Reduction of Drag Forces on Bluff Bodies - Literature review Example

REDUCTION OF DRAG FORCES Name Course Instructor Institution Location Date 1.0 Introduction The accurate and proper assessment of drag forces on different configurations of bodies allows for a better design and understanding of structures such as towers, buildings, aeroplanes, chimneys and automobiles. Drag coefficient is a function of the objects position, its speed, the flow of direction, fluid density, its size and shape and the fluid velocity. Several factors influence the final drag coefficient of vehicles such as the bodies’ surface roughness, the bodies shape (trailing and leading edges), or the vehicles nose. Others include the vehicle different apparatus such as the handles, mirrors, the doors, etc. The drag experienced by the different bodies is a function of the flow of direction, the relative speed, the configuration of the object (size and shape), the objects placement, the fluid velocity and viscosity together with the roughness in the surface of the bodies. A number of studies and experiments have attempted to use drag forces and pressure distribution of cylindrical bodies to solve or decrease the above problems. A review of literature on the above subject has revealed that several investigations on the quality or aerodynamic have been conducted in cylindrical bodies. while these investigations have revealed some great insights, the performance of definite conclusions both quantitative and qualitative have not been reached as to regards their improved performance on a relative basis with respect to the conventional drag forces that may be experienced by these bodies. The literature especially provides little insight that the effect the roughness experienced by the different parameters in the cylindrical bodies and their impact in reducing the drag forces. More especially the cylinders diameter, the free streamed velocity and the different size of roughness. 1.1 Aerodynamics At the heat of every aerodynamic deign is drag. In aerodynamic and hydrodynamics, the body’s resistance as it moves through a fluid is of vital technical importance Aerodynamics can be described as the study of how bodies moving in airstreams perform. Hydrodynamics can be described as the study of moving that have been immersed in liquids especially water. 1.3 Drag on a cylinder The drag force sis the force that the fluid exerts on the cylinder it usually takes place in the direction of the flow and it is dependent on the flows Reynolds number. 2.0 Drag reduction of a circular cylinder 2.1Grosche and Merier (2001) The paper examines experimental investigation conducted on aerodynamic of bluff bodies. The investigation was conducted at institute of Aerodynamics and Flow Technology. It looked in to the reduction of drag forces using passive ventilation of the wake of the body. It investigated how to reduce drag experienced by automobiles through shape optimisation, which would lead to the elimination or reduction of trailing vortices. In additions, it determined the primary sources of the aerodynamic noise that is produced by high velocity trains that is caused by the unsteady flow separation. The experiments also included investigation of active flow controls that can be used to delay flow separation. 2.2Tsutsui and Igarashi (2002) The researchers investigated the reduction of drag forces of a circular cylinder in an air steam and the flow characteristics displayed by a bluff body that has been cut from this circular cylinder. The study employed two distinct types of test models. The results of the study showed that the distributions caused by the Cp were symmetric for several numbers of small cylinders that were tested both sliced and circular. The Cp’s front region value was close to a negative value or zero. It is because there is a formation of a quasi-static vortex between the large cylinder and the I-type small cylinder and the maximum Cp is between 0.1-0.2 at the shear layers retreatment region, which is separated from the small cylinder. The bluff body that was part of the small cylinder was cut form either side of the parallel to the x-axis and was utilised as a passive control measure to reduce the drag experienced by the larger circular cylinder. 2.3Alma and Moriya (2003) The aim of the paper was to determine the characteristics displayed by fluctuating fluid forces, wake and steady frequencies and the switching experience displayed by two side-by-side cylinders. The investigation found a predominant anti-phase vortex in the both cases of a circular and square side-by-side cylinder of transitional flow pattern corresponding vortex shading. For T=D ≥ 0:20, the action displayed by the lift forces on the two types of the cylinders was repulsive and outward. For T = D1/4 0:10; the action displayed by the cylinder that had a narrower wake inward while the other cylinder it was outward. The study examined the aerodynamic characteristics of both the circular and square cylinders that were arranged in a side-by-side manner and with a uniform flow that contained a 5.5 * 10 Reynolds number. 2.4Lee and Choel (2004) The authors displayed the importance and the role that flow controls of bluff bodies in wind engineering. The authors examined this flow controls and came up with two new flow control methods. The first of the two methods can be used to control shear layers, which have been separated from the bluff body while the second method is used to control the surface flows experienced by the bluff bodies by placing a small rod upstream of the bluff body. While investigating the second method, the authors noted that there is a change of the pattern depending on the Reynolds number the rod diameter and its position. 2.5Pasto (2008) The authors investigated and came up with results concerning the behaviour of circular cylinder that is freely vibrating that is turbulent and laminar flow. By changing the mass-damping parameters and the roughness of the cylinder, they conducted wind tunnel tests. The effects of the flow turbulence and surface roughness were taking into consideration practically in terms of an effective and efficient Reynolds number. The authors revealed that is was possible to evaluate the sample prior to and after the commencement of the cylinder boundary layer transition. It also displayed that the Reynolds number and the mz play a crucial role to control the response during the lock in. 2.6Mohammad and Islam et al. (2010) The study displayed the how drag is important in fluid mechanics and aerodynamics more especially as it applies to any type of moving object with different shapes and sizes. The investigation carried out several key experiments that were successful in reducing drag forces especially given the fact that drag forces cause structural failure and consumes a lot of power of the object. The research describes how attached circular rings are used to reduce drag forces experienced by a circular cylinder. Subsonic wind tunnels were used. Drag measurements were conducted. The experiment first verified the drag forces experienced by the circular cylinder before the circular rings were attached. The experiment investigated the drag forces occurring over the circular cylinder once the circular rings were placed. Reference Protas, B., and J. E. Wesfreid. "Drag force in the open-loop control of the cylinder wake in the laminar regime." Physics of Fluids (1994-present) 14.2 (2002): 810-826. Bergmann, Michel, Laurent Cordier, and Jean-Pierre Brancher. "Drag minimization of the cylinder wake by trust-region proper orthogonal decomposition." Active Flow Control. Springer Berlin Heidelberg, (2007): 309-324. Lyotard, Nicolas, et al. "Polymer and surface roughness effects on the drag crisis for falling spheres." The European Physical Journal B 60.4 (2007): 469-476. Loads on a circular cylinder." Journal of Visualization 4.1 (2001): 61-72. Grosche, F-R., and G. E. A. Meier. "Research at DLR Göttingen on bluff body aerodynamics, drag reduction by wake ventilation and active flow control.” Journal of Wind Engineering and Industrial Aerodynamics 89.14 (2001): 1201-1218. Tsutsui, T., and T. Igarashi. "Drag reduction of a circular cylinder in an air- stream." Journal of Wind Engineering and ndustrial Aerodynamics90.4 (2002):527-541. Mahbub Alam, Md, M. Moriya, and H. Sakamoto. "Aerodynamic characteristics of two side-by-side circular cylinders and application of wavelet analysis on the switching phenomenon." Journal of Fluids and Structures 18.3 (2003): 325-346. Lee, Sang-Joon, Sang-Ik Lee, and Cheol-Woo Park. "Reducing the drag on a circular cylinder by upstream installation of a small control rod."Fluid dynamics research 34.4 (2004): 233-250. Read More