bluuebunny/crossref_metadata_2025 huggingface dataset:
Perspective: On the Near Wall Similarity of Three-Dimensional Turbulent Boundary Layers (Data Bank Contribution)
Authors: O¨lc¸men M. S. , Simpson R. L.
Published: May 2008

The possible existence of a “law-of-the-wall” similarity velocity profile for 3-D boundary layers was investigated using nine different proposed relations with the data from nine experiments carried out in 3-D turbulent boundary layers. Both for pressure driven and shear-driven flows, the “law-of-the-wall” relation of Johnston for the local freestream velocity direction component best applies. Although not well described by any relation, the crosswise velocity component of pressure-driven flows and shear-driven flows is best represented by Mager’s relation and Chandrashekhar and Swamy equation, respectively.
Three-Dimensional Finite-Volume Method for Incompressible Flows With Complex Boundaries
Authors: Majumdar S. , Rodi W. , Zhu J.
Published: May 2008

A finite-volume method is presented for calculating incompressible 3-D flows with curved irregular boundaries. The method employs structured nonorthogonal grids, cell-centered variable arrangement, and Cartesian velocity components. A special interpolation procedure for evaluating the mass fluxes at the cell-faces is used to avoid the nonphysical oscillation of flow variables usually encountered with the cell-centered arrangement. The SIMPLE algorithm is used to handle the pressure-velocity coupling. A recently proposed low diffusive and bounded scheme is introduced to approximate the convection terms in the transport equations. The computer code and the relevant data structure are so organized that most of the code except the implicit linear solver used is fully vectorizable so as to exploit the potential of modern vector computers. The capabilities of the numerical procedure are demonstrated by application to a few internal and external three-dimensional laminar flows. In all cases the CPU-time on a grid with typically 28,000 grid nodes was below half a minute.
Vortex Shedding From a Circular Cylinder of Finite Length Placed on a Ground Plane
Authors: Okamoto Shiki , Sunabashiri Yukisada
Published: May 2008

This paper describes a study of changes in the vortex formation and the turbulent wake from a circular cylinder with a finite aspect ratio, placed on a ground plane. The experiment was carried out in an N.P.L. blow down type wind-tunnel, with a working section of 500 mm × 500 mm × 2,000 mm, and between the Reynolds number 2.5 × 104 and 4.7 × 104. The surface-pressure distributions on the circular cylinder were measured and the drag coefficient was determined from these measurements. Vortices of two kinds generated in the flow-field around the cylinder were observed. The power spectrum, auto-correlation, space-correlation, velocity defects, and turbulent intensities in the turbulent wake behind a circular cylinder were also measured. It was found that the flow pattern changed rapidly above aspect ratio H/D = 4, with vortex shedding changing from symmetric “arch” type to antisymmetric “Karman” type.
Redeveloping Turbulent Boundary Layer in the Backward-Facing Step Flow
Authors: Yoo Jung Yul , Baik Se Jin
Published: May 2008

An experimental study has been performed to investigate the redeveloping turbulent boundary layer beyond separation-reattachment for a transitional separated flow. By considering the distribution of the intermittency, it has been confirmed that the turbulent structure changes gradually from a mixing layer to a turbulent boundary layer downstream of reattachment. The balances of the respective terms in the turbulent kinetic energy transport equation are evaluated from the energy dissipation rate obtained through numerical integration of the second moment of the energy spectrum. These terms together with those in the shear stress transport equation indicate the recovery process of the redeveloping boundary layer from nonequilibrium to equilibrium.
Some Characteristics of the Vortical Motions in the Outer Region of Turbulent Boundary Layers (Data Bank Contribution)
Authors: Klewicki J. C. , Falco R. E. , Foss J. F.
Published: May 2008

Time-resolved measurements of the spanwise vorticity component, ωz, are used to investigate the motions in the outer region of turbulent boundary layers. The measurements were taken in very thick zero pressure gradient boundary layers (Rθ = 1010, 2870, 4850) using a four wire probe. As a result of the large boundary layer thickness, at the outer region locations where the measurements were taken the wall-normal and spanwise dimensions of the probe ranged between 0.7 < Δy/η < 1.2 and 2.1 < Δz/η < 3.9, respectively, where η is the local Kolmogorov length. An analysis of vorticity based intermittency is presented near y/δ = 0.6 and 0.85 at each of the Reynolds numbers. The average intermittency is presented as a function of detector threshold level and position in the boundary layer. The spanwise vorticity signals were found to yield average intermittency values at least as large as previous intermittency studies using “surrogate” signals. The average intermittency results do not indicate a region of threshold independence. An analysis of ωz event durations conditioned on the signal amplitude was also performed. The results of this analysis indicate that for decreasing Rθ, regions of single-signed ωz increase in size relative to the boundary layer thickness, but decrease in size when normalized by inner variables.
Turbulent Flow Near a Rough Wall
Authors: Koh Yang-Moon
Published: May 2008

