bluuebunny/crossref_metadata_2025 huggingface dataset:
Modelisation and Experimentations on a Steam Injector
Authors: Durand Frabrice , Dorey Jean-Marc , Fabre Jean
Published: March 2009

A simplified model is proposed to predict the flow in a Steam Injector (SI), based on the splitting in successive two phase flow processes. SI experimentations have been carried out including pressure and void fraction measurements. The results show that the model provides good values of flow rates and pressures inside the device and describes well its behavior. It will have to be enriched with dissipative processes, mainly friction in the mixing chamber and dissipation in the condensation shock in order to achieve the prediction of the outlet pressure that can reach more than 4 or 5 times the steam feeding pressure.
Active Control of Near-Wall Coherent Structures
Authors: Konieczny P. , Bottaro A. , Monturet V. , Nogarede B.
Published: March 2009

This work aims at finding efficient means to reduce skin friction drag in a turbulent boundary layer. The argument on which the study is based is that turbulence exists near a wall because of the presence of an autonomous cycle which is maintained even in the absence of forcing from the free-stream. The central elements of this cycle are the near-wall coherent structures whose dynamics control the turbulence production. It is postulated that an action at the wall capable of disrupting the turbulent wall-cycle can yield a significant skin friction reduction. A model cycle is produced by embedding artificial, large scale streamwise vortices and streaks in a Blasius boundary layer. A control is then conceived, meant to produce an agglomeration of the streaks to hamper the cycle. The action envisaged consists in a movement of the wall, in the form of a spanwise standing or travelling wave of sufficiently long wavelength. The controllers in the present macroscopic simulation are simply cantilever beams whose movement is driven by ceramic piezo-actuators. Piezoelectric fibers realizing the same action (properly rescaled) provide, possibly, the answer to the technological challenge of the integral control of near-wall turbulence.
Acoustic Influence on the Active Control of 3D Disturbances in a 2D Boundary Layer
Authors: Opfer Holger , Ronneberger Dirk , Grosche Friedrich-Reinhard
Published: March 2009

An active wave-cancellation system is designed to cancel 2D- and 3D-disturbances in a 2D-boundary layer taking into account the angle dependency of the dispersion relation of the Tollmien-Schlichting instability waves. Requirements to such a system are specified. The system is tested by exposure to both, ‘naturally’ occurring disturbances and artificially introduced point source disturbances. Up to 22 dB reduction of the ‘naturally’ occurring disturbances is obtained, but only minor additional improvement is achieved when the angle dependence of the dispersion is considered in the control system. On the other hand the range of the controllable lateral wavenumbers has been enlarged by these additional efforts as demonstrated with the point source disturbances. The performance of the system is limited by different acoustic effects due to the detection and generation of acoustic velocity and pressure fluctuations by the system.
Active Control of Nonlinear Disturbances in a Blasius Boundary Layer (Keynote)
Authors: Gmelin C. , Rist U. , Wagner S.
Published: March 2009

Using the tools of Direct Numerical Simulation (DNS) and Linear Stability Theory (LST) we are studying active concepts to control nonlinear stages of transition. Besides the investigation of the well known wave superposition approach we developed a new method to actively control transitional disturbances. This concept uses the feedback of instantaneous flow data (wall shear stress or spanwise vorticity), obtainable at the wall to drive plain actuators. Avoiding long propagation distances between sensor and actuator this procedure (called ωz-control) results in a very effective damping in linear and nonlinear cases. With some extra improvements like spatial filters between sensor and actuator it is possible to delay transition even in strongly nonlinear scenarios like the K-breakdown scenario (transition due to fundamental resonance). Both methods have been investigated in a Blasius boundary layer. Besides the K-breakdown already mentioned for basic investigations a “linear” scenario was used, consisting of Tollmien-Schlichting waves with different propagation angles.
Eigenvalue Sensitivity to Base Flow Variations in Hagen-Poiseuille Flow
Authors: Gavarini Isabella M. , Bottaro Alessandro , Nieuwstadt Frans T. M.
Published: March 2009

Transition in a cylindrical pipe flow still eludes thorough understanding. Most recent advances are based on the concept of transient growth of disturbances, but even this scenario is not fully confirmed by DNS and/or experiments. Based on the fact that even the most carefully conducted experiment is biased by uncertainties, we explore the spatial growth of disturbances developing on top of an almost ideal, axially invariant Poiseuille flow. The optimal deviation of the base flow from the ideal parabolic profile is computed by a variational tecnique, and unstable modes, driven by an inviscid mechanism, are found to exist for very small values of the norm of the deviation, at low Reynolds numbers.
Optimization of Steady Suction for Disturbance Control on Infinite Swept Wings
Authors: Pralits Jan O. , Hanifi Ardeshir
Published: March 2009

Theory and results are presented on transition control using steady suction to suppress convectively unstable disturbances in a growing boundary layer on infinite swept wings. The suction profiles are computed using optimal control theory and the optimization process is gradient based. Here, the gradient is evaluated using the adjoint of the parabolized stability equations and the adjoint of the boundary layer equations. Results are presented for an application of the theory on a wing-profile designed for medium range commercial aircrafts.
Opposition Control of Near-Wall Turbulence With a Piston Type Actuator
Authors: Rebbeck Henry , Choi Kwing-So
Published: March 2009

