[Elaheh 1995]

Hello everyone
I hope you are doing great
I have a question about the velocity contours.
as you can see in the picture I am modeling an open channel spillway with a double gate. to analyze the results of the simulation I generated some 2d cross-sections in the x direction.
my problem is that the velocity near the walls and bottom of my channel is not zero or near zero.
my initial velocity is 324cm/s in the x-direction. and my boundary conditions for the spillway are as follows
xmin= velocity 324cm/s
xmax= pressure outflow
ymin, ymax and zmin=wall
zmax= pressure with fluid fraction=0
I have tried refining mesh, (initially, it was 5cm, now it is 2cm) but so far it is not working.
if anyone could help me with this problem I would really appreciate it.
photo_2023-02-28_15-23-44.jpg
photo_2023-02-28_15-24-19.jpg

[MSM1985]

Almost zero velocity near wall and bottom is for ideal channel, but might not be true in real life problems (see picture). All numerical models take wall friction effect but surely show some velocity near wall and bottom. If you essentially want to see that effect then you just need to model bottom or wall with superfine mesh. Otherwise there would definitely be some velocity around solid surfaces during numerical modeling.

[MSM1985]

Alternatively you can increase surface roughness to such a value that velocity becomes zero ( tried in HEC RAS). But as a hydraulic engineer, i shall consider it incorrect as it will not be a realistic condition.

[Elaheh 1995]

Originally Posted by MSM1985

Almost zero velocity near wall and bottom is for ideal channel, but might not be true in real life problems (see picture). All numerical models take wall friction effect but surely show some velocity near wall and bottom. If you essentially want to see that effect then you just need to model bottom or wall with superfine mesh. Otherwise there would definitely be some velocity around solid surfaces during numerical modeling.

Thank you for the explanation, I guess it makes sense, can you by any chance tell me some references so I can justify it for my supervisor?
thanks a lot.

[MSM1985]

The observations provided on page # 330 & 331 of the book "Hydraulics & Its Applications by A.H.Gibson", supports above argument. To know how numerical model computes velocity profile, refer to Chapter 1 of book "Numerical Modeling in Open Channel Hydraulics by Romuald Szymkiewicz".