A gas turbine engine includes a primary flow path fluidly connecting a compressor section, a combustor section and a turbine section. A cooling air flowpath is disposed radially outward of the primary flowpath. A first seal spans from an inner diameter of the cooling air flowpath to an outer diameter of the cooling air flowpath. The first seal includes at least one axial convolution and a plurality of pass through features defining a purge airflow. A heat shield is positioned immediately downstream of the first seal and is configured in relation to the first seal such that the purge airflow enters a mixing plenum defined between the heat shield and the first seal.