Opposition control of near-wall turbulence was carried out using a wall-normal jet from a piston-type actuator, by selectively canceling the downwash of high-momentum fluid during the sweep events. By employing an innovative methodology we were able to study the effectiveness of the scheme without carrying out real-time control, overcoming experimental difficulties associated with the high frequency responses required for the turbulence control. Observed changes of the burst signature in the turbulent boundary layer suggest that there is a possibility of reducing the skin-friction drag when opposition control is carried out with appropriate timing.
Investigation of Hot Film Calibration for Entropy Generation Rate Calculations
Authors: Mahon R. , Frawley P. , Davies M. R. D.
Published: March 2009

The objective of this paper is to investigate in detail the relationship between results obtained from flow over a circular cylinder in cross flow using Hot Film and Hot Wire Constant Temperature Anemometry (C.T.A.). The experimental results are compared with those obtained using numerical methods. The results obtained from Hot Wire Anemometry are used to attempt to calibrate the Hot Film Sensors for the purpose of evaluating entropy generation rates in the boundary layer of the cylinder.
Experimental Investigation of the Effect of Upstream Conditions on Smooth and Rough Zero Pressure Gradient Turbulent Boundary Layer Flows at Very High Reynolds Numbers
Authors: Castillo Luciano , Seo Junghwa , Johansson T. Gunnar , Hangan Horia
Published: March 2009

A 2D turbulent boundary layer experiment in a zero pressure gradient (ZPG) has been carried out using two cross hot-wire probes. The mean velocity and all non-zero Reynolds stresses were measured in a number of positions, 14–28 m from the inlet of the wind tunnel over a rough and a smooth surface. Wind tunnel speeds of 10 m/s and 20 m/s were set up in order to test the effect of the upstream conditions on the downstream flow. The long test section allowed us to investigate the mean velocity and Reynolds stresses dependence on the local Reynolds number and the initial conditions at very high Reynolds number (i.e. Rθ ∼ 120,000). Furthermore, it will be shown that the mean velocity deficit profiles and some of the Reynolds stresses collapse when the upstream conditions are kept fixed for smooth and rough surface.
An Experimental Investigation of the Flow Downstream of a Low NOx Gas Turbine Nozzle
Authors: Boutazakhti M. , Yimer I. , Thomson M. J. , Sullivan P. E.
Published: March 2009

Achieving rapid mixing is the main challenge to reducing NOx levels in non-premixed liquid fired gas turbine combustors. Multipoint lean direct injection (LDI) is among the techniques used to achieve low emissions and good mixing by injecting fuel in small amounts through different injection ports. This study looks at the flow characteristics of a nozzle using this concept. The Parker Hannifin injector used is a square matrix of nine simplex fuel nozzles. Phase Doppler particle analyzer was used to measure both the spray characteristics as well as the gaseous phase turbulence flow field. The average velocities, Reynolds stresses and the Sauter Mean Diameter were measured at a series of positions downstream of the nozzle exit, x3, ranging from 0.6 to 7 times the swirl cup diameters.
Velocity Profile Measurement in Turbulent Pipe Flow Using Ultrasound Time-Domain Correlation Method
Authors: Yamanaka Gentaro , Kikura Hiroshige , Aritomi Masanori
Published: March 2009

This paper presents a velocity profile measurement technique using a ultrasound time-domain correlation method (UTDC). The system is based on the cross correlation between two consecutive echoes of ultrasonic pulses to detect the velocity. The UTDC has two advantages over a conventional ultrasound pulse Doppler method. First, the system has a higher time resolution than the pulse Doppler method. Second, the system does not have a limitation in maximum measurable velocity, which is limited by Nyquist’s sampling theorem. In this paper, the velocity profile measurement in turbulent pipe flow using the UTDC is performed.
Thermodynamic and Aerodynamic Loss Evaluation of Supersonic Nucleating Steam With Shocks
Authors: Kermani Mohammad J. , Gerber Andrew G.
Published: March 2009

Near saturation steam undergoing rapid expansion is numerically studied in a series of converging diverging nozzles with and without shocks. A detailed examination of the aerodynamic and thermodynamic losses are performed for thermodynamic non-equilibrium conditions. The calculations rely on a new numerical model, previously reported, for non-equilibrium phase change with droplet nucleation. In a systematic approach, the model results are first validated versus experimentally available data and then applied to more general flow situations to assess loss mechanisms. The results indicate that for weak normal shocks situated just downstream of the nozzles throat, the aerodynamic and thermodynamic losses are roughly equivalent. As the back pressure is reduced (i.e. shocks become stronger) the aerodynamic component rapidly becomes the predominant loss mechanism. The thermodynamic loss, associated with heat transfer between the phases, increases only gradually with shock strength. This gradual increase starts from a base level of loss originating with the initial nucleation of moisture, which has a strength and location independent of back pressure.
Comparison of Experimental and Numerical Investigations of Conical Shock Wave Interactions in Steady Flows
Authors: Burtschell Yves , Zeitoun David E.
Published: March 2009

