Velocity Vector Distribution Research Articles

To the Theory of Grain Motion in an Uneven Air Flow in a Vertical Pneumatic Separation Channel with an Annular Cross Section

The possibilities of the action of uneven air flows on the grain material in the separating channels are still not used enough. The reason for this is the insufficient knowledge of the processes of interaction of the components of the grain material with an uneven air flow. The purpose of the research is to increase the efficiency of grain material separation according to aerodynamic properties by purposefully changing the diagram of air velocities in the channel sections using the actions of lateral and aerodynamic forces. The separation efficiency of grain material components was determined by trajectory analysis. The different geometry of the pneumatic separation channel was studied. The study of the distribution of air velocity and air pressure vectors in a vertical annular channel was carried out using the FlowVision software. It has been established that a change in the air velocity diagram can be implemented both by changing the geometric parameters of the channel and by additional distributed air supply through the perforation in the side walls of the pneumatic channel. Based on the analysis of the velocity field, an improved scheme of a pneumatic gravitational separator is proposed for separating grain material into three fractions according to aerodynamic characteristics.

Flow past two tandem square cylinders placed in parallel walls

In this work, pulsating and non-pulsating flow structures past two tandem square cylinders placed in parallel walls was investigated. The variation of the distance between the cylinders and the frequency of flow pulsation was also examined. The Particle Image Velocimetry (PIV) method was applied to reveal hydrodynamic characteristics such as streamlines patterns, <Ψ>, the velocity vector distribution, the vorticity field, <ω>, the normalized streamwise velocity contours, <U/Uavg>, and turbulent statistics such as streamwise velocity fluctuations, urms, cross-streamwise velocity fluctuations, vrms, and turbulent Reynolds stress, u′v′‾/U02 distributions for non-pulsating flow cases. In addition, instantaneous and phase averaged flow data over the flow field is presented in order to evaluate the influence of flow pulsation on the quantitative analyses. The experiments were performed at Re=500. According to the results, the confinement profoundly affects the flow regime past two tandem cylinders. The alteration from the reattach flow to the co-shedding vortex flow regime take place at a lower gap ratio. Moreover, flow pulsation considerably contributes to mainstream penetration into the gap between cylinders. The mechanism of the fluid interactions near the wall and mainstream is highly dependent on the ratio of L/D and pulsation frequency.

PEMYH için COMSOL'da Üç Boyutlu Çoklu Akış Modeliyle Altın Oran Yöntemi ile Oksijen ve Hidrojen Giriş Hızlarının Optimizasyonu

A three dimensional (3D), gas-liquid multi-phase flow and transport model in COMSOL Multiphysics has been developed to simulate flow and transport phenomena in a proton exchange membrane fuel cell (PEMFC) with several operational parameters. The effects of changes in oxygen and hydrogen input velocities on concentration change at electrodes, current density in polymeric membrane and cell performance have been investigated in PEMFC. The simulations, made in COMSOL for numerical method, were presented with an emphasis on the physical and fundamental insight afforded by distributions of velocity vector, local current density, overpotential, oxygen and water concentrations. Using Golden Section Method, optimization of the change in the speed vector was made based on the numerical models for velocity values. Results showed that computational and numerical methods are in great harmony. The polarization curve, which is used as a measure of efficiency in cell performance, were supportive with results. The data show that the power density obtained for the optimum model is higher, with such a model performance of 92.87%. Compared to the currently used PEMFC, while hydrogen saving achieved between 4.2% and 7.1%, electrical efficiency increase were between 1% and 2.4%.

Design and analysis of a new heavy oil pump based on CFD

At present, submersible electric pump is the main oil production equipment in the world’s oil fields. Because the pump is tested with clean water as the medium when it leaves the factory, it can not be widely used in all oil fields. In this paper, a prototype submersible electric pump is improved and designed according to the actual working conditions, and a new heavy oil pump is obtained, which can be widely used in heavy oil Wells. The static pressure distribution and velocity vector distribution under the actual working conditions were simulated by CFD, and the feasibility was verified. It provides theoretical basis and technical guidance for solving the adverse effect of high viscosity produced liquid on pump, and has certain guiding significance for oilfield pump selection. So as to effectively save electricity and rationally exploit energy.

