Hydrodynamic drag of a free-standing wall partially submerged in inundation flow was experimentally investigated in a natural river. A wall plate and sensors for measuring drag force, fluid velocity, and water depth were installed in a testing frame made of stainless steel. Regulator plates were immersed on the river bed in the up and down streams of the frame to provide a uniform and steady flow in the testing area. The drag coefficient CD was significantly influenced by Froude number Fr, but not by Reynolds number Re. The CD had a minimum value slightly over 1.0 at around Fr =1.0, and increased up to 2.0 with the changes of Fr toward 0.5 and 2.0. The blockage ratio of the wall in the flume showed a large effect on the CD for subcritical flow (Fr <1.0), but little effect for supercritical flow (Fr >1.0). The formula CD =1.0+Fr 2/4, is suitable to the test data for Fr >1.0, but underestimates Fr <1.0.
Full Text (PDF)