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A numerical investigation is presented to study the flow characteristics behind an axially-mounted center-body of an confined annular swirling jet flow. The numerical scheme solves the nonlinear, axisymmetric Navier-Stokes equations. The governed equations are transferred to the difference equations by using the finite difference method. The projection method is used to solve the pressure Poisson equation to retain the constraint of the equation of continuity. The velocity is then solved by using the explicit Adams-Bashforth scheme. Bythis numerical algorithm, second order accuracy in both time and space discretizations can be obtained. The advantage of using the linearized convective outflow boundary condition is that the length of the computational domain in theaxial direction can be reduced significantly. Observing from the velocityprofile, it is found that the length of recirculation bubble is strongly associated with the strength of vortex shedding. There are seven different flow patterns which vary with the shape of recirculation bubble, and the structures within the recirculation bubble are effected by the Reynolds number and swirl number. Besides, different flowfield geometric parameters (blockage ratio & expansion ratio)also have large-scale effects on the recirculation bubble.
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