bluuebunny/crossref_metadata_2025 huggingface dataset:
A Plexiglas Research Pump With Calibrated Magnetic Bearings/Load Cells for Radial and Axial Hydraulic Force Measurement
Authors: Baun D. O. , Flack R. D.
Published: February 2008

A research pump intended for both flow visualization studies and direct measurement of hydrodynamic radial and axial forces has been developed. The impeller and the volute casing are constructed from Plexiglas which facilitates optical access for laser velocimetry measurements of the flow field both inside the impeller and in the volute casing. The pump housing is designed for flexibility allowing for each interchange of impellers and volute configurations. The pump rotor is supported by three radial magnetic bearings and one double acting magnetic thrust bearing. The magnetic bearings have been calibrated to characterize the force versus coil current and air gap relationship for each bearing type. Linear calibration functions valid for rotor eccentricities of up to 2/3 of the nominal bearing clearances and force level of ±58 N (13 lbf) and ±267 N (60 lbf) for the radial and axial bearings, respectively, were found. A detailed uncertainty analysis of the force calibration functions was conducted such that meaningful uncertainty bounds can be applied to in situ force measurements. Hysteresis and eddy current effects were quantified for each bearing such that their effect on the in situ force measurements could be assessed. By directly measuring the bearing reaction forces it is possible to determine the radial and axial hydraulic loads acting on the pump impeller. To demonstrate the capability of the magnetic bearings as active load cells representative hydraulic force measurements for a centered 4 vane 16 degree log spiral radial flow impeller operating in a single tongue spiral volute casing were made. At shut-off a nondimensional radial thrust of 0.084 was measured. A minimum nondimensional radial thrust of about 0.007 was observed at the nominal design flow. The nondimensional radial thrust increased to about 0.019 at 120 percent of design flow. The nondimensional axial thrust had a maximum at shut-off of 0.265 and decreased steadily to approximately 0.185 at 120 percent of design flow. Two regions of increasing axial thrust, in the flow range 75 to 100 percent of design flow, were observed. The measurements are compared to radial and axial force predictions using classical force models. The direct radial force measurements are compared to a representative set of radial force measurements from the literature. In addition, the directly measured radial force at design flow is compared to a single representative radial force measurement (obtained from the literature) calculated from the combination of static pressure and net momentum flux distribution at the impeller exit.
Primary/Leakage Flow Interaction in a Pump Stage
Authors: Baskharone E. A. , Wyman N. J.
Published: February 2008

The finite-element analysis of the combined primary and leakage flow streams in a centrifugal pump is presented. To date, this computational model provides the most accurate “zeroth-order” flow field for rotordynamic calculations, short of analyzing the entire flow field on a fully three-dimensional basis. In formulating the problem, the shaft work is modeled via the angular momentum it imparts to the primary flow stream across the impeller blade region. In casting the boundary conditions, special attention is paid to the multi-connectivity of the newly-contoured computational domain in such a way to avoid over-specification of the problem. The analysis is applied to a typical pump stage with a face seal being part of the leakage passage. The numerical results are then compared to the outcome of the existing lower-order analysis where the impeller subdomain was totally extracted.
Computation of Unsteady Viscous Marine-Propulsor Blade Flows—Part 2: Parametric Study
Authors: Paterson Eric G. , Stern Fred
Published: February 2008

In this two-part paper, time-accurate solutions of the Reynolds-averaged Navier-Stokes equations are presented, which address through model problems, the response of turbulent propeller-blade boundary layers and wakes to external-flow traveling waves. In Part 1, the Massachusetts Institute of Technology flapping-foil experiment was simulated and the results validated through comparisons with data. The response was shown to be significantly more complex than classical unsteady boundary layer and unsteady lifting flows thus motivating further study. In Part 2, the effects of frequency, waveform, and foil geometry are investigated. The results demonstrate that uniquely different response occurs for low and high frequency. High-frequency response agrees with behavior seen in the flapping-foil experiment, whereas low-frequency response displays a temporal behavior which more closely agrees with classical inviscid-flow theories. Study of waveform and geometry show that, for high frequency, the driving mechanism of the response is a viscous-inviscid interaction created by a near-wake peak in the displacement thickness which, in turn, is directly related to unsteady lift and the oscillatory wake sheet. Pressure waves radiate upstream and downstream of the displacement thickness peak for high frequency flows. Secondary effects, which are primarily due to geometry, include gust deformation due to steady-unsteady interaction and trailing-edge counter-rotating vortices which create a two-layered amplitude and phase-angle profile across the boundary layer.
Numerical Modeling of Flow in a Vertical Cooling Crystallizer
Authors: Sima M. A. , Harris J. A.
Published: February 2008

