Multiple Reference Frame Method Research Articles

Computational fluid dynamics investigation of pesticide spraying by agricultural drones

Precise control over pesticide spraying by agricultural drones requires fundamental research of multiphase flow, heat and mass transfer of liquid droplets in downwash flow. In this study, water was used as a carrier agent in pesticide formulations, in which the liquid droplets exhibit a Newtonian fluid behavior. A general computational fluid dynamics (CFD) model that characterizes propeller motion coupled with droplet evaporation and deposition was developed. The downwash flow generated by the propeller rotation was simulated using a multiple reference frame method along with the SST-k-ω turbulence model. Spraying of liquid droplets was simulated using a discrete phase model. The flow model validation was conducted by comparing the simulated velocities with experimental data, and the spray model validation was completed by a comparison of droplet depositions from CFD predictions and experiments. The results indicated that the droplet deposition fluctuates with an increase of propeller speed, and that both temperature and relative humidity affect the droplet deposition. In addition, the relation between the number of particles and the impact velocity was identified quantitatively, impact velocity with respect to particle diameter was predicted, and the effects of surface inclination, surface roughness, and crosswind speed on droplet deposition were analyzed. Moreover, an in-depth discussion about the intrinsic relation between downwash flow and droplet spraying was conducted.

Numerical and experimental study of homogenization mechanism of high shear rotor‐stator mixer

AbstractUtilizing computational fluid dynamics (CFD) for analytical purposes, this study developed a fundamental model employing the multiple reference frame (MRF) method, facilitated by the CFX simulation platform. The investigation conducted numerical simulations of the flow field within the rotor‐stator assembly of a high shear mixer, guided by the Navier–Stokes equations and the standard k‐ε turbulence model. To quantify the homogenization efficacy of the high shear mixer under scenarios with and without energy consumption considerations, the study introduced two distinct parameters: the mixing index (γ) and the energy ratio mixing index (λ). The impact of structural parameters such as the number of rotor‐stator teeth, radial clearance, and tooth apex‐base axial clearance on the local flow characteristics—velocity, pressure, turbulent kinetic energy, shear rate distribution, net power consumption, and the specified indices—was meticulously analyzed. This analysis aimed to identify the optimal structural configurations for the mixer, considering energy efficiency and mixing effectiveness, and to determine the relative influence of these structural variations on the mixing index (γ) and the energy ratio mixing index (λ).

Optimizing mixing efficiency of anaerobic digesters with high total solids concentrations using validated CFD simulations

In this article, viscosity dependent mixing in anaerobic digestion (AD) towers is analysed using finite volume based computational fluid dynamics (CFD) simulations validated with ultrasound particle image velocimetry (uPIV). The study focuses on improving mixing characteristics for enhanced biogas production resulting from increased organic loading. Mixing of fluids with viscosity ranges found in real-life AD is investigated using the multiple reference frame (MRF) method. The aim is to increase the energetic efficiency of AD by reducing the energy demand required for sufficient mixing such that microorganisms and organic substrates are homogeneously distributed. The distinguishing feature of this work is the implementation of less power-consuming helical ribbon stirring devices (HRSD) for enhanced mixing in different reactor designs. It is demonstrated that HRSD become progressively effective for increasing total solids concentrations (% TS) ranging from 2.5 % TS to 12.1 % TS, particularly in cylindrical reactors. In comparison with conventional propeller-based mixers, innovative HRSD operation reduces dead volume (DV) by up to 22 %. Additionally, HRSD cause less shear forces and require less power due to lower rotational speed. The most energy-efficient mode of operation reduces the power demand by 9.29 % at 12 rpm, while still providing decreased DV of 13.38 % for the most viscous fluid investigated. The outcome is a more efficient and cost-effective mixing approach, which holds strong potential for mixing applications involving highly viscous fluids.

