Separation flow induced stall flutter and frequency locking phenomena

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Journal of Vibration and Shock ›› 2018, Vol. 37 ›› Issue (19) : 97-103.

LI Guojun1,BAI Junqiang1,TANG Changhong1,LI Yufei1,LIU Nan2

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Abstract

The unsteady Reynold averaged Navier-Stockes (URANS) equation was adopted to simulate unsteady aerodynamic force in stall flutter.Coupled with a structure’s dynamic equation, the time domain aero-elastic analysis method was established.The structure’s dynamic equation was solved in time domain using the fourth order implicit Adams linear multi-step method based on the prediction-correction technique.Firstly, the aerodynamic response of dynamic stall and the prediction accuracy of frequency locking region were verified to ensure the CFD solver being suitable to stall flutter simulation.Then, this aero-elastic analysis method was used to simulate the flutter boundary of NACA23012 airfoil.The results showed that the flutter velocity boundary predicted with the proposed method agrees well with the test results.Through analyzing structural motion responses and flow characteristics in stall flutter, it was found that the generation of leading edge vortices and wake shedding in stall flutter is an energy conversion and an injection mechanism to keep the constant amplitude oscillation of the airfoil; meanwhile, the frequency locking phenomenon occurring in stall flutter is the main reason to cause flutter frequencies abruptly dropping when the initial attack angle are 15°, 16°and 17°, respectively.

Key words

stall flutter / lock-in / dynamic stall / vortex / energy

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LI Guojun1,BAI Junqiang1,TANG Changhong1,LI Yufei1,LIU Nan2. Separation flow induced stall flutter and frequency locking phenomena[J]. Journal of Vibration and Shock, 2018, 37(19): 97-103

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