Study On The Mechanism Of Utilizing SH Guided Wave In Rotors' Ice Thickness Detection

Helicopters normally fly at the height that the icing phenomenon always exists.As the most important system of a helicopter,the rotors provide the lift,maneuverability and driving force.Once the icing problem happens to rotors,the flying safety will be at risk.Study abroad on rotors' ice detecting starts early,which has made some significant breakthrough both in experiment and theory.While domestic study is dropped behind,calling for more efforts in this field.Based on the specialities of ultrasonic guided wave,such as farness of the transmission distance and high sensitivity,this paper proposes a method utilizing SH guided wave in detecting the thickness of the ice layer that covers a rotor,aimed at providing theoretical fundamentals for designing more advanced ice detecting sensors.This paper gives an overview of the references on ice detecting first.Then it discusses the problem from theoretical and finite element perspectives,respectively.The theoretical discussion includes the case of perfect interface and weak interface.In each case,two circumstances of the rotor covered with ice layer at one single side and the rotor covered with ice layers at both sides are considered,respectively.Governing equation under each circumstance is derivated,and the relationship between the thickness of ice layers and the phase velocity of SH wave is obtained.Combined with particular numerical example,the method of using SH wave in ice detecting is introduced in detail.In the finite element discussion,the two-dimensional model of the rotor covered with ice layers up and down is established and analyzed by semi-analytical finite element(SAFE)method.The dispersion characteristic is obtained with coefficients and boundary conditions determined.A comparison is also made between the finite element result and the theoretical result.This paper considers the case of the rotor covered with ice layers up and down and the case of weak interface,which is more practical.The relationship between the characteristics of SH wave and the ice layer's thickness is obtained.The finite element result is compared with the theoretical result,which proves the validity and the feasibility of the regulation that is obtained.