Help!simulation of free water jet

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 May 13, 2001, 02:46 Help!simulation of free water jet #1 Annie Guest   Posts: n/a Hi, everyone: I am trying to use CFD and am inexperienced with it. Can anyone with experience in modelling free water jets help me? I need to calculate a axisymmetry jet spray to air atmosphere, and I am using Fluent to know its velocity and pressure distribution in the air. The jet got high velocity(950m/s) and pressure(350 MPa) after it coming through a very fine nozzle(1 mm). The Re number is 312000. I use a rectangle computational domain(100mm*10mm). i.e.I have got a length of X=100mm downstream of the jet nozzle and the distance from central line of nozzle is y=10 mm. Along the X direction, there are 800 points and along the Y direction, there are approximately 60 points. My settings of model are: Space: Axisymmetric Time: Steady Viscous:RNG k-epsilon turbulence model The settings of boundary condition are: velocity_inlet.1: velocity-inlet pressure_outlet.2: pressure-outlet pressure_outlet.3: pressure-outlet pressure_outlet.4: pressure-outlet axis.6 : axis default-interior : interior and multiphase is used in my simulation. The result which I got is very strange. The velocity along the downstream of jet going down when x reach about 20mm, after that, the velocity going up, or even higher than the initial velocity. I am sure there must be something wrong. My questions are: 1. how to decide free boundary conditions of computational domain. I am not quite sure about the boundary condition what I used. 2. how to define the size of computational domain. It seems to me that Fluent is very sensitive to the size of domain. 3. could anybody give me some reference about the simulation of free jet. Thanks in advance!

 May 15, 2001, 10:18 Re: Help!simulation of free water jet #2 HGG Guest   Posts: n/a hi, (1) which Fluent packdge do you use ? Fluent4.5 or Fluent5? or Fidap? (2) which multiphase model do you select? RNG k-e is ok for jet flow generally.

 May 15, 2001, 18:19 Re: Help!simulation of free water jet #3 Annie Guest   Posts: n/a Hi: Thank you very much for your response. The package which I have is Fluent5. And I use VOF to simulate the jet flow. Best regards Annie

 June 29, 2009, 00:51 #4 New Member   Join Date: Jun 2009 Posts: 15 Rep Power: 16 How is the axial velocity velocity varying. i mean is it fluctuating or increasing.