Reynolds-averaged　Navier-Stokes　(RANS)　model-based　conjugate　heat　transfer　(CHT)　method　is　so　far　popularly　used　in　simulations　and　designs　of　internally　cooled　gas　turbine　blades.　One　of　the　important　factors　influencing　the　RANS-based　CHT　method＇s　prediction　accuracy　is　the　choice　of　turbulence　models　for　different　fluid　regions　because　the　blade　passage　flow　and　internal　cooling　have　considerably　different　flow　features.　However,　most　studies　in　the　open　literature　adopted　the　same　turbulence　models　in　the　blade　passage　flow　and　internal　cooling.　Another　important　issue　is　the　comprehensive　evaluation　of　the　losses　caused　by　the　flow　and　heat　transfer　for　both　fluid　and　solid　regions.　In　this　study,　a　RANS-based　CHT　solver　suitable　for　subsonic/transonic　flows　was　developed　based　on　OpenFOAM　and　then　validated　and　used　to　explore　suitable　RANS　turbulence　model　combinations　for　internally　cooled　gas　turbine　blades.　Entropy　generation,　being　able　to　weigh　the　losses　caused　by　both　flow　friction　and　heat　transfer,　was　used　in　the　analyses　of　two　vanes　with　smooth　and　ribbed　cooling　ducts　to　reveal　the　loss　mechanisms.　Findings　indicate　that　the　combination　of　the　k-ω　SST-γ-Reθ　transition　model　for　passage　flow　and　the　standard　k-　model　for　internal　cooling　provided　the　best　agreement　with　measurement　data.　The　relative　error　of　vane　surface　dimensionless　temperature　was　less　than　3%.　The　variations　of　entropy　generation　with　different　internal　cooling　inlet　velocities　and　temperatures　indicate　that　reducing　entropy　generation　was　contradictory　with　enhancing　heat　transfer　performance.　This　study,　which　provides　a　reliable　computing　tool　and　a　comprehensive　performance　parameter,　has　an　important　application　value　for　the　design　of　advanced　internally　cooled　gas　turbine　blades.　©　2021　American　Society　of　Mechanical　Engineers　(ASME).　All　rights　reserved.