bluuebunny/crossref_metadata_2025 huggingface dataset:
Cavitation Phenomena in Thin Films of Newtonian, Non-Newtonian and Viscoelastic Fluids Due to Rapid Bubble Expansion Under Pulses of Negative Pressure
Authors: Williams P. Rhodri , Williams Rodhri L. , Al-Hussany A.
Published: February 2009

We report studies of the growth of a cavitation bubble in terms of the development of hydrodynamic pressures within the liquid close to the expanding bubble’s surface. The results of this study are discussed in terms of the possible consequences of cavitation bubble expansion in Newtonian and non-Newtonian, shear-thinning fluids (such as synovial fluid). Contrary to previous indications in the literature, non-Newtonian (specifically, shear-thinning) behaviour is found to be significant in this context, insofar as it may result in markedly enhanced tensions due to the pressure waves developed about a growing bubble during the latter stages of its expansion phase. The magnitude of the tensions so developed are compared with estimates of cavitation thresholds (Fc ) which are obtained from experiments involving the reflection of pulsed ultrasound at a flexible boundary. Under some circumstances the tensions developed about the growing cavity are shown to be commensurate with Fc. The possible consequences of these findings are discussed in terms of cavitation damage to blood vessels or other biological tissues.
Thermal Cavitation Experiments on a NACA 0015 Hydrofoil
Authors: Rapposelli Emilio , Cervone Angelo , Bramanti Cristina , d’Agostino Luca
Published: February 2009

The present paper illustrates the main results of an experimental campaign conducted in the Thermal Cavitation Tunnel of the CPRTF (Cavitating Pump Rotordynamic Test Facility) at Centrospazio. Experiments were carried out on a NACA 0015 hydrofoil at various incidence angles, cavitation numbers and freestream temperatures, in order to investigate the characteristics of cavitation instabilities and the impact of thermal cavitation effects. Measured cavity length, surface pressure coefficients and unsteady pressure spectra are in good agreement with the data available in the open literature and suggest the existence of a strong correlation between the onset of the various forms of cavitation and instabilities, the thermal cavitation effects, and the effects induced by the presence of the walls of the tunnel. Further analytical investigations will be carried out in order to provide a better interpretation of the above results.
Wavelet Analysis of Space-Varying Intermittent Wall Pressure Field of Transitional Boundary Layer
Authors: Snarski Stephen R.
Published: February 2009

Measurements of the space-time fluctuating wall pressure field across the transition region of a flat plate zero pressure gradient boundary layer have been performed in an anechoic wind tunnel with a 64-element linear array of sub-miniature hearing-aid microphones (d+ = 15). Wavelet transforms are being used to quantify the structure and nonhomogeneous wavenumber-frequency spectral content of the field. The results illustrate that the fluctuations within the turbulent spots scale with those which exists in a fully developed turbulent boundary layer consistent with previous findings. The spectral contributions due to a second much larger length/time scale associated with the mean spacing between spots (e.g., turbulent spot wavepacket pulse trains) is under investigation. Based on an analysis of sinusoidal pulse train signals and consideration of the well established bursting frequency in turbulent boundary layers, it is conjectured here that the turbulent spot wavepacket pulse trains should produce a statistical distribution of energy about the mean fundamental pulse train frequency.
Phase Averaging Analysis of the Unsteady Velocity Profiles in a Separated Flow
Authors: Yamagishi Masaki , Togano Tomoko , Tashiro Shinichi
Published: February 2009

By using phase averaging technique, turbulent structure in a flow was studied. For the phase angle of the time dependent signal modulated in frequency, data acquisition is difficult. This study proposed a new method of phase averaging by wavelet transformation. The purpose of the present study is to compare the results of the phase averaging by wavelet transformation with those by the traditional phase averaging technique. These two phase averaging techniques were applied to the experimental data of the velocities in a separated flow with periodical fluctuation. Between the results by these techniques, noticeable differences were shown. If the velocity signals include the frequency modulation, the profiles of phase-averaged velocity by the traditional technique will have nearly the same shapes and be similar to those of time-averaged velocity. On the other hand, the profiles by wavelet transformation showed the clear differences at each phase angle even for the velocity signals with modulated frequencies.
Nanometer and Micron Sized Particles in a Bidisperse Magnetorheological Fluid
Authors: Wereley N. M. , Trihan J. , Kotha S. , Suggs A. , Radhakrishnan R. , Love B. J. , Sudarshan T. S.
Published: February 2009

