Sealing of a Shrouded Rotor–Stator System With Preswirl Coolant

Abstract

This paper describes an experimental study of a modeled gas turbine rotor–stator system using both preswirled blade coolant and radially outward flowing disk coolant. A double mitered rim seal was used together with, for some tests, an inner seal below the preswirl nozzles and blade feed holes in the rotor which were situated at the same radius. Some flow visualization results are presented together with measurements of pressure distribution, internal flow distribution, and the minimum seal flow necessary to prevent “mainstream” gas ingress into the wheelspace. The experiments are described for a range of rotational speeds up to Reθ = 1.8×106 for various combinations of preswirl flow, disk coolant flow, and “blade” coolant flow. The preswirled coolant flow is shown to have little effect on the pressure distribution below the preswirl nozzles but a gas concentration sampling technique showed that considerable contamination of the preswirled coolant by the frictionally heated disk coolant can occur. A clear pressure inversion effect was observed when coolant was provided by the preswirl nozzles only, whereby the pressure under the rim seal increased with increasing rotational speed. Except for the lowest flow rates, blade coolant flow is shown to increase the sealing flow requirement, but to a very much reduced extent when disk coolant flow is used simultaneously. A nonlinear relationship between minimum sealing flow and Reθ is produced when the blade cooling system is in operation.