In　real　gas　turbine　engines,　a　gap/step　interface　commonly　exits　between　upstream　of　the　inlet　guide　vane　endwall　and　combustor,　called　upstream　endwall　misalignment,　due　to　the　errors　of　assembly　and　the　thermal　expansion.　This　endwall　misalignment,　commonly　being　presented　as　the　gap/step　geometry　with　different　heights,　has　a　significant　effect　on　the　endwall　heat　transfer　and　film　cooling　coverage　distributions.　This　paper　presents　a　detailed　experimental　and　numerical　study　on　the　effects　of　upstream　endwall　misalignment　(step　geometry)　on　the　vane　endwall　heat　transfer　and　film　cooling　in　a　transonic　linear　turbine　vane　passage.　The　experiment　measurements　were　performed　in　a　blowdown　wind　tunnel　at　simulated　realistic　gas　turbine　operating　conditions　(high　inlet　freestream　turbulence　level　of　16　%,　exit　Mach　number　of　0.85　and　exit　Reynolds　number　of　1.7×106.　Three　types　of　upstream　step　geometry　were　tested　at　design　blowing　ratio　(BR=2.5)　for　the　same　vane　profile:　I)　baseline　geometry　with　zero-step　height　of　ΔH　=　0　mm;　II)　forward-facing　step　geometry　with　negative　step　height　of　ΔH　=　-5　mm;　III)　backward-facing　step　geometry　with　positive　step　height　of　ΔH　=　5　mm.　The　endwall　thermal　load　and　film　cooling　coverage　distributions　were　measured　using　transient　infrared　thermography,　being　presented　as　endwall　Nusselt　number　Nu　and　adiabatic　film　cooling　effectiveness　η,　respectively.　Detailed　comparisons　of　experiment　measurements　with　numerical　predictions　were　also　presented　and　discussed　for　three　types　of　upstream　step　configurations　with　ΔH　=　-5,　0,　5　mm,　respectively.　The　numerical　simulations　were　performed　by　solving　the　steady-state　Reynolds　Averaged　Navier　Stokes　(RANS)　with　Realizable　k-Ε　turbulence　model,　based　on　the　commercial　CFD　solver　ANSYS　Fluent　v.15.　The　effects　of　upstream　step　geometry　were　numerically　studied,　at　the　same　design　blowing　ratio　BR　=　2.5,　by　solving　the　endwall　Nusselt　number,　film　cooling　effectiveness　and　secondary　flow　field　for　various　upstream　step　heights:　three　forward-facing　step　heights　(from　-8　mm　to　-3　mm),　a　baseline　step　height　(0　mm),　and　four　backward-facing　step　heights　(from　3　mm　to　10　mm).　The　results　show　the　upstream　forward-facing　step　geometry　is　beneficial　for　the　endwall　thermal　load　and　film　cooling,　though　the　improvement　is　weak　for　all　step　heights　(less　than　10%　decrease　in　endwall　heat　transfer　and　less　than　10%　increase　in　endwall　film　cooling).　However,　the　upstream　backward-facing　step　geometry　is　pernicious　for　the　endwall　heat　transfer　and　film　cooling,　and　the　influence　increases　with　the　increasing　upstream　backward-facing　step　height.　The　backward-facing　step　geometry　obviously　alters　near　endwall　flow　field,　leading　to　an　enhancement　(up　to　20%)　in　endwall　heat　transfer　and　significant　reduction　(up　to　60%)　in　endwall　film　cooling　effectiveness.　Copyright　©　2020　ASME　and　Solar　Turbines　Incorporated