configurations. The numerically simulated CBL case with temperature fluctuations introduced in the lower portion of the incoming flow appears to be the closest to the basic CBL flow case studied in the wind tunnel. Second-order turbulence statistics derived from the LES are shown to be in good agreement with the wind tunnel measurements. Main features of transition, including the turbulence enhancement within the transition zone, are successfully reproduced by the LES.

A complete hydrodynamic understanding of aquatic locomotion requires knowledge of the thin boundary layer surrounding swimming organisms. In particular, tangential forces acting on the body surface are dependent on the distribution of velocity throughout the boundary layer. Fluid velocities tangent and normal to the bodies of swimming fish and squid were determined throughout the boundary layer (1-10mm thick) by digital particle image velocimetry (DPIV) and digital particle tracking velocimetry (DPTV). Scup (Stenotomus chrysops), smooth dogfish (Mustelus canis), mottled sculpin (Cottus bairdi) and long-finned squid (Loligo pealei) were observed. The friction drag on swimming fish was determined to be greater than the rigid body friction drag. No separation of flow was observed and the shape of boundary layer velocity profiles suggested that the fish were sensing and responding to the surrounding fluid to prevent separation. Both laminar and turbulent flow were observed in the boundary layer under various conditions, and flow sometimes oscillated between the two states with body phase. The behavior of the boundary layers of the carangiform swimming scup and the anguilliform swimming smooth dogfish showed marked differences. Boundary layer flow in mottled sculpin, which spend most of their time stationary on the substrate, was shown to be greatly impacted by the orientation of the pectoral fins. The findings support the existence of different sensory functions in the lateral line system anterior and posterior to the pectoral fins as suggested by structural differences. In L. pealei, the boundary layer yielded estimates of friction drag, and the effect of boundary layer suction at the mantle intake was observed.

A simple and physically consistent expression for the turbulent heat flux equation in the convective atmospheric boundary layer (CABL) has been suggested by Holtslag and Moeng in 1991. In their equation, valid under quasi-steady states and horizontal homogeneity, the countergradient term resulted from the third-moment transport effect rather than from the buoyancy production term. In this paper, experimental observation data from the World Laboratory Applied Research Project on Drought and Desertification (WL-ARPDD94 Experiment), carried out in a flat region of the greater Beijing area, China, have been utilized with the purpose of checking the validity of the Holtslag and Moeng equation. The result of this experimental check proved to be more than satisfactory through most of the CABL.

The mean flowfield of a three-dimensional supersonic turbulent boundary layer, generated by a 20-deg isentropic compression, was studied experimentally and numerically. Experimental data include surface flow visualization, wall static pressures, surface skin friction, and surveys of pitot pressures, yaw angles, and static pressures. Earlier published comparisons with data computed from the three-dimensional Reynolds-averaged compressible Navier-Stokes equations with an algebraic turbulence eddy viscosity closure show good agreement within experimental and computational uncertainties. Focus of the current work is the presentation of different scalings of the experimental data and the proposal of a new model for the mean flowfield scaling. Comparison to a subsonic three-dimensional boundary layer is made for this new scaling law.

The Karhunen-Loeve Galerkin procedure (Park, H. M., and Cho, D. H., 1996, 'Low Dimensional Modeling of Flow Reactors,' Int. J. Heat Mass Transf., 39, pp. 3311-3323) is a type of reduction method that can be used to solve linear or nonlinear partial differential equations by reducing them to minimal sets of algebraic or ordinary differential equations. In this work, the method is used in conjunction with a conjugate gradient technique to solve the boundary optimal control problems of the heat conduction equations. It is demonstrated that the Karhunen-Loeve Galerkin procedure is well suited for the problems of control or optimization, where one has to solve the governing equations repeatedly but one can also estimate the approximate solution space based on the range of control variables. Choices of empirical eigenfunctions to be employed in the Karhunen-Loeve Galerkin procedure and issues concerning the implementations of the method are discussed. Compared to the traditional methods, the Karhunen-Loeve Galerkin procedure is found to solve the optimal control problems very efficiently without losing accuracy. [S0022-0434(00)00603-1]