Research on the effects of slurry uniformity and mixing power of continuous cementing slurry mixers based on statistical and CFD methods

To enhance the efficiency of continuous cement mixing in well cementing, a Computational Fluid Dynamics (CFD) approach was employed to investigate the mud flow and mixing processes within the continuous mixing system. This study aims to analyze the influence of various design factors and their interactions on the mixing of different slurries in the well cementing slurry continuous mixer. Using the Response Surface Methodology (RSM) with a Box-Behnken model, this work combines the Euler-Euler multiphase flow model, k-turbulence model, and the Multiple Reference Frame (MRF) method to simulate two-phase fluid flow and agitator rotation, establishing the CFD model of the mixing system. The CFD model, coupled with the RSM method, analyzed four design factors: impeller diameter (400–800 mm), design density (1.4–2.6 g/cm³), impeller speed (100–300 rpm), and particle size (20–500 μm), studying their impact on two response variables, slurry mixing uniformity, and total power consumption. Through RSM and multiple regression analyses, predictive models for slurry mixing uniformity and corresponding power consumption were established under different design factors. Data comparison analysis revealed excellent agreement between predicted and actual results. Findings indicate that, when using uniformity or power as evaluation criteria, the P-value is smallest for impeller speed and largest for particle size. Hence, the impeller speed exhibited the strongest correlation with both, followed by impeller diameter, and lastly, design density and particle size. Only the interaction between impeller diameter and impeller speed (P-value <0.0001) significantly influenced both power and mixing uniformity, with its significance ranking just below the linear effects of impeller speed and diameter. Slurry uniformity decreased with increased design density and particle size, while power consumption exhibited the opposite trend. Uniformity increased with increasing impeller speed, but when the uniformity reached its maximum, further speed increments led to a slight decrease in uniformity, accompanied by a sharp increase in power. This was significantly influenced by the quadratic effect of impeller speed (P-value <0.0001), with its significance weaker than the linear effects. The proposed predictive model accurately forecasts response values for any given design parameter, providing a research direction for optimizing mixer design and selecting corresponding design parameters. This approach streamlines the study of mud mixing systems, reducing research time and costs. Moreover, it offers scientific guidance for optimizing operational parameters corresponding to well cementing conditions.

Three-Dimensional Numerical Analysis and Operational Optimization of High-Efficiency Sedimentation Tank

The high-efficiency sedimentation tank has a wide range of application prospects in industrial wastewater treatment due to its small footprint, strong resistance to shock loads, and high efficiency. However, the complex flow field distribution inside significantly affects the treatment performance of the high-efficiency tank. In this study, a three-dimensional geometric model of the high-efficiency sedimentation tank was constructed based on an engineering prototype. The corresponding solid–liquid two-phase, whole-process computational fluid dynamics (CFD) model for the high-efficiency sedimentation tank was established using the realizable k-ε turbulent model and the multiple reference frame (MRF) method. The internal structures of the flocculation zone, plug-flow zone, and clarification zone were optimized, and then the influence of operational process conditions on the flocculation treatment performance was investigated. The results indicate that, for the given engineering model, the average turbulent kinetic energy k in the flocculation zone exhibits a trend that initially increases and then decreases with the increase in the diameter and height of the draft tube. The optimal hydraulic conditions for the flocculation zone are achieved when the diameter of the draft tube is 2.5 m and the height is 3.5 m. The average turbulent kinetic energy dissipation rate in the plug-flow/clarification zone tends to decrease first and then increase as the height of the water tunnel and water-retaining weir increases. The optimal hydraulic conditions for the plug-flow and clarification zones are achieved when the height of the water tunnel is 1.0 m and the height of the water-retaining weir is 1.6 m. Under optimal operating conditions (dosage of dense media particles: 40 mg/L, stirring rate: 30 rpm, and inlet velocity: 0.72 m/s), satisfactory overall hydraulic conditions can be achieved throughout the entire high-efficiency sedimentation tank. Comparisons between a high-efficiency settling tank and a conventional clarifier for the treatment of circulating water sewage in a practical implementation reveals that the ballasted high-efficiency settling tank has advantages in terms of high hydraulic loading, high removal efficiency of hardness, small footprint, and low doses of flocculant. This research will provide reference values for the design and operation optimization of high-efficiency sedimentation tanks.

