Learning Forum

[Rick28]

Hi,

I am modeling a long pipe with turbulent flow using axisymmetric geometry. The pipe is oriented along the X coordinate axis and water flow moves in the positive X direction. I would like to include the effect of pressure head in this model to simulate an inclined pipe. So far I have calibrated to pressure drop with the pipe in the horizontal orientation with an analytical expression. I next ran a case with gravity turned on and input the value of g as negative in the X coordinate. Simulation results for pressure drop in this case (vertical pipe?) were the same as the case without gravity. I would like to see the pressure drop for a given flow rate increase as the inclination angle increases. I would appreciate any advice to help me progress on this simulation. Thank You!!!!!

[Rob]

For axisymmetric you can only use gravity in the vertical direction, any other vector is going to give a radial gravity vector which is nonsense. Assuming you're looking for the hydrostatic component set the operating density to zero, and read the documentation.

[Rick28]

Hi Rob Thank you for your response. I am still confused because there is an option for specifying the gravity vector in any coordinate?
I have done more research and am thinking that maybe I must do a multiphase, transient analysis for elevation head to be implemented in the code. My original question was based on a steady-state analysis.
Thank You!!!!

[aitor.amatriain]

As Rob says, it makes no sense to include gravity in a direction different to the axis of revolution. Your problem is 3D, and, as you mention in your previous message, you should consider multiphase simulations if you are expecting to have a liquid/gas interface (for example, if mass flow rate is low and you reach a static solution). As a first test, VOF steady simulation should give you a good estimate.

[Rick28]

Hi
Thank you Aitor!!! My feeling is the axisymmetric formulation should be valid for any coordinate axis? In my model I have assigned gravity to the X coordinate which is the axis of the pipe. At this point I only have one phase in the pipe with no liquid/gas interface. The pipe without gravity has been calibrated with an analytical solution. I thought that I could simulate the effects of pipe inclination by manipulating the gravity vector rather than building a new geometry for each inclination.

Thank You!!!

[aitor.amatriain]

If you create a 3D geometry, you can use the same mesh for all cases. In that situation, you only need to change the direction of the gravity vector, but this is only possible in 3D.

[Rick28]

Hi
Thank you Aitor!!! My feeling is the axisymmetric formulation should be valid for any coordinate axis? In my model I have assigned gravity to the X coordinate which is the axis of the pipe. At this point I only have one phase in the pipe with no liquid/gas interface. Turbulent flow in the pipe, without gravity, has been calibrated with an analytical solution. I thought that I could simulate the effects of pipe inclination by manipulating the gravity vector rather than building a new geometry for each inclination.
Thank You!!!

[Rick28]

Hi Aitor Are you saying that I cannot get the pressure head effect with the axisymmetric option?
Thank You!!!

[aitor.amatriain]

Think about the physical meaning of axisymmetry. If your gravity has two components and you consider an axisymmetric model, do you see that there will be a radial component?

[Rick28]

Hi Aitor Hi Aitor I finally got it!!!!