| Summary: | An assessment has been carried out on the applicability of scaling the hot gas ingestion depth in terms of a non-dimensional sealing parameter for a rim seal cavity wheelspace system representative of that in an industrial gas turbine for power generation. The non-dimensional sealing parameter consists of the ratio of purge mass flow rate to a characteristic mass flow rate based on the rim seal geometry and rim speed, rotational Reynolds number, purge flow Reynolds number, rim-seal Reynolds number, and Rossby number. The geometry and operating conditions of the rim seal cavity wheelspace system were varied to yield a range of variations in the nondimensional sealing parameter and the corresponding hot gas ingestion depth for each. The results have been obtained through a set of three-dimensional computations of flow in the first stage nozzle-rotor between which is a rim seal cavity wheelspace. Post-processing of the computed results demonstrated the scaling of hot gas ingestion in terms of the non-dimensional sealing parameter. Specifically, the scaling provides three distinct regions of variation in the ingestion depth. With increasing non-dimensional sealing parameter there is an almost vertical drop in ingestion extent followed by a short transition to one of marginal changes in ingestion. This provides a guideline for selecting rim seal cavity wheelspace system operation and design. Targeting the short transition region, with required operating margin, results in minimal purge flow with minimal risks from hot gas ingestion. An experimentally tested rim seal cavity wheelspace configuration, which has been arrived at iteratively for its optimality, was shown to be in this short transition region. It was also demonstrated that there is a threshold value of the ratio of Chordal leakage flow to purge flow that demarcates estimated hot gas ingestion. Above the threshold value it limits the rim seal cavity operation to the transition region or the region with near vertical increase in ingestion depth. Below the threshold value its operation cannot be defined in the operating space of hot gas ingestion depth versus sealing parameter. Therefore, while useful the non-dimensional sealing parameter is still needed to demonstrate the full optimality in the rim seal cavity operation.
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