Three-dimensional Flow Analysis Research Articles

On the limitations of two- and three-dimensional linear hydroelasticity analyses applied to a fast patrol boat

The aim of this paper is to study the symmetric (i.e. heave and pitch motions and distortions associated with vertical bending) wave-induced dynamic behaviour of a fast patrol boat using a unified hydroelasticity analysis. This includes two- and three-dimensional structural idealizations using beam and three-dimensional finite element modelling. The fluid—flexible structure interaction is carried out using three-dimensional potential flow analysis, for both structural idealizations, based on a pulsating source singularity distribution on the mean wetted surface. The calculations are carried out in regular waves for two forward speeds (Froude numbers Fn = 0.5 and 0.63) and three heading angles, i.e. 180 (head), 135, and 90 degrees. Results from full-scale trials are also presented in order to compare rigid body motion transfer functions with numerical predictions. There are large differences between numerically predicted and measured motions, as is to be expected for this fast hull form. The paper reports that the evaluation of the dynamic behaviour of the fast patrol boat, with small length to beam ratio, by means of the unified hydroelastic analysis, shows some inherent limitations of the beamlike approach for this particular type of vessel.

Heat transfer analysis of three-dimensional flow in a channel of lower stretching wall

This communication aims to report the heat transfer analysis in generalized three-dimensional channel flow of a viscous fluid over a stretching sheet heated at constant temperature. Energy losses due to viscous dissipation have been taken into account. Highly accurate and purely analytic solution is obtained by homotopy analysis method (HAM). Convergence of the HAM solution is shown through the first table and the residual errors are plotted in the second figure of this article. Effect of the Prandtl number and Eckert number on temperature profiles and heat transfer rate has been discussed in detail.

자오면 형상을 고려한 원심압축기 임펠러 최적설계

In this paper, shape optimization based on three-dimensional flow analysis has been performed for impeller design of centrifugal compressor. To evaluate the objective function of an isentropic efficiency, Reynolds-averaged Navier-Stokes equations are solved with SST (Shear Stress Transport) turbulence model. The governing equations are discretized by finite volume approximations. The optimization techniques based on the radial basis neural network method are used for the optimization. Latin hypercube sampling as design of experiments is used to generate thirty design points within design space. Sequential quadratic programming is used to search the optimal point based on the radial basis neural network model. Four geometrical variables concerning impeller shape are selected as design variables. The results show that the isentropic efficiency is enhanced effectively from the shape optimization by the radial basis neural network method.

100 kW급 증기터빈 설계기술 개발에 관한 연구

Small scale steam turbines are used as mechanical drivers in chemical process plant or power generators. In this study, a design technology was developed for a 100kW class steam turbine which will be used for removing CO₂ from the emission gas on a reheated cycle system. This turbine is operated at a low inlet total pressure of 5 kgf/㎠. It consists of two stages and operates at the partial admission. For the meanline analysis, a performance prediction method was developed and it was validated through the performances on the operating small steam turbines which are using at plants. Their results showed that the output power was predicted within 10% deviation although the steam turbines adopted in this analysis were operated at different flow conditions and rotor size. The turbine blades was initially designed based on the computed results obtained from the meanline analysis. A supersonic nozzle was designed on the basis of the operating conditions of the turbine, and the first stage rotor was designed using a supersonic blade design method. The stator and second stage rotor was designed using design parameters for the blade profile. Finally, Those blades were iteratively modified from the flow structures obtained from the three-dimensional flow analysis to increase the turbine performance. The turbine rotor system was designed so that it could stably operate by 76% separation margin with tilting pad bearings.

Three-dimensional Viscoelastic Analysis of Multi-Layer Polymer Flow by Numerical Simulation

We performed three-dimensional viscoelastic analysis of multi-layer polymer flow by numerical simulation, and investigated the effects of the elongational properties on the encapsulation phenomenon in the coextrusion process. The K-BKZ model with multiple relaxation times was used as viscoelastic constitutive equation, and the PSM type damping function was used for this model. This model is convenient to investigate the effects of the elongational properties, because the parameter β in this model can control only the elongational properties. Also we can extract the effects only of the elongational properties, because the second normal stress difference in this model is zero. In this study, we assumed that multi-layer polymer flow of Fluid I (less viscous) and Fluid II (more viscous) flows in three kinds of channels with different taper angle (parallel, tapered contraction and tapered expansion). As a result, by increasing the β ratio between Fluid I and Fluid II (βI / βII) from 0.1 to 10.0, the degree of encapsulation (DE) hardly changed at confluence, increased at contraction part and decreased at expansion part. These results mean that the elongational properties clearly influence the encapsulation phenomenon especially at contraction part and expansion part.

