"Axial Fan" analyze the reasons for the performance of p-qv curves saddle shape is a fan at different flow rates, fluid enters the airfoil angle of attack changes, causing the airfoil lift coefficient of variation. p-qv performance curves a, b, c, d, e for the operating point, d is the design conditions on the curve, then the fluid flow lines along the blade height distribution, maximum efficiency; when the flow is greater than the design value, leaves top exports generated at the reflux fluid to the wheel deflection, the loss increases, total pressure drop, reduced efficiency; when the flow is reduced in qvc < qv < qvd, angle of attack increases, the lift coefficient increases, the total pressure increased slightly when qv = qvc, the highest total pressure; when the flow is reduced again,when in qvb < qv < qvc, in the back of the blade to produce leaf layer was separated, formed off the flow resistance increases, the total pressure drop, when in qv = qvb minimum total pressure; and when qv < qvb, total pressure starts to rise, it is very small because the energy flow along the blade height deviations greater formation of secondary flow, the fluid flows out from the tip of the blade root to improve energy returned again, so that the entire pressure, until qv = 0, the total pressure reaches a maximum.