Three-dimensional Computational Fluid Dynamics Method Research Articles

Three-dimensional numerical investigation of flow and heat transfer performances of novel straight microchannel heat sinks

Four-type novel single crystal diamond (SCD) straight microchannel heat sinks with different shapes (symmetrically inclined, turned symmetrically inclined, V-shaped, and X-shaped) are designed and investigated by the three-dimensional computational fluid dynamics method. These four-type microchannel heat sinks are evaluated in terms of fluid flow and heat transfer capabilities compared to the conventional rectangular straight microchannel (RSMC) heat sink. Our research indicates that the newly designed novel SCD microchannel heat sinks can enhance the heat dissipation effect in comparison to the conventional RSMC heat sink, thereby substantiating its potential for enhancing thermal management in electronic devices. Each V-shaped and X-shaped straight microchannel heat sink has a higher heat transfer capacity than the RSMC heat sink. Among the heat sinks involved in this work, the V-shaped SCD heat sink has the best surface temperature uniformity. The symmetrically inclined heat sink shows the lowest pumping power, with 14.1 % lower than that of the RSMC heat sink. The X-shaped SCD heat sink exhibits a significantly lower thermal resistance, with an 8.5 % reduction compared to the RSMC heat sink. Additionally, it demonstrates a substantially higher Nusselt number, with a 27.6 % increase relative to the RSMC heat sink. The X-shaped SCD heat sink has the highest heat transfer coefficient of up to 1.08 × 105 W/(m2·K), which is 20.4 % higher than that of RSMC heat sink. Owing to the highest performance evaluation criterion of 1.22, the X-shaped straight microchannel heat sink is the most optimal of the designed heat sinks.

A Comparison of Static and Rotordynamic Characteristics for Three Types of Impeller Front Seals in a Liquid Oxygen Turbopump

Abstract Annular seals are widely used to minimize the leakage, and improve efficiency and rotordynamic stability in turbomachinery. In a liquid oxygen turbopump, the operating conditions of annular seals are harsher with the high-pressure cryogenic propellant. Researches show that the primary leakage of a liquid oxygen turbopump is from the front and rear shoulder seals of the impeller. Moreover, the impeller shoulder seal sustains the largest pressure drop and highest swirl velocity in machine. Therefore, the shoulder seal plays an important role in rotor stability and successful full load operation of the turbopump, due to the significant seal fluid response forces. Previous literature shows that the hole-pattern seal has excellent performance in rotordynamic characteristics, and its leakage rate shows a very weak sensitive to the rotating speed. For helical-groove seal, however, the leakage shows a significant decrease with the increasing rotating speed and the roughness on stator surface can enhance the “pump effect” of helical-groove. The static and rotordynamic characteristics of annular seals with cryogenic liquid oxygen are limited in the previous literature. To make use of the advantages of both types of seals and address the sealing challenge in liquid oxygen turbopump, three types of liquid annular seals were designed for the front shoulder seal of a liquid oxygen turbopump, which include a hole-pattern seal (HPS), a double helical-groove seal (DHG), and a hybrid damper seal (HDS, with hole-pattern on stator and helical-groove on rotor). Computational fluid dynamics (CFD), as an important method to solve fluid dynamic problems, has been widely used to solve fluid governing equations. To assess and compare the leakage and rotordynamic characteristics of the present three types of annular seals under the liquid oxygen medium, a steady three-dimensional CFD method was developed to predict the seal leakage, based on the Frozen Rotor interface model. A transient three-dimensional CFD-based perturbation method was also proposed to predict the seal rotordynamic characteristics, based on the subdomain method, mesh deformation technique, and multiple-frequency elliptical-orbit whirling model. The accuracy and reliability of the present numerical methods were demonstrated based on the experimental data of leakage rates and rotordynamic coefficients for an experimental hole-pattern seal and an experimental helical-groove seal using water as working fluid. The leakage rate and rotordynamic coefficients of these three types of annular seals were calculated and compared under six variable load-operating conditions of a liquid oxygen turbopump, focusing on the seal leakage rate, effective stiffness, and damping. The numerical results show that compared with the traditional hole-pattern seal and helical-groove seal, the novel hybrid damper seal possesses the much less leakage flow rate and much better rotordynamic characteristics, so is a desired seal scheme for the impeller shoulder seal.

