Comparative analysis of the dynamic characteristics of all-metal, composite and composite blades with the same profile, taking into account the influence of the connection of elements and aerodynamic loads

Abstract

The paper presents a comparative analysis of the dynamic properties of the blades of one rotary machine which have the same airfoil shape, but are made of three different materials, namely aluminum alloy, a complex material combining aluminum alloy and steel, and a composite material which is unidirectional fiberglass. In the case of an all-metal blade, its airfoil and root are made of aluminum alloy. In the case of complex blade airfoil material, the root is made of steel which is also a component of the airfoil material. In the case of a composite blade, the root is steel and is connected at the root section to its composite airfoil. The main attention when comparing models of the mechanical behavior of three types of blades is paid to the influence of the connection of complex and composite elements with the root on the dynamic characteristics of the blade as a whole which is achieved by considering the contact interactions of the elements under the action of centrifugal and aerodynamic loads and the subsequent transfer of the prestressed state of the blades to the modal analysis for determination of the dynamic characteristics of samples and their comparison. In order to correctly display the fixation of elements in the fan impeller in the case of an aluminum blade, the sector of cyclic symmetry of the rotor is considered which makes it possible to draw a conclusion about the possibility of further separate consideration of the blade for determination of its dynamic characteristics due to the much greater stiffness of the connection of the blade with the impeller in comparison with stiffness of the blade airfoil, and to generalize this conclusion in the case of a complex blade by considering a steel root with an aluminum profile with rigid clamping of the model on the contact shelves of the root, and in the case of a composite blade by considering an airfoil with rigid clamping in the root section, where the fastening to the steel root of the blade takes place. The results of a comparative analysis of the dynamic behavior of three types of blades with the same airfoil shape are presented in the form of a study of the blade natural frequencies and mode shapes.