Influence of Rainfall Infiltration on Stability of Granite Residual Soil High Slope

The seepage evolution characteristics and stability change rule of granite residual soil inside the high cutting slope under the action of rainfall infiltration were studied. Based on the saturated-unsaturated seepage theory, the numerical simulation of the rainwater infiltration path inside the granite residual soil slope was carried out under the condition of rainwater infiltration. The evolution characteristics of the seepage field of the granite residual soil cutting high slope under the condition of rainfall infiltration were revealed, and the influence of the rainwater infiltration on the stability of the granite residual soil slope was mainly studied. The research results show that with the accumulation of rainfall infiltration, the pore water pressure of the granite residual soil slope increases continuously, and the pore water pressure of the soil below the platform increases the fastest. With the increase in elevation, the water content of the slope presents a wave crest distribution. In the early stage of rainfall, the seepage velocity vector distribution on the slope surface is relatively uniform. In the middle stage of rainfall, the seepage velocity vector is the most dense at the platform, and the rainwater migration rate is accelerated. In the later stage of rainfall, the infiltrated rainwater at the slope angle of the first-level slope spreads to the surrounding area. With the continuous rainfall, the slope stability safety factor gradually decreased unevenly, and after the rainfall stopped, it gradually increased with the rainwater infiltration.

Analysis of the Static Performance of a Cableless Aerostatic Guideway

To develop an innovative aerostatic guideway without cable drag force that can be widely applied to ultra-precision machining and measurement technology, it is necessary to analyze the static performance of the aerostatic guideway. The structural properties of the cableless aerostatic guideway, i.e., the bearing capacity and internal pressure distribution, directly affect the accuracy of processing and measurement. In this work, the relevant flow equations of the cableless aerostatic guideway are established by considering the unbalanced micro-scale air film. Moreover, the finite difference method is used to solve the calculation of the global analysis of air film at different positions. In addition, this work compares and analyzes the pressure and fluid velocity vector distributions in balanced and unbalanced states and investigates the effect of varying the thicknesses of the air film on static characteristics such as bearing capacity and stiffness. By comparing the balanced and unbalanced states under the same conditions, the obtained results show that in the unbalanced situation, the bearing capacity is lower by 11.69 percent and the stiffness is slightly higher (by 16.67 percent). Furthermore, the related experiments verify the predicted dependence of the bearing capacity on the thickness of the air film, and further demonstrate the feasibility of the proposed structure of the cableless aerostatic guideway. This work provides a technical reference for the design of a cableless aerostatic guideway.

Numerical Calculation Analysis and Characteristic Research on Windage Loss of Oil-Jet Lubricated Aviation Gear Pair

The VOF (volume of fluid) multiphase transient simulation model of the windage loss of the gear pair under oil-jet lubrication was carried out by using the dynamic mesh technology with the powerful parallel computing capabilities of the Super Cloud Computing Center. Firstly, a two-phase (oil-gas) turbulence numerical model was established in the process of oil-jet lubrication. The numerical simulation test was designed by orthogonal experiment. The influence of the oil-jet lubrication parameters and their interaction on the windage power loss was studied by means of variance analysis. The results showed that the influence of injection speed on the windage power loss was the largest and proportional, followed by injection temperature and injection pressure, and the latter two factors were inversely proportional. Then, the fitting calculation formula of windage loss related to each influencing factor is obtained based on the numerical simulation results. Furthermore, by observing the velocity vector distribution of the internal flow field of the gearbox with different time, the formation mechanism of windage loss is understood intuitively, and the measures to reduce windage loss are put forward. Finally, the mechanical and energy characteristics of the windage loss under different oil injection parameters are proposed, by analyzing and calculating the differential pressure force, viscous force, turbulent kinetic energy, and turbulent dissipation rate around the gear pair. This paper provides a method guidance for the calculation of windage power loss and efficiency of aviation gear pair under elastohydrodynamic lubrication in engineering application.

