Velocity Reynolds Number Research Articles

Condensation of pure steam and steam-air mixture with surface waves of condensate film on a vertical wall

A series of experiments has been conducted to investigate the effect of wavy interface on film condensation with and without a noncondensable gas present on a vertical wall. Concurrently, the instantaneous film thickness was measured. Overall heat transfer coefficients across the condensate film and the diffusion layer formed by a noncondensable gas were obtained in various parameters such as air-mass fraction (W = 0.1–0.7), mixture vapor velocity (Uin = 3, 5, 7 m/s) and condensate film Reynolds number (Reff,in= 0–19,000). In order to investigate the heat transfer enhancement induced by a dynamic interaction of the surface waves on condensate and the diffusion layer, vapor-side heat transfer coefficient was estimated from the measured overall heat transfer coefficient and the correlation of film-side heat transfer coefficient, and compared with that estimated by Colburn and Chilton-Colburn analogy for a smooth flat plate. The comparison showed that the vapor-side heat transfer coefficient increased clearly with the increase of film Reynolds number. The enhancement effect was dominant for low mixture vapor velocity and decreased with the increase of mixture vapor velocity.

The Influence of Fuel Jet Precession on the Global Properties and Emissions of Unconfined Turbulent Flames

Abstract An investigation was conducted to characterize the shape and size, the global radiation, and the CO and NOx, emissions of precessing jet flames and to compare these results with conventional, free, turbulent jet diffusion flames. Jet precession was accomplished using a mechanically-rotated nozzle. Parameters varied include nozzle diameter, jet deflection angle, initial jet velocity (Reynolds number), dimensionless precession frequency (Strouhal number), and fuel type. Measured quantities included visible flame dimensions; NOx, NO2, and CO emissions; and radiant heat flux. Results of these experiments showed that two broad regimes of flame type exist for precessing jet flames. For precession Strouhal numbers (St p ) less than about 0.01, flames are non-luminous and, in comparison with conventional flames, are short and broad. For St p > 0.03, flames are highly luminous, and of a shape which is between that of a conventional jet flame and the low-St p flame. In general, radiant fractions increase w...

A fluid dynamic analysis using flow visualization of the Baylor/NASA implantable axial flow blood pump for design improvement.

The Baylor/NASA Axial Blood Flow Pump has been developed for use as an implantable left ventricular assist device (LVAD). The pump is intended as an assist device for either pulmonary or systemic circulatory support for more than 3-months' duration. To date the pump provides acceptable results in terms of thrombus formation and hemolysis (IH of 0.018 g/100 L). A fluid dynamics analysis using flow visualization was performed to investigate the flow fields and to determine areas within the pump that could be improved. These studies focused upon the inflow area in front of the pump. A prototype axial flow pump assembly was constructed to facilitate the flow visualization studies. Particle image tracking velocimetry techniques were used to measure Amberlite particles suspended in a blood analog fluid composed of 63% water and 37% glycerin. This method used a pulsed (612 Hz) laser light to determine flow velocity profiles, shear stress, Reynolds numbers, and stagnant areas within the axial pump. These studies showed that the flow straightener (a vaned assembly in the pump inflow) reduced Reynolds numbers from 4,640 to 2,540 (at 8.5 L/min) and that the flow straightener exacerbates a discontinuity found between it and the impeller. Within the inflow area, a maximum of 80 N/m2 shear stress was measured, which is well below published blood damage thresholds. Design variations were investigated resulting in a smoother flow transition between flow straightener and impeller. These variations must be investigated further to establish a correlation with hemolysis and thrombus formation.

Hydraulic parameters and benthic invertebrate distributions in two gravel‐bed New Zealand rivers

