Direct numerical simulations of flutter instabilities over a vibrating turbine blade cascade

Abstract

This paper presents direct numerical simulations (DNS) on unsteady turbulent flow in a vibrating low-pressure turbine blade cascade to predict the flutter instabilities and explores the effects of blade oscillations on the flow structure and flow separation point. The spectral/hp element method is employed for the three-dimensional simulations of the domain. This method enables capturing more details about the flow structure and vortex generations compared to the URANS methods. The method can aid in understanding the physics of these complex fluid–structure interaction problems while it requires much less computational time compared to the other DNS models. The blade vibration frequency is varied from 5.2 Hz to 10.3 Hz with maximum vibration amplitude of 3% of chord length at the blade tip. The results illustrate that the vortex generation becomes stronger over the blades with higher vibration frequencies compared to the stationary ones. The main reason for the additional vortex generation and recirculations over the oscillating blades is the additional flow disturbance due to blade vibration and its interactions with the shear-layer on the turbine blade cascade. It is seen that the vortex shedding is growing around the trailing edge and become stronger on the suction surface of the vibrating blade. The flow separation over the suction surface of the stationary blade occurs at Ssep∕S0=0.391, while it occurs at 0.372 over the oscillating blade with f=5.2Hz.