Fluid Dynamic Design Research Articles

Fluid dynamic design and experimental study of an aspirated temperature measurement platform used in climate observation.

Due to the solar radiation effect, current air temperature sensors inside a thermometer screen or radiation shield may produce measurement errors that are 0.8 °C or higher. To improve the observation accuracy, an aspirated temperature measurement platform is designed. A computational fluid dynamics (CFD) method is implemented to analyze and calculate the radiation error of the aspirated temperature measurement platform under various environmental conditions. Then, a radiation error correction equation is obtained by fitting the CFD results using a genetic algorithm (GA) method. In order to verify the performance of the temperature sensor, the aspirated temperature measurement platform, temperature sensors with a naturally ventilated radiation shield, and a thermometer screen are characterized in the same environment to conduct the intercomparison. The average radiation errors of the sensors in the naturally ventilated radiation shield and the thermometer screen are 0.44 °C and 0.25 °C, respectively. In contrast, the radiation error of the aspirated temperature measurement platform is as low as 0.05 °C. This aspirated temperature sensor allows the radiation error to be reduced by approximately 88.6% compared to the naturally ventilated radiation shield, and allows the error to be reduced by a percentage of approximately 80% compared to the thermometer screen. The mean absolute error and root mean square error between the correction equation and experimental results are 0.032 °C and 0.036 °C, respectively, which demonstrates the accuracy of the CFD and GA methods proposed in this research.

Computational Fluid Dynamic Design of Jet Stirred Reactors for Measuring Intrinsic Kinetics of Gas‐Phase and Gas‐Solid Reactions

ABSTRACTNonreactive and reactive computational fluid dynamic simulations were applied to optimize the design of a laboratory scale jet stirred reactor for measuring intrinsic kinetics of gas‐phase and gas‐solid reactions, i.e. kinetics determined by chemical steps only and not by heat or mass transfer. In the past these reactors were designed and tested based on empirical design criteria and residence time distribution experiments. This work shows that these do not always capture important local effects that are vital for kinetic studies. First the degree of macro–mixing was evaluated for three different geometries (down case, 45° case and 90° case) by performing in silico residence time distribution experiments at 900 K, showing that with these type of experiments only minor differences are observed. However, the ethane steam cracking simulations revealed major differences, with the 45° case being the most uniform in terms of temperature and the 90° case being by far the worst. The species nonuniformity in all geometries was acceptable and was in some cases even partly masked by important shortcut streams such as those observed in the 90° case. The existing gradients on the substrate surface are sufficiently small to be neglected in modeling efforts. As temperature is the major parameter determining the rate of the surface reactions, the 45° case is suggested as the best geometry for measuring intrinsic kinetics.

Design optimization of double-suction volute pumps

The performance required of a double-suction volute pump differs, depending on its application. High efficiency, low shut off head, design point performance and size are all demands that require trade-offs. Here, Ebara investigates design optimization with Design of Experiments (DoE) and Computational Fluid Dynamics (CFD).

Fluid dynamic design of an axial rotor for hydrokinetic riverbed turbine‐improvement introduced by a high lift foil profile

The main objective of this article is to achieve a very high lift rotor to take the maximum advantage of the kinetic energy of a slow velocity water flow, which belongs to a lowland river type. Low speed flux and lack of depth are the main obstacles in hydrokinetic operation. The use of a high lift aerodynamic profile and the gain of the rotor number of blades serve to accomplish the task.This work presents the fluid dynamic design for an axial hydrokinetic turbine rotor, studied in a three‐dimensional (3D) numerical simulation by means of Computational Fluid Dynamics (CFD). The use of CFD techniques avoids some physical model assays.For the hydrokinetic turbine rotor design, first a one‐dimensional (1D) theoretical design was carried out, starting with the selection of a suitable airfoil profile to create the hydrofoil blade. Then, the 3D rotor geometry was defined and studied carefully by means of CFD, to check its hydrodynamic behavior, that is, lift and drag, streamline velocities and pressure fields. The CFD results were obtained using an open CFD code (Kratos). © 2016 American Institute of Chemical Engineers Environ Prog, 35: 1198–1206, 2016

携帯型軸流補助人工心臓に関する研究

Though several kinds of implantable ventricular assist devices (VADs) are available at present, their application is limited to transplantation candidates and other patients, who need partial circulatory assist, cannot use VADs in Japan. We are developing a small portable axial-flow pump whose blood contacting parts are made of polymer. Developed axial flow pump models, KAP5 and KAP6 have different discharge angles as 90 deg and 70 deg respectively. However, both KAP5 and KAP6 found an almost the same hemolysis level at 10000 rpm. Though the low-flow hemolysis level of KAP5 almost proportional to 2.8th power of rotational speed as usual, KAP6 attained lower level of hemolysis for 5000 rpm. We are investigating the suitable ranges of use for partial circulatory assist, while trying to reduce the hemolysis level by changing the fluid dynamic design. Antithrombogenic property of KAP6 was examined through a porcine experiment at a blood flow of 1-2 L/min. The result was that almost no thrombus was observed except for an upstream female pivot.

