Intake Distortion has long been researched in compressor design. Both in civil and military applications, many effects of aircraft design and operation will result in distorted inflow. This in turn affects performance, aerodynamic stability and in some cases even structural integrity. The resulting flow field is fully three-dimensional and often unsteady. Additionally, coupling of the behaviour of multiple components is frequently reported, e.g., the phenomenon of upstream attenuation. The application of URANS for large domains, spanning several components, is thus desirable, but often not feasible in early design stages. An approach is to reduce complexity via sets of scalar distortion parameters and empirical sensitivity correlations, which in turn is no longer adequate for the consistently shrinking margins in design. This inadequacy is further exacerbated by the ambiguity of describing vastly different distortion patterns by scalar distortion parameters. To reduce numerical effort in comparison to URANS simulations, the range of Compressors-in-Parallel (CIP) models has been established based on Meanline and Throughflow calculations. The main goal of this paper is to provide an overview of the literature and state-of-the-art methods to describe various forms of intake distortions and their effects on compressor performance. Therefore, compressor performance descriptors and aerodynamic compressor stability will be evaluated. Subsequently, this paper will describe intake distortions by characterising them via their geometrical and flow behaviour features. Both distortion parameters and the range of Compressors-in-Parallel (CIP) models are outlined. Based on the assumptions of CIP models, the effect of specific distortion types onto compressor aerodynamic stability are discussed. As a result of this literary review, certain assumptions of the aforementioned evaluation practices point to further research needs. For example, CIP-models have already been criticised for the assumption of both distorted and undistorted compressor operating on the same pressure rise characteristic. In the past, some advancements have been made by phenomenologically describing effects of specific intake distortion patterns on certain compressor rigs or complete engines. To further advance this line of research, a systematic approach to assess distorted characteristics is needed. At best, this would go hand-in-hand with validating whether that system is applicable to a range of different compressor architectures. Another challenge lies in the definition of the stability margin in Throughflow calculations. Up until now, these typically rely on stability criteria for stall inception via modal perturbations, but not for spike-type stall. This implies that including a correlation, between either radial gapping or rotor critical incidence, and the probability of spike-type stall inception, could significantly increase the reliability of evaluating distortion-tolerant designs via CIP-models. To summarise, this review presents several motivations for developing Compressors-in-Parallel models to higher standards of fidelity.     «

Intake Distortion has long been researched in compressor design. Both in civil and military applications, many effects of aircraft design and operation will result in distorted inflow. This in turn affects performance, aerodynamic stability and in some cases even structural integrity. The resulting flow field is fully three-dimensional and often unsteady. Additionally, coupling of the behaviour of multiple components is frequently reported, e.g., the phenomenon of upstream attenuation. The appli...     »