Using controlled unsteady fluid mass addition to enhance jet mixing

A rectangular jet was excited by controlled unsteadyuid mass addition using two miniatureuidic jets placed on eithersideof itsnarrow dimension. Thesubharmonicoftheprimary'spreferredjet column frequency ( St(De) = fDe/ Uj = 0.15)wasforcedintheantisymmetricmodebecausesuchforcingpersistsforlongerdownstreamdistances than the fundamental. Details of the phase-averagedow® eld, velocity gradient terms, velocity spectra, and the mean anductuatingow® elds were documented. Theuidically excited mode grew and persisted in theow beyond the potential core region. Unsteadyuid mass addition of 12% (4% momentum addition) peruidic jet resulted in a 35% reduction of the potential core length and about a 60% increase in the normalized massux (percentages are with reference to the primary unforced jet). On the basis of the results, it appears thatuidic devices have the potential for use in shearow control applications. Nomenclature A = nozzle exit area of outerip-¯ op attachment Ap = nozzle exit area of primary nozzle a = nozzle exit area of inner nozzle ofip-¯ op apparatus B = larger dimension of outerip-¯ op attachment Bp = larger dimension of primary nozzle b = larger dimension of inner nozzle ofip-¯ op apparatus c = phase velocity, c = fk = 2p f/a r De = equivalent diameter of the primary rectangular nozzle f = frequency of oscillation H = smaller dimension of outerip-¯ op attachment Hp = smaller dimension of primary nozzle h = smaller dimension of inner nozzle ofip-¯ op apparatus