Tue April 27th 2010 16:00 HR W121 | Seminar | Instability wave models of turbulent jets Kristján Guðmundsson |
Details:We study pressure and velocity fluctuations associated with large-scale coherent structures in turbulent jets from round and serrated nozzles.Large-scale disturbances to the turbulent mean flow are modeled via linear stability analysis (LST) and the Parabolized Stability Equations (PSE). We show that PSE provides better agreement with near-field microphone-array data at low frequencies than previous models based on LST. We examine the extent to which microphone data is contaminated by fluctuations uncorrelated with large-scale structures. By filtering out the uncorrelated fluctuations, via the proper orthogonal decomposition (POD), better agreement between data and theory is obtained. We next project PSE predictions onto a basis of POD-modes constructed from instantaneous cross-stream PIV measurements, finding excellent agreement inside the jet. We conclude that instability wave models provide an accurate description for the near-field large-scale fluctuations of turbulent jets, provided the turbulent mean flow is used in the calculation. |