气压式玉米精量播种机均匀低损配气机构设计与试验

针对气压式玉米精量播种机配气系统存在各行气流分配不均、气压损失及气流速度损耗较大的问题，基于加压导管定常不可压缩湍流模型损失理论，探明了气流损失及分配不均的原因。采用等效仿真简化模型，通过 CFD （computational fluid dynamic，CFD）仿真4种不同气路结构中气压损失及气流速度损耗，分析得出最佳气流分配方式；通过正交试验，得出分配器最优结构形式；确定了配气机构连接段最优母线形状为内凹-外凸组合型曲线，连接段长度以及组合曲线内凹外凸水平长度比是2个影响配气机构性能的关键参数，连接段长度值越大，节锥角越小，且组合曲线内凹外凸水平长度比在3附近时气压损失及速度损耗最小。与常用配气机构进行对比试验，试验结果表明，常用配气机构的气压损失在30%以上，而该低损配气机构能够将气压损失减小到10%以内，气流速度损耗不显著，各行压力一致性变异系数在4%以内。

Design and experiment of balance and low-loss air allotter in air pressure maize precision planter

Abstract: Air pressure maize precision planter is suitable for high-speed planting which needs to work under ensured and stable air pressure. However, significant problems exist in the air supply system such as high pressure loss and velocity loss, serious heating and uneven pressure and flow supply. Air supply system seriously affects the working stability of planter. Reasonable allocation of the air flow is one of the most important factors to air pressure maize precision planter. The importance of the allotter in the air supply system cannot be ignored. To solve the problems of high loss in air pressure and velocity, this paper supplies a new type of air allotter which contains one inlet, four outlets and a connection segment with gradient combined curve. According to the theory of steady incompressible flow in pressure conduits, the phenomena of high air loss and uneven flow distribution can be interpreted. The pressure and velocity loss are usually insignificant in comparison with the loss due to pipe friction when the length of pipe or channel is very long. But if the length of pipe or channel is very short, these so-called minor losses may actually be major losses. As long as the air pressure and velocity at the inlet and outlet of the air allotter are known, pressure and velocity loss can be analyzed easily. Therefore, 4 types of air allotters with different airflow directions are designed by analyzing the relationship between loss and structure in turbulent flow. Because of the difficulty in measuring the velocity in real condition, computational fluid dynamics (CFD) is applied to obtain ideal data which can be simulated by software such as Gambit, Fluent and Tecplot. In order to find the optimal pathway and direction of the air flow, 4 different types of air allotters were simulated. The result indicated that the paralleled axis of the inlet and the outlet was the best way. In order to find the ideal parameter of the allotter, the simulation experiment was carried out further. Compared with all factor experiments, orthogonal experiment is better and faster to select the optimal structure. So, 3 factors including the shape of connection segment of the allotter, the inlet-outlet diameter ratio and the center distance between inlet and outlet were chosen to test and find out the most significant factors. The simulation result of the range analysis and variance analysis showed that the inlet-outlet diameter ratio and the distance between inlet and outlet''s axis in the allotter should be as small as possible within the permitted range. Besides, the results also indicated that the shape of the curve had significant influence on the pressure loss, whereas there was few influence on velocity loss. Structures such as sudden expansion and bends could lead to more pressure and velocity loss which should be avoided in the design of allotters. Thus, the optimal structure of the air allotter consisted of coaxial inlet and outlet and a concave-convex combined curve. Through the dimension driven in SolidWorks, the shape of the concave-convex combined curve could be ensured. An optimal structure with related parameters was estimated finally through the simulation of different types of allotters with different shapes of concave-convex combined curve. The experiment and simulation results indicated that the length of the connection segment of the allotter and the ratio of concave curve to outward curve were 2 significant parameters. Field experiment was conducted with 2 different types of allotters installed on air pressure maize precision planter to validate the result of simulation. The pressure and velocity of the balance and low-loss air allotter were measured by air flow meter KA33 made by KANOMAX. Results proved that the performance of the balance and low-loss air allotter was better than that of other widely used allotters. Comparative experiment showed that the rate of pressure loss of the designed allotter was kept within 10% under different working pressures, while the loss of another allotter was over 30%. The pressure consistency variation coefficient of 4-row seed metering device was less than 4%. The research shows that the allotter cannot be ignored in the research of maize precision planter. Appropriate structure of air allotter can significantly reduce energy consumption and ensure uniform air pressure when the planter works.