Effects of the Main Gas Path Pressure Field on Rim Seal Flows in a Stationary Linear Cascade

Abstract

Rim seals in the turbine section of gas turbine engines aim to reduce the amount of purge air required to prevent the ingress of hot mainstream gas into the under-platform space. A stationary, linear cascade was designed, built, and benchmarked to study the effect of the interaction between the pressure fields from an upstream vane row and downstream blade row on hot gas ingress for engine-realistic rim seal geometries. The pressure field of the downstream blade row was modeled using a bluff body designed to produce the pressure distortion of a moving blade. Sealing effectiveness data for the baseline seal indicated that there was little to no ingress with a purge rate greater than 1% of the main gas path flow. Adiabatic endwall effectiveness data downstream in the trench between the vane and blade showed a high degree of mixing. Extending the seal feature associated with the vane endwall indicated better sealing than the baseline design. Steady computational predictions were found to overpredict the sealing effectiveness due to underpredicted mixing in the trench.

Pressure Distortion Effects on Rim Seal Performance in a Linear Cascade

“…A stationary, linear cascade was used to make spatiallyresolved measurements near the exit of an engine-relevant rim seal. The cascade was part of the large-scale, low-speed wind tunnel facility as previously described by the authors [1]. The facility employs a recirculating flow loop which was split into two streams.…”

“…The correct flow rates provided the best agreement with CFD simulations which predicted those that best matched the conditions found in the turbine engine. Gibson et al [1] provide further information regarding the development of the crossflow. The area of particular interest in the cascade was the rim seal located downstream of the vanes.…”

“…Higher pressures beneath the platform cause purge flow to exit the seal rather than hot gas to enter under the platform. Increasing the overlap at the seal exit decreases hot gas ingress into the seal and increases the cooling effect of the purge flow on the downstream blade endwall [1,17].…”

“…The static-pressure distortion of the blade to be matched by the bluff bodies was determined from a 3D mixing-plane based steady simulation [23]. A bluff body was then designed using a twodimensional CFD simulation to match the leading edge pressure distortion of a downstream blade at two different axial locations as discussed previously by the authors [1]. The bluff bodies were placed 0.54C ax downstream of the vane trailing edge and angled to match the average turning angle of the vanes.…”

“…Increasing the axial overlap at the seal exit decreases the amount of hot gas ingress through the seal. Likewise, decreasing the width of the region where the purge flow mixes with the main gas path also improves sealing performance [1]. The impact of these geometry perturbations on the flowfield at the seal exit however is not fully described.…”