bluuebunny/crossref_metadata_2025 huggingface dataset:
Flow Split Relationships in Two-Phase Parallel Channel Flows
Authors: Iloeje O. C. , Kervinen J. A. , Ireland J. , Shiralkar B. S.
Published: October 2009

The observed flow combinations through the channels were: cocurrent upflow in both channels, cocurrent upflow in one and countercurrent flow in the other channel, and cocurrent upflow in one and single phase liquid downflow in the other channel. The flow regimes in each channel varied from churn-turbulent, through anular flow, to chugging counter-current flow, as the flow conditions were varied. It was observed that the flow combination obtained was history dependent. However, for given flow combinations, certain flow split relationships were established. With both channels in cocurrent upflow, the flow quality into each channel was approximately the same as the flow quality in the lower plenum at the flow split elevation. For the other flow combinations, a simple relationship between the void fractions at the bottom of the channels which had two phase fluid, and the average void fraction and vapour flux in the lower plenum at the flow split elevation, was established.
A New Technique for Computing Viscous-Inviscid Interactions in Internal Flows
Authors: Strawn R. C. , Ferziger J. H. , Kline S. J.
Published: October 2009

A new viscous-inviscid interaction technique has been developed for computing separated flow in planar diffusers. The method couples a set of integral equations for the boundary layers to a fully elliptic potential core flow. Rapid convergence of the method is demonstrated for planar diffusers with large regions of transitory stall. For these cases, convergence of the new method is an order of magnitude faster than that obtained using the interaction schemes of Carter and Le Balleur. Good agreement between the prediction method and experimental data is obtained for diffusers that are operating near peak pressure recovery. More importantly, the onset of asymmetric detachment is successfully predicted for these cases.
Effect of Dilute Polymer Additives on the Acoustic Cavitation Threshold of Water
Authors: Crum L. A. , Brosey J. E.
Published: October 2009

Measurements are presented of the variation of the acoustic cavitation threshold of water with concentration of the polymer additives polyethylene oxide and guar gum. It was found that small amounts of these additives could significantly increase the cavitation threshold. A theoretical model, based upon nucleation of a gas bubble from a Harvey-type crevice in a mote or solid particle, is developed that gives good agreement with the measurements. The applicability of this approach to an explanation of cavitation index reduction in flow-generated or confined jet cavitation, when polymer additives are introduced, is discussed.
A Limited Role of Separation Bubble in Desinent Cavitation
Authors: Ito Y. , Oba R.
Published: October 2009

In order to clarify whether a separation bubble always plays an important role, the desinence of streamer-cavitation, a kind of attached-cavitation, was carefully investigated in typical internal flows through venturies with and without a 40 μm thin backward facing step under a prescribed cavitation nuclei as well as various hydrodynamic conditions. The following facts have been found: (i) the separation bubble can play an important role in the desinence only when the separation bubble thickness H is larger than the diameter of nucleus dnp that may grow up to a critical one [18], (ii) a marked change takes place in the desinent cavitation number σd due to the step, i.e., σd ≅ |Cps| for H > dnp but σd < |Cps| for H ≦ dnp, (iii) for the cavitation there are two geneses, i.e., the nuclei floating within the separation bubble and the bubble-cloud occurring in the reattachment-region.
The Study of Propeller Cavitation Noise Using Cross-Correlation Methods
Authors: Leggat L. J. , Sponagle N. C.
Published: October 2009

This paper presents a technique for the study of the mechanisms responsible for the generation of noise from cavitating propellers. The experimental method, which involves the cross-correlation of the pressure gradient in the near-field of the propeller with the far-field sound, allows the determination of the spatial distribution of acoustic source strength on and near the cavitating propeller. The paper describes the mathematical basis for the cross-correlation technique, and then presents some of the results from experiments with propellers specifically designed to produce vortex and bubble forms of cavitation. Cross-correlations performed at a number of points along a track parallel to the axis of the propeller indicate that most of the noise from propellers producing vortex cavitation originates from the region of vortex collapse. A bubble cavitation propeller showed a region of relatively constant source strength distribution from the propeller disk region downstream to the point of vortex collapse.
Orifice Contraction Coefficient for Inviscid Incompressible Flow
Authors: Grose R. D.
Published: October 2009

The theory for steady flow of an incompressible fluid through an orifice has been semi-empirically established for only certain flow conditions. In this paper, the development of a more rigorous theory for the prediction of the orifice flow contraction effect is presented. This theory is based on the conservation of momentum and mass principles applied to global control volumes for continuum flow. The control volumes are chosen to have a particular geometric construction which is based on certain characteristics of the Navier-Stokes equations for incompressible and, in the limit, inviscid flow. The treatment is restricted to steady incompressible, single phase, single component, inviscid Newtonian flow, but the principles that are developed hold for more general conditions. The resultant equations predict the orifice contraction coefficient as a function of the upstream geometry ratio for both axisymmetric and two-dimensional flow fields. The predicted contraction coefficient values agree with experimental orifice discharge coefficient data without the need for empirical adjustment.
On Liquid Film Pressure Sealing
Authors: Favre Jean-Nicolas , Ryhming I. L.
Published: October 2009

