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prince_pahariaa September 5, 2011 02:43

Velocity Profile Prediction
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I am working on problem from past 2-3 months but with not much success.
My Problem statement :-

There is rectangular block (8.37*8.63*2.66 m3) filled with water. A pipe line (0.2m dia, 9m verical length, and 7.52m horizontal lenth) is running from outside and goes inside the pool. Pipe line is L shaped. On the horizontal side of pipe, 10 nozzles (0.1m dia and 0.1 m length each) are mounted for the supply of water inside the pool. The outlet of water is from the top surface of pool. The inflow velocity of water through pipe is 2.65 m/s.

I need to analyze the velocity profile in pool.

I have used GAMBIT to construct the geometry and used T-grid mesh scheme (quality check gave me around 25% active element) with no highly skewed and inverted element. Total number of elements are roughly 600000. The mesh is successfully transported to FLUENT interface.

I have performed grid check and no error was found. I have used k-epsilon turbulence scheme. Operating conditions were kept at default condition Boundary condition are as follow :-

1) Inlet - velocity inlet - 2.65 m/s. Turbulence intensity 10% and hydraulic dia 0.2m
2) Outlet - pressure outlet - 77322 Pa (water column height) turbulence intensity 10% and hydraulic dia 2.02m.
3) For wall all the default setting are maintained.

URF vaues were kept default and discretization chosen is 2nd order upwind. Initialize as inlet.

For defaults residuals, fluent gives solution are converged. But its not matching with my hand calculation. According to my hand calculation the outflow (mass flow rate) from the first nozzle (i.e near the bend of pipe) is highest and then outflow through other nozzles reduces gradually. Also the difference is only about 3-4 kg/s. But in FLUENT is giving me just reverse answer and difference between outflow from last nozzle to first nozzles is more than 16 kg/s.

I, then, decrease the residuals absolute criteria from 0.001 (defalut) to 1.0e-9 and start the iteration. after 380 iteration i got error "turbulent viscosity limited to viscosity ratio of 1e05 in 3 cells".. I tried to refine the grid more but not with much success.

I am looking forward for any help and sorry for such a long post.


Prince Pahariaa

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