Numerical Simulation and Experiment of Airflow Field of Cleaning Room under Action of Conical Fan

In order to solve the unmatched problem between airflow field generated by traditional cylindrical fan of vibrating screening transverse axial flow combined harvester and the distribution of separated mixture on the screen surface, a conical centrifugal cleaning fan was designed and its working principle was described, which can improve the quality of cleaning by optimization of cross wind. According to the actual structure, a three-dimensional model of the cleaning device was established and a numerical simulation of the flow field distribution of cleaning room under the action of cylindrical cleaning fan and conical cleaning fan with different taper blades was conducted by using the CFDesign software. The results showed that the transverse wind was obviously produced by the conical cleaning fan along with the direction of screen width. The speed of transverse wind was increased with the increase of taper value of the fan blade, but the speed of longitudinal wind along the length of the vibrating screen was decreased with the taper value of the fan blade. The area of low wind speed zone at middle position of the vibrating screen also became larger, which was detrimental to the cleaning of mixture. The best velocity distribution of the cleaning room was appeared when the taper value of the fan blade was 3.5°. The experiment of the flow field under different types of cleaning fans was conducted by using the distributing-point method. The results showed that the speed of transverse wind at the corner of the entrance of the vibrating screen can reach 2.68 m/s, and the speed of transverse wind at middle position of vibrating screen can reach 2.07 m/s, which was obviously bigger than the value produced by the cylindrical cleaning fan and beneficial to the distribution of the separated mixture along with the screen width. At the end of the screen length, the speed of the longitudinal wind produced by the conical cleaning fan was 0.78 m/s, which was smaller than the longitudinal speed and helped to reduce the loss of grain cleaning. The distribution experiment was also conducted for the action of cylindrical cleaning fan and the conical cleaning fan. The results showed that the weight of mixture in main falling area made up 59.21% of the weight of all mixture under the action of conical fan and the number of cylindrical fan was 69.74%. The offset location where the maximum weight mixture appeared under the action of conical fan was adjusted to 166 mm along the width direction compared with cylindrical fan, and the weight dropped by about 27.66%. It was verified that the conical fan can apply the transverse wind to blow away the mixture gathered in the inlet of the vibrating screen, which was conducive to improve the cleaning quality. Field experiment was conducted and the results showed that the performance indexes of combine harvester furnished with conical fan, including loss rate, impurity rate and crushing rate were obviously better than those stipulated in occupation standards. It can reduce the impurity rate index of combine harvester obviously, contrasting the conical fan with cylindrical fan. © 2019, Chinese Society of Agricultural Machinery. All right reserved.