EXPERIMENTAL MEASUREMENTS OF INGESTION THROUGH TURBINE RIM SEALS. PART 2: ROTATIONALLY-INDUCED INGRESS

Part 1 of this two-part paper presented experimental results for externally-induced (RI) ingress, where the ingestion of hot gas through the rim seal into the wheel-space of a gas turbine is controlled by the circumferential variation of pressure in the external annulus. In Part 2, experimental results are presented for rotationally-induced (RI) ingress, where the ingestion is controlled by the pressure generated by the rotating fluid in the wheel-space. Although El ingress is the common form of ingestion through turbine rim seals, RI ingress or combined ingress (where El and RI ingress are both significant) is particularly important for double seals, where the pressure asymmetries are attenuated in the annular space between the inner and outer seals. In this paper, the sealing effectiveness was determined from concentration measurements, and the variation of effectiveness with sealing flow rate was compared with theoretical curves for RI ingress obtained from an orifice model. Using a nondimensional sealing parameter, Phi(0) the data could be collapsed onto a single curve, and the theoretical variation of effectiveness with Phi(0) was in very good agreement with the data for a wide range of flow rates and rotational speeds. It was shown that the sealing flow required to prevent RI ingress was much less than that needed for El ingress, and it was also shown that the effectiveness of a radial-clearance seal is significantly better than that for an axial-clearance seal for both El and RI ingress.