TheevolutionofG?rtlervorticesanditsinteractionwithotherinstabilitiesareinvestigatedinthispaper.BoththeMackmodeandtheG?rtlermodeexistinhypersonicboundary-layerflowsoverconcavesurfaces,andtheirinteractionsarecruciallyimportantinboundarylayertransition.WecarryoutadirectnumericalsimulationtoexploretheinteractionbetweentheG?rtlerandtheobliqueMackmode.TheresultsindicatethattheinteractionbetweentheforcedG?rtlermodeandtheobliqueMackmodepromotestheonsetofthetransition.TheforcedobliqueMackmodeissusceptibletononlinearinteraction.BecauseofthedevelopmentoftheG?rtlermode,theforcedMackmodeandotherharmonicmodesareexcited.
