Learning Forum

[klara.marek]

In the given example there is a metal pin enclosed by a tube (not displayed). Between the pin and the tube is supposed to be vacuum so that it is a non participating fluid. The planar front and back of this domain are insulated free slip walls to mimick a symmetry wall, as recommended in the Online Help. My first question is concerning the setup of the vacuum - idealy I would like to set a reference pressure to 0bar and apply a low static pressure. However I could not find the option to set a reference pressure. Is there a default setting for the operating pressure and can it be altered? The next question that occured to me is concerning the boundary conditions, mimicking the pin and tube walls. For the tube I would idealy set the outer wall to a fixed temperature and apply an emissivity of a certain value. However the addition of emissivity is only possible with a convection boundary condition. This made me wonder if applying this condition and setting the convection and radiation temperature to the fixed temperature will result in the same outcome. I might be misunderstanding the convection boundary condition and would be very grateful for a clarification. I was wondering the same about the boundary conditions for the pin. The temperature here is higher than that of the tube walls and is therefor emmitting radiation energy. Since I cannot (or am not aware of this option) apply a temperature to the solid pin and an emmisivity to its surface in combination with the fluid simulation, I was wondering if it is possible to correctly run a simulation of this problem alltogether.   Thank you very much for all comments, clarifications and inputs regarding this problem!

[Subashni Ravichandran]

Hello Klara

I'm checking on a few things with my colleagues with regard to your query,

I will get back to you soon

[klara.marek]

Hello @Subashni

Has there been any development regarding the problem yet? 

Thank you for your help!  

[Subashni Ravichandran]

Hello Klara

I apologise for the delay. I seem to have overlooked responding to this.

1. There is no option to set a reference pressure. In the simulation you have described there is interaction between 2 fluid volumes, vacuum and fluid. This cannot be simulated. Only one fluid volume can be simulated in Discovery. Therefore the effects of vaccuum need to be approximated as boundary conditions to the fluid volume.
2. For the pin walls, I understand you will need to set emissivity of pin with fluid. This again involved fluid-solid interaction, which cannot be simulated in Discovery. You will need to directly input a temperature on the Fluid wall which could be the approximation after including the emissivity of pin etc. Although, in case of fluid-fluid interface it would make sense to give a convection-radiation boundary condition.