Flow analysis of two-dimensional pulsed jets by particle image velocimetry

A purely alternating jet without mean mass flux and a mixed pulsed jet cont aining an additional blowing component were investigated by particle image velocimetry (PIV). The jets issued from a two-dimensional slit connected to a converging nozzle, opening normally from a flat wall. The pulsation was driven by a loudspeaker. The mean velocity fields were characterized by the combination of downstream directional blowing and omni-directional suction . The velocity fluctuations were dominated by contra-rotating eddy pairs sy nchronized with the pulsation and formed at the jet edges during blowing. P hase-synchronized measurements permit the investigation of the averaged pat terns and the cycle-to-cycle fluctuations of these vortices. The mean traje ctories of vortex centers during a whole injection cycle show how large lat eral jet expansions are achieved. For a purely alternating jet, the expansi on takes place close to the slit. For a mixed pulsed jet, the vortices deve lop farther from the orifice. In addition, proper orthogonal mode decomposi tion demonstrates that only a few modes are required to represent the main events of the flow dynamics.