Flow around a triaxial ellipsoid and a spheroid in a long circular tube

This paper deals with the three-dimensional analysis of ideal fluid flow in a long circular cylinder containing an ellipsoidal obstacle. The center of the ellipsoid coincides with that of the cylinder, and the flow is confined to the space between the ellipsoid and the cylinder when the fluid velocity at the large distance from the ellipsoid is uniform. The equations of the classical theory of fluid dynamics are solved in terms of an unknown function which is then shown to be the solution of a boundary integro-differential equation. An analytical solution of the integro-differential equation is obtained for the moderate values of the radius of the cylinder. The pressure on the ellipsoid is obtained by using Bernoulli's equation and is presented in graphical forms for various values of the radius of the circular tube. The problem of viscous fluid when the ellipsoid reduces to a spheroid is also investigated.

Numerical Experiment of Transient and Steady Characteristics of Ultrasonic-Measurement-Integrated Simulation in Three-Dimensional Blood Flow Analysis

In ultrasonic-measurement-integrated (UMI) simulation of blood flows, feedback signals proportional to the difference of velocity vector optimally estimated from Doppler velocities are applied in the feedback domain to reproduce the flow field. In this paper, we investigated the transient and steady characteristics of UMI simulation by numerical experiment. A steady standard numerical solution of a three-dimensional blood flow in an aneurysmal aorta was first defined with realistic boundary conditions. The UMI simulation was performed assuming that the realistic velocity profiles in the upstream and downstream boundaries were unknown but that the Doppler velocities of the standard solution were available in the aneurysmal domain or the feedback domain by virtual color Doppler imaging. The application of feedback in UMI simulation resulted in a computational result approach to the standard solution. As feedback gain increased, the error decreased faster and the steady error became smaller, implying the traceability to the standard solution improves. The positioning of ultrasound probes influenced the result. The height less than or equal to the aneurysm seemed better choice for UMI simulation using one probe. Increasing the velocity information by using multiple probes enhanced the UMI simulation by achieving ten times faster convergence and more reduction of error.

Molded geometry and viscoelastic behavior of film insert molded parts

AbstractVirgin injection‐molded tensile specimens without any inserted film and four kinds of film insert molded (FIM) tensile specimens were prepared. They were annealed at 80°C to investigate the effect of residual stresses and thermal shrinkage of the inserted film on thermal deformation of tensile specimens. The FIM specimens with the unannealed film were bent after ejection in such a way that the film side was protruded and the warpage was reversed gradually during annealing and the film side was intruded. Warpage of the FIM specimen with the film annealed at 80°C for 20 days was not reversed during annealing. Processing of the FIM specimens have been modeled numerically to predict thermoviscoelastic deformation of the part and to understand the warpage reversal phenomenon (WRP). Nonisothermal three‐dimensional flow analysis was carried out for filling, packing, and cooling stages. The flow analysis results were transported to a finite element stress analysis program for prediction of deformation of the FIM part. The WRP was caused by the combined effect of thermal shrinkage of the inserted film and relaxation of residual stresses in the FIM specimen during annealing. It is expected that this study will contribute towards the improvement of the FIM product quality and prevention of large viscoelastic deformation of the molded part. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Computational Analysis of Swept Compressor Rotor Blades

Three-dimensional blading has been used in the process of turbomachine designs. To meet the need for efficient turbine blade designs, CFD predictions of a complex 3D flow field in turbine blade passages had been used. Because the numerous advantages of 3D CFD have been reported in the open literature, many industries already use 3D blading in their turbomachines. In addition, blade lean and sweep have been implemented to increase the blade row efficiency. Experimental studies have shown the advantages of these features. However, most of the experimental results combined other features together, which is difficult to determine the effects of individual features. The development of the CFD technique had made it possible to do three-dimensional turbulent flow analyses in a very short time. In this study, the numerical studies are presented to study the sweep effects of a transonic compressor airfoil. The focus of the paper is to investigate the sweep effects without changing the compressor blade's other features, i.e. keeping the blade outflow angle the same for all the cases. The purpose of the study is to enhance the understanding of the sweep in a transonic compressor rotor blade. The results show that the sweeps redistribute the flow, which may reduce the secondary flow loss depending on the baseline. It is shown that forward sweep reduces the tip loading in terms of static pressure coefficient.

