Internal FAN thermostat option

[SKDavare]

I am studying internal fans with thermostat option. I want to switch on fan at 37 sec. I have specified trigger as exceed type

trigger temperature curve is defined at other location (not at Internal fan volumes) with below inputs  

I expect the fan to start at 37 sec. Will it work with exceed type or below type trigger?

[karol.suchon]

Hello,

So if I understand properly you take the temperature from the face where you apply the temperature BC with piecewise linear BC. With that conditions, the Fan will start work after 18.5 seconds from the start. 

It looks like you do not want to use the thermostat option but want to turn on the fan after some time. In that case, I think that the better option will be just to divide the simulation into two separate steps.

In the first one run the simulation for 37 seconds and apply the Fan material with Flow equal to 0.

After that change the Internal Fan material volume flow rate to the proper value and continue the calculation.

Best regards,

Karol

[SKDavare]

I want to try thermostat option to turn on the fan after 37 sec. I have steady state results from previous run which are used as initial conditions for current transient run where the fan is not turned on on till 37 sec and the flow which is already developed in steady state reduces to some extent until the fan turns on at 37 sec. 

I raised my query based on following explanation on Autodesk website which is confusing, as it states "fan will run as long as trigger temperature is above or below. also refer point no. 5. Can you please enlighten me on this.

[karol.suchon · Accepted solution]

The trigger work in two possible ways. If the temperature on the surface becomes higher than trigger the fan starts working to cool down the object or if the temperature is lower to increase the temperature. That's why that could be confusing.

The temperature in piecewise linear is a linear function between the points so the Fan starts working in the middle of the range.

From one side you could use the thermostat option to force Fan to work but from the second the increase of the temperature on the wall could have some influence on the results.

If you have previously steady-state calculation results, that should not generate any issue in the method which I propose.  So just check the method which I porpose. And remember in the second phase to edit Fan material. To continue the results from the previous simulation we need to have exactly the same material type in the simulation but we could change the values.

Best regards,

Karol 

[SKDavare]

I tried with your suggested approach to divide solution in two sections. I used  0.05 time step and 740 number of time steps to run. See below. 

But my residual plot shows after completion of 660 timesteps the total time is still 15.3 sec (see below)

will it take sometime to give final results ?

[karol.suchon]

Hello.

Probably you have applied the Inteligent solution control or just do not turned off it after the strady state section.

To turn off the ISC go to solve->Solution Control-> Inteligent solution control.

The ISC keep the Courant number to be equal to 1. So the time step value will not be equal to that one which you chaose.

Best regards,

Karol