Learning Forum

[cs437]

Hi, 

I am studying a vortex; however, I have a problem with a vortex depth using unreal density and viscosity. The density is assumed to be constant while varying viscosity to achieve desired Re. It turned out that the depth of vortex is too depth in that Re, which could not see in the experiment. I also tried a real fluid (e.g. water), the vortex depth looks more reasonable. Is there an exemption not to use unreal fluid? Is that because the model is VOF and operating density is set as the lightest density? This is why a reason that density might have an impact on the results. However, I found some papers that used the unreal fluid as mentioned above. Please correct me if I am wrong.

Best regards,

[DrAmine]

unreal fluid: you mean applying potential theory and all inviscid. I will expect a lot of problems here as it is ideal assumption. Have a look into d'Alembert paradox for flow past a bubble/sphere ending with zero drag,

 

Ask your professor for more details,

[cs437]

I meant the fluid that I varies viscosity to get Re while keeping density constant.

[Rob]

If you alter the material properties you may get a different result from when you use the "correct" values. How did the experiment use an unreal viscosity?

[cs437]

Hi
Thank you. In the experiment, we use normal fluid in general. But in the simulations, we wanted to make our easier. That is why we keep a density constant and change viscosity to achieve desired Re. Also, some papers used that in the simulations. But based on my understandings, it might be because Fr has also impact on the results.

[Rob]

Lots of things will have an effect. Messing with material properties may cause other issues that you've not thought about.