By introducing the equivalent roughness which is defined as the distance from the wall to where the velocity gets a certain value (u/uτ ≈ 8.5) and which can be represented by a simple function of the roughness, a simple formula to represent the mean-velocity distribution across the inner layer of a turbulent boundary layer is suggested. The suggested equation is general enough to be applicable to turbulent boundary layers over surfaces of any roughnesses covering from very smooth to completely rough surfaces. The suggested velocity profile is then used to get expressions for pipe-friction factors and skin friction coefficients. These equations are consistent with existing experimental observations and embrace well-known equations (e.g., Prandtl’s friction law for smooth pipes and Colebrook’s formula etc.) as special cases.
Some Characteristics of Counter Flowing Wall Jets
Authors: Balachandar R. , Robillard L. , Ramamurthy A. S.
Published: May 2008

Experimental results related to the interaction between a uniform flow and a two-dimensional counter flowing wall jet are presented for various ratios of the jet velocity to the freestream velocity. Both visual observations and wall pressure surveys were made in the jet penetration zone. Attempts were made to choose the proper scaling variables to suitably nondimensionalize the wall pressure distributions. The geometrical characteristics of the dividing streamline were determined for a range of test conditions. Limited tests were also carried out to check the influence of the size of the jet injection device on the flow characteristics.
The Development of a Turbulent Junction Vortex System (Data Bank Contribution)
Authors: Pierce F. J. , Shin J.
Published: May 2008

The growth and development of a horseshoe vortex system in an incompressible, three-dimensional turbulent junction flow were investigated experimentally. A streamlined cylinder mounted with its axis normal to a flat surface was used to generate the junction vortex flow. The flow environment was characterized by a body Reynolds number of 183,000, based on the leading edge diameter of the streamlined cylinder. The study included surface flow visualizations, surface pressure measurements, and mean flow measurements of total pressure, static pressure, and velocity distributions in three planes around the base of the streamlined cylinder, and in two planes in the wake flow. Some characterizations of vortex properties based on the measured mean cross-flow velocity components are presented. The results show the presence of a single large, dominant vortex, with strong evidence of a very small corner vortex in the junction between the cylinder and the flat surface. The center of the dominant vortex drifts away from both the body and the flat surface as the flow develops along and downstream of the body. The growth and development of the core of the large, dominant vortex are documented.
Experimental Investigation of a Three-Dimensional Boundary Layer Flow in the Vicinity of an Upright Wall Mounted Cylinder (Data Bank Contribution)
Authors: Agui J. H. , Andreopoulos J.
Published: May 2008

The flow of a three-dimensional boundary layer approaching an upright wall mounted circular cylinder has been experimentally investigated by means of instantaneous flow visualization techniques using a laser sheet and time resolved measurements of the wall pressure, the gradients of which are related to the vorticity flux away from the wall. The mean separation point of the oncoming boundary layer is located on the plane of symmetry, 0.76 and 0.82 diameters upstream of the cylinder for the two investigated Reynolds numbers, based on the cylinder diameter, of 1.0 × 105 and 2.2 × 105, respectively. The present flow visualization studies have shown that there is always a primary vortex present in the flow which induces an eruption of wall fluid. Very often, this eruption results in the formation of counter rotating or mushroom vortices. A secondary vortex further upstream has been observed occasionally. This vortex, as well as the vortices formed by the fast eruption of wall fluid evolve quickly in time and space and therefore cannot be obtained from time-average measurements. The primary vortex consists of several large scale structures which have originated in the oncoming boundary layer and which have acquired substantial additional vorticity. Point measurements indicate that the r.m.s. pressure fluctuations increase as separation is approached and reach a maximum near reattachment. A low degree of space-time correlation and longer integral time scales were also observed downstream of separation. A bimodal probability density function of the fluctuating pressure was observed in the vicinity of the mean separation point, close to the corner region and in the wake of the cylinder. Quasi periodic vortex shedding from the cylinder with a Strouhal number 0.13 was also observed.
Nonlinear Response of Planar Laminar Flow Over a Flat Plate Vibrating in Different Modes
Authors: Venkat N. Kolluru , Spaulding Malcolm
Published: May 2008

A computer model developed by Venkat and Spaulding (1991a) for unsteady flows over vibrating bodies is used to investigate the nonlinear characteristics of external flow over a flat plate, a section of which is subjected to time varying motion of various mode shapes (n). The Reynolds number, Re is fixed at 1000. For the first case, the Strouhal number, St and the vibration amplitude ratio, H0 are fixed at 0.25 and 0.025, respectively while for the second case, St and H0 are increased to 1.0 and 0.1, respectively. Simulations are performed for modes varying in the range 1<n<4. For n=1, upstream and downstream pressure wave propagation is very high compared to higher modes. The transfer of energy from the input frequency to the first harmonic is pronounced for higher modes. A source-sink pair exists over the vibrating section for even modes. For high St and H0 the pressure spectral amplitude of higher harmonics far downstream is quite large for n=4 compared to n=2 thus indicating more nonlinear interaction between the vibrating body and the external flow for large even modes. The pressure coefficient on either side of the vibrating section is controlled by the gradient of vorticity for odd modes and by the convective acceleration terms for even modes.
Flow Instability in a Curved Duct of Rectangular Cross Section
Authors: Belaidi A. , Johnson M. W. , Humphrey J. A. C.
Published: May 2008

