Flow field simulation and establishment for mathematical models of flow area of spool valve with sloping U-shape notch machined by different methods

Precise function expression of the flow area for the sloping U-shape notch orifice versus the spool stroke was derived. The computational fluid dynamics was used to analyze the flow features of the sloping U-shape notch on the spool, such as mass flow rates, flow coefficients, effiux angles and steady state flow forces under different operating conditions. At last, the reliability of the mathematical model of the flow area for the sloping U-shape notch orifice on the spool was demonstrated by the comparison between the orifice area curve derived and the corresponding experimental data provided by the test. It is presented that the bottom arc of sloping U-shape notch （ABU） should not be omitted when it is required to accurately calculate the orifice area of ABU. Although the theoretical flow area of plain bottom sloping U-shape notch （PBU） is larger than that of ABU at the same opening, the simulated mass flow and experimental flow area of ABU are both larger than these of PBU at the same opening, while the simulated flow force of PBU is larger than that of ABU at the same opening. Therefore, it should be prior to adapt the ABU when designing the spool with proportional character.

Structure optimization and flow field simulation of plate type high speed on-off valve

There is a relatively complex flow state inside the high speed on-off valve,which often produces low pressure area and oil reflux in the high-speed opening and closing process of the spool,causing cavitation and vortex and other phenomena.These phenomena will affect the stability of the internal flow field of the plate valve and the flow characteristics of the high speed on-off valve.Aiming at the problems of small flow rate and instability of internal flow field,a new spool structure was designed.The flow field models of two-hole and three-hole plate spools with different openings were established,and software ANSYS Workbench was chosen to mesh the model.The standard k−εturbulence model was selected for numerical simulation using FLUENT software.The pressure distribution and velocity distribution under the same pressure and different opening degree were obtained.The structure and parameters of the optimization model were also obtained.The stability analysis of flow field under different pressure was carried out.The results demonstrate that the three-hole spool has a similar flow field change with the two-hole spool,but it does not create a low pressure zone,and the three-hole spool can work stably at 2 MPa or less.This method improves the appearance of low pressure area and oil backflow in the process of high speed opening and closing of spool.The stability of flow field and the flow rate of high speed switch valve are improved.Finally,the products designed in this paper are compared with existing hydraulic valve products.The results show that the three-hole plate type high speed on-off valve designed in this paper maintains the stability of the internal flow field under the condition of 200 Hz and large opening degree,and realizes the increase of flow rate.

Research on buffer structure and flow field simulation of swash plate plunger type hydraulic transformer

In order to solve the problem of excessive noise and vibration during the operation of the hydraulic transformer,an optimization method of valve plate damping hole structure is proposed to alleviate the phenomenon of pressure shock.Firstly,the mathematical model of oil pressure gradient in the plunger cavity is established,and the incremental equation of pressure change is derived.Secondly,a kind of buffering structure is proposed,the corresponding relationship between the pressure change and the envelopment angle of the buffering hole and the aperture size is determined by analyzing the oil pressure change curve in the plunger cavity.Finally,the flow field models with buffering holes are established,and the transient simulation of the pressure change process under the optimal solution is carried out with ANSYS software and the flow field pressure distribution contours are obtained.Through the analysis of simulation results,it is concluded that the optimal envelope angle of the three buffer holes ofA-T-B-Ais 5°,and the optimal aperture is 1.8 mm,1.6 mm,and 1.7 mm,respectively.The buffer hole can achieve a better-buffering effect in the range of variable pressure angle[0°,101°].The buffer hole structure can effectively alleviate the pressure shock and reduce the noise level,which lays a foundation for the design and theoretical research of hydraulic transformers.

Flow field fusion simulation method based on model features and its application in CRDM

The control rod drive mechanism(CRDM)is an essential part of the control and safety protection system of pressurized water reactors.Current CRDM simulations are mostly performed collectively using a single method,ignoring the influence of multiple motion units and the differences in various features among them,which strongly affect the efficiency and accuracy of the simulations.In this study,we constructed a flow field fusion simulation method based on model features by combining key motion unit analysis and various simulation methods and then applied the method to the CRDM simulation process.CRDM performs motion unit decomposition through the structural hierarchy of function-movement-action method,and the key meta-actions are identified as the nodes in the flow field simulation.We established a fused feature-based multimethod simulation process and processed the simulation methods and data according to the features of the fluid domain space and the structural complexity to obtain the fusion simulation results.Compared to traditional simulation methods and real measurements,the simulation method provides advantages in terms of simulation efficiency and accuracy.

