Based on the engineering application,the angle range of rectifying airflow unit attaching diffusion tank is from 2.5° to 7.5°.In the range of average inlet velocity of 25.0 m/s to 55.0 m/s of diffusion tank,numerical simulations of diffusion tank were done.The results of numerical simulations of diffusion tank are shown as follows:① In cases of the inlet velocity range from 25.0 m/s to 55.0 m/s,and the angle range of rectifying airflow unit from 2.5° to 7.5°,the average value of pressure losses decreases to the minimum when the angle is 4.5°.② In cases of the inlet velocity of 35.0 m/s,the pressure loss of diffusion tank decreases to the minimum when the angle of rectifying airflow unit is 5.5°.③ As far as there are different angles of rectifying airflow unit,pressure loss increases gradually along with the addition of inlet velocity.