Local topology via the invariants of the velocity gradient tensor within vortex clusters and intense Reynolds stress structures in turbulent channel flow

摘要

Previousworkshaveshownthatmomentumtransferinthewall–normaldirectionwithinturbulentwall–boundedflowsoccursprimarilywithincoherentstructuresdefinedbyregionsofintenseReynoldsstress[1].Suchstructuresmaybeclassifiedintowall–attachedandwall–detachedstructureswiththelatterbeingtypicallyweak,small–scale,andisotropicallyoriented,whiletheformerarelargerandcarrymostoftheReynoldsstresses.Themeanvelocityfluctuationwithineachstructuremayalsobeusedtoseparatestructuresbytheirdynamicproperties.Thisstudyaimstoextractinformationregardingthescales,kinematicsanddynamicsofthesestructureswithinthetopologicalframeworkoftheinvariantsofthevelocitygradienttensor(VGT).ThelocaltopologicalcharacteristicsoftheseintenseReynoldsstressstructuresarecomparedtothetopologicalcharacteristicsofvortexclustersdefinedbythediscriminantofthevelocitygradienttensor.Thealignmentofvorticitywiththeprincipalstraindirectionswithinthesestructuresisalsodetermined,andtheimplicationsofthesefindingsarediscussed...