Tip clearance irregularity influence on the flow simulation around the turbine blade end face

Abstract

A modern gas turbine engine must meet high requirements for fuel efficiency, determined by the engine components efficiency. The tip clearance presence in the working crowns and the losses generated by it, which make up about 25-30% of the total losses, have the greatest influence on the turbine efficiency. A change in tip clearance of 0.25% in relative terms corresponds to a turbine efficiency change of approximately 1% for an aircraft engine. Therefore, flow simulation in the tip clearance and its effect on the turbine working process efficiency is a rather important aspect in gas turbine engines efficiency improving.Based on axisymmetric thermal calculations with the subsequent determination of the SSS, the radial displacements of the turbine rotor and stator were found. When summing up the stationary three-dimensional calculation results of the blade thermal state and SSS with displacements of the rotor and stator, the tip clearance actual shape determined, the value of which along the leading edge is 2.4 times greater than along the trailing edge.Based on the results of three-dimensional gas-dynamic analysis, it was determined that taking into account the tip clearance actual shape in the rotor blade model leads to an increase in the efficiency of the turbine stage by 0.40%, a decrease in kinetic energy losses by more than 5% and an increase in torque by 0.28%. The obtained effects are achieved due to the reduced value of the actual gap in the zone of maximum pressure gradient between the trough and the back of the blade, which leads to the sealing of the gap and a decrease in the flow rate of the working fluid through it by 20%.