The　hemodynamics　of　intracranial　aneurysm　(IA)　comprises　complex　transient　flow　patterns　that　affect　its　growth　and　rupture.　Owing　to　the　combined　effects　of　geometrical　factors　and　pulsatile　flow　conditions,　the　transient　flow　patterns　in　the　IA　are　still　unclear.　The　purpose　of　this　work　is　to　reveal　the　effect　of　the　aspect　ratio　(AR,　sac　height/neck　width)　on　the　evolution　of　the　internal　flow　patterns　and　the　hemodynamics　of　the　IA.　We　proposed　an　easy　method　to　fabricate　three　simplified　elastic　IA　models　and　measured　the　transient　flow　characteristics　by　using　particle　image　velocimetry　(PIV).　Transient　vortex　structures　in　the　IA　modes　during　a　cardiac　cycle　were　systemically　measured　and　many　new　flow　phenomena　were　found,　including　the　vortex　morphology　(size,　structure,　and　core　location),　a　high-speed　jet,　wall　compliance　effects,　and　three　flow　modes　during　retrograde　flow　phase.　The　results　show　that　the　AR　of　the　IA　affects　the　transient　flow　patterns　as　well　as　the　wall　shear　stress　(WSS)　in　complex　ways.　The　results　could　deepen　our　understanding　of　the　transient　flow　behaviors　in　IA　and　guide　related　clinical　studies.　[Figure　not　available:　see　fulltext.].　©　2022,　The　Chinese　Society　of　Theoretical　and　Applied　Mechanics　and　Springer-Verlag　GmbH　Germany,　part　of　Springer　Nature.