Design by theoretical and CFD analyses of a multi-blade screw pump evolving liquid lead for a Generation IV LFR

Lead-cooled fast reactor (LFR) has both a long history and a penchant of innovation. With early work related to its use for submarine propulsion dating to the 1950s, Russian scientists pioneered the development of reactors cooled by heavy liquid metals (HLM). More recently, there has been substantial interest in both critical and subcritical reactors cooled by lead (Pb) or lead–bismuth eutectic (LBE), not only in Russia, but also in Europe, Asia, and the USA. The growing knowledge of the thermal-fluid-dynamic properties of these fluids and the choice of the LFR as one of the six reactor types selected by Generation IV International Forum (GIF) for further research and development has fostered the exploration of new geometries and new concepts aimed at optimizing the key components that will be adopted in the Advanced Lead Fast Reactor European Demonstrator (ALFRED), the 300MWt pool-type reactor aimed at proving the feasibility of the design concept adopted for the European Lead-cooled Fast Reactor (ELFR). In this paper, a theoretical and computational analysis is presented of a multi-blade screw pump evolving liquid Lead as primary pump for the adopted reference conceptual design of ALFRED. The pump is at first analyzed at design operating conditions from the theoretical point of view to determine the optimal geometry according to the velocity triangles and then modeled with a 3D CFD code (ANSYS CFX). The choice of a 3D simulation is dictated by the need to perform a detailed spatial simulation taking into account the peculiar geometry of the pump as well as the boundary layers and turbulence effects of the flow, which are typically tri-dimensional. The use of liquid Lead impacts significantly the fluid dynamic design of the pump because of the key requirement to avoid any erosion affects. These effects have a major impact on the performance, reliability and lifespan of the pump. Albeit some erosion-related issues remain to be fully addressed, the results of this analysis show that a multi-blade screw pump could be a viable option for ALFRED from a thermo-fluid-dynamic point of view.

A hybrid solution method for CFD applications on GPU-accelerated hybrid HPC platforms

Heterogeneous multiprocessor systems, where commodity multicore processors are coupled with graphics processing units (GPUs), have been widely used in high performance computing (HPC). In this work, we focus on the design and optimization of Computational Fluid Dynamics (CFD) applications on such HPC platforms. In order to fully utilize the computational power of such heterogeneous platforms, we propose to design the performance-critical part of CFD applications, namely the linear equation solvers, in a hybrid way. A hybrid linear solver includes both one CPU version and one GPU version of code for solving a linear equations system. When a hybrid linear equation solver is invoked during the CFD simulation, the CPU portion and the GPU portion will be run on corresponding processing devices respectively in parallel according to the execution configuration. Furthermore, we propose to build functional performance models (FPMs) of processing devices and use FPM-based heterogeneous decomposition method to distribute workload between heterogeneous processing devices, in order to ensure balanced workload and optimized communication overhead. Efficiency of this approach is demonstrated by experiments with numerical simulation of lid-driven cavity flow on both a hybrid server and a hybrid cluster.

Centrifugal Turbines for Mini-Organic Rankine Cycle Power Systems

Organic Rankine cycle (ORC) power systems are rapidly diffusing as a technology for the conversion of thermal energy sources in the small-to-medium power range, e.g., from 150 kWe up to several MWe. The most critical component is arguably the expander, especially if the power capacity is small or very small, as it is the case for innovative high-potential applications such as waste heat recovery from truck engines, or distributed conversion of concentrated solar radiation. In these so-called high-temperature applications, the expansion ratio is very high; therefore, turbines are the expanders of choice. Recently, multistage radial-outflow turbines (ROT), a nonconventional turbine configuration, have been studied, and first commercial implementations in the MWe power range have been successful. The objective of this work is the evaluation of the radial-outflow arrangement for the turbine of high-temperature mini-ORC power systems, with power output of the order of 10 kWe. To this end, a method for the preliminary fluid-dynamic design is presented. It consists of an automated optimization procedure based on an in-house mean-line code for the one-dimensional preliminary design and efficiency estimation of turbines. It is first shown that usually adopted simplified design procedures, such as that of the so-called repeating-stage, cannot be extended to minicentrifugal turbines. The novel methodology is applied to the exemplary case of the 10 kWe turbine of an ORC power system for truck engine heat recovery documented in the literature. The expansion ratio is 45. The preliminary fluid-dynamic design of two miniturbines is presented, namely, a five-stage transonic and a three-stage slightly supersonic turbine. The outcome of the preliminary design leads to two turbine configurations whose fluid-dynamic efficiency exceeds 79% and 77%, respectively. The speed of revolution is around 12,400 and 15,400 RPM for the five-stage and the three-stage machine, respectively. These results show that the ROT configuration may allow for compact and efficient expanders for low power output applications.

