Transverse velocity in rectangular channel bends: numerical study and development of a prediction formula

The present study was carried out in order to study the effective parameters on the secondary circulation and maximum values of the transverse velocity in river bends using a 3D numerical model. To this end, a total of 569 numerical tests were then performed to investigate the effect of different parameters, namely bed friction, bend angle and channel geometry including relative width (channel width/bend radius,B/R) and relative depth (water depth/bend radius,H/R) on Secondary circulation over a wide range of flow conditions. The results obtained from the numerical model were validated using the collected data sets from three distinct experiments according to which two equations for prediction of the maximum values of transverse velocity at the water surface and near the channel bed of the river bends were proposed. According to the obtained results, the increment of theB/Rratio results in higher transverse velocity both at the water surface (v(ns(max))) and near the channel bed (v(nb(max))). Thev(ns(max))near the surface varying with theH/Rratio follows an incremental trend up to a critical relative depth (H/R)(scr), after which the transverse velocity is decreased. Similarly, a critical relative depth (H/R)(bcr)exists near the channel bed. However, thev(nb(max))remains almost constant after (H/R)(bcr). According to the obtained results, the greater the relative width, bed friction and bend angle, the higher the critical relative depth in the surface and the bed of the channel.