Search

The flow and heat transfer of three-by-eight laminar jet arrays impinging onto a dimpled surface with Reynolds number 100 in steady state have been investigated numerically in the present study. Grid independence was confirmed and good agreement was reached through comparison between the results obtained from the literature and the present work. The effect of jet-to-plate spacing (H/d = 1-10) dimple diameter ([D.sub.d]/d = 2-4) and the dimple relative depth ([delta]/[D.sub.d] = 0.10-0.30) on the flow and heat transfer characteristics of laminar impinging jet arrays was explored numerically. The average Nusselt number decreases with increasing jet-to-plate spacing, dimple relative depth, and dimple diameter. The jet flow in the downstream jets is deflected by crossflow, which makes low-velocity fluid appear in the corresponding dimples and the area is enlarged. Thus, the presence of dimples causes overall heat transfer deterioration in the laminar impinging jet arrays. PACS Nos.: 44.27+g. Nous etudions numeriquement l'ecoulement et le transfert de chaleur d'un jet laminaire de trois par huit incident sur une surface alveolee, avec un nombre de Reynolds de 100 en regime stationnaire. Nous confirmons l'independance sur la grille et verifions que nos resultats sont en bon accord avec ceux de la litterature. Nous explorons numeriquement l'effet de l'espacement jet-plaque (H/d = 1-10), du diametre des alveoles ([D.sub.d]/d = 2- 4) et de la profondeur relative des alveoles ([delta]/[D.sub.d] = 0.1-0.3), sur l'ecoulement et le transfert de chaleur du jet laminaire incident. Le nombre de Nusselt moyen decroit lorsque augmentent l'espacement jet-plaque, la profondeur relative et le diametre des alveoles. L'ecoulement dans les jets en aval est deflechi par l'ecoulement transversal, ce qui permet l'existence de fluide a basse vitesse dans les alveoles et elargit la surface. Ainsi, la presence des alveoles produit une deterioration du transfert de chaleur d'un jet laminaire incident. [Traduit par la Redaction], 1. Introduction The impinging jet has been used widely in industrial and engineering applications for its high heat transfer coefficient near the stagnation zone, such as the cooling of gas [...]

In the present study, both experimental and numerical techniques were employed to study three-dimensional laminar wall jet flows. The wall jet was created using a circular pipe of diameter 7 x [10.sup.-3] m and flows into an open water tank. The inlet Reynolds numbers based on the pipe diameter and jet exit velocity were 310 and 800. A particle image velocimetry (PIV) was used to conduct detailed measurements at various streamwise-transverse and streamwise-spanwise planes. The complete nonlinear incompressible Navier--Stokes equation was also solved using a collocated finite volume based in-house computational fluid dynamics (CFD) code. The computation was performed for three inlet Reynolds numbers, namely, 310, 420, and 800. From the PIY measurements and CFD results, velocity profiles and jet half-widths were extracted at selected downstream locations. It was observed that the numerical results are in reasonable agreement with the experimental data. The distributions of the velocities, jet spread rates, and vorticity were used to provide insight into the characteristics of three-dimensional laminar wall jet flows. [DOI: 10.1115/1.4002653]

In the present, a steady laminar of two dimensional and incompressible fluid flow induces from wall injection in a circular chamber has been studied experimentally and numerically. The water is injected from injection system into the chamber through the wall jets. The centerline static pressure variation with the distance along the chamber length is measured and calculated at different Reynolds numbers and inlet flow angles. The average heat transfer with Reynolds number at different values of the inlet flow angle is obtained. The velocity vectors are presented and Reynolds number is varied between 433 and 910 with inlet flow angle of 0 deg, 15 deg, 30 deg, 45 deg, and 60 deg. The results indicate that the pressure recovery coefficient decreases as both Reynolds number and flow angle increase. The average heat transfer coefficient increases with increasing both Reynolds number and flow angle. The results showed that two recirculation zones occur in the sides of centerline of the chamber behind the step. The size of these recirculation zones decreases by increasing the inlet flow angle. At high value of the inlet flow angle, other recirculation zone occurs on the wall chamber. [DOI: 10.1115/1.4001394] Keywords: annular injection, laminar flow, two dimensional, pressure coefficient, heat transfer

