Ansys Fluent: Axisymmetric Injection Of Air Into Water

This video shows how to simulate air bubbles being injected into a tank of water at a maximum speed of 12.5[m/s], using an axisymmetric model.
#Ansys #AnsysFluent #CFD #AutoDeskInventor

[@arisalba95]

Thanks for the nice video, I have 2 questions : 1. Why you define Air for Primary Phase? 2. What a type of boundary condition for outlet?

[@ratri1023]

Hi sir...I want to simulate a hydrocyclone separator. Where I want to input mixture of two particles (PVC and PET) and separate them and calculate the efficiency ...but i am facing a lot of problem inserting two types particle through inlet...I badly need your help in this case😓

[@raghuvanshnarayan916]

how to you put boundary conditions on the axis, in my case Error is showing : Error: floating point exception Error Object: #f

[@DeepakGupta-hk9vn]

Thanks for your wonderful content. It will help us a lot. I want to simulate bubble formation due to continuous air injection (velocity= 0.8m/s from the nozzle at the bottom) into the water tank (100 mm X 80 mm, 2D). I couldn't understand why you did not provide the absolute velocity but in the form of a function? Will the above model work in my case?

[@fluentsetup1232]

I put the velocity in form of a function because i wanted the air bubbles to be produced on a sinusoidal pattern, of course, you can just put a constant velocity on the boundary condition and it should work just fine. Also, i didn't get based on your message if you wanted your model to be planar 2D or axisymmetric 2D, if you want it to be planar, here's another video: kzbin.info/www/bejne/maXQpqqsg5pnnJY

[@DeepakGupta-hk9vn]

@@fluentsetup1232 Thanks for your quick response. The model needs to be 2D planar. I will follow the suggested tutorial and hopefully, I should be able to replicate the same.

[@DeepakGupta-hk9vn]

@@fluentsetup1232 I followed your model (2D planar) except for constant velocity instead of an expression. But I am getting large bubbles of size greater than 10 mm. Experiments show that it should form fine bubbles of size less than 5 mm. How can I achieve that? Your suggestions can help me to finish my project. Thanks.

[@fluentsetup1232]

@@DeepakGupta-hk9vn Well, it would be difficult to achieve bubbles of 5 mm given that the mesh has 2.5 mm squares(assuming you didn't refine it). Also, it's important to note that i use the k-epsilon model to solve the turbulence, but there are many other models available on Fluent like k-omega or SST, you should check out what results you get with those models(and a smaller mesh).

[@DeepakGupta-hk9vn]

@@fluentsetup1232 I tried different ways to get the desired result. But I could not. 2D planar geometry of 100mm X 80 mm with water filled up to 80mm height and rest 20mm with air at the top. Air at a velocity of 1.25m/s is continuously injected through a 4mm nozzle (just an opening) at the bottom. The desired result is to get fine bubble formation. Though you already made a tutorial on gas injection in water which is slightly different. If you could make one more tutorial, this will help me immensely for my project. I can understand your time constraint. But this is my humble request to consider my case. Thanks.

[@gauravpujar7951]

In the If expression, you are trying to do this ( you are trying to give the cos equation which governs how long the inlet is open, the velocity when the inlet is open, the velocity when the inlet is closed). Have I understood it correctly? Could you please answer, In the second place, why did you multiply the velocity with the first time expression. Would it be okay if I only keep it as 15m/s? Thank you in advance

[@fluentsetup1232]

Right, I use cos so I can choose when the inlet is open (positive cosine) and when it is closed (negative cosine). So, if you just put 15[m/s] as inlet velocity, you will have a continuous amount of air being injected at constant speed through the inlet, which would always be open . It would be okay depending on what you want to simulate.

[@gauravpujar7951]

@@fluentsetup1232 Ahh I see. Thank you for your input in this as well as the previous videos. It really helped me to push my cfd simulation forward. Keep up the good work and god bless you!!!

[@easterraja8306]

Bro.. I'm using Ansys fluent 18.1.. Here there is no NAMED EXPRESSION tool.. Where I need to write that..

[@fluentsetup1232]

In that case you need to write a UDF for the velocity. It would be great it you could change to, at least, the 19 version, given that named expressions make that task much easier.

[@easterraja8306]

@@fluentsetup1232 ok bro.. Thanks for your kind reply

[@m.kharun9494]

Hi sir, how do u define time step sizes?

[@fluentsetup1232]

Do you mean which criteria I use to choose which time step suits the simulation?