Commercial Computational Fluid Dynamics Program Research Articles

Numerical study of performance augmentation of a vertical coil and shell heat exchanger using high frequency ultrasonic waves

This research focuses on the performance augmentation of a coil and shell heat exchanger using high frequency ultrasonic waves by the commercial computational fluid dynamics program FLUENT. The model was validated both heat transfer and ultrasound propagation with the results from other researchers. Then, the simulation of the flow and heat transfer enhancement in the heat exchanger under 1.7 MHz ultrasound. Four ultrasonic transducers were installed at the corners of the shell at the middle height of the coil. The ultrasound from transducers was emitted to induce the vortex flow in the shell with the angle of 0, 15, and 30 degrees with the horizontal line. The results show that the high frequency ultrasound is applicable for heat transfer enhancement of a shell and coil heat exchanger. Therefore, the obtained results can be used to innovate an ultrasonic coil and shell heat exchanger in the future.

Visualization and analysis on the thrust vectoring control in three-dimensional dual-throat nozzles

The dual-throat vectoring nozzle is an efficient technique utilizing less high-pressure secondary streams to control mainstream deflections flexibly. In this article, three-dimensional Reynolds-averaged Navier–Stokes simulations were performed using a commercial computational fluid dynamics program, and the numerical methods applied in this study were validated through comparison with the experimental results. Two parameters of the slot injector have been investigated, namely the incident angle of the secondary stream and the slot length-to-width ratio. Critical performance parameters have been quantitatively analyzed, involving the pitching angle, injected mass flow ratio, system resultant thrust ratio, and resultant pitching thrust efficiency. Furthermore, visual flow-field features are expounded using Mach number contours on the center-plane, Mach number contours on various slices, and streaklines. Some meaningful conclusions are drawn herein. The flow field in this three-dimensional dual-throat nozzle is not fully symmetric based on the reference of the center-plane. Consequently, a full domain is essential to capture the flow characteristics accurately, instead of a half domain. Although the pitching angle for the secondary stream incidence angle of 120° is the highest, comprehensive characteristics in terms of resultant pitching thrust efficiency and system resultant thrust ratio for 150° are more outstanding. The pitching angle, system resultant thrust ratio, and resultant pitching thrust efficiency increase with an increase in the slot length-to-width ratio for a constant secondary stream mass flow rate. Under the circumstance of a constant injection pressure ratio, the pitching angle increases with an increase in the slot length, whereas system resultant thrust ratio and resultant pitching thrust efficiency decline with an increasing slot length.

Heat transfer efficiency enhancement using zigzag louvered fin

The present study numerically examines the impact of zigzag fin surface pattern structures in a micro-channel heat exchanger on heat transfer efficiency using a commercial computational fluid dynamics program. The three newly designed louvered fin structures that comprise four triangular zigzag patterns, alternately spaced structures on both fin sides, a flat or zigzag fin structure on either side, and nine triangular zigzag patterns on both fin sides are compared with the reference flat fin. The air inlet velocity and temperature are 5 m/s and 30 °C, respectively, whereas the pressure at the outlet is atmospheric pressure. The wall temperature remains constant at 10 °C. The heat transfer performance is evaluated using the JF factor value, which reflects a performance comparison with the reference. The results show that the zigzag pattern changes the airflow direction, and the time air is trapped inside a fin domain increases. Air also tends to flow toward the zigzag pattern center, increasing the velocity and the heat transfer. The nine triangular zigzag fin pattern structures with the largest heat transfer area provide the best performance with the biggest JF factor increase of 3.24%. This result is obtained despite the comparison of the biggest friction factor values of the three new fin structures, suggesting that the impact of the JF factor far outweighed that of the friction factor.

Development of computational fluid dynamics model for two initial CO2 concentration in circulating fluidized bed reactor

Nowadays, the global warming is considered as a world problem because it influences the environment by increasing the average temperature of earth surface. One of the greenhouse gases that release from human activities and fossil fuels combustion in industry is CO2. Several technologies are applied to reduce the CO2 emission to atmosphere. In this study, the aim is to capture the CO2 by solid sorbent adsorption with potassium carbonate supported on gamma alumina using full loop circulating fluidized bed reactor in commercial computational fluid dynamics program, ANSYS FLUENT. This study focuses on the effect of initial CO2 concentrations from cement industry and power plant on CO2 removal efficiency. Besides, the solid volume fraction profile is also considered. The simulation results showed the hydrodynamics in circulating fluidized bed reactor that the solid sorbent was high at the reactor wall and low at the reactor center. In addition, the independent input variables were investigated which were percentage of K2CO3 loading on sorbent and gas velocity. The increasing of K2CO3 loading on sorbent and the decreasing of gas velocity increased the CO2 capture efficiency.

