Time-Averaged Flow and Turbulence Structure Over Low-Angle Asymmetric Estuarine Dunes Under Reversing Steady Flows

Abstract Large-scale (1:15), high resolution flume experiments were conducted to characterise in detail the time-averaged flow and turbulence structures over a 2D fixed low-angle estuarine dune field under steady currents from two flow directions. Over a lee side with a mean slope of 12° including a steep section of 22°, a smaller permanent flow separation is detected compared to the typically well-developed flow separation over angle-of-repose dunes. The associated turbulent wake is weak and located close to the bed. When flow is reversed towards the gentle slope of 4°, neither permanent nor intermittent flow separation and no definite turbulent wake structure were detected. Turbulent events characteristics are assessed through quadrant analysis and indicate the presence of macroturbulence such as coherent structures. This study provides further insights into the flow and turbulence properties over low-angle dunes and demonstrates the importance of large-scale dune models and near-bottom flow measurements to detect the details of flow and turbulence processes over a low- to intermediate-angle dunes.