An experimental investigation has been carried out in a curved duct of rectangular cross section in order to study the development of flow instability in such geometries. Hot wire anemometry was used to obtain detailed measurements of velocity on the symmetry plane of the duct for different curvature ratios. As the duct Dean number is increased, a centrifugal instability develops and the Dean vortices are seen to oscillate along the inner wall. To understand the contribution of these vortices to the laminar-turbulent transition, time histories and spectra of the flow were taken on the symmetry plane of the duct for different Reynolds numbers. These data reveal a time-periodic motion along the inner wall where the secondary flows originating from the side wall boundary layers collide. The bend angle where this instability develops depends on the Reynolds number while the frequency of the instability depends on the curvature ratio of the bend.
Secondary Flow and Hydraulic Losses Within Sinuous Conduits of Rectangular Cross Section
Authors: Shimizu Yukimaru , Futaki Yoshiki , Martin C. Samuel
Published: May 2008

This paper describes the relationship between hydraulic losses and secondary flow within sinuous conduits with complicated bends. It has been found that the nature of secondary flow present in the bends is quite sensitive to the geometric configuration of the bend and the actual aspect ratio of the conduit section. Indeed, many different secondary flow patterns have been found to exist as the bend geometry is altered. A wide range of experiments has been conducted for various aspect ratios of a rectangular conduit with different curvatures.
A Power-Law Formulation of Laminar Flow in Short Pipes
Authors: Sherman M.
Published: May 2008

In the quantification of air flow through penetrations in buildings, it is necessary to be able to characterize the flow without detailed knowledge of the geometry of the paths. At the conditions typical of buildings, the flow regime is partially developed laminar flow. This report develops a theoretical description of the hydrodynamic relationship based on a power-law representation between the air flow and applied pressure for laminar flow in short pipes. It is found that short pipes can be described with a simple power law dependence on pressure, but that the exponent of the power law is itself a function of pressure. The entry length of the flow is derived based on a formulation for short, sharp-edged pipes. The theoretical formulation is compared to measured data. A dimensionless quantity, S, is defined to account for the power law behavior and maps simply to the flow exponent. The exponent or S number can be used to infer many of the characteristics of the flow and may prove useful in the inverse problem of determining flow geometry from fluid properties and the measured pressure and flow.
LDV Measurements in a Centrifugal Slurry Pump: Water and Dilute Slurry Flows
Authors: Cader T. , Masbernat O. , Roco M. C.
Published: May 2008

A two-component LDV system was used to investigate single and two-phase flow in a representative section at the impeller outlet of a centrifugal slurry pump. Measurements were performed at Qn and 0.5 Qn with water and dilute slurry flows (C = 0.04 and 0.16 percent by volume). The solids consist of 0.8 mm glass beads. Particle Reynolds number is 65. The point liquid and solid velocities were determined with a Doppler signal amplitude discrimination approach. A rotary shaft encoder was used to represent the velocity as a function of the impeller angular position, and to investigate the effect of a finite number of blades on the flow. The data on liquid and slip velocity distributions show large scale flow structures which dominate the two-phase turbulent flow. Overall, solid particles have a larger radial velocity than the carrier fluid at the impeller outlet, but they lag the fluid in the circumferential direction.
Optimization of the Parameters for a Rotating, Mixed-Phase Reactor
Authors: Cleland J. G. , Kornfeld D. M.
Published: May 2008

The motion of small, monodisperse particles in fluid was studied in a horizontal, cylindrical container rotating about its axis. One instigation for the study was the common requirement for mixed-phase, chemical or biological reactors to maintain particles in suspension for extended periods. A cylindrical, rotating reactor can allow long-term particle suspension without particle collisions and resulting agglomeration. The purpose of this study was to verify parametric effects and optimize the time of particle suspension. The theoretical and experimental results were obtained for inert, constant-diameter particles of nearly neutral buoyancy. The centrifugal buoyancy and gravitation terms were both included in the equations of motion. Laser illumination, photography and computer imaging were used to measure experimental particle concentration.
Low Area Ratio Aircraft Fuel Jet-Pump Performances With and Without Cavitation
Authors: Marini M. , Massardo A. , Satta A. , Geraci M.
Published: May 2008

The experimental analysis performed on several small size low area ratio aircraft fuel jet pumps in JP4 is outlined. The variables investigated were area ratio, nozzle and throat diameters, nozzle and suction pressures. The experimental values of head ratio were compared to a one-dimensional theoretical prediction method previously found to be applicable to moderate and high area ratio pumps. The results show the necessity of making some modifications in the model at low flow coefficient values. Measured wall static pressures were also compared with the results of an axisymmetric finite difference turbulent calculation; the comparisons are generally in good agreement. The development of cavitation and related parameters were also investigated. In order to enhance cavitation resistance, which is particularly important in the field of aeronautics, some studies were carried out on two stage jet pumps. The results obtained are outlined and discussed.
Three-Dimensional Calculation of Bubble Growth and Drop Ejection in a Bubble Jet Printer
Authors: Asai A.
Published: May 2008

