Momemtum (DMST) model is not converging at high TSR for VAWTs
 

Dear all,
I'm facing convergence issue for solving the axis induction factor using double multiple streamtube model at high tip speed ratio (TSR), when the rotor solidity is a bit high, for vertical axis wind turbines. The solution is iterative.

It is agreed that, momentum momentum models in general, have some convergence issues at high rotor solidities and/or high TSRs. However, I heard that, one can introduce some damping effect to get the solution converge, or utilize some low pass filter for that purpose.


For example, the axial inducting factor is obtained from (iteratively):

a = 1/(1-F)
where F is a function of the airfoil characteristics and directly related to tangential and normal force coefficients.
https://mail.google.com/mail/u/0?ui=...xY1Fc&disp=emb
Moreover a = Va/Vinf (the ratio of induced speed at the blade to the free stream velocity), initial guess a = 1, i.e. Va=Vinf.


Cheers