Experimental study on particles directed transport by an alternating travelling-wave electrostatic field

A continuous and controllable lunar regolith directed transport is crucial for the development of the 3D printing technology on the moon. The electrostatic method becomes a promising particle transport method for the extraterrestrial environment due to its irreplaceable advantages over other traditional methods. In this paper, particle directed transport by an alternating four-phase travelling-wave electrostatic field is experimentally investigated. Great efforts are made to carefully present the detailed particle movement trajectories and to deeply understand the particle control mechanism of the electrostatic method. It is found that not only the excitation frequency would affect the particles' transport direction, but also the voltage amplitude and geometric parameters would change the transport direction. For the present experiments, the backward transport of lunar regolith simulant can be realized at the low frequency conditions (2– 30 Hz). By post-processing of the recorded pictures, the detailed particle behaviors and the changes of the particles' velocity vector distribution with the electrostatic field propagation are obtained. The formation processes of both the forward and backward directed transports of particles are carefully demonstrated and discussed. Based on the obtained results, the most important part of particles, which plays a great role in the directed transport formation in an alternating electrostatic field, is determined and valuable investigation suggestion is proposed. Additionally, the impacts of the key influencing parameters on particle transport performance are obtained.

Heat Transfer Characteristic on Wing Pairs Vortex Generator using 3D Simulation of Computational Fluid Dynamic

Vortex generators are addition surface that can increase heat transfer area and change the fluid flow characteristics of the working fluid to increase heat transfer coefficient. The use of vortex generators produces longitudinal vortices that can increase the heat transfer performance because of the low pressure behind vortex generators. This investigation used delta winglet vortex generator that was combined with rectangular vortex generator to Reynold numbers ranging 6,000 to 10,000. The parameters of Nusselt number, friction factor, velocity vector and temperature distribution will be evaluated.

Comparison of the airflow characteristics and yarn properties between conventional and dual-feed-opening rotor spinning units

In order to explore the differences between conventional and dual-feed-opening rotor spinning units (RSUs), this work compares the airflow characteristics of two RSU models utilizing a computational fluid dynamics simulation model with the accuracy verified by airflow behavior observation and air pressure measurement. The effect of two different opening roller speeds on the airflow field distribution of a dual-feed-opening model is also investigated. In addition, the yarn properties of six pure and blended yarns corresponding to the two RSU models are evaluated. The results reveal that the distributions of airflow velocity vector and air pressure in the two RSU models show a strong similarity under the same boundary conditions. However, the dual-feed-opening model possesses a centrosymmetric and more balanced airflow field distribution compared to the conventional model. In addition, the dual-feed-opening yarns show a superior performance in comparison to the conventional yarns. Furthermore, for the dual-feed-opening model, there are equivalent contributions of two separated opening and fiber transmission systems to the airflow field distribution and yarn formation. Compared to the configuration with the same two opening roller speeds, the dual-feed-opening model configured with two different opening roller speeds obtains an improved blended yarn performance with having few effects on the airflow characteristics. This strength of the dual-feed-opening RSU could facilitate the production of blended and fancy yarns employing the fibers with diverse properties. This study could provide some guidelines for the manufacture of rotor-spun yarns and the future design of RSUs.

Application of PIV Technique in Teaching Experiment of Solitary Wave Flow Field Measurement

Particle Image Velocimetry (PIV), as an advanced experimental technique of fluid mechanics, has been widely used in many fields such as experimental fluid mechanics and practical engineering applications. The solitary wave is a kind of advanced wave that has only one peak or trough and only appears in shallow water. This kind of wave is quasi-particle, and its theory is used to study the water depth of wave breaking, which has a guiding effect on the design of offshore structures. To let students understand PIV technology visually, and at the same time, learn the transmission and evolution process of solitary waves, this paper puts forward a PIV measurement platform for the fine flow field of solitary waves, which measures the velocity vector distribution, velocity scalar distribution and vorticity distribution of the flow field in the transmission, climbing deformation and crushing process of the two-dimensional solitary wave. Through this experiment, students have a more direct impression of the fluid phenomenon of transmission and deformation of solidarity waves and understand the principle and use of PIV technology. This experiment deepens students’ understanding of the knowledge, stimulates students’ interest in learning, cultivates their practical ability, improves their innovation ability, and lays a good foundation for future scientific research and exploration.

