The　air-side　heat　transfer　and　fluid　flow　characteristics　of　wavy　fin-and-tube　heat　exchanger　with　delta　winglets　are　investigated　numerically.　The　three-dimensional　simulations　are　performed　with　renormalization-group　(RNG)　k　-　epsilon　model　to　lay　the　foundation　for　the　design　of　the　high-performance　heat　exchanger.　The　wavy　fin-and-tube　heat　exchangers　which　have　three-row　round　tubes　in　staggered　or　in-line　arrangements　are　studied.　The　numerical　results　show　that　each　delta　winglet　generates　a　downstream　main　vortex　and　a　corner　vortex.　For　the　in-line　array,　the　longitudinal　vortices　enhance　the　heat　transfer　not　only　on　the　fin　surface　in　the　tube　wake　region　but　also　on　the　tube　surface　downstream　of　the　delta　winglet;　for　the　staggered　array,　longitudinal　vortices　are　disrupted　at　the　first　wavy　trough　downstream　from　the　delta　winglet　and　only　develop　a　short　distance　along　the　main-flow　direction,　and　the　vortices　mainly　enhance　the　heat　transfer　of　the　fin　surface　in　the　tube　wake　region.　The　longitudinal　vortices　generated　by　delta　winglet　cause　considerable　augmentation　of　heat　transfer　performance　for　wavy　fin-and-tube　heat　exchanger　with　modest　pressure　drop　penalty.　When　Re(Dc)　=　3000,　compared　with　the　wavy　fin,　the　j　and　f　factors　of　the　wavy　fin　with　delta　winglets　in　staggered　and　in-line　arrays　are　increased　by　13.1%,　7.0%　and　15.4%,10.5%,　respectively.　(C)　2009　Elsevier　Masson　SAS.　All　rights　reserved.