Numerical analysis and acoustic optimization of a detached splitter plate applied for passive cylinder wake control

Abstract

Computational aeroacoustics simulations require a considerable amount of time, which makes the comparison of a large number of different geometric designs a difficult task. The goal of the present study were to provide a suitable methodology for aeroacoustic optimization. By means of numerical analyses using commercial computational fluid dynamics tools (Ansys Fluent), the application of a detached splitter plate in the turbulent wake of a circular cylinder as a passive control method for noise generation was investigated. We have employed two-dimensional URANS simulations, so this case can be considered a toy problem, which contains the main challenges of the physical problem and could indicate trends correctly, but was simplified in order to decrease the computational cost to an affordable level, at the cost of making comparison with experimental data not possible. The irradiation of noise caused by the interaction between the flow and both bodies was evaluated using computational aeroacoustics tools based on the Ffowcs-Williams and Hawkings method. Using a commercial optimization software package (modeFRONTIER), various design optimization methodologies were applied to this flow in order to achieve a possible optimal configuration, i.e., one which is capable of reducing the far field noise level without increasing the aerodynamic forces. Using a multi-objective optimization tool, it was possible to evaluate the behavior of heuristic optimization algorithms and the major advantage of algorithms based on response surface methods when applied to a nonlinear aeroacoustics problem, since they require a smaller number of calculated designs to reach the optimal configuration. In addition, we applied a partitive clustering technique to identify and group the cases simulated into five clusters based on their geometric parameters, overall sound pressure level and RMS of the drag coefficient, confirming the efficiency of the application of long detached splitter plates placed next to the cylinder in stabilizing the turbulent wake, whereas the positioning of splitter plates at a distance larger than a critical gap increased the overall sound pressure level radiated due to the formation of vortices in the gap.