Flow simulation in curved compound channels: Effect of changing the sinuosity of the main channel and width of floodplain

In this research, the effect of different sinuosity (s) and width of floodplain on the flow structures in curved compound channels was investigated numerically. Six different sinuosities of main channel (s = 1, 1.026, 1.096, 1.209, 1.381, and 1.641) and three different relative depths (Dr = 0.26, 0.35, and 0.45) have been used. The findings revealed that with the increase in sinuosity from 1 to 1.641 (64% increase), the maximum flow velocity in the apex section (CS1) and the middle crossover section (CS4) decreases by 23% and 62%, respectively. In the relative depth (Dr) of 0.26, 0.35, and 0.45 with the increase in sinuosity from 1 to 1.641 (with the corresponding decrease in width of floodplain), the ratio of main channel discharge to total discharge (Qmc/Q) is reduced by 40%, 45%, and 45%, respectively. Also, with the increase in relative depth (Dr), the main channel discharge is reduced, and the majority of the flows discharge through floodplain, so that with the increase in the relative depth from 0.26 to 0.45, the amount of Qmc/Q in the channel with maximum sinuosity (s = 1.641) and straight channel (s = 1) decreases by 30% and 14%, respectively. With the increase in sinuosity, the changes of v/u and the angle of flow deviation are more noticeable in the middle sections and above the bankfull level, so that in the most critical state, with an increase in the sinuosity from 1 to 1.641, the relative intensity of secondary flow (v/u) increases from 0 to 3.6, and along a meander, the size of the secondary flow cell in each section becomes larger with increasing sinuosity.