bluuebunny/crossref_metadata_2025 huggingface dataset:
Weak Coupling Strategy for Multi-Physics CFD Simulation in Engineering Problems
Authors: Yamamoto Makoto , Suzuki Masaya
Published: June 2012

Multi-Physics CFD Simulation will be one of key technologies in various engineering fields. There are two strategies to simulate a multi-physics phenomenon. One is “Strong Coupling”, and the other is “Weak Coupling”. Each can be employed, based on time-scales of physics embedded in a problem. That is, when a time-scale of one physics is nearly same as that of the other physics, we have to use Strong Coupling to take into account the interaction between two physics. On the other hand, when one time-scale is quite different from the other one, Weak Coupling can be applied. Considering the present computer performance, Strong Coupling is difficult to be used in engineering design processes now. Therefore, we are focusing on Weak Coupling, and it has been applied to a number of multi-physics CFD simulations in engineering. We have successfully simulated sand erosion, ice accretion, particle deposition, electro-chemical machining and so on, with using Weak Coupling method. In the present study, the difference between strong and weak couplings is briefly described, and two examples of our multi-physics CFD simulations are expressed. The numerical results indicate that Weak Coupling strategy is promising in a lot of multi-physics CFD simulations.
A Low-Dissipation Optimization-Based Gradient Reconstruction (OGRE) Scheme for Finite Volume Simulations
Authors: Poe Nicole M. W. , Walters D. Keith
Published: June 2012

Finite volume methods employing second-order gradient reconstruction schemes are often utilized to computationally solve the governing equations of transport. These reconstruction schemes, while not as dissipative as first-order schemes, frequently produce either dispersive or oscillatory solutions, especially in regions of discontinuities, and/or unsatisfactory levels of dissipation in smooth regions of the variable field. A novel gradient reconstruction scheme is presented in this work which shows significant improvement over traditional second-order schemes. This Optimization-based Gradient REconstruction (OGRE) scheme works to minimize an objective function based on the mismatch between local reconstructions at midpoints between cell stencil neighbors, i.e. the degree to which the projected values of a dependent variable and its gradients in a given cell differ from each of these values in neighbor cells. An adjustable weighting parameter is included in the definition of the objective function that allows the scheme to be tuned towards greater accuracy or greater stability. This scheme is implemented using the User Defined Function capability available in the commercially available CFD solver, Ansys FLUENT. Various test cases are presented that demonstrate the ability of the new method to calculate superior predictions of both a scalar transported variable and its gradients. These cases include calculation of a discontinuous variable field, several sinusoidal variable fields and a non-uniform velocity field. Results for each case are determined on both structured and unstructured meshes, and the scheme is compared with existing standard first- and second-order upwind discretization methods.
A Dynamic Procedure for Wall-Modeled Large-Eddy Simulation of High Reynolds Number Flows
Authors: Kawai Soshi
Published: June 2012

This paper addresses the error in large-eddy simulation with wall-modeling (i.e., when the wall shear stress is modeled and the viscous near-wall layer is not resolved): the error in estimating the wall shear stress from a given outer-layer velocity field using auxiliary near-wall RANS equations where convection is not neglected. By considering the behavior of turbulence length scales near a wall, the cause of the errors is diagnosed and solutions that remove the errors are proposed based solidly on physical reasoning. The resulting method is shown to accurately predict equilibrium boundary layers at very high Reynolds number, with both realistic instantaneous fields (without overly elongated unphysical near-wall structures) and accurate statistics (both skin friction and turbulence quantities).
Flame Brush Structure of H2-Air Turbulent Premixed Flames at High Reynolds Numbers
Authors: Shim Youngsam , Tanaka Shoichi , Shimura Masayasu , Fukushima Naoya , Tanahashi Mamoru , Miyauchi Toshio
Published: June 2012

Three-dimensional direct numerical simulations (DNSs) of turbulent premixed planar, jet and V flames of hydrogen-air mixture have been conducted to investigate the flame brush and the local flame structures at high Reynolds number turbulences. The detail kinetic mechanism including 12 reactive species and 27 elementary reactions was used to represent the hydrogen-air reaction. For planar flame, flame front is highly fluctuating, and multi-layer structure, multiply-folded flame front and unburned mixture island which lead to corresponding increase of the flame brush thickness can be observed. The flame brush thickness of the planar flame is relatively uniform along the flame front, and is about 2∼3 times the integral length scale (l), which is defined from an energy spectrum. For the jet and V flames, the flame brush thicknesses grow with the streamwise direction from about 0.5∼1 times the integral length scale (l) to about 2∼3 times the integral length scale (l) due to the highly fluctuating flame front at the downstream region.
A Numerical Analysis of the Behavior of Liquid Film Between Counter-Rotating Rigid and Deformable Rolls
Authors: Lee Sang Hyuk , Lee Moon Kyu , Hur Nahmkeon , Seo Young Jin , Kim In-Cheol , Lee Sung-Jin
Published: June 2012

