Case 3: Flow separation at sloping edge
The Case 3 tests were similar to Case 1 with the main difference being the
angle of the flow separation surface at the gap (see Figure 18(c)). Case 1 used
vertical edges as gap boundaries, whereas the Case 3 tests used sloping edges as
boundaries. Turbulence generated at sloping boundaries was expected to have
significant vertical components; and hence, a turbulent scale effect was expected
to occur.
Experiment setup
The prototype for Case 3 had edge slopes of 1:1, or 45 deg. However,
different horizontal and vertical length scales resulted in steeper edge slope
angles as distortion increased. For model distortions of Ω = 2, 4, and 6, the
corresponding edge slopes were 63 deg (2:1), 75 deg (4:1), and 80 deg (6:1),
respectively. Figure 33 illustrates the relative distortion of the Case 3 tests and
defines the length parameters Xp, Xm, Zp, and Zm. The horizontal dimensions
across the gap are taken at middepth.
The prototype case, and scaled models of the prototype having distortions
ratios (NX/NZ) equal to 2, 4, and 6, were tested for two flow rates (Q = 1.5 L/sec
and 1.0 L/sec). This gave a total of eight experiments. Scaling factors for each
test in the series along with relevant values for discharge and key horizontal
(Xp, Xm) and vertical (Zp, Zm) dimensions were the same as the first eight tests of
Case 1 as listed in Table 5. The horizontal measurement grid was the same as
Case 1, and the grid spacing (∆x, ∆y) for each experiment was the same as listed
in the first eight rows of Table 6. Preliminary dye injection into the flow
indicated significant vertical structure to the turbulent flow. Consequently, the
flow velocity vector field was measured at two depths (one-third and two-thirds
of the water depth (d) above the bottom) for each experiment.
Case 3 results
Partial graphical results obtained from the four tests conducted with a
discharge scale of NQ=1.0 (Q = 1.5 L/sec) are presented here as representative of
this test configuration. Complete graphical results for all eight Case 3 tests are
included in Appendix C.
Measured velocity vectors for the prototype case at an elevation 2/3 d above
the bottom are shown in Figure 34, and the corresponding results from models
with distortion 2, 4, and 6 are shown scaled up to prototype in Figures 35, 36,
and 37, respectively. Scaling was performed using the scale factors listed in
Table 5. A similar distinct jet flow with minimal lateral spreading is seen in all
the velocity vector plots recorded at an elevation of 2/3 d above the bottom.
Corresponding vector plots recorded at a water depth 1/3 d above the bottom
are presented in Figures 38-41. In the prototype test at the lower water depth
there is noticeable spreading of the jet as evidenced in Figure 38. Jet spreading
decreased as distortion increased and the sloping edge became more vertical as
seen in Figures 39-41.
53
Chapter 5 Turbulence Scale Effects Experiments
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