Numerical investigation of partial admission losses in radial inflow turbines

Radial inflow turbines are taken as potential power conversion units for many power cycles where full admission is employed. The partial admission turbine is usually selected for small-scale power output due to the reduced mass flow rate and machining constraints, resulting in substantial low efficiency. The flow characteristics in different partial admission ratios are still unknown. The suitability of existing correlations for partial admission losses is also questionable since the partial admission loss model is usually established upon experimental results of axial turbines. In this paper, the three-dimensional computational fluid dynamics method is utilized to investigate flow characteristics within partial admission radial inflow turbines. The partial admission ratio varies from 0.05 to 0.9. The numerical loss break-down is then performed and compared against existing empirical correlations in literature, where the partial admission ratio from 0.158 to 0.526 is of interest. The suitable partial admission loss model (Stuter & Traupel windage loss model and Stenning expansion loss model) is finally selected and successfully employed to design partial admission radial inflow turbines preliminarily. The relative error of 3% is attained by comparing mean-line and numerical results. This paper provides insight into the partial admission loss mechanism within radial inflow turbines.

A time-domain simulation method to predict insertion loss of a dissipative muffler with exhaust flow

Insertion loss (IL) is a more useful acoustic index than noise reduction and transmission loss for muffler design, but it is harder to predict because the prediction of IL requires knowing the characteristics of the muffler itself and the acoustic source. A muffler with porous material and complex meanflow makes the prediction even more challenging. Although calculation of noise reduction and transmission loss with the transient computational fluid dynamics (CFD) can naturally solve the flow–acoustic interaction problem, the published CFD methods have not been adopted to evaluate the IL of the dissipative muffler with exhaust flow. In this paper, a time-domain simulation method is developed to predict the IL of a complex engine muffler with porous material. The noise reduction and load impedance of the muffler were first calculated using a three-dimensional CFD model, in which the porous material was simulated by the governing equations modified with the material porosity and flow resistivity. The IL was then predicted from the noise reduction, the load impedance, and the engine source extracted from the measured exhaust noise. This developed method explores the application of the three-dimensional CFD method in calculating noise reduction, load impedance, and insertion loss of complex dissipative mufflers with exhaust flow.

Investigations of aerodynamic drag forces during structural blade testing using high-fidelity fluid–structure interaction

Abstract. Aerodynamic loads need to be known for planning and defining test loads beforehand for wind turbine blades that are tested for fatigue certifications. It is known that the aerodynamic forces, especially drag, are different for tests and operation, due to the entirely different flow conditions. In test facilities, a vibrating blade will move in and out of its own wake, increasing the drag forces on the blade. This is not the case in operation. To study this special aerodynamic condition present during experimental tests, numerical simulations of a wind turbine blade during pull–release tests were conducted. High-fidelity three-dimensional computational fluid dynamics methods were used throughout the simulations. In this way, the fluid mechanisms and their impact on the moving blade are clarified, and through the coupling with a structural solver, the fluid–structure interaction is studied. Results are compared to actual measurements from experimental tests, verifying the approach. It is found that the blade experiences a high drag due to its motion towards its own whirling wake, resulting in an effective drag coefficient of approximately 5.3 for the 90∘ angle of attack. This large drag coefficient was implemented in a fatigue test load simulation, resulting in a significant decrease in bending moment along the blade, leading to less load being applied than intended. The confinement from the test facility did not impact this specific test setup, but simulations with longer blades could possibly yield different conclusions. To the knowledge of the authors, this investigation, including three-dimensional effects, structural coupling and confinement, is the first of its kind.

