Self-sustained oscillations in opposed impinging jets in an enclosure

The flow of jets in confining enclosures has significant application in man y engineering processes. In particular, the impingement of axisymmetric jet s in a confined space has been examined using flow visualization, laser Dop pler anemometry, and numerical simulations. Several flow regions were found ; stable steady, regular oscillatory, and irregular oscillatory. Initially, a steady flow field existed for all arrangements for Re-d < <similar to>90 (based on the nozzle diameter d, the fluid kinematic viscosity v and the v olumetric flow rate Q through the nozzle (Q = pid(2)/4(avg))) but subsequen t increments in the fluid velocity caused a regularly oscillating flow fiel d to emerge. The onset of the oscillations and the upper limit of finite os cillations were found to be a function of the Re-d, and the nozzle diameter to chamber dimension ratio. Steady numerical simulations predicted the ste ady flow field well and good agreement was obtained in unsteady simulations of the oscillating flow field. The oscillating flow field is considered to be a class of self-sustaining oscillations where instabilities in the jet shear layer are amplified because of feed back from pressure disturbances i n the impingement region.