The dynamics of the thin film established, by oil injection, on the inside wall of the casing in certain rotary compressors are analyzed both experimentally and theoretically. The film may provide an effective pressure seal to prevent leakage of air from one side of a rotor lobe to the other. It is found that Reynolds’ bearing theory, corrected for Reynolds number and surface tension effects, gives reasonable results for the film thickness needed to sustain typical operational pressure differences in the machine. The theoretical predictions have been verified experimentally in a series of tests performed in a specially designed apparatus.
On the Stability of Vortex Motions in Compressible Stratified Fluids
Authors: Fung Y. T.
Published: October 2009

Necessary conditions for the stability of a general class of compressible vortex flows are obtained using the method of generalized progressing wave expansion. The vortex motion and the density are assumed to vary in both the radial and axial directions. These conditions, representing a generalized state of statically stable distribution for the steady flow, require that the flow be stable in the centrifugal force field created by the rotation of the fluids, in the gravitational force field arisen from the density variation, and in the pressure field constraining the variation of density and forces in both the radial and axial directions. These results also suggest the likely behavior of Richardson criteria for stability of the flow yet to be derived.
Similarity Solutions for Plane and Radial Jets Using a k-ε Turbulence Model
Authors: Paullay A. J. , Melnik R. E. , Rubel A. , Rudman S. , Siclari M. J.
Published: October 2009

When the eddy viscosity is defined by the standard k-ε turbulence model, the equations governing self-similar incompressible plane and radial jets have a solution that is not analytic at the jet edge. A transformation that stretches the similarity variable simplifies the defining set of ordinary differential equations and makes them amenable to efficient numerical integration. Highly resolved solutions for the velocity, turbulent kinetic energy and dissipation rate profiles are tabulated and entrainment, velocity decay rate and growth rate are determined. The growth rate differs by 6 percent from a parabolic marching asymptotic solution to the full partial differential equations.
Near Wake Properties of a Strumming Marine Cable: An Experimental Study
Authors: Peltzer R. D. , Rooney D. M.
Published: October 2009

Resonant flow-induced oscillations of a flexible cable can occur when the damping of the cable system is sufficiently small. The changes in the flow field that occur in the near wake of the cable during these resonant oscillations are closely related to the changes in the fluid forces that accompany these oscillations. The present wind tunnel experiments were undertaken to examine the effects that forced synchronized vibration and the helically-wound cross section of the cable have on near wake vortex shedding-related parameters; specifically the shedding frequency, vortex formation length Lf, reduced velocity Ur, vortex strength and the wake width Lw. The range of flow speeds over which the vortex shedding was locked on to the vibration frequency varied directly with the vibration amplitude. The helical cross section and the synchronized vibration caused significant changes in the near wake development that could be directly related to the increase in hydrodynamic forces associated with unforced synchronized vibration.
A Numerical Study of Pulsed Turbulent Pipe Flow
Authors: Reddy V. , McLaughlin J. B. , Nunge R. J.
Published: October 2009

A numerical study of fully developed turbulent pipe flow due to a sinusoidally varying (with respect to time) axial pressure gradient was carried out using a nonlinear three-dimensional model. Pseudospectral methods were used to solve the model equations. The pulsation frequency was characteristic of the wall region eddies in steady turbulent flow. Attention was focused on the viscous wall region, and it was found that the mean profiles of axial velocity, fluctuation intensities, and turbulence production rate were essentially the same as in steady flow. The fluctuation intensities and the turbulence production rate showed a definite phase relationship to the pressure gradient. The turbulence production rate was the largest at the time in the pulsation cycle at which the largest adverse pressure gradient existed.
Calculation of the Mean Flow Past Circular Cylinders by Viscous-Inviscid Interaction
Authors: Celik I. , Patel V. C. , Landweber L.
Published: October 2009

A method for the calculation of the mean flow past smooth circular cylinders is presented and evaluated. It utilizes an iterative procedure that couples a boundary-layer calculation method, by which the location of separation and the displacement thickness are predicted, and a new two-parameter irrotational-flow model, which predicts the pressure distribution. The displacement effect of the boundary layer is explicitly taken into account in the irrotational-flow model. The location of separation, drag coefficient, and pressure-distribution parameters are predicted at Reynolds numbers as high as 108. The results are compared with experiments in the subcritical and the supercritical flow regimes and with empirically developed design criteria for cylindrical structures at high Reynolds numbers.
Influence of Homogeneous Condensation Inside a Small Gas Bubble on Its Pressure Response
Authors: Matsumoto Y. , Beylich A. E.
Published: October 2009