The three-dimensional Navier-Stokes equation for the motion of ink both inside and outside the nozzle of a bubble jet printer is numerically solved, for the first time, to predict the bubble behavior and the drop ejection. The results of calculation for three types of ink agreed well with experimental data. The effect of initial bubble pressure, viscosity and surface tension on the volume and the velocity of the drop is numerically investigated. The three-dimensional calculation is very useful to the design of bubble jet printers because it saves a lot of time and cost to make and evaluate prototypes.
Non-Darcy Couette Flow in a Porous Medium Filled With an Inelastic Non-Newtonian Fluid
Authors: Nakayama A.
Published: May 2008

Newtonian and non-Newtonian Couette flows through inelastic fluid saturated porous media due to a moving plate boundary have been investigated analytically. The momentum equation which includes both the viscous and inertia terms is solved to examine the effects of the pseudoplasticity, boundary friction, and porous inertia on the velocity profile and wall shear stress at the moving wall. Closed-form exact solutions are presented for three distinct cases of practical interest. A simple expression for the wall shear stress valid for all Newtonian and non-Newtonian cases of small Darcy number has been also derived through an integral treatment, and found to agree closely with the exact values obtained from direct numerical integrations of the momentum equation. The analytical results presented here can be used for possible applications to highly sensitive viscosity measuring devices.
Swirling, Particle-Laden Flows Through a Pipe Expansion
Authors: Sommerfeld M. , Ando A. , Wennerberg D.
Published: May 2008

The present study concerns a particle-laden, swirling flow through a pipe expansion. A gas-particle flow enters the test section through a center tube, and a swirling air stream enters through a coaxial annulus. The swirl number based on the total inflow is 0.47. Numerical predictions of the gas flow were performed using a finite-volume approach for solving the time-averaged Navier-Stokes equations. The predicted mean velocity profiles showed good agreement with experimental results when using the standard k-ε turbulence model. The turbulent kinetic energy of the gas phase, however, is considerably underpredicted by this turbulence model, especially in the initial mixing region of the two jets. The particle dispersion characteristics in this complex flow were studied by using the Lagrangian method for particle tracking and considering the particle size distribution. The influence of the particle phase onto the fluid flow was neglected in the present stage, since only low particle loadings were considered. The particle mean velocities were again predicted reasonably well and differences between experiment and simulation were only found in the velocity fluctuations, which is partly the result of the underpredicted turbulent kinetic energy of the gas phase. The most sensitive parameter for validating the quality of numerical simulations for particle dispersion is the development of the particle mean number diameter which showed reasonable agreement with the experiments, except for the core region of the central recirculation bubble. This, however, is attributed again to the predicted low turbulent kinetic energy of the gas phase.
Particle Dispersion by Vortex Structures in Plane Mixing Layers
Authors: Wen F. , Kamalu N. , Chung J. N. , Crowe C. T. , Troutt T. R.
Published: May 2008

The dispersion of particles in a plane mixing layer between two air streams is investigated using experimental and numerical techniques. The results show that large-scale spanwise vortices strongly influence the particle dispersion process. Particles with aerodynamic response times on the order of the large scale vortex time scales are found to concentrate near the outer edges of the vortex structures. Time average velocity measurements also demonstrate that these particles tend to move away from the center of the mixing layer. Substantial changes in the lateral particle dispersion are producible by controlled forcing of the vortex structures. Comparisons between the experimental particle dispersion patterns and numerical simulations show striking similarities. A two-part model involving stretching and folding is suggested as a particle dispersion mechanism.
Turbulent Diffusion of Heavy-Particles in Turbulent Jets
Authors: Mostafa A. A.
Published: May 2008

The turbulent dispersion of heavy suspended particles in turbulent shear flows is analyzed when crossing trajectory effects are important. A semiempirical expression for particle diffusion coefficient is developed via a comparison with experimental data of two-phase turbulent jet flows. This expression gives the particle momentum diffusion coefficient in terms of the gas diffusion coefficient, mean relatively velocity, and root mean square of the fluctuating fluid velocity. The proposed expression is used in a two-phase flow mathematical model to predict different particle-laden jet flows. The good agreement between the predictions and data suggests that the developed expression for particle diffusion coefficient is reasonably accurate in predicting particle dispersion in turbulent free shear flows.
Freestream Nuclei and Traveling-Bubble Cavitation
Authors: Meyer R. S. , Billet M. L. , Holl J. W.
Published: May 2008

