Characteristics　of　hot　gas　ingestion　through　turbine　rim　seals　in　a　1.5-stage　turbine　are　numerically　investigated　with　the　unsteady　Reynolds-averaged　Navier-Stokes　(URANS)　equations　and　the　SST　turbulence　model.　The　additional　passive　tracer　is　used　to　simulate　the　distribution　of　mainstream　ingestion　and　the　case　mixed　with　sealing　flow.　The　numerical　results　of　the　distributions　of　pre-swirl　ratio　and　pressure　in　the　front　and　aft　wheel-spaces　agree　well　with　experimental　results,　so　the　relative　position　of　domain　interface　and　the　effectiveness　of　the　unsteady　numerical　calculation　of　the　1.5-stage　turbine　rim　seal　are　verified.　The　unsteady　pressure　distribution　and　seal　efficiency　in　the　aft　wheel-space　under　off-design　conditions　are　analyzed,　and　the　results　show　that:　1)　The　seal　efficiency　in　the　aft　wheel-space　is　higher　than　that　in　the　front　wheel-space;　2)　Extraction　of　square　root　of　the　mainstream　circumferential　differential　pressure　at　upstream　of　the　aft　wheel-space　is　proportional　to　mainstream　flow　coefficient;　and　3)　With　the　increase　in　the　main　flow　rate,　the　seal　efficiency　of　the　rear　cavity　is　gradually　reduced　to　0.4,　and　then　the　change　is　slowed　down　at　the　same　cooling　flow　rate.　©　2018,　Editorial　Department　of　Journal　of　Southwest　Jiaotong　University.　All　right　reserved.