Heat transfer enhancement and application of multiple stepped jet cooling in a vertical alloying furnace

Jet impingement cooling of vertical moving plate is widely employed in the energy and metallurgical industries. To improve heat transfer and the cooling of these plates in a vertical channel, an innovative stepwise jet cooling design model was proposed in the present study. To investigate the heat transfer enhancement mechanism of this multiple jet cooling, mixed convection in a three-dimensional model of a soaking zone and a jet impingement cooling tower was simulated using the commercial program ANSYS CFX. Navier–Stokes equations, which were solved using the SIMPLEC algorithm, enclosed by an RNG k-ε two-equation turbulence model were employed to calculate the fluid flow and heat transfer. Based on observations of the airflow velocity vector and temperature distribution, the critical equilibrium state for buoyancy and the inertia force was found to occur at a combined Reynolds number of 1.40 × 107. Based on this double-enhancement effect and the effect of different nozzle heights, a multiple stepped jet impingement cooling design that jet velocity decreased with its height increasing was applied to a vertical alloying furnace. The Nusselt number for stepwise jet cooling in the vertical alloying furnace was 111–118% higher than that for constant jet cooling. Therefore, the stepped jet cooling model offers greater energy conservation than does constant velocity when the total jet flow mass is held constant.

Experimental and Numerical Investigation of Phase Separation with Entrance Mixing

In this paper, experimental and numerical methods are used to investigate the separation of an oil / water mixture. An American Petroleum Institute (API) gravity-based separator was built to conduct the experimental studies. The numerical simulations were developed with the same geometry as the experimental setup. The effect of inlet velocity and the oil volume fraction on the separation process is investigated with the new numerical predictions. Validations of the simulation model show that the numerical predictions of the multiphase Volume of Fluid (VOF) model with the laminar viscosity model agree well with the experimental results. The results of oil volume fraction and velocity vector distribution in the separator showed that there was a mixing zone located at the entrance, which had a lower relative oil volume fraction and a higher velocity. The study of the inlet velocity effect on the mixing length of the entrance mixing zone shows that when the fluid in the separator is in the laminar range, the mixing length is less than 40% of the total separator length. However, when the inlet velocity was increased until the fluid in the separator reached the transient range, the mixing length occupied 90% of the total separator length.

Distribution regularity of downwash airflow under rotors of agricultural UAV for plant protection

In the plant protection spray operation of UAVs, the process of droplet from formation to sedimentation target is affected by airflow, easy to form uneven deposition. Accurately description of rotor downwash flow field, clarification of velocity vector distribution at different heights of the UAV rotor flow field, simulation of the flow field with high precision, which are the prerequisites for accurately analyzing the droplet deposition distribution in rotor downwash flow field. Based on CFD method, the detail of rotor flow field was numerically calculated. Taking LTH-100 single-rotor agricultural UAV as the research object, the three-dimensional solid model of UAV was established, the Reynolds average N-S equation was used as the control equation and the RNG κ-e as the turbulence model to simulate the flow field of UAV in hover and lateral wind conditions, the wind velocity distribution at different altitudes of rotor downwash flow field was studied. The simulation results of the hover state showed that: In the flow field, the peak velocity appears in a circular distribution below the distal axis of the rotor. With the decrease of height, the peak velocity distribution area showed a tendency to expand gradually after small shrinkage; When the distance from the rotor was not more than 1.5 m, the downwash flow field presented an axisymmetric distribution based on the rotor axis, and the variation rate of velocity in the peak velocity was basically the same, turbulence in downwash flow field made the flow field more complex when the distance from rotor was larger than 2.0 m. On this basis, the optimal flight altitude of UAV is 1.5 m. Wind velocity test of the flow field was carried out on a rotor test bench, wind velocities at four altitudes of 0.5 m, 1.0 m, 1.5 m and 2.0 m were measured to verify the coincidence between the simulated and measured values. The test results showed that: the relative error between the measured and simulated values at four measurement heights were between 0.382-0.524, and the overall average relative errors was 0.430, which verified the confidence level of simulated values for measured values. When the lateral wind velocity was 3 m/s, 4 m/s and 5 m/s, the simulation results showed that: The distribution trend of airflow velocity at the same altitude in lateral-wind flow field with different wind speeds was similar; When the lateral wind speed was 5 m/s, the coupling field formed by the lateral wind and rotor airflow cannot reach the height of 2 m below the rotor. The results of this study can provide more accurate environmental conditions for theoretical analysis of droplet deposition regularity in the flow field, and also provide methodological guidance for the related research on rotor flow field of multi-rotor UAV. Keywords: aviation plant protection, downwash flow field, distribution regularity, numerical simulation, single-rotor UAV DOI: 10.25165/j.ijabe.20211403.4036 Citation: Liu X, Zhang W, Fu H B, Fu X M, Qi L Q. Distribution regularity of downwash airflow under rotors of agricultural UAV for plant protection. Int J Agric & Biol Eng, 2021; 14(3): 46–57.