Traveling-bubble cavitation inception tests were conducted in a 30.48 cm water tunnel with a Schiebe headform. A computer code was developed to statistically model cavitation inception on a Schiebe headform, consisting of a numerical solution to the Rayleigh-Plesset equation coupled to a set of trajectory equations. Using this code, trajectories and growths were computed for bubbles of varying initial sizes. An initial off-body distance was specified and the bubble was free to follow an off-body trajectory. A Monte Carlo cavitation simulation was performed in which a variety of random processes were modeled. Three different nuclei distributions were specified including one similar to that measured in the water tunnel experiment. The results compared favorably to the experiment. Cavitation inception was shown to be sensitive to nuclei distribution. Off-body effect was also found to be a significant factor in determining whether or not a bubble would cavitate. The effect of off-body trajectories on the critical bubble diameter was examined. The traditional definition of critical diameter based on the minimum pressure coefficient of the body or the measurement of liquid tension was found to be inadequate in defining cavitation inception.
Dynamical Interactions in a Multi-Bubble Cloud
Authors: Chahine Georges L. , Duraiswami Ramani
Published: May 2008

Results of studies on the dynamics of “clouds” of bubbles via both an analytical technique using asymptotic expansions, and via numerical simulation using a three-dimensional boundary element technique (BEM) are reported. The asymptotic method relies on the assumption that the characteristic bubble size is much smaller than the characteristic inter-bubble distance. Results obtained from the two methods are compared, and are found to agree in the domain of validity of the asymptotic technique, which is for very low void fractions. Next, results of several numerical experiments conducted using the BEM algorithm are reported. The results indicate the influence of the mutual interaction on the dynamics of multiple bubble clouds.
Phase Discrimination in Gas-Particle Flows Using Thermal Anemometry
Authors: Ritsch M. L. , Davidson J. H.
Published: May 2008

A technique to measure gas-phase turbulence modification by micron-sized particles with thermal anemometry is presented. Bridge output is first digitized and then spikes produced by particle impingement on the hot-wire probe detected using a slope threshold method and replaced by holding the last digital value before each spike. This procedure has negligible effect on flow statistics if spike duration is short compared to the time between spikes.
A Near-Wall Model for Separated Turbulent Flows
Authors: Goldberg U. C.
Published: May 2008

A near-wall model for separated turbulent flows is presented and evaluated. The model is based on experimental observations, in particular, the wake-like behavior of turbulence away from walls, the influence of walls on this behavior, the diffusion/dissipation energy balance observed in the backflow portion of detached flow regions, and the near-wall behavior of eddy-viscosity. These lead to two analytically solvable ODE’s for the normal-to-wall behavior of turbulence kinetic energy and eddy-viscosity. The model is applied in conjunction with an outer eddy-viscosity model (such as a k–ε model) to predict eddy-viscosity distribution in separated flow regions. Predictions of two flow cases, using this approach, are shown.
LDV Measurements of Periodic Fully Developed Main and Secondary Flows in a Channel With Rib-Disturbed Walls
Authors: Liou T.-M. , Wu Y.-Y. , Chang Y.
Published: May 2008

Laser-Doppler velocimeter measurements of mean velocities, turbulence intensities, and Reynolds stresses are presented for periodic fully developed flows in a channel with square rib-disturbed walls on two opposite sides. Quantities such as the vorticity thickness and turbulent kinetic energy are used to characterize the flow. The investigated flow was periodic in space. The Reynolds number based on the channel hydraulic diameter was 3.3×104. The ratios of pitch to rib-height and rib-height to chamber-height were 10 and 0.133, respectively. Regions where maximum and minimum Reynolds stress and turbulent kinetic energy occurred were identified from the results. The growth rate of the shear layers of the present study was compared with that of a backward-facing step. The measured turbulence anisotropy and structure parameter distribution were used to examine the basic assumptions embedded in the k–ε and k–ε–A models. For a given axial station, the peak axial mean-velocity was found not to occur at the center point. The secondary flow was determined to be Prandtl’s secondary flow of the second kind according to the measured streamwise mean vorticity and its production term.
An Inverse Inviscid Method for the Design of Quasi-Three-Dimensional Turbomachinery Cascades
Authors: Bonataki E. , Chaviaropoulos P. , Papailiou K. D.
Published: May 2008

The calculation of the blade shape, when the desired velocity distribution is imposed, has been the object of numerous investigations in the past. The object of this paper is to present a new method suitable for the design of turbomachinery stator and rotor blade sections, lying on an arbitrary axisymmetric stream-surface with varying streamtube width. The flow is considered irrotational in the absolute frame of reference and compressible. The given data are the streamtube geometry, the number of blades, the inlet flow conditions and the suction and pressure side velocity distributions as functions of the normalized arc-length. The output of the computation is the blade shape that satisfies the above data. The method solves an elliptic type partial differential equation for the velocity modulus with Dirichlet and periodic type boundary conditions on the (potential function, stream function)-plane (Φ, Ψ). The flow angle field is subsequently calculated solving an ordinary differential equation along the iso-Φ or iso-Ψ lines. The blade coordinates are, finally, computed by numerical integration. A set of closure conditions has been developed and discussed in the paper. The method is validated on several test cases and a discussion is held concerning its application and limitations.
An Investigation of Nucleating Flows of Steam in a Cascade of Turbine Blading
Authors: Bakhtar F. , Webb R. A. , Shojaee-Fard M. H. , Siraj M. A.
Published: May 2008