A CFD–DEM study of the behaviour of single-solid and binary mixtures in a pyramidal spouted bed

We simulated a lab-scale cold-flow spouted bed through computational fluid dynamics (CFD), coupled with the discrete element method (DEM) for the solid phase, using a commercial CFD program, ANSYS FLUENT 18.0. To limit the computational expense, we tested both a simplified pseudo-2D geometry and a complete 3D geometry. We found that the Haider and Levenspiel drag model is suitable for the pseudo-2D geometry; however, this model does not correctly predict fluidisation in the 3D geometry. Conversely, the Gidaspow drag model behaves accurately in the 3D geometry but overestimates the motion of particles in the pseudo-2D geometry. We studied several single-solid and binary mixtures to assess the reproducibility of segregation phenomena. The pseudo-2D model was able to predict the onset and minimum spouting flow rates of all mixtures with good accuracy. An analysis of the volume fraction contours of the binary mixtures permitted us to confirm that segregation phenomena were correctly predicted at low gas velocities. We showed that segregation decreased as the inlet gas flow rate was increased. Calculations performed in the complete 3D geometry were preliminarily assessed as more reliable but required almost four times as much computational time as those for the pseudo 2D geometry.

Computational modeling and experimental validation of heat recovery ventilator under partially wet conditions

This study investigates the effect of condensation on the thermal performance of a plate-type heat recovery ventilator designed for broiler houses. The temperature efficiency of the air-to-air heat exchanger is calculated by a simplified method based on a commercial computational fluid dynamics program. The concept of artificial specific heat of air is introduced in order to take into account the latent heat released by internal condensation. Temperature efficiency is obtained by varying system parameters such as the airflow rate, outdoor temperature, and indoor relative humidity. Results obtained using the model are compared with the experimental results of the authors' previous work. Results of the temperature efficiency are in good agreement with the experimental results for either dry or partially wet conditions within the range of experimental uncertainties. Comparisons are also made for the rates of condensation and the temperature distributions on the internal surface of the heat exchanger.

A Triangular Double Layer Microchannel Heat Sink: Effect of Parallel and Counter Flow

A numerical study is conducted by using ANSYS CFX 14.5, a commercial computational fluid dynamics program to predict the thermal performance of a counter and parallel flow on triangular double layered microchannel heat sink for various channel aspect ratios. Findings reveal that the counter flow configuration leads to a better heat transfer performance for low channel aspect ratio (α < 4) and higher Reynolds Number (Re > 700). For the parallel flow configuration, improved performance is normally shown when channel aspect ratio, α is more than 4 and lower Reynolds Number (Re < 700).

전산유체역학을 이용한 컨테이너 선수갑판 쇄파판에 작용하는 충격하중 계산

In this study, numerical studies using a Computational Fluid Dynamics(CFD) method were carried out to estimate the green water load acting on the breakwater plate of bow deck of container carrier, KCS. For the green load water load analysis, a full load condition was considered. The relative motions at bow deck were calculated from the seakeepig analysis. Statistical analysis were carried out to estimate the long term response of the relative motions with the North Atlantic wave scatter diagram. The equivalent design wave was determined from the RAO of the relative motions at bow and the long term responses. CFD geometry modeling with three different locations and simulations for the green water loads were carried out in the equivalent design waves. A commercial CFD program, STAR-CCM+ Ver. 8.04, was used and the green water pressures on the breakwater plate were calculated successfully. The CFD analysis for green water loads can be used as a useful design tool for the evaluation of the breakwater plate of the container vessel. Ke ywords : Green water(그린 워터), Bow deck(선수 갑판), Breakwater plate(쇄파판)

