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 Sas August 27, 2002 20:51

Please help me to simulate a river using CFD-ACE+

Hi,

Is there anyone who knows how to simulate a river with CFD-ACE+?

I am trying to use CFD-ACE+ to simulate a river flow. I scaled down the model by a factor of 0.01. I have checked the grid and no bad cell has been reported. All the aspect ratios are under 5.0. The number of the cells is 19890. I cannot make it smaller because it will cause a big difference between some cells. The river is open and its width varies, depend on the water elevation. Thus, basically I only make the river bed (as real as possible using field data) and make a big domain on top of it. Then, I set the volume conditon as having two fluids, air and water. Water flows through the inlet.

I set the simulation as: Problem: Flow and Free Surfaces Gravity: -9.81m/s2 Auto Time Step Ref. Density: Automatic Surf. Reconst: 2nd Order (PLIC) Surface Tension: No Marangani Fluids: air and water Inlet: Fix. Vel (Normal): 0.1 m/s

My questions are: 1. What is the best way to simulate a river with CFD-ACE? Do you have any example? (I could not find any from the Internet! Except one about Niagara fall from Canada CFD-ACE website) 2. How can I make the solution faster? The solver did not converge when I used 'Standard' Transient Time Step. (2000 Time step with 0.01 s/step.) 'Automatic' Transient Time Step sounds better. But the Time Steps are very small so that the calculation takes very long. 3. What is the best way to VIEW the result? Should I use RHO or LiqVOF? In both ways, the water density looks strange. It becomes smaller, from 1 to 0.5 (even less). I do not think it is true. 4. Can I use 'mass-flow rate', instead of velocity? What does kg/s mean in 'mass-flow rate'. If I have a 500m2 of a river's section and the water velocity is 2m/s, then the 'mass-flow rate' is 1000000kg/s. (1000m3x1000kg/s). Am I right? 5. Which is better: to set the initial volume for all fluid1 or for fluid2? 6. Why cannot I use 'turbulent' facility for free surface?

Best regards,

Dr Prasasto Satwiko Faculty of Engineering University of Atma Jaya Yogyakarta Jl Babarsari 44 Yogyakarta 55281 INDONESIA

fax. 62 274 487748 e-mail: psat@indosat.net.id

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