Aerodynamic Performance of an Unlocated High Pressure Turbine Rotor With Worn Tip Seal Fins

Abstract

An unlocated shaft failure in the high pressure turbine spool of an engine may result in a complex orbiting motion along with rearward axial displacement of the high pressure turbine rotor sub-assembly. This is due to the action of resultant forces and limitations imposed by constraints such as the bearings and turbine casing. Such motion of the rotor following an unlocated shaft failure, results in the development of multiple contacts between the components of the rotor sub-assembly, the turbine casing, and the downstream stator casing. Typically, in the case of shrouded rotor blades, the tip region is in the form of a seal with radial protrusions called ‘fins’ between the rotor blade and the turbine casing. The contact between the rotor blade and the turbine casing will therefore result in excessive wear of the tip seal fins, resulting in changes in the geometry of the tip seal domain that affects the characteristics of the tip leakage vortex. The rotor sub-assembly with worn seals may also be axially displaced rearwards, and consequent to this displacement, changes in the geometry of the rotor blade may occur because of the contact between the rotor sub-assembly and the downstream stator casing. An integrated approach of structural analyses, secondary air system dynamics, and 3D CFD is adopted in the present study to quantify the effect of the tip seal damage and axial displacement on the aerodynamic performance of the turbine stage. The resultant geometry after wearing down of the fins in the tip seal, and rearward axial displacement of the rotor sub-assembly is obtained from LS-DYNA simulations. 3D RANS analyses are carried out to quantify the aerodynamic performance of the turbine with worn fins in the tip seal at three different axial displacement locations i.e. 0 mm, 10 mm and 15 mm. The turbine performance parameters are then compared with equivalent cases in which the fins in the tip seal are intact for the same turbine axial displacement locations. From this study it is noted that the wearing of tip seal fins results in reduced turbine torque, power output and efficiency, consequent to changes in the flow behaviour in the turbine passages. The reduction in turbine torque will result in the reduction of the terminal speed of the rotor during an unlocated shaft failure. Therefore, a design modification that can lead to rapid wearing of the fins in the tip seal after an unlocated shaft failure holds promise for the management of a potential over-speed event.

Multidisciplinary methodology for turbine overspeed analysis

“…For this reason, the performance is penalized as a function of rotor dislocation and rotor speed. The performance penalty is applied as a scaling factor during the analysis with the magnitude of the factor coming from a parallel activity aimed at characterizing the turbine as a function of axial displacement (20)(21)(22) . This work was aimed at providing full overspeed characteristics of a high-pressure turbine during an unlocated shaft failure, and was based on steady CFD.…”

Investigation of Staggered Labyrinth Tip Shroud on Flow Mechanism of Low-Pressure Turbine

“…Palmer et al (2015Palmer et al ( , 2016 researched on the active control method on the tip shroud with single fin, building the aerodynamic loss model for the mass flowrate of the injected cooling gas and offering the analysis of influence of scalloped tip shroud on the flow field. (Pawsey et al, 2017) studied the loss increasement for the worn labyrinth seal, related the effect of shroud cavity seal structure on the turbine flow field with the circumferential migration of cavity flow.…”