The importance of a full 3D fluid dynamic analysis to evaluate the flow forces in a hydraulic directional proportional valve

Purpose – The purpose of this paper is to present a full 3D Computational Fluid Dynamics (CFD) analysis of the flow field through hydraulic directional proportional valves, in order to accurately predict the flow forces acting on the spool and to overcome the limitations of two-dimensional (2D) and simplified three-dimensional (3D) models. Design/methodology/approach – A full 3D CAD representation is proposed as a general approach to reproduce the geometry of an existing valve in full detail; then, unstructured computational grids, which identify peculiar positions of the spool travel, are generated by means of the mesh generation tool Gambit. The computational grids are imported into the commercial CFD code Fluent, where the flow equations are solved assuming that the flow is steady and incompressible. To validate the proposed computational procedure, the predicted flow rates and flow forces are compared with the corresponding experimental data. Findings – The superposition between numerical and experimental curves demonstrates that the proposed full 3D numerical analysis is more effective than the simplified 3D flow model that was previously proposed by the same authors. Practical implications – The presented full 3D fluid dynamic analysis can be employed for the fluid-dynamic design optimization of the sliding spool and, more generally, of the internal profiles of the valve, with the objective of reducing the flow forces and thus the required control force. Originality/value – The paper proposes a new computational strategy that is capable of recognizing all 3D geometrical details of a hydraulic directional proportional valve and that provides a significant improvement with respect to 2D and partially 3D approaches.

Experimental validation of a low-head turbine intake designed by CFD following Fisher and Franke guidelines

Model acceptance tests evaluate the response of the turbines at different operating conditions. Model tests are mounted so that the velocity profile at the inlet section is uniform, a condition which is not often met in practice. In fact, divergences might render inaccurate model results, obtaining at prototype scale an efficiency drop, structural vibrations and even component failures, in extreme cases. This concern becomes all the more relevant for low-head turbines, as the intake is closer to the turbine runner. With the aim of best estimating the actual flow conditions at the turbine inlet section as a function of the intake design, Voith designers, Fisher and Franke recommended performing scale model tests of the intake structure and listed a series of requirements that a good intake design should meet. These guidelines have not yet been applied on numerical modeling design but rather on more expensive and time-consuming scale model tests. This work presents the results of a computational fluid dynamics (CFD) design of a low-head turbine intake taking into account an upgraded version of Fisher and Franke recommendations. The optimization process was aimed at obtaining the design that best matches the ideal flow conditions at the inlet section. The physical model was built in a scale of 1:40 and involves the complete turbine intake geometry. Different designs were tested on the basis of the evaluation of their corresponding velocity field distributions at a reference section and the best design was measured with an acoustic Doppler velocimeter (Vectrino). The results show that intake design guidelines are very useful tools that allow hydraulic designers to test their proposals with CFD more quickly, objectively and with enough degree of sensitivity to optimize the intake geometry.

Suppression of the secondary flow in a suction channel of a large centrifugal pump

The suction channel configuration of a large centrifugal pump with a 90-degree bend was studied in detail to suppress the secondary flow at the impeller inlet for improving suction performance. Design of experiments (DOE) and computational fluid dynamics (CFD) were used to evaluate the sensitivity of several primary design parameters of the suction channel. A DOE is a powerful tool to clarify the sensitivity of objective functions to design parameters with a minimum of trials. An L9 orthogonal array was adopted in this study and nine suction channels were designed, through which the flow was predicted by steady state calculation. The results indicate that a smaller bend radius with a longer straight nozzle, distributed between the bend and the impeller, suppresses the secondary flow at the impeller inlet. An optimum ratio of the cross sectional areas at the bend inlet and outlet was also confirmed in relationship to the contraction rate of the downstream straight nozzle. These findings were obtained by CFD and verified by experiments. The results will aid the design of large centrifugal pumps with better suction performance and higher reliability.

