Performance of different wall functions in turbulent flow inside a pipe, a diffuser and behind a backward-facing step

In this study, the performance of different wall functions and near wall treatments are investigated numerically. The near wall treatments used are divided into two categories with fine mesh and coarse mesh. The results show that in flow inside the pipe, in general, the performance of the near wall treatments with fine mesh, especially in the entrance region of the pipe, is better than the wall functions with coarse mesh. In addition, the results for the pressure coefficient at points just after the step and at the region of return flow are very different from the experimental results, but they predict the length of the reattachment with good accuracy. Moreover, the results obtained for the diffuser shows the relatively good performance of these functions for estimating the pressure coefficient, although in reproducing the velocity profiles in different sections of the channel, they have significant errors compared to the experimental values.