Reduction of the Excitation of Volute on Turbine Rotor by a Groove Treatment Available to Purchase

Nozzleless volutes are often used to provide required flow conditions to downstream radial and mixed flow turbine rotors. These flow conditions are generally not circumferentially uniform, with a sharp change around volute tongues. Due to this non uniformness, rotors blades will experience an aerodynamic force excitation in rotor rotating frequency. This excitation could cause high cycle fatigue (HCF) of rotor blades if the natural frequencies of rotor blades coincide with those of its harmonics. To avoid this HCF, turbine rotors are designed typically with their natural frequencies several times above the highest rotating frequency of rotors, but this increases rotor weight and reduces rotor efficiency.

Various efforts have been made to reduce the excitation force created by nozzleless volutes. Here we propose a simple method by adding in turbine housing a small groove located near rotor leading edge (LE) shroud. The idea is that when a rotor blade rotates passing through the groove, blade loading around LE will reduce suddenly, creating an excitation to the blade, and by circumferentially positioning the groove correctly, the excitations from volute and the groove will partially cancel each other. A hypothesis to allow easy prediction of the best positions of the groove is also put forward.

The idea was applied to an industrial turbocharger turbine for heavy truck application to reduce the 3^rd order excitation generated by its turbine volute. The nozzleless volute was well designed so that the 4^th order excitation is no longer an issue. The Campbell diagram was first used to obtain the rotor speed of resonance, and unsteady computational fluid dynamics (CFD) then applied to obtain the excitation force on rotor blades both with and without the groove. The resultant alternative vibratory stress of blades was obtained by a harmonic response method and results were compared. They show more than 55% reduction of the maximum vibratory stress, while turbine mass flow is reduced by 0.89% and efficiency by 0.45% points.