TOPT - Free RPM for Kaplan Turbine
Tomáš Krejča
In CFD we generally have a problem when we encounter something that is supposed to move on its "free will". One of these problems is an unknown rotation speed of a turbomachinery rotor. Common practice is that the user prescribes flow boundary conditions for one specific case or does a full spectrum of operational conditions including rotation speed. But what if he knows an input aerodynamic or shaft torque and wants to obtain a stable rotation speed (with no acceleration)?
One way is to use the TOPT algorithm where you look for a minimum of optimization function prescribed as (target_torque - calculated_torque)^2.
First I calculated a torque for 187 RPM. Then I set this torque to our optimization function and ran TOPT with RPMs as a parameter.
After several runs, the RPMs started to converge around the value of 187 as they should. The DIRECT algorithm was still trying other options, but got to the minimum of our function relatively quickly.