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Experimental measurements of the wall shear stress combined with those of the velocity profiles via the electrochemical technique and ultrasonic pulsed Doppler velocimetry are used to analyze the flow behavior in transient flows caused by a downstream short pipe valve closure. The Reynolds number of the steady flow based on the pipe diameter is Re = 148,600. The results show that the quasisteady approach of representing unsteady friction is valid during the initial phase for relatively large decelerations. For higher decelerations, the unsteady wall shear stress is consistently higher than the quasisteady values obtained from the velocity profiles. Attention has been focused on the friction acceleration model. The results obtained from this study show the ability of the electrochemical method in determining the local unsteady wall shear stress even in severe decelerating transient flows. [DOI: 10.1115/1.3112387]

The discovery of vast quantities of hydrocarbons during exploration of the Mackenzie Delta has led to the detection of numerous anomalous deep holes in various delta channels in the past four decades. The proposed pipeline crossing from the Mackenzie Delta to northern Alberta has renewed interest in studying the stability of these deep holes. The main goal of this research project was to study ice-covered flow velocity and bed shear stress distributions using a previously calibrated computational fluid dynamics (CID) model for a 30 m deep hole in the East Channel of the Mackenzie Delta to provide an initial assessment of its stability. In this study, a previously developed 3D CFD model using the FLUENT code with the renormalization group theory (RNG) k-s turbulence closure model with nonequilibrium wall functions was adapted to represent ice-covered flow conditions for the study reach. The numerical model was applied to simulate four flow conditions (500, 720, and 1000 [m.sup.3]/s along with a moving ice cover during a flow rate of 720 [m.sup.3]/s). Results indicated that a single vortex was formed near the inner bend above the hole and deposition may be a key process occurring during ice-covered flow conditions. Key words: computational fluid dynamics, finite element, ice-covered flow, bed shear stress, deep hole. L'exploration du delta du Mackenzie a la suite de la decouverte de vastes quantites d'hydrocarbures a mene a la detection de plusieurs fosses d'affouillement profondes anormales dans les divers canaux du delta an cours des quarante dernieres annees. Le franchissement propose du pipeline du delta du Mackenzie an nord de ''Alberta a renouvele l'interet de verifier la stabilite de ces fosses profondes. Le principal objectif de ce projet de recherche etait d'etudier la vitesse d'ecoulement sous convert de glace et les distributions des contraintes de cisaillement du lit en utilisant un modele numerique de la dynamique des fluides etalonne pour une fosse profonde de 30 m dans le canal Est du delta du Mackenzie afin de fournir une evaluation initiale de sa stabilite. Dans cette etude, un modele numerique tridimensionnel de la dynamique des fluides, developpe anterieurement, utilisant le code FLUENT et le modele de turbulence k-s ' RNG ' muni de fonctions de non equilibre des parois, a ete adapte de maniere a representer les conditions d'ecoulement sous convert de glace pour la portee de l'etude. Le modele numerique a ensuite ete applique pour simuler quatre conditions d'ecoulement (500, 720, 1000 [m.sup.3]/s de meme qu'un convert de glace se deplargant avec un ecoulement de 720 [m.sup.3]/s). Les resultats indiquent qu'un seul vortex s'est forme pres de la portion interne du coude du fleuve au-dessus de la fosse d'affouillement et que la deposition pent etre un processus important survenant durant les conditions d'ecoulement sous convert de glace. Mots-cles : dynamique des fluides numerique, elements fmis, ecoulement sous convert de glace, contraintes de cisaillement du lit, fosse d'affouillement profonde. [Traduit par la Redaction], Introduction The discovery of vast quantities of hydrocarbon reserves in the Mackenzie Delta-Beaufort Sea region during the late 1960s prompted the oil and gas industry to become actively interested in [...]

This paper presents the results of an experimental study of flow around cylindrical objects in an open channel. Cylindrical objects of equal diameter and four heights were tested under similar flow conditions producing four different levels of submergence, including a surface piercing bridge-pier-like cylinder. Different flow elements and their locations were identified using a set of flow visualization tests. Observations made from the flow visualization tests were then verified by measurements of bed-shear stress and deflected flow velocity around the cylinders. Horse-shoe vortex systems were found to appear closer to the submerged cylinders compared to a surface piercing cylinder. The increase in dimensionless bed-shear stress is found to be inversely related to the level of submergence of the cylinders. Bed-shear stress results presented in this paper will be valuable for a qualitative understanding of the scour potential of flow around submerged cylinders. Mean velocity profiles in the deflected flow region were analyzed in terms of the theories of threedimensional turbulent boundary layer. Submergence of a cylinder has been found to suppress alternate vortex shedding and produce stronger three-dimensional flows in the downstream wake. Perry and Joubert's model was found to be sufficiently accurate to predict the deflected velocity magnitudes around submerged cylinders. Overall, the present study will provide valuable knowledge of hydraulics of flow around submerged structures (e.g., simple fish habitat structures). CE Database subject headings: Open channel flow; Boundary layers; Flow visualization; Shear stress; Fish management; Cylinders.

