HELLO. I've simulate a rotating blade using MRF method. The right hand rule was applied when determine the rotational axis. In reality, the blade rotate clockwise (Y = -1), so that in fluent I've put Y = 1 for rotational axis of rotating fluid. The problem is I got a negative lift. The blade orientation is checked for many time and its in correct orientation...

Could anybody out there help me on this problem?

Thank you

Hold on. Is your fan stationary with respect to the fluid? If your fluid rotates, and the fan is stationary with respect to the fluid, and all other walls are moving with an absolute velocity of 0, then your fan and fluid both rotate at Y = 1. Is your set up different? Are you assuming the fluid has 0 rpm, and the fan moves?

Actually, I've used the same way as your suggestion. But the problem is why the vertical force (force perpendicular to blade/disk plane) indicates negative sign when the flow rotate at Y = 1 and when Y = -1, it turn to positive sign.

Based on the theoretical analysis using blade element theory, this vertical force should be positive sign...Can you explain why? or I've doing a wrong simulation?

Thank You

Did you look at the flow features to make sure they were going in the direction you expected? Remember, viewing "relative" velocities is going to be relative to the fan blade... so if you're spinning around Y=1, then you want your relative velocity vectors to spin around Y=-1.

When you assign a rotation to the "fluid" boundary condition, you're not spinning the fluid, you're spinning the computational domain of the fluid... and having a relative velocity of 0 for the fan blades, this means that the fan is spinning in the direction of the computational domain. So, if you want your fan blades to spin at Y=1, then set the rotation of the "fluid" to Y=1. I think this might be where you're getting hung up...

Hope this helps, and goodluck, Jason

Erm, this seems more better...Thank You for your suggestion and help.i'm really appreciate it.