Characteristics of the wake formation and force distribution of the bistable flow on two cylinders side-by-side

Abstract

This numerical study with experimental support examines the bistable phenomenon along two parallel smooth cylinders submitted to a uniform turbulent cross-flow. The spacing ratio P/D of the cylinders is 1.26, being D the cylinder diameter and P the distance between centers. The computational domain and the experimental tests section are equivalents. The Reynolds number based on the free mean velocity and cylinder diameter was Re = 2.2 × 104. For the numerical analysis, the Navier–Stokes equations were solved using finite volumes method for a URANS simulation (unsteady Reynolds averaged Navier–Stokes) with the kω-SST-SAS (shear stress tensor-scale adaptive simulation) turbulence model. Measurements were performed by means of hot wire anemometry technique, firstly to determine actual boundary conditions of flow velocity and turbulence intensity at the test section entrance, secondly to obtain velocity and velocity fluctuation at the wake of the cylinders in different positions along the cylinder height to corroborate the numerical results. By means of the numerical results of velocity, the process of the wake formation is described, showing that the bistability does not occur simultaneously along the cylinder, corroborated by a delay on the switching process of the simultaneously measured velocities and the cross-correlation function. This effect appears also in the results of cylinder wall pressure distribution as well as in lift and drag coefficients.