A suggestion of gap flow control devices for the suppression of rudder cavitation

This paper presents the numerical analysis of rudder cavitation in propeller slipstream and the development of a new rudder system aimed for lift augmentation and cavitation suppression. The new rudder system is equipped with cam devices which effectively close the gap between the horn/pintle and movable wing parts. A computational fluid dynamics code that solves the Reynolds-averaged Navier–Stokes equations is used to analyze the flow field of various rudder systems in propeller slipstream. The body force momentum source terms that mimic flow field behind a rotating propeller are added in the momentum equations to represent the influence of the propeller and its slipstream. For detailed explication of the new rudder system’s lift augmentation and cavitation suppression mechanism, three-dimensional flow analysis is carried out. Simulations clearly display the mechanism of the lift augmentation and cavitation suppression. The computational results suggest that the Reynolds-averaged Navier–Stokes-based computational fluid dynamics reproduces the flow field around a rudder in propeller slipstream and that the present concept for a cavitation suppressing rudder system is highly feasible and warrant further study for inclusion of the interaction with hull and mechanical design for manufacturing and operations.

Tritium Behavior Intentionally Released in the Room

To construct a fusion reactor with high safety and acceptability, it is necessary to establish and to ensure tritium safe handling technology. Tritium should be well-controlled not to be released to the environment excessively and to prevent workers from excess exposure. It is especially important to grasp tritium behavior in the final confinement area, such as the room and/or building. In order to obtain data for actual tritium behavior in a room and/or building, a series of intentional Tritium Release Experiments (TREs) were planned and carried out within a radiologically controlled area (main cell) at Tritium System Test Assembly (TSTA) in Los Alamos National Laboratory (LANL) under US-JAPAN collaboration program. These experiments were carried out three times. In these experiments, influence of a difference in the tritium release point and the amount of hydrogen isotope for the initial tritium behavior in the room were suggested. Tritium was released into the main cell at TSTA/LANL. The released tritium reached a uniform concentration about 30 ~ 40 minutes in all the experiments. The influence of the release point and the amount of hydrogen isotope were not found to be important in these experiments. The experimental results for the initial tritium behavior in the room were also simulated well by the modified three-dimensional eddy flow analysis code FLOW-3D.

Unsteady, three-dimensional fluid mechanic analysis of blood flow in plaque-narrowed and plaque-freed arteries

Fluid mechanic analysis is used to create and implement a metric to quantify the effectiveness of plaque removal (i.e., debulking) modalities in small arteries. The quantification is based on a three-dimensional, unsteady model of blood flow in complex tubular geometries which characterizes plaque-narrowed arteries. Blood flow unsteadiness is due to the heart-imposed temporal variations which occur during the cardiac cycle. The arterial geometries used for the analysis were determined by the reconstruction of ultrasonic images which were captured before and after debulking. Numerical simulation was used to implement the fluid mechanic model, and separate consideration is given to Newtonian and non-Newtonian constitutive equations. The results of the analysis indicates that the removal of the plaque led to an increase in the rate of blood flow of approximately 2.5, both during the systole and diastole portions of the cardiac cycle. This increase corresponds to the application of the same time-varying, end-to-end pressure difference across the artery segments. The shear stress on the artery wall, a major determinant of the buildup of plaque, is found to be higher for a debulked artery than for a plaque-narrowed artery. This outcome is favorable in that the higher the wall shear, the lower the rate of plaque formation.

