I had trouble finding anything on this that is not behind a paywall. Finally found https://books.google.com.au/books?i...zAG#v=onepage&q=flow submerged sluice&f=false. See eqn 5.24mfb said:I don't see how a pressure notably below ambient downstream pressure could be maintained in the stream. Such a pressure difference sucks in water from the outside. That is happening, of course, but I would expect that to form a somewhat stable vortex without large pressure differences.
It has a diagram with H1 as the depth in front of the sluice, H2 as the general depth downstream of the sluice, and H3 as the depth just after the sluice. The surface water is lower just after the sluice than further downstream, so H3 < H2, as per the formula. The height difference used for the flow rate is H1-H3.mfb said:I cannot access the previous page in the preview, which makes the formula unclear.
Ok.mfb said:Interesting, opening the PDF again I can now see the previous page, but not the page I saw before.
It discusses a notable effect as long as "a" (the height of the opening) is relevant compared to H2. For a negligible hole size, and assuming we can adapt this to the vertical case, all the a/H terms vanish.