Cruise flaps are devices designed to minimize drag, and previous research has explored using a wing-based pressure differential to automate them. Different presentations of the pressure-differential data tend to lead to the development of different types of controllers for automated cruise flaps. A presentation used by previous researchers led to an unstable drag-minimizing controller, whereas a presentation used in this research leads to a stable controller that implements multiple functions. Techniques previously used for high Reynolds number natural-laminar-flow airfoils are modified for use with the low Reynolds number SD7037 planned for future flight testing. The results of rigid-aircraft simulations are presented, showing the effectiveness of the multifunction controller, which is able to simultaneously reduce drag and alleviate the effects of vertical gusts.

Steady, laminar flow and heat transfer, inside a rectangular microchannel with a dimpled bottom surface, are numerically studied. The microchannel is 50 x [10.sup.-6] m (50 [micro]m) deep and 200 x [10.sup.-6] m (200 [micro]m) wide. The dimples are placed in a single row along the bottom wall with a pitch of 150 x [10.sup.-6] m (150 [micro]m). The dimple depth is 20 x [10.sup.-6] m (20 [micro]m), and the dimple footprint diameter is 98 x [10.sup.-6] m (98 [micro]m). Fully developed periodic velocity and temperature boundary conditions are used at the inlet and outlet of one unit cell of the dimpled microchannel. Key flow structures such as recirculating flow and secondary flow patterns and their development along the flow directions are identified. The impact of these flow structures on the heat transfer is described. Heat transfer augmentations (relative to a channel with smooth walls) are present both on the bottomdimpled surface, and on the sidewalls of the channel The pressure drops in the laminar-microscale flow are either equivalent to, or less than, values produced in smooth channels with no dimples. It is concluded that dimples, proven to be an effective passive heat transfer augmentation for macroscale channels, can also be used to enhance heat transfer inside microchannels. [DOI: 10.1115/1.2429711] Keywords: dimple, microchannel, heat transfer enhancement

An improved method for simulating frequency-dependent friction in laminar pipe flow using the method of characteristics is proposed. It has a higher computational efficiency than previous methods while retaining a high accuracy. By lumping the frequency-dependent friction at the ends of the pipeline, the computational efficiency can be improved further, at the expense of a slight reduction in accuracy. The technique is also applied to the transmission line method and found to give a significant improvement in accuracy over previous methods, while retaining a very high computational efficiency. [DOI: 10.1115/1.2361320]

The effects of the upstream conditions in favorable pressure gradient boundary layers are studied by carrying out an experiment using laser-doppler anemometry over multiple traverses along a smooth plate. A set of upstream conditions composed of upstream wind tunnel speed, tripwire location, and the strength of the pressure gradient is analyzed. The similarity analysis of the equations of motion for pressure gradient flows is used to obtain the scales for the outer flow. For this study, the mean deficit profiles show a small dependence on the strength of the pressure gradient when scaled with the freestream velocity [U.sub.[infinity]]. Second, the upstream conditions effects are removed from the velocity deficit profiles when normalized by the [U.sub.[infinity]][[delta].sub.*]/[delta] scaling. However, the Reynolds stress profiles show the effects of upstream conditions and the strength of the pressure gradient. Finally, these favorable pressure gradient flows are found to be nonequilibrium flows because the pressure parameter A is not constant. In addition, three quadrants are found to describe all pressure gradient flows: one for adverse pressure gradient, one for favorable pressure gradient, and one for quasi-laminar flows, where different values are obtained and these are dependent on the experimental conditions. The quadrants are obtained by plotting log([U.sub.[infinity]]/ [U.sub.[infinity]i]) versus log([delta]/[[delta].sub.i]). DOI: 10.2514/1.19768

