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

Abstract

A discrete vortex method is implemented with a hybrid control technique of vortex shedding to solve the problem of the two-dimensional flow past a slightly rough circular cylinder in the vicinity of a moving wall. In the present approach, the passive control technique is inspired on the fundamental principle of surface roughness, promoting modifications on the cylinder geometry to affect the vortex shedding formation. A relative roughness size of ε*/d* = 0.001 (ε* is the average roughness and d* is the outer cylinder diameter) is chosen for the test cases. On the other hand, the active control technique uses a wall plane, which runs at the same speed as the free stream velocity to contribute with external energy affecting the fluid flow. The gap-to-diameter varies in the range from h*/d* = 0.05 to 0.80 (h* is the gap between the moving wall and the cylinder bottom). A detailed account of the time history of pressure distributions, simultaneously investigated with the time evolution of forces, Strouhal number behavior, and boundary layer separation are reported at upper-subcritical Reynolds number flows of Re = 1.0 × 105. The saturation state of the numerical simulations is demonstrated through the analysis of the Strouhal number behavior obtained from temporal history of the aerodynamic loads. The present work provides an improvement in the prediction of Strouhal number than other studies no using roughness model. The aerodynamic characteristics of the cylinder, as well as the control of intermittence and complete interruption of von Kármán-type vortex shedding have been better clarified.

Study of Surface Roughness Effect on a Bluff Body—The Formation of Asymmetric Separation Bubbles

“…All numerical simulations run until dimensionless time of t = 75, which is enough to reach a statistical equilibrium; the mean coefficient values (pressure distribution, drag and lift) are computed between 37.5 ≤ t ≤ 75.0. As previously presented by Oliveira et al [18], the adopted criterion to compute aerodynamic loads has sufficiently been refined attaining the saturation state of the numerical simulations; this behavior is typical of a Lagrangian technique.…”

“…Furthermore, Figure 7 indicates that the lift coefficient,C L , oscillates regularly because of the periodic vortex shedding mechanism [41], and the lift force variation of the smooth cylinder is greater than that of the rough cylinder, which agrees with experimental tests conducted by Zhou et al [12]; the dash-dot lines in Figure 7 indicates the mean amplitude of lift force. In the present work, no analysis regarding the vortex shedding frequency is presented, however, a detailed discussion can be easily recuperated [14,17,18].…”

“…The free stream turbulence and surface roughness influence are the most common disturbances in all engineering applications. The wall confinement and the aspect ratio are important influencing parameters that interfere in the comparison between experimental and numerical results, especially when the surface roughness effect is an influencing parameter too [17,18]. These features help us to understand the scatter in the experimental data presented by Guven et al [7].…”

“…In the literature, there are traditional works discussing transition to turbulence e.g., [2][3][4][5][6][7][8][9][10], where the surface roughness influence has also been included. The current scope of the research theme about "surface roughness effect" indicates few experimental and numerical studies e.g., [11][12][13][14][15][16][17][18]. The importance of the more relevant works will be discussed throughout the paper.…”

“…Despite the high Reynolds numbers involved in practical engineering problems, the use of two-dimensional numerical simulations is necessary not only to develop and validate computational codes, but also to help understand the complex physical phenomena involved in such flows, and also to help conservative designs for engineering applications. A wide range of two-dimensional studies can be found in literature e.g., [14,17,18,[25][26][27][28][29][30][31] which includes relevant contributions of our research group.…”