Complex aero-engine intake ducts and dynamic distortion

For many embedded and partially-embedded engine systems, the complexity of the flow field associated with convoluted intakes presents an area of notable research challenges. The convolution of the intake duct introduces additional flow distortion and unsteadiness which must be understood and quantified when designing the turbo machinery components. The aim of the current work is to investigate the capabilities of modern computational methods for these types of complex flows, to study the unsteady characteristics of the flow field and to explore the use of proper orthogonal decomposition methods to understand the nature of the unsteady flow distortion. The unsteady flow field for a range of S-duct configurations has been simulated and assessed using a delayed detached eddy simulation method. The configurations encompass the effects of Mach number, Reynolds number and S-duct centre line offset distance. Analysis of the conventional distortion criteria highlights the main sensitivities to the S-duct configuration and quantifies the unsteady range of these parameters. These results illustrate the strongly dynamic nature of the flow field for both total pressure as well as swirl based distortion. Analysis of the unsteady flow field shows signature regions of unsteadiness which are postulated to be related to the classical secondary flows as well as to the stream wise flow separation. The more aggressive duct, with a larger centre line offset, shows some similar characteristics, but the unsteadiness is more broadband and the distinction between these two mechanisms is less clear. A proper orthogonal decomposition of the total pressure field at the duct exit identifies the underpinning flow modes which are associated with the overall total pressure unsteadiness distributions. For the more aggressive duct, the flow modes are notably different and highlight the reduced demarcation between the unsteady flow field mechanisms