I am using the uniform diameter distribution for DPM surface injection. But I observed something peculiar. The DPM concentration (as shown in picture) is high (RED) on the surface of injection but it decreases significantly right in front of the injection surface (GREEN). What could be the reason behind it? I found the same thing with the rosin rambler distribution. Shouldn't the DPM concentration be constant?
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- Last Post 13 January 2020
What colour scale are you using? Do you have transient flow/particles? Are the particles entering the system at the same speed as the carrier fluid?
Yes, I have a transient flow. And regarding the particle speed, I used the velocity which is obtained from the solution initialization: which is not same as the speed of the carrier fluid. Also, I have used the mass flow rate for the carrier fluid. I am using a workbench color scheme, which is the default in FLUENT. Regarding the coloring scale, it varies from min:0kg/m^3 to 32kg/m^3.
Has the transient flow stabilised? Ie is the solution at (or near enough at) the equilibrium point?
Yes, I have run the simulation for about 2 flow-through times? Do you think it might be happening because the velocity of the particle isn't the same as the carrier velocity? I observed the same behaviour using both uniform distribution and Rosin_Rambler distribution. It's weird because I don't think there is any reason for such a drastic change in the DPM concentration right in front of the surface of injection.
Good to see you've thought through & checked for equilibrium.
Can you replot with node values off. I think the result is correct, and could be explained by a velocity mismatch, as you say: material is being swept away by a faster moving flow.
Thank you for the response. This is the image with node values off. I think I might be having the wrong meaning of DPM_concentration. Could you please help me understand it. Also, does fluent provides features for measuring the mass flow rate at different cross-sections? If not how do we measure the mass flow rate of just the particles?
We tend to use interior surfaces at positions to create DPM Out (or Summary) files. How does the injection velocity compare to the flow velocity?
DPM must not be constant as it depends on residence time and Avg. mass of particle in a cell and frequency.
Best regards, Amine
Till now I have been calculating the mass flow rate of particles through the various cross-section of geometry using the formula: mass_flow_rate= DPM concentration* cross-section Area of geometry*velocity of a particle. Is this the right approach to calculate the mass flow rate?
I would rather sample the particles at cross section . You might need to change the boundaries to interior if not already done. Are the cross section post processing planes?
Best regards, Amine
Regarding cross-section at various locations, I transformed the inlet sections into various axial locations and took the area-weighted average for obtaining various parameters like dpm_concentration and particle velocities. Finally, I multiplied these variables with the cross-section area. In doing so, I found that the mass flow rates of particles are not the same at various cross-sections. This is really weird and I have no clue what might have been causing it.
Also, I didn't get what you mean by changing the boundaries to the interior?
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