It is important to accurately predict the behavior of liquid film between the rotating rigid and deformable rolls in the film coating process of steel and paper industry. The behavior of liquid film between rolls with the negative gap due to the press contact is determined by the interaction between solid rolls and liquid passing between rolls. In the present study, the numerical methodology for the prediction of behavior of solid rolls and liquid film was introduced with the CFD and FEM analysis. The shape of a deformable roll rotating in press contact with a rigid roll was obtained numerically from the FEM simulation. Based on the results of deformed roll shape, the CFD simulation on the liquid flow between rolls was performed with an arbitrary gap between rolls in the contact area. By comparing the pressure distribution of liquid passing through the gap with the contact pressure distribution of solid rolls, the liquid film thickness between rolls was obtained in equilibrium with the pressure between the rolls. From the CFD simulation on two phase flow of liquid film around rotating rolls with the thickness and flow rate of liquid film passing through the contact area, the thickness of liquid film bifurcated along rolls were predicted for various rotating speed.
Numerical Study of a Compact Wavy Heat Exchanger
Authors: Mereu Riccardo , Colombo Emanuela , Inzoli Fabio
Published: June 2012

The present work deals with the design of compact wavy heat exchangers, where high values of heat transfer area per unit volume are looked for in order to reduce size and increase efficiency. A numerical investigation of a rectangular cross-sectional shape geometry, with duct aspect ratio of 7.3, and a corrugation angle of 145° is here proposed. The Reynolds numbers (based on the duct hydraulic diameter) range from 300 to 5000. The numerical analysis is performed by means of a finite volume commercial CFD code. Laminar and Unsteady Reynolds Averaged Navier-Stokes (U-RANS) approaches are applied to a three-dimensional fluid domain over a single module with periodic conditions, respectively for, lower (<1000) and higher (≥1000) Reynolds numbers. Mean velocity and temperature fields are obtained. The average values of Fanning friction factor and Nusselt number are compared with experimental data from literature for the same geometry operating at the same Reynolds number range. For the evaluation of heat transfer quantities obtained in the numerical study the analogy between Sherwood and Nusselt number is used. The numerical results agree with experimental data, by showing the capability of laminar and U-RANS two-equation approach, via RNG model, to capture the mean fluid flow including the Taylor-Gortler instability that appear at low Reynolds numbers. The qualitative comparison of heat results shows an agreement between experimental and numerical data, whereas the extension to quantitative comparison is limited by some deficiencies in experimental correlation for mass/heat transfer analogy.
Numerical and Experimental Study of the Influence of Damage on the Aerodynamic Characteristics of a Finite Wing
Authors: Abdolahipour Soheila , Mani Mahmoud , Ahmadi Dehaghi Ghazaleh M.
Published: June 2012

In this paper the flow on a finite wing with star shape damage is numerically and experimentally investigated to understand the influences of damage on the aerodynamic characteristics of wing. To study the effects of different span positions, the damage was considered in tip, middle and root position of the wing span. The aerodynamic coefficients and their increments due to damage were extracted and the results were compared to each other and also to the results of experimental. Then flow visualizations were practiced to make evident the flow structure on the model and to help to understand the influences of each position of damage on the aerodynamic coefficients. There was the flow through the damage which was driven by the pressure difference between the upper and lower wing surfaces. The flow could take two forms dependent on the angle of attack. The first form was a “weak-jet” which formed an attached wake and resulted in small changes in force and moment coefficients. The second form resulted from increased incidence. This was the “strong-jet” where through flow penetrated into the free stream flow with large separated wake and reverse flow. The effect on the force and moment coefficients was significant in this case. Generally comparing to an undamaged model, increasing incidence for a damaged model resulted increase loss of lift coefficient, increased drag coefficient and more negative pitching moment coefficient.
Numerical Simulation of Flow in a Photocatalytic Reactor Containing Baffles
Authors: Ahmed Saber , Rasul M. G. , Brown R. J. , Duran J. Esteban
Published: June 2012

In this study a new immobilized flat plate photocatalytic reactor for wastewater treatment has been investigated using computational fluid dynamics (CFD). The reactor consists of a reactor inlet, a reactive section where the catalyst is coated, and outlet parts. For simulation, the reactive section of the reactor was modelled with an array of baffles. In order to optimize the fluid mixing and reactor design, this study attempts to investigate the influence of baffles with differing heights on the flow field of the flat plate reactor. The results obtained from the simulation of a baffled flat plate reactor hydrodynamics for differing baffle heights for certain positions are presented. Under the conditions simulated, the qualitative flow features, such as the distribution of local stream lines, velocity contours, and high shear region, boundary layers separation, vortex formation, and the underlying mechanism are examined. At low and high Re numbers, the influence of baffle heights on the distribution of species mass fraction of a model pollutant are also highlighted. The simulation of qualitative and quantitative properties of fluid dynamics in a baffled reactor provides valuable insight to fully understand the effect of baffles and their role on the flow pattern, behaviour, and features of wastewater treatment using a photocatalytic reactor.
Numerical Simulation of Porous Medium Internal Combustion Engine
Authors: Mohammadi Arash , Jazayeri Ali , Ziabasharhagh Masoud
Published: June 2012

