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The interaction of opposing jets Quick, Jeffrey William


Opposing jets under conditions typical of industrial furnace air systems are studied using isothermal numerical and physical modelling. The prime motivation for the study comes from an interest in the development of modelling capabilities for the recovery furnaces used in the wood pulping process. The instability of the jet interaction and nature of the resulting flow states are the foci of the work. Cases for opposing jets in confined ducts with either a cross flow or a closed floor are investigated, which exhibit sonae of the main features of recovery furnaces and a number of other applications. The numerical modelling is based on the UBC-MGFD finite volume, multi grid code, under development in the Department of Mechanical Engineering at U.B.C., which is modified for transient computations in this work. Two and three dimensional computations are performed for a variety of parametric configurations; resulting in bifurcations to stable asymmetric flows in the 2D cases and unsteady, oscillatory flows in the 3D cases. Extensive testing of the numerical method is carried out for one case of opposing jets in a closed floor cavity to determine convergence level requirements and time step and grid dependence; which shows that reliable results can be obtained. Physical modelling is performed for one case of opposing jets in a closed floor cavity. Laser doppler velocimetry measurements of velocity time series are compared with corresponding time series data from the numerical modelling and excellent agreement is obtained for the total root mean square velocity at a strategic point where the jets are colliding. Flow visualization studies using a laser light sheet with a seeded flow, and a particle image velocimetry analysis reveal flow patterns that are in good, qualitative agreement with the numerical results.

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