Scaling laws for aerodynamic loads and acoustics of wall-mounted plates at different deflection angles

Abstract

Inclined flat plates mounted on horizontal surfaces have applications in the aerospace, renewable energy and automotive sectors. While previous studies have examined how aspect ratio and proximity to a mounting surface affect aerodynamic loads on a plate, a systematic investigation of scaling laws for aerodynamic loads and acoustics is lacking. This paper establishes scaling relationships for the aerodynamic loads and the flow-induced noise generated by a wall-mounted flat plate inclined to the flow. Wind tunnel experiments were conducted using a Kevlar-walled test section, with a wall-mounted flat plate deflected between 10◦ and 90◦ across various Reynolds numbers. A correction method based on the bluff body blockage corrections of Maskell and calibrated using open test section wind tunnel data is presented in this work to account for solid and wake blockage effects in the Kevlar test section experiments. For aerodynamic loads, the normalised normal force coefficient collapses when scaled with projected frontal area, converging to a fixed value of the drag coefficient at 90◦. This provides a simple predictive methodology for the aerodynamic loads with maximum errors of ΔCD = 0.073 and ΔCL = 0.081. The scaling law presented in this work is unique for wall-mounted flat plates and differs for flat plates in freestream. Aeroacoustic analysis reveals broadband noise without coherent vortex shedding. The noise scales approximately, but not perfectly, with the sixth power of velocity. The slight variations in the value of the velocity exponent at different deflection angles highlight that it does not simply scale as a compact dipole but other effects are present, including non-compactness and edge scattering effects. The acoustic scaling with projected area exhibits different behaviour at low and high deflection angles. At low deflection angles, the plate is partially immersed in the boundary layer, reducing the acoustic intensity variation with deflection angle. At higher deflection angles (> 30◦), the acoustic intensity scaled with the projected area to a power of 1.2 again indicating additional sources besides the scaling of pure compact dipole sources.

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ORCID for David Angland: orcid.org/0000-0001-5451-2763

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