Computational fluid dynamics analysis of a novel continuous cementing slurry mixer

To improve the uniformity of continuous slurry mixing in well cementing, a novel continuous mixing system is proposed in this paper. The CFD model of the mixing system is established by employing the Eulerian multiphase flow model, k-ε model, and Multiple Reference Frames (MRF) method to simulate the flow of the two-phase fluids and the rotation of the agitator, respectively. A segmented control simulation method, which includes a dynamic “monitoring-assignment” approach capable of handling secondary mixing processes in engineering, is proposed to calculate the slurry mixing process in the continuous system. A comparative analysis of the control effectiveness is conducted to demonstrate the feasibility of this method. Using the validated model and method, the mixing process of the slurry in the system is investigated. The obtained data is analyzed based on four indicators: uniformity calculation, power, velocity component, and solid volume fraction, to evaluate the effects of impeller diameter and rotational speed on slurry uniformity. The data shows that both impeller diameter and rotational speed significantly affect the slurry uniformity in the continuous mixing system, while only impeller diameter has a greater impact on the flow field and flow pattern inside the stirred tank. It is observed that increasing the impeller diameter and rotational speed beyond a certain point does not further improve slurry uniformity, and excessive impeller diameter and rotational speed may lead to a decrease in uniformity due to stratification in the tank, along with a significant increase in power consumption. The proposed novel structure and method can provide valuable references for the industry, and the research findings can offer scientific guidance for achieving efficient well cementing operations in engineering.

Research on Air-Duct Optimization and Temperature Uniformity Analysis of Domestic Frost-Free Refrigerator-Freezer

In this paper, numerical simulation and experimental research are utilized to improve the temperature uniformity inside the storage chambers of a top-mounted air-cooled refrigerator. Firstly, in order to accurately predict the temperature distribution characteristics inside the storage chambers, porous media technique as well as multiple reference frame method are used to simulate the temperature field. The comparison of monitored points between calculated and measured temperatures are conducted to demonstrate simulations show relatively acceptable agreement with experimental results. Secondly, by using computational fluid dynamics simulation, two new air-duct structures were designed on the basis of the original air-duct system, which significantly reduced freezer temperature deviation and optimized the air volume distribution ratio between freezer and refrigerating storage chamber. Finally, the influence of outlet size on the temperature uniformity, air volume and velocity distribution inside both storage chambers was investigated based on the optimized air-duct structure. The results indicate that temperature deviation in freezer storage chamber reduced from 3.7 °C/3.1 °C to 1.1 °C/0.3 °C during damper-on/damper-off condition after optimization.

Numerical method investigation on the aggregation characteristics of non-spherical particles.

Under the background of the mechanical mechanism research of microfluidic technology for separating and screening pipeline particulate matter, this paper proposes an improved relative motion model by combining the multiple reference frame method and the relative motion model. Worked with a quasi-fixed constant method, this model can numerically calculate the aggregation features of non-spherical particles in the low Reynolds number channels. The results demonstrate that when Re = 40~80, ellipsoids exhibit an aggregation trend similar to circular particles with the same diameter as its largest circumscribed sphere. The aggregation position is affected by the ratio of long and short axes of particles, and the distribution trend is determined by the relative size of these particles. When the channel's Reynolds number is less than the critical Reynolds number, the aggregation position of elliptical particles will be closer to the pipe center with the increase in the Reynolds number, which is contrary to the aggregation tendency of circular particles more proximate to the pipe wall with the increase in the Reynolds number. This finding provides a novel idea and method for further exploring the aggregation rules of non-spherical particles and offers substantial guidance for separating and monitoring pipeline particulate matter via microfluidic technology and other related industrial applications.

Numerical simulation and multi-objective parameter optimization of gas−liquid flow in horizontal stirred tank

AbstractThe gas−liquid two-phase flow behavior in a stirred tank was numerically simulated using Euler−Euler two-fluid model, SST k−ω turbulence model and the multiple reference frame method. The results showed that among all the influencing factors, the rotation speed had the most significant effect on the stirred tank performance, followed by the damping board width. The parameter combination that can produce the most effective stirring was found through orthogonal test and matrix analysis, to be a paddle height of 950 mm, a paddle spacing of 1300 mm, a damping board width of 525 mm and a rotation speed of 123 r/min. Under this condition, the mixing time decreased from 31.620 to 25.845 s when the gas holdup and relative power consumption was basically unchanged.

