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Chapter 4 - Experimental setup and test procedure
the model. Consequently, the grain size diameter can be chosen according to the geometric model
scale.
d) Geometry of the macro-roughness
Macro roughness was created by trapezoidal ribs, placed vertically on the outer wall (Fig. 4.11)
with a spacing of 1° (or 114 mm), 2° (227 mm), 4° (454 mm) and 8° (908 mm). The curved part of
the channel as well as 1 m of the entry reach and 2 m of the straight exit reach were equipped with
these macro roughness elements. In the straight (entry and exit) reaches, the spacing of the ribs
was incremented by a factor 2 compared to the previous spacing with increasing distance to the
bend (Fig. 5.3 on page 111).
Flow direction
Radius
Spacing of
the ribs
20
vertical
ribs
Longitudinal slope
30°
40
Channel width
50
50 mm
Figure 4.11: Scheme of the macro-roughness elements and picture of the flow around ribs
Figure 4.12: Macro-roughness on the protection wall, Reuss River in Gurtnellen (Switzerland)
page 78 / November 9, 2002
Wall roughness effects on flow and scouring