Hi everyone

I have created a very basic 3 blade rotor and hub which I wish to pass water over in FLUENT. The most important thing is that I can get the model to rotate so i can look at eth effects of swirl. I have set the model up so the x-axis passes right through the centre of the hub. A box defining the fluid volume is wrapped around the turbine.

Could someone give me some basic instructions as to how to get it to do this? I read a couple of tutorials that overcomplicated things for me a bit, they told me to change the motion type of my fluid to 'moving reference frame' where i defined my rotational velocity and staed which axis it was rotating around (x axis in my case). I also set my wall boundary (my rotor) to 'moving wall' of motion type 'rotational' and left the speed at 0.

Some guidance from someone 'in the know' would be really helpful

Cheers

D

Sounds like your doing fine so far. To set up a rotational problem, do the following:

1) Define -> Boundary Conditions -> (select fluid volume and specify rotation origin and axis. Also, motion type is Moving reference frame and specify rotation speed. 2) Define -> Solver -> Velocity formulation is relative 3) Define -> Boundary Conditions -> Select walls and specify "relative" movements (ie: with fluid volume specified as rotational, a "stationary wall" bounding the volume is rotating the same as the fluid volume. One can also select "moving wall" and specify movements "relative to the fluid volume". Hope this helps.

Yes but don't you need to set the wall at 0 rad/sec of rotation?

This was the best way I found - set the fluid to rotate at any rad/s then set the wall at 0 rad/s.

Phil

Glenn

Do you mean i have to set my fluid volume to a moving reference with reference speed, and for my wall I set it to a rotational motion with zero velocity and my axis origin/direction to 1?

I have done this but when I solve the unsteady state solution with the following settings:

Time-step size: 0.01 No of time steps: 40 max iterations per timestep: 5

I dont see a change in the velocity profile at the end of every timestep...is this because my settings are wrong ?

I haven't got experience with unsteady flow, sorry.

The above technique works with steady flow but maybe its a good idea to look at the Fluent tutorial for sliding meshes and see how they did it.

I assume you are using sliding meshes for unsteady flow because you should be (unless there's something I don't know). If not then do the tutorial I mentioned and you should make a better attempt.

TO CLARIFY: The way I have found to get this to work is to set: a) the fluid with rotational velocity (any). b) the wall (rotor) with rotational velocity but at 0 rad/s. This is then the same as having a moving rotor and stationary fluid like in real life.

I have tried this but im not really getting what im looking for in the post-processing.

Can i ask you a couple of questions...

When you set your boundary conditions for the rotor/fluid, did you set rotation origin AND direction to a value of '1' for each case? Did you use a moving reference frame for the rotor or a moving mesh?

When i look at the velocity vectors afterwards in my control volume, i dont really see any effects of swirl. How do I set up pathlines that run from my inlet boundary to my outlet boundary? I would alternatively look at particle tracks but i dont get the option of display where they are, im thinking this function is only for use with the unsteady solver

Let me know what you think, would be a great help

Cheers

D

For the rotor I set it to a moiving wall at 0 rad/s. For the fluid I used a moving reference frame, with a rotational velocity equal to the rad/s that the ACTUAL rotor should be moving at. There should be an interface or interior or something between them if I remember correctly.

For unsteady flow you should still be using sliding meshes rather than moving reference frames. Then it calculates the velocities at different locations as the rotor mesh physically moves fast the fluid. THIS WILL RESULT IN A VARIED VELOCITY AND SOLVE YOUR PROBLEM.

Sliding meshes are more complicated but they should give you far superior results.

Phil