SUMMARY1. Benthic invertebrates were sampled over a matrix of about eighty combinations of mean velocity (10–150cms−1) and depth (10–150cm) in two rivers that differed in substrate size variability. Vertical velocity profiles were measured at each sample site and substratum roughness was measured and estimated from percentage cover by stone size classes. The influence of depth on periphyton biomass was also measured.2. The hydraulic and substrate data were used to investigate the correlations between conventional (mean velocity, depth, substrate size) and complex hydraulic variables (Froude number, shear velocity, and water column and boundary Reynolds number) that were either calculated from direct measurements or inferred from mean velocity, depth, kinematic viscosity and substrate roughness. The ecological relevance of these hydraulic variables was investigated by comparing their degree of correlation with invertebrate densities and community metrics.3. The invertebrate variables had similar correlations with mean velocity and the complex near‐bed hydraulic variables in the river with uniform cobble substrates. In the river with diverse substrates, however, average correlations with Froude number, and inferred shear velocity and boundary Reynolds number were 25–45% higher than with velocity. Of all the individual hydraulic parameters, the boundary Reynolds number, calculated from simple measures, was most strongly correlated with benthic invertebrate distributions and taxa richness. However, invertebrate distributions were more strongly correlated with predictions of multiple regression models, incorporating substrate size, depth and mean velocity, than with any single hydraulic variable.4. Hydraulic influences on food availability and oxygen concentration in the benthos are likely mechanisms affecting the hydraulic preferences of several taxa. Lower periphyton biomass with depth, partly attributable to light attenuation, appeared to have a non‐hydraulic influence on a collector‐browser species.

Correlation of Mass Transfer Coefficient in Stratified Gas‐Liquid Two‐Phase Flow in a Horizontal Rectangular Duct

AbstractLiquid‐side mass transfer coefficients were determined using a horizontal rectangular duct (3cm x 3cm and 4m length) with carbon dioxide desorbing from water and from aqueous solutions of malt syrup. Simultaneously, measurements were made of the parameters characterizing the liquid film flow such as the liquid film thickness and surface velocity. Experiments were mainly conducted within the range of stratified gas‐liquid two‐phase flow. Based on the analogy between mass and momentum transfer at the liquid film surface, the experimental data for the liquid‐side mass transfer coefficient were correlated with the liquid‐film flow velocity. In order to estimate the parameters of film flow, a correlation for the average film thickness was obtained, and the surface velocity was represented graphically as a function of the gas velocity, slip velocity and superficial liquid Reynolds number.

Life and Death in Moving Fluids: Hydrodynamic Effects on Chemosensory‐Mediated Predation

Previous studies in taxonomically diverse marine animals have established the general existence, and importance, of the olfactory sense in a wide variety of behavioral processes. Evidence suggests that the sense of smell mediates predatory search in many marine animals. Past investigations have not, however, been designed to link either the degree of successful olfactory—mediated search or guidance mechanisms with the hydraulic environment in which predatory activities naturally take place. In an effort to examine the interaction between hydrodynamics and chemoreception, we investigated predatory success and search strategies of blue crabs foraging in controlled hydrodynamic environments generated in a flume. Hydrodynamics were characterized by quantifying boundary layer shear velocity (°) and roughness Reynolds number (Re°), two measures that describe the structure of boundary layer flows. Flow properties affected the ability of crabs to orient to odor plumes emanating from actively pumping infaunal bivalves (Mercenaria mercenaria). High flow speed or large sediment particle size increased boundary layer turbulence, thereby decreasing the success of crab chemo—orientation ability. In addition, high flow speed also lessened the probability that crabs contacted odor plumes. Thus, habitats with high flows can provide hydrodynamic refuges from olfactory—mediated predation. Because search ability is contingent on the magnitude of boundary layer turbulence, olfactory—mediated predation may also be ineffective in slow flows, if bottom roughness elements can generate sufficient turbulence. Further, search ability in blue crabs is extremely sensitive to small changes in benthic boundary layer structure. The presence of a thick viscous sublayer, dominated by quasilaminar flow, seems especially critical for successful location of an odor source by crabs. Benthic estuarine crustaceans inhabit an environment where flows are transitional between smooth—and rough—turbulence conditions. Accordingly, chemosensory systems appear geared primarily to extracting information from hydraulically smooth flows. These results indicate that mechanisms governing the physical transport of odor signals can have profound influences, not only on the development of sensory and behavioral mechanisms, but also on biotic interactions such as predation, which, in turn, can mediate community structure.

Parameters governing the turbulent wall jet in an external stream

Mean velocity distributions in a plane, turbulent, and fully developed wall jet embedded in a uniform stream were measured for a variety of initial velocity ratios and Reynolds numbers. It was determined that the bulk of the flow is self-similar, provided the maximum velocity in the jet is twice as large as the freestream velocity. The normalized velocity profile depends on two velocity scales and on two length scales that, in turn, depend on the momentum flux at the nozzle, the viscosity, and the initial velocity ratio between the jet and the freestream defined by R≡(U j -U ∞)/(U j +U ∞). The width of the nozzle that was commonly used to reduce these data has no part in the similarity considerations

