The Wall Jet Formed on an Abrupt Drop Boundary Downstream of an Apron

The experiments on the character of flow along an abrupt drop boundary at downstream of an apron are performed. From measurement of velocity distribution, it makes evident that the main flow along an abrupt drop boundary downstream of an apron can be devided in to three regions, accelated, constant and decreased velocity region. The character of main flow, variation of maximum velocity, growth of charactristic width of main flow, non-dimentional eddy viscocity of jet-like main flow and etc, are determined experimentaly. Under the main flow model as decided above, the growth of boundary layer and the coefficient of local skin friction was calculated. The calculated results are good agreement with each experimental results. From this agreement, we confirm that the presented velocity low (friction low) will be help to make clear the mechanism of local scour and the criterion for scour downstream of an apron, and to make up basic relationships for determining the length of an apron.