The interaction of two oblique conical shock waves has been investigated in an axisymmetrical flow. The first one is produced by a conical ring with a sharp leading edge located at the exit of a supersonic nozzle. The second one is generated by a curvilinear cone placed in the test chamber and along the symmetry axis of the nozzle. This flow field is absolutely free of three-dimensional effects. The displacement of the mobile cone leads to an interaction of an oblique shock wave with a diverging curvilinear shock which the strength changes. Recently, the experimental results have shown three different structures of the two shock wave interactions and hysteresis effects between them. A description of these shock wave interactions is obtained by solving numerically the unsteady Euler or Navier-Stokes equations. By comparison with the experimental ones, the results show the important role of viscous effects for a correct description and understanding of these shock interactions.
LES of Three-Dimensional Turbulent Separated and Reattached Flow Around a Surface-Mounted Square Plate
Authors: Ota Terukazu , Takeuchi Eishi , Yoshikawa Hiroyuki
Published: March 2009

LES method is applied to simulate numerically a three-dimensional turbulent separated and reattached flow around a surface-mounted square plate. Smagorinsky model is used in the analysis and fundamental equations are discretized by mean of the finite difference method. The calculations are made on the flow in a relatively narrow channel width at Re = 105. It is found that the flow around the plate separates and reattaches onto the surface and the horseshoe vortices are formed, resulting in a complicated structure of flow.
Numerical Simulation of the DLR-F4 Wing/Body Configuration With Wall Functions
Authors: Goncalves Eric , Houdeville Robert
Published: March 2009

This paper deals with the three-dimensional RANS computations of the transonic flow around the DLR-F4 wing-body configuration with a wall law approach. A study of the behaviour of different transport-equation turbulence models is given with comparisons to experimental data. The structure of the three-dimensional flow separation predicted by the computations is described and its topological coherence is checked. Moreover, to drastically reduce the CPU cost, a computation with a multigrid method coupled to wall functions has been tested.
Parallel Dynamic Large Eddy Simulation of Turbulent Flow Around MIRA Model
Authors: Choi H. G. , Kang S. W. , Yoo J. Y.
Published: March 2009

For the large scale computation of turbulent flows around an arbitrarily shaped body, a parallel LES (large eddy simulation) code has been recently developed in which domain decomposition method is adopted. METIS and MPI (message passing interface) libraries are used for domain partitioning and data communication between processors, respectively. For unsteady computation of the incompressible Navier-Stokes equation, 4-step splitting finite element algorithm [1] is adopted and Smagorinsky or dynamic LES model can be chosen for the modeling of small eddies in turbulent flows. For the outlet (open) boundary condition, a Dirichlet boundary condition for the pressure is proposed. For the validation and performance-estimation of the parallel code, a three-dimensional laminar flow generated by natural convection inside a cube has been solved. We have confirmed that our code gives accurate results compared with previous studies. Regarding the speed-up of the code, the present parallel code with parallel block-Jacobi preconditioner is about 50 times faster than the corresponding serial code with 64 processors when approximately one million grid points are used. Most of the CPU time is consumed in solving elliptic type pressure equation. For the validation of LES models, turbulent channel flows are simulated at Re = 180, which is based on the channel half height and friction velocity using 51 × 71 × 71 grid system. It has been shown that our results agree well with the well-known results by Kim et al. [2] with less grid points than used by them in terms of time-averaged velocity field and velocity fluctuation. Lastly, we have solved the turbulent flow around MIRA (Motor Industry Research Association) model at Re = 1.6 × 106 which is based on the model height and inlet free stream velocity. Both Smagorinsky and dynamic models are tested, comparing estimated drag coefficients and pressure distribution along the model surface with the existing experimental data [3]. With the help of the parallel code developed in this study, we are able to obtain a unsteady solution of the turbulent flow field around a vehicle discretized by approximately three million grid points within two weeks when 32 IBM-SP2-processors are used. The calculated drag coefficient agrees better with the experimental result [3] than those using two equation turbulence models [4].
Study of the 3D Flows in the Forward-Curved Blades Centrifugal Fans
Authors: Bouquet Thomas , Bakir Farid , Kouidri Smai¨ne , Rey Robert
Published: March 2009

The study presented in this paper is part of the research work on forward-curved blades centrifugal fans carried out the last years by the « Laboratoire d’Energe´tique et de Me´canique des Fluides Interne » (Lemfi – Site Paris). The objective of this study is to better understand the internal flow in this type of machine in order to be able to correlate the aeraulic and acoustic behavior with the geometrical characteristics of the machine. Two impellers with different profiles were manufactured and tested. The aeraulic and acoustic tests were carried out on a test bench standardized ISO 5801. The 3D CFD of the flow was carried out with a commercial code based on the resolution of the Navier-Stokes equations in finite volumes. The analysis of these results confirms that a more organized flow field leads to a better acoustic performance.
Wavelet Analysis of the 3-D Wake Topology for a Square Prism
Authors: Dobre Adrian , Hangan Horia
Published: March 2009