Theoretical predictions of wall shear stresses in unsteady turbulent flows in pipes are developed for all flow conditions from fully smooth to fully rough and for Reynolds numbers from [10.sup.3] to [10.sup.8]. A weighting function approach is used, based on a two-region viscosity distribution in the pipe cross section that is consistent with the Colebrook-White expression for steady-state wall friction. The basic model is developed in an analytical form and the resulting weighting function is then approximated as a sum of exponentials using a modified form of an approximation due to Trikha. A straightforward method is presented for the determination of appropriate values of coefficients for any particular Reynolds number and pipe roughness ratio. The end result is a method that can be used relatively easily by analysts seeking to model unsteady flows in pipes and ducts. DOI: 10.1061/(ASCE)0733-9429(2007)133:11(1219) CE Database subject headings: Unsteady flow; Skin friction; Shear stress; Surface roughness; Pipe flow.

Jet flows are encountered in a variety of industrial applications. Although from the points of view of manufacturing with ease and small spatial requirement it is convenient to use short slit nozzles, most of the available studies deal with turbulent jets issuing from contoured nozzles. In the present work, experiments have been conducted in the moderate Reynolds number range of 250-6250 for a slit jet. Mixing characteristics of slit jets seem to be quite different from those of jets emerging out of contoured nozzles. This is primarily due to the differences in the decay characteristics and the large scale eddy structures generated in the near field, which are functions of the initial momentum thickness. It is evident that, in the range of 250 [less than or equal to] Re [less than or equal to] 6250, the overall spreading characteristics of the slit jet flow have stronger Reynolds number dependence than those of contoured nozzle jets. In particular, the slit jets exhibit slower mean velocity decay rates and slower half-width growth rates. Normalized power spectra and probability distribution functions are used to assess the spatial evolution and the Reynolds number dependence of jet turbulence. It is seen that the fluctuating components of velocity attain isotropic conditions at a smaller axial distance from the nozzle exit than that required for mean velocity components to become self-similar [DOI: 10.1115/1.2776959] Keywords: jets, transition to turbulence, self-similarity in jets, shear layer, Reynolds number, jet structures

Cliff-ramp patterns (CR) are a common feature of scalar turbulence, characterized by a sharp temperature increase (cliff) followed by a more gradual temperature decrease (ramp). Aircraft measurements obtained from NOAA best aircraft turbulence probes (BAT) were used to characterize and compare CR patterns observed under stably stratified conditions in the upper troposphere, a region for which there are few such studies. Experimental data were analyzed for three locations, one over Wales and two over southern Australia, the latter in correspondence with the Southern Hemisphere winter subtropical jet stream. Comparison of observed CR patterns with published direct numerical simulations (DNS) revealed that they were likely signatures of Kelvin-Helmholtz (KH) billows, with the ramps associated with the well-mixed billows and the cliffs marking the highly stretched braids. Strong correlation between potential temperature and horizontal velocity supported the KH link, though expected correlations with vertical velocity were not observed. The temperature fronts associated with the cliffs were oriented in a direction approximately normal to the mean wind direction. Locally high values of temperature structure constant near these fronts were associated with steep temperature gradients across the fronts; this may be misleading in the context of electromagnetic propagation, suggesting a false positive indication of high levels of small-scale turbulence that would not correspond to scintillation effects. Billow aspect ratios, braid angles, and length scales were estimated from the data and comparisons with published DNS provided a means for assessing the stage of evolution of the KH billows and the initial Richardson number of the layer.

Investigating shear flows is important in technical applications as well as in fundamental research. Velocity measurements with high spatial resolution are necessary. Laser Doppler anemometry allows nonintrusive precise measurements, but the spatial resolution is limited by the size of the measurement volume to ~50 [micro]m. A new laser Doppler profile sensor is proposed, enabling determination of the velocity profile inside the measurement volume. Two fringe systems with contrary fringe spacing gradients are generated to determine the position as well as the velocity of passing tracer particles. Physically discriminating between the two measuring channels is done by a frequency-division-multiplexing technique with acousto-optic modulators. A frequency-doubled Nd:YAG laser and a fiber-optic measuring head were employed, resulting in a portable and flexible sensor. In the center of the measurement volume of ~1-mm length, a spatial resolution of ~5 [micro]m was obtained. Spatially resolved measurements of the Blasius velocity profile are presented. Small velocities as low as 3 cm/s are measured. The sensor is applied in a wind tunnel to determine the wall shear stress of a boundary layer flow. All measurement results show good agreement with the theoretical prediction. OCIS codes: 060.2370, 120.7250.

