Investigation of Under-Relaxation Factors in 2D Dam Break Simulation of OpenFOAM®

Computational fluid dynamics (CFD) is one of the most significant applied sciences in the industry. For this reason, many expensive CFD software is available in the market. OpenFOAM® is a free CFD software that has been used extensively in many ranges of fields. But, even with the free charge, it is still hard to get a good result with OpenFOAM® without extensive computational resources. This study aims to find a way to get good results with minimum computation time by investigating the under-relaxation effects. This study chose the dam break case due to its simple and readily available validation data. The simulation domain was a 200 × 200 mm² dam filled with 50 × 100 mm² water in the dam’s bottom left corner. The simulations were performed with under-relaxation factors, ranging from 0.3 to 1. By changing the under-relaxation factor to 0.95, the mean absolute percentage error became six times smaller, and the simulation was 366 times faster. It shows that the under-relaxation factor is essential in the quality of results and simulation time. However, the most optimal under-relaxation factor may differ from one case to another.