Computational Fluid Dynamics Modeling Studies on Bacterial Flagellar Motion

Kumar, Manickam Siva,Philominathan, Pichai Korean Society for Fluid machinery 2011 International journal of fluid machinery and syste Vol.4 No.3

The study of bacterial flagellar swimming motion remains an interesting and challenging research subject in the fields of hydrodynamics and bio-locomotion. This swimming motion is characterized by very low Reynolds numbers, which is unique and time reversible. In particular, the effect of rotation of helical flagella of bacterium on swimming motion requires detailed multi-disciplinary analysis. Clear understanding of such swimming motion will not only be beneficial for biologists but also to engineers interested in developing nanorobots mimicking bacterial swimming. In this paper, computational fluid dynamics (CFD) simulation of a three dimensional single flagellated bacteria has been developed and the fluid flow around the flagellum is investigated. CFD-based modeling studies were conducted to find the variables that affect the forward thrust experienced by the swimming bacterium. It is found that the propulsive force increases with increase in rotational velocity of flagellum and viscosity of surrounding fluid. It is also deduced from the study that the forward force depends on the geometry of helical flagella (directly proportional to square of the helical radius and inversely proportional to pitch).

A Study on the Multi-Objective Optimization of Impeller for High-Power Centrifugal Compressor

Kang, Hyun-Su,Kim, Youn-Jea Korean Society for Fluid machinery 2016 International journal of fluid machinery and syste Vol.9 No.2

In this study, a method for the multi-objective optimization of an impeller for a centrifugal compressor using fluid-structure interaction (FSI) and response surface method (RSM) was proposed. Numerical simulation was conducted using ANSYS CFX and Mechanical with various configurations of impeller geometry. Each design parameter was divided into 3 levels. A total of 15 design points were planned using Box-Behnken design, which is one of the design of experiment (DOE) techniques. Response surfaces based on the results of the DOE were used to find the optimal shape of the impeller. Two objective functions, isentropic efficiency and equivalent stress were selected. Each objective function is an important factor of aerodynamic performance and structural safety. The entire process of optimization was conducted using the ANSYS Design Xplorer (DX). The trade-off between the two objectives was analyzed in the light of Pareto-optimal solutions. Through the optimization, the structural safety and aerodynamic performance of the centrifugal compressor were increased.

Machine Fault Diagnosis and Prognosis: The State of The Art

Tung, Tran Van,Yang, Bo-Suk Korean Society for Fluid machinery 2009 International journal of fluid machinery and syste Vol.2 No.1

Machine fault diagnostic and prognostic techniques have been the considerable subjects of condition-based maintenance system in the recent time due to the potential advantages that could be gained from reducing downtime, decreasing maintenance costs, and increasing machine availability. For the past few years, research on machine fault diagnosis and prognosis has been developing rapidly. These publications covered in the wide range of statistical approaches to model-based approaches. With the aim of synthesizing and providing the information of these researches for researcher's community, this paper attempts to summarize and classify the recent published techniques in diagnosis and prognosis of rotating machinery. Furthermore, it also discusses the opportunities as well as the challenges for conducting advance research in the field of machine prognosis.

Review of Fluid Structure Interaction Methods Application to Floating Wave Energy Converter

Zullah, Mohammed Asid,Lee, Young-Ho Korean Society for Fluid machinery 2018 International journal of fluid machinery and syste Vol.11 No.1

Computational fluid dynamics (CFD) is a highly efficient paradigm that is used extensively in marine renewable energy research studies and commercial applications. The CFD paradigm is ideal for simulating the complex dynamics of Fluid-Structure Interactions (FSI) and can capture all kinds of nonlinear fluid motions. While nonlinear simulations are considered more expensive and resource intensive compared to the frequency domain approaches, they are much more accurate and ideal for commercial applications. This review study presents a comprehensive overview of the computation fluid dynamics paradigm in context of wave energy converter (WEC) and highlights different CFD tools that are available today for commercial and research applications. State-of-the-art CFD codes such as ANSYS CFX that are highly ideal for WEC simulation problems are highlighted and aspects such as time and frequency domains are also thoroughly discussed along with efficacy of the nonlinear simulations compared to the linear models. The paper presents a comparative evaluation of different WEC modelling codes available today and illustrates the code framework of different CFD simulation software suites.

Fluid-Structure Interaction Study on Diffuser Pump With a Two-Way Coupling Method

Xu, Huan,Liu, Houlin,Tan, Minggao,Cui, Jianbao Korean Society for Fluid machinery 2013 International journal of fluid machinery and syste Vol.6 No.2

In order to study the effect of the fluid-structure interaction (FSI) on the simulation results, the external characteristics and internal flow features of a diffuser pump were analyzed with a two-way flow solid coupling method. And the static and dynamic structure analysis of the blade was also caculated with the FEA method. The steady flow field is based on Reynolds Averaged N-S equations with standard $k-{\varepsilon}$ turbulent model, the unsteady flow field is based on the large eddy simulation, and the structure response is based on elastic transient structural dynamic equation. The results showed that the effect of FSI on the head prediction based on CFD really exists. At the same radius, the van mises stress on the nodes closed shroud and hub was larger than other nodes. A large deformation region existed near inlet side at the middle of blades. The strength of impeller satisfied the strength requirement with static stress analysis based on the fourth strength theory. The dynamic stress varied periodically with the impeller rotating. It was also found that the fundamental frequency of the dynamic stress is the rotating frequency and its harmonic frequency. The frequency of maximum stress amplitude at node 1626 was 7 times of the rotating frequency. The frequency of maximum stress amplitude at node 2328 was 14 times of the rotating frequency. No matter strength failure or fatigue failure, the root of blades near shroud is the key region to analyse.