Heat Generation Measurement of Li-Ion Battery Cells Under Fast Charging Conditions By Employing Isothermal Calorimeter

Introduction Lithium-ion batteries are employed in so many applications including electric vehicles (EVs), hybrid electric vehicles (HEVs) and many consumer products such as cell phones, tablets and computers. Notwithstanding the foregoing, there are still concerns about the safety of Lithium-ion batteries. Abuse conditions such as excessing external heat, over-charging, over-discharging, nail penetration, crush, high charging currents and external and internal short-circuit can cause battery temperature to go far beyond the manufacturer ratings. If the heating rate exceeds dissipation rate for the longer time, then thermal runaway will occur. Thermal runaway leads to many unwanted accidents such as a leak, smoke, gas venting , flames and rapid battery disassembly. Several previous studies have been conducted on the thermal safety of Lithium-ion batteries. Bernardi et al. [3] constructed a heat-generation model for battery systems containing the mixing enthalpies ,electrochemical reactions and phase changes. Guo et al. [4], by employing a finite element method, developed a three-dimensional thermal model. Kim et al. [5] developed a three-dimensional thermal abuse model concerning the chemical reactions. He et al. [6] investigated the thermal management of a Li-ion battery module by employing a two-dimensional computational fluid dynamics model. Wang et al. [7] studied the thermal management of the battery module and optimum structure through employing a lumped model and three-dimensional computational fluid dynamics method. Future electric vehicles will need to be charged in time comparable to refilling time of nowadays conventional combustion vehicles. In consequence, in this work, the thermal behaviour and heat generation of different Lithium-ion battery chemistries subjected to fast charging protocols will be investigated. Heat generation of different Lithium-ion battery cells will be measured by employing isothermal calorimeter. Methodology The experiment is performed by means IBC (Isothermal Battery Calorimeter) 284 from NETZSCH, which is illustrated in Figure 1. Calibration of the IBC 284 consists in applying a controlled electrical current to a precision resistance located inside the calorimeter chamber of the IBC 284[8]. Figure 1: External system components - IBC 284 [8]. First,the calibration of the calorimeter was performed at different temperatures (from -30°C to +60°C). Results Three different chemistries (LTO, NMC and LFP) will be tested during fast charging. Heat generation will be quantified and will be compared amongst these three li-ion battery cell chemistries. Processing of the data was accomplished by means of Proteus Analysis Software (PAS). An example of standard calibration graph and calibration polynomial are shown in figure 2. Exemplary graphs for determination of different parameters are shown in figure 3. Figure 2: Standard calibration graph and calibration polynomial [8]. Figure 3: Example of the graph [8]. References 1 J. Wen, Y. Yu and C. Chen, Mater. Express, 2, 197–212(2012). 2 C.-Y. Jhu, Y.-W. Wang, C.-M. Shu, J.-C. Chang and H.-C. Wu,J. Hazard. Mater.,192, 99–107(2011). Bernardi, D.; Pawlikowski, E.; Newman, J. A general energy balance for battery systems. J. Electrochem. Soc., 132, 5–12(1985).Guo, G.F.; Long, B.; Cheng, B.; Zhou, S.Q.; Xu, P.; Cao, B.G. J. Power Sources, 195, 2393–2398(2010).Kim, G.H.; Pesaran, A.; Spotnitz, R. J. Power Sources, 170, 476–489(2007).He, F.; Li, X.; Ma, L. Int. J. Heat Mass Transf., 72, 622–629(2014).Wang, T.; Tseng, K.; Zhao, J.; Wei, Z. Appl. Energy, 134, 229–238(2014).http://www.netzsch-thermal-analysis.com.

Novel multi-tubular fixed-bed reactors’ shell structural analysis based on numerical simulation method

In the present contribution, a numerical study of fluid flow and heat transfer performance in a pilot-scale multi-tubular fixed-bed reactor with a novel configuration for propylene-to-acrolein oxidation reaction is presented using a three-dimensional computational fluid dynamics method (CFD) to ensure the uniformity condition using molten salt as a heat carrier medium on shell side. The effects of multiscale structural parameters including the number of baffles, baffles cut, central nontube region and the number of flow channels on pressure drop and heat transfer are considered. The simulations suggest that heat transfer coefficient per pressure drop is reduced with increasing number of baffles. By the single factor sensitivity analysis it was shown that the central region is the key factor in the structural design of a multi-tubular fixed-bed reactor.

