# Evaluation of Three-Dimensional Environmental Hydraulic Modeling in Scour Hole
## 1 Introduction  
Due to the rapid development of computing technology, currently using computers have the super computational capacity that leads to a boost in modeling many different issues or simulating complicated systems. This method is widely accepted as a less expensive option compared to the laboratory experiment or real-field operation when related to large-scale studies. Instead of building a big and high-cost apparatus for testing new concepts, numerical modeling can reduce the work down to some effective computer codes. The reliable software can help to investigate or provide more insight on the behavior of large systems that are limited in measurement options [1]. This method fits well while studying large environmental systems such as rivers, estuaries, or oceans. A scour hole developed on a sandy bed channel near hydraulic structures, such as a bed protection of weir, has a considerable effect not only on the safety of the structure, but also on the habitat. In general, physical studies of the scour hole in a hydraulic laboratory take more time and effort than numerical studies, while the former is much more accurate if the mathematical equations for the physical mechanism are not well developed. The flow characteristics are complicated in the scour hole with recirculation, sediment transport, and effect of boundary layer. Both physical and numerical modeling studies were conducted by many previous researchers in scour holes. In the most of numerical modeling studies, the results and accuracy depend on selection of numerical model and method due to the complexity of physical presses. There are many options for numerical modeling. A free computational fluid dynamic (CFD) code named OpenFOAM and the commercial software Ansys Fluent were chosen to compare in this present study. OpenFOAM was developed by OpenCFD Ltd. and OpenFOAM Foundation [2], and the company provides it as an open-source code;therefore, the users can modify or add more codes for the part they want. OpenFOAM also has a wide range of applications of fluid dynamics, with no limitation for parallel computing. These characteristics make it become one of the most widely used CFD packages recently in both industrial and academic sectors [3]. Meanwhile, ANSYS Fluent is a commercial software model developed by ANSYS Inc [4]. Besides the strong capacities for CFD modeling, this option also comes with a powerful graphical user interface and various supporting services, such as the integration with several grid-generating and post-processing software, and a typical support team [5]. However, the users have to pay for the license and cannot interfere with its inside codes and functions. This study focused on a comparison of the accuracy of these widely used tools and especially their performances in hydraulic modeling of flow in the scour hole near the bottom wall. Previously, several related research studies have been done to compare the performance of these two CFD codes in simulations of specific targets. [PERSON] et al. [3] conducted an experiment using OpenFOAM and Ansys Fluent for simulating the turbulence separated flows, and their analyzed data show essentially equal results. A possibility to archive the agreeing results from both models was proved by [PERSON] and [PERSON] [6] when they examined the exterior flow field around simplified passenger sedan geometry. However, research result from [PERSON], et al. [7] has shown some differences. In the study by [PERSON], et al. [7], the authors used Reynolds Average Navier Stokes (RANS) with \(k\)-\(\epsilon\) turbulence model for both OpenFOAM and Ansys Fluent codes for the simulations. They concluded that the flow velocity was more accurately predicted by OpenFOAM, but the turbulent kinetic energy was more accurately predicted by Ansys Fluent. For the flow near the wall, such as flow in scour hole, there also are many studies conducted by OpenFOAM [8; 9; 10; 11; 12] or Ansys Fluent [13; 14; 15; 16; 17].