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To reduce the variability of cleaning performance caused by uneven airflow distribution, the theory of fan design and the characteristic parameters of threshed rice outputs were used to develop a prototype of cleaning fan. Computational Fluid Dynamics (CFD) was employed to simulate the air distribution inside the fan and the airflow speed distribution at the fan outlet. Response surface methodology (RSM) with three factors and three levels was employed to optimise fan impeller geometry parameters, this included blade inlet mounting angle, blade curvature and blade inlet curvature. According to the least squares analysis of RSM, the influence of each factor on the airflow distribution at each sub-outlet was estimated. The optimal values of blade inlet mounting angle, blade curvature and blade inlet curvature were 107°, 190 mm and 135 mm, respectively. The uniformity of the outlet airflow distribution of the optimised fan was clearly improved. The number of eddy currents in the flow passage were reduced, and the transporting performance of optimised fan was improved. The maximum pressure at 5% blade height away from the central plate was reduced by 37.78%, which indicates that the service life of the cleaning fan could be increased.

To predict the cleaning performance of rice combine harvesters, numerical simulations of the air-and-screen cleaning unit using coupled computational fluid dynamics and discrete element method were used to study the gas–solid two-phase flow behaviour of the threshed mixture. The calculation methods investigated the centroid velocities of three particle classes: grains, stems and light impurities, and the degree of dispersion of all particles. It was found that the centroid velocity of the grain particles was the least affected by different working conditions at the same cleaning time, and the movement of grain particles did not reflect the varying cleaning performances. The degree of dispersion of all particles at each working condition reached a relatively stable state with cleaning times 1.3 s–2.0 s, and this period was taken as the analysis period. Cleaning performance experiments were carried out on the developed air-and-screen cleaning test-bed under corresponding conditions. The mathematical relationships between the centroid velocity of each particle class, the degrees of dispersion of all particles and the cleaning performance were studied. After comparison and analysis, it was concluded that the prediction model between the degree of dispersion of all particles and the cleaning loss ratio had an error less than 9.4%. The centroid velocity of short stem particles in X direction and the grain impurity ratio had an error less than 11.7%. This simulation method therefore had relatively good accuracy and can be used make up for the shortcomings caused by the seasonality of field testing and also save costs in designing cleaning units.

As the grain-cleaning process in a combine harvester relies on pneumatic separation of the grain and chaff, the aerodynamic forces created by the airflow have a large impact on the cleaning performance. Therefore, to optimise a multi-duct cleaning device in a rice combine harvester, First, the equivalent resistances for the different fan ducts were quantified with a resistance model of fluidised grain and an airflow resistance model for the cleaning sieve. Perforated plates with different opening ratios were designed to simulate working loads. A computational fluid dynamics (CFD) model was validated by comparing simulation results with hot-wire anemometer measurements. The effects of working loads on airflow velocity and volume distribution at the ducts, and total pressure distribution inside the fan were studied in simulation and experiments. After integration of the designed multi-duct fan into the cleaning system, airflow measurements inside the cleaning shoe were made and cleaning performance tests were carried out on a test bench. The ideal airflow velocity within the cleaning shoe was investigated by correlating airflow velocities at different measuring points and analysing the cleaning performance. An evaluation of this multi-duct cleaning system in the field showed large improvements in terms of the grain sieve losses ratio and grain impurity ratio compared to a combine harvester with the single-duct cleaning system. The corresponding grain sieve loss decreased from 2.46% to 0.08%, while the grain impurity ratio decreased from 4.78% to 0.511%. ispartof: BIOSYSTEMS ENGINEERING vol:190 pages:25-40 status: published

The influences of throughput and operating parameters on internal airflow and cleaning performance for the air-and-screen cleaning unit were investigated. The throughput experiment showed that, the airflow velocities above the vibrating screen decreased by 1.3–15.5% for every 1.0 kg s−1 increase of throughput and which below the vibrating screen decreased by 2.7–8.1%. As a result, the cleaning performance has declined. Then, the airflow velocity measurement and cleaning performance tests were taken under 4.0 kg s−1 throughput with single factor experiment in which fan speed, airflow deflector angle and sieve opening were as factors. And, the Computed Fluid Dynamic (CFD) numerical simulations were carried out to analyze the movement trend of internal airflow as an auxiliary analysis method. The following viewpoints were obtained, the fan speed has a large effect on cleaning performance by affecting the overall airflow velocities in the cleaning unit. And, the airflow velocities above the vibrating screen increased from 0.2 m s−1 to 0.4 m s−1 for every 150 r min−1 increase of fan speed, which below the vibrating screen increased from 0.4 m s−1 to 1.1 m s−1; The highest airflow velocities area above the vibrating screen moved forward to the central position in the longitudinal direction as the airflow deflector angle increased; With the reduction for each 4 mm of chaffer opening, the airflow velocities above the vibrating screen increased by 0.2–0.4 m s−1. At last, making mathematical relations between each operating parameter and the cleaning performance, and proposing the method of adjusting the single operating parameter under rated condition according to the throughput. They provide a basis for real-time automatic adjustment of the operating parameters in the air-and-screen cleaning unit.

In order to improve the cleaning quality and efficiency of a rice combine harvester, a cleaning system comprising a cen-trifugal fan and four outlet ducts was developed. Three multi-duct centrifugal fans with the same rotor but different up-per outlet positions and volute walls were studied numerically and experimentally to evaluate the impact of the upper outlet on the inner flow field distribution of the fan. Computational fluid dynamics (CFD) was used to analyze the veloc-ity profiles, flow rate, internal velocity, and pressure of the centrifugal fan. Experiments were performed using hot-wire anemometers to measure the velocity at the four outlets of the fan to validate the simulations. CFD simulations were used to perform detailed flow visualization, velocity profile and flow rate estimation, and internal velocity field and pressure field analysis. Special attention was paid to the effect of the upper outlet on the inner flow field distribution and on achieving a balanced airflow division between the four outlets. It was observed that the internal field distribu-tion and the mass flow rate division between the four outlets can be greatly influenced by the upper outlet position. The optimal structure of the multi-duct centrifugal fan was obtained for the rice combine.

In this work, a numerical study of the gas-solid flow in an air-and-screen cleaning shoe is carried out by use of the combined Discrete Element Method (DEM) and Computational Fluid Dynamics (CFD) model where the motion of discrete particles phase is obtained by DEM which applies EDEM software and the flow of continuum fluid by the traditional CFD which solves the Navier-Stokes equations at a computational cell scale. The effect of inlet airflow velocity is studied and analyzed in terms of grains and short straws' longitudinal velocity and vertical height, and cleaning loss. Simulation results showed that, in a certain range, different inlet airflow velocity only affects the magnitude of airflow velocity in the cleaning shoe, but does not affect the distribution regularity of flow field in the cleaning shoe. With the inlet airflow velocity increase, vibrating screen processing power improves, while grain losses increase. Grains mainly concentrate on 4-12 sections under the screen surface. Comparison of numerical simulation results with experiments has demonstrated adequate agreement. It showed that numerical simulation of material motion on vibrating screen of air-and-screen cleaning device based on CFD-DEM is feasible. The results provide a basis for improving the design on air-and-screen cleaning device of combine harvester.