Study of the Impact of Multi-Row Interaction on Flutter Analysis for a Representative LPT Geometry

Acoustic reflections and multiple blade-row effects have an impact on aeroelastic behavior, which can change the aerodynamic damping by a significant amount. However, conventional flutter analyses neglect these effects as they ignore any information about the multistage unsteady interaction. In order to capture them, the authors of this paper have developed a multistage coupling methodology for ITP’s in-house unsteady 3D frequency-domain linearized RANS solver. The current approach allows carrying out CFD simulations on a multistage environment built upon an arbitrary number of blade-rows; each one of them could also have an arbitrary number of frequencies and/or interblade phase angles. The coupling mechanism between consecutive blade-rows arises in a somewhat straightforward way after the solutions are decomposed as the sum of several spinning modes in the inter-row boundaries and the continuity of acoustic, vortical and entropic waves is enforced. This method is suitable for flutter and forced response computations, and also for tonal noise propagation. The focus of this paper is on the study of multiple blade-row effects on flutter stability margin. A brief analysis of results for a couple of simple test cases is presented to demonstrate the correctness of the method. Then, a detailed flutter analysis for a representative LPT geometry is performed and the results are compared with a single row conventional analysis. The impact of neighboring and further blade-rows, as well as spinning modes scattered from the fundamental circumferential mode, are accounted for in the unsteady aerodynamic loading of the excited blade.