bluuebunny/crossref_metadata_2025 huggingface dataset:
A New Circulation Model Combined With a Detailed Network Model of Arterial Blood Flow
Authors: Kim Y. T. , Kwon S. S. , Kim E. B.
Published: June 2012

This study developed a model of the entire cardiovascular system combined with a Laplace heart based on the numerical cardiac-cell model and a detailed arterial-network structure. Our model incorporates the Laplace heart model and pulmonary model using a lumped-parameter model with a distributed arterial-system model. The Laplace heart acts as a pump and consists of an atrium and ventricle. We applied a cellular-contraction model modulated by the calcium concentration and action potential in a single cell. The numerical arterial model is based on a numerical solution of the one-dimensional momentum equations and the continuity equation of flow and vessel wall motion in a geometrically accurate branching network of the arterial system that includes energy loss at bifurcations. To validate our method, the computed pressure waves were compared with existing experimental observations. Using the combined cell–system–arterial network model, pathophysiological events at levels from cells to the arterial network are delineated.
Magnetic Control of Biologically Inspired Robotic Microswimmers
Authors: Cheang U. Kei , Lee Jun Hee , Kim Paul , Kim Min Jun
Published: June 2012

Bacterial flagella have been employed as nanoactuators for biomimetic microswimmers in low Reynolds number fluidic environments. The microswimmer is a dumbbell-like swimmer that utilizes flagellar hydrodynamics to achieve spiral-type swimming. Flagellar filaments from Salmonella typhimurium are harnessed and functionalized in order to serve as couplers for polystyrene (PS) microbeads and magnetic nanoparticles (MNPs) using avidin-biotin chemistry. The MNP have an iron oxide core that will allow us to actuate the microswimmer under a rotating magnetic field. Using a micromanufacturing process, microswimmer of different configurations can be created to mimic mono- and multi-flagellated bacteria. A magnetic control system consists of electromagnetic coils arranged in an approximate Helmholtz configuration was designed, constructed, and characterized. In conjunction with a LabVIEW input interface, a DAQ controller was used as a function generator to generate sinusoidal waveforms to the power supplies. AC current outputs were supplied from the power supplies to the coils in order to generate a rotating magnetic field. A rotating magnetic field will induce rotation in the flagella conjugated MNP which in term will rotate the flagellar filament into a spiral configuration and achieve propulsion, as in polarly-flagellated bacteria. A high-speed camera provided real-time imaging of the microswimmer motion in a static fluidic environment inside a closed PDMS (Polydimethylsiloxane) chamber. The microswimmers exhibited flagellar propulsion in a low Reynolds number fluidic environment under a rotating magnetic field, which demonstrates its potential for biomedical applications.
Swimming Hydrodynamics and Maneuverability in C-Start of Zebrafish Larvae: An Integrated Computational Study
Authors: Li Gen , Liu Hao , Mu¨ller Ulrike K. , van Leeuwen Johan L.
Published: June 2012

Fishes often exhibit stable body undulating in body and caudal fin (BCF) mode during cyclic swimming, but can perform remarkable maneuverability with significantly different swimming modes in case of C-start. Aiming at unveiling the mechanisms of swimming hydrodynamics and maneuverability of C-start, we have developed an integrated computational framework to model a free-swimming larval zebrafish (Danio rerio) by coupling the equations of 3DoF (Degrees of Freedom) motion and Navier-Stokes (NS) equations. Unsteady hydrodynamics is resolved by integrating models of realistic fin-body morphology and body-undulatory kinematics with an in-house NS solver. The instantaneous forces and moments on the body provided by the NS-solutions serve as input for 3DoF equations of motion. In this study, with a specific focus on a C- start as well as a subsequent transient phase till the cyclic swimming phase, we construct a larval zebrafish model, which can mimics realistic body motions and deformations based on measurements. Validation of the simulation is discussed by comparing model predictions with experimental measurements, which indicates that the present integrated model is capable to accurately predict free-swimming dynamics and hydrodynamics. The model successfully simulated a swimming bout of C-start and cyclic swimming: a wake topology of double row vortex ring structures is observed behind the fish; and a strong jet is visible at the center of the vortex ring, pushing water backward as the fish accelerates.
Influence of Sinus of Valsalva on Aortic Valve Movements by Lattice Boltzmann Method
Authors: Fukui Tomohiro , Morinishi Koji
Published: June 2012

Aortic valve is a membrane that plays an important role in controlling effective outputs of blood flow from the heart. Aortic stenosis is a disease that aortic valves barely open in systole, which cause considerable reduction of amount of blood flow. It is important to know aortic valve movements due to blood flow in order to consider mechanism of development of the aortic stenosis. In this study, we consider the influence of the sinus of Valsalva on aortic valve movements by Lattice Boltzmann method. The virtual flux method is applied to describe thin aortic valve leaflets. The shape of the sinus of Valsalva is approximated as a semi-ellipse. The aortic valve opens due to high pressure at the left ventricle side, and blood flows toward the aorta. The blood also flows into the sinus of Valsalva, and forms vortices. The aortic valve closure starts due to high pressure at the aorta side and vortices in the sinus of Valsalva as well. We successfully reproduced the aortic valve movements due to blood flows during cardiac cycle by means of virtual flux method.
A Discrete-Forcing Immersed Boundary Method for the Fluid-Structure Interaction of an Elastic Slender Body
Authors: Lee Injae , Choi Haecheon
Published: June 2012