The response of a small gas bubble to an ambient pressure reduction is investigated theoretically. Numerical results show that the temperature inside the bubble decreases due to adiabatic expansion at the first stage, then it recovers almost to the surrounding liquid temperature because of latent heat release caused by mist formation inside the bubble. Consequently, the bubble behaves apparently isothermally. The relation between the initial bubble radius and the critical pressure for cavitation inception to stepwise ambient pressure reduction becomes close to the relation under the assumption of isothermal change in the gas mixture inside the bubble.
Boundary-Layer Control as a Means of Reducing Drag on Fully Submerged Bodies of Revolution
Authors: Bar-Haim B. , Weihs D.
Published: October 2009

The drag of axisymmetric bodies can be reduced by boundary-layer suction, which delays transition and can control separation. In this study, boundary-layer transition is delayed by applying a distributed suction technique. Optimization calculations were performed to define the minimal drag bodies at Reynolds numbers of 107 and 108. The saving in drag relative to optimal bodies with non-controlled boundary layers is shown to be 18 and 78 percent, at Reynolds numbers of 107 and 108, respectively.
Numerical Investigations Into the Mechanisms of Microbubble Drag Reduction
Authors: Madavan N. K. , Merkle C. L. , Deutsch S.
Published: October 2009

Computational results of an initial attempt to model the phenomenon of skin-friction reduction by microbubble injection are presented. A well-tested boundary-layer code employing a simple mixing length model for the turbulence is used. The action of the bubbles is simulated by allowing the viscosity and density to vary locally as a function of a prescribed bubble concentration profile. Parametric studies of bubble location in the boundary layer, peak concentration and mixture viscosity model are performed. The order of magnitude and trends of the experimental skin-friction reduction are reproduced quite well by this simple model.
Wake Flow Stabilization by the Action of Base Bleed
Authors: Wong H. Y.
Published: October 2009

Experimental investigation into the effects of base bleed on wake stabilization for the suppression of flow-induced oscillation has shown that when the bleed flow rate is increased, the initial vortices are formed downstream, thus constituting the main cause of the removal of vortex excitation from the body which has produced them. Base ejections, if unsuitably placed, however, could aggravate oscillation. In wake buffeting, the situation can be greatly improved if base bleed is introduced from the downstream body but not from the upstream body.
Flow Formed by Spanwise Gaps Between Roughness Elements
Authors: Logan Earl , Lin Shu Ho , Islam Obaidul
Published: October 2009

Measurements of the three mean velocity components and the three Reynolds shear stresses were made in the region downstream of gaps between wall-mounted roughness elements of square cross section and high aspect ratio in a thick turbulent boundary layer. The effect of small and large gaps was studied in a wind tunnel at a Reynolds number of 3600, based on obstacle height and free-stream velocity. The small gap produces retardation of the gap flow as with a two-dimensional roughness element, but a definite interaction between gap and wake flows is observed. The interaction is more intense for the large gap than for the small. Both gaps generate a secondary crossflow which moves fluid away from the centerline in the wall region and toward the centerline in the outer (y > 1.5H) region.
Calculation of 1-D Unsteady Flows in Pipe Systems of I.C. Engines
Authors: Bulaty T. , Niessner H.
Published: October 2009

Linear finite-difference methods of higher than first-order accuracy applied to the calculation of 1-D unsteady flow inevitably produce numerical overshoot at discontinuities. Several remedies have been proposed in the past; a simple and effective one is flux correction. We propose it in the naive form, which destroys neither the order of accuracy nor the stability of the underlying method. Particular problems arise at the boundaries, where appropriate precautions help to fulfill the conservation laws. Additionally allowing for elasticity of the valve control system, results with acceptable accuracy are obtained in supercharging practice. A comparison of computing time, accuracy and storage requirements confirms the advantages of naive flux correction.
Steady and Unsteady Airflow Through the Intake Valve of a Reciprocating Engine
Authors: Bicen A. F. , Vafidis C. , Whitelaw J. H.
Published: October 2009

An experimental investigation of the airflow through various axisymmetric intake ports of a motored reciprocating engine is reported. Detailed velocity field measurements obtained by laser Doppler anemometry and for steady and various unsteady flow conditions are presented together with valve discharge coefficients from steady flow tests. The results showed that over the lift range investigated the valve flow exhibited various regimes indicated by the changes in the flow pattern at the valve exit. With a 45-deg seat angle, four regimes were identified compared to three in the case of a 60-deg valve. The overall behavior of the 45-deg valve, however, was found to be generally better. Rounding of the edges of the 45-deg valve reduced the number of flow regimes to two with marked improvements on discharge coefficient. The flow angle at the valve exit depended less on the flow regimes and more on the cylinder confinement, in the absence of which the transition from one regime to another was delayed. The mean flow pattern at the valve exit was found to be insensitive to flow unsteadiness, piston confinement and valve operation and thus could be predicted with reasonable accuracy from steady flow tests. The in-cylinder flow characteristics were also insensitive to valve operation, but strongly depended on piston interaction, flow unsteadiness and residual effects from the previous cycle.
Calculation of the Aerodynamic Forces on Automotive Lifting Surfaces
Authors: Katz J.
Published: October 2009

