NUMERICAL INVESTIGATION OF TANDEM EFFECTS ON BLUFF BODIES AERODYNAMICS

Abstract

Flow over bluff body is an interesting subject in recent time, which has always attractive the attention of aerodynamic researchers due to their unique flow behavior. Bluff bodies in tandem have a wide range application in engineering, such as in road vehicles (truck-trailer), railway trains, high tower building, industrial chimneys…etc. However, the non-streamed with sharp leading edges bodies exposure to high pressure drag at front face and flow separation from the leading sharp corners. Understanding the flow over these bodies led to optimize the design and control flow field by means of active or passive technique. Therefore, the main aim of the present study is to describe numerically the flow field and shielding effects of various square plates, placed coaxially as front body upstream of the square flat-faced sharp leading-edges with rounded back rear body. Analysis of 3D fluid flow behavior around the rear body alone and for the different geometrical combinations (width and gap ratios) at three Reynolds numbers based on the width of rear body in the range 1-1.8 ×105 were considered. The Computational Fluid Dynamic (CFD) using ANSYS FLUNET (19.1) with K-Ɛ turbulence model are considered for solving the governing equations for tested models. The simulated results of the flow properties such as flow stream velocity components, pressure distribution contours and pressure coefficient (Cp) around the rear body alone and front-rear body combinations, show that the optimum combination occurred at (b1/b2=0.75 and g/b2=0.5) with maximum drag reduction of 48% and 12% for the speeds 15 and 20 m/s, respectively. This reduction is due to the shielding effect of the front body that cause the separation streamlines from the front body reattachment onto or very close to the rear body shoulder. The contours of instantaneous streamline velocity patterns, pressure (Cp) and drag coefficients distributions were performed. The numerical results show a good agreement with the experimental results.