Learning Forum

[ananyas]

Hello,

I am trying to simulate a system with different volumes and a heat source. The idea is that I initialize the system with the heater temperature set. After the thermal equilibrium is reached [say 1 sec] as in the figure below. I want to introduce an energy source term (or atleast temperature term) for eg. 10 [W/m^3] * (1 + sin (10[Hz] * 2 * PI * 1 [rad / sec / Hz] * t)) . I have following issues:

1. Do I have to use patching or I can just introduce an "energy source" in the cell zone condition and run the calculation?
2. If I have to use patching tool, there is no energy variable and even for temperture variable I can't provide a periodic function of the form 10 [K] * (1+sin(10[Hz] * 2 * PI * 1[rad / sec / Hz] * t)).

How can I patch/add the energy/temperature term for a particular cell zone after some time in transient simulation?

Ananya

[Rob]

You have patching to set an initial condition and then energy sources or temperature FIX to set a cell zone condition. From your description I think the latter two may be of use. n

[ananyas]

Hello Rob,nThanks for the reply.nThe problem is, after 1 sec of simulation [thermal equilibrium], I want to introduce an energy source term. How can I do this? If I just turn on the energy source term, specify a energy term and run the calculation again after 1 sec, will that be correct way or I have to patch the source term to the cell zone and then run the calculation. Which of the two is correct method. It wasn't so clear from your previous reply.n

[Rob]

It depends. If you want to switch just stop the model & change the cell zone settings, the calculation activities (solution steering) may be of use, but doing it manually may be safer. n

[ananyas]

Just a quick followup question,nFrom what I understood, if I introduce the energy source term after 1 sec (~5000 iterations) and run the calculations, then for iterations beginning from 5001, the system solution will contain the effect due to the energy term as well. Right?n

[Karthik Remella]

Yes, that is right.n

[ananyas]

I am trying to compare both the methods mentioned above. For one system I use pressure equivalent energy using energy source term and for other system patching the pressure directly. I use field function to provide the pressure of the form Pstatic + 50[mPa](1+sin(wt)). nPlease refer the figure. Is the way of defining the pressure field function correct? The frequency that I specify in the field function is angular frequency or radial?.

[Karthik Remella]

Your units have to be consistent when using Fluent expressions. Please take a look into Chapter 5 (Fluent Users Guide).nThis should help you with the details.nThanks.nKarthikn

[ananyas]

I know that we have to make sure that the units have to be consistent in case of expressions. IN case of field functions, we don't define the units. Please have a look at the figure below. I want to patch this pressure p-in on one of the volumes, using custom field functions. Is the pressure definition correct? The frequency that I specify in the field function is angular frequency or radial? nPS: I am not talking about expressions, but about custom field functions. I didn't find much information about field functions in the guide nn

[Rob]

I'm fairly sure it's radians in Fluent, but keep an eye on the results to check. Depending on what you're doing you may be better off with Expressions. n I'd also suggest keeping the function simple so 50*(10^(-3)) would be better written as 0.05 n

[ananyas]

Thanks for the reply Rob. I'll simplify the function. nWE can only use constant or field function for patching. nAre you telling that we can somehow use expressions for patching physical quantities as well? That would make my life so much easier.n

[Rob]

Ah, maybe not, I'd missed that you were patching that value. n

[Karthik Remella]

,nI missed this as well. You were talking about CFFs and patching all along. My bad! nKarthikn

[Rob]

technically he asked about source terms, so I think we're good. nmake sure you read the release notes for 2021R1 when it's out, they're interesting (if you like that sort of thing) and will tell you what's new in the code. n