A numerical technique was developed to investigate the performance of automotive lifting surfaces in close proximity to ground. The model is based on the Vortex Lattice Method and includes freely-deforming wake elements. The ground effect was simulated by reflection and both steady and unsteady pressures and loads on various wing planforms were considered. Calculated results are presented for wings having both positive and negative incidences, with and without ground effect. Also the transient lift of a wing in a plunging motion was analyzed in ground proximity and at a negative angle of attack. Finally the periodic lift fluctuations on the front winglet of a racing car, due to its suspension oscillations, were calculated and found to exceed approximately twice the steady-state value.
Flow Around Two Intersecting Circular Cylinders
Authors: Zdravkovich M. M.
Published: October 2009

One aspect of the flow around two intersecting cylinders, which has attracted little attention so far, is the structure of a three-dimensional near-wake behind the intersection. Some preliminary measurements of pressure distributions along the span were complemented by oil-film surface flow visualization. A strong secondary flow was found in the near-wake which extended spanwise more than three diameters from the intersection. The main feature was the formation of four symmetrically positioned pairs of swirling vortices which originated from the surface of the cylinders. The secondary flow caused an increase in the local drag coefficient.
An Investigation of Compressible Flow Characteristics of Butterfly Valves
Authors: Addy A. L. , Morris M. J. , Dutton J. C.
Published: October 2009

Compressible flow characteristics including mass flowrate, onset of “choked” flow, stagnation pressure loss, and static pressure recovery have been investigated for butterfly valves. A simplified sudden-enlargement in flow area theoretical model has been used to characterize the overall mass flowrate and pressure characteristics of the valve flow. A series of small-scale compressible flow experiments has also been conducted using sudden-enlargement configurations with different nozzle geometries and using geometrically similar model valves. These experiments provided a database for augmenting the simplified theoretical model with needed empirical information and for assessing the range of applicability of the theoretical model. This method can be used to predict the mass flow and pressure characteristics of full-scale valves based on model experiments and/or to determine the overall operating characteristics of full-scale valves from in situ pressure measurements.
Interaction Between Impeller and Volute of Pumps at Off-Design Conditions
Authors: Lorett J. A. , Gopalakrishnan S.
Published: October 2009

In a centrifugal pump of volute type, the respective characteristics of the impeller and the volute are such that at only one operating point can the flow parameters be constant along the length of the volute. At off-design conditions the mismatching of characteristics causes variations of velocity and pressure along the periphery of the impeller. This in turn forces cyclic variation of the flow in the impeller channels, introduces variations of the inlet incidence and contributes significantly to the direction and the magnitude of the radial thrust. Furthermore, below a certain pump output, a complete flow reversal occurs over a part of the impeller periphery, thus explaining the onset of recirculation. The paper describes the calculation approach used to derive this aspect of the flow behavior. Because of difficulties in obtaining a closed analytical solution, a step by step computation is employed. Beginning with arbitrarily chosen conditions at the volute tongue, the program computes the flow parameters for following segments, using the continuity and the momentum equations, until the exit from the last segment is reached. The inherent unsteadiness of the relative flow in the impeller is explicitly accounted for. Since the inflow and the velocity in the first segment depend upon the exit conditions of the last, the initial input must be modified, and the computation repeated, until the values are compatible with the exit conditions. In spite of several simplifying assumptions, the results of the calculations show very good agreement with published test results.
A Two-Dimensional Analysis of Unsteady Torque on Mixed Flow Impellers
Authors: Tsujimoto Y. , Imaichi K. , Tomohiro T. , Gotoo M.
Published: October 2009

A new method is given for the analysis of unsteady flows through mixed flow impellers under an assumption of a two-dimensional flow in a representative flow surface of revolution. The flow is mapped to one around a two-dimensional annular cascade. If the thickness of the impeller flow passage changes in a certain functional form, the flow can be represented by using a two-dimensional potential flow in the mapping plane. For impellers with such a thickness distribution, small sinusoidal and/or large transient fluctuations of flow rate and/or rotational velocity are considered. Special attention is paid to the unsteady torque on the impeller. The unsteady torque is divided into three components—quasisteady, apparent mass and wake, and the effects of the geometry of the flow surface on each component are discussed. Apparent mass torque coefficients are determined for fluctuations of flow rate and rotational velocity. Stability of torsional vibration and surging are discussed from energy considerations.
Scrutinizing the k-ε Turbulence Model Under Adverse Pressure Gradient Conditions
Authors: Rodi W. , Scheuerer G.
Published: October 2009

The k-ε model and a one-equation model have been used to predict adverse pressure gradient boundary layers. While the one-equation model gives generally good results, the k-ε model reveals systematic discrepancies, e.g. too high skin friction coefficients, for these relatively simple flows. These shortcomings are examined and it is shown by an analytical analysis for the log-law region that the generation term of the ε-equation has to be increased to conform with experimental evidence under adverse pressure gradient conditions. A corresponding modification to the ε-equation emphasizing the generation rate due to deceleration was employed in the present investigation and resulted in improved predictions for both moderately and strongly decelerated flows.
A Fast Approximate Solution of the Laminar Boundary-Layer Equations
Authors: Iida Sei-ichi , Fujimoto Akira
Published: October 2009

