[Marcus.filho]

Dear all,

I´m trying simulate the intake of a powerhouse of a Hydroeletric Power Dam. My simulation consists of having a part of the resevoir upstream and the intake itself. See attachment for a picture.

I´m trying to use, as upstream BC´s, the option Volume Flow Rate. I would like to understand better how does it work. I´ve done a simulation and the velocity entering the domain at the BC varies at each element. So my question is how does FLOW3D understands the value of discharge I´ve described? My first thought was that he would calculate the open area and put a constant velocity into the domain but it doesn´t seem that way.

I would like to take the opportunity and also ask if anyone think of a better BC for this kind of problem.

Thank you in advance.
Marcus

[JBurnham]

Marcus - you are correct that FLOW-3D calculates the open area and finds velocity from the flow rate. The velocity will be the same in all cells, except where the specified fluid elevation is lower than the actual fluid elevation: in this case fluid can leave the simulation. Also, in cells that contain solid boundary (like river bed), the velocity will be modified by the near-wall effect. If you are seeing different velocities in every cell, it means that the flow is interfering with the boundary condition, and the boundary condition should be moved farther away from the region of interest.

[JBurnham]

Marcus - one other note: based on the image you sent, it appears you have two volumetric-flow-rate boundaries that are adjacent and 90 degrees from each other. They will interfere with the flow rate near the corner, unless you specify 45-degree flow rate vectors on the boundary condition dialog. See the User Manual for instructions on how FLOW-3D interprets the flow rate vectors. Also make sure that the free surface elevation (fluid "height") on the boundary conditions is the same for both flow rate boundaries. Ideally, you would like to have only one inflow boundary, but you can work with two. - Jeff

[Marcus.filho]

Dear Jeff,

Thank ou for your remarks. I´ve been able to sucessfully run the simulation now. I´ve change my BC`s to stagnation pressure at the reservoir and VFR at the outlet. It´s working perfectly.

Thank you for your help.

Marcus

[JBurnham]

Awesome! Thanks for asking your question so clearly. - Jeff

[Marcus.filho]

Thank you for the prompt reply!

Marcus

[NTF]

Originally Posted by Marcus.filho

Dear Jeff,

Thank ou for your remarks. I´ve been able to sucessfully run the simulation now. I´ve change my BC`s to stagnation pressure at the reservoir and VFR at the outlet. It´s working perfectly.

Thank you for your help.

Marcus

Dear Marcus,

I am doing the same thing as you explained. I did the setup as you mentioned. But I couldn't come up with the expected result. Free Surface Vortex doesn't appearing. Please help me if you have the same experience.

BR,

[NTF]

Originally Posted by JBurnham

Marcus - you are correct that FLOW-3D calculates the open area and finds velocity from the flow rate. The velocity will be the same in all cells, except where the specified fluid elevation is lower than the actual fluid elevation: in this case fluid can leave the simulation. Also, in cells that contain solid boundary (like river bed), the velocity will be modified by the near-wall effect. If you are seeing different velocities in every cell, it means that the flow is interfering with the boundary condition, and the boundary condition should be moved farther away from the region of interest.

Dear JBurnham,

I am doing the same thing as explained here. However I wanna study the Free Surface Vortex at the intake which doesn't appearing with my simulation. Please help me if you have the any experience.

I used, Static BC for upstream of the intake and VFR BC for downstream tunnel side.

BR,

BR,