How to calculate torque,very urgent
 

Hi everyone:

I am now simulating Francis turbine model.I have known that Torque = Fu*r,Where Fu represents the circumferential component of the (integral) forces along the turbine blades (friction and pressure). But I don't know how to get the Fu which is perpendicular to r(radius). Could anybody help me? Thanks ahead.

Mangnan

Re: How to calculate torque,very urgent
 

Is this a difficult problem?

Re: How to calculate torque,very urgent
 

Hi Mangnan,

It shouldn't be difficult, but I have not tried it as such. Have you had a look at the turbo machinery wizard in CFX-Post? That might have some things to help you.

Regards, Glenn

Re: How to calculate torque,very urgent
 

If you are using CFX-5, just use the "Torque" function in the function calculator.

-RK

Re: How to calculate torque,very urgent
 

Hello roadkill:

Thanks for your advice.The "Torque" function in the function calculator can only calculate the 2D plane torque.My problem is how to calculate the torque of the whole domain.Could you give me other information?

Mangnan

Re: How to calculate torque,very urgent
 

The "Torque" function calculates torque about an axis and is not restricted to a 2D plane. What gave you that idea?

-RK

Re: How to calculate torque,very urgent
 

Hi roadkill: I got that idea from the following article which I copied from CFX-Post document.

torque

Returns the torque on a 2-D locator about the specified axis. The forcecalculated during evaluation of the torque function has the same behaviour as the force function (see force (p. 106)). You can select the Fluid(s) to perform your calculation with, the result returned in thetorque on the location due to the selected Fluid(s).

To include the required momentum flow data in your Results file to calculate torques, you should set the the option Output EquationFlows to ON on the Solver Control Form in CFX-Build (please see Output Equation Flows (p. 1168 in CFX-Build: Chapter 10) for more information).

• Function: torque, Location: Plane1, Axis: Global Z, Fluid: .All Fluids. This example calculates the torque on Plane1 about the z-axis due to all fluids in the domain.

torque [<Fluid>.]torque_<Axis>()@<Location> An error is raised if the location specified is not 2-D.See torque (p. 110 in CFX-Post) for a function description.

Re: How to calculate torque,very urgent
 

Hi Mangnan,

As roadkill indicated, the Torque function in Post is not limited to a 2D plane, although it does require a 2D surface. However, that is exactly what you need.

All forces will balance at the boundaries and what you are really interested in is not the torque in the volume, but rather the torque on the blades. Alternatively, to evaluate the net contribution of the turbine, you can take the difference between the torque at the inlet and outlet of your system. Evaluating the torque at an open boundary essentially gives you the flux of angular momentum through that boundary.

Best regards, Robin

Re: How to calculate torque,very urgent
 

Hi Robin:

Thanks for your advices. I am simulating a Francis Turbine model.I use the rotation coordinate frame which is not a inertial frame.And there must be some pseudo-forces added (in the steady rotating case they are Coriolis and Centripetal forces). So I want to get zero net torque on the impeller.From your post message I got a problem. Is there any connection between the angular momentum and the zero net torque? Hope you return. Best regards, Mangnan

Re: How to calculate torque,very urgent
 

Mangnan,

The net sum of all the torques at all the boundaries will be zero. As in the physical system, the only contribution of torque occurs at the walls. The rotating frame of reference does not do any work on the fluid. The difference between the torque at the inlet vs. the outlet will be exactly equal to the sum of the torque contribution at walls.

Regards, Robin

How to calculate torque,unsolved
 

Hi Robin: All your message is very useful. I am sure what I have post in the last message is not detail enough.Could you open the following links and read about it. http://www.cfd-online.com/Forum/cfx.cgi?read=7321 http://www.cfd-online.com/Forum/cfx.cgi?read=7322 http://www.cfd-online.com/Forum/cfx.cgi?read=7329

So my purpose is to get a constant rotation speed in short.

Best regards, Mangnan

Torque calculation in CFX
 

Dear All,
Can anybody help me to find torque on a aircraft wing at a specified point in CFX POST.

Actually i want to find Coefficient of Moment(Cm) at a point on a wing,I have the formula to find it by knowing the value of Torque along three mutually perpendicular directions, Please help me soon



Thanks and Regards
Manjunatha S