A new approximate method of calculating steady laminar boundary-layers is presented. This method is based on the mutual relationships between boundary-layer characteristic quantities. The governing equations are efficiently solved without assuming a specific velocity profile. Moreover, a method of estimating the velocity profile using the characteristic quantities is also proposed. Comparison of the results obtained for a wide variety of applications to boundary-layer flows with separations with exact solutions indicates that the present method enables one to obtain solutions with sufficient accuracy and shorter computational time when compared with existing computational techniques.
Transient Characteristics of a Centrifugal Pump During Stopping Period
Authors: Tsukamoto H. , Matsunaga S. , Yoneda H. , Hata S.
Published: October 2009

A theoretical and experimental study has been made on the transient characteristics of a centrifugal pump during its rapid deceleration from initial speed to zero. Instantaneous rotational speed, flow-rate, and total pressure rise are measured for various stopping schemes. Theoretical calculations for the prediction of transient characteristics are developed and compared with the corresponding experimental results. As a result of this study, it becomes clear that impulsive pressure and the lag in circulation formation around impeller vanes play predominant roles for the difference between dynamic and quasi-steady characteristics of turbopumps. Moreover, a criterion for the assumption of quasi-steady change is presented.
Integral Skin Friction Prediction for Turbulent Separated Flows
Authors: Das D. K. , White F. M.
Published: October 2009

An integral method is presented for computing incompressible two-dimensional turbulent skin friction for separated flows based on the inner-variable theory. Using a velocity profile in the form of the logarithmic law and wake, continuity and momentum equations are integrated across the boundary layer in terms of inner-variables u+ and y+. With the aid of correlations relating the wake parameter to the pressure gradient parameter, derived from experimental results of several near-separating and separated flows, the governing equations are reduced to a single differential equation in skin friction. Predictions by the theory for several separated flows show satisfactory agreement with experimental data.
Dynamics of Liquid Sloshing in Upright and Inverted Bladdered Tanks
Authors: Dodge F. T. , Kana D. D.
Published: October 2009

The sloshing of liquids in tanks that use a flexible, inextensible bladder to contain the liquid is investigated experimentally and theoretically. The bladder affects both the configuration of the liquid in the tank and the sloshing frequencies and motion. The governing equations of liquid sloshing coupled to the structural dynamics of the bladder are formulated and examined to determine the interaction between the body forces of the liquid and the stiffness of the bladder and to show that the slosh dynamics can be represented by equivalent mechanical models. Tests are conducted to establish such mechanical models for normal and low-gravity conditions. For an inverted tank (liquid above the bladder), the sloshing is sufficiently different from conventional sloshing that the form of the equivalent mechanical model as well as the numerical values of the model parameters must be derived from the test results.
Drop Size Distribution and Air Velocity Measurements in Air Assist Swirl Atomizer Sprays
Authors: Mao C.-P. , Oechsle V. , Chigier N.
Published: October 2009

Detailed measurements of mean drop size (SMD) and size distribution parameters have been made using a Fraunhofer diffraction particle sizing instrument in a series of sprays generated by an air assist swirl atomizer. Thirty-six different combinations of fuel and air mass flow rates were examined with liquid flow rates up to 14 lbm/hr and atomizing air flow rates up to 10 lbm/hr. Linear relationships were found between SMD and liquid to air mass flow rate ratios. SMD increased with distance downstream along the center line and also with radial distance from the axis. Increase in obscuration with distance downstream was due to an increase in number density of particles as the result of deceleration of drops and an increase in the exposed path length of the laser beam. Velocity components of the atomizing air flow field measured by a laser anemometer show swirling jet air flow fields with solid body rotation in the core and free vortex flow in the outer regions.
Pressure Fluctuations on the Surface of a Hemisphere Immersed in a Thick Turbulent Boundary Layer
Authors: Suzuki Y. , Kiya M. , Sampo T. , Naka Y.
Published: October 2009

Statistical properties of pressure fluctuations on the surface of a hemisphere immersed in a thick turbulent boundary layer are described. The height of the hemisphere tested was 0.275 thicknesses of the boundary layer. Reynolds number based on the model diameter D and the time-mean approaching flow velocity at the level of the top Ur was 3.0 × 105. Time-mean and root-mean-square (rms) values, probability density and power spectra of the pressure fluctuations are presented and discussed. The pressure fluctuations are related to the fluctuating approaching-flow velocity in terms of the pressure-velocity admittance and the cross correlation. Main results are that the time-mean and rms pressures attained a primary maximum at the front stagnation point; that the pressure-velocity admittance near the front stagnation point was approximately unity at frequencies less than about 0.4 Ur/D; that the pressure fluctuation in front of the hemisphere is positively correlated with that in the rear side and negatively correlated with that in the middle.
Experimental Investigation of an Orifice Meter Pressure Gradient
Authors: Teyssandier R. G. , Husain Z. D.
Published: October 2009

