[bietchetlien1995]

Hi all!
I do the analysis of flow over a building.
The inlet constant velocity at 30m/s.
My domain has size of 1000x1000x4000 m, and distance from inlet to building is 1000.
I use LES model to analysis with the turbulence properties at default (Synthetic Turbulence Generator)
........
After 30,000 of iterations using the Adaptive Time Method,
It showed me at console "time flow" = 1.49.....s
I wanna ask is it a "real time" flow?
And when I check the result: the velocity and also pressure on my building were balance.
But, how can after near 1.5 second, how can it make pressure on the building when it just came (30m x 1,5s).?
OR I got wrong about flow time?
Pls help me, thank so much
https://www.cfd-online.com/Forums/at...1&d=1556703480

[FMDenaro]

If the flow is modelled as incompressible, the fluid moves istantaneouysly everywhere.

[LuckyTran]

The flow time is like the time on your clock.

Pressure waves travel at the sound speed so there is a force at a distance.

[bietchetlien1995]

So. If I want to capture the pressure acting on the building. I just need to see the balance in results and stop or any suitable time for guarantee the results will not change any more.
Thank you so much for all replies

[FMDenaro]

Originally Posted by bietchetlien1995

So. If I want to capture the pressure acting on the building. I just need to see the balance in results and stop or any suitable time for guarantee the results will not change any more.
Thank you so much for all replies

It is not so simple... In LES you need to run the code for a quite long time, until the initial condition is disregardeble and the flow statistics are fully developed. Only after that, you can collect the fields over a period of time and performing the average.

[bietchetlien1995]

Originally Posted by FMDenaro

It is not so simple... In LES you need to run the code for a quite long time, until the initial condition is disregardeble and the flow statistics are fully developed. Only after that, you can collect the fields over a period of time and performing the average.

for example, if my initial velocity at inlet is 25m/s, so, when the outlet (outflow) have value around 25 or more (maybe less).
is this that time, the flow will be fully developed?
Thank you for your answering

[FMDenaro]

Originally Posted by bietchetlien1995

for example, if my initial velocity at inlet is 25m/s, so, when the outlet (outflow) have value around 25 or more (maybe less).
is this that time, the flow will be fully developed?
Thank you for your answering

No. You need to check the global field. For example compute the total kinetic energy in the domain and check it along the time. When you get a period where it oscillates in time across a constant averaged value you have a fully developed solution. Only after that the LES is physically relevant.