ON INFLOW DISTORTION DECAY IN THE BLADE CASCADES

Flow distortions in front of turbomachines can lead to additional mechanical and thermal loading of the blades, and may influence the operational stability of the engine and the lifetime of its parts. In current design practice the impact of inflow distortions is accounted by safety margins, which are often conservative. Therefore the knowledge of real limits helps to increase operational flexibility and recommended service intervals. The distortions inside turbomachines have a wide spectrum of sizes and frequencies depending on their origin. Some of them were extensively studied in the recent years, including wakes interaction with blades, hot streaks propagation in turbines, and some other phenomenon. However, there are areas of practical importance, which are not yet covered by available studies. One of this distortion types is investigated in the present work. These are distortions of a size, comparable with the inlet guide vane pitch of a compressor or the nozzle guide vane pitch of a turbine, both steady in the absolute frame of reference. Such distortions in front of a compressor can be caused, for example, by fouling of the intake, or by some structures purposely installed inside the intake. The distortions in front of the expansion turbine can be caused by structures. Main purpose of the study is to provide an understanding of the decay mechanism of distortions considered. For this purpose the numerical and theoretical analysis of inflow distortion propagation inside the set of stationary and rotating blades cascades is performed. These cascades represent the mid-section of a typical multistage compressor and turbine. The analysis showed that the decay mechanism is different for temperature distortions and total pressure distortions, and that the latter one is stronger affected by the blading configuration.