How to keep the water level constant at inlet
 

Hello all,

For keeping the water height constant at inlet, which BC should I use when I don't know the mass flow rate ( for mass flow rate inlet) and velocity ( velocity inlet) ? I used pressure inlet, but from static pressure contour , I found negative pressure at inlet portion. I am using multiphase ( VOF) model .

It will be great help if anyone can suggest me anything. Thanks in advance.

You want to establish a constant water level? I think you have to possibilities (based on your model and settings).

The easy one is working with profiles for the inlet (non constant velocity and non constant mass inlet). -> If you can calculate your massflow.

The other way is using UDF for your inlet. You may set a pointer for (pressure, velocity, VolumeFraction) on a Cellzone or face and regulate your inlet velocity by it.

I imagine something like a sensor for the volume fraction. If the Volume fraction in one cell is higher than X (because of raising water level) the pointer activates a clipping function in the inlet and reduces or stopps the velocity inlet.

What I don't know without using the manual is how to point pressure or an other value in a seperate cellzone, but I've read it ones.

Hi Jim,

Thank you very much for your reply. you know any way that I can calculate mass flow rate ? I am working with 2D and 3D both.

Unfortunately, I couldn't understand your UDF part. can you explain a little bit ?

Thanks in advance. :)

I don't know your model, so I can't say if you can calculate your needed mass flow inlet. If it is a easy model you can calculate with analytic and use fluid mechanics...

The UDF is a function written to adapt the flow inlet to a a criteria you choose.

In an experiment you could set an sensor in a position X, when the water level arrives the sensor he would give a signal and regulate the inlet.

An UDF has the possibility to do the same in your numeric system. The sensor could be a pointer and activate a function (maybe stop velocity inlet) if a physical value (temperatur, volume fraction etc.) reachs a special magnitude.

Hope my Position is clearer now.

HI JIm,

Thank you very much . My model contains two part. One is filled with gravel and water will pass through this porous zone to a pipe. I want to keep water height constant at this porous region. I don't have any discharge or velocity data. So is it possible to calculate mass flow rate here?

And about UDF, now I am reading UDF manual fluent. Hopefully, after reading some example , I will be little bit familiar with it.


Thanks for your generous help. :)

To set a constant height at inlet area, you may try to split the domain to two. set the volume fraction of the sub-domain which includes inlet BC as fixed value (=1).

But first you have to make sure that such a setting is physically correct.

Hi John, I am sorry that I just missed the notification that someone has answered my query. I am not sure how to split the domain to two, but as a normal VOF model, Inlet had three phase, one is water, one is air and third one is mixture. I allowed to water volume fraction =1. From the volume fraction of water contour shows that water level is constant, but from static pressure contour I found that there are negative pressure just below the inlet with a magnitude of -84 pascal. So I got worried. Do you have any idea about that ?

Have you used specified operating density option with the density of lighter phase.

Yup, I did.

My problem is somehow solved now..... what I did wrong there is I plotted the contour with static pressure. After plotting the total pressure, pressure is zero at inlet, which means that water level remains constant.

Hi Tanjina,

Could you please clarify more how you solved your problem? I also need to set my inlet flow level to be constant.

Thanks,
Ali

Hello AliRezab,

I had two type of settings. For one case, I had side inlet (water entered into the domain from side) and I needed to top water level of the domain be constant. For that case, I used symmetry boundary condition, which means I forced the domain's water surface to be constant. And for another case, I had top inlet (water entered into the domain from top) and again I needed top water level be constant. That case, I used pressure inlet with zero pressure. Reference pressure was atmospheric pressure.

Hope it helps.

Regards,
Tanjina