NUMERICAL SIMULATION ANALYSIS OF EXTERNAL FLOW FIELD OF WAGON-SHAPED CAR AT THE MOMENT OF PASSING

In the course of studying on aerodynamic change and its effect on steering stability and controllability of an automobile in passing, because of multi interaction streams, it is difficult to use traditional methods, such as wind tunnel test and road test. If the passing process of an automobile is divided into many time segments, so as to avoid the use of moving mesh which takes large calculation resource and CPU processing time in calculating, the segments are simulated with computational fluid dynamics （CFD） method, then the approximate computational results about external flow field will be obtained. On the basis of the idea, the change of external flow field of wagon-shaped car at the moment of passing is simulated through solving three-dimensional, steady and uncompressible N-S equations with finite volume method. Numerical simulation analysis of side force coefficient, stream lines, body surface pressure distribution of wagon-shaped car are presented and a preliminary discussion of aerodynamic characteristics of correlative situations is obtained. Finally, the C3 -x/l curve of side force coefficient（C3） of car following relative distance （x/l） between cars is obtained. By comparison, the curve is coincident well with the experimental data, which shows creditability of numerical simulation methods presented.

The mesoscale numerical simulation of the flow field of the Hainan Island and the Leizhou Peninsula

The flow field over Hainan Island and the Leizhou Peninsula in summer and winter is discussed with three-dimensional mesoscale model developed in the University of Virginia and using the representative meteorological data of January and July.Simulation results indicate that the local weather characteristics over the Hainan Island are distinctly influenced by theWuzhi Mountain terrain. The cloudy or rainfall weather over the northeast of the Wuzhi Mountain occurs easily, under proper large-scale conditions of flow, temperature and humidity. while west wind prevails. The overcast or rainfall weather is often induced by strong convection in the afternoon over west of the Hainan Island under easterly prevailing wind.

Simulation and Analysis of Fiber Motion in Condensing Zone of Compact Spinning with Lattice Apron

To get fiber motion in condensing zone of compact spinning,velocity of this area is achieved by simulation,and then a bead-elastic rod fiber model is established.Based on simulation and dynamic analysis on this zone,governing equations are constructed and Runge-Kutta approach is used.Lastly,trajectories of fibers are calculated by specially designed Matlab procedure according to the principles mentioned above.Results show that fiber motions at different initial positions are different;X-axis velocity component makes fibers gathering on sides of suction slot;Y-axis airflow gets fibers gradually close and then stick to the surface of lattice apron.Fiber motions also reflect that the compact spinning process in condensing zone can be divided into three parts:fast convergence zone,adjustment convergence zone,and steady convergence zone.

Performance Prediction of an Optimized Centrifugal Pump with High Efficiency

The main structural parameters of the IR100-80-100A type chemical centrifugal pump have been optimized by means of an orthogonal test approach.The centrifugal pump has been modeled using the CFturbo software,and 16 sets of orthogonal-test schemes have been defined on the basis of 4 parameters,namely,the blade number,blade outlet angle,impeller outlet diameter,and impeller outlet width.Such analysis has been used to determine the influence of each index parameter on the pump working efficiency and identify a set of optimal combinations of such parameters.The internalflowfield in the centrifugal pump has been simulated by using the PumLinx software.These numerical results have shown that,compared with the prototype pump,the outlet pressure and shaft power of the optimized pump can be significantly reduced,and the pump working efficiency can be improved by 5.59%.In the present study,some arguments are also provided to demonstrate that,with respect to other optimization methods,the orthogonal test approach is more convenient,and requires less test times.

Experiment Study on the Exhaust-Gas Heat Exchanger for Small and Medium-Sized Marine Diesel Engine

This paper aims to design a special exchanger to recover the exhaust gas heat of marine diesel engines used in small and medium-sized fishing vessels,which can then be used to heat water up to 55°C–85°C for membrane desalination devices to produce fresh water.A new exhaust-gas heat exchanger of fins and tube,with a reinforced heat transfer tube section,unequal spacing fins,a mixing zone between the fin groups and four routes tube bundle,was designed.Numerical simulations were also used to provide reference information for structural design.Experiments were carried out for exhaust gas waste heat recovery from a marine diesel engine in an engine test bench utilizing the heat exchanger.The experimental results show that the difference between heat absorption by water and heat reduction of exhaust gas is less than 6.5%.After the water flow rate was adjusted,the exhaust gas waste heat recovery efficiency was higher than 70%,and the exhaust-gas heat exchanger’s outlet water temperature was 55°C–85°C at different engine loads.This means that the heat recovery from the exhaust gas of a marine diesel engine meets the requirement to drive a membrane desalination device to produce fresh water for fishers working in small and medium-sized fishing vessels.

NUMERICAL SIMULATION AND EXPERIMENTAL STUDY OF THE FLOW FIELD AROUND A CIRCULAR CYLINDRICAL ARTIFICIAL ISLAND UNDER THE ACTION OF WAVES AND VISCOUS CURRENT

Experimental study and theoretical research were described in the paper on the characteristics of the flow field around a vertical circular cylindrical artificial island under the . action of waves and viscous current. Flow field and hydrodynamic coefficientS of an artificial island under the action of waves and viscous current were computed and compared with those for the cases of pure viscous current and pure incident waves and those of measured resultS with good agreement.