Constitutive model for solid-like, liquid-like, and gas-like phases of granular media and their numerical implementation

Granular media, a macroscopic amorphous matter composed of mesoscopic discrete particles, exhibits different behaviour characteristics (e.g., solid-, liquid-, and gas-like phases) depending on the volume fraction and loading conditions. Therefore, it poses a significant challenge to three-phase modelling and analysis. In this study, a description of multiple phases in granular media is realised by establishing the transition criteria and parameter conversion relations between different phases, using the already established theories of the elastic-plastic constitutive relation in solid mechanics, the viscoplastic constitutive relation in rheology, and the kinetic theory of granular flow. The new model realises the coexistence of different phases and the conversions therebetween. Smoothed discrete particle hydrodynamics are introduced to discretise the new theoretical model, and the correspondence between the smoothed and actual particles for different phases and discrete formulas under different models are described in detail. Two typical cases are used for numerical tests: the collapse of one side of a three-dimensional granular column and the collapse and flow of a granular column on an inclined surface. The calculated morphology of granular flow, distributions of velocity vectors, scaling law of spreading range under different height-width ratios, and the transient characteristics of particle spreading all accord well with the experimental results. Furthermore, quasi-static, slow, fast, and other phases of particle motions are well captured. Thus, we verify the feasibility of the new model and method for the multiple-phase simulation of granular media.

Heat dissipation performance of a heat pipe radiator with rectangular longitudinal fin under natural convection

To solve the cooling problem of electronic equipment with small heat dissipation area under high uneven power, this paper presents a natural convection radiator with L-shaped heat pipe and rectangular longitudinal fin module. The radiator has the advantages of compact structure, flexible layout, and didn’t occupy the side space due to the structural advantages. A numerical study was carried out, and the results are in good agreement with the experimental results. The thermal performance of the rectangular longitudinal fin module is also studied, the radiation heat loss of the fins accounts for about 25% of the total heat dissipation. The temperature and velocity vector distribution near the fin was analysed to research the influence of flow characteristics on the heat transfer of the fin. Additionally, the numerical results also show that the fin heat sink has an optimal fin height, which is 14mm.

Self-Adaptive Asymmetrical Artificial Potential Field Approach Dedicated to the Problem of Position Tracking by Nonholonomic UAVs in Windy Enivroments

Abstract Artificial potential fields (APFs) are a popular method of planning and controlling the path of robot movement, including unmanned aerial vehicles (UAVs). However, in the case of nonholonomic robots such as fixed-wing UAVs, the distribution of velocity vectors should be adapted to their limited manoeuvrability to ensure stable and precise position tracking. The previously proposed local asymmetrical potential field resolves this issue, but it is not effective in the case of windy environments, where the UAV is unable to maintain the desired position and drifts due to the wind drift effect. This is reflected in the growth of position error, which, similar to the steady-state error in the best case, is constant. To compensate for it, the asymmetrical potential field approach is modified by extending definitions of potential function gradient and velocity vector field (VVF) with elements based on the integral of position tracking error. In the case of wind drift, the value of this integral increases over time, and lengths and orientations of velocity vectors will also be changed. The work proves that redefining gradient and velocity vector as a function of position tracking error integrals allows for minimisation of the position tracking error caused by wind drift.