Residual stresses analysis of friction stir welding using one-way FSI simulation

When certain mechanisms, such as plastic deformations and temperature gradients, occur and are released in a structure, stresses remain because of the shape of the structure and external constraints. These stresses are referred to as residual stresses. The base material locally expands during heating in the welding process. When the welding is completed and cooled to room temperature, the residual stresses are left at nearly the yield strength level. In the case of friction stir welding, the maximum temperature is 80% to 90% of the melting point of the materials. Thus, the residual stresses in the welding process are smaller than those in other fusion welding processes; these stresses have not been considered previously. However, friction stir welding residual stresses are sometimes measured at approximately 70% or above. These residual stresses significantly affect fatigue behavior and lifetime. The present study investigates the residual stress distributions in various welding conditions and shapes of friction stir welding. In addition, the asymmetric feature is considered in temperature and residual stress distribution. Heat transfer analysis is conducted using the commercial computational fluid dynamics program Fluent, and results are used in the finite element structural analysis with the ANSYS Multiphysics software. The calculated residual stresses are compared with experimental values using the X-ray diffraction method.

Model Sensitivity Test of Large Eddy Simulation for Wind Flow and Pollutant Dispersion in a Street Canyon

This paper reports on the model sensitivity analysis of a commercial computational fluid dynamics program, ANSYS FLUENT v14. The purpose of the analysis was to determine the appropriate modeling settings for numerical model of the case study. A full scale of a simplified urban street canyon was modelled and the turbulent flow was calculated using Large Eddy Simulation (LES) techniques. The model sensitivity tests involved are mesh sensitivity, statistically steady state and sampling. Adequate numbers of cells, period time to achieve statistically steady state (SST) and sampling time to simulate wind flow and pollutant dispersion in street canyon were determined through systematic tests.

Numerical Validation for Wind Flow Field in a Street Canyon under Unstable Atmospheric Condition

This paper reports on the validation study of a commercial computational fluid dynamics program, ANSYS FLUENT v14. The purpose of the study was to determine the best turbulent model that can reproduce appropriately the wind flow field of turbulent flow in street canyon under different thermal atmospheric condition. Standard k-ε (SKE) and Large Eddy Simulation (LES) techniques were chosen as the turbulent model for the validation study. It was found that LES could well calculate a complex simulation involving isothermal flow and thermal flow with different thermal intensity and different heat location in street canyon.

The impact of mass flow and masking on the pressure drop of air filter in heavy-duty diesel engine

This paper presents a computational fluid dynamics (CFD) calculation approach to predict and evaluate the impact of the mass-flow inlet on the pressure drop of turbocharger`s air filtfer in heavy-duty diesel engine. The numerical computations were carried out using a commercial CFD program whereas the inlet area of the air filter consisted of several holes connected to a channel. After entering through the channel, the air passes among the holes and enters the air filter. The effect of masking holes and hydraulic diameter is studied and investigated on pressure drop. The results indicate that pressure drop increase with decreasing of hydraulic diameter and masking of the holes has considerable affect on the pressure drop.

Modeling and Validation of Repair Grout Flow in Voided Ducts

External post-tensioned (PT) tendons in bridges are installed inside box girders with high-density polyethylene ducts. Voids in these ducts can lead to corrosion of the PT strands, which could lead to tendon failure. A grout injection is commonly used to protect exposed tendons. Although experiments using external PT tendons have been performed to investigate effective grouting repair methods and materials, these experiments cannot simulate all parameters of grouting repair encountered in the field. In response, the current study uses a commercial computational fluid dynamics program to investigate grout flows in void-containing ducts. A simplified numerical model then is developed based on previous experimental results. This model can consider all parameters of repair grouting methods not covered by experiments. A validation of the proposed model shows close agreement between numerical and experimental results regarding grout flow and repair performance.

Multi-component gas transport in micro-porous domains: Multidimensional simulation at the macroscale

For decades, models based on the Maxwell–Stefan diffusion equations have been used to predict mass transfer of multi-component gases in porous media. However, the validity of these models is restricted to transport processes that are dominated by diffusion and wall-friction. Therefore, a new computational model is presented, which is based on a comprehensive theory of multi-component gas transport. It comprises conservation equations of mass and momentum for each species contained in the gas mixture together with an energy balance for the mixture. The model is intended to be used for investigations on the macroscopic scale. Thus, the local volume averaging technique is applied and friction coefficients, which encompass the full range of Knudsen numbers, are used to describe the drag forces exerted by the pore structure. In the volume averaged energy equation the gas and solid phases are considered a pseudo-homogeneous medium. The resulting set of highly coupled transport equations is implemented in a commercial computational fluid dynamics program. For validation purposes, the mass transfer model is first used to simulate the isothermal diffusion problem in a Loschmidt tube. Then, the simultaneous mass and heat transfer in a porous duct with cooled walls is investigated. In both cases, the numerical results are in very good agreement with experimental data.