The relationship between free-stream turbulence and boundary layer behavior has been investigated using spectral measurements. The power spectral densities of turbulence quantities in transitional and fully turbulent boundary layers were computed and compared to the power spectra of the same quantities measured in the free stream. Comparisons were made using the 'transfer function.' The transfer function is the ratio of two spectra at each frequency in the spectra. Comparisons were done in flows with low (0.6 percent) and high (8 percent) free-stream turbulence intensities. Evidence was gathered that suggests that relatively low-frequency, large-scale eddies in the free stream buffet the boundary layer, causing boundary layer unsteadiness at the same low frequencies. These fluctuations are present in both transitional and fully turbulent boundary layers. They are seen under both high and low free-stream turbulence conditions, although they are stronger in the high-turbulence case. Examination of the turbulent shear stress suggests that the low-frequency fluctuations enhance transport in the boundary layer but they are not so effective in promoting eddy transport as are turbulent eddies produced and residing within the boundary layer. In the fully-turbulent boundary layer, higher-frequency fluctuations are added to the low-frequency unsteadiness. These higher-frequency fluctuations, not seen in the transitional boundary layer, are associated with turbulence production in the boundary layer and appear not to be directly related to free-stream unsteadiness. [S0889-504X(00)00403-7]

A fundamental experimental investigation is described of the structure and streamwise development of a confluent boundary layer generated by the interaction of a leading-edge slat wake with the turbulent boundary layer on the main element of a multi-element airfoil model. The slat and airfoil model geometry are both fully two dimensional. The research is performed in an attempt to investigate the flow physics of confluent boundary layers and to build an archival database on the interaction of the slat wake and the main element wall layer. In addition, an attempt is made to identify clearly the role that slat wake/airfoil boundary-layer confluence has on lift production and how this occurs. Although complete laser Doppler velocimetry flow surveys were performed for a variety of slat gap and overhang settings, the focus is on two cases representing both strong and weak wake boundary-layer confluence. For those interested in performing numerical simulations, the full database is available from the authors.

Presented are experimental results describing the effects of orientation angle of film cooling holes on boundary layer temperature distributions and film cooling effectiveness. Film flow data were obtained from a row of five film cooling holes on a flat test plate. The inclination angle of the hole was fixed at 35 deg and four orientation angles of 0, 30, 60, and 90 deg were investigated. The velocity ratios surveyed were 0.5, 1.0, and 2.0. The boundary layer temperature distributions were measured at three downstream locations using 1 [micro]m platinum wire. Detailed adiabatic film cooling effectiveness distributions were measured using thermochromic liquid crystal. Results show that the increased lateral momentum in the case of large orientation angle injection strongly affects boundary layer temperature distributions. Temperature distribution characteristics are, in general explained in the context of the interactions between injectant and free-stream fluid and between injectants issuing from adjacent holes. The adiabatic film cooling effectiveness distributions are discussed in connection with the boundary layer temperature distributions. Spanwise-averaged effectiveness distributions and space-averaged effectiveness distributions are also presented with respect to the velocity ratios and the orientation angles.

Covariances and fluxes of reactive species in the clear convective atmospheric boundary layer (CABL) are studied and parameterized. The covariances result from correlations between reactive species. These covariances may have a considerable influence on the modeled reaction rates in atmospheric chemistry models, but usually are neglected. To facilitate the representation of covariance effects in large-scale atmospheric chemistry models, the authors have developed a new first-order closure for covariances. The closure is based on top-hat distributions, as is common in mass-flux schemes. In addition, the authors utilize an existing nonlocal first-order closure expression for the flux, which represents the combined effects of gradient mixing and nonlocal convective mixing. The authors show how the latter also includes the impact of chemistry on the nonlocal flux contribution. The impact of the closures is illustrated first for artificial, simple chemistry cases. The results are evaluated using large-eddy simulation (LES). By comparing results for the entraining and solid-lid CABL it is established that the covariance closure works satisfactorily away from the inversion. Subsequently, the closures are evaluated against LES for a photochemical case with 10 reactions involving six modeled species. The accuracy of the modeled covariances is found to be within a factor of 2, which is sufficient to improve the modeled concentrations.

