## Fluids

#### Negative torque value

• abbas
Subscriber

Hello every one,

I tried to simulate the turbine and in a post CFX I noticed that the torque value is negative (-0.2 [Nm]). However, I looked at CFX tutorial and in "Chapter 17: multiphase flow in a mixing vessel" the torque value is -67.4 [N.m] and multiplying by -4 to find the torque required by all of the impeller blades. Why it is multiplying by -4 instead of 4?

Therefore, can I say that my simulation is correct and because I have 4 blades, total torque would be (-4*-0.2=0.8Nm) and  P=T*w so P=(0.8*3000=240 W) because otherwise P=-0.8*3000=-240W that means the turbine instead of producing power, it needs power.

Best regards

Abbas

• DrAmine
Ansys Employee

In the tutorial power is required to turn the impeller. The action of the fluids on the impeller bladed needs to have a reaction and this reaction requires that we add power to the system.

Action and Reaction principle.

• abbas
Subscriber

I am simulating the turbine and I think that the torque value should be positive for turbine however, I have a negative value. At first, I simulated the turbine with air and the torque value was positive. However, when I change it to the CO2, the torque value is negative.

How is that possible?

best regards

Abbas

• DrAmine
Ansys Employee

Force and Moments calculation are actions of fluids on bodies. From Body perspective as for an impeller one requires torque to be added.

Regarding your question: might be due to convergence, not consistent setup, (Axis of rotation,..). For turbine moment will provided by the Fluid and expelled to the outside.