Wall and plate pressure gradients were investigated in a 3.5 in. (89 mm) air flow orifice meter facility for 3 orifice plates covering a pipe Reynolds number range of 21,000 to 160,000. The influence of the orifice plate on the upstream wall pressure gradient extended to 0.62D location. It was also found that the pressure gradient is a weak function of the orifice plate β ratio. The downstream location of the minimum pressure point located at about 3.3 dam heights. The pressure gradient on the face of the orifice plate shows that the deflection calculation based on any differential pressure taps is conservative.
Improved Form of the k-ε Model for Wall Turbulent Shear Flows
Authors: Nagano Y. , Hishida M.
Published: October 2009

An improved k-ε turbulence model for predicting wall turbulence is presented. The model was developed in conjunction with an accurate calculation of near-wall and low-Reynolds-number flows to meet the requirements of the Evaluation Committee report of the 1980–1981 Stanford Conference on Complex Turbulent Flows. The proposed model was tested by application to turbulent pipe and channel flows, a flat plate boundary layer, a relaminarizing flow, and a diffuser flow. In all cases, the predicted values of turbulent quantities agreed almost completely with measurements, which many previously proposed models failed to predict correctly, over a wide range of the Reynolds number.
Motion of Particles in Gases: Average Velocity and Pressure Loss
Authors: Michaelides E. E.
Published: October 2009

A simplified physical model is developed for the motion of solid particles in gaseous streams confined by walls (channel or pipe flow). The equations of motion for the particle are solved and expressions for the average slip and pressure loss are developed. The pressure loss expression is supplemented with a statistically derived constant from a bank of approximately 1600 data. This pressure loss expression was compared with others, used by designers and was observed that it shows the lowest average error; the resulting standard deviation also compared favorably with that of other expressions used in the past.
Numerical Simulation of Spray Cooling Pond Performance
Authors: Moussiopoulos N.
Published: October 2009

A mathematical model for predictions of the performance of spray cooling ponds is presented. In contrast to previous methods, the present model requires neither empirical information from field measurements nor an adaptation of model constants. The airflow is described by partial differential equations for the vorticity and the stream function. Turbulence is taken into account by a modified version of the k-ε model. Temperature and humidity of air are obtained by solving appropriate transport differential equations. The equation system is solved by means of a finite difference method. The utilized numerical algorithm has been proved to be reasonably accurate. Predicted distributions for the dependent variables are presented for a circular spray cooling pond and the case of zero wind velocity. Results for the thermal performance of this pond are in good agreement with observations.
Improved Approach to the Streamline Curvature Method in Turbomachinery
Authors: Abdallah S. , Henderson R. E.
Published: October 2009

Quasi three dimensional blade-to-blade solutions for stators and rotors of turbomachines are obtained using the Streamline Curvature Method (SLCM). The first-order velocity gradient equation of the SLCM, traditionally solved for the velocity field, is reformulated as a second-order elliptic differential equation and employed in tracing the streamtubes throughout the flow field. The equation of continuity is then used to calculate the velocity. The present method has the following advantages. First, it preserves the ellipticity of the flow field in the solution of the second-order velocity gradient equation. Second, it eliminates the need for curve fitting and strong smoothing under-relaxation in the classical SLCM. Third, the prediction of the stagnation streamlines is a straightforward matter which does not complicate the present procedure. Finally, body-fitted curvilinear coordinates (streamlines and orthogonals or quasi-orthogonals) are naturally generated in the method. Numerical solutions are obtained for inviscid incompressible flow in rotating and non-rotating passages and the results are compared with experimental data.
The Recirculatory Flow Induced by a Laminar Axisymmetric Jet Issuing From a Wall
Authors: Schneider W. , Zauner E. , Bo¨hm H.
Published: October 2009

The laminar, axisymmetric, submerged jet issuing from a plane, infinite wall perpendicular to the jet axis is considered at very large distance from the nozzle. Based on previous results of an asymptotic analysis, an approximate analytical solution for the complete flow field is obtained. The structure of the far field is discussed by considering various regions the size of which depends strongly on the Reynolds number. The main region is a toroidal eddy in which both inertial and viscous forces are of importance. Closer to the nozzle there is a slender jet flow with slowly varying momentum flux together with a self-similar viscous outer flow. At larger distances, the flow resembles the creeping flow due to point sources of momentum and mass, with the former decaying more rapidly than the latter as infinity is approached. Analytical predictions of the location of the eddy center compare favorably with experimental and numerical results.
Spray Photographs, Poppet Lift, and Injection Pressure of an Oscillating Poppet Injector
Authors: Chehroudi B. , Lombardi P. , Felton P. G. , Bracco F. V.
Published: October 2009