Aerodynamic study of slotted box girder using computational fluid dynamics

Joint study with Mitsui Engineering & Shipbuilding Co. Ltd. and Public Works Research Institute, etc. has been focused on aerodynamics of the slotted box girder to ensure wind-resistance characteristics for achieving a super-long span bridge of which central span is over 2800 m. The section is made of a slotted box girder, and a permeability fence is arranged on the top of the guard rail as windshield barrier. As a new approach, three-dimensional static analysis of unsteady flow was carried out by finite element technique with LES turbulence model. The designed section was confirmed in actual scale model to have enough resistance to the wind velocity over 80 m/s by means of the countermeasures. In this study, a very fine mesh model was adopted to represent the real section in detail including complicated wind counter measures. The result of the analysis with modified attack angles has proved a good agreement with that of the wind tunnel test in terms of three components of the static aerodynamic wind forces. The flow patterns are visualized by these analyses and have verified the mechanism between the modified attack angles and their resultant aerodynamics.

Three-Dimensional Dialysate flow Analysis in a Hollow-Fiber Dialyzer by Perfusion Computed Tomography

Perfusion computed tomography (PCT) is a means to rapidly and easily evaluate cerebral perfusion in patients presenting with acute stroke symptoms, which provides insights into capillary-level hemodynamics. In this study, we used PCT to analyze the 3-dimensional dialysate flow in a low-flux hemodialyzer equipped with a standard fiber bundle. The dynamic CT studies were performed with 64-channel multi-detector row CT (MDCT) at a dialysate flow rate of 500 ml/min and a 1.0 ml/sec injection rate of contrast agent. Central volume principle was used to calculate hydrodynamic parameters by deconvolution of time-density curves (TDCs). Functional maps of dialysate flow (DF), dialysate volume (DV), and mean transit time (MTT) could quantitatively describe the dialysate flow maldistribution, variations in fiber packing, and perfusion pressure distribution in a hemodialyzer, respectively. PCT by means of analysis was able to overcome the limitations of conventional imaging techniques for analyzing dialysate flow distributions in hollow-fiber dialyzers. Not only local hydrodynamic phenomena at microscopic level but also macroscopic flow behavior of dialysate were visualized quantitatively. Therefore, we concluded that PCT is a quantitative analysis method to provide better insights into hydrodynamics of hollow-fiber dialyzers and is expected to contribute to optimization of artificial kidneys.

Numerical Experiment for Ultrasonic-Measurement-Integrated Simulation of Three-Dimensional Unsteady Blood Flow

Integration of ultrasonic measurement and numerical simulation is a possible way to break through limitations of existing methods for obtaining complete information on hemodynamics. We herein propose Ultrasonic-Measurement-Integrated (UMI) simulation, in which feedback signals based on the optimal estimation of errors in the velocity vector determined by measured and computed Doppler velocities at feedback points are added to the governing equations. With an eye towards practical implementation of UMI simulation with real measurement data, its efficiency for three-dimensional unsteady blood flow analysis and a method for treating low time resolution of ultrasonic measurement were investigated by a numerical experiment dealing with complicated blood flow in an aneurysm. Even when simplified boundary conditions were applied, the UMI simulation reduced the errors of velocity and pressure to 31% and 53% in the feedback domain which covered the aneurysm, respectively. Local maximum wall shear stress was estimated, showing both the proper position and the value with 1% deviance. A properly designed intermittent feedback applied only at the time when measurement data were obtained had the same computational accuracy as feedback applied at every computational time step. Hence, this feedback method is a possible solution to overcome the insufficient time resolution of ultrasonic measurement.