Conventional magnetorheological (MR) fluids are suspensions of micron sized particles in a hydraulic or silicone oil carrier fluid. Recently, research has been conducted into the advantages of using bidisperse MR fluids, which are mixtures of two different powder sizes in the MR suspension. The MR fluids investigated here use a mixture of conventional micron sized particles and nanometer sized particles. The settling rate of such bidisperse fluids using nanometer sized particles is reduced because thermal convection and Van der Waals forces experienced by the nanometer sized particles compete favorably with gravitational forces. This reduction in the settling rate comes at a cost of a reduction in the maximum yield stress that can be manifested by such an MR fluid at its saturation magnetization. There is a measurable and predictable variation in rheological properties as the weight percent of the nanometer sized particles is increased relative to the weight percent of micron size particles, while maintaining a constant solids loading in the MR fluid samples. All bidisperse fluids tested in this study have a solids loading of 60 weight% (wt%) of Fe particles. This study investigates the effect of increasing the weight percent of 30 nanometer (nominal) Fe particles relative to 30 micron (nominal) Fe particles on rheological characteristics such as yield stress and postyield viscosity. The goal of this study is to find an optimal composition of the bidisperse fluid that provides the best combination of high yield stress and low settling rate based on empirical measurements. The applicability of rheological models, such as the Bingham-plastic and the Hershel Buckley models, to the measured flow curves of these MR fluids is also presented.
Pressure Sensitivity of a Thermal Shear Stress Sensor
Authors: Clendenin Jason , Gordon Matt , Tung Steve
Published: February 2009

This paper reports on the pressure sensitivity testing of MEMS thermal shear stress sensors. The MEMS sensor is a micromachined, vacuum-cavity insulated, thermal shear stress sensor for underwater applications. This paper is focused on the combined experimental and numerical study carried out to examine the effects of changing environmental pressure on the MEMS-based shear stress sensors. Four different sensors were tested experimentally and numerically. The silicon nitride diaphragms for each sensor are 4-μm thick. The length of each diaphragm is 210-μm while the widths are 210-μm, 150-μm, 100-μm, and 75-μm respectively. It is found that reducing the surface area size and increasing the thickness of the sensor diaphragms are effective in minimizing the pressure sensitivity.
Bow Shock Effect on Particle Transport and Deposition in a Hypersonic Impactor
Authors: Abouali Omid , Ahmadi Goodarz
Published: February 2009

Supersonic/hypersonic impactors are used as a collector and/or size separator of nano- and micro-particles. Thin film and fine line pattern deposition by aerosol jets are other applications of deposition of supersonic/hypersonic impactors. At extremely low backpressures, the exiting flow from a nozzle forms a supersonic free jet. The supersonic jet forms a strong normal shock in the front of the impactor plate. The stagnation pressure, backpressure and distance between the nozzle exit and the impactor plate affect the flow field. Due to the rather complicated flow in the impactor, studies of particle motions in supersonic impactors are rather scarce. In this study the airflow and particle transport and deposition in a supersonic/hypersonic impactor are numerically simulated. The axisymmetric compressible Navier-Stokes equation is solved and the flow properties are evaluated. It is assumed that the particle concentration is dilute, to the extent that the presence of particles does not alter the flow field. Deposition of different size particles under different operating conditions is studied. The importance of drag, lift and Brownian forces on particle motions in supersonic impactors is discussed. Sensitivity of the simulation results to the use of different expressions for the drag force is also examined. A strong bow shock on the flowfield has much effect in drag forces on particles. It is shown that the Stokes-Cunningham drag with variable correction coefficient is most suitable for computer simulation studies of nano-particles in supersonic/hypersonic impactors. The computer simulation results are shown to compare favorably with the experimental data.
Quantitative Hot-Wire Measurements in Supersonic Boundary Layers
Authors: Matlis Eric H. , Corke Thomas C.
Published: February 2009

Mean and time-resolved measurements in a supersonic boundary layer were performed in the Mach 3.5 quiet tunnel facility at the NASA Langley Research Center. This facility uses an annular bleed suction system to remove the turbulent boundary layer, thus reducing the disturbance intensities in the measurement region. A frequency-compensatedconstant current hot-wire anemometer was used to obtain fluctuation data in the boundary layer of a sharp cone at zero angle of attack. The hotwire was calibrated against the mean mass-flux profiles provided by solutions of the similarity profiles for compressible Blasius flow. A stability analysis code provided by Langley was used to solve parabolized stability equations to provide predictions of the most amplified wave-numbers, frequencies, and N-factors for the Tollmien-Schlicting instability. The results from these computations are compared to the experimental measurements performed with the anemometer. In addition, these measurements are compared to spectra obtained in high-disturbance conditions with the bleed system turned off.
Numerical and Experimental Evaluation of Turbulent Flow in Volute
Authors: Igarashi Akitomo , Toda Kazuyuki , Yamamoto Makoto , Sakai Toshimichi
Published: February 2009

The performance of centrifugal fans is considerably influenced by the design of tongue at the re-circulation port. The flow in the volute of a centrifugal fan was studied both experimentally and numerically. In this experiment, flow angle, pressure and velocity profiles were measured at a large number of locations in the volute. The flow field in the volute passage was analyzed using Computational Fluid Dynamics. The flow was assumed to be three dimensional, turbulent and steady. The numerical simulation produced qualitatively good agreement with the experimental result. The results from experiment and numerical simulation indicated that the adoption of a re-circulating flow port improved fan performance for all flow conditions. In addition, the existence of strong secondary flow was apparent at the cross-section of the volute passage.
Applying CAx Technology for the Design of a Gas Turbine Exhaust
Authors: Itter L. , Cagna M. , Wiedermann A. , Boehle M.
Published: February 2009