Byline: Hidekazu Yasuda (1) Keywords: Longitudinal matter dispersion; mass flux in a tidal basin; matter with settling velocity; negative flux Abstract: The fundamental nature of the mass flux due to the shear effect is examined analytically in a basin with steady and oscillatory currents to promote a better understanding of the mass transport process in coastal waters. The currents are given from solutions of the simplified motion equation so as to be consistent with the diffusion equation. The matter concentration used is given by an analytical solution of the diffusion equation with the settling flux term contained. Mass flux, yielding the depth-averaged dispersion coefficient, is rather varied vertically in both steady and oscillatory currents. In the oscillatory current with a Stokes layer in particular, the vertical profile of flux is more complicated and even negative flux is induced near the basin floor. This negative flux does not necessarily yield a negative value of the vertically averaged dispersion coefficient. The exact dispersion coefficient given by the flux analysis is realized only in the steady state of the matter concentration distribution, though we can scarcely observe the steady state in the actual sea. The vertically uniform longitudinal dispersion coefficient at the stationary stage is shown to be caused from the vertical complexity of mass flux by the action of the vertical diffusing and the settling flux. Author Affiliation: (1) Department of Fisheries Information and Management, National Fisheries University, Nagata-Honmachi, Shimonoseki, Yamaguchi, 759-6595, Japan Article History: Registration Date: 17/09/2004

The lattice Boltzmann method (LBM) is used to simulate the particle resuspension process in a two-dimensional simple shear flow. At first, the lift force on a single disk-shaped particle attached at the channel wall is computed. It is found that when the particle is allowed to freely move in the viscous fluid, the resulting lift force is smaller than that when the particle is constrained to be stationary. The bulk properties of fluids with particles suspended under various concentrations are numerically calculated. The results agree reasonably well with analytical results by Batchelor when the volume fraction is lower than 50%. The resuspension process of a group of particles (up to 500) is simulated at different particle-to-fluid density ratios. It is found that the height and shape of particle bed depend on the particle density ratio and flow conditions. Interactions of groups of particles as well as the final shape of the bedform of the particles were studied during this resuspension process. Finally, the pressure distribution and flow above the bedform of particles was examined. The results obtained agree well with those observed in naturally occurring bedforms of sediments. DOI: 10.1061/(ASCE)0733-9429(2003)129:12(985) CE Database subject headings: Suspended sediments; Sediment transport; Stratified flow; River flow; River beds; Shear flow; Particles.

Studies of wavy stratified and stratified/atomization two-phase flow in horizontal pipes are outlined. Notable features of this flow regime include the appearance of disturbance waves, the atomization onset and the drastic change of the gas/liquid interface profile from flat to 'concave.' Liquid-to-wall shear stress tends to decrease circumferentially. A computational procedure for predicting main flow characteristics, which takes into account the above results in its design relations, is first assessed with detailed experimental data and is then combined with a CFD code, aiming at enhancing the predictive capability. [DOI: 10.1115/1.1576265] Keywords: Gas/Liquid Flow, Stratified Flow, Horizontal Pipes, Liquid Holdup, Pressure Drop, Shear Stress, Computational Method.

A silicon sensor is developed and its ability to measure both compressive and shear forces at the skin--object interface is characterized. The sensor is designed based on the piezoresistive effect and fabricated using integrated circuit and microelectromechanical systems technologies. The sensor utilizes a mesa structure that leads to asymmetric diaphragm deformations in response to nonnormal loading. Four independent ion-implanted piezoresistors are used to detect the stresses induced in diaphragm and resolve both the compressive- and shear-force components. The sensor is calibrated on human subjects over a range of applied force (5- to 40-N shear force at increments of 1.25 N; 0- to 30-N compressive force). Force measurement via a tracking experiment is evaluated at four shear (9, 18, 25, and 35 N) and three compressive (7,15, and 26 N) force levels. The sensor has good repeatability (SD [congruent to] 1.7 N) with an average error of 12.1%. Index Terms--Force, human--object interface, MEMS, sensor, shear, silicon.

Local bed shear stress ([[tau].sub.w]) is a fluid dynamic parameter of importance in determining the physical and biological characteristics of stream-bed environments. Unfortunately, it is often difficult to measure ([[tau].sub.w]) under field conditions. Herein we describe the use of a Preston-static tube, which is essentially a surface-mounted Pitot-static tube, to measure [[tau].sub.w] in mountain streams. Our results indicate that it is possible to measure local shear stress quickly, consistently, and inexpensively in the field. This technique also provides high spatial resolution, which should allow for detailed in situ studies of local shear stress at scales relevant to lotic organisms. Such information will be invaluable in studies of benthic organisms and hydraulically relevant phenomena in the near-bottom zone of lotic systems.

In this paper, a new series expansion for calculating the bending moment and the shear force in a proportionally damped, one-dimensional distributed parameter system due to moving loads is suggested. The number of moving forces, which may be functions of time and spatial coordinate, and their velocities are arbitrary. The derivation of the series expansion is not limited to moving forces that are a priori known, making this method also applicable to problems in which the moving forces depend on the interactions between the continuous system and the subsystems it carries, e.g., the moving oscillator problem. A main advantage of the proposed method is in the accurate and efficient evaluation of the bending moment and shear force, and in particular, the shear jumps at the locations where the moving forces are applied. Numerical results are presented to demonstrate the rapid convergence of the new series representation.