During the course of expansion in turbines steam first supercools and then nucleates to become a wet mixture. To reproduce turbine nucleating conditions realistically requires a supply of supercooled vapor. This can be achieved under blow-down conditions and an experimental facility for such studies has been constructed. The results of the first experimental investigation of nucleating flows of steam in a cascade of nozzle blading using the equipment are presented. The experimental results presented consist of surface pressure measurements, Mach-Zehnder and shadow photography. Comparisons with theoretical solutions show reasonable agreement.
A Theoretical Analysis of Rotating Cavitation in Inducers
Authors: Tsujimoto Y. , Kamijo K. , Yoshida Y.
Published: May 2008

Rotating cavitation was analyzed using an actuator disk method. Quasi-steady pressure performance of the impeller, mass flow gain factor, and cavitation compliance of the cavity were taken into account. Three types of destabilizing modes were predicted: rotating cavitation propagating faster than the rotational speed of the impeller, rotating cavitation propagating in the direction opposite that of the impeller, and rotating stall propagating slower than the rotational speed of the impeller. It was shown that both types of rotating cavitation were caused by the positive mass flow gain factor, while the rotating stall was caused by the positive slope of the pressure performance. Stability and propagation velocity maps are presented for the two types of rotating cavitation in the mass flow gain factor-cavitation compliance plane. The correlation between theoretical results and experimental observations is discussed.
Near-Wake Flow of a V-Gutter With Slit Bleed (Data Bank Contribution)
Authors: Yang Jing-Tang , Tsai Go-Long
Published: May 2008

The cold-flow characteristics of a v-shape flame holder with flow bleed from a slit located at the leading edge have been investigated. According to experimental evidence, a nonsymmetric wake structure is developed behind the symmetric slit v-gutter. The flow through the slit induces greater reverse flow and greater back pressure in the near wake. It also provokes more extensive transport across the shear layers and reduces both the turbulent intensity and the Reynolds shear stress of the wake flow. These results indicate that the slit v-gutter can have a better flame holding ability and less pressure loss compared with the traditional v-gutter. In view of fluid dynamics features, the slit v-gutter is indeed a potentially useful design of flame holder.
The Accuracy of a Three-Component Laser Doppler Velocimeter System Using a Single-Lens Approach
Authors: Chevrin P.-A. , Petrie H. L. , Deutsch S.
Published: May 2008

An analysis of the effects of misalignment on the on-axis velocity component measurements made with a three-component LDV system using two colors and five beams issuing from a single lens is discussed. A slight misalignment of the center beam from the optical axis is shown to cause large changes in the measured “on-axis” component of velocity. The effect of misalignment on the ensemble averaged velocity statistics in turbulent flows is also considered. The error analysis of Neti and Clark (1979) is applicable to on-axis component of the present system and it shows that even when the system is perfectly aligned, the relative uncertainty of the on-axis component of velocity is much larger than that of the other components of velocity. Measurements taken in a laminar pipe flow support this conclusion.
A Simple and Accurate Method of Calibrating X-Probes
Authors: John J. , Schobeiri T.
Published: May 2008

This paper presents an improved method of calibrating hot-film X-probes in incompressible flow. The yaw response of a hot-film X-probe was investigated for different velocities and found to be strongly velocity dependent at low velocities. A simple relation was developed to correct for the variation of yaw response at low velocities. The method using the yaw correction is compared with the single-velocity yaw calibration method. The correction to the yaw response considerably improves accuracy at low velocities.
A New Approach to the Dynamic Parameter Estimation of a Viscoelastic System
Authors: Bennis S.
Published: May 2008

This work involves the study of newtonian transitory flow regimes in a rigid tube that has been extended to include an elastic enclosure. Three different techniques have been applied and compared. The first approach is the classical one, in which the calculations, which are based on the Laplace transform, enable direct integration of the Navier-Stokes equations and make it possible to determine longitudinal velocity and fluid flow. The solution, however, involves real or complex parameters that are solutions to a nonlinear equation involving Bessel functions. Where the flow regime in the tube is oscillating, we find a natural frequency of oscillation there, and a flow damping ratio. A comparison will be made with the other two methods partly on the basis of these two parameters. The second is an approach based on time series analysis of flow in the tube, and consists in applying auto-regressive moving-average (ARMA) models to the fluid flow in order to identify the natural frequency and the damping coefficient of the flow. The flow series analyzed by this method come from two sources: 1. The flow series obtained from the theoretical solution using the first method; these flow series were artificially contaminated with random noise to simulate real situations. 2. The flow series obtained experimentally by direct measurement and integration of the velocity profile in the tube. Finally, with the third technique, the experimental method, we have succeeded in validating the first two approaches. The approach based on the analysis of the time series through the use of ARMA models appears to perform best and is the simplest to use.
A Unifying Method for Sizing Throttling Valves Under Laminar or Transitional Flow Conditions
Authors: Baumann H. D.
Published: May 2008

