Figure 49. Comparison of horizontal flow magnitudes in lee of a vertical step

Horizontal velocities at the elevation of the step show remarkable

correspondence considering this is near the flow separation boundary. Farther

down in the entrainment region, the plots show similar magnitude envelopes, but

the details differ due to the turbulent nature of the flow. Nevertheless, the

comparison was judged to be reasonable. Close to the bottom, the flow is almost

motionless.

The vertical step generated flow separation turbulence predominantly in the

vertical plane with only weak horizontal turbulent fluctuations. Consequently,

the turbulence terms in the equations of motion that are not in similitude (i.e.,

terms containing products of the horizontal and vertical fluctuations) are small

relative to the dominant terms. Therefore, turbulent scale effects arising from the

distorted models were very minor, and good similitude was seen throughout the

flow field. Details within the entrainment region exhibited variations in the

average due to the turbulence, but the bounds of the magnitudes were similar.

The flow separation boundary seemed to be well reproduced.

An extensive set of experiments was conducted to determine potential

turbulence scale effects that might arise due to flow separation in geometrically

distorted physical models. Four distinct cases were examined: (a) flow

65

Chapter 5 Turbulence Scale Effects Experiments

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