In the present study, a new immersed boundary method for the simulation of flow around an elastic slender body is suggested. The present method is based on the discrete-forcing immersed boundary method by Kim et al. (J. Comput. Phys., 2001) and is fully coupled with the elastic slender body motion. The incompressible Navier-Stokes equations are solved in an Eulerian coordinate and the elastic slender body motion is described in a Lagrangian coordinate, respectively. The elastic slender body is modeled as a thin flexible beam and is segmented by finite number of blocks. Each block is then moved by the external and internal forces such as the hydrodynamic, tension, bending, and buoyancy forces. With the proposed method, we simulate several flow problems including flows over a flexible filament, an oscillating insect wing, and a flapping flag. We show that the present method does not impose any severe limitation on the size of computational time step. The results obtained agree very well with those from previous studies.
A Vortex Penalization Method for Flows With Moving Immersed Obstacles
Authors: Cottet Georges-Henri , Gallizio Federico , Magni Adrien , Mortazavi Iraj
Published: June 2012

The aim of this work is to couple vortex methods with the penalization methods in order to take advantage from both of them. This immersed boundary approach maintains the efficiency of vortex methods for high Reynolds numbers focusing the computational task on the rotational zones and avoids their lack on the no-slip boundary conditions replacing the vortex sheet method by the penalization of obstacles. This method that is very appropriate for bluff-body flows is validated for the flow around a moving vertical axis turbine for two transitional and turbulent Reynolds numbers.
Migration of an Elastic Capsule in a Channel Flow
Authors: Shin Soo Jai , Sung Hyung Jin
Published: June 2012

The inertial migration of a two-dimensional elastic capsule in a channel flow was studied over the Reynolds number range 1≤Re≤100. The lateral migration velocity, slip velocity, and the deformation and inclination angle of the capsule were investigated by varying the lateral position, Reynolds number, capsule-to-channel size ratio (λ), membrane stretching coefficient (φ), and membrane bending coefficient (γ). During the initial transient motion, the lateral migration velocity increased with increasing Re and λ, but decreased with increases in φ, γ an the lateral distance from the wall. The initial behavior of the capsule was influenced by variation in the initial lateral position (y0), but the equilibrium position of the capsule was not affected by such variation. The balance between the wall effect and the shear gradient effect determined the equilibrium position. As Re increased, the equilibrium position initially shifted closer to the wall and then moved towards the channel center. A peak in the equilibrium position was observed near Re = 30 for λ = 0.1, and the peak shifted to higher Re as λ increased. Depending on the lateral migration velocity, the equilibrium position moved toward the centerline for larger λ, but moved toward the wall for larger φ and γ.
Study on the Interfacial Layers Between the Turbulent/Non Turbulent Regions in Two Dimensional Turbulent Jet
Authors: Terashima Osamu , Sakai Yasuhiko , Nagata Kouji
Published: June 2012

The interface between the turbulent and non turbulent regions in a two dimensional turbulent jet is investigated by the simultaneous measurement of the velocity and pressure. The measurement is performed by using a combined probe comprising an X-type hot-wire and a static pressure tube. The measurement data are analyzed by the conditional sampling technique and an ensemble averaged technique on the basis of the intermittency function for the turbulent/non turbulent decision. The experimental data at the cross-streamwise edge of the turbulent region show that there is a thin interfacial layer with a sharp jump of physical quantities (such as mean streamwise velocity) at the cross-streamwise edge of the turbulent region, and the thickness of the interfacial layer is 0.08 times the half-width of the cross-streamwise profile of the mean streamwise velocity. The turbulent diffusion term in the turbulent energy transport equation near the interfacial layer is examined. It is also found that the turbulent energy is transported from the inside of the interfacial layer to both the inner side (the side of the turbulent fluid) and the outer side (the side of the non turbulent fluid) by the diffusion term. Furthermore, the components of the diffusion term are separately estimated. It is found that the turbulent diffusion term shows the gain of the turbulent energy at the inner side of the interfacial layer, and the pressure diffusion term transports the turbulent energy to the non turbulent fluid. Moreover, small scale vortices are found in the interfacial layer. From these results, there is a possibility that the existence of the interfacial layer (existence of the vortices) contributes to the transport of the turbulent energy to the non turbulent fluid since the velocity and the pressure field that determine the pressure diffusion is greatly influenced by the existence of the interfacial layer. This hypothesis indicates that the outward propagation from a turbulent fluid can be attributed to the presence of vortices in the interfacial layer.
Effects on Momentum Thickness and Density Ratio for Side-Jet Formation in Round Jets With Variable-Density
Authors: Kaneda Yasuhiro , Muramatsu Akinori
Published: June 2012