Numerical simulation of two-dimensional blunt body sampling in viscous flow

This paper presents a numerical investigation of the aspiration efficiency of a cylindrical blunt body sampler with a forward facing suction opening. The paper: (1) describes and validates the numerical procedure for calculating laminar viscous flow around a two-dimensional blunt cylindrical sampler; (2) combines the flow field calculations with particle dynamics to determine the aerosol aspiration efficiency of the sampler as a function of the particle Stokes number, with a physical explanation for the shape of the aspiration efficiency curve; and (3) examines the effects of the suction to freestream velocity ratio, Reynolds number, and suction opening size on the viscous flow field and aspiration efficiency. The results of the study indicate the particle size ranges and flow conditions where the viscous boundary layer affects the aerosol sampling process. Comparing the results from the viscous calculations with results from inviscid calculations shows qualitative agreement but quantitative differences. In particular, the viscous calculation produces generally lower aspiration efficiencies, indicating that the viscous boundary layer can play an important role in particle inhalability.

Velocity of Particles Falling in Vertically Oscillating Flow

The instantaneous velocity of particles driven by an oscillating flow can be determined by means of Fourier analysis. A simple numerical method based on the principle of least square error is presented to obtain the solutions of the Fourier coefficients. The computed zeroth harmonic term, which is the effective fall velocity and is less than the terminal velocity in still fluid, is in good agreement with experimental observations. The reduced velocity is caused by the nonlinear modification of the drag force exerted on the particle by the fluid because the relative velocity between the particle and the fluid is no longer the constant terminal velocity. There are three parameters that determine the effectiveness of fall velocity reduction: The terminal velocity Reynolds number, the ratio of the flow velocity amplitude to the terminal velocity, and a quantity characterizing the frequency response of the particle to the unsteadiness of the flow motion.

Generalized Correlations for Inertial Impaction of Particles on a Circular Cylinder

The trajectories of spherical particles impacting a relatively larger circular cylinder in crossflow are calculated using finite difference methods to solve the equations of motion in a Lagrangian form. Drag forces on the particles are described using an empirical correlation for the drag coefficient (as a function of Reynolds number) and the solution for steady, inviscid, incompressible flow (potential flow) around a circular cylinder. Numerical integration of the particle equations of motion is started upstream of the cylindrical target, and calculations are carried out until the particle impacts the cylinder or bypasses it completely. The effects of particle interception are neglected. Results for target efficiency and angle of impingement compare favorably with previous numerical solutions at low-particle Reynolds numbers but are found to be more accurate for free-stream velocity Reynolds numbers (Re0) > 1. In addition, results for particle velocity, angle of impact, and particle concentration are pre...

On the structure of jets in a crossflow

Spectral analysis and flow visualization are presented for various velocity ratios and Reynolds numbers of a jet issuing perpendicularly from a developing pipe flow into a crossflow. The results are complete with conditional averages of various turbulent quantities for one jet-to-cross-flow velocity ratio R of 0.5. A unique conditional-sampling technique separated the contributions from the turbulent jet flow, the irrotational jet flow, the turbulent crossflow and the irrotational crossflow by using two conditioning functions simultaneously. The intermittency factor profiles indicate that irrotational cross-flow intrudes into the pipe but does not contribute to the average turbulent quantities, while the jet-pipe irrotational flow contributes significantly to them in the region above the exit where the interaction between the boundary-layer eddies and those of the pipe starts to take place. Further downstream, the contributions of the oncoming boundary-layer eddies to the statistical averages reduce significantly. The downstream development depends mainly on the average relative eddy sizes of the interacting turbulent fields.

Fall Velocity of Particles in Oscillating Flow

The paper presents results of harmonic analysis in studying particle motion in oscillating flows. An approximate equation is derived to solve the zeroth harmonic equation, which governs the effective fall velocity ν¯s, of particles in oscillating flows. The equation reveals that the drag force on the particles is significantly modified by the instantaneous relative velocity between particles and fluids. Three major factors that govern the variation of ν¯s (as compared to the terminal velocity in still water are the terminal velocity Reynolds number, the phase lag, and the velocity amplitudes of the flow and particle oscillations. The dimensionless equation is given. Applying to the sediment suspension under wave action, the analysis suggests that an enhancement of suspension should occur.

