Learning Forum

[Yves Feisel]

Hello together,

I'm trying to wrap my head around how to define the fluid flow conditions for my specific simulation case. 
I want to simulate a high temperature flow of a gas through a cylindrical furnace. The pressure inside the furnace is in the range of 10 - 500 mbar, i.e. below atmospheric pressure. The inflow is defined by a steady massflow. 
Now, to set the pressure in the simulation, should I simply set the pressure at the outflow according to the pressure in the furnace? (e.g. if I wanted to have a furnace pressure of 100 mbar I set the outflow pressure to 10 000 Pa?) 
Or is the pressure at the outflow to be considered as an overpressure compared to the inflow? But how can I set underpressure if that is the case? 

If I run a simulation at different pressures and monitor the max gas velocity, the velocity increases with higher furnace pressures. This doesn't make sense. At 0 Pa outflow conditions the gas flow is the slowest, but if 0 Pa would mean vacuum, the gas flow should be the fastest. 

Can somebody clarify this for me?

Regarding this topic I have another question:
Does Discovery take the set underpressure into account to calculate the effective volume of the gas in the simulation? The same question applies to the temperature. 

I'm trying to simulate gas temperatures in the range of 800 - 2000 °C at pressures of 10 - 500 mbar, but I'm not quite sure if Discovery really takes these parameters into account. 

I would be very grateful for any insights. 

Thanks,

Yves

[Federico]

Hello Yves, 

after initializing your solution, you can patch the fluid with the desired pressure (100 mbar). Just setting the outlet pressure will not be sufficient for this.

[Yves Feisel]

Dear Federico, 

thank you. Could you please elaborate on your reply a little more? When is the solution initialized and how can change the pressure then? I would be grateful for a more detailed response if possible. 

I'm working with Ansys Discovery 2023 R2, soon to be updated to 2024 R1.

[Federico]

Once your solution is initialized, you then have the option to "Patch", or assign values, to entire cell zones in your domain. In Fluent, you will find the option to Patch in the Solution Initialization task page.

[Yves Feisel]

Thanks Federico! 
I don't think that option is available with Ansys Discovery, am I right? Or am I missing something here?

If this is possible in Ansys Discovery I'd be grateful for advise on how to do so or where to find some instructions online. 

[Federico]

Hi Yves, 

sorry I missed the part where you said you were using Discovery.

Unfortunately, you're correct. Patching is not currently available in Discovery.

[Yves Feisel]

So, is there really no other way to simulate the gas flow at the desired conditions (high temperature/underpressure)?

I saw that I can set the overall pressure when simulating ideal gases. This would actually be my preferred way of handling this topic, but in this case I cannot set a defined mass flow as the inflow condition. But this is essential for me as in the real case that I am trying to simulate, we can precisely define the amount of gas going into the furnace, but the pressure at the inlet may slightly fluctuate and is dependent on other variables as well. 

However, trial runs setting input/output/overall pressures never lead to a result anyway. Discovery would always stop solving after some seconds without an apparent reason. 

Any further ideas would be highly appreciated. Simulating this scenario is basically the reason why we bought the licence.