Sprays from an injector with a conical oscillating poppet and supplied with fuel at injection rates similar to those used in direct-injection stratified-charge engines have been characterized. Instantaneous injection pressure and poppet lift were measured and short-exposure backlit photographs were taken at several times during injection. Spray axial tip penetration and velocity were determined from the photographs. The experiments were conducted in a constant-volume pressure vessel. The gas was nitrogen and the liquid was hexane. The gas temperature was either 25° or 55°C. The experiments included a systematic variation of the ambient pressure, pump speed and injected liquid volume. It was found that the structure of the spray was strongly affected by the chamber pressure. The hollow cone collapsed and injection duration, spray axial initial velocity and tip penetration decreased with increasing chamber pressure. Increasing pump speed decreased both injection duration and number of oscillations.
Velocity Characteristics of the Flow Around Disks and Cones
Authors: Dura˜o D. F. G. , Firmino F. C.
Published: October 2009

A direction-sensitive laser-Doppler anemometer was used to measure the aerodynamic characteristics in and around the wake of disks and cones located in the center line of a jet exiting from a tube. The tube inner diameter was 42 mm; the maximum jet velocities were 8.2 and 10.6 m/s; and disks and cones of 10 and 15 mm diameter were located at 10 and 75 mm from the jet-exit plane. Profiles of the axial and radial mean velocity components and rms values of the three fluctuating components of velocity and shear stress were obtained. The measurements indicate for disks and cones of 10 mm diameter, recirculation lengths of 1.35 d and 1.60 d, respectively. The recirculation lengths increase with baffle diameter are independent of initial velocity and slightly decrease with the increase of the distance from the jet exit to the baffle. The turbulence intensity in the recirculation region is never less than 30 percent and strongly anisotropic. Periodic oscillations corresponding to a Strouhal number of 0.18 were found.
Removal of a Thin Liquid Film From a Flat Surface Using an Axisymmetric Impinging Jet
Authors: Chilukuri R. , Aeling D. , Middleman S.
Published: October 2009

A simple theory is presented which allows prediction of the rate of thinning of a viscous liquid film, initially coated upon a rigid plane surface, subjected to the action of an impinging jet. A set of experimental data provides confirmation of the theory. The removal of a thin film of liquid contaminant from a flat surface is often accomplished by flushing the surface with a jet of a second fluid. The rate of removal of the liquid contaminant is expected to be a function of the physical properties of the two fluids involved, the dynamic and geometric parameters that describe the impinging jet, and the topography of the surface itself. Although the impingement of a jet on clean, smooth, rigid surfaces has been well studied, (Giralt, et al. (1977), Scholtz and Trass (1970)) there has been almost no work done on the relatively more complex problem of jet impingement onto thin deformable surfaces. The present study focusses on the removal of a liquid spill (which is a deformable surface) from under an impinging air jet.
Temporally Stable Density Patterns in Liquids
Authors: Kafri O. , Livnat A. , Glatt I.
Published: October 2009

By applying a new optical technique, moire deflectometry, we have observed complex density patterns in apparently homogeneous solutions, under ambient conditions. The density patterns of the liquids are attributed to cooling due to evaporation, precipitation caused by gravity, or dissolution.
Thermal Hydraulic and Two-Phase Phenomena in Reflooding of Nuclear Reactor Cores
Authors: Ghiaasiaan S. M. , Catton I. , Duffey R. B.
Published: October 2009

A quasi-steady, two-dimensional thermal hydraulic analysis of the two-phase region formed ahead of a quench front during reflooding of a slab or cylindrical core is carried out, and the results for slab geometry are compared with the experiment. It is shown that the two-phase level variation in the core is due to the transverse heat flux power profile, and is sensitive to the assumed pressure-drop boundary condition for the bundle, while the effects of crossflow and axial friction are small. Implicit expressions are given for predicting the quasi-steady two-phase level variation across slab and cylindrical cores.
Simulation of the Pressure Field Due to a Submerged Oscillating Jet Impacting on a Solid Wall
Authors: Genoux Ph. F. , Chahine G. L.
Published: October 2009

This paper presents some results obtained with the simulation of a submerged oscillating jet impacting on a solid wall. The oscillating jet which organizes into large vortical structures is simulated by the emission of vortex rings at a constant frequency. Outside of the cores of the rings the fluid is assumed to be inviscid and irrotational. The positions of the tori are obtained by combining for each torus its self-induced velocity with the velocity induced by all other rings and ring-images in the wall. The tangential velocities and the pressures in the fluid at the wall are then computed. The high shearing and suction forces found at the wall may explain the enhanced erosivity and cleaning action of oscillating jets.
Exploration of the Iceformation Method Applied to a Diffuser
Authors: LaFleur R. S.
Published: October 2009