Today’s market for gas turbines is getting bigger since there is a huge demand for power generation and mechanical drive applications. To meet the market requirements gas turbine components have to be very efficient to play a leading role. In order to accelerate component improvement the introduction of integrated CAx Technology is a key to achieve a less time-consuming and therefore cheaper design. This paper will describe a procedure which can be used to design an exhaust system for gas turbines with hot-end drive. It shows how to combine various technologies like CAD and CFD and make them work together rapidly. Firstly a 1D design is done and compared with a performance chart of conventional use. Then, a 2D parametric study of a 90 degree bend will be performed by the combination of a CAD-system and a CFD-solver. Thirdly a full 3D-simulation of the entire exhaust will be performed with a calibrated solver. Different complex geometry modifications are applied and their influence on the performance of the exhaust will be discussed.
Thrust Prediction in Screw-Type Centrifugal Pump
Authors: Tatebayashi Yasushi , Tanaka Kazuhiro , Kobayashi Toshio
Published: February 2009

A screw-type centrifugal pump is a kind of non-clog type pump and has been widely used, for instance, for drainage of rainwater as well as slurries and mud in sewage control systems (Reference to Fig. 1). In order to avoid choking the impeller passage with the congestion of solids, the impeller is designed to have a wide passage whose configuration is screw formed by a three-dimensional spiral blade added to a conical hub cone. The prediction of radial and axial thrust is important and useful information for the safe operation and the impeller design, to say nothing of the internal flow prediction and pump performance prediction. Particularly, the fluctuation of radial and axial thrust in this pump is large because of one blade. Therefore, to predict the thrust correctly is important. In this paper, the radial and axial thrust has been numerically predicted. Especially, the numerical result on the radial thrust is compared with the experimental results. The validity of thrust prediction has been discussed.
Computational Analysis of Cryogenic Flow Through a Control Valve
Authors: Daines Russell L. , Woods Jody L. , Sulyma Peter R.
Published: February 2009

The initial efforts to develop the capability to model valves used in rocket engine component testing at Stennis Space Center are documented. An axisymmetric model of a control valve with LN2 as the working fluid was developed. The goal was to predict the effect of change in the plug/seat region of the valve prior to testing. The valve flow coefficient was predicted for a range of plug positions. Verification of the calculations was carried out to quantify the uncertainty in the numerical answer. The modeled results compared well qualitatively to experimental trends. Additionally, insights into the flow processes in the valve were obtained. Benefits from the verification process included the ability to use coarser grids and insight into ways to reduce computational time by using double precision accuracy and non-integer grid ratios. Future valve modeling activities will include shape optimization of the valve/seat region and dynamic grid modeling.
Influence of an Electrohydrodynamic Actuator on a Turbulent Boundary Layer Along a Flat Plate
Authors: Le´ger Luc , Moreau Eric , Touchard Ge´rard
Published: February 2009

For some years, the use of electrohydrodynamic actuators has been receiving special attention. These actuators have important advantages like simplicity, no moving part, a short electrical response time and a total electric control. The electrohydrodynamic actuator used here consists in two electrodes flush mounted on a flat plate, generating a corona discharge at close vicinity of the wall. Positive ions created at the anode move outside the immediate vicinity of the ionization zone and drift to the negative electrode. Momentum transfer as a result of collision between drifting ions and neutral air molecules gives rise to the electrohydrodynamic flow known as ionic wind. In this paper the ionic wind is used in order to modify the properties of a turbulent boundary layer. Profiles of the boundary layer are presented for velocity up to 25 m/s. They show the influence of the polarity of the discharge, resulting in a velocity decreasing or increasing. In the case of increasing velocity, they show an important drag reduction (30% at 10 m/s) and a boundary layer thickness reduction of about 20% at 10 m/s.
Lattice Boltzmann Simulation of Drops in a Shear Flow
Authors: Takada Naoki , Tomiyama Akio , Hosokawa Shigeo
Published: February 2009

In this paper, we present simulation results of two- and three-dimensional motions of drops in a shear flow based on the lattice Boltzmann method (LBM), where a macroscopic fluid flow results from averaging collisions and propagations of mesoscopic particles. The binary fluid model in LBM used here can reproduce two-phase interface in a self-organizing way by repulsive interaction between particles consistent with the van der Waals-Cahn-Hilliard free energy theory. A finite difference scheme is applied to the lattice-Boltzmann equations governing time evolution of velocity distributions of particle number density. When a drop is suspended in an immiscible second liquid with the same mass and viscosity between moving parallel plates, the numerical results of deformation of drop agree with theoretical solutions and previous numerical results obtained by the volume-of-fluid (VOF) method. Breakup motions of drops in LBM are also reasonable in comparison with the critical Reynolds and capillary numbers predicted by the VOF method. In the simulations of two-drop interaction, it is shown that the breakup motion depends on not only number density of drops but also initial positioning of their volumetric center away from a halfway cross section between the plates.
Three-Dimensional Simulation of Skimmer on Water
Authors: Takizawa Kenji , Yabe Takashi
Published: February 2009

