Application of Mesh Morphing in STAR-CCM+ to Analysis of Scour at Cylindrical Piers

Mesh morphing is a fluid structure interaction capability in STAR-CCM+ to move vertices in the computational mesh in a way that preserves mesh quality when a boundary moves. The equations being solved include terms that account for the motion of the mesh maintaining mass and property balances during the solution process. Initial work on leveraging the mesh morphing FSI capability for efficient application to scour problems has been completed.

The scope of this work was to test mesh morphing in a simple case of clear water scour at a cylindrical pier without the complications of sediment transport and settling. The primary goals were to test mesh morphing for this out of the ordinary application of the capability and to verify that field functions could be used to specify the bed recession rate (scour) as a function of the bed shear stress. Part of the process was to develop any procedures needed to keep the computation numerically stable and accurate as the analysis is carried out. The procedures provide a framework for the implementation and testing of more sophisticated physics models for the scour process, including sediment transport in follow on work.


Sand bed shear stress distribution during the scour process around a cylindrical pier


Highlights of University of Iowa Research Carried Out on the TRACC Cluster

Researchers at the University of Iowa have made extensive use of the TRACC cluster in their research. The main CFD projects were related to the study of scour and erosion phenomena around bridge abutments with sloped walls, study of mechanisms for scour at a river confluence situated in Illinois and estimation of the pressure distributions and resultant forces and moments on large traffic structures (DMS cabinets used generally on highways) that are becoming more and more popular in the Midwest. The first two projects used a massively parallel research code developed in Dr. Constantinescu's group. This code uses hybrid Reynolds-Averaged Navier Stokes-Large Eddy Simulation (RANS-LES) techniques to simulate flow and turbulence structure at field conditions. The simulations performed as part of both projects can be considered as advancing the state of the art in their fields.

Previously, LES and RANS-LES simulations of flow past abutments were limited to simplified geometries in which the abutment was modeled as a vertical wall obstruction. The simulation of the flow past an abutment of a more realistic shape with both a flat and deformed bed corresponding to equilibrium scour conditions revealed important differences when compared to the simplified cases simulated in the past using eddy resolving techniques. This was true both for the region situated upstream of the abutment where the scour is driven by the horseshoe vortex (HV) system and laterally where both the legs of the necklace vortices and the eddies convected within the separated shear layer contribute to scour. A major future effort will focus on understanding the differences in the scour patterns when rip rap protection is placed around the abutment.

Vortical structure in the flow at (a) the free surface;
(b) at 0.5D from the bed; and (c) at 0.2D from the bed