Abstract. Large-scale unsteady graphical processor unit (GPU) based calculations are used to study the flow in realistic transonic fan geometries and shown to produce useful insights into the complex unsteady flow physics in systems of practical engineering relevance. Inlet flow distortion produces complex flow patterns which can significantly reduce stall margin. In order to design efficient, well targeted fan stabilizing technologies, it is essential to gain understanding into which specific features of distorted flow patterns are important in causing instability.In this paper, the use of large-scale, high-fidelity 3D unsteady Reynolds-Averaged Navier Stokes (URANS) calculations with sliding planes is shown to allow the isolation of a wide range of inlet distortion features and a high throughput of calculations is achieved. This facilitates a comprehensive investigation into stall margin loss and the observation of complex instability processes, which is in turn used to support the development of specialized design solutions. The costs of simulations and turnaround times are given. The potential for mixed fidelity simulations, in particular mixing one-dimensional low order models and large eddy type simulations to generate inlet conditions, is discussed. 7544Figure 1: Aerospace airframe and propulsion technology under development.