The purpose of this paper is to develop a new three-dimensional hydrodynamic simulation algorithm for strongly-coupled fluid-structure interaction and demonstrate its ability to capture the complex surface of solid and liquid. For such an example, we use the skimmer phenomena with rotational motion. This result is compared with the experimental result given by Chino et.al. in this conference FEDSM2003-45171.
Experimental Research on Rotating Skimmer
Authors: Chino Minoru , Takizawa Kenji , Yabe Takashi
Published: February 2009

This paper provides the experimental results on skimmer and gives some detailed information useful for benchmark test of computer codes that are now able to simulate the fluid-structure interaction. For this purpose, we specially designed the injection system that imposes reproducible rotational speed and injection speed on the skipper. The effect of rotation is discussed by changing rotation speed in a wide range.
Hydrodynamic Behavior of Swirling Liquid Film Flow on Rotating Disc
Authors: Yoshida Kenji , Adachi Tomoya , Kataoka Isao , Horiki Hiroyuki , Yoneya Akira , Kaji Toshimitsu , Horii Kiyoshi
Published: February 2009

Experimental and analytical studies have been carried out on the hydrodynamic behavior of swirling liquid film flow on a rotating disc. Film flow formation and swirling waves on the liquid film were analyzed through observation using high speed video. Liquid film thickness was measured using the Laser refraction method and compared with prediction. The rotating disc is 200 mm in diameter and was made of Silicon (Silicon wafer in industrial use). The rotating speed is up to 100 rad/sec (2000 rotations per min.) Water is supplied to the center of the disc at a flow rate of 8.3 × 10−6 m3/s (500 cc/min). The film flow is divided into three regimes depending upon rotating speed. For the lower rotating speed (up to 10 rad/sec), formation of liquid film flow is incomplete and some part of the peripheral region of the disc is not completely covered by liquid film. For the intermediate rotating speed (15–25 rad/sec), laminar film flow covered the whole disc. Furthermore, there are swirling waves on the liquid film. This wave is considered to be a continuity wave arising at the center portion of disc due to the water flow rate variation form the nozzle. Wave propagation speed and behavior of these swirling waves were well explained by the theory of continuity wave. For the high rotating speed (more than 30 rad/sec), the liquid film flow changed its flow regime from laminar flow to turbulent flow. The estimated film Reynolds number at transition is about 1200 which is consistent with turbulent flow transition for pipe flow and film flow on non-rotating surface. Three dimensional turbulent waves were observed on this turbulent liquid film. The behavior of such three dimensional turbulent waves were quite random in time and space. Measured film thicknesses ranged from 50 to 300 micron. Film thickness and its fluctuation decreased as the rotation speed of disc increased and distance from disc center increased. The analysis was made on the film thickness based on the force balance between shear stress and centrifugal force acting on the film. The predicted film thickness agreed well with the measured value.
Slit Flow Stabilization by Swirl in the Boundary Region Between Concurrent Thin-Liquid Layers
Authors: Umeda Shinzaburo , Hasegawa Seizou , Taniguchi Akira , Manmoto Shinzou , Horii Kiyoshi
Published: February 2009

A duct nozzle with an X-shaped flow network has dramatically stabilized a slit liquid flow. This stability has been deduced by the swirl in the boundary region between concurrent thin-liquid layers. The concurrent-flow is the slit flow (thin-liquid layer) that is placed over the intersecting-flow in X-shaped channels. The swirl has been produced by flow oscillations in a right angle to the flow direction caused by the flip-flop phenomena in X-shaped channels. The swirl has absorbed the instability of a slit liquid flow as the energy for a swirling motion. An experimental study was performed to investigate the phenomena of two flows; a slit flow and a flip-flop flow placed over it. An experiment has been performed in two different ducts; a duct with X-shaped channels consisting of large diamond-shaped bundles and a duct with small size X-shaped channels in both sides. The velocity variations in their flow fields were measured using two-dimensional PIV and LDV. This study clarified the characteristics of velocity variations on the horizontal and vertical sections with different depths of their X-shaped channels.
Control of Compressible Flows Using Cavities
Authors: Sforza P. M.
Published: February 2009

Using the existing body of data on cavity flows it is demonstrated that specific rectangular cavity configurations emulate synthetic jet behavior and act to alter transverse flow mixing characteristics. Effective control of compressible flows can possibly be maintained by the use of shallow cavities aligned with the mainstream direction individually, or in spanwise arrays. Important benefits of such cavity flow configurations include passive operation, no moving parts, no protuberances, thereby contributing to reducing drag and heating penalties common in supersonic flows.
Transient Analysis of Mixed Free-Surface-Pressurized Flows With Modified Slot Model: Part 1 — Computational Model and Experiment
Authors: Arai Kazutoshi , Yamamoto Katsuhiro
Published: February 2009