Diffusive boundary layers, photosynthesis, and respiration in Phaeocystis colonies were studied by the use of microelectrodes for oxygen and pH during a bloom in the Barents Sea, 1993, and in the Marsdiep, Dutch North Sea, 1994. The oxygen microenvironment of a Phaeocystis colony with a mean diameter of 1.4 mm was mapped from 346 [O.sub.2] measurements and showed gradients of oxygen concentration in the water phase up to 1 mm distance from the colony surface. The effective diffusive boundary layer was 0.4-0.9 mm thick. Oxygen concentrations inside colonies reached 180% of the bulk water, and pH increased up to 0.4 units when measured in light at saturating intensities ([is greater than] 90 [micro]mol photons [m.sup.-2] [s.sup.-1]). The respiration in the dark was low, resulting in a 6% lowering in oxygen concentration and 0.04 units lowering in pH inside colonies, compared to the bulk water phase. Such colonies were net heterotrophic communities at light intensities up to 10 [micro]mol photons [m.sup.-2] [s.sup.-1]. A week later, colonies were net heterotrophic at light intensities up to 80 [micro]mol photons [m.sup.-2] [s.sup.-1]. The effective diffusion coefficient for oxygen in the gelatinous colonies was not significantly different from that in sea water.

The impact of colony formation on cellular nutrient supply was calculated for Phaeocystis in a turbulent environment using a diffusion--reaction model. The model included diffusive boundary layer as predicted by Sherwood numbers in mass transfer to a sphere. Literature values for nutrient uptake ([V.sub.max], [K.sub.m]) of single cells and colonies and the size dependence of cell numbers in colonies were used in the model. Colony formation was shown to decrease nutrient uptake by Phaeocystis cells because of the presence of diffusive boundary layers with concentration gradients surrounding the colonies. At diffusion limitation, this concentration gradient was reflected by an apparently higher half-saturation constants for nutrient uptake, [K.sub.M], for colonial cells compared with that for single cells. The diffusion limited supply of inorganic nitrogen and orthophosphate from the bulk water phase with concentrations of 2 and 0.2 [micro]M, respectively, was sufficient to support nutrient demands for 1 cell doubling in colonies in 6-10 h, respectively, at a shear rate of 0.1 [s.sup.-1]. The same nutrient concentration levels could theoretically support nutrient demands of single cells for one cell doubling within 2-3 h. It was concluded that the lower grazing pressure in the size class of colonies relative to that of single free-living cells may be more important for colony formation than nutrient concentrations.

A study investigated the structure of melts derived from the dissolution of orthopyroxene in three different alkali-rich silica-undersaturated melts. Findings revealed that a common composition of silicon oxide contents results from the combination of the boundary layer melts. Results indicated that certain silica-heavy melts may have been created through the dissolution of xenolith orthopyroxene at low pressure probably by their silica-undersaturated host magmas.

Far-field computational boundary conditions for two-dimensional external flow problems are developed from the linearized Euler solutions. These first-order boundary conditions are applicable in the far-field region beyond a computational boundary and are solved using integral transform techniques and an iterative procedure. They represent a logical asymptotic extension of the zero-order conditions, and they are linear about a constant pressure. The first-order boundary conditions are computationally compared with the zero-order conditions, and the first-order boundary conditions are found to provide substantial computational efficiency and accuracy.

Four-dimensional velocity fields derived from dual Doppler radar observations are the basis of a description and statistical analysis of a convective, sheared planetary boundary layer during an afternoon over the High Plains of eastern Colorado. Mean velocities and momentum fluxes are calculated directly from the radar data and are verified with aircraft and tower data. Perturbation pressure and buoyancy fields are recovered for turbulent kinetic energy budgets, and for estimates of horizontal heat advection across the analysis area. The surface layer and lowest third of the observed boundary layer were similar to minimally sheared convective boundary layers, but there were significant differences in the upper two-thirds of the boundary layer. An overrunning residual mountain boundary layer merged with the locally generated convective boundary layer, producing a deep, continuously sheared layer of turbulent activity. Computer visualization reveals a complicated flow characterized by clusters of vortical structures extending well into the slightly stable overrunning region, frequently dominated by clusters of large, long-lived vortices. First- and second-order statistics vary with time of day and averaging volume, suggesting that appropriate parameterizations of similar boundary layers should be functions of the required spatial and temporal scales and mesoscale environment. A number of common simplifying assumptions, scalings, and parameterizations employed for purely convective boundary layers would be inappropriate for this flow.

