separation at a vertical edge resulting in a free jet, (b) flow separation at a vertical
edge with a constrained jet, (c) flow separation at a sloping edge resulting in a
free jet, and (d) flow separation at a vertical step. In all cases the impact of
model distortion was evaluated by comparing the measured velocity fields of the
prototype experiment with the velocity fields of the distorted models scaled to
prototype size using appropriate scale ratios. Judging whether or not good
similitude existed between model and prototype was subjective, and good
correspondence was noted where variations between vector fields were thought
to be small enough to have been caused by measurement error or small
misalignment of boundary geometry between experiments. The conclusions
from the turbulence scale effects experiments are as follows:
a. Flow separation and turbulence generated at vertical edges will not have
a scale effect in geometrically distorted models because vertical turbulent
fluctuations are small.
b. Flow separation at vertical edges with constraining downstream jetties
will be similitude in distorted models with good correspondence in
resulting flow patterns in the main flow and in the entrainment region.
c. Flow separation at a vertical step where the turbulence is manifested
primarily in the vertical plane will not have any significant scale effect in
geometrically distorted models.
d. Flow separation initiated by a sloping edge will exhibit a scale effect in
geometrically distorted models. However, the scale effect is strongest
near the bottom and appears to lessen closer to the free surface. Also, the
scale effect seemed to be restricted to the immediate vicinity of the jet
boundary; however, potential impacts farther downstream were not
evaluated due to the limited measurement region of the experiments.
e. Evaluation of potential turbulent scale effects in proposed distorted
physical models requires good understanding of dominant flow patterns
in the prototype along with knowledge of boundaries where flow
separation and/or turbulence generation might occur. Evaluation must be
site-specific.
f.
Importance of turbulent scale effects is a geometrically distorted physical
model relates directly to the problem being studied, and whether or not
flow turbulence is a dominant forcing of that problem.
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Chapter 5 Turbulence Scale Effects Experiments
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