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The relevance of damper pre-optimization and its effectiveness on the forced response of blades

[+] Author and Article Information
Chiara Gastaldi

Dept. of Mechanical and Aerospace Engineering, Politecnico di Torino, Corso Duca degli Abruzzi, 24, 10129 - Turin, Italy
chiara.gastaldi@polito.it

Teresa Berruti

Dept. of Mechanical and Aerospace Engineering, Politecnico di Torino, Corso Duca degli Abruzzi, 24, 10129 - Turin, Italy
teresa.berruti@polito.it

Muzio M. Gola

Dept. of Mechanical and Aerospace Engineering, Politecnico di Torino, Corso Duca degli Abruzzi, 24, 10129 - Turin, Italy
muzio.gola@polito.it

1Corresponding author.

ASME doi:10.1115/1.4038773 History: Received October 04, 2017; Revised November 04, 2017

Abstract

The purpose of this paper is to propose an effective strategy for the design of turbine blades with underplatform dampers. The strategy involves damper "pre-optimization", already proposed by the authors, to exclude, before the blades-coupled nonlinear calculation, all those damper configurations leading to low damping performance. This paper continues this effort by applying pre-optimization to determine a damper configuration which will not jam, roll or detach under any in-plane platform kinematics (i.e. blade bending modes). Once the candidate damper configuration has been found, the damper equilibrium equations are solved by using both the multi-harmonic balance (MHB) method and the direct time integration (DTI) to the purpose of finding the correct number of Fourier terms to represent displacements and contact forces. It is shown that, contrarily to non-preoptimized dampers which may display an erratic behavior, one harmonic term together with the static term ensure accurate results. These findings are confirmed by a state-of-the-art code for the calculation of the nonlinear forced response of a damper coupled to two blades. Experimental FRFs of the test case with a nominal damper are available for comparison. The comparison of different damper configurations offers a "high level" validation of the pre-optimization procedure and highlights the strong influence of the blades mode of vibration on the damper effectiveness. It is shown that the pre-optimized damper is not only the most effective, but also the one that leads to a faster and more flexible calculation.

Copyright (c) 2017 by ASME
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