A simple four-cell model of the tropical atmosphere in equilibrium with its boundaries is introduced, which can support a variable diabatic circulation and prognostic temperature and humidity profiles. The model is used to predict atmospheric perturbations away from the observed base state. Prognostic variables include radiation, surface fluxes, and dynamic transports, with temperature and water vapor levels determined by conservation constraints. The model includes a specially developed water vapor scheme that performs favorably compared with observations. The model is used to simulate the local and nonlocal sensitivity of the tropical maritime atmosphere to changes in surface temperature and other boundary conditions at very large horizontal scales. The main findings are as follows. (i) The sensitivity of boundary layer convergence to sea surface temperature (SST) variations depends on the behavior of convective heating over cooler regions and may be overestimated by heuristic models that ignore or oversimplify thermodynamic and radiative constraints. (ii) The maintenance of humidity equilibrium over weakly convective areas is modulated by local radiative feedback. (iii) Evaporation feedbacks on SST may be overestimated by heuristic arguments that do not carefully treat atmospheric water transport. An explanation for the constant-relative humidity behavior of general circulation models under climate changes is also offered based on the results.

A study was conducted to characterize a technique that can be used to determine different degrees of accuracy for compressible laminar boundary layers. Steady compressible two-dimensional laminar boundary layer equations were based on nondimensional form. Independent variables and velocity components were also integrated into the equation. Results showed that the integral method produced a result of the same order of accuracy when applied to transformed equations.

Jack Pike's comments on the factors involved in formulating an upstream boundary layer for novel self-similar solutions are correct. A number of arbitrary constants related to the pressure and boundary-layer solution properties are useful in tailoring a match to the similarity solution. The four solutions correspond to solutions of the general function differential equation.

The subsonic near-wake of a class of slanted-base bluff bodies has been examined. The incoming boundary-layer momentum thickness affects base pressure and wake stagnation point locations. If the Reynolds number based on the Re(theta) value is selected as the independent factor, than resemblance is evident.

The effects of increasing Reynolds number on the boundary-layer transition of turbulent flows is investigated. Planar and conical boundary-layer transition are compared at aMach number of eight to obtain the unit-Reynolds number effects. Hot-wire anemometry experiments are also conducted at the same Mach number. Results showthat the cone transitin data obtained produces a unit-Reynolds-number that is steeper than the wind-tunnel planar slope.

Experimental measurements of flow and heat transfer in a concave surface boundary layer in the presence of streamwise counter-rotating Gortler vortices show conclusively that local surface heat-transfer rates can exceed that of the turbulent flat-plate boundary layer even in the absence of turbulence. We have observed unexpected heat-transfer behavior in a laminar boundary layer on a concave wall even at low nominal velocity, a configuration not studied in the literature: The heat-transfer enhancement is extremely high, well above that corresponding to a turbulent boundary layer on a flat plate. To quantify the effect of freestream velocity on heat-transfer intensification, two criteria are defined for the growth of the Gortler instability: [P.sub.z] for primary instability and [P.sub.rms] for the secondary instability. The evolution of these criteria along the concave surface boundary layer clearly shows that the secondary instability grows faster than the primary instability. Measurements show that beyond a certain distance the heat-transfer enhancement is basically correlated with [P.sub.rms], so that the high heat-transfer intensification at low freestream velocities is due to the high growth rate of the secondary instability. The relative heat-transfer enhancement seems to be independent of the nominal velocity (global Reynolds number) and allows predicting the influence of the Gortler instabilities in a large variety of situations. [DOI: 10.1115/1.4001307]