Simplified Analysis of Radiation Heat Exchange in Boiler Superheaters

This article describes the determination of the radiation heat transfer coefficient in radiant platen superheaters and on convective heating surfaces. A new simple formula for determination of the heat transfer coefficient is derived on the basis of a diffusivity model of radiation heat exchange. The radiation heat transfer coefficients are determined on the tube surface in a convective evaporator, in a second stage convective heat superheater, and in a platen superheater of a pulverized coal-fired boiler. The calculations were carried out applying the method presented in this article, the Central Institute for Boilers and Turbines method, and formulas resulting from the analysis of heat exchange in an enclosure containing a gas of a constant temperature. In order to assess the accuracy of the achieved results, the flow of flue gas and the heat exchange were modeled using a commercial computational fluid dynamics program.

Coronary Artery WSS Profiling Using a Geometry Reconstruction Based on Biplane Angiography

Computational fluid dynamics (CFD) methods based on three-dimensional (3D) vessel reconstructions have recently been shown to provide prognostically relevant hemodynamic data. However, the geometry reconstruction and the assessment of clinically relevant hemodynamic parameters may depend on the used imaging modality. In this study, the silicon model of the left coronary artery (LCA) was acquired with a biplane angiography. The geometry reconstruction was done using commercial CAAS 5.2 QCA 3D software and compared with an original geometry. The original model is an optically digitized post-mortem vessel cast. The biplane angiography reconstruction achieved a Hausdorff surface distance of 0.236 mm to the original geometry that is comparable with results obtained in our earlier study for computed tomography (CT) and magnetic resonance imaging (MRI) reconstructions. Steady flow simulations were performed with a commercial CFD program FLUENT. A comparison of the calculated wall shear stress (WSS) shows good correlation for histograms (r=0.97) and good agreement among the four modalities with a mean WSS of 0.65 Pa in the original model, of 0.68 Pa in the CT-based model, of 0.67 Pa in the MRI based model, and of 0.69 Pa in the biplane angiography-based model. We can conclude that the biplane angiography-based reconstructions can be used for the WSS profiling of the coronary arteries.

탄소나노튜브 가스센서의 SF6분해생성물 검출 및 확산현상에 관한 연구

가스절연개폐장치 (Gas-insulated switchgear, GIS)의 내부에는 절연에 관한 이상 여부를 감시하고 판단할 수 있는 시스템이 요구된다. 부분방전에 의해 발생되는 <TEX>$SF_6$</TEX> 분해생성물에 관한 단일벽 탄소나노튜브 (Single-walled carbon nanotube, SWNT)가 지닌 우수한 검출기능 때문에 SWNT를 이용한 가스센서 개발이 활발히 진행되고 있다. 하지만 아직까지 부분방전에 의해 발생된 분해생성물의 확산현상에 관한 해석적 연구는 미흡한 실정이다. 본 논문에서는 실험 데이터 및 상용 CFD (Computational Fluid Dynamics) 프로그램을 이용하여 SWNT 가스센서에 포획되는 분해생성물의 코로나 방전에 의한 발생 과정과 챔버 내부에서의 확산과정을 모델링하여 부분방전 발생 시 챔버 내부의 온도, 압력, 그리고 분해생성물의 농도 등을 수치계산하였다. 분해생성물의 시간당 질량생성율과 발생온도는 각각 <TEX>$5.04{\times}10^{-10}$</TEX> [g/s]와 773 K이라 가정하였다. 농도방정식을 계산함에 있어 미지의 확산계수를 임의의 값으로 가정하여 직접 부여하는 방법을 사용하지 않고, 확산계수를 정의하는데 사용되는 Schmidt수의 값을 지정하여 확산계수가 <TEX>$SF_6$</TEX> 가스의 물성치인 점성계수와 밀도의 함수로 계산되도록 하였다. 수치결과로부터 분해생성물의 농도구배가 확산을 일으키는데 주요 구동포텐셜 (Drive potential)이 됨을 확인하였다. 센서 설치위치가 부분방전 발생영역에서 멀리 떨어질수록 분해생성물 농도가 낮음을 알 수 있었고, 부분방전이 지속될수록 분해생성물의 농도가 증가함을 확인하였다. 다수의 센서를 챔버 내부에 설치하면 각 센서의 응답시간을 확인하여 PD 발생위치를 판단할 수 있을 것이고, 이를 통해 GIS 진단 및 유지보수에 관한 유용한 정보로 사용될 수 있을 것이다. The detection methods are required to monitor and diagnose the abnormality on the insulation condition inside a gas-insulated switchgear (GIS). Due to a good sensitivity to the products decomposed by partial discharges (PDs) in <TEX>$SF_6$</TEX> gas, the development of a SWNT gas sensor is actively in progress. However, a few numerical studies on the diffusion mechanism of the <TEX>$SF_6$</TEX> decomposition products by PD have been reported. In this study, we modeled <TEX>$SF_6$</TEX> decomposition process in a chamber by calculating temperature, pressure and concentration of the decomposition products by using a commercial CFD program in conjunction with experimental data. It was assumed that the mass production rate and the generation temperature of the decomposition products were <TEX>$5.04{\times}10^{-10}$</TEX> [g/s] and over 773 K respectively. To calculate the concentration equation, the Schmidt number was specified to get the diffusion coefficient functioned by viscosity and density of <TEX>$SF_6$</TEX> gas instead rather than setting it directly. The results showed that the drive potential is governed mainly by the gradient of the decomposition concentration. A lower concentration of the decomposition products was observed as the sensors were placed more away from the discharge region. Also, the concentration increased by increasing the discharge time. By installing multiple sensors the location of PD is expected to be identified by monitoring the response time of the sensors, and the information should be very useful for the diagnosis and maintenance of GIS.

