|
[Sponsors] |
June 19, 2020, 07:52 |
Air inlet BC for airblast DPM model
|
#1 |
Member
Join Date: Nov 2019
Posts: 98
Rep Power: 7 |
I have a two-fluid atomizatinon nozzle of the airblast/air-assist type as per this picture: https://imgur.com/xgoG975
The airflow is sonic (supply pressure is over 4 bar) and the ratio of air mass flow to water mass flow is about 100. Given the high air velocity, I guess the nozzle is "air-assist" rather than "airblast", but that's probably not too important. I would like to use the built-in atomization model in Fluent but I'm not sure how to model the air intake. My thoughts so far:
The air is actually swirling a bit due to the shape of the passage inside the nozzle, but I'm leaving that complexity out for now. Thanks for any tips! |
|
June 19, 2020, 08:04 |
Atomizer
|
#2 |
Senior Member
|
Air flow has to be compressible if Ma is more than 0.3. And it does affect DPM.
1. If the nozzle geometry is simulated, then atomizer model is not required. You can use VOF-to-DPM transition model. 2. If you want to use inbuilt atomizer models, then the actual geometry of the nozzle is not important from the DPM view point. However, you need to include its effects on the boundary conditions for air inlet. So, if gas is swirling because of the nozzle, then you must provide that swirl to the air. 3. Incompressible air only if Ma < 0.3. Rest of the setup could be same as either 1 or 2. Since the flow channels for air and liquid are different, you can calculate velocities based on mass flow rate and compressibility. Then you can calculate relative velocity. Users also use this as a tuning parameter to match data with the experiments.
__________________
Regards, Vinerm PM to be used if and only if you do not want something to be shared publicly. PM is considered to be of the least priority. |
|
June 19, 2020, 11:53 |
|
#3 | |
Member
Join Date: Nov 2019
Posts: 98
Rep Power: 7 |
Thanks for the quick reply.
Quote:
Regarding the air velocity calculation, I know how mass flow changes with pressure difference across the nozzle from the manufacturer's catalogue. It turns out this is a linear function - doubling the pressure doubles the flowrate. Am I right that this indicates choked flow? I tried using these formulas: https://en.wikipedia.org/wiki/Orific...pressible_flow and I managed to tune the discharge coefficient to match the catalogue data reasonably well. However, I'm still unsure how to use the fact that Ma=1 to get the air velocity. The speed of sound at nozle exit still depends on temperature, which I don't have, or do I? Just a remark: VOF-to-DPM (let alone pure VOF) is too expensive for this simulation so that's something I already ruled out. |
||
June 19, 2020, 12:01 |
Air Flow
|
#4 |
Senior Member
|
If you are not interested in using VOF-to-DPM, then it does not matter how complex the geometry of the nozzle is. All that matter is the annular area where the air comes out. Its not a simplification, there are no assumptions. You just have to apply correct velocity vector. You don't need to know exact temperature, just an order of magnitude, which you can get from the application of the nozzle. At STP, air velocity higher than 100 m/s implies compressible flow. If it is lesser than that, then keep it incompressible.
__________________
Regards, Vinerm PM to be used if and only if you do not want something to be shared publicly. PM is considered to be of the least priority. |
|
Thread Tools | Search this Thread |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Thread Starter | Forum | Replies | Last Post |
CFD analaysis of Pelton turbine | amodpanthee | CFX | 31 | April 19, 2018 19:02 |
Wrong flow in ratating domain problem | Sanyo | CFX | 17 | August 15, 2015 07:20 |
Superlinear speedup in OpenFOAM 13 | msrinath80 | OpenFOAM Running, Solving & CFD | 18 | March 3, 2015 06:36 |
VOF model: Make extra inlet for air in the tank? | Blue | FLUENT | 2 | January 11, 2013 07:56 |
DPM model w/ Wave model - errors in documentation | HS | FLUENT | 0 | April 12, 2006 05:37 |