Rotor CFD Simulation
 

Hi,

I am trying to model a Rotor in CFD (star-ccm+). My current model is massively under predicting lift. I am not entirely sure if this is because of the initial conditions or because the mesh is not fine enough.

I have set up a moving reference frame for the rotor to which I have specified a rotational velocity. I am using the k-epsilon turbulence model for which I have calculated turbulence dissipation and kinetic energy. The Reynolds number of my rotor is based upon the rotor diameter and tip velocity and was found to be 65 million. I am also modelling it as steady state.

I am expecting around 6000N of lift force but at the moment I am only achieving 1100N. I am aware that it is difficult to accurately model a Rotor but I am sure a lot of people have achieved it. I wanted some advice on what I could do to better simulate this.

Thanks

Kishen

Have you looked at the post pro? Have the blades stalled?

Yeah I've checked it and the blades haven't stalled. Also in reality my rotor isn't powered It is acting like a wind turbine. by applying a rotation to it I'm adding energy into the system rather than taking energy out. maybe I could apply a 1DOF to it or something. I have a feeling it's my model set up and initial conditions that are the problem.

I've created a much finer mesh and the load increased to 2000N. but I'm afraid that is the limit of my resources. The uni clusters won't be able to run anything better.

Ps: I've heard of TotalSim. you guys do some cool stuff :)

Thanks Kishen.

The relative velocity of the blade and fluid can be super critical to predicting the right forces. Have you done a speed sweep? You may only have to be 1% your blade or fluid speed to make up your deficit.

Actually now that you mention it, I have been thinking about the relative velocities and this may be where I am going wrong.

What do you mean by a speed sweep? I have assigned a rotation of 250rpm to the rotor. The free stream velocity is 30m/s. Btw I am using Star-ccm+.

Best Wishes

Kishen

You can sweep either speed and it should have a similar effect.

I would tend to sweep the RPM. Maybe +/- 10%.
You then can get a power curve. It may be that only a small different in RPM will get you to your 6000N. When compared blades/turbines/propellors this is often the best way to compare different options.

Good luck.

Hi Kishen, some questions

What are the reference values of lift you are using? Theory, Wind Tunnel?

I manage years ago to obtain decent results (for lift) in 3 dimensional rotors for various angle of attack. I obtained these results in StarCCM+ with both Dynamic Meshing and MRF methods. Some comments about my experience:

- First of all. I made sure I could obtain an almost perfect cl/cd curve for the 2D airfoil.
- I made sure that my reference values was reliable and extrapolable to my case.
- Those things may sound kind of obvious but I last longer in solve those than in obtain a good 3D simulation.

Good luck