Measurement and Analysis of Ingestion Through a Turbine Rim Seal

Abstract

Experimental measurements from a new single stage turbine are presented. The turbine has 26 vanes and 59 rotating blades with a design point stage expansion ratio of 2.5 and vane exit Mach number of 0.96. A variable sealing flow is supplied to the disc cavity upstream of the rotor and then enters the annulus through a simple axial clearance seal situated on the hub between the stator and rotor. Measurements at the annulus hub wall just downstream of the vanes show the degree of circumferential pressure variation. Further pressure measurements in the disc cavity indicate the strength of the swirling flow in the cavity, and show the effects of mainstream gas ingestion at low sealing flows. Ingestion is further quantified through seeding of the sealing air with nitrous oxide or carbon dioxide and measurement of gas concentrations in the cavity. Interpretation of the measurements is aided by steady and unsteady computational fluid dynamics solutions, and comparison with an elementary model of ingestion.

Numerical Simulation of the Flow Interaction Between Turbine Main Annulus and Disc Cavities

“…This geometry is representative of industrial design, used to limit ingestion of hot gas inside the cavity. Measurements have been carried out by Gentilhomme et al [9,16] at the University of Sussex, and are used for comparison with the present computations. Figure 1 presents the central part of the computational domains.…”

“…The numbers of vanes and blades have been modified to 27:54 for the computations, in order to reduce the domain to 1 vane passage and 2 blade passages. The operating conditions are presented in Table 1 for the computations and the corresponding experiments from Gentilhomme et al [9,16]. The reference names are composed of the turbine operating condition (Design or OffDesign, according to the rotational speed), plus '1' for a low coolant mass-flow or '2' for a medium coolant mass flow.…”

“…More detailed analysis has been undertaken using CFD. Based on these studies and experimental data a number of workers have concluded that unsteady CFD models including both disc cavities and blading flow effects are required for a satisfactory physical description [5,[8][9][10]. Circumferential asymmetries due to either stationary or rotating blades can drive hot gas ingestion, and in the engine these combine producing unsteady flow.…”

Use of Pressure Measurements to Determine Effectiveness of Turbine Rim Seals

“…[4][5][6]; as well as simpli fied engine rigs specifically designed for detailed instrumentation access to a more benign environment, e.g., Refs. Usually, this has been accomplished by seeding the sealing air with C 0 2 or another tracer gas and measuring the concentration on the stator.…”

“…Facilities like the large hot gas ingestion rig described by Palafox et al [4] and the Sussex rig used by Gentilhomme et al [6] are ideally suited for the validation of theoretical models; a 1.5-stage rig with asymmetrical blades is currently being commissioned at Bath, and this too will be used for validation. Facilities like the large hot gas ingestion rig described by Palafox et al [4] and the Sussex rig used by Gentilhomme et al [6] are ideally suited for the validation of theoretical models; a 1.5-stage rig with asymmetrical blades is currently being commissioned at Bath, and this too will be used for validation.…”