Rotordynamic Characteristics of Floating Ring Seals in Rocket Turbopumps

Tokunaga, Yuichiro,Inoue, Hideyuki,Hiromatsu, Jun,Iguchi, Tetsuya,Kuroki, Yasuhiro,Uchiumi, Masaharu Korean Society for Fluid machinery 2016 International journal of fluid machinery and syste Vol.9 No.3

Floating ring seals offer an opportunity to reduce leakage flows significantly in rotating machinery. Accordingly, they have been applied successfully to rotating machinery within the last several decades. For rocket turbopump applications, fundamental behavior and design philosophy have been revealed. However, further work is needed to explore the rotordynamic characteristics associated with rotor vibrations. In this study, rotordynamic forces for floating ring seals under rotor's whirling motions are calculated to elucidate rotordynamic characteristics. Comparisons between numerical simulation results and experiments demonstrated in our previous report are carried out. The three-dimensional Reynolds equation is solved by the finite-difference method to calculate hydrodynamic pressure distributions and the leakage flow rate. The entrance loss at the upstream inlet of the seal ring is calculated to estimate the Lomakin effect. The friction force at the secondary seal surface is also considered. Numerical simulation results showed that the rotordynamic forces of this type of floating ring seal are determined mainly by the friction force at the secondary seal surface. The seal ring is positioned almost concentrically relative to the rotor by the Lomakin effect. Numerical simulations agree quite well with the experimental results.

Fluid-Oscillation Coupled Analysis for HAWT Rotor Blade (One Degree of Freedom Weak Coupling Analysis with Hinge-Spring Model)

Imamura, Hiroshi,Hasegawa, Yutaka,Murata, Junsuke,Chihara, Sho,Takezaki, Daisuke,Kamiya, Naotsugu Korean Society for Fluid machinery 2009 International journal of fluid machinery and syste Vol.2 No.3

Since large-scale commercial wind turbine generator systems such as MW-class wind turbines are becoming widely operated, the vibration and distortion of the blade are becoming larger and larger. Therefore the soft structure design instead of the solid-design is one of the important concepts to reduce the structural load and the cost of the wind turbine rotors. The objectives of the study are development of the fluid-structure coupled analysis code and evaluation of soft rotor-blade design to reduce the unsteady structural blade load. In this paper, fluid-structure coupled analysis for the HAWT rotor blade is performed by free wake panel method coupled with hinge-spring blade model for the flapwise blade motion. In the model, the continuous deflection of the rotor blade is represented by flapping angle of the hinge with one degree of freedom. The calculation results are evaluated by comparison with the database of the NREL unsteady aerodynamic experiment. In the analysis the unsteady flapwise moments in yawed inflow conditions are compared for the blades with different flapwise eigen frequencies.

Historical Perspective on Fluid Machinery Flow Optimization in an Industry

Goto, Akira Korean Society for Fluid machinery 2016 International journal of fluid machinery and syste Vol.9 No.1

Fluid-dynamic design of fluid machinery had heavily relied on empiricism and experimental observations for many years. Since 1980s, thanks to the advancements in Computational Fluid Dynamics (CFD), a variety of flow physics have been revealed. The contribution by CFD is indispensable; however, the challenge is required not only on the advancements in CFD technologies but also innovation of "design (optimization) technologies" because of the complex interactions between 3-D flow fields and the complex 3-D flow passage configurations, etc. This paper presents historical perspective on fluid machinery flow optimization in an industry with some messages for the future.

Numerical Analysis of Damping Effect of Liquid Film on Material in High Speed Liquid Droplet Impingement

Sasaki, Hirotoshi,Ochiai, Naoya,Iga, Yuka Korean Society for Fluid machinery 2016 International journal of fluid machinery and syste Vol.9 No.1

By high speed Liquid Droplet Impingement (LDI) on material, fluid systems are seriously damaged, therefore, it is important for the solution of the erosion problem of fluid systems to consider the effect of material in LDI. In this study, by using an in-house fluid/material two-way coupled method which considers reflection and transmission of pressure, stress and velocity on the fluid/material interface, high-speed LDI on wet/dry material surface is simulated. As a result, in the case of LDI on wet surface, maximum equivalent stress are less than those of dry surface due to damping effect of liquid film. Empirical formula of the damping effect function is formulated with the fluid factors of LDI, which are impingement velocity, droplet diameter and thickness of liquid film on material surface.

Thermal Effects on Cryogenic Cavitating Flows around an Axisymmetric Ogive

Shi, Suguo,Wang, Guoyu Korean Society for Fluid machinery 2010 International journal of fluid machinery and syste Vol.3 No.4

Cavitation in cryogenic fluids generates substantial thermal effects and strong variations in fluid properties, which in turn alter the cavity characteristics. In order to investigate the cavitation characteristics in cryogenic fluids, numerical simulations are conducted around an axisymmetric ogive in liquid nitrogen and hydrogen respectively. The modified Merkle cavitation model and energy equation which accounts for the influence of cavitation are used, and variable thermal properties of the fluid are updated with software. A good agreement between the numerical results and experimental data are obtained. The results show that vapor production in cavitation extracts the latent heat of evaporation from the surrounding liquid, which decreases the local temperature, and hence the local vapor pressure in the vicinity of cavity becomes lower. The cavitation characteristics in cryogenic fluids are obtained that the cavity seems frothy and the cavitation intense is lower. It is also found that when the fluid is operating close to its critical temperature, thermal effects of cavitation are more obviously in cryogenic fluids. The thermal effect on cavitation in liquid hydrogen is more distinctively compared with that in liquid nitrogen due to the changes of density ratio, vapour pressure gradient and other variable properties of the fluid.