色素法による平板に衝突する噴流の流れ様式の観察

Flow visualizatione xperiments were conducted in a water submerged jet to study impingement flow from a long channel with a rectangular exit of aspect ratio five as well as from the one with a circular exit. The flow-types on a large flat plate were observed and classified with the dye-method by mixing blue-black ink with the efflux water. As parameters for the data, the distance from the exit to the plate, the exit velocity( Reynolds number) and the impinging angle caused by rotation of the flat plate around the exit major axis were taken. It is found that: even at normal impingemen tangle the impingement jet of a shorter distance from the rectangular exit to the flat plate flows only along the directions of the exit minor axis; the change of flow direction on the flat plate highly depends on the distance from the exit to the flat plate and on the exit velocity( Reynolds number); and the spreads on the flat plate become larger in case of the turbulent jet impingement than in case of the laminar one. It is postulated that the overall flow field may be strongly influenced by the entrainment of the turbulent flows as well as the arrangement of the exit and the flat plate.

A contribution on the effects of inlet conditions when modelling stenoses using sudden expansions

Using three diameter ratios, and up to four inlet velocity profiles, the laminar flow in axisymmetric sudden expansions is investigated numerically. For inlet Reynolds numbers of 250 or lower, the vortex reattachment length is found to be a linear function of the Reynolds number regardless of either the diameter ratio or inlet velocity profile; however, the inlet velocity profile plays an important role in contributing to a non-linear relationship between the vortex length as a function of the expansion step height. The wall shear-stress distribution in the larger pipe is found to depend strongly upon the diameter ratio, inlet velocity profile and Reynolds number.

Forced-Convection Heat Transfer from Irregular Melting Wavy Boundaries

The problem of turbulent flow past freezing or melting ice is formulated for the case of random boundary waves, with particular attention to the distribution of heat-transfer rate along wavy surfaces. Relations are obtained for the celerity and unsteady spectrum of the boundary waves. The results of 21 laboratory experiments are reported and used to establish the values of certain quantities appearing in the heat-transfer relation adopted. The velocity Reynolds number of the phase shift between the boundary waves and heat-transfer variation is found to have a nearly constant value of 4 × 104.

Numerical Calculations of Turbulent Swirling Flow

A numerical technique is developed for solving axisymmetric, incompressible, turbulent swirling flow problems. The Reynolds stresses are expressed in terms of a scalar turbulent viscosity, μt = ρCμk2/ε. The turbulent kinetic energy, k, and ε, the turbulent energy dissipation rate, are obtained by solving the corresponding transport equations; Cμ is an empirical constant. Flow calculation results are presented for the coaxial flow configuration shown in Fig. 1. Of particular interest is the presence of flow recirculation due to vortex breakdown. Effects of inner and outer swirl, axial velocity ratio and Reynolds number on the formation, size, and location of the recirculation zone are considered.

Incipient Motion and Sediment Transport

A review of existing literature reveals some disadvantages of using Shields diagram as the criterion for incipient motion of sediment particles on an alluvial bed. A new criterion based on average flow velocity, fall velocity, and shear velocity Reynolds number is proposed herein with the supporting data collected by different investigators. This new criterion is used to calculate the dimensionless critical unit stream power in a dimensionless unit stream power equation for sediment transport. The dimensionless unit stream power is the ratio of the time rate of potential energy expenditure per unit weight of water and the terminal fall velocity of the sediment. More than 1,000 sets of data from both laboratory flumes and natural streams published by different authors are used to support this dimensionless equation for sediment transport.