Porous media (PM) has interesting advantages compared with free flame combustion due to the higher burning rates, the increased power range, the extension of the lean flammability limits, and the low emissions of pollutants. Future internal combustion (IC) engines should have had minimum emissions level, under possible lowest fuel consumption permitted at all operational conditions. This may be achieved by realization of homogeneous combustion process in engine. In this paper, possibility of using PM in direct injection IC engine, with cylindrical geometry for PM to have homogeneous combustion, is examined. A three-dimensional numerical model for the regenerative engine is presented in this study based on a modified version of the KIVA-3V code that is very popular for engine simulation. Methane as a fuel is injected directly inside hot PM that is assumed mounted in cylinder head. Very lean mixture is formed and volumetric combustion occurs in PM. Mixture formation, pressure, temperature distribution in both phases of PM and in-cylinder fluid with the production of pollutants CO and NO, in the closed part of the cycle is studied.
Lattice Boltzmann Simulations of Flow in Two-Dimensional Lid-Driven Semi-Circular Cavity
Authors: Yang Fan , Liu Lianguo , Shi Xuming , Guo Xueyan
Published: June 2012

The flow pattern in a two-dimensional lid-driven semi-circular cavity is analyzed using the lattice Boltzmann method (LBM). The treatment of curved boundary with second-order accuracy is used. The streamline contours as well as dimensionless velocity component along the central line of a semi-circular cavity are obtained for different Reynolds numbers. The numerical results show that the LBM can capture the formation of primary, secondary and tertiary vortices exactly as the Reynolds number increases and has a great agreement with those of current literatures.
Interface Tracking Simulation of Mass Transfer From a Dissolving Bubble
Authors: Hayashi Kosuke , Tomiyama Akio
Published: June 2012

An interface tracking method for predicting bubble dissolution process is proposed. A non-diffusive scheme for advecting species concentrations is adopted to accurately compute the volume change due to mass transfer. The applicability of the proposed method is examined through several benchmark tests, i.e. mass transfer from a static bubble and that from free rising bubbles. Predicted species concentration distributions and mass transfer coefficients agree well with theoretical and empirical models. Dissolution of single carbon dioxide bubbles in a vertical pipe filled with water is also simulated. The bubbles consist only of carbon dioxide, and nitrogen and oxygen are initially dissolved in water. The volume change due to dissolution of carbon dioxide from the bubbles and evaporation of nitrogen and oxygen from water are well predicted.
Numerical Simulation of Bubbles Contaminated With Soluble Surfactant
Authors: Kurimoto Ryo , Hayashi Kosuke , Tomiyama Akio
Published: June 2012

An interface tracking method for predicting motions of bubbles contaminated with soluble surfactants is presented. A level set method is utilized to track the interface. Transportations of surfactants in the bulk liquid and those at the interface are taken into account. The amount of adsorption and desorption is evaluated by using the Frumkin & Levich model. Simulations of bubbles contaminated with soluble surfactants are carried out, i.e., single air bubbles rising through stagnant water, Taylor bubbles in a vertical pipe filled with water, and a wobbling bubble in a vertical duct. As a result, the following conclusions are obtained: (1) the increase in drag coefficients of spherical bubbles due to the presence of surfactant, i.e. Marangoni effect, is well predicted, (2) surfactants mainly accumulate at the rear edge of a Taylor bubble and the Marangoni effect is very small in the nose region at high Eo¨tvo¨s and low Morton numbers, and therefore, the effects of surfactant on the bubble rising velocity are small in low viscosity systems, and (3) the surfactant concentration is low in the top region of a wobbling bubble, whereas it is high in the bottom region. The peak concentration appears at the side edge of the bubble and the location of the peak concentration moves with the bubble and wake movements.
Numerical Simulation of Unsteady Flows Through a Francis Turbine Runner Using Vortex Methods
Authors: Zhu Baoshan , Wang Longbu , Zhai Jie , Cao Shuliang
Published: June 2012

A grid-free numerical scheme is provided for the solution of unsteady flow in the hydraulic turbines. The Lagrangian vortex method is utilized to evaluate the convection and stretch of the vorticity, and the boundary element method is used to solve the Neumann problem to define the potential flow. The no-slip boundary condition is satisfied by generating vortex sticks at the solid surface. A semi-analytical regularization technique is applied to evaluate the singular boundary surface integrals of the potential velocity and its gradients accurately. The fast multipole method (FMM) has been extended to evaluate the velocity and velocity gradients induced by the discretized vortex blobs in the Lagrangian vortex method. The successful simulation for the unsteady flow through a hydraulic turbine’s runner has manifested the effectiveness of the proposed method.
Numerical Simulation of the Flow in a Centrifugal Pump With a Vaned Diffuser
Authors: Segala Willian , Stel Henrique , Hungria Vanessa , Morales Rigoberto E. M. , Vicent Sergio C. , Bannwart Antoˆnio , Negra˜o Cezar O. R.
Published: June 2012

