Control of blade flutter by smart casing treatment

In this paper, a novel kind of acoustic liner with adjustable impedance is introduced for casing treatment to suppress compressor blade flutter. The paper studies the effect of wall acoustic impedance on compressor blade flutter and describes a method to calculate the fluctuating lift and moment coefficient of compressor blade under the soft wall condition. A lot of numerical results have been given to show the variation of the fluctuating lift and moment coefficient as the functions of the liner cavity depth and the bias flow Mach number through the orifices of the liner. It can be seen from these results that the liner with different impedance would have an either positive or negative effect on compressor blade flutter under a given compressor working condition. But an optimal impedance value which match with a specific working condition to suppress the blade flutter can be found by numerical method. Correspondingly, two curves which determine the control values of liner cavity depth and bias flow Mach numbers under any given compressor working condition can also be obtained. By these control curves, active control of compressor blade flutter can be realized by a feed-forward control methodology. Compared with the traditional methods for compressor flutter suppressing, this paper indeed shows a novel conception of blade flutter control by smart casing treatment.