A model is presented to determine the threshold shear stress for noncohesive sediment (uniform and nonuniform) motion on horizontal and stream-wise sloping sedimentary beds, under a unidirectional steady-uniform streamflow. Hydrodynamic and particle-mechanic forces on a solitary sediment particle, resting over a sedimentary bed under the slip-spinning condition, are analyzed including the effect of turbulent fluctuations. Hydrodynamic forces such as drag, shear lift, and Magnus lift are taken into consideration. The drag coefficient is determined using an empirical formula. The inclusion of Magnus lift is significant because spherical particles spin just before dislodging downstream from their original position due to the differential hydrodynamic force along the vertical. The experimental data of sediment threshold are used to calibrate the model making the lift coefficient as a free parameter. The dependency of normalized threshold shear stress on particle parameter for various angles of repose and stream-wise bed slopes is presented graphically. The results obtained using the present model are compared with the curves proposed by different investigators and the experimental data of sediment (uniform and nonuniform) threshold for horizontal and stream-wise sloping beds.

Research is conducted to examine turbulent heat fluxes in homogeneous curved shear flow. The measurements are performed far downstream of a thermal line source in both destabilized and stabilized curved shear flow. The curvature is observed to affect the heat fluxes due to its impact on the turbulence kinetic energy of the flow. Results are in good agreement with previous findings showing that momentum transport in curved boundary layers are more strongly affected by flow curvature than heat transport.

Experimental results, obtained from hot-wire measurements using a conditional sampling technique, demonstrate feasibility of controlling large-scale spanwise vortices (coherent structures) in the near wake region behind a rectangular base by means of suction through a slit at just one of the trailing edges. The suction thus employed, is found to influence the near wake topology with strong asymmetry and disturb the net vorticity balance. Moreover, a significant reduction in the base drag is achieved as a consequence of the trailing edge suction. The mechanism of the drag reduction is understood to lie in a marked change in the wake dynamics including attenuation in the size and strength of the coherent structures.

A turbulence probability density function (pdf) equation model is employed to solve a self-similar turbulent plane shear layer. The proper similarity variable was introduced into the problem of interest to reduce the pdf equation into a spatially one-dimensional equation, which is still three dimensional in velocity space. Then the approximate moment method is employed to solve this simplified pdf equation. By the solutions of this equation, the various one-point mean quantities are immediately available. Agreement of the calculated mean velocity, turbulent energy and Reynolds stress with the available experimental data is generally satisfactory indicating that the pdf equation model and the moment method can quantitatively describe the statistics of free turbulence. Additionally, the balance of turbulence energy was calculated and discussed subsequently. It shows that the pdf methods are of more potential in revealing turbulence structure than conventional turbulence models.

Stability analyses, simplified problems, and practical applications demonstrate the extension of time-marching computation of flows with arbitrary equations of state. Applications to flows of supercritical hydrogen was made to prove the effectivity of a unified preconditioning method. Both perfect gas cases and incompressible flows were also considered to demonstrate generality.

Prediction of a spatially developing three-dimensional turbulent boundary layer over a bump swept at 45 deg with respect to upstream flow can be accomplished via large eddy simulation (LES) and Reynolds-averaged Navier-Stokes (RANS) computation. The LES utilized the parameterization of subgrid-scale stresses while RANS used the the v2-f and Spalart-Allmaras single-equation models. Mean flow is accurately defined by both techniques. However, turbulence kinetic energy predictions using RANS was not totally reliable.

The results of new experiments on bed load transport on steep longitudinal slopes are presented. The experiments were carried out in a large tilting duct with a fine sand ([d.sub.50] = 208 [[micro]meter]) covering the range of slope angles [Beta] of [+ or -] angle of repose for the sand [Phi], (32 [degrees]). Measurements included bed shear-stress, flow discharge, and the sediment pickup rate on slopes. The results suggest that existing theories for bed load transport on slopes are not adequate for all bed slopes and the new data are used to formulate a semiempirical relation that satisfactorily predicts the transport rate on horizontal as well as mild and steep slopes. The following are two important findings: (1) Correcting the threshold term (for slope) in the Meyer-Peter and Muller formula adequately describes the transport rate on positive slopes (elevation increasing in direction of flow) and on small negative slopes. On steeper negative slopes an extra correction term is required, although the value of [Beta]/[Phi], at which this term becomes necessary is a function of shear stress; and (2) the influence of slope vanishes at high shear stresses.