Numerical study on the hull–propeller interaction of autonomous underwater vehicle

The hull–propeller interaction of autonomous underwater vehicle (AUV) in straight and oblique flow is numerically studied. The study is performed based on computational fluid dynamics (CFD) and the general commercial software ANSYS Workbench. The multiple reference frames (MRF) method and the shear stress transport (SST) k−ω turbulence model are adopted. Firstly, the drag of Suboff AUV and the open water performance of the Wageningen B-3-50 propeller are simulated numerically. The errors are all within 5%, validating the reliability of the method in this paper. Then, the Sailfish AUV and B-3-35 propeller developed by the Underwater Vehicle Laboratory (UVL) of Ocean University of China are simulated. The maximum incremental drag produced by the appendages reaches even more than 1.5 times the hull drag. Propeller rotation causes an additional hull drag increment of over 25%. With an inlet velocity of 1.5 m/s, the thrust and torque behind the bare hull increase by 16.7% and 6.4%, respectively. The effect of angle of attack on drag is more significant at high velocity. Finally, the numerical simulation result 1.825 m/s and experimental result 1.75 m/s are compared. This study has implications for guidance on AUV integration analysis.

Modeling of CSTR flow field for Agaricus bisporus residue fermentation based on CFD numerical simulation.

Agaricus bisporus production gets a lot of residues, which could be fermented by a continuous stirred tank reactor (CSTR). This research was conducted to study the characteristics of the multiphase flow field in the reactor and its influence on the efficiency of biogas production in the CSTR fermentation process of Agaricus bisporus residue by using CFD numerical simulation technique. The aim is to reveal the relationship between the reactor operating conditions, flow field characteristics, and biogas production efficiency at the micro-level. We compared the results of different turbulence models by evaluating the power quotients and flow quotients with the experimental results to derive the most suitable flow field model inside the reactor for the Agaricus bisporus residues. The results showed that, under the condition that the number of grids does not affect the simulation results, and considering the model accuracy and efficiency, the numerical method can be chosen as the multiple reference frame (MRF) method of the second-order upwind discrete scheme with the realizable k - ε model. In this way, we can make use of edible mushroom residue as a substrate for resource utilization and provide basic data and theoretical basis for the design and scale-up with anaerobic fermentation to biogas reactor.

Forward Flight Performance Analysis of Supercritical Airfoil in Helicopter Main Rotor

In this research, the aerodynamic performance and flow characteristics of NASA SC (2)-0714 airfoil and HH02 airfoil in the helicopter main rotor are evidently analyzed. The supercritical airfoil is used in the aircraft for attaining better transonic and high-speed flow characteristics. Moreover, a specialized helicopter airfoil called HH02 is used in the Apache helicopter rotor for increasing the operational speed. As most of the high-speed helicopters are using four-bladed main rotor configuration, it is analyzed with prior attention. The lift and thrust act in different directions for the forward phase of the flight whereas the lift and thrust act in the same direction for the other phases of flight, which is analyzed in this work. The computational analysis is done by using ANSYS Fluent whereas the rotational analysis is done by using the Multiple Reference Frame (MRF) method. An analysis is carried out for different RPM of 400,600 and 800 with the combination of 0.3, 0.4 and 0.5 Mach numbers with the assistance of grid independence test. The result shows that the NASA SC (2)-0714 rotor increases the thrust of the rotor around 5% to 10% under various rotor and forward speeds. Thus, the results proves that the supercritical airfoil is highly capable of producing higher thrust and good aerodynamic characteristics.

Studi Numerik Centrifugal Fan Tipe Impeller Backward dengan Variasi Putaran Fan

The primary air fan functions as a primary air producer which is used as air to transport coal powder from the pulverizer to the burner to be burned in the boiler furnace. This study aims to obtain the effect of the rotation variation of fan to fluid flow characteristics such as the distribution of total pressure, the dynamic pressure, the pressure static contours, velocity distribution, and the fan optimal efficiency. This study was numerical study with simulated a backward impeller type centrifugal fan in a two-dimension model using Fluid Computational software with the multiple reference frame method with the variation of fan rotation. Based on the visualization of the pressure contour and velocity distribution, it could be concluded that there was a volute phenomenon, this was indicated that the greater the volume area in the volute is the greater the total pressure value too. Based on the visualization of the outlet velocity distribution at the position of -0,8531m to -1,01301m, it was found that the velocity is close to the value of 0 m/s2. It showed that the minimum velocity in the area due to the volute tongue radius occurs a flow collision and it impacted the velocity in the area decreased up to V=0. From the simulation results, it was found that the greater the fan rotation value was the greater the efficiency value too. It would be verified by the actual operating data of the centrifugal fan with a minimum rotation range value of 1194 rpm to a maximum of 1468 rpm