Simulations of the flow field and temperature distribution in a low grade vertical continuous cooling sugar crystallizer were carried out by numerically solving the Navier-Stokes equations in a cylindrical coordinate system. The model results indicate highly nonuniform massecuite cooling, primarily due to the massecuite’s large Prandtl number, and significant short-circuiting of flow between inlet and outlet. Modifications to the crystallizer design are proposed and demonstrated to be successful in improving the performance of the vessel.
High Flux Rate Particle Filtration From Liquids
Authors: Chahine G. L. , Kalumuck K. M. , Aley Patrick D. , Frederick G. S.
Published: February 2008

A method for efficient solid particle removal from liquids using microporous tubes with flow swirl and flow interruption is presented. Experiments were performed using particle laden water obtained from an actual field project of high pressure water jet paint stripping. The flow rate, orientation, flow interruption, and swirl index were varied, and their effect on performance observed and measured as a function of time. Flux rate increases of a factor of 20 over a conventional microporous tube cross flow filtration were generated. Flux rates were found to increase both with increasing swirl and with moderate increases in the shear exerted on the tube wall. Results of independent testing by the US Navy at Port Hueneme of a small field unit demonstrate high flux rate performance with high permeate quality and turbidity removal.
Mechanics of Immersed Particle Collisions
Authors: Zenit Roberto , Hunt Melany L.
Published: February 2008

The present work investigates the mechanics of particle collisions submerged in a liquid using a simple pendulum experiment. Particle trajectories for different particles in water are measured using a high-speed digital camera and the magnitude of the collision is recorded using a high-frequency-response pressure transducer at the colliding surface. The particle deceleration occurs at distances less than half a particle diameter from the wall. The measured collision impulse increases with impact velocity and particle mass. Comparisons are drawn between the measured pressures and the predictions of basic impact mechanics assuming a perfectly elastic collision. A control-volume model is proposed that accounts for the fluid inertia and viscosity. When a particle approaches a planar surface or another particle, the fluid is squeezed prior to contact, reducing the initial kinetic energy and decelerating the particle. The pressure profile is integrated over the surface of the particle to obtain a force that is a function of the initial particle Reynolds number, Reo, and the ratio of the densities of the particle and fluid phases, ρp/ρf. The model predicts a critical Stokes number at which the particle reaches the wall with zero velocity. Comparisons between the proposed model and the experimental measurements show qualitative agreement.
Study of Tip Vortex Cavitation Inception Using Navier-Stokes Computation and Bubble Dynamics Model
Authors: Hsiao Chao-Tsung , Pauley Laura L.
Published: February 2008

The Rayleigh-Plesset bubble dynamics equation coupled with the bubble motion equation developed by Johnson and Hsieh was applied to study the real flow effects on the prediction of cavitation inception in tip vortex flows. A three-dimensional steady-state tip vortex flow obtained from a Reynolds-Averaged Navier-Stokes computation was used as a prescribed flow field through which the bubble was passively convected. A “window of opportunity” through which a candidate bubble must pass in order to be drawn into the tip-vortex core and cavitate was determined for different initial bubble sizes. It was found that bubbles with larger initial size can be entrained into the tip-vortex core from a larger window size and also had a higher cavitation inception number.
A Computer-Controlled Pressure Standard
Authors: Rediniotis Othon K.
Published: February 2008

The operating principles, as well as the technical aspects of the implementation of a new computer-controlled pressure standard are presented. The instrument can have dual use: either as a pressure source or as a pressure sensor. The device is intended mostly for use in problems where small differential pressures are of interest, i. e., 0–2.5 KPa and high accuracy is desired. Such a pressure range encompasses, for example, most of the pressure measurement applications in subsonic wind-tunnel testing. The device interfaces to a PC and is ideal for fully-automated pressure transducer calibration applications. The accuracy of the pressures produced or measured by the device is 0.08 percent F. S. (Full Scale).
Experimental Study of the Behavior of Confined Variable Density Jets in a Time Varying Crossflow
Authors: Raud N. , Bury Y. , Bazile R. , Bore´e J. , Charnay G.
Published: February 2008

An experimental work and a physical analysis dedicated to the study of a low density jet subjected to a time varying crossflow with high acceleration/deceleration levels are presented in this paper. Relevant nondimensional numbers are derived and show that unsteady effects associated with the presence of the jet in the acceleration field have noticeable consequences on the flapping of the jet. The Schlieren technique is applied in the test section of a square duct to obtain time resolved images of the jet. Analysis of the results is focused on the influence of the unsteady effects on the global dynamic behaviour of the jet in the near field. The interaction between the jet and the crossflow is analysed in three contrasted situations corresponding to different values of the jet outlet velocity U0. We predict and observe an increase of the jet deflection during the acceleration phase and a competition between drag and acceleration during the deceleration. This competition is particularly clear for the two lowest ejection velocities of the jet and we have shown that the jet is initially deflected upstream the nozzle. The influence of exit jet injection angle is finally considered. We show that upstream or downstream injections induce a very strong modification of the mixing process of the jet fluid with the pulsed crossflow.
A pdf Description of Turbulent Axisymmetric Free Jet Flow
Authors: Chen Ming-Hua , Hong Zuu-Chang
Published: February 2008