Using a Laser-Doppler anemometer, mean velocities are measured in developing and fully developed turbulent subcritical smooth open channel flows. Experiments are conducted in a rectangular laboratory channel for 12 different test conditions with Reynolds number ranging from 28,026 to 136,842. From the experiments it is found that the boundary layer along the centerline of the channel develops up to the free surface for a flow aspect ratio b/h [greater than or equal to] 3. Shear velocities are calculated using the measured velocity profiles in the viscous sublayer of the boundary flow. The experiments show that shear velocity varies in an oscillatory manner across the flow section around b/h = 3. In the turbulent inner regions of developing and fully developed boundary flows, the measured velocity profiles agree well with the logarithmic 'law of the wall' distribution when the coefficients in the expression are 2.44 and 5.5, respectively. The 'wake' effect becomes important in the velocity profiles of the fully developed boundary layers. A reasonable agreement between the modified velocity-defect law and the experimental profile in the inner and outer regions is obtained with a profile parameter of 0.1 in the Coles's 'law of the wake.'

The goal of this study was to determine how vessel compliance (wall motion) and the phase angle between pressure and flow waves (impedance phase angle) affect the wall shear rate distribution in an atherogenic bifurcation geometry under sinusoidal flow conditions. Both rigid and elastic models replicating the human abdominal aortic bifurcation were fabricated and the wall shear rate distribution in the median plane of the bifurcation was determined using the photochromic flow visualization method. In the elastic model, three phase angle conditions were simulated (+12, -17, -61 deg), and the results compared with those obtained in a similar rigid model The study indicates a very low (magnitude close to zero) and oscillatory wall shear rate zone within 1.5 cm distal to the curvature site on the outer (lateral) wall. In this low shear rate zone, unsteadiness (pulsatility) of the flow greatly reduces the mean (time-averaged) wall shear rate level Vessel wall motion reduces the wall shear rate amplitude (time-varying component) up to 46 percent depending on the location and phase angle in the model. The mean wall shear rate is less influenced by the wall motion, but is reduced significantly in the low shear region (within 1.5 cm distal to the curvature site on the outer wall), thus rendering the wall shear rate waveform more oscillatory and making the site appear more atherogenic. The effect of the phase angle is most noteworthy on the inner wall close to the flow divider tip where the mean and amplitude of wall shear rate are 31 and 23 percent lower, respectively, at the phase angle of-17 deg than at -61 deg. However, the characteristics of the wall shear rate distribution in the low shear rate zone on the outer wall that are believed to influence localization of atherosclerotic disease, such as the mean wall shear rate level, oscillation in the wall shear rate waveform, and the length of the low and oscillatory wall shear rate zone, are similar for the three phase angles considered. The study also showed a large spatial variation of the phase angle between the wall shear stress waveform and the circumferential stress waveform (hoop stress due to radial artery expansion in response to pressure variations) near the bifurcation (up to 70 deg). The two stresses became more out of phase in the low mean shear rate zone on the outer wall (wall shear stress wave leading hoop stress wave as much as 125 deg at the pressure-flow phase angle of -61 deg) and were significantly influenced by the impedance phase angle.

The flow field inside a model of a polytetrafluoroethylene (PTFE) canine artery end-to-side bypass graft was studied under steady flow conditions using laser-Doppler anemometry. The anatomically realistic in vitro model was constructed to incorporate the major geometric features of the in vivo canine anastomosis geometry, most notably a larger graft than host artery diameter. The velocity measurements at Reynolds number 208, based on the host artery diameter, show the flow field to be three dimensional in nature. The wall shear stress distribution, computed from the near-wall velocity gradients, reveals a relatively low wall shear stress region on the wall opposite to the graft near the stagnation point approximately one artery diameter in axial length at the midplane. This low wall shear stress region extends to the sidewalls, suture lines, and along the PTFE graft where its axial length at the midplane is more than two artery diameters. The velocity distribution inside the graft model presented here provides a data set well suited for validation of numerical solutions on a model of this type.

The extensional viscosity measurement technique helps in evaluating the interaction between ingredients, and the sensory properties of sugar and syrup solutions. The rheological technique, combined with shear viscosity measurement, shows that syrup thickened with xanthan gum is more pseudoplastic and extensionally thinning than that thickened with cellulose gum only. An increase in the strain rate leads to an increase in the viscosity of the extensional flow. The viscosity of the xanthan gum decreases with an increase in the strain rate.

A rotational parallel plate rheometer that enables simultaneous measurement of the transient or steady-state rheological properties and infrared dichroism was designed and constructed to study orientation in molten polymers. Measurements can be carried out at shear rates between 0.05 and 300 [s.sup.-1] and at temperatures between 20 and 300 ° C. Both shear stress and axial normal force together with dichroism are continuously measured during shear flow. Infrared dichroism data for polypropylene showed excellent agreement with data obtained with a FTIR-instrument. The Hermans orientation function for molten poly(dimethyl siloxane) at steady state showed a strong shear-rate dependence in the region 0.1-20 [s.sup.-1]. Rheological data for molten poly(dimethyl siloxane) agrees with data obtained from a conventional rheometer., INTRODUCTION We describe the design and the operation of a novel rotational rheometer that includes a system for the measurement of infrared dichroism. We demonstrate that reliable rheological data can [...]

