Novel method for evaluating intake unsteady flow distortion

Closer integration between the airframe and the propulsion system is expected for future aircraft to reduce fuel consumption, emissions, weight and drag. The use of embedded or partially embedded propulsion systems will require the use of complex intakes. However, this can result in unsteady flow distortion which can adversely affect the propulsion system efficiency and stability. Relative to conventional measurement systems, time-resolved Particle Image Velocimetry provides sufficient spatial and temporal resolution to enable the development of new methods to assess unsteady flow distortion. This work proposes a novel analysis approach to assess the unsteady flow distortion. For an S-duct configuration, the method was successfully used to evaluate the unsteady flow distortion in terms of idealized incidence angle perturbations. This example showed peaks up to ± 30° incidence and a duration equivalent to the passing time of 3 blades. The introduction of a non-uniform total pressure profile at the S-duct inlet increased the probability of peak distortion events with higher magnitude. The method provides an estimate of the likelihood, magnitude and duration of distortion events and is a new way to evaluate flow distortion that could induce instabilities for the propulsion system.