This study presents the applications of a turbulence probability density function (pdf) equation to compute an axisymmetric turbulent free jet flow. In view of the difficulty of solving this pdf equation directly by conventional numerical methods, an approximate moment method is applied. The Calculated triple velocity correlations appearing in the second-order moments equation are calculated and compared with measured values and with those estimated by moment-closure models. The results reveal that the pdf approach gives consistency in the higher-order moments and radial budget of third moments of velocity, and that the neglect of the mean-strain production, the rapid part of the pressure correlation and the dissipation are responsible for deviations between moment-closure models and experiments. Therefore, pdf methods appear to be more suitable than conventional moment-closure models in terms of revealing turbulence structure.
A Generic Centerline Velocity Decay Curve for Initially Turbulent Axisymmetric Jets
Authors: Papadopoulos George , Pitts William M.
Published: February 2008

Recently the authors introduced a length scale which effectively collapsed the near field centerline development of velocity and mass fraction for variable density axisymmetric jets whose initial conditions correspond to those of fully developed turbulent pipe flow. The new length scale incorporated the initial mass, momentum, and turbulence intensity per unit area to capture the Reynolds number dependence of near field development for the velocity and scalar distributions observed in low Reynolds number turbulent jets. The presents paper extends the analysis for a constant density jet to the intermediate and self-similar far fields further downstream using a dynamic length scale based on the local centerline turbulence intensity. The normalized mean velocity distributions of an air jet collapse over the entire flow distance investigated velocity distributions of an air jet collapse over the entire flow distance investigated velocity distributions of an air jet collapse over the entire flow distance investigated when the axial distance is normalized by the proposed length scale, thus scaling the virtual origin shift and effectively incorporating the Reynolds number dependence.
Experimental Modeling of Circular Hydraulic Jump by the Impingement of a Water Column on a Horizontal Disk
Authors: Naraghi Mehdi N. , Moallemi M. Karim , Naraghi M. H. N. , Kumar Sunil
Published: February 2008

An experimental study is performed to investigate the relationship between an unsub-merged water jet impinging onto a horizontal surface and radius of hydraulic jump. Experiments are undertaken over a wide range of pipe Reynolds numbers for which the pipe flow is laminar. The laminar impinging jet produced a smooth circular hydraulic jump, at which the film thickness experienced a sudden increase in thickness. Effects of various parameters on a stable and stationary hydraulic jump are studied. The impingement point radius ri, is taken as a characteristic length of the film flow, and correlations are obtained for radius of hydraulic jump in terms of various dimensionless parameters.
Transient Turbulent Gaseous Fuel Jets for Diesel Engines
Authors: Hill Philip G. , Ouellette Patric
Published: February 2008

Existing data on transient turbulent jet injection in to large chambers demonstrates self-similar behavior under a wide range of conditions including compressibility, thermal and species diffusion, and nozzle under expansion. The Jet penetration distance well downstream of the virtual origin is proportional to the square root of the time and the fourth root of the ratio of nozzle exit momentum flow rate to chamber density. The constant of proportionality has been evaluated by invoking the concept of Turner that the flow can be modeled as a steady jet headed by a spherical vortex. Using incompressible transient jet observations to determine the asymptotically constant ratio of maximum jet width to penetration distance, and the steady jet entrainment results of Ricou and Spalding, it is shown that the penetration constant is 3 ± 0.1. This value is shown to hold for compressible flows also, with substantial thermal and species diffusion, and even with transient jets from highly under-expanded in which, as in diesel engine chambers with gaseous fuel injection, the jet is directed at a small angle to one wall of the chamber. In these tests, with under expanded nozzles. Observations of transient jet injection have been made in a chamber in which, as in diesel engine chambers with gaseous fuel injection, the jet is directed at a small angle to one wall of the chamber. In these tests, with under-expanded nozzles it was found that at high nozzle pressure ratios, depending on the jet injection angle, the jet penetration can be consistent with a penetration constant of 3. At low pressure ratios the presence of the wall noticeably retards the penetration of the jet.
Pump Research and Development: Past, Present, and Future
Authors: Hergt Peter H.
Published: February 2008

As in all areas relevant to the development and production of pumps the tasks the hydraulic engineer has to deal with have undergone a remarkable change in recent decades: from a more or less unrestricted design of components to design roles dictated by manufacturing techniques. These general trends are accompanied by developments related to changes of the market requirements. This is demonstrated for three particular pump types. The consequences of the demand to save energy—with all the different aspects—are described for the example of heating circulation pumps. The still growing environmental awareness is a challenge for an enlargement of the presently valid operation limits of sealless pumps and for the development of intelligent monitoring systems. It is demonstrated that the developments in the field of boiler feed pumps are closely related to the growing unit sizes. Availability and reliability, and as far as very large pumps are concerned the efficiency, have always been and still are the dominant criteria.
Pump Research and Development: Past, Present, and Future—Japanese Perspective
Authors: Ohashi Hideo , Tsujimoto Yoshinobu
Published: February 2008

