© 2018 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.The scope of this study is to develop a numerical framework for design of a multi-megawatt vertical axis wind turbine (VAWT) that yields low cost of energy. Determination of the optimum design requires a delicate balance between maximizing the energy produced from the turbine and minimizing the amount of material used to build the turbine. Thus, a coupled analysis that combines both aerodynamics and structural mechanics of the turbine is needed to discover this delicate balance. State of the art simulation tools are used to simulate the coupled aerodynamic and structural response of the turbine in the time domain. These tools include HAWC2 and BECAS codes developed at the Denmark Technical University, Department of Wind Energy (DTU Wind Energy). These simulation tools are interfaced with MATLAB numerical optimization routines to find the shape and internal structural makeup of the turbine rotor that gives the optimum cost based on a defined objective function and constraints. Two optimum designs were obtained using the present optimization framework; one design was obtained by coupling the aerodynamic and structural variables employing a single objective function while the other design was obtained by sequentially varying the aerodynamic and structural variables by employing two separate objective functions. Final results show that the coupled approach results in lower cost of energy, while the sequential approach gives higher annual energy production at slightly higher cost.