Torque definition
 

I am now using CFX 10.0 to evaluate the power coefficient for a vertical layout marine turbine. The turbine consists of three separated blades which are immersed in water and rotating in a constant speed. The whole computational domain is separated into two zones for ease of designating boundary condition: (1). Stationary outer zone. This outer zone almost covers the whole domain except the circular region occupied by the rotating blades. Inflow, outflow and symmetric boundary conditions are included in this region; (2). Rotating inner zone. It is this circular zone that includes the blades (no-slip wall boundary condition has been employed on the blades surface). On the interface, GGI scheme (by default) is used to synchronize the zones.

I used the "cel" expressions to obtain the torque value at the blades. What confusing me so much is that by looking at the transient curve the torque is sometime positive and will change to negative after a while. In my humble opinion, a "positive" torque means it helps the turbine running in the same direction as it rotate at that moment. Likewise, a "negative" torque means the overall effect of the fluid is retarding the rotating of the turbine, which is harmful. Am I right on this point? If not, is there anyone here who can help me on it? It is quite important for me to understand it.

Re: Torque definition
 

Hi,

The torque returned is referenced to a right hand coordinate system, the direction of rotation is not considered.

Glenn Horrocks

Re: Torque definition
 

Hi, Glenn Could you please put it more clear? what is the exact meaning of "positive" or "negative" torque?

Thanks Yali

Re: Torque definition
 

This is high school mechanics.

http://en.wikipedia.org/wiki/Torque

Glenn Horrocks

i'm doing the simulation for vertical axis wind turbine using steady state and mrf function setting..
my torque from fluent result sometime positive and sometime negative..why is that happen? is there anything wrong with my simulation setup?

Either it is real or your simulation has a big error. Could be either.