Numerical experiments of the flow around a bluff body with and without roughness model near a moving wall

Abstract

Numerical tests at high Reynolds number flows were taken on circular cylinder placed near and parallel to a moving ground. A moving ground running at the same speed as the free stream eliminates the confusing effects of the boundary layer formed on the ground being, therefore, more effective to establish a better understanding of the relationship between complete vortex shedding suppression and surface roughness. A detailed quantitative measurement of the flow field around the cylinder using Lagrangian vortex method with roughness model was carried out. The effect of higher surface roughness heights is studied because it introduces greater instabilities in the boundary layer of bluff bodies. The purpose is to investigate supercritical flow patterns from subcritical Reynolds number flow simulations. The present results are compared against those measured for smooth cylinder under the same flow conditions. It is found that certain critical gap ratio between the rougher cylinder bottom and the moving wall significantly reduces the drag force. The lift force points away from the wall plane. The full vortex shedding suppression is successfully anticipated. In addition, the Strouhal number vanishes. The contribution of this research is to report that von Kámán-type vortex shedding totally ceases and instead two nearly parallel shear layers are formed behind the cylinder in moving ground when employing two-dimensional modeling of roughness. Previous numerical results for flow around smooth cylinder placed closer to the moving ground did not capture the behavior of Strouhal number equal to zero. Unfortunately, there is a lack of experimental results for rough cylinder near a moving wall, which motives the present study.

Control and Suppression of Vortex Shedding from a Slightly Rough Circular Cylinder by a Discrete Vortex Method

“…The main contribution of the present paper is shown that the methodology proposed by Alcântara Pereira et al [10] also captures important changes in the flow dynamics of the slightly rough circular cylinder in the vicinity of a moving wall. Thus, the effect of small relative roughness size, namely, ε*/d* = 0.001, on flow dynamics around the cylinder is investigated and compared to smooth cylinder configurations.…”

“…That result showed a slight increase of the viscous drag force as compared as that of the smooth cylinder. Alcântara Pereira et al [10] have reported differences above 10% between the smooth cylinder and other rough when integrating only static pressure, and, therefore, as discussed by them, the surface roughness effect has been captured by their numerical approach.…”

“…In the context of the present work, the literature has reported studies of surface roughness effect on flow past a bluff body with low frequency [2,5,6,[9][10][11][12][13][14][15][16][17][18][19]. It is important to mention that numerical analysis of rough bluff body aerodynamics near a ground plane is very limited, which valorizes the recent methodology proposed by Alcântara Pereira et al [10] and classified such as "hybrid control technique of vortex shedding" [20].…”

“…In a recent paper, Alcântara Pereira et al [10] proposed a hybrid control technique of vortex shedding, combining passive and active controls, to study the flow past the rough circular cylinder in the vicinity of a moving wall at upper-subcritical Reynolds number of Re = 1.0 × 10 5 . They successfully associated the methodologies developed by Bimbato et al [11,21,22] focusing on the effect of higher relative roughness sizes, namely, ε*/d* = 0.0045 and 0.007, on flow dynamics of the cylinder at small-gap regime, which was identified in past investigation by Bimbato et al [22] at h*/d* < 0.20.…”

“…It is important to observe that Alcântara Pereira et al [10] only computed the form component of the drag force. According to the discussions of Achenbach [9], the form (or pressure) component dominates the drag force on the smooth cylinder contributing more than 98% of the total drag force.…”