Methodology to optimize fluid-dynamic design in a redox cell

The present work is aimed at the optimization of a redox cell design. The studied redox cell consists on a device designed to convert the energy of reactants into electrical energy when a liquid electrolyte reacts at the electrode in a conventional manner. In this particular sort of cells, the two electrolytes are present and separated by a proton exchange membrane. Therefore, the flow of the electrolyte and the interaction with the membrane takes a paramount importance for the general performance of the cell. A methodology for designing the inlet part of the cell based on optimizing the uniformity of the flow and the initial position of the membrane is presented in this study. This methodology, based on the definition and optimization of several parameters related to the electrolyte flow in different regions of the geometry, is depicted. The CFD (Computational Fluid Dynamics) model coupled with the statistical study pointed to several practical conclusions on how to improve the final geometry construction of the redox cell. A particular case study of redox cell is implemented in order to validate the proposed methodology.

Fluid-dynamic design optimization of hydraulic proportional directional valves

This article proposes an effective methodology for the fluid-dynamic design optimization of the sliding spool of a hydraulic proportional directional valve: the goal is the minimization of the flow force at a prescribed flow rate, so as to reduce the required opening force while keeping the operation features unchanged. A full three-dimensional model of the flow field within the valve is employed to accurately predict the flow force acting on the spool. A theoretical analysis, based on both the axial momentum equation and flow simulations, is conducted to define the design parameters, which need to be properly selected in order to reduce the flow force without significantly affecting the flow rate. A genetic algorithm, coupled with a computational fluid dynamics flow solver, is employed to minimize the flow force acting on the valve spool at the maximum opening. A comparison with a typical single-objective optimization algorithm is performed to evaluate performance and effectiveness of the employed genetic algorithm. The optimized spool develops a maximum flow force which is smaller than that produced by the commercially available valve, mainly due to some major modifications occurring in the discharge section. Reducing the flow force and thus the electromagnetic force exerted by the solenoid actuators allows the operational range of direct (single-stage) driven valves to be enlarged.

Performance improvement of a radial organic Rankine cycle turbine by means of automated computational fluid dynamic design

There is a growing interest in organic Rankine cycle turbogenerators because of their ability to efficiently utilize external heat sources at low-to-medium temperature in the small-to-medium power range. High-temperature organic Rankine cycle turbines typically operate at very high pressure ratio and expand the organic working fluid in the dense-vapour thermodynamic region, thus requiring computational fluid dynamics solvers coupled with accurate thermodynamic models for their performance assessment and design. In this article we present a steady-state three-dimensional viscous computational fluid dynamics study of the Tri-O-Gen organic Rankine cycle radial turbine, including the radial nozzle, the rotor and the diffuser. The turbine operates with toluene as the working fluid, whose accurate thermophysical properties are obtained with a look-up table approach. Based on the three-dimensional simulation results, together with a two-dimensional fluid dynamic optimisation procedure documented elsewhere, an improved nozzle geometry is designed, manufactured and experimentally tested. Measurements show it delivers 5 kWe or 4% more net power output, as well as improved off-design performance.

DESIGN, SIMULATION AND COMPARISON OF ASCENDING AND DESCENDING CURVILINEAR MICROCHANNELS FOR CANCER CELL SEPARATION FROM BLOOD

Separation of rare cells such as circulating cancer and fetal cells from blood has potential importance in disease monitoring and prevention. In this paper, we report a new method of cancer cells separation from patient blood by inertial focusing technique. A design and simulation of ascending and descending curvilinear microchannels for separation of particles resembling cancer cells have been presented. In simulation, polystyrene particles have been used which represent the size of red blood cell (RBC), white blood cell (WBC) and cancer cells. Computational fluid dynamics (CFD) design and simulation of ascending and descending microchannels is used for cell separation. The simulation was carried out in two stages including focusing and separation. The ascending curvilinear channel design demonstrated favorable focusing and separation. Separation with 100% purity and efficiency of the unwanted particle was achieved at Reynolds number (Re) = 8.50 and velocity 0.105 m/s. In case of descending curvilinear channel, cell separation was not good. Considering cancer cells size about 15 μm, our proposed ascending microchannel is a good candidate for cancer cells separation from blood.

Computational Fluid Dynamics and Thermal Analysis to Estimate the Skin Temperature of Cockpit Surface in Various Flight Profiles

AbstractThis paper discusses a simplified approach for estimation of skin temperature of aircraft at various flight conditions using computational fluid dynamics to aid precise estimation of cockpit heat load. Major heat load generated inside the cockpit is because of skin friction of air at high speeds. Hence, estimation of the stagnation temperature on aircraft skin is important. Accurate estimation of heat loads will enable the optimum design of air conditioning system with minimal weight and fuel penalty to improve endurance of aircraft. This paper gives a methodology for the calculation of skin temperature by carrying out three-dimensional (3D) modeling of the cockpit in computer aided design software, tetrahedral meshing and simulation in computational fluid dynamics (CFD) design software at various angles of attack (AoA), aircraft speed, and ambient temperatures using CFD software. The solver results are validated by comparing experimental results of Robinson and Hannemann’s standard force referenc...