Drilling Hydraulics-A Study of Chip Removal Force Under a Full-Size jet Bit

Abstract Bit hydraulics play an important role in the drilling process. The beneficial action of the fluid's impacting, cleaning the bottom of the hole and the bit teeth, and carrying particles into the annulus is well established. What is not well known or commonly agreed upon is bow this beneficial action can be made most effective. To understand better the drilling hydraulics phenomenon, laboratory tests were carried out with phenomenon, laboratory tests were carried out with full-scale bits and a simulated hole bottom. An earlier paper described the pressure distribution on the hole bottom as it varied with nozzle size, number, and extension. This paper discusses the way the force acting on a stationary chip varies with these same parameters and also includes The effect of chip size and fluid density and viscosity. The results show that closing one or two nozzles or extending the nozzles increases chip removal force and should assist is cleaning the hole and, in some cases, increase penetration rate. Fluid velocity, nozzle diameter, and chip size are the most important factors affecting chip removal force. Fluid viscosity plays a minor role. These findings reinforce and broaden the conclusions reached in the pressure distribution studies. It was also found that chip removal force correlates more closely with jet impact and horse power than with velocity or nozzle Reynolds number. Introduction Bit hydraulics are difficult to study. If tests are carried out in the field, there are uncertainties regarding down-hole conditions and whether these conditions change during a test. If the tests are carried out in the laboratory, results are usually more clear-cut, but then there is the question of how well the tests simulate field conditions. The most reliable insight into the over-all hydraulics problem is probably reached by blending the results problem is probably reached by blending the results of all types of work; no single study fits together more than a few pieces of the intricate puzzle. Past work in drilling hydraulics has been in the following categories: field testing, similar to that of Thompson, Spear, and Eckel; drilling tests in the laboratory, similar to those of Horner el al, van Lingen, Feenstra and van Leeuwen, and Eckel; and laboratory nondrilling tests like those of McLean and Cheatham and Yarbrough. other significant work includes the Kendall and Goins theoretical paper on optimization and that portion of Bingham's series on "a new approach portion of Bingham's series on "a new approach to interpreting rock drillability" that deals with bit hydraulics. The work reported here fits in the category of laboratory nondrilling. It is aimed at explaining how nozzle size, jet velocity, fluid properties, etc., affect what takes place as the fluid leaves the nozzle impinges on the hole bottom, and begins to return to the surface. This work differs from Refs. 4 through 7 in that no actual drilling took place. In a sense, this detracts from its usefulness; on the other hand, we feel that we were able to maintain closer control over test conditions because we did not have the problems of rock variability, drilling fluid problems of rock variability, drilling fluid contamination, and the other phenomena involved in drilling tests. The work in Refs. 8 and 9 described the measurement of velocities and pressures under a jet bit. Maximum jet velocity was 171 ft/sec. The work reported in this paper describes the forces caused by fluid velocities and pressures as they act on a chip. Maximum jet velocity was 286 ft/sec. An earlier paper, described the pressure distribution on the bottom of the hole as it is affected by nozzle size, number, and extension. Conclusions included the desirability of plugging one or two nozzles, using extended nozzles and a correlation of pressure distribution with jet velocity, nozzle diameter, and the distance between the nozzle and hole bottom. The present work is a continuation of the same study and was set up to find out what happens when fluid moving across the hole bottom meets an object in its path. In a sense, it a basic attempt to study hole cleaning under closely controlled conditions.

Feasibility of a high-performance aerodynamic impulse facility.

A study has been conducted to ascertain the feasibility of a high-performance aerodynamic impulse facility capable of producing a high velocity and high Reynolds number environment. Of many facilities considered, those most promising were magnetic annular arc tunnels and expansion tubes as single-stage techniques, and a shock tunnel driving a j X B accelerator as a two-stage technique. The expansion tube can theoretically achieve the conditions required, but experimental results indicate that prohibitive lengths and energies above 108 joules will be required to achieve the times necessary for aerodynamic testing. The shock tunnel driving st j X B accelerator necessary to achieve the environment will be physically large and consequently require more than 108 joules energy, but experiments to date indicate no limitations that will prevent attainment of the desired environment. Experimental performance of the magnetic annular arc (a new device considered for this application) implies that it can achieve the environment considered, but research directed more specifically to this goal must be performed to fully evaluate its potential.

Interaction of the wake from bluff bodies with an initially laminar boundary layer.

An experimental investigation was conducted to determine the mechanism and conditions governing transition induced by small bluff bodies suspended in a laminar boundary layer. The experiment was performed in the inlet section of a tube. The mechanism by which transition occurred appeared to be a local effect dependent upon the stability characteristics of the element wake rather than the stability characteristics of the boundary layer over the range of boundary-layer Reynolds numbers examined. That is, transition of the boundary layer appeared to involve the direct seeding of turbulence in the boundary layer from the wake of the element, rather than amplification of wavelike disturbances as considered in classical boundary-layer stability theory. In the central region of the boundary layer, the critical value of the element Reynolds number which resulted in transition of the boundary layer coincided, approximately, with the Reynolds number for incipient transition in the wake of the element. Laminar vortices shed by disturbance elements at subcritical values of element Reynolds numbers were found to decay in propagating downstream. For elements located outside the boundary layer, transverse turbulence contamination of the boundary layer was found to depend on diffusion of the turbulent wake below a critical (trigger) value of y/d. Turbulent patches were generated by elements traversing the boundary layer when the instantaneous slip velocity Reynolds number was slightly higher than the value of critical Reynolds number for elements fixed within the boundary layer.