Near wake flow features of polygonal cylinders in different incidence angles

Masoudi, Esmaeel; Gan, Lian; Sims-Williams, David

Abstract

In this study, large eddy simulation (LES) is used to simulate flow of incidence angle α around polygonal cylinders of side number N=5-8 at Reynolds number Re=10,000. Six incidence angles are studied on each cylinder, which covers the entire α spectrum from face to corner orientation. Time-mean aerodynamic forces including lift, drag and vortex shedding frequencies as well as the near wake flow features are discussed in detail. It is found that because of the intrinsic quasi asymmetric shape of polygons in non-principle orientations, flow separation characteristics and hence the induced aerodynamic forces exhibit unique and complex dependence on both alpha and N. Even though the canonical inverse relation of drag coefficient and Strouhal number, which was previously proposed from experimental observations, still holds at arbitrary alpha, the variation of the two is found to be non-monotonic on both alpha and N. Furthermore, mean shear layer length measured from the cylinder centre is found to be a powerful scaling factor for all the quantities investigated, including lift and drag coefficients, Strouhal number and pressure coefficient. Furthermore, a flapping behavior is observed in the separated shear layer which could be responsible for flow reattachment that enforces double separation (instead of single separation) from top or bottom of the cylinders. This flapping behaviour found to be an essential factor that determines highest mean shear layer length in asymmetric incidence angles, which contributes to lowest drag and/or highest
frequency of the vortex shedding.

Citation

Masoudi, E., Gan, L., & Sims-Williams, D. (2021, September). Near wake flow features of polygonal cylinders in different incidence angles. Paper presented at UK Fluids Conference 2021, Online

• Presentation Conference Type: Conference Paper (unpublished)
• Conference Name: UK Fluids Conference 2021
• Start Date: Sep 8, 2021
• End Date: Sep 10, 2021
• Deposit Date: Dec 3, 2021
• Public URL: https://durham-repository.worktribe.com/output/1137342
• Publisher URL: https://www.southampton.ac.uk/engineering/news/events/2021/09/10-uk-fluids-conference-2021.page?