Study On Digital Design Method Of Air-blowing Seed-metering Device Based On Coupled CAD-DEM-CFD

In this paper, a kind of precision soybean metering device is treated as research object, in order to deal with the continuous gas media and analysis the gas motion information through solving equations on the basis of further research in domestic and foreign gas-solid coupling theories, as The Computational Fluid Dynamics (CFD); The soybean seeds are treated as discrete media, through Newton's second law each granule'velocity and trajectory can be obtained, as The Discrete Element Method (DEM), meanwhile the two way coupling effect of gas-solid is taken into consideration, on this foundation a two-dimensional design and analysis software of gas blown precision soybean metering device is developed based on CAD-DEM-CFD coupling technology. We can use this software to change the metering device's CAD model, seed model and simulation parameter to analysis the performances of different kinds of metering devices, and we can also compare the simulation results and the test results of the metering device's experiments, looking forward to establish a novel method to the research and the optimization of air-blowing seed-metering device. The main work and results of the paper are as follows:1) The physical and mechanical properties of three soybean seeds (GK, GX, G)have been tested, include moisture content, density, triaxial dimension, static and dynamic friction coefficient, stiffness coefficient, elastic modulus and coefficient of restitution, which static friction coefficient and coefficient of restitution are tested by homemade instruments.2) A visual gas blown precision soybean metering device has been designed and tested in the PSJ-type metering device test bed, the working process and performance of the air-blowing seed-metering device are able to be analyzed in the condition both with and without gas by the use of high speed video camera technology and BLASTER'S MOTION ANALYSIS SOFTWARE, include the seeding performance, speed and trajectory of the seed, dropping angles, the analysis shows:①In the condition without gas, when the rotational velocities(13.99r/min~33.01r/min) of the wheel increase, the rate of single seed decrease, the rate of empty increased, the double seed rate has no change law and values of the double seed rate are all less than 0.6%, The velocity and displacement of the seed that is far from the wheel is very small, basically at the original location or at rest. The velocity of the seed that is in towing layer and dropping exit increase while the velocity of the wheel increase. When the rotational velocity of the wheel is stable, the dropping angles of the 3 kinds of soybean seeds have little difference, but when the rotational velocities increase, they increase. After dropping the trajectory of the seed is a downwards-opening parabola and when the wheel's velocities increase, the parabola's opening increase. It has almost the same discipline when seeding the 3 kinds of soybean seeds.②When filling gas and the blowing direction has a 60°angle between horizon, if the wheel's velocity is unchanged, the single seed rate increase, the empty rate decrease, while the double-seed rate has no change law and values of the double-seed rate are small according to the increase of wind pressure(0.4kPa~2.0kPa), especially when the rotation velocity is 26.67r/min and the wind pressure is 1.2kPa, the seeding performance is better than no-gas condition. If the wind pressure is unchanged, the single seed rate increase, the empty rate decrease, while the double-seed rate has no change law and values of the double-seed rate are small according to the increase of wheel's velocity, the same tendency with no-gas condition. The velocity and displacement of the seed that is far from the wheel is very small, basically at the original location or at rest. The velocity of the seed that is in towing layer increase while the velocity of the wheel increase and decrease while the wind pressure increase. If the wind pressure is unchanged, the dropping angle increase according to the increase of wheel'speed, the same tendency with no-gas condition. If the rotation speed is unchanged, the dropping angles decrease according to the increase of wind pressure. After dropping the trajectory of the seed is a downwards-opening parabola and if the wind pressure is unchanged, the parabola's opening increase according to the increase of wheel's velocity, if the wheel's velocity is unchanged, the parabola's opening decrease according to the increase of wind pressure. It has almost the same discipline when seeding the 3 kinds of soybean seeds.③When filling gas and the blowing direction has a 90°angle between horizon, if the wheel has a velocity of 26.67r/min, the seeding(GK) single seed rate increase, the empty rate decrease, while the double-seed rate has no change law and values of the double-seed rate are less than or equal to 1.3%, the result is just in contrast with the way of incline blown seeding. After dropping the trajectory of the seed is parabola which the opening has no regular change according to the change of wind pressure, except this, it has the same discipline with the 60°angle.3) Based on deep researching of two-dimensional structured and unstructured grid's generation method, improvements of two grid generation have been established, as the TM-Wei improvement and spring balance system based method, these two methods are able to improve the body-fitted, orthogonal nature and the density of the gird quality.4) Based on deep researching DEM, CFD and the coupling method of DEM-CFD, an improved algorithm—SIMPLERC has been established according to collocated grid and finite volume method. This algorithm has absorbed the advantages of SIMPLER algorithm and overcome the defective of SIMPLER algorithm in pressure correction, at the same time it has absorbed the core idea of SIMPLER algorithm, as omitting the item in velocity correction