Measuring and Modeling Turbulence Using Particle Image Velocimetry and Smoothed Particle Hydrodynamics; Applications to External Flows

Abstract

Understanding the flow field around objects (i.e. external flow) is very important for various engineering and scientific application at all scales. The overall objective of this study is to better understand the flow field and turbulence in a wave-current flume for internal and external flow studies using particle image velocimetry and to investigate the capabilities and limitations of the Lagrangian smoothed particle hydrodynamics (SPH) method to simulate external flows using the collected experimental data in the wave-current flume. Laboratory studies are useful for observation of physical phenomena in a controlled environment in addition to their being less expensive and more accessible than field testing. Numerical methods are additionally advantageous because they are less expensive than experimental and field work, they can be more easily applied at various scales, and they require less time and preparation than observational studies. Smoothed Particle Hydrodynamics (SPH) is a popular Lagrangian numerical method to simulate the flow and wave fields around coastal and marine structures in a complex ocean environment. Currently, SPH models usually incorporate simple turbulence models to simulate real viscous flows as a default. At first, an experimental study was conducted to determine the effects of surface roughness on wake turbulence. A bare aluminum cylinder of diameter 0.0508 m (2") and an identical aluminum cylinder treated with an antifouling marine paint were set up individually across the channel of a recirculating flume in which a sheared flow was present. Using particle image velocimetry (PIV), the wake across approximately 5.5 diameter-lengths trailing the cylinder and with various Reynolds numbers was measured and the turbulence parameters and wake widths estimated. Further, a 2-D model of the cylinder system was developed in an SPH model to closely examine how the turbulence setting and parameterization can affect the hydrodynamic fields in the wake of the cylinder and how the model parameters can be tuned to refine the turbulent eddy representation. We focused on the turbulence modeling in DualSPHysics which is a SPH-based open-source code that can implement a Large Eddy Simulation (LES) method based on the Smagorinsky eddy viscosity model (Smagorinsky, 1963). The performance of the SPH model in simulating the turbulence was examined using the PIV data. In particular, the limitations of SPH regarding high Reynolds number simulations were explored. Results can be applied in SPH in the simulation of the flow field around marine and coastal structures. The wave-current flume exhibited a sheared velocity with