Fully developed compound shear and buoyancy driven mixing layers are predicted using a k-[Epsilon] turbulence model. Such mixing layers present an exchange of equilibrium in mixing flows. The k-[Epsilon] buoyancy constant [C.sub.[Epsilon]3] = 0.91, defined in this study for buoyancy unstable mixing layers, is based on an approximate self-similar analysis and an accurate numerical solution. One-dimensional transient and two-dimensional steady calculations are presented for buoyancy driven mixing in a uniform flow field. Two-dimensional steady calculations are presented for compound shear and buoyancy driven mixing. The computed results for buoyancy alone and compound shear and buoyancy mixing compare well with measured data. Adding shear to an unstable buoyancy mixing layer does not increase the mixing growth rate compared with that from buoyancy alone. The nonmechanistic k-[Epsilon] model which balances energy generation and dissipation using constants from canonical shear and buoyancy studies predicts the suppression of the compound mixing width. Experimental observations suggest that a reduction in growth rate results from unequal stream velocities that skew and stretch the normally vertical buoyancy plumes producing a reduced mixing envelope width.

We present a Preston tube device that combines both total and static pressure readings for the measurement of wall shear stress. As such, the device facilitates the measurement of wall shear stress under conditions where there is streamline curvature and/or over surfaces on which it is difficult to either manufacture an array of static-pressure taps or to position a single tap. Our 'Preston-static' device is easily and conveniently constructed from commercially available regular and side-bored syringe needles. The pressure difference between the total pressure measured in the regular syringe needle and the static pressure measured in the side-bored one is used to determine the wall shear stress. Wall shear stresses measured in pipe flow were consistent with independently determined values and values obtained using a conventional Preston tube. These results indicate that Preston-static tubes provide a reliable and convenient method of measuring wall shear stress.

Atherosclerosis, thrombosis, and intimal hyperplasia are major forms of cardio-vascular diseases in the United States. Previous studies indicate a significant correlation between hemodynamics, in particular, wall shear rate, and pathology of the arterial walls. While results of these studies implicate morphologic and functional changes related to wall shear rate magnitude, a standard technique for wall shear rate measurement has not been established. In this study, theoretical and in-vitro experimental fully developed steady and physiologic pulsatile flow waveforms have been used to obtain velocity profiles in the near-wall region. The estimated wall shear rates from these results are compared to the theoretical value to assess the accuracy of the approximating technique. Experimentally obtained results from LDA suggest that in order to minimize the error in velocity data, and subsequently, the wall shear rate, the first measured velocity has to be 500 [[micro]meter] away from the wall. While a linear approximation did not produce errors larger than 16.4 percent at peak systole, these errors substantially increased as the velocity magnitudes decreased during late systole and diastole. Overall, a third degree polynomial curve fit using four points produced the most accurate estimation of wall shear rate through out the cardiac cycle. Results of higher degree curve-fitting functions can be unpredictable due to potential oscillations of the function near the wall. Hence, based on the results of this study, use of a linear approximation is not recommended; a third degree curve-fitting polynomial, using four points provided the most accurate approximation for these flow waveforms.

The large amplitude oscillatory shear test has been used to discriminate subtle differences in nonlinear viscoelasticity between two high density polyethylene blow molding resins with different processability. Structural network theory was used to explain the subtle differences in terms of entanglement kinetics with remarkable accuracy. The resin with better shape retention characteristics in programmed parison blow molding was found to have a higher kinetic rate constant for molecular re-entanglement.

Previous research on the numerical prediction of turbulent shear flow over two- or three-dimensional prismatic obstacles omitted the second term of the continuity equation, thereby making it difficult to obtain the first term of the equation. This makes the equation virtually useless for wind engineering applications. The presentation of the time-averaged quantities for three-dimensional flow over a cubical obstacle is also inadequate. In addition, the prohibitive cost for time-averaged flow calculation is appropriate only for the computation of unsteady wind pressures.

A sliding plate rheometer has been developed to measure the normal thrust of a molten plastic in large amplitude oscillatory shear. The normal thrust of a molten plastic in large amplitude oscillatory shear is a significant nonlinear effect that has previously been unobtainable. Normal thrust measurements may now be used to help understand and characterize nonlinear viscoelastic behavior inherent in most molten plastics. The new rheometer incorporates a piezoelectric pressure transducer in a very stiff plate that minimizes compliance. Normal thrust measurements with cone and plate rheometers are made by measuring the total force on the plate (or cone) and are subject to error due to edge effects. The new rheometer measures the local pressure in the sample and is therefore unaffected by sample size or edge effects. Normal thrust measurements in large amplitude oscillatory shear are reported for both molten Phillips TR480 high density polyethlene pipe resin which contains 2% by weight of carbon black filler and IUPAC LDPE X. Crosstalk due to shear stress on the active face of the pressure transducer causes signal error which for oscillatory shear is filtered out using a discrete Fourier transform.