The three-dimensional flow topology of square prism intermediate wake flow based on multi-point hot-wire measurements is investigated using wavelet analysis. A number of continuous wavelet techniques combining time and scale analysis are applied systematically to detect the primary and the secondary flow structures and to validate previously proposed topological models. Our results suggest that a preferred alternate rib spanwise arrangement similar to the one proposed by Meiburg and Lasheras [1] is plausible for the vortex topology of high Reynolds number square prism intermediate wakes. Moreover, it seems that the wake topology has a preferred spanwise wavelength of approximately 2b = 2.4d, which gives a relative spanwise/ streamwise wavelength ( 2b / λ ) of 2/5.
Phase Averaging by Wavelet Transformation and the Application to Periodically Fluctuated Separation Flow
Authors: Yamagishi Masaki , Togano Tomoko , Tashiro Shinichi
Published: March 2009

The vortex structures in a separated region are generated by the motion of the separated shear layer caused by the introduction of periodic fluctuation. The main cause of the motion of the separated shear layer is the external fluctuation with the characteristic frequency. In order to investigate the principal motion of the velocity field, phase averaging was conducted to the velocity signals obtained by single hot-wire measurement. In phase averaging, wavelet analysis was applied to obtain the dominant frequency and the characteristic phase in the fluctuation. The profiles and the contours of the phase-averaged velocity could be found and discussed. The profiles vary dynamically at each phase and show the periodic motion of the shear layer. The separated shear layer flutters with the external fluctuation in the mean flow. If the suitable frequency is selected in the external fluctuation, the separated region disappears in almost all each phases owing to the depression of the shear layer near the wall.
Modeling High Density Ratio Incompressible Interfacial Flows
Authors: Bussmann Markus , Kothe Douglas B. , Sicilian James M.
Published: March 2009

We present an approach to modeling incompressible interfacial flows on fixed meshes that yields solutions at any density ratio. There are two aspects of the methodology that are crucial for obtaining accurate high density ratio solutions: a consistent approach to mass and momentum conservation, by using mass flux information from an interface advection algorithm as the basis for the momentum advection calculation, and a careful evaluation of pressure gradients near the interface. Our particular implementation couples a volume tracking algorithm with a predictor/projection solution of the flow equations on unstructured meshes. We present the methodology, and then the results of several calculations.
Computation of the Fluid-Structure Interaction Between an Impinging Jet and a Flexible Plate
Authors: Namkoong Kak , Choi Hyoung G. , Yoo J. Y.
Published: March 2009

For computation of the FSI (Fluid-Structure Interaction) problems, the combined formulation (Hesla, 1991) is adopted which incorporates both the fluid and structure equations of motion into a single coupled variational equation so that it is not necessary to calculate the fluid force on the surface of structure explicitly when solving the equations of motion of the structure. Before tackling complex FSI problems, laminar flow around a freely falling cylinder is considered. The Navier-Stokes equations are solved using a P2P1 Galerkin finite element formulation with ALE (Arbitrary Lagrangian-Eulerian) algorithm and Newton’s equations of motion for cylinder are solved. The adaptive mesh refinement technique is also adopted which uses stress error as a posteriori error estimator together with an efficient variable reordering and element-reordering method for unstructured finite element meshes. The newly reordered global matrix has a much narrower bandwidth than the original one, making the MILU (Nam et al., 2002) preconditioner perform better. The cylinder falls oscillating in the transverse direction and rotating about the center. It rotates in the positive rotational direction while it moves to the positive transverse direction and vice versa. The Strouhal number for a freely falling cylinder is lower than that for a fixed cylinder at the same Reynolds number and this is mainly due to the transverse oscillation. As a second FSI problem, laminar channel flow divided by a thin plate is considered and the dynamic response of the plate under the influence of channel flows is studied. For simplicity, we assume a 2-D laminar flow so that the plate can be modeled by a Bernoulli-Euler beam. The numerical simulation results are compared with Wang (1999). As a third FSI problem, oscillations of a vertical plate in resting fluid are studied and the results are compared with Glu¨ck et al. (2001). Finally, an impinging jet flow on a flexible plate is considered. There exists clearly an interaction between the impinging jet and the plate; the plate is deflected due to the impinging jet and the deflected plate then affects the flow field. This fluid-structure interaction continues until the damping by fluid viscosity terminates the vibration of the plate. The frequency response of the plate is different from that in free vibration case because the vibration of the plate is damped by fluid viscosity.
Effect of Normal Body Force on Fingering Instability of a Liquid Sheet Driven by Shear Stress or Gravity
Authors: Wang S. , Marshall J. S.
Published: March 2009