The design of optimum flow surfaces has been a challenging task for fluid dynamicists ever since the concept of fluid drag was realized. This paper will serve to introduce another method of flow surface design which has the potential to overcome the difficulties of present analytic and experimental methods. Natural design is introduced as an alternative to scientific design. The iceformation method is defined as harnessing the natural process of ice formation to perform geometric variations. The flow field has the direct opportunity to influence and optimize the geometry development. The hypothesis of design optimization is tested by an exploratory example of the method. The example is a fundamental but nevertheless difficult design problem of a diffuser. Use of the iceformation method resulted in the design of diffusers with higher pressure recovery performance than conical diffusers of the same length and area ratio.
Turbulence Measurements With Symmetrically Bent V-Shaped Hot-Wires. Part 2: Measuring Velocity Components and Turbulent Shear Stresses
Authors: Hishida M. , Nagano Y.
Published: October 2009

An analysis of the response of a V-shaped hot-wire to velocity component fluctuations is presented. A V-shaped hot-wire works in the same manner as a conventional inclined straight wire. The great differences are: the V-shaped wire is less sensitive to the w component of velocity; the V-shaped wire can be supported just like a cantilever, and thus the wire may be brought closer to the wall until it touches the wall surface, whereas an inclined straight wire is kept away from the wall by the supports, and a probe body distorts the flow field.
Vectorizable Implicit Algorithms for the Flux-Difference Split, Three-Dimensional Navier-Stokes Equations
Authors: Hartwich P-M. , Hsu C-H. , Liu C. H.
Published: October 2009

The computational efficiency of four vectorizable implicit algorithms is assessed when applied to calculate steady-state solutions to the three-dimensional, incompressible Navier-Stokes equations in general coordinates. Two of these algorithms are characterized as hybrid schemes; that is, they combine some approximate factorization in two coordinate directions with relaxation in the remaining spatial direction. The other two algorithms utilize an approximate factorization approach which yields two-factor algorithms for three-dimensional systems. All four algorithms are implemented in identical high-resolution upwind schemes for the flux-difference split Navier-Stokes equations. These highly nonlinear schemes are obtained by extending an implicit Total Variation Diminishing (TVD) scheme recently developed for linear one-dimensional systems of hyperbolic conservation laws to the three-dimensional Navier-Stokes equations. The computations of vortical flows over a sharp-edged, thin delta wing have been chosen as numerical test cases. The convergence performance of the algorithms is discussed, and the accuracy of the computed flow field results is assessed. The validity of the present results is demonstrated by comparisons with experimental data.
Laser Velocimeter Measurements in a Model Propeller Flowfield
Authors: Lepicovsky J.
Published: October 2009

The objective of this work was to demonstrate the usability of a laser velocimeter data acquisition and reduction techniques for ensemble-averaged velocity measurements near and between rotating propeller or fan blades. A relatively simple experiment was set up to measure the flowfield of a two-bladed model propeller operating at static (non-flight) conditions to verify the data reduction procedures. The mean velocity and ensemble-averaged blade-to-blade velocity distributions were acquired. The experimental results, plotted in a novel consise form, showed separated and reversed flow regions on a rotating static propeller. The flowfield distortion along the blade height in the vicinity of the propeller disc was also observed.
Measurement and Prediction of the Effects of Nonuniform Surface Roughness on Turbulent Flow Friction Coefficients
Authors: Taylor R. P. , Scaggs W. F. , Coleman H. W.
Published: October 2009

The status of prediction methods for friction coefficients in turbulent flows over nonuniform or random rough surfaces is reviewed. Experimental data for friction factors in fully developed pipe flows with Reynolds numbers between 10,000 and 600,000 are presented for two nonuniform rough surfaces. One surface was roughened with a mixture of cones and hemispheres which had the same height and base diameter and were arranged in a uniform array. The other surface was roughened with a mixture of two sizes of cones and two sizes of hemispheres. These data are compared with predictions made using the previously published discrete element prediction approach of Taylor, Coleman, and Hodge. The agreement between the data and the predictions is excellent.
A Weakly Compressible Flow Model and Rapid Convergence Methods
Authors: Song Charles C. S. , Yuan Mingshun
Published: October 2009

A weakly compressible flow model for small Mach number flows is applied to the computation of steady and unsteady inviscid flows. The equations of continuity and motion are decoupled from the energy equation, but, unlike the equations for incompressible fluids, these equations retain the ability to represent rapidly changing flows such as hydraulic transients and hydroacoustics. Two methods to speed up the process of convergence when an explicit method is used to calculate steady incompressible flows are proposed. The first method which is quite similar to the artificial compressiblity method is to assume an arbitrarily small sound speed (equivalent to large Mach number) to speed up the convergence. Any positive finite number may be used for M. One disadvantage of this method is the contamination of the steady flow solution by acoustic noise that may reverberate in the flow field for some time after the steady flow has been essentially established. The second method is based on the concept of valve stroking or boundary control. Certain boundary stroking functions that will unify the hydroacoustic and hydrodynamic processes can be found by using the inverse method of classical hydraulic transients. This method yields uncontaminated steady flow solution very rapidly independent of the Mach number.