Cell Separation Through Ascending and Descending Curvilinear Microchannels

Separation of rare cells such as fetal cells from blood has potential importance in disease investigation and prevention. In this paper we report a new method of cancer cells separation from patient’s blood by inertial focusing technique. A design and simulation of ascending and descending curvilinear microchannels for separation of particles resembling cancer cells have been presented. Computational fluid dynamics (CFD) design and simulation of ascending and descending microchannels is used for cell separation. The simulation was carried out in two stages including focusing and separation. The ascending curvilinear channel design demonstrated favorable focusing and separation. Separation with 100% purity and efficiency of the unwanted particle was achieved at Reynolds number (Re) = 8.50 and velocity 0.105m/s. Reynolds number 9.25 and 10.06 with corresponding velocities 0.115 m/s and 0.125 m/s were also investigated for cell seperation. In case of descending curvilinear channel, cell separation was not good. Considering cancer cells size about 15 µm, our proposed ascending microchannel is a good candidate for cancer cells separation from blood.

Problems, potentials and future of industrial crystallization

This review discusses important research developments and arising challenges in the field of industrial crystallization with an emphasis on recent problems. The most relevant areas of research have been identified. These are the prediction of phase diagrams; the prediction of effects of impurities and additives; the design of fluid dynamics; the process control with process analytical technologies (PAT) tools; the polymorph and solvate screening; the stabilization of non-stable phases; and the product design. The potential of industrial crystallization in various areas is outlined and discussed with particular reference to the product quality, process design, and control. On this basis, possible future directions for research and development have been pointed out to highlight the importance of crystallization as an outstanding technique for separation, purification as well as for product design.

Microfluidics for in vitro biomimetic shear stress-dependent leukocyte adhesion assays

Recruitment of leukocytes from blood to tissues is a multi-step process playing a major role in the activation of inflammatory responses. Tethering and rolling of leukocytes along the vessel wall, followed by arrest and transmigration through the endothelium result from chemoattractant-dependent signals, inducing adhesive and migratory events. Shear forces exerted by the blood flow on leukocytes induce rolling via selectin-mediated interactions with endothelial cells and increase the probability of leukocytes to engage their chemokine receptors, facilitating integrin activation and consequent arrest. Flow-derived shear forces generate mechanical stimuli concurring with biochemical signals in the modulation of leukocyte–endothelial cell interactions. In the last few years, a host of in vitro studies have clarified the biochemical adhesion cascade and the role of shear stress in leukocyte extravasation. The limitation of the static environment in Boyden devices has been overcome both by the use of parallel-plate flow chambers and by custom models mimicking the in vivo conditions, along with widespread microfluidic approaches to in vitro modeling. These devices create an in vitro biomimetic environment where the multi-step transmigration process can be imaged and quantified under mechanical and biochemical controlled conditions, including fluid dynamic settings, channel design, materials and surface coatings. This paper reviews the technological solutions recently proposed to model, observe and quantify leukocyte adhesion behavior under shear flow, with a final survey of high-throughput solutions featuring multiple parallel assays as well as thorough and time-saving statistical interpretation of the experimental results.

Multi-objective Computational Fluid Dynamics (CFD) design optimisation in commercial bread-baking

Changing legislation and rising energy costs are bringing the need for more efficient baking processes into much sharper focus. High-speed air impingement bread-baking ovens are complex systems used to entrain thermal air flow. In this paper, Computational Fluid Dynamics (CFD) is combined with a multi-objective optimization framework to develop a tool for the rapid generation of forced convection oven designs. A design parameterization of a three-dimensional generic oven model is carried out to enable optimization, for a wide range of oven sizes and flow conditions, to be performed subject to appropriate objective functions measuring desirable features such as temperature uniformity throughout the oven, energy efficiency and manufacturability. Optimal Latin Hypercubes for surrogate model building and model validation points are constructed using a permutation genetic algorithm and design points are evaluated using CFD. Surrogate models are built using a Moving Least Squares approach. A series of optimizations for various oven nozzle sizes, oven depths and flow conditions are performed using a genetic algorithm with responses calculated from the surrogates, from which appropriate oven designs for a wide range of specific applications can be inferred. Results from various oven design and objective functions under investigation are presented together with ensuing energy usage and savings. Analysis suggests that 10% energy savings can be achieved for the baking process.