equation, so as to reduce the burden directly from rate of pressure, accelerate the speed of solving in velocity field and avoid the'inconsistent'mistake happened in SIMPLER algorithm too.5) Based on redevelopment of CAD software, grid generation module, gas-solid coupling calculation module has been developed and integrated into the two-dimensional DEM software developed by the research group. OpenGL has also been used to improve the dynamic display of simulation result. On the foundation of this, CAD-DEM-CFD coupling analysis software has been developed. By instances of the software testing and validation, including grid generation module, gas-solid coupling calculation module etc, it demonstrated the two-dimensional design and analysis software introduced in this paper is able to work out the gas and gas-solid coupling calculation.6) According to the physical and mechanical parameters of three soybean seeds tested in experiment, six kinds of soybean seed analysis model have been established using round and oval-shaped particle model, the working processes and performances of the gas blown precision soybean metering device both in gas and no-gas condition have been simulated by the software introduced in this paper, comparison between simulation and experimental results shows:①When the simulation without gas, in the condition of 2 particle models(round and oval-shaped) and 4 rotation speeds(13.99r/min,20.33r/min,26.67r/min,33.01r/min), each of the seeding single seed rate is 100%, each of the empty rate and double seed rate is 0, it has great difference with the test bed result and the reason needs further study.②When the simulation without gas, the velocity and displacement of the seed which is far from the wheel is very small, basically at the original location or at rest, basically the same with the test. In the condition of 2 particle models and 4 rotation speeds, the velocity of the seed(GK) which is in towing layer and dropping exit increase according to the increase of wheel's velocity, the same changing tendency with the test. When using the round-shaped particle model and the wheel's velocity is 13.99r/min, the test error of dropping angle between simulation and test is 1.01%. When using oval-shaped model, the error is 1.49%, increase while the wheel's velocity increase, the dropping angles error of two seed models increase both, but the changing tendency are the same with test. After dropping, the trajectory of seeds and seeds in towing layer has the same changing tendency with test.③When filling gas and the blowing direction has a 90°angle between horizon, in the condition of 2 particle models(round and oval-shaped), 3 rotation speeds(13.99r/min,26.67r/min,39.35r/min) and 3 wind pressures(0.4kPa,1.2kPa,2.0kPa), the seeding performances are familiar with the simulation without gas and has a large difference between test results. The velocity and displacement of the seed that is far from the wheel is very small, basically at the original location or at rest, basically the same with the test. The velocity of the seed in towing layer is larger than the test result, the velocity of the seed in dropping exit is smaller than the test result, but the whole changing tendency is the same with the test result. When the wind pressure is unchanged, the dropping angle (GK) increase according to the increase of wheel's velocity, it has the same changing tendency with test result and no-gas condition. When the rotation speed is unchanged, the dropping angle's error between simulation and test increase, but they have the same changing tendency. After dropping the trajectory of the seed is a downwards-opening parabola, when the wind pressure is unchanged, the parabola's opening increase according to the increase of wheel's velocity, it has the same changing tendency with the test result, but smaller than no-gas condition. When the rotation speed is unchanged, after dropping the trajectory of the seed (GK) is a parabola which its opening decreases according to the increase of wind pressure, it has the same changing tendency with test result. Although the trajectory of seed in towing layer in simulation has error when compared with test result, they have the same changing tendency.④When filling gas and the blowing direction has a 90°angle between horizon, in the condition of 2 particle models (round and oval-shaped), 3 rotation speeds(13.99r/min,26.67r/min,39.35r/min) and 3 wind pressures(0.4kPa,1.2kPa,2.0kPa), the seeding performance of GK seed are the same with incline blown seeding and no-gas seeding. The velocity and displacement of the seed that is far from the wheel is very small, basically at the original location or at rest, basically the same with other test. The velocity of the seed (GK) that is in towing layer and dropping exit has the same changing result with test result. After dropping the trajectory of the seed (GK) is a parabola which its error between simulation and test increase according to the increase of wind pressure, but they have the same changing tendency. The trajectory of seed in towing layer has the same changing tendency with test result. When the wind pressure is 0.4kPa and using oval-shaped particle model, the dropping angle of GK seed has an error of 4.28% compared with test result, and 8.92% when using round-shaped model, but when the wind pressure increase, the errors of the two seed model both increase, and oval-shaped model has a larger number than round one.⑤When using the stiffness coefficient and friction coefficient in the range of measured values, it has little effect to the simulation result.In summary we can see, although there is error between simulation and test result, except the performance of seeding, the velocity, trajectory and seeding angle all have the same changing tendency with test result, so it initially proved that using DEM-CFD coupling method and the software introduced in this paper to research gas blown precision soybean metering device is feasible.