A thin liquid sheet driven by either gravity or shear force along a flat plate exhibits a long-wave fingering instability at the liquid front that leads to development of small rivulets of liquid penetrating into the unwetted part of the plate. Rivulet formation causes uneven surface wetting and degrades coating efficiency of the liquid film. The fingering instability occurs because thicker regions of the liquid sheet experience less resistance from the solid surface, and can hence move forward at a faster rate, than thinner regions of the sheet. As this process proceeds, mass conservation acts to make the thin regions of the sheet thinner in order to supply fluid for the thicker regions of the sheet to move forward. The current paper examines the effect on the fingering instability of a body force, such as gravity or centrifugal acceleration, oriented normal to the plate. The presence of a normal body force gives rise to a normal pressure gradient within the liquid sheet. When one region of the sheet becomes thinner than a neighboring region, the normal body force leads to a pressure force acting parallel to the plate that pushes fluid from the thick regions toward the thin regions of the sheet, thus inhibiting the fingering instability. The paper reports both a linear stability analysis of the fingering instability in the presence of a normal body force and a computational study of the effect of normal body force on rivulet development.
Spiralling Liquid Jets
Authors: King Andrew , Decent Stephen , Wallwork Iain , Parau Emilian , Simmons Mark , Wong David
Published: March 2009

We examine the dynamics of a spiralling slender liquid jet which emerges from a rotating cylindrical drum. Such jets arise in the manufacture of fertiliser and magnesium pellts in the prilling process. Exploiting the slenderness of the jet we determine the steady trajectory of the jet, and find that at leading-order it is a function of the rotation rate of the drum, the surface tension and density of the liquid, the exit speed and exit radius of the jet, the radius of the cylinder, but not of the viscosity of the liquid. We carry out a linear stability analysis of the steady solution, using both inviscid and viscous perturbations, and considering both temporal and spatial stability. We compare our results to experiments, obtaining favourable agreement.
Do Small Bubbles Follow Stokes Law?
Authors: Rodrigue Denis
Published: March 2009

The motion of gas bubbles in a liquid medium is known to be affected by the presence of surface active molecules which modify the hydrodynamic conditions prevailing at the gas-liquid interface. In the past, gas bubbles rising in aqueous solutions have been said to follow Stokes law (rigid interface). In this work, we present some theoretical calculations and experimental data on the influence of surfactants for the motion of air bubbles rising in non-Newtonian solutions. It is shown that the rheology of the system introduces a complex balance of forces acting on the bubble.
A Compressible Model for Separated Two-Phase Flows Computations
Authors: Chanteperdrix Guilhem , Villedieu Philippe , Vila Jean-Paul
Published: March 2009

In order to simulate numerically the physical behaviour of a free surface between two fluids, we have developped a compressible model, able to correctly reproduce sloshing at high Bond number (capillary forces neglectible). We will first present the model. It is composed of four equations in two space dimensions : two for each fluid mass conservation, and two for momemtum conservation. The gas and liquid phases are supposed to be compressible fluids following an isothermal linearized equation of state. A mechanical equilibrium relation closes the model (the equilibrium model). Relaxing this relation, we obtain a new model (the relaxation model) that is more adapted for numerical treatment. The second part of the paper is dedicated to the presentation of the numerical method that we used. We explain why it does not need a scheme for the volume fraction. In particular, there is no specific algorithm to localize the interface, as in VOF, Level-Set or Front Tracking methods. The last part of the paper is devoted to some validation results, compared to analytical solution or experimental data.
Effects of Adjacent Printer Heads in Electrostatic Inkjet Printer
Authors: Sou Akira , Sasai Kosuke , Nakajima Tsuyoshi
Published: March 2009

In order to develop a high speed printing system, the system must be operated in high frequency, and must have multiple heads in rows. Through the present simulation, it was found that successive shots of high frequency (about 2kHz) were possible. By additional optimization of pulse shape and by decreasing the delay time for switching voltage to rise up, it will be possible to realize much higher speed printer. Then, the effects of adjacent printer heads in a row were investigated. It was found that a distance of 254µm (corresponding to 100dpi) was still not enough to achieve stable and well-controlled ink transportation if no electrostatic barriers in between were assigned in the present head design.
Unsteady Behavior of a Rising Bubble in Contaminated Water
Authors: Takagi Shu , Uda Touki , Watanabe Yuji , Matsumoto Yoichiro
Published: March 2009

In the present study, we investigate the effect of contaminant to the motion of a rising bubble. As is well-known, a bubble in contaminated water rises much slower than that in pure water and the rising velocity in contaminated system can be less than a half of that in pure system. Further, Zhang & Finch [1] recently reported very interesting phenomenon through experiment. They reported that transient distance to reach steady terminal velocity also strongly depends on the surfactant concentration in bulk liquid. Here, we conducted numerical simulations of rising bubble related to this phenomenon, taking “Marangoni effect” into account. We also conducted the experiment related to this phenomenon, using super-purified water with the addition of various amount of three kinds of surfactants (1-pentanol, 3-pentanol and Triton X-100). It is shown that the present numerical results represent the experimental results well and that the transient phenomenon largely depends on the surfactant characteristics.
PIV Measurements in a Confined Jet
Authors: Shinneeb A. , Bugg J. D. , Balachandar R.
Published: March 2009

