Hot Gas Ingestion Model Employing Flow Network With Axisymmetric Solvers

Abstract

This paper discusses a method for predicting hot gas migration into turbine disk cavities using two incompressible orifices for ingress and egress flows at the main flow path-to-rim seal interface. The method employs a flow network system that involves axisymmetric disk cavity flow solver elements to model inflows and outflows that exist in a turbine disk cavity subject to a simulated main gas path pressure field. A modified lumped-parameter two-orifice model in which ingress/egress discharge coefficients and the corresponding orifice physical areas are explicitly defined is demonstrated for predicting sealing effectiveness as part of a flow network system. This model has been calibrated against CO2 concentration measurements results previously reported for a 1.5-stage disk cavity research rig at Arizona State University. The boundary pressures for the entire flow network system were defined to be the peak and trough pressures measured. Two fractional variables are introduced in defining the ingress orifice physical area and driving pressure difference between the main gas flow path and the rim cavity. An exponential curve-fit model for the ingress area fraction was developed to compute orifice egress discharge coefficients for a pre-determined ingress discharge coefficient. Excellent agreement with sealing effectiveness data was observed for a radial-gap rim seal geometry for the tested ranges of rotational Reynolds number and non-dimensional purge flow rate. Assumptions employed in developing the model were supported by a 90 degree sector RANS CFD result for the same disk cavity geometry and flow conditions.