Numerical simulation of 3D turbulent bend flow based on unstructured grids

Focusing on the continuous bends in Shapotou section of the Yellow River, this paper probes into the water level variation, planar flow field variation, longitudinal flow variation and secondary flow in the continuous bends. Specifically, a mathematical model for 3D turbulent flow was discretized by the finite-volume method based on unstructured grids, a numerical solution equation was set up under the unstructured grids, and the model was solved by the SIMPLE algorithm using unstructured non-staggered grids. Then, the calculation area was meshed into triangular grids, the grids were densified for the bends, and the vertical direction was divided into multiple layers by the equidistant layering method. The simulated results agree well with the measured value. The convex bank generally had a lower water level than the concave bank. In the first bend, the water level of the concave bank was 0.02m higher than that of the convex bank; in the second bend, the water level of the convex bank was 0.04m higher than the convex bank. The mainstream flow rate was biased towards the concave bank in the continuous bends. With the increase of the central angle in the second bend, the mainstream gradually moved to the convex bank and reached the bank at the tip of the bend. Besides, the surface-bottom vortex on the convex bank became increasingly obvious and intense, the short transition area between the two bends was significantly affected by the high flow rate area of the first bend, and scouring occurred near the convex bank at the inlet and the convex bank at the outlet. These results prove that the proposed model can accurately simulate the 3D bend water flow of natural rivers with complex boundaries; apart from planar spiral flow, the proposed model could simulate the sectional distribution of mainstream flow rate.