gravity defying droplets

[Emily Lane]

Hi,

I am having something strange happen with one of my simulations where  a small droplet starts to accelerate unboundedly diagonally upwards contrary to gravity.

I have tried specifying gravity using the reduced or just by specifying the acceleration and the same thing happens in both. It seems to only be when a small droplet goes rogue. I have tried removing the small droplets using the remove droplet command and it slows the onset but doesn't seem to stop it. 

I am wondering whether I have gravity properly specified because the splashes I get seem bigger than I expect too.

A version of the code I am using can be found in http://basilisk.fr/sandbox/Emily/vof/Injection_at_Ramp.c and I am compiling it using  

>> qcc -fopenmp Injection_at_Ramp.c -o Injection_at_Ramp.exe -lm -L. -ldl -lstdc++ -Wall -O2 -lGLU -lOSMesa -lglutils -L$BASILISK/gl -lfb_osmesa 

Plotting the locations of where the maximum speed for the air and the water occur we can see the rogue droplet. The black is the air/water interface. The red dot shows where the maximum speed was at the timestep when the interface was output. You can see there is a small droplet underneath the red cross.

In this version I am removing all but the three largest droplets so it took a while before it went haywire. Without that it goes off far faster.

Any idea why this is happening and more importantly, what I can do to stop it?

Thanks

Emily

[Shyam Sunder Yadav]

Dear Emily

I tried compiling your code, it is asking for waveprobes.h header file which is not on your sandbox.

In the meantime, try adding an acceleration event as follows instead of specifying gravity in the main program

event acceleration (i++) {
  face vector av = a;
  foreach_face(y)
    av.y[] -= 9.81;

} 

This assumes you want to specify gravity along -y direction.

Best wishes

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Dr. Shyam Sunder Yadav
Associate Professor
Mechanical Engineering
BITS Pilani
09902346342
http://www.bits-pilani.ac.in/pilani/ssyadav/Profile

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[Stephane Popinet]

Hi Emily,

Did you try with the momentum conserving option?

https://basilisk.fr/src/navier-stokes/conserving.h

Stephane