Coherent Dynamics of a Turbulence Structure around Streamlined Piers

In our previous study, pier streamlining was demonstrated to help reduce local scour tendency based on the excess shear stress theory, and thus can potentially serve as an alternative scour countermeasure. However, the Reynolds-averaged Navier-Stokes (RANS) numerical method we previously employed inherently fails to capture the coherent dynamics of turbulence around pier, which also plays an important role in scour mechanism. To address the limitation, this paper employs the detached eddy simulation (DES) method to simulate the flow physics around piers with different extents of streamlining efforts. A total of four test cases were simulated in this study. Systematical comparison of the simulation results among different cases reveals significant variation of the flow physics with different extent of pier streamlining effort in terms of coherent structure dynamics, turbulence statistics, and bed shear stress distribution. Distribution and fluctuation of the pressure acting on channel bed, as well as its indication to scour extent, are also discussed. Findings in this study confirm that pier streamlining helps reduce the local turbulence intensity and therefore can serve as a scour countermeasure alternative.