The evolution of pump research and production in Japan after 1955 is surveyed. The post-war period has been divided into three stages of development with unique social and industrial characteristics: expansion, conversion, and globalization. The growth of pump production in sales amount and quantity is shown for various types of pumps. The post-war direct and indirect research on pumps is classified into eight groups of topics and their past trends are analyzed. These changes are correlated with the characteristics of the corresponding background stage. These analyses with the past suggest new trends of research for pumps of tomorrow.
Performance Analysis of Automotive Torque Converter Elements
Authors: Ejiri E. , Kubo M.
Published: February 2008

The hydrodynamic performance of a three-element automotive torque converter is analyzed by measuring flow between the elements with five-hole Pitot tubes. The performance of each element, including head, head loss, and efficiency, is defined and evaluated. The results show that the pump is the major source of loss in the speed ratio range where vehicles are most frequently operated in everyday driving. The loss coefficients for the three elements are also evaluated using a one-dimensional flow model. The friction loss coefficient of the turbine shows small variation over the entire tested speed ratio range, whereas the coefficients of the pump and stator vary considerably according to the operating speed ratio. The cause of loss in the pump and stator is investigated by flow visualization and three-dimensional numerical flow analysis. A low kinetic energy region in the pump and leading edge separation in the stator are clearly visualized or computed.
Experimental Study on the Aeroacoustic Behavior of a Forward-Curved Blades Centrifugal Fan
Authors: Velarde-Sua´rez Sandra , Santolaria-Morros Carlos , Ballesteros-Tajadura Rafael
Published: February 2008

In this paper, an aeroacoustic study on a forward-curved blades centrifugal fan has been carried out. As a first step, the fan performance curves, i.e., total pressure, power, efficiency and sound power level versus flow rate were obtained, showing its unstable behavior over a wide operating range. Second, the fan sound power level spectra for several working conditions were determined. For this purpose a normalized installation for testing in laboratory was designed and constructed. Afterwards, the velocity and pressure fields, both at the inlet and outlet planes of the impeller were measured using hot wire probes and pressure transducers, for different operating conditions. Finally, the aeroacoustic behavior of the fan was determined measuring the vorticity field at the impeller outlet, which is known to be related to tonal noise generation. This relation is worked out using the theory of vortex sound, developed by several authors during the second half of this century. The paper shows that the generation of tonal noise is produced at the blade passing frequency and it increases with the flow rate. Although the main contribution to fan noise generation is due to mechanical sources, the bands in which aerodynamic noise is generated by these fans correspond to frequencies especially unpleasant to the human ear. Therefore, the research presented in this paper may be of considerable interest, establishing a starting point for the design of quieter and more efficient fans.
Investigation of Unsteady Sheet Cavitation and Cloud Cavitation Mechanisms
Authors: Pham T. M. , Larrarte F. , Fruman D. H.
Published: February 2008

Sheet cavitation on a foil section and, in particular, its unsteady characteristics leading to cloud cavitation, were experimentally investigated using high-speed visualizations and fluctuating pressure measurements. Two sources of sheet cavitation instability were evidenced, the re-entrant jet and small interfacial waves. The dynamics of the re-entrant jet was studied using surface electrical probes. Its mean velocity at different distances from the leading edge was determined and its role in promoting the unsteadiness of the sheet cavitation and generating large cloud shedding was demonstrated. The effect of gravity on the dynamics of the re-entrant jet and the development of interfacial perturbations were examined and interpreted. Finally, control of cloud cavitation using various means, such as positioning a tiny obstacle (barrier) on the foil surface or performing air injection through a slit situated in the vicinity of the leading edge, was investigated. It was shown that these were very effective methods for decreasing the amplitude of the instabilities and even eliminating them.
Numerical Model of Cavitating Propeller Inside of a Tunnel
Authors: Choi Jin-Keun , Kinnas Spyros A.
Published: February 2008

The unsteady cavitating flow of a propeller subject to a nonaxisymmetric inflow inside of a tunnel is addressed. A numerical method is developed which solves for the fully unsteady propeller problem and the tunnel problem separately, with the unsteady effects of one on the other being accounted for in an iterative manner. The propeller influence on the propeller is considered via velocity. The iterative process is found to converge very fast, usually within three iterations, even for a heavily loaded propeller. The effect of the tunnel extent and the number of panels on the predicted mean propeller forces is investigated. In the case of uniform inflow the equivalent open water velocity is calculated and then compared to that predicted from Glauert’s formula. The two velocities are found to be very close to each other in the case of light propeller loading, and to deviate from each other as the propeller loading increases. In the case of nonuniform flow the predicted unsteady propeller forces are found not to be affected appreciably by the tunnel effects in the case of noncavitating flow. In the case of cavitating flows the tunnel effects have been found to be appreciable, especially in terms of the predicted cavity extent and volume. The predicted cavity patterns are shown to be very close to those observed in CAPREX, a CAvitating PRopeller Experiment performed at MIT’s cavitation tunnel.
Steady and Unsteady Computations of Turbulent Flows Induced by a 4/45° Pitched-Blade Impeller
Authors: Wechsler K. , Breuer M. , Durst F.
Published: February 2008

