# 'unstroemung_neuer_mh' simulation project by bbrem

#1

I created a new simulation project called 'unstroemung_neuer_mh':

Neuer Modellboot-Motorhalter

More of my public projects can be found here.

#2

Hi @bbrem,

interesting model and sim! Just took a quick look and noticed two things:

• Are you intentionally applying a slip boundary condition to the walls of the device? Why not a no-slip? Is there a specific reason that you want to model the walls of your device with slip?
• You’re driving the flow with a velocity inlet flow condition and fixed all walls with zero-gradients. In addition you’re constraining the outlet as well with a fixed flow condition. This means, the flow patter across the outlet is forced to be of the same velocity everywhere which is probably unphysical (or I’m missing something in your specific application). So I’d recommend using a pressure outlet condition and set the pressure to zero (incompressible anyways). That way the flow pattern can really develop across the outlet patch - with this change, I’m confident that the residual convergence of the sim will also look better.

Hope that helps!

Best,

David

#3

Thanks David!
That really helps!

#4

Hi @bbrem,

glad I could help. Your “Run 3” setup looks to me much better - BC choice is good in my opinion. A few additional hints: Is it really 72 m/s velocity you’re looking to simulate? That’s 260 km/h, so quite a speed. What application is it actually? Some sort of boat engine fixture?

Without having done the math, I’m pretty sure that with this flow speed, the Reynolds number will be in a turbulent regime, so you’d need to switch your analysis type details to “turbulent”. This then might also help to get a better convergence behavior, as the pressure residual is currently dropping only by 2 orders of magnitude:

3 or more would be good to be sure to have reached a steady-state solution. Once the turbulent solution is in, there are also some numerical settings that can be optimized.

Best,

David

#5

O, You are so right! I multiplicated the desired speed with 3.6 instead deviding it: It is really the motor support for a 20 cm long model boat - nothing You want to move with 260 km/h…

Thanks a lot!

#6

However a 260km/h fast model boat would definitely be something I’d consider buying ;)!