To　reveal　the　anti-swirl　performance　of　the　swirl　brake　on　improving　the　seal　rotordynamic　performance　and　enhancing　rotor　stability　in　turbomachinery,　the　effects　of　swirl　brakes　on　the　transient　flow　excitation　characteristics　and　rotordynamic　coefficients　of　a　hole-pattern　seal　are　numerically　investigated.　With　computational　fluid　dynamics　(CFD)　method　based　on　the　multi-frequency　elliptical　orbit　rotor　whirling　model　and　mesh　deformation　technique,　the　rotordynamic　coefficients,　transient　fluid　response　forces　and　flow　pattern　of　the　hole-pattern　seal　are　solved　and　analyzed　for　two　types　of　swirl　brakes　at　inlet　preswirl　ratios　of　0　and　0.6.　The　predicted　rotordynamic　coefficients　are　compared　with　the　experiment　data.　The　numerical　results　show　that　the　present　transient　numerical　method　enables　to　accurately　predict　the　frequency-dependent　rotordynamic　coefficients　of　hole-pattern　seal.　Inlet　preswirl　significantly　decreases　effective　damping　in　the　hole-pattern　seal　and　increases　in　the　crossover　frequency　of　the　effective　damping　term,　which　usually　induces　rotor　instability　vibration.　The　swirl　brake　is　very　useful　to　eliminate　rotor　instability　vibration　because　it　can　obviously　reduce　the　cross-coupling　stiffness　and　the　crossover　frequency,　and　increase　the　hole-pattern　seal　effective　stiffness　and　effective　damping　by　reducing　the　inlet　preswirl　velocity.　©　2016,　Editorial　Office　of　Journal　of　Xi＇an　Jiaotong　University.　All　right　reserved.