Using Controlled Unsteady Fluid Mass Addition

A rectangular jet was excited by controlled unsteady uid mass addition using two miniature uidic jets placed on either side of its narrow dimension.The subharmonicof the primary’s preferred jet column frequency [St(De) = fDe / Uj = 0.15]wasforced in the antisymmetricmodebecausesuch forcing persists for longerdownstreamdistances than the fundamental. Details of the phase-averaged ow® eld, velocity gradient terms, velocity spectra, and the mean and uctuating ow® elds were documented. The uidically excited mode grew and persisted in the ow beyond the potential core region. Unsteady uid mass addition of 12% (4% momentum addition) per uidic jet resulted in a 35% reduction of the potential core length and about a 60% increase in the normalized mass ux (percentages are with reference to the primary unforced jet). On the basis of the results, it appears that uidic devices have the potential for use in shear ow control applications.

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