This paper reports PIV measurements made at three locations in an axisymmetric, confined jet that is approaching a free surface from below. The apparatus consists of a tank 40.5 cm × 40.5 cm at its base and 61 cm high. A 9 mm diameter nozzle is centered in the base of the tank and directs a jet of water upwards. The jet produced has a top-hat velocity profile with a maximum deviation of 0.32% of the mean and an axial relative turbulence intensity of 0.60%. The water is removed from the tank by an overflow around the perimeter of the tank. The PIV measurements achieved a spatial resolution of between 0.425–1.08 mm. The measurements show details of the velocity field in three regions of the flow; at the jet exit, near the surface on the centerline of the jet, and near the top corner of the tank. The centerline velocity remains at the exit velocity until ≈5D from the exit. The axial confinement of the jet begins to significantly influence the centerline velocity at ≈13D from the free surface. All entrained fluid is deflected downward from the horizontal surface flow as it approaches the overflow around the perimeter of the tank. This creates a large recirculation region in the upper region of the tank driven by the downward flow along the wall and the upward flow of the jet itself at the center of the tank.
Periodic Velocity Measurements in a Wide and Large Radius Ratio Automotive Torque Converter at the Pump/Turbine Interface
Authors: Kraus S. O. , Flack R. , Habsieger A. , Gillies G. T. , Dullenkopf K.
Published: March 2009

The unsteady flow field due to blade passing at the pump/turbine interface of a torque converter was studied. The current geometry is wide and has a large outer to inner radius ratio. A laser velocimeter was used to measure the periodic velocity components at four operating conditions determined by the speed ratios between the turbine and pump of 0.065 (near stall), 0.600, 0.800, and 0.875 (coupling point). The flow fields at the pump exit and turbine inlet planes were visualized and are presented. Using instantaneous pump and turbine blade positions with the velocity data, animations (“slow-motion movies”) are generated to effectively visualize and understand the unsteady behavior. The turbine inlet flow was markedly periodic due to the exiting jet/wake from the upstream pump passage; however, the pump exit flow field showed little dependence on the turbine blade positions. The highest unsteadiness was seen for the highest speed ratios. Four “shots” from the sequences of one cycle for all speed ratios and each plane are presented herein. The results are also compared to unsteady results for a previously examined torque converter with a small radius ratio to determine the effect of parametric geometric changes on the flow field. Generally, the unsteady velocity fields show no significant difference for the two geometries — the trends are the same.
A Comparison of a Spray Penetration Correlation by an Optical Obscuration Technique to Other Correlations Obtained by Different Techniques
Authors: Jawad Badih A.
Published: March 2009

Previous studies dealing with sprays have used a variety of techniques to determine spray droplets and spray penetration. In particular, the sedimentation tower method and the liquid immersion sampling technique were most popular. However, in these techniques sampling is done after spray formation is complete. The completion time of spray formation appears to vary with the conditions of injection and ambient factors, thus making measurements under transient conditions during injection difficult. A pulsed Malvern drop-size analyzer, based on Fraunhofer diffraction, was utilized to determine spray penetrations of diesel fuels under different conditions of injection, along with the effects of fuel properties. In these study, the spray is formed by injecting a calibrated amount of fuel into air. A two mm diameter collimated beam illuminated a cylindrical volume perpendicular to the axis of the fuel spray, and its attenuation was recorded and stored on the oscilloscope. With the optical measurement being synchronized to the needle lift of the injector, the output of the needle lift transducer and the optical signal was recorded simultaneously. Thus, the arrival and the duration of the spray at various positions along its axis were measured. A spray penetration correlation is obtained, and is compared to other existing correlations in the literature.
A Numerical Analysis of a Mixed Flow Pump
Authors: Ferna´ndez J. , Blanco E. , Santolaria C. , Scanlon T. J. , Stickland M. T.
Published: March 2009

The rotating passages of turbomachinery contain some very interesting and complex fluid flow phenomena. This paper presents the three-dimensional turbulent flow through the impeller passages and surroundings of a mixed-flow pump. The model has five impeller blades mounted on a conical hub and nine stator blades in a diffuser which brings the diagonally outward flow back to the axial direction. This pump was tested with air, giving a nominal flow-rate of 1.01 m3/s and 250 Pa at 1200 rpm. Temporal discretization has second order accuracy and this is in line with the discretization of convection which is also second order. For turbulence closure the standard k-e model has been applied with conventional wall functions employed at solid surfaces. For this transient, three-dimensional computation, the numerical grid has been decomposed into five separate regions in order to process these in a parallel cluster of five individual PC’s. The results show entirely reasonable correlations with published experimental data as detailed in the flow rate-head comparisons and the numerical / experimental flow fields. These outcomes allow us to confirm that such a complex transient phenomenon may be reasonably captured by employing a commercial CFD code.
An Open Water Numerical Model for a Marine Propeller: A Comparison With Experimental Data
Authors: Marti´nez-Calle Julia´n , Balbona-Calvo Laureano , Gonza´lez-Pe´rez Jose´ , Blanco-Marigorta Eduardo
Published: March 2009

