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Modeling 2d Savonius rotor

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Old   September 17, 2008, 07:23
Default Modeling 2d Savonius rotor
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Hi all,

I need help in modeling simple 2d Savonius rotor. I'm new user to Fluent so I would be grateful if someone could answer my questions.

The construction in my simulation - 2 semicircles connected at one edge (without any offset). Something like that: ( ) <- wall

Boundries are far away from construction (had problem with reversed flow).

Fluid - air (outdoor). Velocity (form velocity_inlet) 10 m/s in X axis, 0 in Y axis. Triangle mesh used.

I used Inviscid, Spalart-Allmaras and k-epsilon model with standard variables. Discretization for pressure - PRESTO!, all other - Secend Order Upwind. SIMPLE

What is my main problem? Simulation never reaches convergence (all criteria on e-6 <- read in one tutorial)... Even after 10 000 iterations.

So my question is: a) what is the best model and discretization settings for simulation like this? (accurate) b) what must I do to obtain criteria? or should I change criteria? (if so, to what number?) c) when I simulate with k-epsilon model I get something like that: turbulent viscosity limited to viscosity ratio of 1.000000e+020 in 20 cells (I changed limit range and still get that error)

All above I made with static walls as rotor. And one last thing - very important. How to make walls spin (rotation axis in center) when wind flow is simulated? Need to change something back in Gambit model?

Please F1.

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Old   October 15, 2008, 18:10
Default Re: Modeling 2d Savonius rotor
Cesar Villarreal
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I have done this kind of unsteady simulations, and by the way, it must be done as unsteady simulation.

Here you can find some videos

About the "turbulent viscosity limited to viscosity ratio of 1.000000e+020 in 20 cells", i had the same problem but it was solved using - k-E Realizable - checking the scale of the model if it was ok (it wasnt several times) menu: GRID - SCALE - If you want to compute the Cp results, you must add some reference values. Try the menu: REPORT - REFERENCE VALUES Area: swept area of the rotor Depth: As it is a 2D analysis you must select a value for the haight of the rotor Lenght: radius of the rotor Velocity: velocity of the wind (in your case it is 10m/s)

For the rotation, you must create two diffrerent surfaces to be meshed. One is the fluid (it must be big, as 10 times the rotor diameter in each direction in order to avoid wind concentration effects), and the other is the rotor, typically it is a circle with the blades in it. After you mesh that surfaces you must define as a "interface" the boundaries of the two surfaces that are touching (the exterior circle of the rotor, and the interior circle of the fluid).

Then you can select the velocity of the rotor on the menu: DEFINE - BOUNDARY CONDITIONS

Hope it helps

César Villarreal
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Old   August 20, 2010, 10:56
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how exactly do you define a "interface" of this two surfaces?
im new at this...also making savonius wind turbine and have huge problems making a model in fluent that rotates
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Old   August 23, 2010, 01:06
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the interfaces have to be disconnected (2 surfaces superposed). One belong to the stator volume, the other belongs to the rotor volume
In memory of my friend Hervé: CFD engineer & freerider
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