Performance of Rim-Seals in Upstream and Downstream Cavities over a Range of Flow Coefficients

This paper presents measurements of CO2 concentration and pressure in a new, highly instrumented and versatile, 1.5-stage gas turbine facility. The rig, which has been specifically designed for investigations related to hot gas ingestion, features interchangeable rim-seals, blading configurations, and the capability to operate at a wide range of flow coefficients. The turbine section includes an upstream and a downstream wheel-space on either side of a rotor disc featuring turned blades. Measurements of CO2 concentration and steady static pressure were used to assess the pressure field in the turbine annulus and to investigate the performance of a radial clearance rim seal in both wheel-spaces. The wealth of data presented will be of great significance for computational fluid dynamics (CFD) validation studies considering downstream cavities. Pressure measurements were made at various locations in the turbine annulus for a range of flow coefficients. In the annulus upstream of the rotor blades the square root of the peak-to-trough pressure difference was shown to increase linearly with the flow coefficient. The radial variation in concentration effectiveness in the upstream and downstream wheel-spaces is provided for a range of sealing flow rates at an operating point near the design condition for the stage. In both cases, the concentration on the stator walls was virtually invariant with the radius and equal to that in the rotating core. The results also showed that for the same effectiveness, a smaller value of non-dimensional sealing flow is required in the downstream wheel-space, indicating a weaker driver for ingress. Off-design measurements of the value of the sealing flow parameter when the concentration effectiveness is 95% in both wheel-spaces are also provided for a range of flow coefficients. In the upstream wheel-space, the sealing flow parameter, and hence ingress, is shown to increase linearly with flow coefficient and be proportional to the square root of the peak-to-trough difference of the circumferential pressure variation in the annulus. Downstream of the blades, both the sealing flow parameter and the square root of the peak-to-trough pressure difference reach a minimum near the operating point, indicating that ingress is affected by the vane pressure field immediately downstream of the seal clearance.