A new computational model is developed here to analyze the influence of entrapped air on free-surface-pressurized flows in a drainage system. A virtual slot with ceiling on the top of the pipe is introduced to treat a separated gas-liquid flow. This model is a modified model of Preissmann’s and is applicable not only to open channel flow and closed conduit flow but also pressurized flow with entrapped air. Compared to experimental results using the model of 1/50 scale of actual drainage system, the calculation results show that the entrapped air in a horizontal pipe advances the time of pressure rising and makes the maximum value of pressure higher. The escape flow of entrapped air at a dropshaft is caused by long waves pushing the air in the horizontal pipe, and then the pipe slope affects the flow rate of air. The air compressibility has less effect on the transient separated air-water flow in the small-scale model.
Propagation of Steam Hammer in Branch and Run of Steam Piping After Closing of Safety Relief Valve and Dynamic Response of Steam Piping
Authors: Pecˇi´nka L. , Krupa Vl.
Published: February 2009

Propagation of pressure fluctuation in steam piping and feedwater lines may cause many problems in piping operation. The problems are generated either at the pump discharge both for gas and liquid medium or after opening or closing of safety relief valves of the overpressure protection. All these events are classified as expected steam / water hammer. Most dangerous is the case of unexpected water hammer caused by the sudden collapse of steam or air bubble due to man-induced error, for example bad venting or draining or cavitation effects in feedwater pump. In this paper the case of opening and closing of secondary circuit safety relief valves of NPPs with Russian type of PWR called VVER (water-water energy reactor) 1000 MW is discussed.
New Chaotic Approach for Mixing Shear-Thinning Fluids in Stirred Tanks
Authors: Ascanio Gabriel , Foucault Ste´phane , Tanguy Philippe A.
Published: February 2009

The mixing of inelastic shear-thinning fluids has been investigated by using a chaotic approach. Two different scenarios based on single and dual off-centered impellers have been proposed and compared to the standard configuration (steady stirring) showing the potentialities and drawbacks of the proposed arrangements. Mixing times were evaluated by means of color-discoloration technique based on a fast acid-base indicator reaction. An aqueous solution of low concentrated purple bromocresol was used as tracer and added to the tank in the beginning of the experiments and then NaOH or HCl were added to the fluid to be tested in order to change its pH and as a consequence its color. It is demonstrated that, if the operating conditions of the proposed scenarios are properly set, the mixing times can be drastically reduced compared to those obtained under the standard configuration.
A Numerical Simulation of a Bypass Conduit With Steady and Pulsatile Flow
Authors: Chua Leok Poh , Zhang Junmei , Yu Simon Ching Man , Zhou Tongming
Published: February 2009

Intimal hyperplasia (IH) has been cited as a major cause of vascular graft failure, which is associated with the hemodynamic conditions [1, 2]. Most of the earlier studies were concentrated at the distal anastomosis, therefore in this study computational methods were used to describe the blood motion in the proximal anastomosis models. Both steady and pulsatile flow conditions have been investigated. For steady flow cases, low velocity regions were found to appear on both the heels and the toes of the junction. The spatial extent of these low velocity regions was dependent on the graft Reynolds number as well as on the grafting angle and the flow rate ratio of the graft and aorta. For the pulsatile flow, a low velocity recirculating region was formed during the peak flow phase and the flow was reverted from the graft back to the aorta during the deceleration phase of the cycle. Wall shear stress distributions for various cases were also computed. A reasonable good agreement was found between the present results and the previous PIV measurements.
Hydrodynamic Design of the Flow Noise Simulator
Authors: Mori Takayuki , Komatsu Yoshinao , Kaneko Hirobumi , Sato Ryuichi , Izumi Hajime , Yakushiji Ryo , Iyota Masashi
Published: February 2009

The Flow Noise Simulator (FNS) of the 1st Research Center of TRDI/JDA (Japan Defense Agency) is a large, variable pressure, recirculating water tunnel with very low background noise level. (Figure 1) The hydrodynamic goals of the FNS include an excellent flow uniformity of 1% deviation, low turbulence intensity level of 0.5% and it requires careful design of circuit components, for example, contraction, diffusers, bends and turning vanes. In the conceptual design of the FNS, a series of detailed CFD analysis and component model experiment has been conducted to determine the geometry of the circuit component. Further, the entire circuit performances have been evaluated by following scale model studies. This paper discusses some hydrodynamic design considerations for the FNS.
High Resolution DNS of Shear-Convective Turbulence and Its Implications to Second-Order Parameterization
Authors: Tse K. L. , Mahalov A. , Nicolaenko B. , Joseph B.
Published: February 2009

High resolution 3D direct numerical simulation (DNS) of a model tropopause jet, with an underlying convectively unstable layer, is performed. We obtain quasi-equilibrium turbulent dataset, in which the budgets are nearly balanced. Vertical profiles of turbulence statistics and budgets are presented. Using this DNS dataset, we evaluate the performance of some popular models used in second-order closure of turbulence. To our knowledge, this is first time that such a study is conducted for turbulence under the combined influence of shear and convection. From this quasi-equilibrium dataset, we unambigously identify layers of countergradient momentum and heat fluxes which occur near regions of penetrative convection. These are also regions where conventional second-order closure models fail.
Identification of Wind Turbine Response to Turbulent Inflow Structures
Authors: Hand M. Maureen , Kelley Neil D. , Balas Mark J.
Published: February 2009

