Learning Forum

[Anadi_Mondal]

Hello,

I am using EWF and DPM for simulating annular flow. DPM for discrete droplet and continuous vapor phase whereas EWF for the liquid film. Here a surface injection on wall film which creates a loop over the faces adjacent to the wall is used by DEFINE_DPM_INJECTION_INIT macros for injecting droplets that are entrained from the liquid film. When I try to get a summary of this injection under the Discrete Phase, all the values are zero. Why is this happening and how can I get a summary for the injection defined by DEFINE_DPM_INJECTION_INIT macros?

[DrAmine]

Why using a UDF for that if the built-in method allows particle stripping from the film.

[Anadi_Mondal]

Thank you for your reply. I checked the ANSYS theory guide and noticed that Bertodano and Mayer models are in-built for calculating film stripping(stripping off droplets from film surface) under EWF.

1. Now, how can I get the droplet stripping rate(droplet entrainment rate(kg/m2.s)) as only 'film stripped mass' is available in the post-processing variables?

2. Previously I was using DPM with an injection(for droplets entrained from the film), but now I have no injection in DPM as the stripping model is handling injection(stripping droplets). Will the DPM model work without any injection?

3. How can I track entrained droplets(stripped droplets) and obtain droplet deposition rate(kg/m2.s) on liquid film?

Notes: I was using DPM multiphase for core (air and droplets) and EWF for the liquid film of annular flow.

[Anadi_Mondal]

Hello Amine!

Will you kindly comment on the above questions? If I have no injection in DPM model, the stripping model is not activated in the EWF model. So how do I track stripped droplets , entrainment, and deposition rates?

Regards,

Anadi

[DrAmine]

You enable a dummy injection to be the placeholder of stripped particles. If you have already DPM and active injection you do not require anything. You can fitler the particles based on some input to just see the stripped particles. Film DPM Mass  is the mass of particles being absorbed by the film.

There is a film stripping rate which you can use and divide by face area.

[DrAmine]

.

[Anadi_Mondal]

Hello Amine,

I got Film DPM mass source rate and Film stripping rate under EWF variables. However, how do I enable a dummy injection under DPM to be the placeholder for stripped particles?

Regards,

Anadi

[DrAmine]

Just create a single point injection leave it everything as default and set flow rate to zero.

[Anadi_Mondal]

I created a single-point injection as your recommendation. But, I got zero film stripping rate and film DPM mass source rate for the default settings in the particle stripping model. I changed critical shear stress from 100 to 90, 80, but got the same results(no striping and DPM source rate). Why is this happening? 

When I used UDF entrainment correlation and created an injection from the wall by DEFINE_DPM_INJECTION_INIT macros, I got entrainment rate only. I got DPM mass source rate only when I created a second injection under DPM at the inlet and injected a fraction of liquid as droplets. What might be the reason for getting DPM mass source only when I have inlet injection and no DPM mass source for other cases?

[DrAmine]

What is happening: No Stripping. 

Just ensure that you have the proper material defined for the particles and that it corresponds with the film material (Film Material: water-film, DPM Material: water-film-particle).

 

There is another criterion to stripp particles based on weber number but that one is not supported.

[Anadi_Mondal]

I defined film material as water-liquid and DPM material as water-liquid-particle. Is there any problem?

Will you also comment on the user-defined injection for entrainment by DEFINE_DPM_INJECTION_INIT macros? What may be the reason for no DPM mass source here? I can use many entrainment correlations for simulation and comparison if they capture DPM mass source perfectly.

[DrAmine]

I think you will require spawning particules in the middle of the domain and that will require some internal macros which are not supported. So is not something  I can discuss or evaluate on a public forum. Stick first to what is built-in.

Another idea is to write a file injection every time step and update an Injection based on File with that.

Or you inject dummy particles as place holder (so very small particles, almost massless) and these particls will gain main based on your criteria in cells.

[Anadi_Mondal]

I even tried injecting particle[ entrained droplet] at the middle of the domain by following UDF[it's part here]

Position: 

F_CENTROID(pos,f,tf);
angle = acos(pos[0]/r);
x_inj = r*cos(angle);
y_inj = r*sin(angle);
z_inj = pos[2];

Injection:[ inside DEFINE_DPM_INJECTION_INIT]

P_POS(p)[0]=C_UDMI(c,tc,6);   // inj_x

P_POS(p)[1]=C_UDMI(c,tc,7);  // inj_y

P_POS(p)[2]=C_UDMI(c,tc,8); // inj_z

 

P_FLOW_RATE(p)= C_UDMI(c,tc,5); //got from entrainment rate correlation

P_DIAM(p)=p_diam; // define from another droplet correlation

P_VEL(p)[0]=C_U(c,tc);

P_VEL(p)[1]=C_V(c,tc);

P_VEL(p)[2]=C_W(c,tc);

Still, it's showing no Film DPM mass source. What might be the reason? Does ANSYS really count Film DPM mass source for the injection defined by DEFINE_DPM_INJECTION_INIT macros? Because when I have a surface injection with fixed droplet mass flow rate at inlet ANSYS print info [ like injection N particle, escape n, absorbed n..] in the console window. But, for DEFINE_DPM_INJECTION_INIT , ANSYS shows no information in the console window.

Moreover, will you add more words like the type of injection, and surface for the 2nd and 3rd method mentioned in your last comment?

 

[Anadi_Mondal]

Hello Amine,

Would you kindly respond to my last comment?

Anadi