The wake of a wall-mounted rectangular cylinder: Cross-sectional aspect ratio effect

Abstract

Abstract Large-eddy simulations are performed to study the wake of a wall-mounted finite-length rectangular prism at a Reynolds number Re ​= ​1.2 ​× ​104 for the prism aspect ratio AR (= h/a) ​= ​7 and the boundary-layer thickness ratio δ/h ​= ​0.08, where h is the prism span and a is the frontal width of the prism cross-section. Besides, parallel experiments are conducted to provide validation for the numerical simulations. This work aims to explore the dependence of the wake dynamics on the prism cross-sectional aspect ratio CR (= b/a) that is varied from 1 to 4, where b is the side width of the prism cross-section. It has been found that the flow separating from the leading edges of the side and top faces does not reattach for CR ​= ​1–2 but does once CR ​> ​2. This difference produces a profound effect on Strouhal number, drag coefficient, and flow structure. Two types of spiral streamwise tip vortices are captured over the top face, i.e. the primary and secondary vortices. The primary vortices give rise to the dipole structure in the wake for CR ​≤ ​2 but the spiral vortices on the side faces for CR ​> ​2. The formation and evolution mechanisms of these vortical structures including their interconnections and dependence on CR are discussed in detail. The conceptual models for the near-wake flow structures are also proposed with and without flow reattachment.