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-   -   Spray total droplet momentum calculation help (http://www.cfd-online.com/Forums/avl-fire/104949-spray-total-droplet-momentum-calculation-help.html)

 tarnsharma July 19, 2012 08:17

Spray total droplet momentum calculation help

Hi All,

I am trying to calculate the spray droplet total momentum for the total number of parcel injected inside the spray box by following script:

// --- Spray_droplets_momentum ---
// computes spray momentum [kg m/s];

\$\$init
int i;
double momentumx,momentumy,momentumz, momentotal;
if (init==0)
{
momentumx = 0.0;
momentumy = 0.0;
momentumz = 0.0;
momentotal = 0.0;
for(i = 0; i < NDROPS; i++){
momentumx += CDROPN[i]*DDROPN[i]*UDROPN[i]*pow(SDROPN[i],3.0)*Pi/6.0;
momentumy += CDROPN[i]*DDROPN[i]*VDROPN[i]*pow(SDROPN[i],3.0)*Pi/6.0;
momentumz += CDROPN[i]*DDROPN[i]*WDROPN[i]*pow(SDROPN[i],3.0)*Pi/6.0;
momentotal = sqrt(momentumx*momentumx+momentumy*momentumy+momen tumz*momentumz);;
}
sum=momentotal;
}
MPI_SUM_D(sum);
\$\$formula
return 0;

I have calculated spray droplet momentum x , y and z sepeartely and taken moduls to get the total momentum.

But my porblem here is when I comparing the calculated total droplet momentum with the injection momentum (injected mass* injected velocity as given as boundary condition for six hole injector) and as extracted from .fla file for the given time of the injection doesn't make sense to me.

The droplet momentum which calculated by the script (as mentioned above) value comes very high compared to the injection momentum and thoretically the droplet momentum has to be lower then injection momentum as spray droplet undergoes evaporation and drag.

I just want to know if I have made any mistake on the script or any body could suggest me what should I do to get more clarity on this problem.

Appreciate any help on this. :)

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