Energy balance studies on the structure of turbulence close to a free surface reveals that the pressure-strain term dominates the spanwise component of turbulent kinetic energy. Dissipation rates for horizontal components of turbulence are markedly attenuated close to the free surface while dissipation rate for vertical components is constant. Vital free surface induced effects are revealed by two-point correlations, energy spectra and length scales.

Cohesive sediment beds Occur in a variety of natural and man-made environments. A parameter that has a very significant influence on the sediment behavior is the critical shear stress. This is the shear stress at the sediment surface above which erosion will take place. The critical shear stress can be evaluated in the laboratory under conditions closely resembling those found in the field by use of an annular flume. The main purpose of the work described in this paper is to determine experimentally and numerically the velocity and surface shear stress fields generated by the flow of water in an annular flume. Very good agreement is found between measured circumferential velocity profiles, obtained by laser doppler anemometry, and profiles predicted by the computational fluid dynamics program HARWELL-FLOW3D. Measurements of the bed and wall shear stresses are made using hot-film probes and these also agree reasonably well with numerical predictions. Also of interest is the dependence of the sediment shear strength on sediment depth. By comparing measured eroded sediment contours with predicted shear stress profiles a simple method emerges for describing this dependence.

A novel substrate micromachining step is presented for wafer front-to-backside alignment. The single-etch, single-mask process uses resist-patterned etch control to produce various final thicknesses on a single-crystal silicon wafer. It was employed to simplify the fabrication of wafers with two-sided alignment as thin film microphones. The new approach may also be implemented on other microdevices manufactured by integrated circuit technology.

The design of a microfabricated floating-element sensor is presented. Fabricated via wafer-bonding technology, the sensor measures liquid shear stresses at high levels and at high pressure. An analytical and finite element analysis of the device's operation in a cone and plate viscometer is described alongside test results of its mechanical strength in high pressure surroundings. The sensor was developed for application in the industrial extrusion process.

An evaluation of a second-order finite-volume method for studying transition flows is presented. The method has previously been used in computing Navier-Stokes equations for laminar flows. A parallel shear layer perturbing at one or more wavelengths is analyzed and the interaction and behavior of unexcited modes are investigated. Results show that the method can correctly predict the mechanics of a turbulence of any amplitude with sufficient spatial resolution. The behavior of multiple modes could also be forecast if the modes are excited at similar amplitudes.

A commercial thermotropic polyesteramide and its blends with polyarylate are the object of a slit die flow rheological study. The measurements are carried out at 280 [degrees] C, a temperature slightly above the melting temperature of the thermotropic, covering a shear rate range [10.sup.-1] [s.sup.-1] to [10.sup.2.s.sup.-1]. Except in the case of the thermotropic polymer, the pressure profiles are upward parabolic which is attributed to the dependence of the viscosity on pressure. The most striking result is the observed downward curvature in pressure profiles obtained for the liquid crystalline polyesteramide: no explanation is given for this phenomenon, for the present. The elasticity of the polymer melts is expressed in terms of the exit pressure and the extrudate swell. The thermotropic polyesteramide presents negative values of both parameters (e.g. samples shrink instead of swell). Viscosity and elasticity present negative deviation from linearity when plotted against composition; this reduction in the rheological functions, caused by the addition of the liquid crystal, is more pronounced at high shear rates., A slit die flow rheological analysis measures a commercial thermotropic polyesteramide and its blends with polyarylate at 280 degrees Celsius and with a shear rate range of 10 to the negative first power s to the negative first power to (10)(2)s to the negative first power. The dependence of the viscosity on pressure causes the upward parabolic curves of all pressure profiles except for the thermotropic polymer. However, liquid crystalline polyesteramide pressure profiles show a downward curvature and negative values of exit pressure and the extrudate swell.

An exact solution is obtained for the three-dimensional deformations of simply supported laminated rectangular thick plates with embedded shear mode piezoelectric actuators, subjected to mechanical and electrical loading on the upper and lower surfaces. Each layer of the laminate is made of either an orthotropic elastic material or a piezoelectric material whose poling direction lies in the plane of the plate, with perfect bonding between the adjoining layers. The exact displacements and stresses for a homogeneous piezoelectric plate for various length-to-thickness ratios are compared with those obtained by the first-order shear deformation theory. Results are also presented for a sandwich plate consisting of a shear mode piezoelectric core sandwiched between two elastic layers. A comparison of the stresses with those in the corresponding surface-mounted extension actuation configuration shows that for the same transverse deflection of the plate centroid, the maximum longitudinal stress within the actuator is significantly smaller for the shear actuation mechanism. The exact results presented here can be used to assess the accuracy of different plate theories and/or for validating finite element codes.

