Control of Sediment Entry into Intake Canals …
213
3.2 Effect of Collar Diameter on the Maximum Local Scour
Depth Ratio
Collars of diameters (D) 3H v and 4H v were installed to the leading edge of vanes
at the bed level. Figure 3 shows the variation of S r, max with time for vanes with
and without collars for different vane angles. Earlier, it was seen that vanes without
collar attained equilibrium after 120 min. Typically, flow happens around vanes with
the formation of a helical vortex, a phenomenon which has been long established.
However, in the case of vanes with collar, the mechanism is bound to be different
with the collar restriction at the bed level, and the equilibrium scour was attained
after 180 min. Nevertheless, the local scour at the downstream end of each vane has
reduced as can be seen from the figure. The S r, max values for D = 3H v reduced by
68.06%, 14.15%, 13.76%, and 8.49% for α = 15°, 35°, 40° and 45°, respectively. For
D = 4H v , S r, max reduced by 36.11%, 4.72%, 5.5%, and 1.89%, respectively. Also, it
is inferred that the effect of collar is prominent at lower vane angles. For α = 35°,
40° and 45°, the effect is considerably less. In all cases, the lowest equilibrium S r, max
is observed for D = 3H v . At D = 4H v , the increased collar diameter results in closer
Fig. 3 Comparison of temporal variation of maximum scour depth ratio S r, max for vanes with and
without collar at different vane angles: a 15°, b 35°, c 40°, and d 45°
213
3.2 Effect of Collar Diameter on the Maximum Local Scour
Depth Ratio
Collars of diameters (D) 3H v and 4H v were installed to the leading edge of vanes
at the bed level. Figure 3 shows the variation of S r, max with time for vanes with
and without collars for different vane angles. Earlier, it was seen that vanes without
collar attained equilibrium after 120 min. Typically, flow happens around vanes with
the formation of a helical vortex, a phenomenon which has been long established.
However, in the case of vanes with collar, the mechanism is bound to be different
with the collar restriction at the bed level, and the equilibrium scour was attained
after 180 min. Nevertheless, the local scour at the downstream end of each vane has
reduced as can be seen from the figure. The S r, max values for D = 3H v reduced by
68.06%, 14.15%, 13.76%, and 8.49% for α = 15°, 35°, 40° and 45°, respectively. For
D = 4H v , S r, max reduced by 36.11%, 4.72%, 5.5%, and 1.89%, respectively. Also, it
is inferred that the effect of collar is prominent at lower vane angles. For α = 35°,
40° and 45°, the effect is considerably less. In all cases, the lowest equilibrium S r, max
is observed for D = 3H v . At D = 4H v , the increased collar diameter results in closer
Fig. 3 Comparison of temporal variation of maximum scour depth ratio S r, max for vanes with and
without collar at different vane angles: a 15°, b 35°, c 40°, and d 45°