This paper presents detailed investigations related to active transition control in laminar separation bubbles. The investigations rely on direct numerical simulations based on the complete Navier--Stokes equations for a flat-plate boundary layer. A laminar separation bubble is created by imposing a streamwise adverse pressure gradient at the freestream boundary of the integration domain. Different steady and unsteady boundary layer disturbances are then introduced at a disturbance strip upstream of separation and their effects on the separation bubble are studied. It is shown that the size of the separated region can be controlled most efficiently by very small periodic oscillations, which lead to traveling instability waves that grow to large levels by the hydrodynamic instability of the flow. Indications for the preferred frequency of these waves can be obtained from linear stability theory, but since the problem is nonlinear, only direct numerical simulations can really qualify or disqualify the predictions. Overall, it turns out that unsteady two- or three-dimensional disturbances have a stronger impact on the size of the bubble than steady disturbances, because they directly provide initial amplitudes for the laminar-turbulent transition mechanism.

Heat sinks with radial and constructal branching microchannel networks with loops are examined numerically. Radial and constructal networks are embedded in disk-shaped heat sinks. Constructal nets with loops are found to be more robust than the radial ones, when one or more channel segments are blocked. Since complex constructal networks would involve problems in manufacturing, constructal channel nets with loops may be a better choice in engineering applications. Networks with loops and without loops are compared. Results show that the constructal nets with loops provide a great advantage when the structure experiences accidental damage in one or more subchannel segments, since the loop assures the continuity of flow. In spite of blockage, the performance of the network has only a small drop considering the increased pressure drop. [DOI: 10.1115/1.2229228] Keywords: constructal theory, constructal network, loops, complexity, temperature

Characteristics of small vortices were studied in axisymmetric jets wherein the Kolmogorov scale was approached by progressively decreasing the Reynolds number while still maintaining turbulent flow. A periodic forcing introduced far upstream of the jet nozzle ensured that the jet was turbulent. A vortex eduction tool was developed and applied to the high-pass filtered 2D velocity field in the axial plane of a turbulent jet while varying Re between 140 and 2600. Vortex population, energy, vorticity, and rms (root-mean-square velocity fluctuations) of the high-pass filtered field were measured to elucidate vortex characteristics. The observed population of vortices decreases dramatically at the Kolmogorov scale. The observed increase in vortex population with decreasing vortex size appears to be in accord with the space-filling argument, in that the vortex population in a two-dimensional domain should grow as [R.sup.-2]. The energy density curve obtained from vortex statistics reproduces the -5/3 slope for the inertial subrange, and the highpass filtered field accounts for approximately two-thirds of the total rms. [DOI: 10.1115/1.2173292]

Simultaneously developing three-dimensional laminar flow and heat transfer in the entrance region of trapezoidal channels are investigated using numerical methods in the Reynolds number range from 10 to 1000. It is shown that boundary-layer type of approximations, which lead to Reynolds-number-independent Poiseuille and Nusselt numbers, can be used for Reynolds numbers over 50 and after a few hydraulic diameters from the channel inlet.

The capabilities of a relatively new direct simulation Monte Carlo (DSMC) code are examined for the problem of hypersonic laminar shock/shock and shock/boundary-layer interactions, where boundary-layer separation is an important feature of the flow. Flow about two model configurations is considered, where both configurations (a biconic and a hollow cylinder-flare) have recent published experimental measurements. The computations are made using the DS2V code of Bird, a general two-dimensional/axisymmetric time-accurate code. The current focus is on flows produced in ground-based facilities at Mach 12 and 16 test conditions with nitrogen as the test gas and the test models at zero incidence. The freestream Knudsen numbers, with the characteristic length equal to the test model diameter, range from 0.0008 to 0.0004, consequently demanding computations for DSMC simulations. Results presented highlight the sensitivity of the calculations to grid resolution, sensitivity to physical modeling parameters, and comparison with experimental measurements. Information is provided concerning the flow structure and surface results for the extent of separation, heating, pressure, and skin friction.

