Aerothermal Impact of Stator-Rim Purge Flow and Rotor-Platform Film Cooling on a Transonic Turbine Stage

Abstract

The sealing of the stator-rotor gap and rotor-platform cooling are vital to the safe operation of the high-pressure turbine. Contrary to the experience in subsonic turbines, this paper demonstrates the potential to improve the efficiency in transonic turbines at certain rim seal rates. Two types of cooling techniques were investigated: purge gas ejected out of the cavity between the stator rim and the rotor disk, and cooling at the rotor-platform. The tests were carried out in a full annular stage fed by a compression tube at M2is=1.1, Re=1.1×106, and at temperature ratios reproducing engine conditions. The stator outlet was instrumented to allow the aerothermal characterization of the purge flow. The rotor blade was heavily instrumented with fast-response pressure sensors and double-layer thin film gauges. The tests are coupled with numerical calculations performed using the ONERA’s code ELSA. The results indicate that the stator-rotor interaction is significantly affected by the stator-rim seal, both in terms of heat transfer and pressure fluctuations. The flow exchange between the rotor disk cavity and the mainstream passage is mainly governed by the vane trailing edge shock patterns. The purge flow leads to the appearance of a large coherent vortex structure on the suction side of the blade, which enhances the overall heat transfer coefficient due to the blockage effect created. The impact of the platform cooling is observed to be restricted to the platform, with negligible effects on the blade suction side. The platform cooling results in a clear attenuation of pressure pulsations at some specific locations. The experimental and computational fluid dynamics results show an increase in the turbine performance compared with the no rim seal case. A detailed loss breakdown analysis helped to identify the shock loss as the major loss source. The presented results should help designers improve the protection of the rotor platform while minimizing the amount of coolant used.

Unsteady Flows in Turbines

“…Leakage flows from upstream cavities on engines generally emerge with lower momentum and less swirl than the mainstream flow, thus reducing the incidence at the inlet of the downstream blade row. The leakage flows may strengthen the endwall secondary flow on the downstream blade row (Anker & Mayer, 2002;Hunter & Manwaring, 2000;Paniagua et al, 2004;Pau et al, 2008). In addition, the ejection swirl angle can have a considerable effect to the efficiency of turbine stage, but the gain was restricted to the rotor due to a reduction in viscous dissipation and secondary losses (Ong et al, 2006).…”

Experimental Investigation of Disc Cavity Leakage Flow and Hub Endwall Contouring in a Linear Rotor Cascade

“…Dénos et al [10], Paniagua et al [17], and Pau et al [18]) focused on the effects of leakage flow on the mainstream flow. Their geometry essentially matches the case previously discussed of a radial outflow disc cavity with no step between the stator rim and the rotor hub; however, it included also the effects of blading, temperature ratio, Figure 6.…”

Delineating Loss Sources Within a Linear Cascade With Upstream Cavity and Purge Flow

“…Due to the pressure difference across shaft sealing, part of this air called cavity purge flow blows into the mainstream through the rim seal. This low-momentum emerging flow interacts with the incoming main flow under a complex mixing process inducing losses that reduces turbine performance and needs to be correctly predicted in design phase [3]. The secondary system must provide a sufficient amount of purge flow to the cavity while keeping it to the minimum to reduce both mixing losses and penalty associated to bleed air at the compressor.…”