# Effect of Surface Roughness on Aerodynamic Loads of Bluff Body in Vicinity of Smoothed Moving Wall
## 1 Introduction  
The significant availability of studies on cylinder wakes [1; 2; 3; 4; 5; 6], without the influence of other solid boundaries, is due to their importance to engineering and the simplicity of setting up laboratory arrangements--experimental or computational [7]. Downstream wakes of bluff bodies are complex because they are involved in the same problem of the interaction of three shear layers (the boundary layer developed from the body surface and the two shear layers formed from the separation points). In this framework, the flow can be divided into three regions of interest: within the boundary layer; in the undisturbed flow domain; and in the wake formed downstream of the body. In practice, the phenomena surrounding the shedding of vortical structures are even more complex, as they coexist with phenomena related to turbulence, surface roughness, interference from other solid boundaries, and the influence of mixed convection heat transfer. According to [PERSON] [8], the problem of flows in bluff bodies remains almost entirely in the fields of empirical and descriptive knowledge. The evolution of the computational field has changed this point of view. Nowadays, Computational Fluid Dynamics--CFD--are widely used to study vortex shedding suppression and wake control, considering various suppression induction techniques [9]. The focus of this paper is the computational investigation of turbulent flow configurations with passive or hybrid control for inducing vortex suppression. [PERSON] et al. [9] and [PERSON] et al. [10] have classified wake control and vortex suppression techniques. These can be separated broadly into passive control and active control methods. Passive control is dependent on modifications to the geometry of the body, and active control needs some external source of energy. The control of vortex shedding through the proximity effects of a moving wall, for instance, can be classified as an active method [11] of controlling both the hydrodynamic boundary layer and viscous wake development behind a bluff body. The mentioned example was originary of experimental investigations resulting in the use of a belt moving [12; 13; 14]. In fluid-structure interactions, surface roughness (passive technique) can control the dynamics of vortex shedding by inducing suppression. The flow modification can be quantified in terms of the variation in hydrodynamic forces and vortex shedding frequency [15]. However, the flow in rough cylindrical bodies requires further investigation [16]. [PERSON] et al. [17] pondered that despite the efforts made, the fundamental mechanism of the different types of roughness lacks a thorough understanding. In order to reduce the drag force and improve aerodynamic performance, different roughness patterns have been applied on solid surfaces [9; 18; 19; 20; 21]. Experimentally, the k-type roughness, for widely spaced ribs or grooves, and the d-type roughness for compacted ribs or grooves can be used [21; 22]. These were initially linked to the length scale involved [23]. However, the conceptualization and distinctive characteristics of these two types of roughness have been significantly discussed and expanded [21; 22; 24; 25; 26]. The characterization of roughness on solid surfaces represents a difficulty for computational simulations. The determining parameters for characterizing the roughness are as follows: the relative roughness \(\varepsilon/\mathrm{D}\) (\(\varepsilon\) is the average height of the roughness element, and \(\mathrm{D}\) is the diameter of the cylinder); the protuberance shape; and the protuberance distribution on the surface (regular or irregular) [27]. The shape and protuberance distribution constitute what is known as the roughness texture [28]. Due to the thin boundary layers, small roughness heights have an important effect on the flow [29]. In marine structures, for example, there is an increase in surface roughness because of the growth of marine organisms over a period of time [30].