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Turbulence in a small microjet cooling system

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Old   June 3, 2012, 09:56
Post Turbulence in a small microjet cooling system
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Hello everyone,
I am modeling a microjet cooling system. Basically, it is a small 40x40x11 (WxLxH) mm flow system. It has two chambers of 5 mm height, the lower one is the inlet chamber and the upper one is the outlet chamber, both have a 4 mm diameter duct to allow the flow go in/out. Both chambers are connected by 64, 1 mm diameter ducts. For now, I am just modeling the flow in the system and trying to validate experimental results of an article where the authors claim that they achieved convergence of the continuity equation bellow 1e-3 using a Reynolds number inlet condition of 7000. That means 1.47 m/s using water!!! This is a huge velocity for such a small device.
Anyway, I am using ANSYS FLUENT 14, a mesh made of hex-dominant elements, 900,000 elements, green-based node for the gradient, SIMPLE solver, second order spatial discretization, and k-e turbulence with 5% of turbulence at the inlet and 0.004 of diameter.
I have troubles getting a steady solution and residuals below 1e-3, another convergence criterion is the pressure at the outlet. Both, residuals and pressure at the outlet, oscillate at this high Reynolds number, however, for lower inlet velocities the solution is smooth. What can I do to get convergence at high RN?
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