Conical diffusers are used in hundreds of engineering applications in various industries. Some of the operating conditions that they operate under cause swirling flow to enter the diffuser. It is generally well documented that the addition of swirl to the flow of a diffuser allows for greater divergence angles without wall separation, resulting in better overall performance of the diffuser and the machine it’s attached to. It is also known that as swirl strength is increased, the flow will eventually breakdown, resulting in internal flow recirculation and decreased diffuser performance. However, the relationship between the diffuser geometry and its performance at these higher swirl strengths has not been investigated in detail. This link between diffuser geometry, swirl, and performance is investigated using a hybrid RANS-LES based computational model. A series of simulations are performed with the computational model, varying the swirl strength and diffuser half angle ϕ. Overall, there was found to be little relationship between adjusting the diffuser geometry and diffuser performance at high swirl numbers.