Scaling Sealing Effectiveness in a Stator-Rotor Cavity for Differing Blade Spans

As engine development continues to advance toward increased efficiency and reduced fuel consumption, efficient use of compressor bypass flow, commonly used as cooling flow, becomes increasingly important. In particular, optimal use of compressor bypass flow yields an overall reduction of harmful emissions. The cooling flows used for cavity sealing between stages are critical to the engine and must be sufficiently maintained to prevent damaging ingestion from the hot gas path. To assess these cavity seals, the present study utilizes a one-stage turbine with true-scale engine hardware operated at engine-representative rotational Reynolds number and Mach number. Past experimental studies have made use of part-span rather than full-span blades to reduce flow rate requirements for the turbine test rig; however, such decisions raise questions about potential influences of the blade span on sealing effectiveness measurements in the rim cavity. For this study, a tracer gas facilitates measurements of sealing effectiveness in the rim cavity to compare measurements collected with full-span engine airfoils and simplified, part-span airfoils. The results from this study show sealing effectiveness does not scale as a function of relative purge flow with respect to main gas path flow rate when airfoil span is changed. However, scaling the sealing effectiveness for differing spans can be achieved if the fully-purged flow rate is known. Results also suggest reductions of purge flow may have a relatively small loss of seal performance if the design is already near a fully-purged condition. Rotor tip clearance is shown to have no effect on measured sealing effectiveness.