Ducted Turbine Blade Optimization Using Numerical Simulation

This paper presents a combined blade element (BE), computational fluid dynamics (CFD) method for performance analysis and optimization of ducted turbines. The model is similar to standard blade element momentum theory, except that CFD replaces the momentum equation for determining the induction factors. This eliminates many assumptions used in applying the typical blade element momentum (BEM) theory to a turbine and provides much richer flow information. It is also required for ducted turbines, since there is no fundamental momentum theory model that includes the impact of the duct on the flow field. The simulations use an axi-symmetric domain, which is computationally efficient since only a thin wedge of the entire geometry needs to be represented. A simple algorithm was developed to determine the optimum rotor loading and tip speed ratio for a given duct geometry within a user-defined level of granularity. This paper also demonstrates that for certain ducts, a non-uniform loading over the disk can improve overall performance by limiting flow separation within the duct.