[rupsmundra]

Dear sir, I am doing analysis of a engine cooling fan in ANSYS. TO complete boundary conditions I need to apply forces on fan. So can you tell me how to analytically calculate forces in fan at any point? I know total area of fan, pressure, and mass flow rate. Also to calculate force analytically on fan surface is
( force = press. * area ) correct approach ? Or is there any other method ?

[ebaines]

Trying to determine the aerodynamic forces on the fan blades can be quite complicated, and given the chaotic nature of the air flow should probably be measured experimentally retaher than simply modelled. But in general the forces would consist of (1) air pressure on the front surface of the fan blades, which varies as the square of the velocity of the point on the fan blade times the sine of the angle of incidence of the fan blade into the wind; (2) a corresponding vacuum effect on the back side of the fan blade, which for modelling purposes you could perhaps assume is equal and opposite to (1); and (3) the dynamic force of the rotation and centripedal acceleration of the fan blade. You say you know the total pressure generated by the fan, but due to effect (1) above that pressure is not evenly distributed over the fan blade but rather varies with the square of the distance from the center of rotation (since v^2 = w^2 r^2) and the angle of incidence of the blade. The dynamic forces are a bit easier to model: [math] d \vec F = d(m \vec a), where - note that this includes both radial and tengential acceleration, llowing you to calculate forces as the fan accelerates, decelerates, or runs at a steady speed.