This work presents a numerical investigation of the water flow in the first stage of a two-stage centrifugal pump with a vaned diffuser. The geometry consists of a pipe intake, a 8-blade impeller, a 12-blade diffuser and an outlet extension chamber. The numerical modeling comprises a transient rotorstator interface connection between the impeller and the other static domains, and it was implemented in the commercial code ANSYS-CFX. The numerical runs were carried out for four impeller speeds and a wide range of volumetric flow rates. The standard k-ε turbulence model was used. An experimental loop is also used to measure pump head values to validate the numerical approach. Comparison of numerical head values with the experimental data showed a good agreement. Similarity relations used for the numerical head values for different impeller speeds also shows good agreement within the range studied. A transient analysis of the pressure values at the impeller-diffuser interface showed that, using a steady state frozen rotor approximation as the initial condition for the transient calculation, generally no more than half of a complete impeller revolution is needed for the pump to achieve temporal periodicity. This numerical procedure saves significantly the computational time. Moreover, the numerical results confirm that, once the periodic regime is achieved, an azimuthal periodicity at each 90° interval is also achieved, just as expected from the 8-to-12 blades ratio between impeller and diffuser. Comparison of the numerical efficiencies of the single-stage pump with the experimental counterpart showed significant discrepancies. These must be related to the geometric simplifications of the numerical model and volumetric pressure losses of the real pump not included in the numerical model. Consequently, the Best Efficiency Point of the single-stage pump was found to be different from the two-stage assembly, and the flow field analysis apparently confirms this feature.
Design Optimization of Strongly Interacting Diffuser Pump Stage
Authors: Zangeneh Mehrdad , Daneshkhah Kasra
Published: June 2012

In this paper the flow field in a diffuser pump stage consisting of a centrifugal impeller and a radial diffuser is investigated by using unsteady computations. The time-averaged unsteady results are used to understand the main sources of loss in the stage. Then 3D inverse design method used to redesign the impeller and diffuser blades in order to improve the stage efficiency.
Toward Optimum Configuration of Circumferential Groove Casing Treatment in Transonic Compressor Rotors
Authors: Hah Chunill
Published: June 2012

The current paper first reviews experimental and numerical investigations to understand flow physics and to develop optimum configurations of circumferential grooves in compressor rotors. Circumferential grooves are used mainly to increase stall margin in axial compressors with small decrease in aerodynamic efficiency. Although circumferential groove casing treatment has been used widely, flow mechanisms of the circumferential grooves at near stall conditions are not well understood yet. Detailed time-dependent flow measurement inside tip gap in a high speed compressor is still a big challenge even though significant advance has been made in non-intrusive flow measurement technique. Therefore numerical approaches have been used to study relevant flow physics. However, optimum design of circumferential grooves to a given compressor with the computational tools is not practical yet. In the present paper, various investigations to study flow physics of circumferential groove casing treatment in axial compressor are reviewed first. Possible missing flow physics are identified and future research efforts for the optimum design are discussed.
Design and Experimental Research of Self-Suction Sprinkler Irrigation Jet Pump
Authors: Liu Jianrui , He Xiaoke , Shi Weidong , Su Qiqin
Published: June 2012

A new type of self-suction sprinkler irrigation jet pump was presented in this paper. A jetted self-priming set with Venturi Tube was installed in the inlet of the pump, and the self-priming performance was improved. The valve of the jetted self-priming set shut off when the pump self-priming was finished and the pump efficiency was increased. The design method, working mechanism and structure of the pump were introduced. The experiment results of the jet aerator of the pump, the self-shutoff of the reflowing valve and performance were obtained. The results showed that the self-priming performance of the pump was principal concern with the size of the jet aerator and the pump efficiency was increased as the reflowing valve automatically closing. The efficiency of the pump is higher by 5.3%∼8.9% and the time of the self-priming is shorter by 25∼73s and the average weight is lighter by 16% than the national standard, which indicates that comprehensive technical index is on the top of international level.
Influence of Blade Outlet Angle and Blade Thickness on Performance and Internal Flow of Mini Centrifugal Pump
Authors: Shigemitsu Toru , Fukutomi Junichiro , Kaji Kensuke
Published: June 2012

Mini centrifugal pumps having a diameter smaller than 100mm are employed in many fields; automobile radiator pump, ventricular assist pump, cooling pump for electric devices and so on. Further, the needs for mini centrifugal pumps would become larger with the increase of the application of it for electrical machines. It is desirable that the mini centrifugal pump design be as simple as possible as precise manufacturing is required. But the design method for the mini centrifugal pump is not established because the internal flow condition for these small-sized fluid machines is not clarified and conventional theory is not suitable for small-sized pumps. Therefore, we started research on the mini centrifugal pump for the purpose of development of high performance mini centrifugal pumps with simple structure. Three types of rotors with different outlet angles are prepared for an experiment The performance tests are conducted with these rotors in order to investigate the effect of the outlet angle on performance and internal flow condition of mini centrifugal pumps. In addition to that, the blade thickness is changed because blockage effect in the mini centrifugal pump becomes relatively larger than that of conventional pumps. On the other hand, a three dimensional steady numerical flow analysis is conducted with the commercial code (ANSYS-Fluent) to investigate the internal flow condition. It is clarified from the experimental results that head of the mini centrifugal pump increases according to the increase of the blade outlet angle and the decrease of the blade thickness. In the present paper, the performance of the mini centrifugal pump is shown and the internal flow condition is clarified with the results of the experiment and the numerical flow analysis. Furthermore, the effects of the blade outlet angle and the blade thickness on the performance are investigated and the internal flow of each type of rotor is clarified by the numerical analysis results.
Experimental Study of Mechanism of Silt Abrasion Influenced by Cavitation in Hydraulic Machinery
Authors: Zhang Tao , Chen CiChang , Li Dan , Lv DongLi
Published: June 2012