If the mass density of an issuing gas is sufficiently lower than that of the ambient gas, radial ejections of the jet gas may be generated near the nozzle exit. These radial ejections are referred to as side jets. The parameters for side-jet formation have been reported to be the density ratio of the jet gas and the ambient gas and the momentum thickness at the nozzle exit. In the present experimental study, gases with variable density were discharged into still air. Two round nozzles having different area contraction ratios were used in order to vary the momentum thickness. The momentum thicknesses were obtained after the velocity profiles at the nozzle exit were measured by a hot-wire probe and a hot-wire concentration probe for jets with various density ratios and issuing velocities. The existence of side jets was confirmed by flow visualization of the jets using a laser sheet. The domain for side-jet formation is illustrated using the non-dimensional momentum thickness and the density ratio.
An Experimental Study on Turbulent Mixing of High-Schmidt-Number Scalar in Grid Turbulence by Means of PIV and PLIF
Authors: Suzuki Hiroki , Nagata Kouji , Sakai Yasuhiko , Ukai Ryota
Published: June 2012

Turbulent mixing of high-Schmidt-number passive scalar in shear-free grid turbulence is experimentally investigated using a water channel. The Reynolds number based on the mesh size of the grid and cross-sectionally averaged mean velocity is 2,500. Rhodamine B (fluorescent dye) was used as a high-Schmidt-number passive scalar. The Schmidt number is about 2,100. The time-resolved particle image velocimetry (PIV) and the planar laser induced fluorescence (PLIF) technique were used to measure instantaneous two-component velocities and nondimensional concentration. Our PLIF algorithm corrects the following errors: spatiotemporal variation of local excitation intensity due to an inhomogeneous concentration field along the light path, time variation of fluorescence quantum yield, and spatiotemporal variation of incident laser intensity. The results show that the vertical profile of mean scalar can be well approximated by the error function. In contrast, the profile of scalar variance in outer region of the mixing layer cannot be approximated by the Gaussian profile. In addition, the half width of mean scalar is larger than that of the scalar variance profile.
Numerical Simulation of Entrainment and Transport of Gas Bubbles by Vortex Ring
Authors: Uchiyama Tomomi , Yoshii Yutaro
Published: June 2012

The possibility to control the motion of small gas bubbles by a vortex ring is explored through a numerical simulation. Hydrogen bubbles with diameter of 0.2 mm are arranged in quiescent water, and a vortex ring is launched toward the bubbles. The behavior of the vortex ring and the bubble motion are analyzed. The diameter of the vortex ring at the launch is 42.5 mm, the Reynolds number is 500, and the bubble volume fraction at the launch is less than 0.04. The simulation highlights that the vortex ring convects in the bubble cluster with shoving the bubbles and that the bubbles are entrained and involved by the vortex ring. It also clarifies the changes of the diameter and circulation of the vortex ring.
An Experimental Study on Methane/Oxygen-Air Combustion With a Rapidly Mixed Type Tubular Flame Burner
Authors: Shi Baolu , Kowari Tatsuya , Shimokuri Daisuke , Ishizuka Satoru
Published: June 2012

Methane/oxygen-air combustion has been attempted by using a rapidly mixed type tubular flame burner with four slits, from two of which a fuel is injected and from another two an oxidizer is injected. The oxygen concentration (molar) in the oxygen-air oxidizer has been varied from 21% (air) to 100% (pure oxygen). Results show that uniform tubular flame combustion can be obtained for a wide range of equivalence ratios, if the oxygen molar concentration in the oxygen-air oxidizer is less than about 50%. Above 50%, however, very intense turbulent combustion occurs frequently and the circular-shaped tubular flame is deformed as oval-shaped for most equivalence ratios. The uniform tubular flame range is reduced and quite limited in the vicinity of lean condition. Detailed observations show that for pure (or near pure) oxygen oxidizer, two diffusion flames are established between the fuel and oxidizer streams at the exits of the fuel slits, which prevents fuel from mixing with oxygen, resulting in a violent turbulent combustion downstream the slits. With use of a burner with smaller slit width, however, formation of the diffusion flame is inhibited and a uniform tubular flame can be established, although still limited close to the lean extinction limit. To fully understand the flame characteristics above, the burning velocities are calculated for various equivalence ratios as well as for various oxygen concentrations in the oxygen-air oxidizer using the CHEMKIN PREMIX code with the GRI kinetic mechanism.
Effects of the Air-Fuel Ejection Velocity Ratio on the Combustion Characteristics and the Unburned Gas Compositions of the Propane–Air Rapidly Mixed Tubular Flame Combustion
Authors: Wang Y. , Kimura K. , Gokita N. , Shimokuri D. , Ishizuka S.
Published: June 2012

