Determination of natural frequencies and forms of turbine blade oscillations made of an alloy based on titanium aluminide

Abstract

This paper investigates the possibility of manufacturing the working blade of the 2nd stage of the free turbine from an experimental alloy based on titanium aluminide of the Ti-28Al-7Nb-2Mo-0.3 (Y, Re, B) system. Alloys of this class are important structural materials with a unique set of physical and mechanical characteristics. Alloys based on aluminide are characterized by low density, high heat strength, and heat resistance and have a high potential to replace nickel-based alloys designed for operation at temperatures no higher than 850°C. However, the use of a new alloy for the manufacture of a turbine blade involves calculations of the strength and oscillations of the blades. The purpose of the calculations is to determine the possibility of using an aluminide-based alloy of the Ti-28Al-7Nb-2Mo-0.3 (Y, Re, B) system instead of the VZHL12E-VI alloy for the selected working blade. The research was carried out by performing a modal analysis, determining the stress-deformed state, and checking the strength and mass characteristics. The physical properties of the materials were used as the initial data for the calculation. The geometry and temperature distribution of the blade and its fixing remained constant for the two options. A three-dimensional model of the experimental vane was built using the Unigraphics NX system, and a finite element model was developed using the Ansys software complex. It was established that when an experimental alloy is used, the mass of one blade is reduced by almost 40%. Using the finite element method, the natural frequencies and forms of blade oscillations were calculated, and Campbell’s diagrams were constructed for the original and experimental blades for the nominal operation of the engine. When using an experimental alloy, the frequencies of the blades’ natural oscillations are further from the resonant frequency. The distribution of equivalent stresses was determined, and it was shown that the maximum stresses act in the root section of the blade feather. When using the experimental alloy based on titanium aluminide, the equivalent stresses are reduced by 35% compared with the initial values. It is shown that the safety margin of the proposed material is not less than that of the VZHL12E-VI alloy.

Keywords

• алюмінід титану
• лопатка турбіни
• тривимірна модель
• скінченноелементна модель
• власні частоти коливань
• діаграма кемпбела