Inner Workings of Shrouded and Unshrouded Transonic Fan Blades

This paper reports on the numerical assessment of the differences in aerodynamic performance between part span shrouded and unshrouded fan blades generally found in the first stage of multistage fans in low bypass ratio aircraft engines. Rotor flow fields for both blade designs were investigated at two operating conditions using a three-dimensional viscous flow analysis. Although designed to the same radius ratio, aspect ratio, and solidity, the unshrouded fan rotor had a slightly increased tip speed (+3%) and somewhat lower pressure ratio (−3.2%) due to engine cycle requirements. Even when allowing for these small differences, the analysis reveals interesting differences in the level and in the radial distribution of efficiency between these two rotors. The reason for the improved performance of the shrouded rotor in part can be attributed to the shroud blocking off the radial migration of boundary layer fluid centrifuged from the hub on the suction side. As a result, the shock boundary layer interaction seems to be improved on the shrouded blade. At the cruise condition, the efficiency is the same for both rotors. The slightly better efficiency of the shrouded blade in the outer panel is nullified by the large efficiency penalty in the vicinity of the shroud. As there is no significant radial migration of fluid in the suction side boundary layer, as indicated by the analysis at this condition relative to the design speed case, the benefit due to the shroud is greatly reduced. At this speed and at lower speeds, the shroud becomes a net additional loss for the blade. Also of interest from the numerical results is the indication that significant blade ruggedization penalties to performance can be reduced in the case of the unshrouded blade through custom tailoring of its mean camber line.

Flow analysis and flow-induced vibration evaluation for low-pressure feedwater heater of a nuclear power plant

This paper performs a three-dimensional flow analysis and flow-induced vibration evaluation of a tube bundle for the low-pressure feedwater heater of a nuclear power plant. Using a commercial computational fluid dynamics software, CFX-4, a detailed shell side flow analysis model is first developed and the near-field cross flow around different locations of the tube bundle within a feedwater heater can be thus obtained. Additionally, the cross-flow velocity is then used to evaluate the flow-induced vibration of the tube bundle. Mechanisms of vortex shedding and fluid-elastic instability are both taken into account by use of an industry standard TEMA in this work. Flow velocity margin to avoid the flow-induced vibration can be thus shown in different locations of the low-pressure feedwater heater. The analysis results will be helpful for the evaluation of performance, operation and maintenance of the low-pressure feedwater heater of a nuclear power plant.

Finite Element and Experimental Analysis of Three-Dimensional Flow State of Plastic Melt in Slit Die Section

In this paper, penalty finite element method is applied to the simulation of three-dimensional incompressible viscous steady flow, and the program is coded for analysis of three-dimensional flow process of plastic melt in extrusion die. Slit die is typical in polymer extrusion process, and the relevant part is used widely. Because the flow law is different for various polymers with different rheological character even in the same die, the polymer flow in slit die is simulated for Newtonian fluid and power-law fluid by the program and ANSYS, respectively. Flow laws of two kinds of fluid are compared, and the result shows that the non-uniform velocity distribution in outlet is caused by the non-Newtonian effect of material. The penalty factor is important for the penalty finite element model, which decides the precision and efficiency to a great extent. The proper penalty value is decided by some factors, for example, the character of the whole equations and geometric model. Numerical solution with change of penalty value and viscosity is analyzed, and the result shows that the penalty value should be suited with viscosity in special range for penalty finite element model. The experiment has been developed, and the velocity distribution in outlet of slit die is measured. The result of finite element analysis is consistent with experimental result basically, and the reason of result divergence of the two ways is analyzed. The results show that the given model is suited for the polymer extrusion process, and the advice of the selection of penalty value is instructional for penalty element model.

An Application of Overset Grids To Payload/Fairing Three-Dimensional Internal Flow CFD Analysis

The application of overset grids to the computational fluid dynamics analysis of three-dimensional internal flow in the payload/fairing of an expendable launch vehicle is described. In conjunction with the overset grid system, the flowfield in the payload/fairing configuration is obtained with the aid of OVERFLOW Navier-Stokes code. The solution exhibits a highly three-dimensional complex flowfield with swirl, separation, and vortices. Some of the computed flow features are compared with the measured Laser-Doppler Velocimetry (LDV) data on a 1/5th scale model of the payload/fairing configuration. The counter-rotating vortex structures and the location of the saddle point predicted by the CFD analysis are in general agreement with the LDV data. Comparisons of the computed (CFD) velocity profiles on horizontal and vertical lines in the LDV measurement plane in the faring nose region show reasonable agreement with the LDV data.

630 せん断中に縦に置かれた円柱周りの三次元剥離流れ解析(OS8.流体の数値計算手法と数値シミュレーション(1),オーガナイズドセッション)

630 せん断中に縦に置かれた円柱周りの三次元剥離流れ解析(OS8.流体の数値計算手法と数値シミュレーション(1),オーガナイズドセッション)