Numerical study of complex flow physics and coherent structures of the flow through a convoluted duct

Abstract

The open source computational fluid dynamics (CFD) software OpenFOAM is used to investigate the flow through the Wellborn s-duct. Numerical simulations with two different modelling techniques are performed. Transient simulations with Unsteady Reynolds Averaged Navier Stokes (URANS) and Detached Delayed Eddy Simulation (DDES) formulations are compared and validated against experimental data. Given its nature, URANS results show a low unsteadiness level with an almost static shear layer. DDES simulations correspond closely to experimental data. Total pressure recovery is within 2.07% of values recorded in experiments. The highest standard deviation values of velocity components are located in the central interface plane region. Modal decomposition techniques are applied to determine coherent structures and the dynamic nature of the complex flow physics. One horizontal shifting mode and two vertical shifting modes are clearly identified. The two vertical shifting modes oscillate at very different frequencies of 460 and 70 Hz. Phase information and frequency of occurrence are determined through dynamic mode decomposition and frequency domain analysis of snapshot flow field data. Frequency maps of flow properties at the aerodynamic interface plane (AIP) are also presented. Phase analysis of modes in convoluted ducts are reported in the public domain for the first time and offer promise of a tailored, active flow control strategy.