In this paper, effects of the difference between the air injection velocity and the fuel injection velocity on the rapidly mixed tubular flame have been investigated. A parameter of αst which is the ratio of the air injection velocity to the fuel injection velocity at stoichiometric condition has been introduced, and five tubular flame burners with different αst, 0.6, 1.2, 2.4, 6.0 and 11.9 were examined. Stability limits of the propane-air flame and the local fuel concentrations of unburned mixture have been determined. Results show that, with αst = 0.6 and αst = 1.2, in burner a stable tubular flame can be established in the range of Φ = 0.45 to 2.1 and Φ = 0.48 to 2.15. When αst is increased to 2.4, in which the air injection velocity is almost two times higher than that of the fuel at stoichiometric condition, the stable combustion range shifts to the relatively fuel rich side of Φ = 0.55 to 2.35. With further increase in the αst to 6.0 and 11.9, stable combustion range shifts to richer side of Φ = 0.6 to 2.45, and Φ = 0.7 to 2.9, respectively. Results of gas analysis have revealed that, for αst = 0.6 and αst = 1.2, although the total equivalence ratio of supplied air and fuel were stoichiometric, a fuel rich mixture gas of Φ = 1.13 and Φ = 1.17 was formed locally at the center of the burner. Increasing in the αst leads to a decrease in the local equivalence ratio, such as Φ = 0.95, 0.42, and 0.19 for αst = 2.4, 6.0 and 11.9, respectively. These results indicate that the mixing process of air and fuel in the rapidly mixed tubular flame is greatly affected by the injection velocity ratio, suggesting the possibility of the flame front structure control by the injection velocity ratio.
The Impact of Bleeding on Compressor Stator Corner Separation
Authors: Zhao Bin , Li Shaobin , Li Qiushi , Zhou Sheng
Published: June 2012

Bleed air from the high pressure compressor has taken up 3–5% in the air system. However, there are not many studies on the compressor performance after bleeding. By analyzing a low-speed single-stage compressor and a transonic single-stage compressor, this paper presents several plans with different bleeding rates on the casing near stator corner, in order to study the influence of bleeding rates on the compressor stator corner separation. The results showed that for the stators of subsonic compressor with large flow separation in the corner, there is an optimum value in the stator casing bleed air amount. The flow field is better at resisting the radial flow caused by bleed air in the transonic compressor stator. The more the bleeding rates of the stator, the more the compressor efficiency improves.
Scale Effects on the Cavitation Development in Fluid Machinery
Authors: Yu Weiping , Luo Xianwu , Zhang Yao , Ji Bin , Xu Hongyuan
Published: June 2012

The prediction of cavitation in a design procedure is very important for fluid machinery. However, the behaviors of cavitation development in the flow passage are believed to be much different due to scale effects, when the characteristic size varies greatly for fluid machines such as pumps, turbines and propellers. In order to understand the differences in cavitation development, the evolution of cavity pattern in two hydro foils were recorded by high-speed video apparatus. Both foils have the same section profile, and their chord lengths are 70mm and 14mm respectively. For comparison, the cavitating flows around two foils were numerically simulated using a cavitation model based on Rayleigh-Plesset equation and SST k-ω turbulence model. The experiments depicted that for both hydro foils, there was attached sheet cavitation near the leading edge, which separated from the rear part of the cavity and collapsed near the foil trailing edge. There was clear cloud cavitation in the case of the mini foil. The results also indicated that the numerical simulation captured the cavitation evolution for the ordinary foil quite well compared with the experiments, but could hardly predict the cloud cavitation for the mini foil. Thus, it is believed that both the cavitation model and the turbulence model should be carefully treated for the scale effect on cavitation development in fluid machinery.
Numerical Study on Film-Cooling Effectiveness for Various Film-Cooling Hole Schemes
Authors: Kim Sun-min , Lee Ki-Don , Kim Kwang-Yong
Published: June 2012

Film-cooling has been widely used as the important alternative to protect the turbine blade. Since the film-cooling hole geometry is one of the most influential parameters for film-cooling performance, various film-cooling hole schemes have been developed to increase cooling performance for the past few decades. In the present work, numerical analysis has been performed to investigate and to compare the film-cooling performance of various film-cooling hole schemes such as fan-shaped, crescent, louver, and dumbbell holes. For analyzes of the turbulent flow and film-cooling, three-dimensional Reynolds-averaged Navier-Stokes analysis has been performed with shear stress transport turbulence model. The validation of numerical results has been performed in comparison with experimental data. The flow characteristics and film-cooling performance for each hole shape have been investigated and evaluated in terms of local- and averaged film-cooling effectivenesses.
Effect of Interfacial Flow on the Coherency of Ultra-High Speed Water Jet in Air
Authors: Wang YuLi , Yang MinGuan , Kang Can , Chen Bo
Published: June 2012

Water jet cutting is a novel machining technology. Effective jet cutting requires a highly coherent jet to achieve a perfect surface finish. However, the jet breaks up just in a short distance downstream the nozzle exit. Interfacial shear is considered to have a dominate effect on the jet surface instability and its breakup. This work focuses on the turbulence both in the jet and its ambient air. The Fluent code is employed to simulate the air-water flow inside and outside a jet cutting nozzle. We get insight into the original interfacial turbulence near the nozzle exit. The contribution of the interfacial flow to the jet coherency is analyzed. It is expected the original turbulence can be reduced by changing the shape of nozzle exit. Several nozzles with different configurations in their outlets are tested both experimentally and numerically. Through these work, it is found that the jet is more coherent as the air flow is more consistent with the jet flow in the nozzle tip. The cone-down with modest cone angle in nozzle outlet is an appealing design for creating a fine jet.
Characteristics of Surge and Rotating Stall in a Three-Stage Axial Flow Compressor Using Shock Tube
Authors: Morita Daisuke , Fujita Yutaka , Ohta Yutaka , Outa Eisuke
Published: June 2012