The mass flow passing through a given valve will decrease in Reynolds number ranges below approximately 10,000 due to the transition from fully developed turbulent to laminar flow. The objective of this study is to provide a uniform prediction method to establish, with reasonable accuracy, the ratio between the turbulent and transitional or laminar flow rate passing through a given valve, taking into account the valve’s hydraulic diameter and the initial turbulent velocity head loss coefficient. Experimental data from prior research tends to support a proposed “unified sizing method” that is applicable for all single-stage valves regardless of size or type.
Incompressible Fluid Flow Through Pipes Packed With Spheres at Low Dimension Ratios
Authors: Fand R. M. , Sundaram M. , Varahasamy M.
Published: May 2008

This technical note reports the results of the last of a series of three studies of the flow of incompressible fluids through pipes packed with spheres. In the first of these studies, published in the Journal of Fluids Engineering in 1987, it was shown that certain experimentally determined parameters which govern incompressible fluid flow through such packings are substantially independent of the dimension ratio, D/d, for D/d ≥ 40, where D and d represent the pipe and sphere characteristic dimensions (diameters), respectively. The second of the aforementioned studies, published in the Journal of Fluids Engineering in 1990, focused on the range 1.40 ≤ D/d < 40. In this range the flow parameters are functionally dependent upon D/d due to the so-called “wall effect.” The present investigation deals with the range 1.08 ≤ D/d ≤ 1.40, for which it is shown that the results are quite different from those obtained for higher D/d. Correlation equations are presented here by means of which the flow is characterized in the range 1.08 ≤ D/d ≤ 1.40. It is anticipated that this information will have practical applications, such as, for example, calculating the “cost,” in terms of pressure drop, of enhancing the rate of convection heat transfer in heat exchangers by packing the tubes of the heat exchangers with spheres.
A Numerical Study on the Generation Mechanism of Turbulence-Driven Secondary Flow in a Square Duct
Authors: Myong Hyon Kook
Published: May 2008

The generation mechanism of turbulence-driven secondary flows in a square duct is numerically investigated in the present study by using an anisotropic low-Reynolds-number k–ε turbulence model. Special attention is directed to the distributions of turbulence quantities, which are responsible for the secondary flow generation, such as the anisotropy of normal Reynolds stresses and the secondary Reynolds shear stress acting on the cross-sectional plane. The vorticity transport process is also discussed in detail, based on the numerical evaluation of the individual terms which appear in the streamwise vorticity transport equation.
Drag Reduction of a Cylinder/Endwall Junction Using the Iceformation Method
Authors: LaFleur R. S. , Langston L. S.
Published: May 2008

The iceformation design method was used to reduce the drag of a juncture between a cylinder and flat endwall. Ice was formed on a subfreezing flat endwall in a warmer laminar water flow. The ice shape was influenced by and altered the three-dimensional separated boundary layer and the cylinder wake. Preliminary experiments were used to indicate control parameter relationships. An adaptive selection theory was used to determine optimal control parameters. A sample optimal contour was generated and tested for juncture drag performance. High Reynolds number wind tunnel drag tests showed that the iceform contour had an average of 18 percent lower drag than a flat plate juncture given the same upstream boundary layer conditions. Flow visualizations showed that the iceform contour produced three larger diameter vortices compared to the laminar four vortex model of Baker (1979).
Evaluation and Comparison of Bounding Techniques for Convection-Diffusion Problems
Authors: Sharif M. A. R. , Busnaina A. A.
Published: May 2008

The effects of bounding the skew upwind and the second-order upwind discretization schemes for the convection terms in convection-diffusion transport equations have been studied. Earlier studies indicated that these two schemes produce less numerical diffusion but introduce unacceptable numerical dispersion or oscillations in the solution if not bounded. A simplified analytical treatment exploring the reason for this behavior is presented. Two bounding techniques, the flux-corrected transport and the filtering remedy and methodology were evaluated. Test problems used in the evaluation are (i) one-dimensional convection of a rectangular pulse, (ii) transport of a scalar step in a uniform velocity field at an angle to the grid lines, (iii) Smith and Hutton problem, (iv) two-dimensional convection of a square scalar pulse in a uniform velocity field at an angle to the grid lines, and (v) two interacting parallel streams moving at an angle to the grid lines. The results indicate that the flux-corrected transport eliminates the oscillations in the solution without introducing any additional numerical diffusion when used with both schemes. The filtering remedy and methodology also eliminates the oscillation when used with the skew upwind scheme. This technique, however, is not effective in reducing the over-shoots when used with the second-order upwind scheme.
Hydraulic Characteristics of Mixed Convection in a Heated Vertical Pipe
Authors: Han Jian-Chiu
Published: May 2008