Human evacuation affected by smoke movement in mine fires

The objective of this work is to investigate the influence of smoke movement during mine fires on miner evacuation behaviors. A three-dimensional computational fluid dynamics method was conducted to reconstruct the laneway conveyor belt fire scenes under two ventilating conditions. The parameters, including temperature–time histories, soot density, carbon monoxide and heat release rate, were simulated to characterize the mine fires at various ventilating speeds. A miner evacuation model affected by fire smoke movement was advanced to describe the miner evacuation behaviors, which can be divided into three stages. Based on the evacuation model coupled with the mine fire smoke movement, the available safety evacuation time for miners involved in coal mine fire located in different sites was estimated. Two evacuation patterns were advanced according to the ventilating speeds combined with the model of miner evacuation behaviors. The results show that the miners located between the inlet-air end and the air door in lane 1 should be evacuated to the inlet-air end and other miners involved in coal mine fire could choose the air door as the escaping destination, when the ventilation speed is greater than 3 m/s. Accordingly, the research can be used as references for the mine safety administration authorities to design the safety evacuation.

Numerical investigation of flow and heat transfer in a novel configuration multi-tubular fixed bed reactor for propylene to acrolein process

In the present contribution, a numerical study of fluid flow and heat transfer performance in a pilot-scale multi-tubular fixed bed reactor for propylene to acrolein oxidation reaction is presented using computational fluid dynamics (CFD) method. Firstly, a two-dimensional CFD model is developed to simulate flow behaviors, catalytic oxidation reaction, heat and mass transfer adopting porous medium model on tube side to achieve the temperature distribution and investigate the effect of operation parameters on hot spot temperature. Secondly, based on the conclusions of tube-side, a novel configuration multi-tubular fixed-bed reactor comprising 790 tubes design with disk-and-doughnut baffles is proposed by comparing with segmental baffles reactor and their performance of fluid flow and heat transfer is analyzed to ensure the uniformity condition using molten salt as heat carrier medium on shell-side by three-dimensional CFD method. The results reveal that comprehensive performance of the reactor with disk-and-doughnut baffles is better than that of with segmental baffles. Finally, the effects of operating conditions to control the hot spots are investigated. The results show that the flow velocity range about 0.65 m/s is applicable and the co-current cooling system flow direction is better than counter-current flow to control the hottest temperature.

Influence of trailing edge flap on wind turbine blade using three-dimensional computational fluid dynamics method

This paper investigates the influence of the trailing edge flap on integrated loads and the flow field structure of wind turbine blades. The dynamic trailing edge flap under sinusoidal wind velocity is simulated using three-dimensional computational fluid dynamics method, and SST k-ω turbulence model coupled with γ-Reθ transition model is adopted to model the turbulence. The results show that the variation of root flap bending moments can be reduced by up to 38%. A proper phase difference added to the flap deflection could improve the ability of loads reduction for some cases. The flap deflection impacts almost all sections of the blade, and the blade elements momentum method should be modified to obtain better results.

Effect of the tubular-fan drum shapes on the performance of cleaning head module

The geometrical effects of a tubular-fan drum on the performance improvement of the cleaning head module of a vacuum cleaner were investigated. In this study, the number of blades and the width of the blade were selected as the design parameters. Static pressure, eccentric vortex, turbulence kinetic energy (TKE) and suction efficiency were analysed and tabulated. Three-dimensional computational fluid dynamics method was used with an SST (Shear Stress Transfer) turbulence model to simulate the flow field at the suction of the cleaning head module using the commercial code ANSYS-CFX. Suction pressure distributions were graphically depicted for different values of the design parameters.