The present paper summarizes steady and unsteady computations of turbulent flow induced by a pitched-blade turbine (four blades, 45° inclined) in a baffled stirred tank. Mean flow and turbulence characteristics were determined by solving the Reynolds averaged Navier-Stokes equations together with a standard k-ε turbulence model. The round vessel had a diameter of T = 152 mm. The turbine of diameter T/3 was located at a clearance of T/3. The Reynolds number (Re) of the experimental investigation was 7280, and computations were performed at Re = 7280 and Re = 29,000. Techniques of high-performance computing were applied to permit grid sensitivity studies in order to isolate errors resulting from deficiencies of the turbulence model and those resulting from insufficient grid resolution. Both steady and unsteady computations were performed and compared with respect to quality and computational effort. Unsteady computations considered the time-dependent geometry which is caused by the rotation of the impeller within the baffled stirred tank reactor. Steady-state computations also considered neglect the relative motion of impeller and baffles. By solving the governing equations of motion in a rotating frame of reference for the region attached to the impeller, the steady-state approach is able to capture trailing vortices. It is shown that this steady-state computational approach yields numerical results which are in excellent agreement with fully unsteady computations at a fraction of the time and expense for the stirred vessel configuration under consideration.
A Domain Decomposition Approach for Incompressible Flows Past Multiple Objects
Authors: Ku Hwar-Ching , Ramaswamy Bala
Published: February 2008

A domain decomposition approach has been developed to solve for flow around multiple objects. The method combines features of mask and multigrid algorithm implemented within the general framework of a primitive variable, pseudospectral elements formulation of fluid flow problems. The computational domain consists of a global rectangular domain, which covers the entire flow domain, and local subdomains associated with each object, which are fully overlapped with the rectangular domain. There are two key steps involved in calculating flow past multiple objects. The first step approximately solves the flow field by the mask method on the Cartesian grid alone, including on those grid points falling inside an object (a fuzzy boundary between the fluid-object interface), but with the restriction that the velocity on grid points within and on the surface of an object should be small or zero. The second step corrects the approximate flow field predicted from the first step by taking account of the object surface, i.e., solving the flow field on the local body-fitted (curvilinear) grid surrounding each object. A smooth data communication between the global and local grids can be implemented by the multigrid method when the Schwarz Alternating Procedure (SAP) is used for the iterative solution between the two overlapping grids. Numerical results for two-dimensional test problems for flow past elliptic cylinders are presented in the paper. An interesting phenomenon is found that when the second elliptic cylinder is placed in the wake of the first elliptic cylinder a traction force (a negative drag coefficient) acting on the second one may occur during the vortex formation in the wake area of the first one.
Theoretical Modeling of Central Air-Jet Pump Performance for Pneumatic Transportation of Bulk Solids
Authors: Wang D. , Wypych P. W.
Published: February 2008

A mathematical model to predict the air-solids performance of central air-jet pumps has been developed based on the fundamentals of fluid and particle mechanics. The influence of throat entry configuration on performance has been incorporated into the analytical model by introducing a throat entry function and suction area ratio. Nondimensional parameters to represent air-solids jet pump performance has been defined and used in the analytical procedure. The performance predictions obtained by this model show good agreement with experimental results.
Near Surface Characterization of an Impinging Elliptic Jet Array
Authors: Arjocu Simona C. , Liburdy James A.
Published: February 2008

In this study naturally occurring large-scale structures and some turbulence characteristics within an impinging jet array are investigated. The dynamics of a three-by-three elliptic jet array are analyzed relative to the flow structures within the array. With applications to electronic component cooling, low Reynolds number conditions, Re = 300 to 1500, are presented. Two jet aspect ratios are used, 2 and 3, with identical jet hydraulic diameters and jet-to-jet space. The effects of impinging distance are studied in the range of one to six jet hydraulic diameters. Flow visualization and PIV are used for the identification of structures and quantitative analysis. These results are used to evaluate the integrated surface layer vorticity, Γ*, which is shown to depend on the jet aspect ratio and impingement distance. Also, a transport coefficient is presented, based on a turbulence velocity and length scales. This coefficient is shown to experience a maximum value versus impingement distance that coincides with the location of axis switching.
Energy Concentrated and Self-Resonating Mini-Extended Jet Nozzle Used for Jet Drilling
Authors: Sun B. J. , Yan D. C.
Published: February 2008

