Özet:
Scour caused by a water jet impinging the bedsediment layer is a significant concern for hydraulic engineers. Although several studies investigated the maximum
scour depth on the non-cohesive bed-sediment layer, the effect of the bed-sediment layer’s thickness on the scour was
not studied. This study investigated the effect of the thickness
of the non-cohesive sediment layer at the canal bed on the
depth of the scour caused by a water jet. The dimensionless
parameters affecting the depth of the scour were obtained via
dimensional analysis. Experiments were conducted on two
different, non-cohesive bed-sediment layers at the bottom of
a rectangular canal for different jet Froude numbers. Experimental results indicated that the depth of the scour increases
with the thickness of the bed-sediment layer; this is because
as the thickness of the sediment layer increases, the penetration depth of the air bubbles (dragged and enforced by the
impinging water jet) through the sediment layer just under
the scour hole increases. Due to the buoyancy force, as the
air bubbles rise upward, they apply uplift forces and dynamic
effects onto sediment particles, dislodging, suspending, and
carrying the sediment particles away from the bed. If the
thickness of the sediment layer is increased beyond a limiting value for a given flow condition, the maximum depth of
the scour does not change (it remains almost constant). The effect of the thickness of the bed-sediment layer on the depth
of the scour is present but not excessively large.