The National Renewable Energy Laboratory conducted an experiment to obtain detailed wind measurements and corresponding wind turbine measurements in order to establish a causal relationship between coherent turbulent structures and wind turbine blade fatigue loads. Data were collected for one entire wind season from October 2000 to May 2001. During this period, the wind turbine operated under atmospheric conditions that support the formation of coherent turbulent structures 31% of the time. Using the equivalent fatigue load parameter as a measure of wind turbine blade fatigue and using statistical measures of the turbulent fluctuations of the wind, general correlation between the turbulence and the wind turbine response is shown. Direct correlation cannot be resolved with 10-minute statistics for several reasons. Multiple turbulent structures can exist within a 10-minute record, and the equivalent fatigue load parameter is essentially a 10-minute statistic that cannot estimate turbine response to individual turbulent structures. Large-magnitude turbulent fluctuations in the form of instantaneous Reynolds stresses do not necessarily correspond directly to large-magnitude blade root moment amplitudes. Thus, additional work must be done to quantify the negative turbine response and to correlate this response to turbulent inflow parameters over time scales less than 10 minutes.
Unsteady Flow Analysis of the Stator-Rotor Interaction in an Axial Flow Fan
Authors: Ferna´ndez Oro J. , Argu¨elles Di´az K. , Santolaria Morros C. , Ballesteros Tajadura R.
Published: February 2009

In the usual operation of turbomachinery, some unsteady flow phenomena appear due to the non uniformity of the flow inside the rotor, when observed in the fixed reference frame. These phenomena are often related to the unsteady character of the pressure and velocity fields, which produce oscillating forces on the blades, superimposed to the steady force. These oscillating forces are the main mechanism of noise generation, which appear even at a constant rotational speed and at flow rates where the performance curves are stable. In axial turbomachines, the interaction is due to relative motion between the static and rotating blade rows. Considering the case of a fixed blade row (stator) placed upstream of the rotor, the non uniform flow leaving those blades (usually referred as IGV blades) is observed as an unsteady flow by the rotor blades. The effect of this interaction is the generation of unsteady forces on the rotor blades, which generate vibrations (risk of fatigue failure) and noise, and non-uniformity and unsteadiness of the pressure field, that propagates as an acoustic wave. The first part of this work is a brief description of a URANS numerical modeling of the unsteady flow characteristics of a one-stage subsonic axial flow fan with a reaction degree greater than 1. The focus is placed on the statorrotor interaction performance. Both 2D and 3D models of the fan, with 13 IGV’s and 9 rotor blades, were developed and an unsteady simulation was achieved to carry out the main characteristics of the flow inside the turbomachine. Once the actuating forces are determined, the influence of the radial position, the operating conditions and the distance of the fixed and the rotating blade rows is also analyzed. The final part of the paper is focused over the identification, through the definition of deterministic stresses — related to the characteristic blade-passage frequency of every row — that provoke the interaction between fixed and rotating blade rows and its evolution through time. The object is to obtain, in a stress tensor form, the contribution of the velocity field, that is changing because of the sucessive relative positions between blade rows, to the pressure distribution over the blade surfaces in the interior of the stage. Finally, a map of deterministic stresses and even, deterministic kinetic energy, can be obtained to show the influence of the blade rows in the interaction, unsteady phenomena.
Predicting Skin Friction for Turbulent Flow Over Randomly-Rough Surfaces Using the Discrete-Element Method: Part II — Skin Friction Validation
Authors: McClain Stephen T. , Hodge B. Keith , Bons Jeffrey P.
Published: February 2009

The discrete-element method for predicting skin friction for turbulent flow over rough surfaces considers the drag on the surface to be the sum of the skin friction on the flat part of the surface and the drag on the individual roughness elements that protrude into the boundary layer. The discrete-element method has been widely used and validated for roughness composed of sparse, ordered, and deterministic elements. This paper extends the validation of the discrete-element to include real (random and closely packed) surface roughness. To analyze flow over a randomly-rough surface using the discrete-element method, the roughness element blockage fraction and the roughness element cross-section area distributions as a function of height must be determined from surface profilometer measurements. The technique developed for determining these distributions was described in Part 1. This paper, Part 2, describes the modifications that were made to the discrete-element roughness method to extend the validation to real surface roughness. These modifications include accounting for the deviation of the roughness element cross sections from circular configurations and the determination of the location of the computational “surface,” that differs from the physical surface. Two randomly-rough surfaces, two analog surfaces were generated using a three-dimensional printer for wind-tunnel testing. The analog surfaces were created by replacing each random roughness element from the original randomly-rough surface with an elliptical roughness element with the equivalent plan area and eccentricity. The results of the wind tunnel skin friction measurements and the discrete-element method predictions for each of the six surfaces are presented and discussed. For each randomly-rough and analog surface studied, the discrete-element method predictions are within 7% of the experimentally measured skin friction coefficients.
CFD Applications on Selective Catalytic NOx Reduction (SCR) Systems
Authors: Mi Jia , Pitsko Dan A. , Haskew Tim
Published: February 2009

