Low-order modeling of ocean-current turbine blades with dynamic trailing edge flaps in the presence of external disturbances

Ocean current Turbines (OCTs) operating in arrays experience unsteady inflow

conditions due to their interactions with the wake emanating from upstream

turbines. The complex unsteady flow phenomena resulting from the interaction

between the oncoming wake and the moving rotors can lead to fluctuating forces and

loads on the blades of downstream devices, deteriorating their performance and

eventually causing fatigue and failure. We present a novel approach for tailoring the

performance of OCT blades in unsteady inflow conditions using a dynamic

trailing-edge flap (TEF) mechanism. We combine unsteady hydrodynamic theory with

high-fidelity numerical simulations to develop a low-order hydrodynamic model to

predict the unsteady flow phenomena and the resulting loads on OCT blade sections

with dynamic TEFs in the presence of external flow disturbances (EFD). The blade is

modeled as a bound-vortex distribution with time-varying camber at the flap location.

The flowfield comprising of the EFDs and the vorticity shed from the blade is

represented using free discrete vortices. Unsteady flow conditions result in the

formation and shedding of leading-edge vortices (LEVs), the intensity and timing of

which have a significant role in determining the trailing edge vortex shedding pattern

and the load fluctuations. The model is capable of predicting the LEV shedding pattern

of the blade using the concept of leading-edge suction parameter (LESP) and

computing the associated loads. High-fidelity unsteady RANS simulations are used to

validate the model. Parametric studies are conducted to identify and quantify the

relationship between the EFD parameters and the hydrodynamic quantities of the blade

such as lift, drag, pitching moment and vortex shedding pattern. Finally, the low-order

modeling framework is used to formulate strategies to mitigate the destructive effects of

the EFDs through active TEF deflection by tailoring the flowfield and loads of the blade.