# How do I inject bubbles of a particular size ?

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• Last Post 09 April 2019
AbhayCharan posted this 14 February 2019

I am facing an issue with using multiphase.

I want to inject air bubbles of a particular diameter through my model and calculate the drag.

i would request if someone can please guide me through it.

abenhadj posted this 14 February 2019

Which models are you using? Discrete Particles (DPM) or Eulerian Models?

Best regards,

Amine

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kkanade posted this 15 February 2019

if you are using only dpm then injection panel has option of specifying dia.

you may want to look at following for setting up ddpm

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AbhayCharan posted this 15 February 2019

Thank you sir. I havent yet figured which model to use.

rwoolhou posted this 15 February 2019

You need to work out what the question is that you intend to answer using simulation. Once you know that, and things like volume fraction, particle size etc then you can (possibly with help) work out which model is best suited to the task.

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AbhayCharan posted this 26 February 2019

Sir, I want to calculate the skin friction coefficient of a flat plate by injecting air bubbles at 10% of the length of the plate at a velocity of 0.1 m/s at Fr no. 0.2.

Also the diametre of the bubbles is to be 50 um. The outer flow is of sea water.

Request to know which model is best suited and how do i go about it.

abenhadj posted this 26 February 2019

Go for DPM at first and do that as post processing step for the beginning.

Best regards,

Amine

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AbhayCharan posted this 06 March 2019

Thank you sir.

Sir, Currently Im stuck in validation of a 2 D flat plate. The shape of the Cf vs. Re plot for Re at 1x10e6, 2.5x10e6, 5x10e6, 7.5x10e6, 1x10e7, 2.5x10e7, is following a upward trend. where as the paper im refering to, follows a downward trend. Request to know if there is a better way to validate a 2D flat plate turbulent flow.

https://www.grc.nasa.gov/www/wind/valid/fpturb/fpturb02/fpturb02.html This is the paper in trying to validate.

rwoolhou posted this 07 March 2019

Please can you plot your data on here & show how you've set up whatever it is that you're monitoring?

AbhayCharan posted this 08 April 2019

Sir,

I am trying to prove the reduction in the skin friction coefficient of a flat plate. The normal value of the skin friction resistance of a 2m flat plate at a reynold number of 31000 is 0.00245, (validated using David Eaton's paper on "The reynold number scaling of a flat plate), Velocity of water : 0.027m/s.

Now I want to reduce the drag by injection microbubbles.

For that, i used the same domain, Intel (velocity inlet), Outlet (pressure), Upper wall (Wall), initial free slip, and then the plate. (1m free slip, 2m plate, ht of domain was 1m).

I used VOF method, Descrete Phase : ON. Implict. Injection :  single, at a location of 1.2m, at 0.01m/s, Flow rate of 0.001m/s. diameter of bubbles as 0.00001m, stop time as 100s.

Im using k-omega model.

Phase 1 : Water

Phase 2 : Air

But my Skin Friction Coefficient has increased to 0.075.

Request to know where my mistake is.

Request for urgent help sir.

Thank you sir.

AbhayCharan posted this 08 April 2019

AbhayCharan posted this 09 April 2019

Also, any change i make in the injection setting is not reflected in the solution.

It is my sincere request if you could help me identify my problems.

Thank you.