The open water model tests technique is well known and commonly used to predict propellers performance. In this paper, a quite different approach is intended and the main propeller variables are numerically modelled using a finite volume commercial code. Particularly, a fishing-boat propeller is numerically treated using a three-dimensional unstructured mesh. Mesh dependency and different turbulent models are considered together with an sliding technique to account for the rotation. Typical turbomachinery boundary conditions for a volume containing the propeller are imposed (inlet velocity and outlet static pressure). In order to get the open water test performance coefficients for the considered propeller (KT, KQ, η), different advance coefficient (J) are imposed as boundary conditions for the numerical model. The results of such simulations are compared with experimental data available for the open water tests of the propeller. Once the model is validated with the experimental data available, a wake field simulation would be possible and would lead to the definition of the fluid-dynamic variables (pressure, iso-velocity maps, etc.) which are needed during any design process. Also some comparisons with real scale thrust measurements are intended.
Numerical Simulation of the Two-Phase Flow in Centrifugal Pump Impellers
Authors: Schilling Rudolf , Frobenius Moritz
Published: March 2009

The numerical simulations of three types of two-phase flow in centrifugal pump impellers are described. First, the liquid-solid particle flow is modeled by an Euler-Lagrangeian approach assuming a mass concentration less than 5% and particle diameters being less than 1000 microns. The empirical erosion model to predict the local and total wear is calibrated by measurements. Second, the influence of the relative air contents on the head-drop is simulated assuming a relatively small volume fraction and applying a simple one-fluid model. The mixture is characterized by a common density depending on the flow field. Finally, the cavitating flow is studied by implementing the Rayleigh equation into the numerical procedure describing the transient process of bubble growth and collapse. The developed simulation tools are applied to predict the three types of two-phase flows in impellers. Within the defined ranges of application the simulation results agree fairly well with the experimental data.
Werle´-Legendre Separation in a Hydraulic Machine Draft Tube
Authors: Mauri S. , Kueny J.-L. , Avellan F.
Published: March 2009

The three-dimensional turbulent flow in a compact hydraulic machine elbow draft tube is numerically investigated for several operating conditions, covering an extended range around the best efficiency point. Comparisons with the experimental data are presented as validation. The interest is focused on the experimentally observed pressure recovery drop occurring near the best efficiency point. The flow is first analyzed locally by means of a topological analysis, then globally with an energetic approach. The study provides evidence for the role played by a Werle´-Legendre separation originating in the bend. The separation is due to the contrasting flow angles imposed by the blades, and the angle resulting from the secondary flow.
Parallel Simulation of the Turbulent Flow Through a Pump-Turbine Runner
Authors: Xu Yu , Wu Yulin
Published: March 2009

In this paper, authors use the parallel calculation methods to solve the incompressible turbulent flow through a pump-turbine runner. The calculation aims at probing the road using parallel calculation methods to simulate complex flow field. The simulation is conducted based on the N-S equations, by using the k-ε model. SIMPLEC algorithm [1] is adopted in the numerical procedure with body-fitted coordination [2] and staggering grid system. The calculation is carried out on the THTF “Explore 108” Cluster Computer, where Solaris8.0 plays the roles of operating system and MPI1.2 as message-passing interface. The results of parallel simulation agree well with those of serial simulation, which shows that the parallel algorithms are feasible and useful to numerical simulation.
Numerical Investigations of Hysteretic Characteristics on Wells Turbine
Authors: Kinoue Y. , Setoguchi T. , Kim T. H. , Kaneko K. , Inoue M.
Published: March 2009

A Wells turbine for wave power conversion has hysteretic characteristics in a reciprocating flow. The hysteretic loop is opposite to the well-known dynamic stall of an airfoil. In this paper, the mechanism of the hysteretic behavior was elucidated by an unsteady 3-dimensional Navier-Stokes numerical simulation. It was found that the hysteretic behavior was associated with a streamwise vortical flow appearing near the blade suction surface. In the accelerating process of axial flow velocity, the vortex is intensified to enlarge the flow separation area on the blade suction surface. In the decelerating flow process, the flow separation area is reduced because of the weakened vortex. Therefore, the aerodynamic performance in the accelerating flow process is lower than in the decelerating flow process, unlike the dynamic stall. Based on the vortex theorem, the mechanism to vary the intensity of the vortex can be explained by the trailing vortices associated with change in the blade circulation.
A Particle-Center-Averaged Two-Fluid Model for Wall-Bounded Bubbly Flows
Authors: Larreteguy Axel E. , Drew Donald A. , Lahey Richard T.
Published: March 2009

