Experimental study on steady flow ring to improve the flow of small axial flow fan

2 When Shandong Huaju Energy Co., Ltd. reduces the flow, the performance curve of the axial fan has a pressure drop zone, forming a saddle-shaped area. For a fan with a small change in operating conditions, the fan can be operated near a high efficiency point. However, for a fan with a large change in working conditions, if the fan is working at a non-designed operating point, the wind pressure and the air volume are unstable, which may cause stall and surge, cause mechanical vibration, and even damage the machine. The function of the steady flow ring is to slow down or eliminate the saddle characteristics of the axial flow fan and expand the safe working range of the fan. In this paper, the experimental research and analysis of the working characteristics of the steady flow ring are carried out.

The steady flow ring is to install an annular cascade on the inlet side of the Impeller near the impeller, as shown.

When the fan becomes more resistant due to the ventilation network, or because of the outflow phenomenon of the fan, the fan condition is forced to leave the design point and enter the unsteady condition under the low flow condition. As the flow rate decreases, the flow occurs at the top of the blade. Gradually moving to the roots, causing the flow to deteriorate and the gas pressure to drop drastically. Due to the pressure difference between the two sides of the blade, a part of the air flows from the high pressure side to the air inlet side (low pressure side) of the fan through the gap between the tip of the blade and the casing under the action of the pressure difference, and collides with the intake air flow. The impact loss severely destroys the intake conditions at the entrance. When the steady flow ring is used, the flow condition changes under variable working conditions. Since the steady flow ring and the casing form a certain space, which is not interfered by the main air flow, the vortex gas generated by the tip of the blade is in the centrifugal force and the working wheel. Under the combined action of the gas pressure behind, the annular passage flows into the steady flow area along the top of the blade. Under the joint action of the cascade and the steady flow ring on the steady flow ring, after a certain distance, it gradually becomes stable, and returns to the main air flow through the opening at the front end of the steady flow ring. In this way, the return gas is continuously pumped away to form a fixed loop flow, thereby preventing the development of the detachment zone in the working impeller, reducing the stall of the tip of the blade, avoiding the instability of the low flow condition, and expanding the efficient working range of the fan. It is helpful to eliminate the saddle area in terms of pressure characteristics. Since the inlet speed of the second-stage vane of the counter-rotating axial fan is the exit velocity of the first-stage vane, and the pressure at the secondary vane varies greatly, the tip de-flow is easily generated during operation, which interferes with the inlet air flow, which is It is possible to improve the inflow of the second stage of the cyclone before the steady flow ring is improved. The structure of the steady flow ring and the installation diagram are as shown.

1. Working impeller 2. Cascade (b) structure diagram fc) Installation instructions. Annular channel 4. Steady flow ring 5. Current collector 6. Dipole impeller 7. Structure principle of the impeller steady flow ring and installation. Determination of the characteristic parameters of the steady flow ring The main geometrical dimensions of the booklet6 steady flow are: steady flow ring Diameter, thickness and width, the bending angle and width of the small vanes, the number of small vanes, and the distance of the steady flow ring from the leading edge of the moving vane.

2.1 Steady flow ring diameter Dw and thickness 5bookmark7 Under the design conditions, the gas flow in the working wheel is ideal, and theoretically there should be no outflow. At this time, there should be no airflow in the steady flow ring. The diameter of the ring should be the same as the inner diameter of the casing without the stabilizer. Connect to page 33) M0.4; unloading to unloading pressure, one loading process is completed. The number of loadings is increased by 1. If the number of times is less than the number of loadings, return to the initial step M0.1, the number of times is equal to the number of loadings, and the loading ends automatically. At each step of the manual, the voice prompts the operator to perform the operation of the manual reversing valve to unload the load.

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