steady vs transient fluid flow behaviour

vkt1993 · August 30, 2018, 06:07

I am doing my project on odor source localization. I am doing the simulation using ansys fluent 19.1 software to understand the behavior of CO2 gas.
1st I performed simulation in steady state and then in the transient state.
but I am not able to understand the reason why flow behavior in both cases is different. I want to understand it mathematically. I am attaching the images of both.

blackmask · August 30, 2018, 21:00

The flow in transient simulation might be not well established. The height of your domain is estimated as 40m, and the upward convection velocity is about 4m/s, which result in a flow pass through time to be 10s. You need to simulate for more than 10s. Another question is, why do not you start transient analysis based on the fields from steady analysis? Note that if you are able to obtain a converged result from steady analysis and it is physically sounding, there is no need to do a transient simulation.

vkt1993 · August 31, 2018, 10:46

Quote:

Originally Posted by blackmask

The flow in transient simulation might be not well established. The height of your domain is estimated as 40m, and the upward convection velocity is about 4m/s, which result in a flow pass through time to be 10s. You need to simulate for more than 10s. Another question is, why do not you start transient analysis based on the fields from steady analysis? Note that if you are able to obtain a converged result from steady analysis and it is physically sounding, there is no need to do a transient simulation.

thanks for your reply... actually I am using ANSYS software first time and currently, my aim is to trace the trajectory of the plume of different gases in the different environment as well as in different boundary conditions.
so I want to know am I going in the right direction?

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August 30, 2018, 21:00		#2
blackmask Senior Member Join Date: Aug 2011 Posts: 421 Blog Entries: 1 Rep Power: 21	The flow in transient simulation might be not well established. The height of your domain is estimated as 40m, and the upward convection velocity is about 4m/s, which result in a flow pass through time to be 10s. You need to simulate for more than 10s. Another question is, why do not you start transient analysis based on the fields from steady analysis? Note that if you are able to obtain a converged result from steady analysis and it is physically sounding, there is no need to do a transient simulation.