Transient characteristics as well as unsteady cascade flow fields of a three-stage axial flow compressor with compression plane wave injection from the compressor downstream were experimentally investigated by detail measurements of casing wall pressure fluctuations and unsteady velocity. The main feature of tested compressor is a shock tube facility connected in series to the compressor outlet duct in order to supply a compression plane wave which simulates the sudden rise of the compressor back pressure in a gas turbine system. Research attention is mainly focused on the unsteady behavior of surge and rotating stall coexistence phenomenon, and influence of the compression plane wave injection on the compressor operating conditions. When the compressor is connected to the capacity tank, surge and rotating stall occur simultaneously according to the capacitance increment of the whole compression system. The surge cycle changes irregularly with a throttling of the valve installed just behind the compressor and several different types of surge behaviors are observed. Furthermore, even though the compressor is operating under the stable condition, it goes into surge by injecting the compression plane wave.
The Effect of Surface Roughness and Favorable Pressure Gradient on Turbulent Boundary Layers
Authors: Shin Ju Hyun , Song Seung Jin
Published: June 2012

Rough wall turbulent boundary layers subjected to pressure gradient have engineering interest for many fluid machinery applications. A number of investigations have been made to understand surface roughness and pressure gradient effects on turbulent boundary layer characteristics, but separately. In this paper, turbulent boundary layers over a flat plate with surface roughness and favorable pressure gradient (FPG) are experimentally investigated. Boundary layers in different streamwise locations were measured using boundary layer type hot-wire anemometry. Rough wall zero pressure gradient (ZPG) turbulent boundary layers were also measured to compare the result from the investigation. The surface roughness was applied by attaching sandpapers on the flat plate. The magnitude of surface roughness is representative of land-based gas turbine compressor blade. Pressure gradient was adjusted using movable endwall of the test section. Results from the measurement show characteristics of the turbulent boundary layer growth affected by both surface roughness and favorable pressure gradient.
The Optimization Analysis on Piezoelectric Micromixer With Modified Tesla Tubes
Authors: He Xiuhua , Zhuo Hongcai , Deng Xulian , Wang Jian , Li Fu
Published: June 2012

With consideration of the good configuration of Tesla tube and its perfect performance used in micromixer and micropump, an integration of micromixer and micropump, a novel type of piezoelectric micromixer has been designed. In order to improve the performance of the micromixer, analysis on structure parameters of the Tesla tube, and the optimization on it is the chief work in this paper. Firstly, a novel type of piezoelectric micromixer with Tesla tubes and piezoelectric actuator has been designed, and its structure and working principle were described. Secondly, the numerical analysis on the micromixer with prearranged parameters was carried out to analyze its pumping and mixing performances. Thirdly, an optimization on the structure to improve its performance was carried out. The values of three main structure parameters of the Tesla tube, K = W1/W3, L1 and L2 were changed to analyze their effects on λ and σ which stand for pumping and mixing performances respectively, then two groups perfect values of those three parameters were selected for optimization. Finally, a perfect design scheme was selected to be structure of mixer; numerical analysis was carried out on it in application of dynamic mesh model. Two fluids arrived perfect mixing after 0.4s with the value of Reynolds number 200, at driven frequency 100Hz, middle displacement amplitude of piezoelectric actuator 15μm. This result demonstrates that, pumping and mixing performances of the piezoelectric micromixer were validated, and its working performance has been improved with the optimization on Tesla tubes, which can be reference for study afterward.
Internal Flow Conditions of Contra-Rotating Small-Sized Axial Fan
Authors: Shigemitsu Toru , Fukutomi Junichiro , Okabe Yuki , Iuchi Kazuhiro
Published: June 2012

Small-sized axial fans are used as air cooler for electric equipments. But there is a strong demand for higher power of fans according to the increase of quantity of heat from electric devices. Therefore, higher rotational speed design is conducted, although, it causes the deterioration of efficiency and the increase of noise. Then the adoption of contra-rotating rotors for the small-sized axial fan is proposed for the improvement of performance. In the present paper, the performance curves of the contra-rotating small-sized axial fan with 100mm diameter are shown and the velocity distributions at a partial flow rate at the inlet and the outlet of each front and rear rotor are clarified with experimental results. Furthermore, the flow conditions between front and rear rotors of the contra-rotating small-sized axial fan are investigated by numerical analysis results and causes of the performance deterioration of the contra-rotating small-sized axial fan at the partial flow rate is discussed.
Diagonal Flow Pump Impeller With NACA65 Series Blade (Correction of Blade Geometry)
Authors: Kinoue Yoichi , Shiomi Norimasa , Setoguchi Toshiaki , Sawamura Kazuhiro , Maeda Hideaki
Published: June 2012