This paper demonstrates that the range of a fluidic flow meter can be significantly extended by connecting it in parallel with a fixed laminar by-pass resistance. Analysis shows how for any particular specification, there is an optimum combination of meter and by-pass which maximizes the flow range. Validation tests were done in air, using a fluidic target meter integrated into a housing with a laminar by-pass of parallel rectangular cross section passages formed between flat plates. Results obtained showed excellent agreement with analytical predictions, almost doubling the operating range for the typical specification chosen, a major advance in the context of the previous research aimed at extending meter range. In principle the concept should be applicable to any flowmeter having a suitable Eulerian pressure-flow characteristic. [DOI: 10.1115/1.2060729]

The authors' research work into fully developed pulsating and oscillating laminar pipe and channel flows raised questions regarding the development length of the corresponding steady flow. For this development length, i.e., the distance from the entrance of the pipe to the axial position where the flow reaches the parabolic velocity profile of the Hagen-Poiseuille flow, a wide range of contradictory data exists. This is shown through a short review of the existing literature. Superimposed diffusion and convection, together with order of magnitude considerations, suggest that the normalized development length can be expressed as L/D=[C.sub.0]+[C.sub.1]Re and for Re [right arrow] 0 one obtains [C.sub.0]=0.619, whereas for Re [right arrow] [infinity] one obtains [C.sub.1] = 0.0567. This relationship is given only once in the literature and it is presumed to be valid for all Reynolds numbers. Numerical studies show that it is only valid for Re [right arrow] 0 and Re [right arrow] [infinity]. The development length of laminar, plane channel flow was also investigated. The authors obtained similar results to those for the pipe flow: L/D = [C'.sub.0]+[C'.sub.1]; Re, where [C'.sub.0]=0.631 and [C'.sub.1] = 0.044. Finally, correlations are given to express L/D analytically for the entire Re range for both laminar pipe and channel flows. [DOI: 10.1115/1.2063088]

The regular perturbation method is introduced to investigate the influence of two-dimensional roughness on laminar flow in microchannels between two parallel plates. By superimposing a series of harmonic functions with identical dimensional amplitude as well as the same fundamental wave number, the wall roughness functions are obtained and the relative roughness can be determined as the maximal value of the product between the normalized roughness functions and a small parameter. Through modifying the fundamental wave number, the dimensionless roughness spacing is changed. Under this roughness model, the equations With respect to the disturbance stream function are obtained and analyzed numerically. The numerical results show that flowing in microchannels are more complex than that in macrochannels; there exist apparent fluctuations with streamlines and clear vortex structures in microchannels; the flow resistances are about 5-80% higher than the theoretical value under different wall-roughness parameters. Furthermore, analysis shows that the effect of roughness on the flow pattern is distinct from that on the friction factor. [DOI: 10.1115/1.2060733]

The uptake of H2SO4 and CH3SO3H onto particles composed of water and sulfuric acid in a laminar flow reactor was examined at atmospheric pressure. Study revealed variance in relative humidity from 6 percent to 97 percent at 295 - 297.5 K.

Numerical studies of unsteady heat transfer in grooved channel flows are made and these flows are of special relevance to electronic systems. It is found that the downstream flow development is dependent on geometry.

Research describes the macroscopic pressure gradient and interfacial heat transfer coefficient for the analysis of fluid flow and thermal non-equilibrium heat transfer within an anisotropic porous medium. Data indicate that the directional interfacial heat transfer coefficient is analogous to that of the directional permeability.

Detailed study was carried out in order to investigate flow phenomena occurring at the junction of two incoming stratified flow layers with junction angles. Various combinations of fluids with Newtonian [...]

A technique of fractionation for microparticles was proposed that utilized a unique combination of a dielectrophoretic (DEP) field generated by a quadrupole electrode and a laminar flow in a capillary of 82.5 [micro]m in radius. The fabricated capillary possessed four platinum wires in its inside wall as a quadrupole electrode. In a nonuniform electric field generated by the quadrupole electrode, microparticles, such as polystyrene and carbon, in water experienced DEP forces in the radial direction. When a sample solution was pumped in, an ideal laminar flow perpendicular to the DEP force was formed inside the capillary. The microparticles dynamically migrated by the DEP force across the laminar flow while they were carried by the flow. A theoretical model taking the DEP force and the laminar flow pattern into account predicted the elution profiles of the single microparticles quantitatively. The elution times of the microparticles depended on the dielectric properties and the sizes of the microparticles, as well as the voltage and frequency of the applied alternating current.

