Effect of wall proximity on the flow over a cube and the implications for the noise emitted

Abstract

The flow over an object such as a cube and the resulting aerodynamic noise are affected by its proximity to a wall. To evaluate the effect of wall proximity on the aerodynamics induced by a cube, numerical investigations have been performed for the flow past the cube elevated to different heights above a solid surface, using the delayed detached eddy simulation method. A benchmark case of a wall-mounted cube in uniform flow is first studied, which gives commendable agreement with the available measurement results, validating the numerical methodology adopted. Subsequently, the cube is elevated to different heights above the ground. Detailed flow topologies around the cube affected by the elevated height are investigated. In addition, the effect of wall proximity on near-wall flow patterns and distributions of the surface pressure are also analyzed. After examining the flow features, the far-field noise emitted from the cube at different elevated heights is predicted by using the Ffowcs Williams-Hawkings acoustic analogy and some implications of the effect of wall proximity on the emitted noise are summarized. For the wall-mounted cube, the noise is greatest along the lateral direction. As the cube is lifted, the radiated sound in the vertical direction increases rapidly and peaks at one quarter of its side length above the ground. The noise induced by the cube tends to be broadband although broad peaks at a Strouhal number of around 0.1 are observed in the vertical and the lateral directions.