Time Curve

[Berkan_vent]

Hi,

I have fire and smoke curves for simulating fire in the tunnel. I assigned fire curve values on fire resistance with using piecewise linear time curve and also assigned scalar on the top surface with using piecewise linear time curve.

Here is my values for fire curve just for 10 seconds;

Time    Values (watt)

0                0
1               47
2               188
3               423
4               752
5               1175
6               1692
7               2303
8               3008
9               3807
10            4700

For fire curve, when i simulate my model in transient analysis, for example i set the time step size is 0,25 but in my data set, the time is beginning with 0 and it ends 10 seconds so how the cfd choose the right value for 0,25-0,5-0,75 seconds? is it interpolating between values? Or do i have to begin the time with the same time step size?

For smoke curve, the car generates 80 m3/s smoke, how can i assign the values to piecewise linear time curve?

I tried to put the values like this but i got strange results;

Time       Values
   0                   0
   1                   0,003
   2                   0,00122
   3                   0,00274
   4                   0,00486
   5                   0,0076
   6                   0,01094
   7                   0,0149
   8                   0,01946
   9                   0,02462
   10                 0,0304

Thanks in advance,

Berkan,

[Berkan_vent]

Any Comment Please?

[Jon.Wilde]

Hi Berkan,

THere is a defect at the moment that means we cannot apply a transient scalar as you are attempting to. I am afraid the only approach is to have this set to constant.

Apologies for the inconvenience this looks like it will cause.

Kind regards,

Jon

[Berkan_vent]

Hi Jon,

Thank you for your reply, hope Autodesk will solve this defect 🙂

Still im working on tunnel fire model, I added my .cfz file, so could you check my boundary and inital condition please?

Because my advisor want me to finish this project so i need your help 🙂

Also when i assign gravity factor to my model, i couldnt see chimney effect due to fire, i think i assigned gravity factor wrong? 

My gravity factor like this;

X= 0.342

Y=0

Z=-9.801

Here is my tunnel slope (Uphill);

*By the way There will be huge temperature differences in tunnel when the fire occurs, because of this reason should i check radiation box? 

* Can CFD calculate automatically heat transfer between tunnel walls and hot smoke gases?

Thank you,

Berkan,

[Jon.Wilde]

Hi Berkan,

I think you need to have graivity in the x direction negative (so it is downhill)

You should probably use film coefficients on the external walls (5W/m2/K) is a good start and yes, we will take heat transfer from the internal gas through the wall and into whatever is outside.

Radiation will likely be key here also - check each material's emmisivity to ensure it is representative of reality.

Kind regards,

Jon

[Berkan_vent]

Jon im sorry but still im confused, from pythagoras;

X= 9.804

Y= 0

Z= -0,342

Am i wrong? 

I assigned film coeffcient to external walls, should i assign film coefficient constantly? and ref. temperature constantly also? 

Should i take ref. temperature from ambient temperature?

Also Jon what do you think about my boundary and initial condition?

Thank you so much for your help

Berkan, 

[Jon.Wilde]

Hi Berkan,

Yes, that is right. It just needed to be negative rather than positive.

Initial Conditions should be applied to all volumes. 

Yes, just set them at constant and steady state. The actual heat lost will change depending on the temperature differential (driven by the internal air).

Kind regards,

Jon

[Berkan_vent]

Thank you Jon,

But you told me before set the gravity factor like this;

But now;

X=   -9.804

Y=    0

Z=   -0.342

Which one is it, i really need your help for here Jon 🙂

Also you told me "I would run with a P=0 on all inlets." and after you said "you would really need to decide which is an inlet (with all the BC's) and which is an outlet, with just a P=0."

So im confused little bit.

I assigned boundary condition for tunnel enter like this:

* Velocity Normal (0 m/s)

* Temperature 14.2 Celcius

*Scalar 0

For tunnel exit:

* Pressure ( 0 Pa Gage)

Thank you

Berkan,

[Jon.Wilde]

Hi Berkan,

I said before that I did not know the sign of the x direction as I was not sure which was it tilted. Now I see it must be negative rather than positive. But you will still have the -9.804 in the z direction, as that is where the gravity is acting. Make sense?

X=   -0.342 

Y=    0

Z=   -9.804

I did not see the v=0, that just seals the entrance by fixing a zero velocity. I imagine you either need a real value for the velocity there or try it without one at all, but a zero will not help. Does the reason for this also make sense?

You also cannot set both velocity and pressure on the same face, one or the other.

Thanks,

Jon

[Berkan_vent]

Thank you so much Jon,

Please forgive me im just confused.

Now i understand 🙂 I deleted velocity

Tunnel entrance:

Scalar 0

Temperature: 14.2

Tunnel Exit:

 Pressure ( 0 Pa Gage)

These are my now boundary condition,

Thank you so much.

Berkan