Control of Blade Flutter by Smart-Casing Treatment

A novel acoustic liner with adjustable impedance is introduced as a casing treatment to suppress compressor blade e utter. Numerical results are presented to show the variation of the e uctuating lift and moment coefe cients as functions of the liner cavity depth and the bias-e ow Mach number through the orie ces of the liner. It can be seen from these results that liners with different impedances would have an either positive or negative effect on compressor blade e utter under a given compressor working condition. However, an optimal impedance value that matches a specie c working condition to suppress the blade e utter can be found by a numerical method. Correspondingly, two curves that determine the control values of liner cavity depth and bias-e ow Mach numbers underanygivencompressorworkingconditioncanbeobtained.Bymeansofthesecontrolcurves,itisproposedthat the active control of compressor blade e utter may be realized by a feedforward control methodology. Compared with the existing methods for the control of blade e utter, smart-casing treatment indeed shows a novel conception of blade e utter control. Nomenclature Aab = periphery of a blade Ab = the upper or lower surface of a blade a0 = speed of sound b = blade semichord CFqi;CF®i = imaginary part of blade lift coefe cient CFqr;CF®r = real part of blade lift coefe cient CMqi;CM®i = imaginary part of blade moment coee cient CMqr;CM®r = real part of blade moment coefe cient G = the Green’ s function G! = Fourier transform of the Green’ s function for time