Geometric effects on static turbine rim seals.

摘要

High turbine inlet temperatures pose a danger to the uncooled cavities beneath the turbine platform. High-pressure air, known as purge flow, is taken from the compressor and introduced beneath the platform to prevent the hot gas in the main gas path from entering into these cavities. It is desirable to minimize the amount of purge flow required to seal the cavities as it reduces engine output. To reduce purge requirements, a geometric feature called a rim seal is installed below the platform between the stationary and rotating airfoil rows. A rim seal consists of a series of overlaps that hot gas must negotiate in order to enter beneath the platform. Advances in rim seal design require spatially-resolved measurements in and around the seal to identify the mechanisms through which conditions in the main gas path affect hot gas ingress.;The current research presents spatially resolved measurements of ingress levels, endwall temperatures, and flowfields in and around a state of the art rim seal design in a linear cascade. Flowfield measurements show that the vane passage vortex and high velocities in the outer portions of the seal, called the trench region, reduce the cooling effect of the purge flow on the downstream blade endwall. High turbulence levels in the trench region thoroughly mix the purge flow and hot gas from the mainstream, resulting in minimal gradients in the endwall and thermal field. Steady Reynolds averaged Navier-Stokes (RANS) predictions fail to capture this mixing and as a result over estimate sealing effectiveness.;The impact of the main gas path pressure field on hot gas ingress was studied by using an upstream vane row and bluff bodies downstream of the trench to model the pressure distortion of a rotating blade. Adding the bluff bodies introduced more hot gas into the trench and the seal. A parametric study of seal geometry showed that extending the axial overlap at the seal exit improved sealing and endwall cooling. Flowfield measurements indicated that the flow structures that caused hot gas to enter the baseline seal were mitigated by this modification. As a result, the purge flow entered the trench more uniformly and remained closer to the blade endwall.;Although rotational and unsteady effects were not captured by the stationary linear cascade, several important trends in rim seal flows have been identified in the present work that are of interest to seal designers. These trends included the importance of the strong cross passage flow in the trench, the extremely high turbulence that mixed the purge flow and hot gas, and the underprediction of that turbulent mixing by RANS methods. These findings may guide further investigations that do include the effects of the rotating blade.