A simplified approach to describe complex diffusers in displacement ventilation for CFD simulations

With the capability to improve indoor air quality while simultaneously reducing energy demand, displacement ventilation is becoming popular. However, the numerical simulation of air distribution in an indoor space with displacement ventilation using computational fluid dynamics (CFD) is challenging because of the complexity of air diffuser geometry and the complicated airflow pattern generated. Typical air diffusers used for displacement ventilation systems include, but are not limited to, quarter-circular-perforated, grille, floor-perforated, and swirl diffusers. None of them can be treated as a simple opening in CFD simulations because their effective area ratios are small. We have developed a new, simple method to describe those diffusers by directly specifying the correct jet momentum from the diffusers while adjusting the airflow rate by changing the effective areas. This is done by setting some CFD cells for a diffuser with a certain momentum, while other cells are randomly blocked. By implementing this method into a commercial CFD program, this study used the method to simulate air distributions in an office and a workshop with those diffusers under cooling or heating conditions. The distributions of air velocity, temperature, and airborne contaminant concentration are in good agreement with the corresponding experimental data obtained from an environmental chamber. This paper presents a simplified method for description of complex diffusers in computational fluid dynamics simulation of displacement ventilation at high computational efficiency. It may be used to assist the design and analysis of air distribution for displacement ventilation as well as other types of ventilation with complex diffusers.

Numerical analysis of a pulsation damper in fuel injection rails

It is important to maintain a stable fuel rail pressure at all operating conditions for optimal engine operation. Pressure fluctuations within the system are created by the rapid opening and closing of the fuel injectors. The wave amplitude can be reduced by the use of a pressure-damping device. The commercial computational fluid dynamics program, CFX, was used to model pressure pulsation within the rail. The numerical results compared favourably to the measurements. Based on the parametric studies, a general guideline was developed to identify the optimal damper configuration for better engine performance under different conditions.

Effect of Angle of Attack on the Performance of an Airborne Counterflow Virtual Impactor

A three-dimensional model has been developed within the framework of the commercial computational fluid dynamics program, FLUENT®, to investigate the collection efficiency of an airborne counterflow virtual impactor (CVI). The model assumes steady-state, isothermal, compressible, and turbulent flow. Particle trajectories are computed based on the Lagrangian discrete phase model (DPM). In addition to predicting the effects of flight velocity and counterflow rate on the particle collection efficiency, as do prior models, the model quantifies the effect of flight attack angle on the particle collection efficiency. With an angle of attack as small as 5°, the CVI collection efficiency drastically degrades at large particle sizes, and only particles with intermediate sizes are collected. Smaller particles do not have sufficient inertia to fight the counterflow, and larger particles tend to impact the CVI inner walls and are lost to the CVI walls. The modeling results show that the alignment between the free stream flow and the CVI inlet is critical to the performance of the CVI.