By studying the integrated governing equations for mixed convection in a vertical pipe heated with constant wall heat flux, several concepts (or misconcepts) regarding convection mode and flow regimes are examined. A new alternative definition of convection mode reflecting the force balance in mixed convection is given. A new parameter, m (M), is introduced to quantatively characterize various regimes for mixed convection. Two specific cases for laminar and turbulent air flow with Re = 500 and 5000 respectively are studied numerically in detail. Typical behavior of m (M) for each case and other associated hydraulic characteristics of mixed convection are illustrated and discussed.
Parametrical Investigation of the Interaction Between Turbulent Wall Shear Layers and Normal Shock Waves, Including Separation
Authors: Kaldellis J. K.
Published: May 2008

The existence of strong shock waves plays a major role in the performance of modern aero-mechanical devices, since it is primarily responsible not only for the shock induced total pressure drop, but also for the increased shear layer losses due to flow separation. In this paper a fast energy-type integral method along with an approximate shock-turbulent shear layer interaction procedure are presented. This integral method, based on the two-zone model, is able to predict attached and fully detached shear flows. An extended turbulence model is also used in order to take the influence of the turbulence inside the interaction region better into account. The external flow pressure distribution results from an improved and extended form of an approximate small disturbance theory. A detailed investigation is carried out to estimate the influence of the inlet Mach number, the shear layer characteristics and the confinement of the geometry upon the static pressure field. The resulting method has been successfully applied to several test cases including ones where separation appears. Comparison between results of previous calculations, experimental data and results of the proposed method is also presented, along with the convergence history of the shear layer—shock wave interaction procedure. Finally, the method has been applied to one-stage high pressure supersonic flow compressor with normal shock appearance inside the rotor of the machine. The major conclusion drawn from the present work is that the shear layer characteristics (e.g., displacement thickness and form factor) have a dominant effect upon the flow field near the interaction region. Additionally, the proposed method requires no more than five overall iterations to reproduce the real flow field for all cases examined.
Prediction of Turbulent Boundary Layers With a Second-Moment Closure: Part I—Effects of Periodic Pressure Gradient, Wall Transpiration, and Free-Stream Turbulence
Authors: Shima N.
Published: May 2008

The purpose of this two-part paper is to assess the performance of a second-moment closure applicable up to a wall. In the present part, the turbulence model is applied to the boundary layers with periodic pressure gradient, with wall transpiration and with free-stream turbulence. The predictions are shown to be in good agreement with experiments and a direct simulation. In particular, a tendency towards relaminarization and a subsequent retransition in the oscillating boundary layer are faithfully reproduced, and the effect of the length scale of free-stream turbulence is correctly captured.
Perspective: Systematic Study of Reynolds Stress Closure Models in the Computations of Plane Channel Flows (Data Bank Contribution)
Authors: Demuren A. O. , Sarkar S.
Published: May 2008

This paper investigates the roles of pressure-strain and turbulent diffusion models in the numerical calculation of turbulent plane channel flows with second-moment closure models. Only high Reynolds number models are considered. Three turbulent diffusion and five pressure-strain models are utilized in the computations. The main characteristics of the mean flow and the turbulent fields are compared against experimental data. All the features of the mean flow are correctly predicted by all but one of the Reynolds stress closure models. The Reynolds stress anisotropies in the log layer are predicted to varying degrees of accuracy (good to fair) by the models. It is found that, contrary to previous assertions, wall-reflection terms are not necessary to obtain the correct Reynolds stress anisotropy in the log-layer. The pressure-strain models determine the level of anisotropy in the log-layer, while the diffusion models strongly influence the rate of relaxation towards isotropy in the outer-layer. None of the models could predict correctly the extent of relaxation towards isotropy of the streamwise and lateral components of the Reynolds stresses in the wake region near the center of the channel. Results from direct numerical simulation are used to further clarify this behavior of the models.
Prediction of Turbulent Boundary Layers With a Second-Moment Closure: Part II—Effects of Streamline Curvature and Spanwise Rotation
Authors: Shima N.
Published: May 2008

Further testing of the second-moment closure employed in Part I is made. The present part considers the effects of streamline curvature and spanwise system rotation. As expected, the exact stress production terms broadly account for these effects. In addition, the present model, which is applied right up to a wall, successfully captures the laminarization in the rotating boundary layer. Attention is also given to the capability to reproduce the recovery process from curvature.
Application of the k–ε Turbulence Model to the Simulation of a Fully Pulsed Free Air Jet
Authors: Graham L. J. W. , Bremhorst K.
Published: May 2008

The work describes application of the k–ε turbulence model to a fully pulsed air jet. The standard model failed to predict the change in slope of the velocity decay where the jet changes from pulsed to steady jet behavior. A change in one of the constants of the k–ε model based on the behavior of the periodic velocity component relative to the intrinsic component yielded satisfactory results. Features of the pulsed jet which were successfully simulated included the flow reversal near the edge of the jet, increased entrainment when compared to steady jets and large radial outflow near the leading edge of the pulse and large radial inflow near the outer edge of the jet for the remainder of the pulse.