A facile and simplistic approach to the analysis of the effects of diffusion in laminar chaotic flows is discussed. The approach is based on the definition of diffusional thickness and area of diffusional influence that provides a compact and quantitative description of the spatiotemporal evolution of partially mixed structures.

Research examines the unsteady laminar, bidirectional flows in infinitely long circular pipes at a fixed and varied time dependent volume flow rates as a function of time. Several variations of the flow rate are analyzed under different flow set ups.

The continuity and momentum equations of laminar flow through poroelastic media and the sufficient boundary conditions are found in the present paper. The land subsidence equation, Brinkman equation, Darcy's law, and so forth, can be recovered by the simplified governing equations of the present model. A water wave passing over a poroelastic bed is taken as an example of application of this laminar poroelastic media flow model. It is found from the example that, besides the two kinds of longitudinal waves and one kind of transverse wave inside the porous media that the conventional poroelastic model can provide, a second kind of transverse wave is obtained by this model. It is also found that the tangential stress and flow velocity inside the porous bed, according to the laminar poroelastic media flow model, are very different from those obtained by the conventional potential poroelastic media flow model. Finally, the limiting rigid bed solution of the application example, which is useful for the experimental verifications, is also given in this study.

A study on the performance of regenerative and recuperative plate heat exchangers was conducted to numerically analyze flow structure and its impact on heat transfer in cross-corrugated ducts where the inclination angle between corrugation and main stream direction is 45 degrees. Comparisons of the numerical results with available experimental data showed good agreement. Experimental methodology, results and conclusions are presented.

A study was conducted to analyze N-factor integration methods for determining boundary-layer transition predictions using flight test information. Some of the methods considered in the study include the N-factor calculation, envelope methodology and the two N-factors-based method. Results indicated that all the N-factor integration methods supported pathological cases and did not produce an ideal correlation for boundary-layer transition predictions.

Speckle decorrelation can be attributed to the velocity gradients in flowing blood which resulted in relative scatterer motion. The ultrasonic speckle, which is formed by the complex sum of echoes from resolution scatterers, can be sensitive to the angle of flow and to the beam-vessel angle. Thus, flow gradients are important contributors in the speckle decorrelation under certain conditions.

The hydrodynamic characteristics of a buoyancy-driven convection loop containing an electrically-conducting fluid in a transverse magnetic field are investigated analytically using a one-dimensional model. One side of the loop is isothermally heated and the other side isothermally cooled, and the upper and lower sections are insulated. The model which is based on the use of the Hartmann Plane-Poiseuille flow solution for estimating loop shear stress, predicts the flow velocity and the induced current of the magnetohydrodynamic generator in terms of the flow and geometric parameters. The study covers ranges of Grashof number, Gr, from [10.sup.2] to [10.sup.6], the Hartmann number, Ha, from 0 to 20, the Prandtl number, Pr, from .003 to 7, and loop height to thickness ratio, L/d, from 10 to 50. It is shown that at low Prandtl numbers, Pr [much less than] 1, there exists an optimal Hartmann number, [Ha.sub.opt], that maximizes the induced electric current. This [Ha.sub.opt] depends weakly on the Grashof number. The side-heated loop performance is also compared with the bottom heated loop model of Ghaddar, (1997a). It is found that at a low Prandtl number, side heated loop induces the higher velocity whereas at high Prandtl numbers the bottom heated loop induces higher velocity.

The flow in vaneless diffusers with large width-to-radius ratios is analyzed by using three-dimensional boundary-layer theory. The variations of the wall shear angle in the layer and the separation radius of the turbulent boundary layer versus various parameters are calculated and compared with experimental data. The effect of the separation point on the performance of vaneless diffusers and the mechanism of rotating stall are discussed. It is concluded that when the flow rate becomes very low, the reverse flow zone on the diffuser walls extends toward the entry region of diffusers. When the rotating jet-wake flow with varying total pressure passes through the reverse flow region near the impeller outlet, rotating stall is generated. The influences of the radius ratio on the reverse flow occurrence as well as on the overall performance are also discussed.