CFD-based calculation method of convective heat transfer coefficient of spiral bevel gear in intermediate gearbox under splash lubrication

Purpose This paper aims to propose a numerical method to calculate the convective heat transfer coefficient of spiral bevel gears under the condition of splash lubrication and to reveal the lubrication and temperature characteristics between the gears and the oil-air two-phase flow. Design/methodology/approach Based on computational fluid dynamics, the multiple reference frames (MRF) method was used to simulate the rotational characteristics of gears and the motions of their surrounding fluid. The lubrication and temperature characteristics of gears were studied by combining the MRF method with the volume of the fluid multiphase flow model. Findings The convective heat transfer coefficient can be improved by increasing the rotational speed and the oil immersion depth. Moreover, the temperature of the tooth surface having a large convective heat transfer coefficient is also found to be low. A large convection heat transfer coefficient could lead to a good cooling effect. Originality/value This method can be used to obtain the convective heat transfer coefficient values at different meshing positions, different radii and different tooth surface positions. It also can provide research methods for improving the cooling effect of gears under the condition of splash lubrication. Peer review The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-07-2020-0233/

Aerodynamic performance of a small-scale tilt rotor: Numerical simulation and experiment in steady state

The present work studies the aerodynamic performance of a small-scale rotor in tilting transition states through wind tunnel tests and numerical simulations. Firstly, the test platform for the rotor aerodynamics is built up, and the Computational Fluid Dynamics (CFD) model of flow field around the rotors is established based on the multiple reference frame method. Secondly, the effects of flow velocity, tilt angle and advance ratio on the aerodynamic performance of the rotor are investigated using both the numerical simulation and the wind tunnel test. It is found that for the Model 8038 rotor with maximum effeciency of 0.567 at advance ratio of 0.43, the rotor thrust coefficient increases with the increase of the Reynolds number. At Reynolds number of 410 thousand to 820 thousand, the thrust coefficient increases slightly with the increase of the rotating speed. The results also show that the thrust coefficient decreases with the increase of the advance ratio. With high-speed airflow and relatively low-speed rotation, “windmill” phenomenon is found in the experiment. The tilting of the rotor from level flight to hovering increases the thrust coefficient. Highly dependency of the tilt angle on the thrust coefficients at given advance ratios is found in the wind tunnel tests.

Gas‐Liquid Mixing in a Grid‐Disc Impeller Stirred Tank

AbstractTo enhance the gas‐liquid mixing performance in stirred tanks, the grid‐disc impeller was designed by replacing the solid disc of the standard Rushton impeller with a grid disc. Gas‐liquid hydrodynamics of the new impeller was studied by employing the Eulerian‐Eulerian two‐phase model coupled with the dispersed k‐ε turbulence model. Rotation of the impeller was simulated with the multiple reference frame method. Flow field, gas holdup, and power consumption were investigated and compared with the standard Rushton impeller. The numerical method was validated by comparing the gas holdup with literature. The grid‐disc impeller performed better than the Rushton impeller in terms of gas dispersion performance, axial pumping capacity, and energy requirement, indicating its potential for gas‐liquid mixing applications.

Investigation of the flow characteristics of liquid–liquid two-phase mixing in an agitator equipped with a “V-shaped” horizontal baffle

An agitator is an important operating unit in industrial production, and baffles play a vital role in the performance of the agitator. Compared to the performance of unbaffled agitators, traditional baffles can break vortices and improve the mixing in a stirred tank, but traditional baffles can also contribute to high energy consumption. A newly invented “V-shaped” horizontal baffle is introduced based on a traditional baffle, and the new baffle is attached to the inner wall of the agitator at the height of the impeller. Based on several different baffle conditions (an agitator without the “V-shaped” horizontal baffle and agitators with “V-shaped” horizontal baffles at angles of 30°, 60° and 90°), the fluid flow characteristics of the liquid–liquid two-phase flow mixing process are investigated by the computational fluid dynamics (CFD) method. The multiple reference frame method, the standard k − e model and the Eulerian–Eulerian two-fluid model are adopted. The “V-shaped” horizontal baffle is found to reduce energy consumption and improve mixing, which provides new approaches for the optimization and innovation of baffles.