The accurate prediction of void fraction profiles near solid walls using the two-fluid model is still an unresolved issue. These profiles result from the combination of two factors: a) forces acting on the bubbles, and, b) geometric constraints imposed by their shape. We propose herein a two-fluid model that involves a particle-center-averaging procedure for the disperse phase, and a reinterpretation and postprocessing of the results obtained. This center-averaged approach averages the disperse phase (bubbles) based on a particle center indicator function, while using the standard phase indicator averaging for the continuous phase (liquid). The solution fields obtained are then postprocessed to introduce the geometry of the bubbles in order to recover the values that should be representative of measured fields. The key idea here is to separate the geometric aspect from the dynamic aspect of the problem into two independent, successive steps. The new model may be easily incorporated into existing two-fluid model codes. Results obtained with the new model showing agreement with experimental data (Moursali et al, 1995) are also presented.
A Numerical Method for the Analysis of a New Model for Two-Phase Bubbly Flow in Elastic Pipes
Authors: Kim D.
Published: March 2009

A new approach and numerical method for study gas-liquid two-phase flows in elastic pipes is suggested. “A nonlinear wave dynamical model for liquid containing gas bubbles” is applied to derive governing equations for two-phase flow-filled pipelines. On assuming the hydraulic approximation the continuity and momentum equations of two-phase flow in a pipe are obtained for the first time. From these equations the inhomogeneous wave equation of Lighthill-type for two-phase flow in pipelines is derived. The shear stress at the tube surface, deformation of the tube cross-section, and liquid’s phase compressibility are taken into account. A high effectively and accurate finite difference technique for the exact solution of the basic equations in the case of Neumann boundary conditions is developed. Based on the proposed algorithm various numerical experiments have been carried out to investigate the major fluid dynamical features of hydraulic shocks and shock waves in the horizontal pipes. Comparisons with both the experimental data and computational results obtained with a second-order accurate predictor-corrector method support our numerical technique as well as the model.
Finite Volume Simulation of an Airlift Loop Reactor With Coupled Algebraic Multigrid
Authors: Zwart Philip J. , Burns Alan D. , Phillipson Sarah , Gobby Darren
Published: March 2009

An efficient algorithm for solving the equations of multi-phase flow has been developed and implemented in the software CFX-5. The motivation for this method is to obtain scalable behaviour for solving industrial multiphase flow problems. This is achieved using a finite volume discretization of the equations on unstructured meshes, preserving important inter-equation coupling at the algebraic level, and solving the algebraic equations using an efficient multigrid solver. The method also features a high resolution advection scheme for the volume fraction equations, which is particularly important for obtaining accurate solutions on tetrahedral meshes. The algorithm is also parallelized so that fast turn-around times can be achieved. The method is validated for an Enichem airlift loop reactor studied in an ADMIRE project. The results compare well with experimental data and with previous CFX-4 calculations. Solutions are obtained in the same number of iterations independent of the mesh size and with near-linear parallel speedup.
Calculation of Two-Phase Flows in an Oil Separator by Using a Cubic Interpolated Propagation Code on Unstructured Grid Spaces
Authors: Ishii Eiji , Kameya Hirotaka , Watanabe Atsushi , Urashin Masayuki
Published: March 2009

We have developed a cubic interpolated propagation (CIP) code combined with a finite volume method using unstructured grid spaces. The CIP code, which can solve both compressible and incompressible flows simultaneously, was used to calculate gas-liquid flows — in this case, waterspouts — in an oil separator. We found that waterspouts raise the oil at the bottom of the separator’s chamber and lower the efficiency of oil separation remarkably. We also found that the waterspouts can be classified as circulatory or non-circulatory and that they are caused by a low-pressure core in the discharge pipe. Furthermore, we predicted the critical conditions under which the waterspouts occur, and these predictions agree with measurements taken with a test separator.
Three-Phase Flow Calculation With Conservative Semi-Lagrangian CIP Method
Authors: Yabe T. , Xiao F. , Takizawa K. , Sakurai K.
Published: March 2009

We present a review of the CIP method, which is a kind of semi-Lagrangian scheme and has been extended to treat incompressible flow in the framework of compressible fluid. Since it uses primitive Euler representation, it is suitable for multi-phase analysis. The recent version of this method guarantees the exact mass conservation even in the framework of semi-Lagrangian scheme. Comprehensive review is given for the strategy of the CIP method that has a compact support and sub-cell resolution including front capturing algorithm with functional transformation.
Local Bubble Dynamics in Two-Phase Flows
Authors: Schlu¨ter Michael , Scheid So¨ren , Ra¨biger Norbert
Published: March 2009

For the development of environmentally sustainable processes e.g. in chemical engineering or biotechnology detailed knowledge of hydrodynamics and mass transfer is essential. A calculation of the exact design layout of reactors and processes required for multiphase flows has been impossible to achieve because of the complex transient coupling between the continuous and dispersed phases. Due to the lack of exact models to describe local and transient phenomena the calculation of hydrodynamics and mass transfer is over-simplified by using time- and space-averaged data, thus neglecting important facts. Recently developed measurement techniques allow the investigation of these local effects in multiphase flows and indicate that e.g. the behavior and slip velocity of fluid particles in a particle swarm differ from the behavior of single particles and depend on particle hold-up and flow conditions of the continuous phase. Measurements in two-phase flows in co-current and counter-current flow have shown that generally used models for homogeneous flow are dissatisfying.