Laminar separation bubbles are commonly observed on turbomachinery blades and therefore require effective methods for their prediction. Therefore, a newly developed transition model by Gostelow et al. (1996) is incorporated into an upwind-biased Navier-Stokes code to simulate laminar-turbulent transition in the boundary layer. A study of the influence of the two adjustable parameters of the model, the transition onset location and the spot generation rate, is conducted and it is found that it can predict laminar separation bubbles, measured on a NACA 0012 airfoil. Additional results are presented for separation bubbles in an annular compressor cascade.

The transient conjugated heat transfer in forced convection for simultaneously developing laminar flow inside a microchannel heat sink is studied by solving the steady momentum equation and the transient energy equation. A parametric study is performed to understand the effects of channel depth and width, Reynolds number, spacing between channels, and solid to fluid thermal conductivity ratio. Silicon as well as indium phosphide are used as wafer's material. Step and pulsed variations of the heat load are analyzed. Results show that the time required for the heat transfer to reach steady state condition is longer for the system with larger channel depth or spacing and smaller channel width or Reynolds number. Characteristic results for the fluid mean temperature at the exit, solid maximum temperature, local Nusselt number, and local heat flux are presented graphically as functions of position and time.

The laminar flow in a hydrostatic pocket is described by a mathematical model that uses the three-dimensional Navier-Stokes equations written in terms of the primary variables, u, v, w, and p. Using a conservative formulation, a finite volume multiblock method is applied through a collocated, body fitted grid. The flow is simulated in a shallow pocket with a depth/length ratio of 0.02. The flow structures obtained and described by the authors in their previous two dimensional models are made visible in their three dimensional aspect for both the Couette, and the jet dominated flows. It has been found that both flow regimes formed central and secondary vortical cells with three dimensional corkscrew-like structures that lead the fluid on an outward bound path in the axial direction of the pocket. In the Couette dominated flow the position of the central vortical cell center is at the exit region of the capillary restrictor feedline, while in the jet dominated flow a flattened central vortical cell is formed in the downstream part of the pocket. It has also been determined that a fluid turn around zone occupies all the upstream space between the floor of the pocket and the runner, thus preventing any flow exit through the upstream exit of the pocket. The corresponding pressure distribution under the shaft for both flow regimes is presented as well. It was clearly established that both for the Couette, and the jet dominated cases the pressure varies significantly in the pocket in the circumferential direction, while its variation is less pronounced axially.

The influence of inlet hot streak temperature distortion on turbine blade heat load was explored on a transonic axial flow turbine stage test article using a three-dimensional, multiblade row unsteady Euler code. The turbine geometry was the same as that used for a recently reported testing of hot streak influence. Emphasis was placed on elucidating the physical mechanisms by which hot streaks affect turbine durability. It was found that temperature distortion significantly increases both blade surface heat load nonuniformity and total blade heat load by as much as 10-30 percent (mainly on the pressure surface), and that the severity of this influence is a strong function of turbine geometry and flow conditions. Three physical mechanisms were identified that drive the heat load nonuniformity: buoyancy, wake convection (the Kerrebrock-Mikolajczak effect), and rotor-stator interactions. The latter can generate significant nonuniformity of the time-averaged relative frame rotor inlet temperature distribution. Dependence of these effects on turbine design variables was investigated to shed light on the design space, which minimizes the adverse effects of hot streaks.

This paper describes a program of work, largely experimental, which was undertaken with the objective of developing an improved blade profile for the low-pressure turbine in aero-engine applications. Preliminary experiments were conducted using a novel technique. An existing cascade of datum blades was modified to enable the pressure distribution on the suction surface of one of the blades to be altered. Various means, such as shaped inserts, an adjustable flap at the trailing edge, and changing stagger were employed to change the geometry of the passage. These experiments provided boundary layer and lift data for a wide range of suction surface pressure distributions. The data were then used as a guide for the development of new blade profiles. The new blade profiles were then investigated in a low-speed cascade that included a set of moving bars upstream of the cascade of blades to simulate the effect of the incoming wakes from the previous blade row in a multistage turbine environment. Results are presented for two improved profiles that are compared with a datum representative of current practice. The experimental results include loss measurements by wake traverse, surface pressure distributions, and boundary layer measurements. The cascades were operated over a Reynolds number range from O. 7 x [10.sup.5] to 4.0 x [10.sup.5]. The first profile is a 'laminar flow' design that was intended to improve the efficiency at the same loading as the datum. The other is a more highly loaded blade profile intended to permit a reduction in blade numbers. The more highly loaded profile is the most promising candidate for inclusion in future designs. It enables blade numbers to be reduced by 20 percent, without incurring any efficiency penalty. The results also indicate that unsteady effects must be taken into consideration when selecting a blade profile for the low-pressure turbine.