Numerical aerodynamic analysis of bluff bodies at a high Reynolds number with three-dimensional CFD modeling

This paper focuses on numerical simulations of bluff body aerodynamics with three-dimensional CFD (computational fluid dynamics) modeling, where a computational scheme for fluid-structure interactions is implemented. The choice of an appropriate turbulence model for the computational modeling of bluff body aerodynamics using both two-dimensional and three-dimensional CFD numerical simulations is also considered. An efficient mesh control method which employs the mesh deformation technique is proposed to achieve better simulation results. Several long-span deck sections are chosen as examples which were stationary and pitching at a high Reynolds number. With the proposed CFD method and turbulence models, the force coefficients and flutter derivatives thus obtained are compared with the experimental measurement results and computed values completely from commercial software. Finally, a discussion on the effects of oscillation amplitude on the flutter instability of a bluff body is carried out with extended numerical simulations. These numerical analysis results demonstrate that the proposed three-dimensional CFD method, with proper turbulence modeling, has good accuracy and significant benefits for aerodynamic analysis and computational FSI studies of bluff bodies.

Numerical study of flow field characteristics for triplet impingement injector and combustor

The chemical reactions in combustor are described by integrating Eddy-Dissipation Model with Arrhenius rate coefficients. The cold and react flow fields of triplet impingement injector and combustor are simulated using the three-dimensional computational fluid dynamics method. Both helicity and mixing length are introduced to study the mixing mechanism and the effect of triplet impingement injector. The key characteristic parameters of combustor, e.g., spatial distributions of total temperature and pressure, residence time of gas flow in combustor, are obtained. The flow field characteristics of triplet impingement injector and combustor for Fuel-Oxidizer-Fuel (F-O-F) and Oxidizer-Fuel-Oxidizer (O-F-O) triplet arrangements are analyzed. The degree of F2 dissociation in combustor exit plane for O-F-O triplet arrangement is 13.5% higher than that for the F-O-F triplet arrangement under conditions of specified composition proportioning and combustor characteristic length. Experimental result demonstrates that the output power of laser is increased by 17%.

Three-dimensional simulation of water droplet movement in PEM fuel cell flow channels with hydrophilic surfaces

SUMMARY Water management is one of the critical issues in proton exchange membrane fuel cells, and proper water management requires effective removal of liquid water generated in the cathode catalyst layer, typically in the form of droplets through cathode gas stream in the cathode flow channel. It has been reported that a hydrophilic channel sidewall with a hydrophobic membrane electrode assembly (MEA) surface would have less chance for water accumulation on the MEA surface. Therefore, a comprehensive study on the effect of surface wettability properties on water droplet movement in flow channels has been conducted numerically. In this study, the water droplet movements in a straight flow channel with a wide range of hydrophilic surface properties and effects of inlet air velocities are analyzed by using three-dimensional computational fluid dynamics method coupled with the volume-of-fluid (VOF) method for liquid–gas interface tracking. The results show that the water droplet movement is greatly affected by the channel surface wettability and air flow conditions. With low contact angle, droplet motion is slow due to more liquid–wall contact area. With high air flow velocities, increasing the contact angle of the channel surface results in faster liquid water removal due to lesser liquid–wall contact area. Copyright © 2010 John Wiley & Sons, Ltd.

Airflow Simulation of the Huge Telescope Assemble

With the three-dimensional computational fluid dynamics method, the airflow effects over the huge telescope assemble is investigated in this article. The distributing of velocity field and natural convection are studied by modeling and simulating the turbulent airflow of the huge telescope. Numerical simulations show the best observation direction is the 90o angle between the main optics axis and the horizontal line in which the air velocity distribution is the least. And the air temperature distribution and uniformity around the telescope are also provided by simulation.

Building pressure coefficients: Application of three-dimensional CFD methods to prediction

Wind-induced pressure coefficients are required for evaluating the energy performance of existing buildings, validating new building designs and, most recently, for multizone air flow computer models as input data. However, the traditional method of obtaining pres sure coefficients, by experiment, is time consuming, expensive and not amenable to parametric changes. Work with an existing computational fluid dynamics (CFD) code, FLUENT, has been carried out for the new application of predicting building pressure coefficients. The equations describing three-dimensional, turbulent flow fields around a building are solved using a finite difference technique. Comparison between experimental data and those of the CFD program showed good agreement. In addition, it is much more efficient and economical. To demonstrate the flexibility of the CFD model, a new design concept was also examined; this shows that building a through slot in the middle of a high-rise building reduces the wind induced pressure and thus the rate of air infiltration.