Theoretical, experimental, and field test studies of the self-resonating pulsating jet have been carried out. The interaction mechanism of vortices and outlet wall is described. On the basis of theoretical calculations and experimental data, a new mini-extended and energy concentrated self-resonating pulsating jet nozzle can be recommended. Hydrodynamic experiments, rock erosion tests, and field tests in a drilling engineering environment were carried out using the new nozzle. The results show that the new nozzle has stronger erosion capability than the cone-type or conventional organ-pipe self-resonating nozzle jet. The field test results in drilling engineering show that the outlets of the newly designed nozzles have strong anti-scouring ability. The new exit design of the nozzle can increase its life span.
High-Lift Optimization Design Using Neural Networks on a Multi-Element Airfoil
Authors: Greenman Roxana M. , Roth Karlin R.
Published: February 2008

The high-lift performance of a multi-element airfoil was optimized by using neural-net predictions that were trained using a computational data set. The numerical data was generated using a two-dimensional, incompressible, Navier-Stokes algorithm with the Spalart-Allmaras turbulence model. Because it is difficult to predict maximum lift for high-lift systems, an empirically-based maximum lift criteria was used in this study to determine both the maximum lift and the angle of attack at which it occurs. Multiple input, single output networks were trained using the NASA Ames variation of the Levenberg-Marquardt algorithm for each of the aerodynamic coefficients (lift, drag, and moment). The artificial neural networks were integrated with a gradient-based optimizer. Using independent numerical simulations and experimental data for this high-lift configuration, it was shown that this design process successfully optimized flap deflection, gap, overlap, and angle of attack to maximize lift. Once the neural networks were trained and integrated with the optimizer, minimal additional computer resources were required to perform optimization runs with different initial conditions and parameters. Applying the neural networks within the high-lift rigging optimization process reduced the amount of computational time and resources by 83% compared with traditional gradient-based optimization procedures for multiple optimization runs.
Comparison of Flying-Hot-Wire and Stationary-Hot-Wire Measurements of Flow Over a Backward-Facing Step
Authors: Badran O. O. , Bruun H. H.
Published: February 2008

This paper is concerned with measurements of the flow field in the separated flow region behind a backward-facing step. The main instrument used in this research was Flying X Hot-Wire Anemometry (FHWA). Stationary (single normal) Hot-Wire Anemometry (SHWA) was also used. Comparative measurements between the SHW probe and the FHW system were conducted downstream of the step (step height H = 120 mm) and results are presented for axial locations of 1H and 2H. Two step configurations were considered; (i) a blunt leading edge with flow underneath (Case I) and (ii) a blunt leading edge with no flow underneath (Case II). It is observed from the results presented that the two Hot-Wire methods produce significantly different mean velocity and turbulence results inside the separation bubble. In particular, the SHWA method cannot detect the reverse flow velocity direction, while the Flying Hot-Wire clearly identifies the existing reverse flow. Also, in the shear flow region, the results presented indicate that measurements with a SHW probe must be treated with great caution.
A Multiple Disk Probe for Inexpensive and Robust Velocimetry
Authors: Green Sheldon I. , Rogak Steven N.
Published: February 2008

A novel velocimeter consisting of multiple orthogonal disks fitted with pressure transducers has been developed. Dynamic pressure differences are measured between the center of one disk face and the center of the other face, on each of the disks. While previously-developed anemometers based on dynamic pressure differences (such as yaw or three-hole probes) can only measure velocities with a small range of directions, the new disk probe can measure three components of velocity, even in highly three-dimensional flows where the approximate direction of the flow is not known. Wind tunnel tests have shown the velocimeter to be quite accurate; it can measure velocities to ±1.4% and wind directions to ±4 deg. The velocimeter is very robust and therefore can make measurements in environments too harsh for most other velocity transducers.
Biologically-Inspired Bodies Under Surface Waves—Part 1: Load Measurements
Authors: Bandyopadhyay Promode R. , Nedderman William H. , Dick James L.
Published: February 2008

Measurements have been carried out in a tow tank on cylindrical bodies submerged in proximity of traveling surface waves. Two bodies are considered: a reference plain cylinder and another cylinder containing a pair of wings (or hydrofoils) below the cylinder, not above. The latter body owes its origin to certain species of fish which has small wings for maneuverability. The wavelength of the surface waves (λ) is of the order of the cylinder length (L) or higher (1 < λ/L < 10). Temporal measurements of axial and vertical forces and pitching moments, phase matched to the surface elevation of traveling waves, have been carried out. The time periods of the waves and depth of water pertain to deep water and intermediate depth waves. The forces and moments exhibit characteristic phase relationship with water elevation. Towing affects only vertical forces in the speed range of 0 to 1 m/s. The effect of towing and surface waves on vertical forces is roughly additive. Within the low speed range of towing evaluated, the effects of surface waves dominate those of towing. The presence of the hydrofoil and intermediate depth waves bring in some additional effects which are not well understood. In intermediate depth waves, a small plain cylinder may encounter a resonance with traveling waves which can be averted by attaching a pair of small wings to dampen pitching moment and make it speed invariant, although at a cost of increased vertical forces.
Biologically-Inspired Bodies Under Surface Waves—Part 2: Theoretical Control of Maneuvering
Authors: Bandyopadhyay Promode R. , Singh Sahjendra N. , Chockalingam Francis
Published: February 2008