Computer Technologies of 3D Modeling by Combustion Processes to Create Effective Methods of Burning Solid Fuel and Reduce Harmful Dust and Gas Emissions into the Atmosphere

Using numerical methods, studies have been carried out to determine the effect of the introduction of the technology of two-stage combustion of high-ash Karaganda coal on the main characteristics of heat and mass transfer processes in the furnace of the BKZ-75 boiler at Shakhtinskaya TPP (Kazakhstan). Various regimes of supplying additional air into the combustion space, the volume of which varied from 0% (traditional basic version) to 30% of the total volume of air required for fuel combustion, have been investigated using 3D computer modeling methods. The performed computational experiments made it possible to obtain the distributions of the total velocity vector, temperature fields, concentration fields of carbon monoxide CO and nitrogen dioxide NO2 over the entire volume of the furnace and at the outlet from it. The introduction of the two-stage combustion technology made it possible to optimize the combustion of high-ash coal, since in this case there is an increase in the temperature in the torch core and a decrease in it at the outlet from the furnace, which has a significant effect on the chemical processes of the formation of combustion products. Based on the results obtained, it can be concluded that an increase in the percentage of air supplied through additional injectors to 18% leads to a decrease in the concentrations of carbon monoxide CO by about 36%, and nitrogen dioxide NO2 by 25% compared to the base case. A further increase in the volume of additional air leads to a deterioration in these indicators. The results obtained will make it possible to optimize the combustion of low-grade fuel in the furnace of the BKZ-75 boiler, increase the efficiency of fuel burnout, reduce harmful emissions into the atmosphere, and introduce a two-stage combustion technology at other coal-fired TPPs.

PIV test of the flow field of a centrifugal pump with four types of impeller blades

Abstract Flow fields for various impellers were measured using water and a two-phase liquid–solid mixture with a particle image velocimetry system in a centrifugal rotating frame in controlled conditions. After measuring absolute velocity vectors in impeller passages, the vectors were decomposed based on the triangle speed principle and the distribution of relative velocity vectors within the impeller was obtained. Then, the distribution of particles and their influence on the performance of different impellers were analyzed. The following conclusions were made from the comparison of relative velocity vector field: first, the wear on the outlet of blades can be mitigated effectively by reducing the outlet angle of impeller blades; second, the pump with a double-arc-shaped profile had a more uniform and stable flow field distribution and higher performance than that with a single-arc profile; and finally, the “jet–wake” structure can be improved significantly by using impellers with long and short blades, resulting in a remarkable reduction in energy loss and improvement in pump efficiency. We also found that solid particles were mainly distributed at the outlet of the impeller and volute wall, while the concentration distribution of large particles tended to match the pressure surface. This research can provide some theoretical guidance for the design and optimization of two-phase flow centrifugal pumps.

Effect of jet inflow angle on heat transportation in an impinging jet interfering with a Couette flow

The effect of the incoming angle of a jet that interferes with a Couette flow is studied using numerical simulations. When the jet flows against the direction of the Couette flow, the instantaneous vortex structure and heat transfer on the jet-impinging surface become complex and irregular. In contrast, when the jet flows in the same direction as the Couette flow, the instantaneous vortex structure has a strong and distinct periodicity about the main flow direction as a vortex street with a sine wave velocity fluctuation. This periodicity also affects the heat transfer on the jet-impinging surface. The Strouhal number calculated from these time periodicity increases with increasing jet angle. In the time-averaged flows and temperature fields, the Nusselt number exhibits a few characteristic distributions. The heat transfer concentrates around the jet impingement region at a negative jet angle whereas the area associated with significant heat transfer coefficient separates symmetrically about the flow in spanwise direction at a positive jet angle and the value of heat transfer coefficient on the center axis is low. Furthermore, a large and strong counter-rotating vortex pair is formed when the jet flows in the same direction as the Couette flow. As reported in our previous study, this pair vortex involves a main flow fluid and results in a characteristic Nusselt number distribution. Comparing the overall heat transfers on the jet-impinging surface, the lowest time-averaged heat transfer is obtained when the jet is orthogonal to the Couette main flow. Generally, the heat transfer over the surface is higher when the jet flows against the Couette flow than when the jet flows in the same direction as the Couette flow. However, since the pressure loss also increases drastically at the same time, it is found that the ratio of heat transfer over pressure loss increases with increase in jet angle. Considering the temperature and velocity vector distributions, and plots of turbulent heat flux, when the jet flows against the Couette main flow, the effect of jet impingement is dominant on heat transfer. However, when the jet flows in the same direction as the Couette main flow, most of the heat transfer is carried by the pair vortex. Although the contributing vortex type is different from similar previous studies conducted, the mechanism of generating this pair vortex is based on time-averaging the legs of the periodic vortex street.