We conducted a flow simulation to study the laminar flow in a three-dimensional rectangular cavity. The ratio of cavity depth to width is 1:1, and the span to width aspect ratio (SAR) is 3:1. The governing equations defined on staggered grids were solved in a transient context by using a finite volume method, in conjunction with a segregated solution algorithm. Of the most apparent manifestation of three-dimensional characteristics, we addressed in this study the formation of corner vortices and its role in aiding the transport of fluid flows in the primary eddy and the secondary eddies.

Micro-inertia effects of surface roughness on hydrodynamic lubrication are analyzed in the light of similitude principles, viz. a newly conceived reduced Reynolds number and the classical parameter of relative roughness. In particular, the dynamic properties of laminar sheet flow in a two-dimensional channel between a sinusoidal wall and a flat wall are studied. FEM solutions of the Navier-Stokes equation are compared with corresponding experimental findings. The latter are gathered in an especially designed laminar-flow wind tunnel. Conclusions are drawn concerning the roughness sensitivity of laminar thin-film flows.

The pressure gradient increases with increasing flow rate due to an increase in the viscous dissipation rate for non-Newtonian liquids at high flow rate. During the solidification of flowing liquids, a layer of frozen material is formed and maintained on the duct wall. The thickness of the frozen layer is less than the duct radius due to viscous dissipation. In this process the mechanical energy is converted into thermal form.

Extensive wake surveys of the peculiar drag characteristics of low Reynolds number airfoil flows reveal the prominent role of the laminar separation bubble and airfoil geometry in spanwise drag variation. The amplitudes of the oscillations decrease with the increase in Reynolds number, and the spanwise locations of the oscillations shift with changes in the angle of attack. The largest fluctuations are observed for low angles of attack and at the lowest point of the low drag range. A weak agreement is observed in profile drag measurements between different wind-tunnel facilities.

Measurements of pressure losses in a sine-waved hydraulically smooth pipe, having a centerline described by the formula y = h sin (2[Pi][Xi]/[Lambda]), are presented. The effect of the dimensionless wave-length ([Lambda]/d) and amplitude (h/d) on the Darcy friction factor was investigated in the range of the Reynolds number from about 100 to 10 000, and in the ranges of wavelength from [Lambda]/d = 17.7 to 150 and amplitude from h/d = 1.5 to 32. The Dean number, based on the minimum radius of the sine-waved centerline curvature, below which the influence of the sine-pipe shape in comparison to the straight tube was not seen is De [less than or equal to] [approximately] 20. A smooth transition from laminar to turbulent region in the friction factor versus Reynolds number plot was observed. In turbulent region the effect of the sine-pipe shape can be neglected for [Lambda]/d [greater than or equal to] 1.36*h/d + 36.2.

Equations governing compressible boundary-layer laminar flow of a two-phase particulate suspension are developed based on a continuum representation of both phases. These equations include such effects as particle-phase viscous stresses, variable position-dependent particle slip coefficient, and general power-law viscosity-temperature and thermal conductivity-temperature relations. The dimensionless form of the equations are applied to the problem of flow over a semi-infinite flat surface. An appropriate transformation is employed to allow proper comparison with previously published results for special cases of this problem. The full coupled system of equations is solved numerically via an implicit finite-difference method. Graphical results for the density, and temperature profiles as well as the displacement thicknesses, skin-friction coefficients, and the wall heat transfer coefficient for both the fluid and particle phases are presented and discussed in detail. In addition, a parametric study is performed to illustrate the influence of the particle to fluid viscosity ratio and the viscosity-temperature power exponent on the flow properties.