The theoretical control of low-speed maneuvering of small underwater vehicles in the dive plane using dorsal and caudal fin-based control surfaces is considered. The two dorsal fins are long and are actually mounted in the horizontal plane. The caudal fin is also horizontal and is akin to the fluke of a whale. Dorsal-like fins mounted on a flow aligned vehicle produce a normal force when they are cambered. Using such a device, depth control can be accomplished. A flapping foil device mounted at the end of the tailcone of the vehicle produces vehicle motion that is somewhat similar to the motion produced by the caudal fins of fish. The moment produced by the flapping foils is used here for pitch angle control. A continuous adaptive sliding mode control law is derived for depth control via the dorsal fins in the presence of surface waves. The flapping foils have periodic motion and they can produce only periodic forces. A discrete adaptive predictive control law is designed for varying the maximum tip excursion of the foils in each cycle for the pitch angle control and for the attenuation of disturbance caused by waves. Strouhal number of the foils is the key control variable. The derivation of control laws requires only imprecise knowledge of the hydrodynamic parameters and large uncertainty in system parameters is allowed. In the closed-loop system, depth trajectory tracking and pitch angle control are accomplished using caudal and dorsal fin-based control surfaces in the presence of system parameter uncertainty and surface waves. A control law for the trajectory control of depth and regulation of the pitch angle is also presented, which uses only the dorsal fins and simulation results are presented to show the controller performance.
Laminar Flow of a Nonlinear Viscoplastic Fluid Through an Axisymmetric Sudden Expansion
Authors: Hammad Khaled J. , O¨tu¨gen M. Volkan , Vradis George C. , Arik Engin B.
Published: February 2008

A combined experimental and computational study was carried out to investigate the laminar flow of a nonlinear viscoplastic fluid through an axisymmetric sudden expansion. The yield-stress, power-law index, and the consistency index of the yield shear-thinning test fluid were 0.733 Pa, 0.68, and 0.33 Pa · s0.68, respectively, resulting in a Hedstrom number of 1.65. The Reynolds number ranged between 1.8 and 58.7. In addition, the flow of a Newtonian fluid through the same expansion was also studied to form a baseline for comparison. Velocity vectors were obtained on the vertical center plane using a digital particle image velocimeter (PIV). From these measurements. two-dimensional distributions of axial and radial velocity as well as the stream function were calculated covering the separated, reattached and redeveloping flow regions. These results were compared to finite difference numerical solutions of the governing continuity and fully-elliptic momentum equations. The calculations were found to be in good agreement with the experimental results. Both computational and experimental results indicate the existence of two distinct flow regimes. For low Reynolds numbers, a region of nonmoving fluid is observed immediately downstream of the step and no separated flow zone exists. For the higher Reynolds numbers, a recirculating flow zone forms downstream of the expansion step, which is followed by a zone of stagnant fluid adjacent to pipe wall characterizing reattachment.
Experimental Analysis of Bubble Shapes During Condensation in Miscible and Immiscible Liquids
Authors: Kalman Haim , Ullmann Amos
Published: February 2008

The initial volume of a condensing bubble released from an orifice and the shape oscillations of the bubble during the collapse process were studied. Results of a large number of original experiments of bubbles condensing in miscible and immiscible liquids were analyzed to evaluate the initial volume, the instantaneous shape, and the average aspect-ratio of the bubbles. The results were compared to common empirical correlations that were originally developed to evaluate these parameters for noncondensing bubbles. It is demonstrated that such correlations can satisfactorily predict the initial volume of condensing bubbles and their mean aspect ratio throughout the collapse process.
Mechanisms of Heat Transfer Enhancement of Gas–Solid Fluidized Bed: Estimation of Direct Contact Heat Exchange From Heat Transfer Surface to Fluidized Particles Using an Optical Visualization Technique
Authors: Kurosaki Y. , Satoh I. , Ishize T.
Published: February 2008

This paper deals with mechanisms of heat transfer in a gas–solid fluidized bed. Heat transfer due to heat exchange by direct contact from a heat transfer tube immersed in the bed to fluidized particles was studied by means of visualization of contact of the fluidized particles to the heat transfer surface. The results show that the duration of contact of fluidized particles was almost uniform over the tube circumference and was hardly affected by the flow rate of fluidizing gas. On the other hand, the contact frequency between the particles and heat transfer tube was evidently influenced by the gas flow rate and particles diameter, as well as the location on the tube circumference. Using the visualized results, the amount of heat conducted to fluidized particles during the contact was estimated. This result showed that unsteady heat conduction to the fluidized particles plays an important role in the heat transfer, especially at the condition of incipient fluidization.
Effect of Imposed Wall Temperature Oscillations on the Stability of Natural Convection in a Square Enclosure
Authors: Xia Q. , Yang K. T. , Mukutmoni D.
Published: February 2008

