Effect of Ingress on Turbine Disks

Abstract

The ingress of hot gas through the rim seal of a gas turbine depends on the pressure difference between the mainstream flow in the turbine annulus and that in the wheelspace radially inward of the seal. This paper describes experimental measurements which quantify the effect of ingress on both the stator and rotor disks in a wheelspace pressurized by sealing flow. Infrared (IR) sensors were developed and calibrated to accurately measure the temperature history of the rotating disk surface during a transient experiment, leading to an adiabatic effectiveness. The performance of four generic (though enginerepresentative) singleand doubleclearance seals was assessed in terms of the variation of adiabatic effectiveness with sealing flow rate. The measurements identify a socalled thermal buffering effect, where the boundary layer on the rotor protects the disk from the effects of ingress. It was shown that the effectiveness on the rotor was significantly higher than the equivalent stator effectiveness for all rim seals tested. Although the ingress through the rim seal is a consequence of an unsteady, threedimensional flow field, and the cause–effect relationship between pressure and the sealing effectiveness is complex, the timeaveraged experimental data are shown to be successfully predicted by relatively simple semiempirical models, which are described in a separate paper. Of particular interest to the designer, significant ingress can enter the wheelspace before its effect is sensed by the rotor.