Experiments are performed in a blowdown wind tunnel to analyze shock/boundary-layer interaction in two-dimensional hypersonic wedge flow. Different type of nozzle are used to simulate the various aspects of the interaction phenomenon. An infrared system is employed to record the measured data. Results indicate that the interaction phenomenon is affected by several parameters, notably the flat plate length and the average heat transfer of reattachment.

Three-dimensional laminar boundary layers past an infinite swept bump and free wing were investigated numerically using the fractional step method. The objective of the work was to study the effect of surface curvature induced changes in pressure gradient and changes in the freestream flow on boundary layer skewness and growth. Simulation results demonstrate that for flows over the bump the first transition from adverse to favorable pressure gradient occurs at the front concave/convex inflexion and the second transition from favorable to adverse pressure gradient occurs at the summit. For flows past a free wing, the only transition from favorable to adverse pressure gradient occurs in front of the summit and the subsequent adverse pressure gradient is larger than the corresponding value for the bump. For both the bump and wing, the increase of initial skewing angle from 0 to 30 deg causes a 10 percent reduction in the length of the wake; the wake behind the wing is about 12 percent longer in streamwise extent than the corresponding wake behind the bump. Integral parameters in the flows over the bump display a wavy trend due to the two transitions of the pressure gradient. On the other hand, the single transition from favorable to adverse pressure gradient brings about a monotonic increase of the integral parameters for flows past the wing. Near separation and reattachment, surface-streamlines are skewed strongly in the span wise direction. Conditions of flow detachment for the bump and wing are in good agreement with correlations for laminar separating flows with power-law velocity profiles as well as correlations for wall-curvature-induced turbulent separating flows.

The effect of length scale in free-stream turbulence is considered for heat transfer in laminar boundary layers. A model is proposed that accounts for an 'effective' intensity of turbulence based on a dominant frequency for a laminar boundary layer. Assuming a standard turbulence spectral distribution, a new turbulence parameter that accounts for both turbulence level and length scale is obtained and used to correlate heat transfer data for laminar stagnation flows. The result indicates that the heat transfer for these flows is linearly dependent on the 'effective' free-stream turbulence intensity.

Bed roughness and rainfall impact affect hydraulic friction in overland flow. The relationship between friction, velocity, discharge, and channel slope was examined for the case of shallow, spatially varied flow on rough surfaces. Rainfall was simulated on artificially roughened surfaces in a laboratory. Measured flow velocities were compared to theoretical velocities computed from a dynamic equation for spatially varied flow and from the Darcy-Weisbach uniform flow equation. The measurements showed that the constant that relates the Darcy-Weisbach friction coefficient to Reynolds number can become larger than the theoretical value for smooth laminar flow. An analysis of the dynamic equation showed that frictional forces were much larger than forces resulting from changes in hydrostatic pressure and momentum. Water-surface profiles based on the Darcy-Weisbach friction equation nearly matched those from the dynamic equation for spatially varied flow. A regression was developed from the Darcy-Weisbach equation. The regression accurately predicted flow velocity when absolute roughness, rainfall rate, channel discharge, slope, slope length, and viscosity were known.

The high-speed boundary-layer instability and transition can be studied by the newly constructed short-duration, low-cost, quiet-flow wind tunnel. The flow quality is achieved up to Reynolds numbers at over 400,000 on the axial length of the quiet-flow test region. The Ludwieg tube lacks the NASA-Langley boundary-layer bleed slots in the nozzle. This performance is achievable with clean, high-quality mirror finish.

A 'reverse' delta wing that has a straight leading edge and forward-swept trailing edges can perform extended natural laminar flow runs during supersonic flights. Euler calculations with a supersonic Mach number proves that the air flow over the wing is two dimensional. A subsonic to supersonic shift in the Mach number induces a large aerodynamic center change in the reverse delta wing whose leading-edge flaps are active with a reduction in drag and increase in maximum life at nominal attack angles.