Ducted Wind Turbine Optimization

Abstract

This study presents a numerical optimization of a ducted wind turbine (DWT) to maximize power output. The cross section of the duct was an Eppler 423 airfoil, which is a cambered airfoil with a high lift coefficient (CL). The rotor was modeled as an actuator disk, and the Reynolds-averaged Navier–Stokes (RANS) k–ε model was used to simulate the flow. The optimization determined the optimal placement and angle for the duct relative to the rotor disk, as well as the optimal coefficient of thrust for the rotor. It was determined that the optimal coefficient of thrust is similar to an open rotor in spite of the fact that the local flow velocity is modified by the duct. The optimal angle of attack of the duct was much larger than the separation angle of attack of the airfoil in a freestream. Large angles of attack did not induce separation on the duct because the expansion caused by the rotor disk helped keep the flow attached. For the same rotor area, the power output of the largest DWT was 66% greater than an open rotor. For the same total cross-sectional area of the entire device, the DWT also outperformed an open rotor, exceeding Betz's limit by a small margin.

Ducted wind turbine optimization and sensitivity to rotor position

“…(Jamieson, 2009) also used a similar momentum analysis and derived the same value of 8/9 for optimal loading on the rotor and noted that it should be independent of duct design. (Werle and Presz, 2008) in another study based on 1-D momentum analysis found that the maximum attainable power from a DWT is determined by shroud force coefficient, C s = F s /T , where F s is the axial force on the duct (shroud) and T is the thrust of the rotor. (Hjort and Larsen, 2014) used an axisymmetric CFD model with an actuator disc modeling the wind turbine for a multi-element DWT.…”

“…(Aranake and Duraisamy, 2017) also utilized an axisymmetric Reynoldsaveraged Navier-Stokes (RANS) solver with an actuator disc model for the turbine to optimize the airfoils used for the duct cross section and blades and verified the result with 3-D simulations. (Venters et al, 2017) investigated the optimal design of a DWT using the same approach (i.e., using a RANS solver and actuator disc model). The design variables investigated were the rotor loading, the angle of attack of the duct cross section, the rotor gap, and the axial position of the rotor.…”

“…However, the results for effect of the rotor gap and axial position of rotor were not conclusive. This paper improves on the work of (Venters et al, 2017) with a more accurate CFD model, a direct optimization technique, and a wider range of design variables. One of the goals of this study is to continue the investigation of (Venters et al, 2017) into how the objective of the optimization changes the optimal design.…”

A New Approach Toward Power Output Enhancement Using Multirotor Systems With Shrouded Wind Turbines

“…Diffuser-augmented wind turbines (DAWTs) have been developed to increase the rotor performance of a conventional wind turbine [15][16][17][18][19][20][21][22][23][24][25][26][27][28]. The aerodynamics of brimmed diffuser-augmented wind turbines (B-DAWT, named "wind-lens turbine," (WLT) is used henceforth) has been investigated [24][25][26][27][28].…”

Experimental validation of a ducted wind turbine design strategy

“…Second, moving the rotor to a location aft of the throat (Fig. 3b) provides an increased power output for a given duct geometry (Visser, 2016). Most rotor designs seek to exploit the high velocity at the throat of the duct; however, the presence of the rotor modifies the velocity where it is stationed, and more power can be extracted from the design, for a given duct, by moving the rotor aft.…”