Estudo do escoamento ao redor de cilindro circular: influência da proximidade ao solo, efeito de vizinhança e da intensidade de turbulência

Abstract

Risers, widely used in offshore engineering, are long multilayer tubes designed to transport fluids - such as oil and natural gas - from the seabed to offshore platforms. The seasonality and variation of sea currents over time make it necessary to study different flow regimes and boundary conditions. This work aims to study the effects of flow around the circular cross section of a tube in a two-dimensional computational analysis. Therefore, a study is made on the influence of the Reynolds number and the type of flow, obtaining results for the laminar and turbulent regimes. In the flow around an obstacle, it is interesting to study the characteristics of the vortex shedding and the force coefficient. This phenomenon generates pressure variations on the surface of the structure, causing dynamic efforts that can induce oscillations, vary the drag and lift forces and cause structural failures if the frequency of the vortex shedding approaches one of the natural frequencies of the structure. The analyzes were performed through computational modeling using the computational fluid dynamics software ANSYS c Fluent and then compared with the results of other models in the literature. Initially, simulations were carried out with laminar flows. In these, a study of the influence of the proximity of one riser on the other was also carried out. Thus, the force coefficients are obtained as a function of the distance from one riser to the other and the proportion of the domain asymmetry, respectively. It is observed that, for low distances between the cylinders, there is a region of speed considered null, appearing not to be two bodies, but only one. And, as the cylinders move away, the region narrows, until the second cylinder has a speed profile similar to the first. In addition, the influence of the vertical position of the riser (depth) in relation to the seabed was investigated. It was observed that, when the cylinder was in contact with the seabed, the values of the coefficients varied significantly, as well as the number of Strouhal. Subsequent studies consider turbulent flows. In these simulations, the k − ω SST turbulence model was used. In many cases in the literature, fixed values of turbulence intensity are used for all Reynolds numbers. This work varies this parameter to verify its influence on some aerodynamic coefficients, taking into account the Reynolds number. It was found that fluctuations in the lift coefficient are the most affected by this parameter.