Using the design method based on the design for axial-flow type turbomachine, the diagonal flow pump impellers were designed for two cases of the centrifugal effect parameter a. In addition, three-dimensional Navier-Stokes numerical calculations for single-phase were conducted in order to examine the tendency of the suction performance as well as the head performance. The head increases from the NS calculation of the impeller are the same between for a = 0.4 and for a = 1.0 because major specification are the same between for a = 0.4 and for a = 1.0. For the minimum pressure on the rotor blade, however, there is a difference between for a = 0.4 and for a = 1.0. The value of minimum pressure for a = 0.4 is −324 kPa, whereas the value for a = 1.0 is −294 kPa. The blade geometry for a = 1.0 is better than the one for a = 0.4 in terms of the suction performance because the trough of the minimum pressure is shallower for a = 1.0 than a = 0.4. Furthermore, Navier-Stokes numerical calculations were also conducted for off-design flow rate. For all cases in this paper, the minimum pressure on the rotor blade occurred at both near the leading edge and near the tip on the suction side of the blade. In addition, for all cases in this paper, the blade geometry for a = 1.0 is better than the one for a = 0.4 in terms of the suction performance.
Influence of Internal Objects in Flow Characteristics of Darrieus Turbine
Authors: Takeshima Kotaro , Tasaka Yuji , Murai Yuichi
Published: June 2012

Since Darrieus turbine is omnidirectional against the wind, it has a great essential advantage in turbulent wind environment. However, a disadvantage on the starting up is known in low velocity conditions of the wind compared with propeller turbines. Darrieus turbine has a low efficiency problem at low tip-speed ratios due to this disadvantage. Some studies have done to overcome this problem, but these have been on the beginning of the way toward the solution. The reason is that the angle of attack for Darrieus blades is changed largely during the rotation relative to the wind direction. In this study, we found a new technique to improve the efficiency. The technique is the providing a large internal cylinder rotating together with the blades, which can control the angle of attack of the blades. We evaluated the influence of cylindrical diameter on the blade performance by the time-averaged velocity distribution and the intensity of the velocity fluctuation comparing between with cylinder and without cylinder. The flow field around the blades is measured with two kinds of instruments. One is Hot Wire Anemometer for analyzing temporal variations of flows, and the other is Particle Image Velocimetry for analyzing the spatial flow structure in detail. Angles of attack and lift coefficients are calculated from the measured relative velocity vector field. As a result, the angles of attack and the lift coefficients are improved in some rotational angles, which are also confirmed by numerical simulations.
Analysis of Unsteady Flow Velocity Fields Inside the Impeller of a Radial Flow Pump: PIV Measurements and Numerical Calculation Comparisons
Authors: Cavazzini Giovanna , Dupont Patrick , Pavesi Giorgio , Dazin Antoine , Bois Ge´rard , Atif Abdelmadjid , Cherdieu Patrick
Published: June 2012

PIV measurements were performed at mid hub to shroud section inside the impeller of a vaned diffuser pump model working with air. The measurements were restricted to the outlet section of the impeller where the diffuser blades interacted with the impeller flow. Each PIV measuring plane was related to one particular impeller blade to blade channel and analysed according to different relative positions of the vaned diffuser. Two frame change models were considered: the so-called frozen rotor approach for different impeller passage positions relative to the vaned diffuser and a fully unsteady calculation of the whole pump. Comparisons between numerical and experimental results are presented and discussed for a specific mass flow rate corresponding to an off-design point for the impeller and a design point for the vaned diffuser.
Stochastic Optimization Models and Method in the Turbomachines System Improvement Problem
Authors: Ugryumov Mykhaylo L. , Afanasjevska Victoria E. , Tronchuk Aleksej A. , Myenyaylov Andriy V.
Published: June 2012

The approach of system improvement, methodology and information technology of turbofan engine elements main parameters and operating tolerances robust estimation on basis of inverse problems concept by stochastic optimization problem are proposed. The method of multicriterion system modification problem quasisolution searching with input data uncertainly and with bordering of feasible solution class is offered. Quasisolution synthesis is realized by regularization of smoothing functional minimum searching with using the A.N. Tihonov’s method. The multicriterion modification problem numerical solution searching evolution method was created, it based on genetic algorithm using. On basis of development methodology the system aerodynamic turbofan engine (TFE) compressor improvement were made.
Flow Field Analysis Around a Lockup Clutch Inside a Torque Converter
Authors: Yamaguchi Takeshi , Ikeda Shogo , Yamakawa Sho , Tanaka Kazuhiro
Published: June 2012

The performance of a torque converter has been one of the most important areas of improvement for an automatic-transmission equipped automobile. Improving the torque converter’s performance and efficiency is key to saving fuel consumption, which is an important consideration with recent environmental awareness. Moreover, the locking up operation or slipping control of an automatic transmission is another good opportunity for improving fuel economy. For this reason, there has been much research carried out to predict hydrodynamic performance and to understand the flow field inside a torque converter either experimentally or analytically using Computational Fluid Dynamics (CFD). Most of the research to date has focused on the inside of a torque converter torus. In recent years, the usage of a lockup clutch has expanded, and the lockup control system has become more complex. Understanding the flow field around the lockup clutch has become a very important issue. Only a few studies have focused on the lockup clutch, and most of the numerical research was solved at steady state conditions. In this paper, not only was an unsteady solution applied to solve the flow field, but also two new techniques were attempted. One was “virtual weight” and the other was “moving mesh.” By using these techniques, the lockup clutch was moved by the balance of its own weight and the opposing pressure acting on its surface. With this approach, the lockup clutch engagement time or the responsiveness of the lockup clutch could be estimated. The flow field calculated by a transient solution was found to be different from the flow field calculated by a steady state solution. The transient solution also revealed that the lockup engagement time and the lockup clutch moving speed were dependent on the lockup engagement pressure and rotation speed.
Experimental Investigation on Ducted Counter-Rotating Axial Flow Fans
Authors: Nouri Hussain , Ravelet Florent , Bakir Farid , Sarraf Christophe
Published: June 2012