Effects of Blade Number on Characteristics of Centrifugal Pumps

The blade number of impeller is an important design parameter of pumps, which affects the characteristics of pump heavily. At present, the investigation focuses mostly on the performance characteristics of axis flow pumps, the influence of blade number on inner flow filed and characteristics of centrifugal pump has not been understood completely. Therefore, the methods of numerical simulation and experimental verification are used to investigate the effects of blade number on flow field and characteristics of a centrifugal pump. The model pump has a design specific speed of 92.7 and an impeller with 5 blades. The blade number is varied to 4, 6, 7 with the casing and other geometric parameters keep constant. The inner flow fields and characteristics of the centrifugal pumps with different blade number are simulated and predicted in non-cavitation and cavitation conditions by using commercial code FLUENT. The impellers with different blade number are made by using rapid prototyping, and their characteristics are tested in an open loop. The comparison between prediction values and experimental results indicates that the prediction results are satisfied. The maximum discrepancy of prediction results for head, efficiency and required net positive suction head are 4.83%, 3.9% and 0.36 m, respectively. The flow analysis displays that blade number change has an important effect on the area of low pressure region behind the blade inlet and jet-wake structure in impellers. With the increase of blade number, the head of the model pumps increases too, the variable regulation of efficiency and cavitation characteristics are complicated, but there are optimum values of blade number for each one. The research results are helpful for hydraulic design of centrifugal pump.

Numerical Study on the Hydrodynamic Characteristics of Biofouled Full-Scale Net Cage

The effect of biofouling on the hydrodynamic characteristics of the net cage is of particular interest as biofouled nettings can significantly reduce flow of well-oxygenated water reaching the stocked fish. For computational efficiency, the porous-media fluid model is proposed to simulate flow through the biofouled plane net and full-scale net cage. The porous coefficients of the porous-media fluid model can be determined from the quadratic-function relationship between the hydrodynamic forces on a plane net and the flow velocity using the least squares method. In this study, drag forces on and flow fields around five plane nets with different levels of biofouling are calculated by use of the proposed model. The numerical results are compared with the experimental data of Swift et al.（2006） and the effectiveness of the numerical model is presented. On that basis, flow through full-scale net cages with the same level of biofouling as the tested plane nets are modeled. The flow fields inside and around biofouled net cages are analyzed and the drag force acting on a net cage is estimated by a control volume analysis method. According to the numerical results, empirical formulas of reduction in flow velocity and load on a net cage are derived as function of drag coefficient of the corresponding biofouled netting.

DBN-GABP model for estimation of aircraft wake vortex parameters using Lidar data

Aircraft wake turbulence is an inherent outcome of aircraft flight,presenting a substan-tial challenge to air traffic control,aviation safety and operational efficiency.Building upon data obtained from coherent Doppler Lidar detection,and combining Dynamic Bayesian Networks(DBN)with Genetic Algorithm-optimized Backpropagation Neural Networks(GA-BPNN),this paper proposes a model for the inversion of wake vortex parameters.During the wake vortex flow field simulation analysis,the wind and turbulent environment were initially superimposed onto the simulated wake velocity field.Subsequently,Lidar-detected echoes of the velocity field are simulated to obtain a data set similar to the actual situation for model training.In the case study validation,real measured data underwent preprocessing and were then input into the established model.This allowed us to construct the wake vortex characteristic parameter inversion model.The final results demonstrated that our model achieved parameter inversion with only minor errors.In a practical example,our model in this paper significantly reduced the mean square error of the inverted velocity field when compared to the traditional algorithm.This study holds significant promise for real-time monitoring of wake vortices at airports,and is proved a crucial step in developing wake vortex interval standards.

Shafting Alignment Based on Hydrodynamics Simulation Under Larger Rudder Corner Conditions

With the rudder angles getting larger and larger,the moment and force on propeller shafts,which are caused by complex flowing field,become more and more.They influence the shafting alignment greatly.Stress analysis of propeller shafts has been done under increasing rudder corner conditions with complex hydrodynamics simulation for a great domestic liquified natural gas(LNG) vessel,which is with dual propulsion systems.The improved three-moment equation is adopted in the process of dual propulsive shafting alignment.The calculated results show that the propeller hydrodynamic characteristics,which affect dual propulsive shafting alignment greatly,must be considered under large rudder angle conditions.Shafting accidents of Korean LNG vessels are interpreted reasonably.At the same time,salutary lessons and references are afforded to the marine multi-propulsion shafting alignment in the future.

Effect of methane-hydrogen mixtures on flow and combustion of coherent jets

Coherent jets are widely used in electric are furnace （EAF） steelmaking to increase the oxygen utilization and chemical reaction rates. However, the influence of fuel gas combustion on jet behavior is not fully understood yet. The flow and combustion characteristics of a coherent jet were thus investigated at steelmaking temperature using Fluent software, and a detailed chemical kinetic reaction mecha- nism was used in the combustion reaction model. The axial velocity and total temperature of the supersonic jet were measured via hot state experiments. The simulation results were compared with the experimental data and the empirical jet model proposed by Ito and Muchi and good consistency was obtained. The research results indicated that the potential core length of the coherent jet can be prolonged by optimizing the combustion effect of the fuel gas. Besides, the behavior of the supersonic jet in the subsonic section was also investigated, as it is an important factor for controlling the position of the oxygen lance. The investigation indicated that the attenuation of the coherent jet is more notable than that of the conventional jet in the subsonic section.