Experiments of cavitation erosion, silt abrasion and their synergetic erosion on Al hydrofoils were made in a testing-section. The erosion depth on hydrofoils was measured, and results showed that the depth value increased gradually with the condition changed from silt abrasion to synergetic erosion (lie due to contemporary action of silt abrasion and cavitation bubble collapse) and meanwhile with the position changed form the front part to the trailing edge of hydrofoil. The microtopography on hydrofoils was observed under the three experimental conditions. The cavitation erosion results appeared as regular-shape pits which differed only in the number per unit area at different position. The silt abrasion patterns was uniform in characteristics around one fixed point on hydrofoil. From the front part to the trailing edge of hydrofoil, the main abrasive wear patterns changed from ploughing type to wedge type. Small scale ploughing or cutting type and large scale wedge type were the main erosion patterns of the synergetic erosion directly caused by solid particles. From the front part to the trailing edge of hydrofoil, the size of small and large scale abrasive wear patterns increased gradually. Combining the analysis and processing of cavitation structure with the silt abrasion and synergetic erosion patterns, a viewpoint about silt abrasion influenced by cavitation was put forward. During the stage of growth of attached cavity, the hydrofoil was eroded by solid particles at small angle as a result of solid particles subjected to cavitation nucleation being accelerated along the surface of hydrofoil, and the erosion patterns were dominated by ploughing or cutting type. During the stage of cavitation cloud collapse in main flow, the hydrofoil was eroded by impact abrasion of solid particles at large angle resulted from solid particles being accelerated to high velocity by micro-jet or pressure wave, and the dominating erosion pattern was wedge type.
Effects of Swirl Brakes on the Leakage Flow Between the Casing and the Shroud of a Centrifugal Impeller
Authors: Kimura Toshiya , Kawasaki Satoshi , Shimagaki Mitsuru , Uchiumi Masaharu
Published: June 2012

CFD simulations were performed for the leakage flow in the gap between the casing and the shroud of a centrifugal impeller. The effects of swirl brakes created in the casing on the leakage flow were numerically investigated. The leakage flow swirling due to impeller rotation was trapped inside a swirl brake and interacted with the walls of the swirl brake, generating a very complex flow and a vortex structure inside. By the interaction with swirl brakes, the leakage flow rapidly lost its angular momentum mainly in the outer region of the swirl brake. The loss of swirl resulted in a decrease of the pressure difference in the radial direction due to the centrifugal force effect. The radial distribution of pressure in the gap between the casing and the shroud was largely modified, and thus the axial thrust force on the impeller was changed as well. The thrust balance of the impeller can be adjusted by an appropriate design of swirl brakes and the instability of rotating shaft can be reduced by decreasing the swirl of the leakage flow.
Numerical Analysis of Design and Off-Design Performance of High Specific Speed Mixed Flow Pumps
Authors: Sekino Yumiko , Tanabe Yoichi
Published: June 2012

In most cases of high specific speed mixed flow pump applications, it is necessary to control off-design performance such as shutoff power/head and unstable characteristic as well as design point performance. The authors have been working on multi-objective optimization strategy of mixed flow pump design considering off-deign performance by means of Computational Fluid Dynamics (CFD). In the design optimization process, it was found that the steady CFD analysis using one pitch blade passage adopting periodic boundary condition could be used for relative comparison of the important performance characteristics such as the level of efficiency, the shutoff performance and the stall characteristics of different designs. However, the steady CFD analysis with one pitch blade passage showed that absolute values of head and shaft power were estimated lower than those of the experimental results especially in the partial capacity range. In order to improve the accuracy of CFD results it should be necessary to use full pitch model. In this paper, the evaluation results of three CFD approaches on the capability of the performance prediction of the mixed flow pumps will be shown. The approaches evaluated are steady flow analysis with one pitch blade passage using periodic boundary conditions, full pitch steady flow analysis and unsteady flow analysis. It was found from the evaluation results that the full pitch steady flow analysis showed the same tendency as one pitch analysis and the unsteady CFD provided higher accuracy of the shutoff head. However, the steady analysis should still be useful to reduce the high computational cost and the amount of time. Meanwhile the unsteady analysis clarifies the details of the off-design flow patterns. The effects of the turbulence models and the details of the off-design flow patterns were also discussed in this paper.
Streamlines in Mixed-Flow Impeller Deduced by Solving Partial Differential Equations and Visualized Via CFD/PIV
Authors: Qian Kunxi
Published: June 2012

