An Investigation of Ingress for an “Air-Cooled” Shrouded Rotating Disk System With Radial-Clearance Seals

In order to model the flow between an air-cooled gas turbine rotor and its stationary casing, a simple isothermal plane rotating disk and stator are used. In tests reported earlier, the cavity between the rotor and stator was sealed by a stationary cylindrical shroud, and the dimensionless minimum amount of “coolant,” C_{w, min}, necessary to prevent a radial inflow (or ingress) of “hot gas” through the axial clearance between the shroud and the rotor, was determined. In the current tests, a number of seals with a radial clearance between the cylindrical shroud and the rotor are tested. Unlike their axial-clearance counterparts, radial-clearance seals can exhibit a pressure-inversion effect, where the pressure inside the cavity increases, rather than decreases, with increasing rotational speed. Using pressure measurements and flow visualization, correlations showing the variation of C_{w, min} with clearance ratio and rotational Reynolds number are presented, and it is shown that — under equivalent conditions — a seal with a radial clearance can be much more effective than one with an axial clearance.