In　a　direct-transfer　pre-swirl　system,　cooling　air　expands　through　stationary　pre-swirl　nozzles　and　flows　through　the　cavity　to　the　receiver　holes　located　in　the　rotating　turbine　disc　for　blade　cooling.　This　paper　investigates　the　effect　of　the　length-to-diameter　ratios　of　pre-swirl　nozzles　on　the　performance　of　a　direct-transfer　pre-swirl　system　in　a　rotor-stator　cavity.　The　commercial　code　CFX　12.1　is　used　to　solve　the　Reynolds-averaged　Navier-Stokes　equations　using　the　SST　turbulence　model.　Computations　are　performed　for　seven　length-to-diameter　ratios,　L/D=1,　2,　3,　4,　5,　6,　and　7,　a　range　of　pre-swirl　ratios,　0.5＜(p)＜2.0,　and　varying　turbulent　flow　parameters,　0.12＜(T)＜0.36.　The　rotational　Reynolds　number　for　each　case　is　10(6).　The　computational　fluid　dynamics　model　presented　in　this　paper　is　validated　with　the　experimental　results　available　in　the　literature.　The　nozzle　exit　flow　angle　decreases　as　length-to-diameter　ratio　L/D　increases　for　L/D＜1/tan　(　is　pre-swirl　nozzle　angle).　When　L/D＞1/tan　,　is　approximately　invariant　and　below　.　The　discharge　coefficient　C-d,C-b　for　the　receiver　holes　reaches　a　peak　as　the　fluid　in　the　rotating　core　is　in　synchronous　rotation　with　the　receiver　holes.　For　small　turbulent　flow　parameters　(T),　a　peak　of　C-d,C-b　can　be　observed　as　L/D=3.　For　large　turbulent　flow　parameters　(T),　the　shift　of　the　position　for　a　peak　occurs.　When　L/D=3,　the　synchronous　rotation　can　be　achieved　with　the　smallest　value　for　turbulent　flow　parameters　(T).　The　adiabatic　effectiveness　of　the　system　increases　with　turbulent　flow　parameters　(T).　A　peak　of　(b,ad)　is　seen　as　L/D=3　for　each　case.　When　L/D＜1/tan　,　there　is　a　significant　increase　in　(b,ad),　especially　for　L/D＜2,　with　an　increase　in　L/D.　When　L/D　is　increased　further,　a　slight　decrease　occurs.　Both　performance　parameters　show　that　the　optimum　value　for　all　cases　can　be　achieved　as　L/D=3,　which　is　slightly　above　1/tan　.