Performance Analysis and Cavitation Prediction of Centrifugal Pump Using Various Working Fluids

Background: The application of centrifugal pumps is found in domestic and petrochemical industries. Industrial centrifugal pumps are designed and tested using water as working fluid before supplied to industries, as water is commonly available. However, centrifugal pumps are used in industries for various applications, which involve the handling of fluids other than water- like saline-water, crude oil, gasoline, etc. Consequently, hydraulic performance of the pump differs from the designed and tested values and pump performance becomes unpredictable. Cavitation characteristics of the pump handling different fluids other than water are also changed and many a time, cavitation starts prematurely. As a result, the operating cost of pump is increased. Objective: A CFD based computational analysis of a single-stage, single-entry industrial centrifugal pump having double-volute casing is carried out to compare the performance and cavitation characteristics for various working fluids, namely water, saline water with varying salinity, gasolene and crude oil. Methods: Multiple Reference Frame method (MRF) available in Reynolds-Averaged Navier-Stokes (RANS) equations based CFD solver Ansys-CFX is used in the present study. CFD simulation is carried out for five flow rates with Standard k-ε turbulence model. Rayleigh-Plesset equation describing the growth of a single vapor bubble in a liquid is used for predicting the cavitation flow behaviour. Results: Minimum static pressure is computed at the suction side of saline water as compared to the other working fluids studied here. Hydraulic efficiency of crude oil is found to be the lowest as compared to other fluids. Supercavitation (excessive formation of vapor bubbles and sudden drop in head up to 3%) starts early for saline water with 40g/kg salinity. Conclusion: The results show little variation in pump efficiency when water and saline water are used as working fluids. However, cavitation characteristics differ considerably with the working fluids. Recent patents filed/published in this area revealed that efforts are needed to develop effective cavitationresistant centrifugal impellers and pumps.

Evaluation of the Multiple Reference Frame Approach for the Modelling of an Axial Cooling Fan

The modelling of rotating parts, such as axial fans, is one of the main challenges of current CFD simulations of industrial applications. Different methods are available, but the most commonly used is the multiple reference frame (MRF) method. This paper investigates how different flow properties, such as temperature, pressure and velocity, develop when passing through the MRF domain. The results are compared to the more physical rigid body motion (RBM) approach. It is found that the MRF method transports the upstream properties with the streamlines of the relative velocity from the upstream to the downstream interface. This leads to a non-physical rotation by an angle that is dependent on the length of the domain and the ratio between axial and tangential velocity in the MRF region. The temperature field is more affected than the flow field, since wake structures from upstream obstacles are destroyed due to the wake of the blades. Downstream structures affect the flow in the upstream region by an increase in static pressure, which causes the streamlines in the MRF zone to slow down. Depending on the size of the obstacle, this can cause substantial distortions in the upstream and downstream flow field.

Numerical analysis on gas-solid mixing in ceramic dry granulation room with baffles

In order to investigate the influence of baffles on the mixing effect of particles during ceramic dry granulation process.Air-particles interaction was analyzed by euler gas-solid two phases flow model, the granulation area was simplified.The three dimensional physical model of particles mixing process was constructed, granulation room rotary motion was simulated by sliding grid method and multiple reference frame method, turbulent motion was analyzed by modified RNG discrete model. The influence of different baffles on particles mixing was investigated according to the volume fraction distribution and velocity field, changed the position of the baffle can increase the blending effect by about 22%.The results showed: when there were no baffles, wall baffles and middle baffles in the granulation room, the average volume fraction of powder was about 0.22, 0.18 and 0.26 respectively. The average speed of powder was about 0.6m/s, 0.9m/s and 0.4m/s respectively. The wall baffle made the powder have significant axial movement, the experimental data showed: when granulation room had wall baffles, the content of active particles accounted for about 73%. It is helpful to improve the understanding of gas-solid two phase flow field in ceramic drying granulation room and provide some theoretical guidance for the design and optimization of the baffle.