This work examines the effect of stratification on open channel flow around bends. We use direct numerical simulation of fully turbulent, two-layer stratified flow, in an idealised open channel with rectangular cross-section and a 120 degree bend, with a radius to channel breadth ratio of 1.5. The bulk Richardson number for the flow is 2.4. We additionally perform a non-stratified DNS simulation of the same flow. Our stratified flow results compare well with published field studies in estuaries. The near bed measurements provided by our DNS simulations demonstrate a quite novel observation, that even in stratified conditions, the shear stress in the channel base is inwards directed, the same as for the non-stratified flows. Previous field studies of estuaries have not obtained such near bed measurements. This has important implications for near bed transport of sediment and cross stream circulation. We show that stratification can introduce strong variation in vertical shear magnitude and orientation across the mixing layer. At the bottom and at the top of the mixing layer, the vertical shear is directed towards the outer side wall. In the center of the mixing layer it is oriented towards the inner wall.
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