For the last several years, CFD modeling has been successfully used in Southern Company as one of the design and analysis tools to provide engineering insight to retrofitting Selective Catalytic NOx Reduction (SCR) systems to coal-fired steam power generation plants. SCR technology is the most effective method for reducing NOx emissions by at least 75% ∼ 90%. This paper will summarize a few selected CFD applications that were proved to be essential in the SCR design and optimization processes. For validation purposes, some of the CFD results, such as pressure drop, were compared with the available measurement data from the scaled physical flow models. They generally agreed well.
Flow Induced Acoustic Resonance and Vortex Shedding From Staggered Tube Banks
Authors: Hamakawa Hiromitsu , Fukano Tohru , Nishida Eiichi
Published: February 2009

In the present paper our attention is focused on the relation between the vortex shedding phenomena and acoustic resonance in tube banks. We measured a spectrum, coherence function, phase delay of velocity fluctuations in the tube banks and sound pressure level at the duct exit. A model of tube banks had used the same pitch ratio as that of a boiler heat exchanger of a commercial use. As a result, we found three types of vortex shedding with different Strouhal number, 0.29, 0.22 and 0.19. The vortex shedding of St = 0.29 and 0.22 were generated inside of the tube banks. On the other hand St = 0.22 and 0.19 were in the wake of the last row of the tube banks. The velocity fluctuation and the periodicity of the vortex shedding were the most intense in the wake of the second row of the tube banks in whole area of the tube banks. When acoustic resonance generated at the natural frequency of the duct, 342.5Hz, at a gap velocity of 39.2m/s, we found two types of vortex shedding with different frequencies, mainly about 342.5Hz (St = 0.29) and 262.5Hz (St = 0.22), inside of the tube banks. The amplitude of velocity fluctuation due to the vortex shedding became large in accordance with the generation of the acoustic resonance which has the fundamental natural frequency of the acoustic resonance in the transverse direction of the duct.
Axisymmetric Stagnation Point MHD Flow Over a Porous Plate With Heat Transfer
Authors: Attia Hazem Ali
Published: February 2009

The steady axisymmetric hydromagnetic flow of an incompressible viscous electrically conducting fluid impinging on a porous flat plate with heat transfer are investigated. An external uniform magnetic field and a uniform suction or injection are applied normal to the plate which is maintained at a constant temperature. Numerical solution for the governing nonlinear equations is obtained.
Vortex Shedding From a Square Cylinder With Ground Effect
Authors: Bhattacharyya S. , Maiti D. K.
Published: February 2009

Numerical study on the wake behind a square cylinder placed parallel to a wall has been made. Flow has been investigated in the laminar Reynolds number (based on the cylinder length) range. We have studied the flow field for different values of the non-dimensional gap length between cylinder and the wall. The case when the cylinder is placed on the wall has also been considered. The governing unsteady Navier-Stokes equations are discretised through the finite volume method on staggered grid system. A SIMPLER type of algorithm has been used to compute the discretised equations iteratively. Vortex shedding has been found to be influenced by the wall. Vortex shedding suppression occurs beyond a critical value of the gap length. Due to the shear, the drag experienced by the cylinder is found to increase with the reduction of gap length. The flow is found to be steady when the cylinder is placed on the wall at a range of Reynolds number.
Gas-Liquid-Particle Three-Phase Flows in Bubble Columns
Authors: Ahmadi Goodarz , Zhang Xinyu
Published: February 2009

An Eulerian-Lagrangian computational model for simulations of gas-liquid-solid flows in three-phase slurry reactors is developed. In this approach, the liquid flow is modeled using a volume-averaged system of governing equations, whereas motions of bubbles and particles are evaluated by Lagrangian trajectory analysis procedure. It is assumed that the bubbles remain spherical and their shape variations are neglected. The two-way interactions between bubble-liquid and particle-liquid are included in the analysis. The discrete phase equations include drag, lift, buoyancy, and virtual mass forces. Particle-particle interactions are accounted for by the hard sphere model approach. The bubble collisions and coalescence are also included in the computational model. The simulation results show that the transient characteristics of the three-phase flow in a column are dominated by time-dependent staggered vortices. The bubble plume moves along a S-shape path and exhibit an oscillatory behavior. While most particles are located outside the vortices, some bubbles and particles are retained in the vortices. Bubble upward velocities are much larger than both liquid and particle velocities. Particle upward velocities are slightly smaller than the liquid velocities.
Noninvasive Measurement of the Bubble Boundary Layer in Bubbly Flows Using Ultrasonic Velocity Profile Monitor (UVP)
Authors: Nakagawa Masamichi , Suzuki Yumiko , Aritomi Masanori , Mori Michitsugu
Published: February 2009

We discussed the reasons why the measurement error due to the measuring volume reduces against the anticipation, and why the data appropriate to fluid dynamics are obtained clean, in the case where we measure the bubble boundary layer using an Ultrasonic Velocity Profile Monitor (UVP). The previous estimations of the error due to measuring volumes based on only the shape of bubbles, leaving the behavior of bubble boundary layers out of consideration, have possibilities to estimate it fairly larger than the practical. Because the separated shear layer could be measured in almost parallel with the disk-like measuring volumes, the flow structure in the liquid phase around bubbles, namely the structure of bubble boundary layers, could be captured with little distortion in spite of large measuring volumes of the UVP.
Rapid Experimentation in Complex Internal Flow Passages Using SLA and MRV
Authors: Elkins Christopher J. , Eaton John K. , Wicker Ryan B.
Published: February 2009