Streamlines in mixed-flow impeller were deduced by solving partial differential equations of continuity, motion and energy; they could be simplified to be logarithmic spiral and parabola in vertical and horizontal sections respectively. Then a mixed-flow impeller was designed and manufactured, its vane had a logarithmic spiral and its shroud had a parabola form. Computational fluid dynamics (CFD) demonstrated that the streamlines in the impeller were coincided with the vane and shroud; particle image velocimetry (PIV) exhibited also that the streamlines in vane channel were really logarithmic spiral at the designing point of pumping flow rate and pressure head. It concludes that both theoretical and experimental methods presented in this paper are informative and convincing, and thus are worthy to be investigated further.
Flapwise and Edgewise Blade Loads Analysis of HAWT Rotor by Using Fluid-Oscillation Coupled Calculation Model
Authors: Hasegawa Yutaka , Takagi Yusuke , Murata Junsuke , Kikuyama Koji
Published: June 2012

A horizontal axis wind turbine suffers fluctuating aerodynamic loads, which result in oscillations of the rotor blades. Since the blade oscillation has considerable effects on the blade fatigue life, the influence on the fatigue loads from the interaction between the aerodynamic loads and the structural oscillations should be considered in the design process of the wind turbine rotor. The objective of this work is to analyze the aerodynamic effects on the fatigue loads of rotor blade due to structural oscillation and inflow conditions, by using numerical calculation method. This paper explains a calculation model which can estimate the aerodynamic loads on the rotor blade of the horizontal axis wind turbine in the inflow conditions with the turbulence and yawed misalignment. The fluid-oscillation coupled calculation has been performed for the geometry of the NREL test turbine. The calculated results are compared with the experimental results to evaluate the validity of the calculation model.
Experimental Study on Performance of Darrieus-Type Open Hydroturbine With Inlet Nozzle in Low Downstream Water Level Conditions
Authors: Hirowatari Koutarou , Shimokawa Kai , Iwamoto Shunsuke , Okuma Kusuo , Watanabe Satoshi , Matsusita Daisuke , Furukawa Akinori
Published: June 2012

A Darrieus-type open hydro turbine with inlet nozzle has been proposed for utilization of extra-low head hydropower though a ducted type is in general used, consisting of an intake, runner section and draft tube. The open turbine means the simplified one, which has no runner casing and no draft tube. By installing inlet nozzle for the open turbine, the turbine efficiency is never deteriorated in comparison with the ducted one. The role of inlet nozzle is to increase generated torque with higher efficiency on the upstream path of the Darrieus blade passing and to decrease the torque with lower efficiency on the other path by removing the runner casing as the Darrieus turbine is cross flow type. In the present paper, the more simplified open turbine, consisting of only the inlet nozzle and the quarter covered upper casing to support the runner shaft, is experimentally examined. It is found that the depth of water level, covering or uncovering the runner in downstream pond, which might be changed by flow rate in practical use due to river-flow type turbine, influences on the turbine performance. When the depth of water level is kept deeper than the runner height of vertical axis turbine, the performance is almost the same as that of the case with whole covered upper casing. With decreasing the water level shallower than the runner height, the generated power and the efficiency become deteriorated due to making the wavy motion of the water surface at first. Then the stable operation at the maximum efficiency point in normal condition cannot be obtained. The cause on the mechanism of performance deterioration is considered with visualization of fluid behavior around Darrieus blades.
Analytical and Numerical Modeling of Performance Characteristics of Cross-Flow Axis Hydrokinetic Turbines
Authors: Johnston Alex , Wosnik Martin
Published: June 2012

A model for cross-flow axis hydrokinetic turbines based on blade element theory (BET) was developed. The model combines an extensive experimental and numerical high Reynolds number data set for symmetric airfoils with governing equations to predict performance characteristics of the turbines. The model allows for any number of turbine blades and for variable hydrofoil sweep angles; both straight blade (H-Darrieus) and helical blade (Gorlov) cross-flow axis turbines are modeled. In this model the free stream velocity and the turbine’s rate of rotation are not coupled hydrodynamically, and experimental calibration of the model for a specific turbine design is necessary. The calibrated model is then used with real inflow data from an actual tidal energy site to predict instantaneous power and energy yield over a period of time. Investigation of tip speed ratios allows for predictions of unsteady loadings, optimal performance and power outputs. The model provides the versatility to predict characteristics of many different shapes and sizes of cross-flow axis turbines. Through investigation of turbine stall characteristics predicted by the model, two, turbine-specific tip speed ratios of interest were determined: the critical and optimal tip speed ratios. The “critical tip speed ratio” is defined as the tip speed ratio above which there are no longer regions of negative torque during the turbine rotation. The “optimal tip speed ratio” is defined as the tip speed ratio for which the coefficient of torque, averaged over one rotation, is maximized. It is hypothesized that these tip speed ratios correspond to specific turbine operating points: A turbine operating under no load conditions will spin near the optimal tip speed ratio, and a turbine operating at peak power conditions will spin near the critical tip speed ratio.
Influence of Surge Tank and Relief Valve on Transient Flow Behaviour in Hydropower Stations
Authors: Riasi Alireza , Nourbakhsh Ahmad
Published: June 2012

