Large-eddy simulation of the flow in Z-Shape duct

A numerical study is conducted of the transient flow in a z-shape three-dimensional duct using large-eddy simulation (LES) with dynamic eddy viscosity subgrid-scale (SGS) model with a fully structured grid system. The numerical results of the velocity profiles are quantitatively validated against experimental data for z-shape ducts with various lateral separation distance configurations. The framework of the current LES model has been studied and discussed and the performance of LES in predicting the flow in z-shape ducts as a function of separation distances was evaluated. LES predictions of the mean flow velocity profiles are in good agreement (within the experimental uncertainty) with experimental data for the investigated wide range of l/d configurations. This is attributed to the well-resolved large-scale flow structures. Some slight over-predictions and under-predictions were found at certain separation distances. These numerical errors are due to the limited modeling approach to predict small eddies structures with the current SGS model. The main key features of the flow after the first elbow are also identified as separation and re-attachment regions. Some discrepancies are identified for lateral separation distances at sections x/d = 3 and x/d = 5 inside the flow transition regions. These discrepancies are believed to be inherited from the upstream flow numerical errors that arise in the non-uniform flow mixing regions. The potential remedy includes applying finer mesh resolution and/or higher order spatial discretization to accurately resolve the local velocity gradients and the complex flow structures.