Designing complex internal cooling passages is extremely difficult without detailed information about the flow behavior due to the presence of separated flow zones and strong secondary flows. This paper describes a new approach to designing internal flow passages called Rapid Iterative Design Using Experimentation (RIDUE). RIDUE utilizes rapid prototyping (RP) manufacturing to quickly build an accurate model of a complex internal flow passage and magnetic resonance velocimetry (MRV) to measure the full three dimensional velocity field. Because both techniques offer very fast turnaround, it is feasible to conduct iterative design with a cycle time of 1–2 days. RIDUE is demonstrated using a generic turbine blade internal cooling passage with four serpentine channels. Two channels have rectangular cross-section and two are square. In each channel, two of the four walls have ribs (also called turbulators) angled at 45 degrees to the main flow direction. Two models based on the generic geometry are studied, each with different turbulator cross-sections, one square and one rounded. Both models were built using a stereo lithography apparatus. MRV provided three-component velocity vectors for flow at a Reynolds number of 10,000 based on the hydraulic diameter of the first passage. Sample vector fields are presented to illustrate the detail with which the flow can be investigated. Although little difference is seen in the flows between the two models, it is demonstrated that through its use of RP processes and the MRV measurement technique, RIDUE is a viable technique for modern internal passage design.
Ultrasound Gas Flow Measurement
Authors: Hans Volker
Published: February 2009

Measurements of flow velocity with cross correlation functions of ultrasonic signals show that the travelling time of structures deviates from the mean flow velocity. This difference usually is explained by the difference between the line integral of measurement and the area integral of the mean flow velocity. A comparison of the probability distribution of velocity components shows that the most frequent components in the fluid are in accordance with the travelling time of structures. The explanation is given by systems theory. In vortex shedding flow meters an ultrasonic wave is modulated by vortices behind a bluff body. The frequency of the vortices is proportional to the flow velocity. It depends on the size and arrangement of bluff bodies. As ultrasound is very sensitive to all kinds of modulating effects the size of bluff bodies can be drastically reduced in comparison to measurements with pressure sensors. Additionally the sensitivity can be increased, pressure losses behind the bluff body are considerably decreasing.
Multimode Laser Doppler Anemometer for Turbulence Measurements With High Spatial Resolution
Authors: Bu¨ttner Lars , Czarske Ju¨rgen
Published: February 2009

The advantageous employment of multimode fibres for beam delivery in laser Doppler anemometers (LDA) is presented. Turbulent boundary layers can be investigated with high precision and high spatial resolution. For measurements of turbulence data usually hot wire anemometers are employed which, however, do not fulfil the requirement of non-intrusiveness. Therefore laser Doppler anemometers are employed which are limited by the size of their measurement volume of usually about 50 μm × 100 mm. The spatial resolution can be improved by a stronger focusing or by using a side receiver, which restricts the detection area. Furthermore, the measurement of turbulence data is limited by the varying fringe spacing, which pretends a non-existing degree of turbulence (“virtual turbulence”) and is caused by the wave-front curvature of the employed Gaussian laser mode. In this contribution it is demonstrated, that the employment of multimode-light with beam quality factors M2 >> 1 the length of the measurement volume is reduced to a few percent compared to the intersection volume length of the two laser beams because of the low spatial coherence of the multimode light. The uniformity of the fringe spacing is significantly improved. The variation of fringe spacing (“virtual turbulence”) is less than 0.05%. The multimode-fibre LDA (MMF-LDA) combines the advantages of both a short measurement volume guaranteeing a high spatial resolution as well as low virtual turbulence in one device. It is therefore well suited for high accurate determination of velocity gradients in laminar or turbulent boundary layers. A MMF-LDA with about 100 fringes and 5·10−4 fringe spacing variation within a measurement volume of length 80 μm was used to perform fluid measurements in a wind tunnel. The remaining turbulence intensity of the free wind tunnel stream was determined to 0.3%. Boundary layer measurements on a well-known laminar velocity profile, the Blasius boundary layer, were performed and the wall shear stress was determined. All results are in excellent agreement with the theory. Measurements of turbulent boundary layers are presented. Multimode fibres allow the transfer of significantly higher power into the LDA measurement volume and need lower alignment effort compared to the usually employed single-mode fibres. Powerful laser diodes can now be applied for LDA set-ups, enabling sensitive velocity measurements of fluid flows.
3-D Numerical Simulation of Flow Around a Rectangular Cylinder
Authors: Rokugou Akira , Okajima Atsushi , Isogawa Takanori
Published: February 2009

Three-dimensional numerical simulations of the flow around rectangular cylinders with depth-to-height ratios (side ratio) of 3 and 6 at various Reynolds numbers were carried out using the Large eddy simulation (LES), which employs the Smagorinsky eddy-viscosity model, a type of subgrid scale (SGS) model. Computed results compared well with experimental ones. The irregular fluctuation of aerodynamic forces can be simulated. The time history of the lift force corresponded well to the variation of flow pattern.