Abstract. Diffuser Augmented Wind Turbines (DAWTs) are promising regarding energy costs by increasing the energy output without changing the rotor size. The project focuses on numeric investigations of the Generalized Actuator Disc (GAD)theory. This study aims to develop a new diffuser augmented wind turbine by following existing diffuser design concepts which are diffuser with single-element and diffuser with multi-elements. It consists of two main parts: the design of diffuser and the design of rotor. The numeric investigations for diffuser design were carried out on the Star-CCM+. Rotor geometries, which were designed with an edited version of Glauert Optimization Method, concluded the evaluation of the optimized diffuser designs by comparing the performance increase. A steady-BEM code, which was adopted to model diffuser augmented turbines, was used in the process. It is found that all the design options result in significant performance increases in comparison to the bare rotor. However, the single-element diffuser is the optimum design, among others, due to its high-performance increase with less design complexity.