Unsteady flow analysis in water power stations is one of the most important issues in order to predict undesirable pressure variations in waterways and also probable changes in rotor speed for the power plants safe operation. Installation of surge tank and relief valve is the two main methods for controlling of hydraulic transient. The relief valve is used in several medium and small hydropower stations instead of the surge tank and mounted on the penstock near the powerhouse. The recent generation of relief valves are reliable and beneficial and consist of fully control system that directly conducted by governor. This paper presents a numerical method for transient flow in hydropower stations using surge tank and relief valve. For this purpose the governing equations of transient flow in closed conduit are solved using the method of characteristics (MOC) using unsteady friction. Hydraulic turbine, surge tank and relief valve are considered as internal boundary conditions. The influence of surge tank and also relief valve on the maximum pressure in spiral case and turbine over speed has been studied for a real case. The results show that the transient condition is considerably improved by using a relief valve and this device can be mounted in lieu of an expensive surge tank.
A Formula for Prediction of Frequency of Tonal Sound in Cavity Flows With Acoustic Resonance
Authors: Yokoyama Hiroshi , Terao Keitaro , Suzuki Tatsuya , Iida Akiyoshi
Published: June 2012

Self-sustained oscillations with tonal sound in flows over a cavity are investigated by experiments using a wind tunnel and direct numerical simulation of flow and acoustic fields. The effects of the length-to-depth ratio of the cavity and the ratio of the cavity length L to the momentum thickness of the incoming boundary layer on the mode of the oscillations are clarified. The simultaneous measurements of flow pattern and sound pressure are also performed. The results show that a time lag between the generation of an expansion wave due to the collision of a vortex with the downstream edge and the radiation of the expansion wave from the cavity becomes larger for the cavity flow with the acoustic resonance. The computational results explain why the delay becomes larger. Moreover, considering this delay, a new formula for the frequency of the tonal sound in cavity flows with the acoustic resonance is proposed. The frequencies predicted by this formula agree well with those measured.
Numerical Study on Air-Reed Instruments With LES
Authors: Takahashi Kin’ya , Miyamoto Masataka , Ito Yasunori , Takami Toshiya , Kobayashi Taizo , Nishida Akira , Aoyagi Mutsumi
Published: June 2012

The acoustic mechanisms of 2D and 3D edge tones and a 2D small air-reed instrument have been studied numerically with compressible Large Eddy Simulation (LES). Sound frequencies of the 2D and 3D edge tones obtained numerically change with the jet velocity well following Brown’s semi-empirical equation, while that of the 2D air-reed instrument behaves in a different manner and obeys the semi-empirical theory, so called Cremer-Ising-Coltman theory. We have also calculated aerodynamic sound sources for the 2D edge tone and the 2D air-reed instrument relying on Ligthhill’s acoustic analogy and have discussed similarities and differences between them. The sound source of the air-reed instrument is more localized around the open mouth compared with that of the edge tone due to the effect of the strong sound field excited in the resonator.
Solids Shear Stress in Sheet Flow Above Eroded Plane Bed
Authors: Matousˇek Va´clav
Published: June 2012

Solids shear stress at the bottom of a shear layer is described and quantified on a basis of characteristic shapes of concentration- and velocity profiles across a thickness of the layer. A comparison with experimental data shows that the bed friction coefficient associated with the solids shear stress correlates with the Shields number, relative height of the discharge area and the delivered concentration of solids in the sheet flow.
Experiments on Cake Development in Crossflow Filtration for High Level Waste
Authors: Duignan Mark R. , Nash Charles A.
Published: June 2012

Crossflow filtration is a key process step in many operating and planned waste treatment facilities to separate undissolved solids from supernate slurries. This separation technology generally has the advantage of self cleaning through the action of wall shear stress, which is created by the flow of waste slurry through the filter tubes. However, the ability of filter wall self cleaning depends on the slurry being filtered. Many of the alkaline radioactive wastes are extremely challenging to filtration, e.g., those containing compounds of aluminum and iron, which have particles whose size and morphology reduces permeability. Low filter flux can be a bottleneck in waste processing facilities such as the Salt Waste Processing Facility at the Savannah River Site and the Waste Treatment Plant at the Hanford Site. Any improvement to the filtration rate would lead directly to increased throughput of the entire process. To date, increased rates are generally realized by either increasing the crossflow filter axial flowrate, which is limited by pump capacity, or by increasing filter surface area, which is limited by space and increases the required pump load. In the interest of accelerating waste treatment processing, DOE has funded studies to better understand filtration with the goal of improving filter fluxes in existing crossflow equipment. The Savannah River National Laboratory (SRNL) was included in those studies, with a focus on startup techniques and filter cake development. This paper discusses those filter studies. SRNL set up both dead-end and crossflow filter tests to better understand filter performance based on filter media structure, flow conditions, and filter cleaning. Using non-radioactive simulated wastes, which were both chemically and physically similar to the actual radioactive wastes, the authors performed several tests to demonstrate increases in filter performance. With the proper use of filter flow conditions filter flow rates can be increased over rates currently realized today. This paper describes the selection of a challenging simulated waste and crossflow filter tests to demonstrate how performance can be improved over current operation.
Analysis of Turbulence Structure and Void Fraction Distribution in Gas-Liquid Two-Phase Flow Under Bubbly and Slug Flow Regime
Authors: Kataoka Isao , Yoshida Kenji , Ikeno Tsutomu , Sasakawa Tatsuya , Kondo Koichi
Published: June 2012