The present numerical study is directed toward buoyancy-driven laminar flows in a two-dimensional square enclosure with differential heating at the vertical walls. The top and bottom walls are insulated. A time-dependent temperature varying sinusoidal perturbation is imposed on the hot vertical wall. The cold vertical wall is maintained at a constant temperature. The fluid is air with a Prandtl number of 0.72. Computations were carried out at one imposed frequency, which is of the same order as the first natural frequency of the system. It was found that the perturbations destabilized the flow in that higher amplitudes lead to lower critical Rayleigh numbers for the flow transitions. Computations spanned four regimes: periodic, quasi-periodic with two frequencies, quasi-periodic with three-frequencies, and chaotic.
Study of Natural Convection in an Enclosure Bounded by Two Concentric Cylinders and Two Diametric Planes
Authors: Sarr J. , Mbow C. , Chehouani H. , Zeghmati B. , Benet S. , Daguenet M.
Published: February 2008

The two-dimensional heat transfer induced by free laminar convection in an enclosure is numerically investigated in this work. A constant wall heat flux is applied on the inner cylinder while the outer is maintained at an uniform temperature, the others walls being adiabatic. The influence of the modified Grashof number (102 ≤ Gr ≤ 106) and an aspect Fr on convective motion and heat transfer is examined. A comparison of the heat transfer between different fluids such as air, ammonia–liquid, and carbon dioxide–liquid is also displayed. Holographic interferometry is used to visualize the temperature field within the enclosure and to confirm the two-dimensional behavior of the convective flow. The results show that maximum heat transfer is found for Fr = 1, when the Grashof number is up to 103, and the conduction regime is reached for a modified Grashof number less than 103. On the other hand, the average Nusselt number increases with the Prandtl number, Fr = 1.
In-Depth Absorption of Externally Incident Radiation in Nongray Media
Authors: Manohar S. S. , Kulkarni A. K. , Thynell S. T.
Published: February 2008

During flame spread along a surface, the thermal radiation emitted by high-temperature combustion products supports the advancement of the flame front. To model the response of the solid to the externally incident radiation, it is necessary to consider the spectral variation of radiative properties of the solid. For highly absorbent solids, such as wood or particle board, almost all of the externally incident radiation is absorbed at or very near the surface. However, for highly semitransparent materials, such as a plastic material whose surface is not clean, the externally incident radiation is absorbed both at the surface and within the material. In this work, the objective is to study both theoretically and experimentally the importance of in-depth radiation. A transient, one-dimensional model is formulated and solved numerically. The spectral radiative properties employed in the radiation model have been obtained from separate experiments on polymethylmethacrylate (PMMA), a clear plastic. The model demonstrates the importance of in-depth absorption. Model results exhibit the same trend as those revealed in experiments for the rise in surface temperature of the sample.
Subcooled Flow Film Boiling Across a Horizontal Cylinder: Part II—Comparison to Experimental Data
Authors: Chou X. S. , Sankaran S. , Witte L. C.
Published: February 2008

In this paper, the results of a rigorous heat transfer analysis of subcooled flow film boiling over a heated cylinder are compared to experimental data. The analysis includes both the influence of the front part of the heater and the wake region behind the heater. Experiments using Freon-113 were conducted at subcooling levels up to 58°C and at velocities up to 3.81 m/s. The configuration was upflowing Freon-113 in crossflow over a 0.635-cm electric heater. A comparison of these data as well as other available experimental data to the analysis of Chou and Witte showed good agreement as long as the subcooling level of the liquid was substantial—that is, for liquid Jakob numbers above about 0.04. This represents a considerable improvement over other models that have been developed to predict subcooled flow boiling heat transfer. A method using a temperature correction to a constant-property heat transfer solution that corresponds to the full variable-property solution is also presented, and applied to water and Freon-113.
An Experimental Study of Flow Boiling Heat Transfer in Rib-Roughened Tube Annuli
Authors: Hsieh Shou-Shing , Wen Mao-Yu
Published: February 2008

Heat transfer measurements were performed on six rib-type roughened tube annuli (4.67–9.01 mm Dh, 6–16 ribs, rib pitch 19.7–63.0 mm, rib height 4 ram, rib width 15 mm, rib angle 20–60 deg) with two phases of refrigerant R-114 under evaporating conditions. Based on the same heat transfer area of the test section, the effects of heat flux, quality, and rib spacing on flow boiling heat transfer coefficient were presented and discussed. Correlations of two-phase enhancement factor F and suppression factor S were developed by modifications and extensions of Chen’s model for the present geometric configurations.
Two-Dimensional Rotating Heat Pipe Analysis
Authors: Harley C. , Faghri A.
Published: February 2008

A detailed transient numerical simulation of rotating heat pipes is presented. This two-dimensional, axisymmetric formulation accounts for the thin liquid condensate film on the inner surface of the rotating pipe wall, the vapor flow in the vapor space, and the unsteady heat conduction in the pipe wall. The thin liquid film is coupled to the vapor velocity at the liquid–vapor interface, and the effects of the vapor pressure drop and the interfacial shear stress are included in the Nusselt-type condensation analysis.