3.3.2. Field Test Verification of Centrifugal Fan Air Flow

The method of spot placement was adopted [23], according to the structural parameters of the three-duct centrifugal fan. The point at the lowest position on the volute area of the centrifugal fan and 50 mm away from the left inlet were taken as the origin points, the radial direction of seed-conveying auger was chosen as the *X* axis and the vertical direction of the sieve surface was chosen as the *Y* axis. The air velocity measurement space and the distribution of measuring points are shown in Figure 7.

**Figure 7.** Air velocity measurement site and measurement points distribution. (**a**) Air velocity measurement. (**b**) Measurement points distribution.

The air velocity of each measuring point measured by AR856 digital anemometer is shown in Table 2. The sensitivity and features of the digital anemometer are as follows: airflow speed measurement ranged from 0.3 m·s−<sup>1</sup> to 45.0 m·s−1, the measurement error was ±3% and the resolution ratio was 0.001 m·s−1. Additionally, 3 planes of 42, 103 and 160 mm in the Y direction corresponded to 3 central measuring planes of air ducts, and each measuring plane was arranged with 5 measuring points at 125, 275, 425, 575 and 725 mm in the X direction. By comparing the results of numerical simulation and experimental study on airflow field, it can be seen that the airflow velocity distribution of each outlet was consistent. The horizontal airflows both at the upper and lower outlets were more uniform, which were conducive to the pre-cleaning of threshed materials and the discharge of impurities in the tail. The middle outlet presented the law of high airflow velocity in the middle and low airflow on both sides, which was conducive to the blowing and stratification of the threshed mixture during the falling process. In addition, the air velocity values were slightly different, the reason for which lied in that the numerical simulation process was completed without considering the gas compression and gas viscosity, and assuming that the whole flow channel was closed. However, in practical work, the cleaning air flow would be attenuated due to the existence of material groups [24].


