Desenvolvimento de um modelo de rugosidade para a simulação numérica paralela do escoamento ao redor de um corpo rombudo

Abstract

There are two groups of methods to control wake destructive behavior and vortex shedding behind bluff bodies. The first one is the active method, where an external source of energy is needed to control the flow. The second one is the passive method, which is characterized by the modification of the body's geometry. Thus, the combination of the surface roughness of a body (passive control) and the approximation of that body to a moving horizontal flat surface (active control) was recently classified as a “hybrid control technique of vortex shedding and suppression”, during the development of this Doctoral Thesis. However, it is reported in the literature that some restrictions imposed by the current roughness models need to be overcome. Furthermore, there are few results in the literature combining both effects of surface roughness and ground plane. And for certain flow conditions, the results of a third overlap, which would be the effect of structural vibration of the body induced by the vortex shedding, are very rare. Especially if high numbers of Reynolds of practical interest are considered. In this Doctoral Thesis, a new roughness model is designed and developed, which is integrated with the Discrete Vortex Method, which already has an adaptation with the inclusion of a Large Eddy Simulation turbulence model. With this contribution, simulations and investigations of the effect of the surface roughness of a two-dimensional circular cylinder in the control of vortex shedding of it are performed for flows in a wide range of high Reynolds numbers. Other flow configurations are also simulated to test the sensitivity of the computational method. Parallel programming in the OpenMP standard is implemented to reduce the final processing time. The new roughness model was successfully implemented and was named the Lagrangian Dynamic Roughness Model – MLDRVL. The vortex formation regimes downstream of the body and the reduction of the drag force were mapped in accordance with the physics of the problem. The drag crisis was captured and investigated for 8 different surfaces of the circular cylinder, including flows in the critical and supercritical regimes which have greater difficulty in being numerically simulated. In particular, the results for the drag coefficient show a good approximation to the values obtained experimentally. The developed method was able to capture, even, the so-called separation bubble, which is a phenomenon that is difficult to reproduce, both by numerical simulation and by experimental investigation. The surface roughness of the circular cylinder isolated from other solid boundaries was able to reduce the drag coefficient by up to 51.6% compared to a smooth surface under the same flow conditions. The application of the hybrid control technique of vortex shedding allowed the drag coefficient to be reduced by 45.4% for the stationary circular cylinder and 57.7% for the circular cylinder vibrating in-line with the incident flow. Finally, parallel programming allowed a significant reduction in the processing time of a typical simulation, around 67% on average.