An experimental study on counter-rotating axial-flow fans was carried out. The fans of diameter D = 375 mm were designed using an inverse method. The counter-rotating fans operate in a ducted-flow configuration and the overall performances are measured in a normalized test bench. The rotation rate of each fan is independently controlled. The axial spacing between the fans can vary from 10 to 50 mm by steps of 10 mm. The results show that the efficiency is strongly increased compared to a conventional rotor or to a rotor-stator stage. The effects of varying the rotation rates ratio on the overall performances are studied and show that the system is highly efficient on a wide range of flow-rates and pressure rises. However, the change of the axial distance between rotors from 10 to 50 mm does not seem to change the overall performances. This system has thus a very flexible use, with a large patch of high efficient operating points in the parameter space. Further local studies including velocity measurements and wall-pressure fluctuations in the space between the rotors are needed to better understand the interactions between the rotors and to optimize the system.
Design of a Typical Gas Turbine Based on Thermodynamic Relations and CFD Analysis of its Rotor Blade
Authors: Mohammadi Maryam , Khamesi Seyed Sina , Poursaeidi Esmaeil
Published: June 2012

The process of reverse designing of gas turbine based on thermodynamic relations has been studied in this paper. Reverse designing is the process of perceiving and recognizing technical principles of a system through its structure and performance. This designing has been carried out by mathematics and thermodynamic relations. The height and the exit angle of the fluid obtained from the rotor blade and gas turbine nozzle, has been optimized in comparison with existing sample and the result from this optimizing, is increasing the gas turbine power and output. The entire processes of designing, is carried out by a software code written in Matlab, and the results of thermodynamic analysis are obtained in the form of pressure distribution, velocity and temperature. The optimized profiles of different stages of turbines are illustrated in the software output. The results from designed process, has an acceptable conformity with existing gas turbine in power station industries. These results can be used for upgrading the turbine efficiency and consequently for increasing the power station efficiency.
Optimal Design of Mixed-Flow Pump Impeller Based on Direct Inverse Problem Iteration and Genetic Algorithm
Authors: Bing Hao , Cao Shuliang
Published: June 2012

Based on the continuity and motion equations of fluid, the direct problem is settled by using iterative calculation for two kinds of stream surfaces to obtain the flow field of the mixed-flow pump impeller. The inverse problem of the mixed-flow pump impeller is solved by employing point-by-point integration method to draw the blade shape, thickening the blade and smoothing the leading edge of the blade by conformal mapping. The meridional velocity will not be determined until the iterative calculation of direct and inverse problems is converged. Based on the meridional velocity field, the impeller performance is predicted with loss models. Then an optimal design model of the mixed-flow pump impeller is developed. This model, which applies genetic algorithm, takes the highest efficiency and the velocity moment distribution as the optimum objective and the optimum parameter, respectively. The obtained velocity moment distribution is then used in the next iterative calculation of direct and inverse problems. The impeller will not be finally determined until the difference between the velocity moment distributions, which are obtained from two consecutive iterative calculations, can meet the set requirements. Based on SIMPLEC algorithm, the three-dimensional turbulent flow field of the mixed-flow pump impeller is obtained by solving the Reynolds averaged Navier-Stokes equation and RNG k-ε turbulent model equation. The simulation results show that the impeller designed by this method has higher hydraulic efficiency, the pressure distribution is well uniform and the flow is steady without separation. The characteristic of this method is to determine blade shape by satisfying both the continuity and motion equations of fluid, so it can lead to high accuracy of impeller design. Meanwhile, the blade has the smooth surface and the complete data, which is convenient for blade manufacturing with numerical control machines.
Prediction of the Thermal Injury Around Exhaust System of Passenger Car by Practical Procedure: 1st Report—Development of 1D Model for Heat Analysis
Authors: Kohri Ituhei , Hara Eriko , Komoriya Tohru , Miyamoto Shuji
Published: June 2012

In case that heat injury performance is analyzed with CFD, large calculations are required to solve heat and mass flow field inside the exhaust pipes, in the engine compartment and around vehicle body simultaneously. Since it spends much time for the generation of the analytic models and their solution by full CFD, such calculations are not practical to the industrial development of the vehicle in which many parameter studies on various conditions are required. Wherein, we suggest new method for prediction of the heat injury on exhaust systems, which is simplified with 1 dimensional models though the engine compartment flow is calculated with 3 dimensional calculations, i.e. CFD. Basic idea of this method is to divide exhaust systems into several elemental modules where heat transfer characteristics are given individually and to imitate actual systems by connecting them. Then 3D calculation is processed coupling heat and flow field with radiant filed outside exhaust systems. Above all, chemical reaction occurs in the catalytic converter is solved carefully to estimate heat production. This report introduces an overview of their 1-dimensional model and the calculation results.
Experimental and Numerical Investigation of Automotive Wind Throb Phenomenon
Authors: Iida Keiichiro , Hashizume Yoshimitsu , Narita Hiroshi , Wu Long , Balasubramanian Ganapathi , Crouse Bernd
Published: June 2012