The flow through a curved tube model of a coronary artery was investigated computationally to determine the importance of time-varying curvature on flow patterns that have been associated with the development of atherosclerosis. The entry to the tube was fixed while the radius of curvature varied sinusoidally in time at a frequency of 1 or 5 Hz. Angiographic data from other studies suggest that the radius of curvature waveform contains significant spectral content up to 6 Hz. The overall flow patterns were similar to those observed in stationary curved tubes; velocity profile skewed toward the outer wall, secondary flow patterns, etc. The effects of time-varying curvature on the changes in wall shear rate were expressed by normalizing the wall shear rate amplitude with the shear rate calculated at the static mean radius of curvature. It was found that the wall shear rate varied as much as 94 percent of the mean wall shear rate at the mid wall of curvature for a mean curvature ratio of 0.08 and a 50 percent change in radius of curvature. The effects of 5 Hz deformation were not well predicted by a quasi-static approach. The maximum values of the normalized inner wall shear rate amplitude were found to scale well with a dimensionless parameter equivalent to the product of the mean curvature ratio ([Delta]), normalized change in radius of curvature ([Epsilon]), and a Womersley parameter ([Alpha]). This parameter was less successful at predicting the amplitudes elsewhere in the tube, thus additional studies are necessary. The mean wall shear rate was well predicted with a static geometry. These results indicate that dynamic curvature plays an important role in determining the inner wall shear rates in coronary arteries that are subjected to deformation levels of [Epsilon][Delta][Alpha] [is greater than] 0.05. The effects were not always predictable with a quasi-static approach. These results provide guidelines for constructing more realistic models of coronary artery flow for atherogenesis research. [DOI: 10.1115/1.1351806]

Computational techniques are widely used for studying large artery hemodynamics. Current trends favor analyzing flow in more anatomically realistic arteries. A significant obstacle to such analyses is generation of computational meshes that accurately resolve both the complex geometry and the physiologically relevant flow features. Here we examine, for a single arterial geometry, how velocity and wall shear stress patterns depend on mesh characteristics. A well-validated Navier-Stokes solver was used to simulate flow in an anatomically realistic human right coronary artery (RCA) using unstructured high-order tetrahedral finite element meshes. Velocities, wall shear stresses (WSS), and wall shear stress gradients were computed on a conventional 'high-resolution' mesh series (60,000 to 160,000 velocity nodes) generated with a commercial meshing package. Similar calculations were then performed in a series of meshes generated through an adaptive mesh refinement (AMR) methodology. Mesh-independent velocity fields were not very difficult to obtain for both the conventional and adaptive mesh series. However, wall shear stress fields, and, in particular, wall shear stress gradient fields, were much more difficult to accurately resolve. The conventional (nonadaptive) mesh series did not show a consistent trend towards mesh-independence of WSS results. For the adaptive series, it required approximately 190,000 velocity nodes to reach an r.m.s. error in normalized WSS of less than 10 percent. Achieving mesh-independence in computed WSS fields requires a surprisingly large number of nodes, and is best approached through a systematic solution-adaptive mesh refinement technique. Calculations of WSS, and particularly WSS gradients, show appreciable errors even on meshes that appear to produce mesh-independent velocity fields. [DOI: 10.1115/1.1351807]

Measurements of mean velocity and turbulent shear stress are presented for the mixing region of a film cooling situation in which the coolant is streamwise injected with an injection angle of 35 deg. Measurements are performed using triple-sensor anemometry so that all three instantaneous velocity components are documented. The free-stream turbulence intensity level is 12 percent, the ratio of the integral length scale to injection hole diameter is 4.0, the coolant-to-mainstream momentum flux ratio is 1.0, and the density ratio is unity. From these measurements, values for the eddy diffusivities of momentum in the lateral and wall-normal directions are calculated. Additionally, calculated values of the ratio of eddy diffusivity in the spanwise direction to eddy diffusivity in the wall-normal direction are presented, which provide documentation of the anisotropy of turbulent transport in this film cooling flow.

Author Affiliations: An analysis of almost 15 million distant galaxies reveals that dark matter may be slightly less dense and more evenly distributed throughout space than was thought. Dark matter [...]

Recent developments in computing turbulent and buoyant flow in sedimentation tanks are introduced. The test case is a circular, center-feed secondary clarifier with inclined bottom and central sludge withdrawal. Axisymmetry is assumed, and the flow and settling processes are modeled in a radial section by using the [Kappa]-[Epsilon] turbulence model on a two-dimensional, nonorthogonal grid. The computation domain includes the sludge blanket where the viscosity is affected by the theological behavior of the sludge. The aim of the present study is to evaluate the sensitivity of the flow and concentration fields to parameters that characterize (1) the rheological properties of highly concentrated regions; (2) the settling of sludge; and (3) the effect of stratification on the turbulent diffusion. The overall appearance of the fields proves to be similar, whereas the regions of high velocities and high gradients are strongly affected by using different parameters or approaches on theology, settling, and diffusive transport, resulting in different sludge blanket heights.