Accurate analyses of turbulence structure and void fraction distribution are quite important in designing and safety evaluation of various industrial equipments using gas-liquid two-phase flow such as nuclear reactor, etc. Using turbulence model of two-phase flow and models of bubble behaviors in bubble flow and slug flow, systematic analyses of distributions of void fraction, averaged velocity and turbulent velocity were carried out and compared with experimental data. In bubbly flow, diffusion of bubble and lift force are dominant in determining void fraction distribution. On the other hand, in slug flow, large scale turbulence eddies which convey bubbles into the center of flow passage are important in determining void fraction distribution. In turbulence model, one equation turbulence model is used with turbulence generation and turbulence dissipation due to bubbles. Mixing length due to bubble is also modeled. Using these bubble behavior models and turbulence models, systematic predictions were carried out for void distributions and turbulence distributions for wide range of flow conditions of two phase flow including bubbly and slug flow. The results of predictions were compared with experimental data in round straight tube with successful agreement. In particular, concave void distributions in bubbly flow and convex distribution in slug flow were well predicted based on the present model.
Analysis of the Instability for Two Nano-Scale Liquid Threads Coexisting in a Periodic Fundamental Cell
Authors: Yeh Chun-Lang
Published: June 2012

This paper investigates the vaporization process of two nano-scale liquid threads coexisting in a periodic fundamental cell by molecular dynamics (MD) simulation. The influences of liquid thread radius, fundamental cell length, and relative position of the two threads are discussed. Snapshots of molecules, the number of liquid particles formed, and density field are analyzed. Two linear stability criteria, namely, Rayleigh’s stability criterion and Kim’s stability criterion, are accessed for their validity in molecular scale. It is found that more liquid particles are formed when the separation of the two threads is larger. Moreover, vaporization is slower when the two liquid threads are close to each other. It is also found that the trends of Rayleigh’s stability criterion and Kim’s stability criterion agree with MD simulation results. However, when the two threads coalesce into a single thread and remain intact, the critical wavelength of perturbation may be increased and the stable domain is broadened. Under such a situation, Rayleigh’s stability criterion and Kim’s stability criterion underpredict the stable domain.
The Influence of Gas and Liquid Flow Rates on the Transient Bubble Characteristics in a Liquid Cross-Flow
Authors: Siddiqui Kamran , Chishty Wajid A.
Published: June 2012

The paper reports on an experimental study conducted to investigate the dynamics of gas bubbles when injected from an orifice that is subjected to a liquid cross-flow. The experiments were conducted over a range of gas and liquid flow rates and at various orientations of the liquid channel. An image processing algorithm was developed for the detection and characterization of the bubbles in both temporal and spatial coordinates. The transient behaviour of bubble dynamics at different channel orientations under different liquid and gas flow conditions are presented in the paper. Results show that the equivalent bubble diameter in the vertical plane decreased with increase in time as well as with increase in the gas-to-liquid velocity ratio. The channel inclination has no appreciable effect on the bubble diameter. The streamwise bubble velocity showed significant transient fluctuations, which diminished with an increase in the channel inclination angle. The fluctuations of the bubble vertical velocity were found to be unaffected by the channel inclination angle. The magnitudes of both streamwise and vertical velocities were influenced by the channel inclination, however, the trends were found to be opposite.
Application of Level Set / Immersed-Boundary Method to Simulate Fluid-Fluid and Fluid-Solid Problems
Authors: Yu C. H. , Sheu Tony W. H.
Published: June 2012

Free surface generated by a complex structure will be predicted in Cartesian grids by our proposed approach, which combines the immersed boundary and level set methods to model the solid-fluid and fluid-fluid interface, respectively. For accurately predicting the level set value, the spatial derivative terms in the pure advection equation are approximated by the seventh-order accurate upwinding combined compact difference scheme. For ensuring that the predicted interface has a finite thickness all the time, the re-initialization equation is used. In the immersed boundary method we proposed a differential based interpolation scheme at points near the solid boundaries. The discretized linear system of Poisson pressure equation is solved using the DFC (Divergence free compensated) method. Dam-break flow at the Reynolds number Re = 42792 is modeled to get the results that agree well with the experiment data. For the verification of the level set / immersed boundary method, water column collapsed over a submerged structure is also investigated.