Sunroof wind throb can generate annoyingly high sound-pressure levels (SPL) inside the vehicle cabin. In this study, several deflector configurations were installed to investigate this flow-acoustic coupled resonance phenomenon in passenger cars. In each condition, comparisons between the experimental results and numerical simulations were performed over a range of wind speeds to validate the capability of the PowerFLOW numerical simulation for wind throb prediction. Experiments were performed at the Suzuki full scale wind tunnel. One microphone in the cabin was set to record the pressure history and SPL. Flow around the sunroof was also measured by PIV. In both experiments and simulations, the following phenomena were observed. In case of strong wind throb, flow separates from the deflector and strong periodic vortices in the shear layer were observed. These vortices break down due to the impingement at the back-end of the sunroof and generate a strong peak noise in the cabin. In case of no wind throb, the periodic vortices were not observed resulting in a very weak peak with low SPL in the cabin. The deflector study shows that wind throb is a highly sensitive phenomenon where even a small geometry variation at the critical region can affect the phenomenon significantly. In this study, the same trend was obtained in the experimental results and simulations. It shows that the numerical simulation can be used for a priori predictions in the early stages of the vehicle design process.
Determination of Suitable MRF-Region for Practical Prediction of Engine Cooling Fan Performance
Authors: Kobayashi Yuji , Kohri Itsuhei , Matsushima Yukio
Published: June 2012

Recently, CFD technology has become popular to the prediction of the engine cooling performance for the design of the automotive engine cooling systems. Particularly, the practical prediction of the cooling fan performance is one of the important issues. In the design phase of the vehicle development, combinations of multiple parameters are generally examined. Certainly, the unsteady calculations such as LES or LBM, which require high resolution of the space, give good accuracy meanwhile they spend much time for their executions so that they are not always practical. Therefore, the steady RANS coupling with MRF method is indispensable. However, it has been pointed out that, in case of complicated layout around the fan of an actual vehicle, the size of the MRF-region dominates predictive accuracy while the symmetry of the flow structure is taken account. Then, in this study, attracting on the discontinuity at the boundary surface of the MRF-region, authors found the method to determine adequate MRF-region to predict the fan performance in practical accuracy. This paper deals with the outline of the method and their applications.
Fan Modeling in CFD Using MRF Model for Under Hood Purposes
Authors: Gullberg Peter , Lo¨fdahl Lennart , Nilsson Peter
Published: June 2012

Computational Fluid Dynamics (CFD) is today an important tool in the design process of fuel and energy efficient vehicles. Under hood Thermal Management (UTM) is one of the design fields which CFD has proven itself to be a very competitive design tool over other available tools and techniques. To simulate the under hood environment it is very important to predict cooling airflow accurately, and for this, it is very important to model all components in the cooling airflow path accurately. Important components are the heat exchangers, fan, grille-, and engine blockage. This paper has focused on CFD modeling of the fan using the most common fan model of the industry; Multiple Reference Frame (MRF). Several different aspects of this modeling strategy are examined that is of high importance to the CFD-engineer working with fan modeling. The finding of this paper is that the MRF model is highly capable of simulating fan airflow however some sensitivity are noted and documented. The model is very sensitive towards end-user working procedure. The CFD engineer working with this methodology in the under hood should be made aware of that the choice of reference frames and frozen position of the blade can have a very big impact on the simulated result.
Development of a New HVAC Flow System for the Next Generation Automated People Mover
Authors: Nagaoka Miho , Kawai Masafumi , Takai Norihiro
Published: June 2012

IHI has succeeded in development of a new generation Automated People Mover (APM). One of the features of this APM is the composite car body which enables stylish exterior, spacious cabin and light weight. This feature demanded the development of a new Heating, Ventilating, and Air-Conditioning (HVAC) system, which does not have any devices on the roof of the car, to avoid heavy weight on the composite body and to keep the cabin ceiling high for passenger comfort. Consequently we adopted a new HVAC flow system in which the air is supplied upwards from the bottom of the side windows while all the mechanical devices are placed under the floor. However, when the prototype was first designed, it caused congested flow channel due to its location and we had to have ducts that were too small. It was unexpectedly difficult to keep the space for HVAC system like in an ordinary layout. So at first, the prototype vehicle did not have enough HVAC performance due to lack of air flow. Therefore we performed full review of the duct system. We made desk analysis, duct model test, experiment on the prototype, and CFD simulation, for the improvement of the new HVAC flow system. Finally, we have established an excellent system with the new layout which has been validated on the prototype vehicle. In this paper, we describe the process of developing a new HVAC system, based on the results of actual measurement as well as CFD simulation.