Unsteady forces on elongated bluff bodies

The aerodynamic shape of the bluff body plays a significant role in determining the unsteady drag force resulting from the three-dimensional (3D) distortion of approaching free-stream turbulence. This paper conducted pressure measurements of bluff bodies with four different cross sections (square, rectangular, circular, elliptic, with different aspect ratio δ = B/D, and B and D are the width and height of the cross section) to study the unsteady aerodynamic behavior of drag force, considering the influence of reduced dimension Lu/D (Lu is the longitudinal integral length scale). Generally, the body with a fixed separation point and a relatively small δ is more blunt, resulting in a higher drag coefficient, spectrum, and coherence than streamlined cross sections in turbulent flow compared to smooth flow. The aerodynamic shape significantly influences the high-frequency component of the one-wavenumber and two-dimensional aerodynamic admittance function (2D AAF). The greater the degree of bluntness of the model, the more pronounced the three-dimensional effect. As Lu/D increases, the drag coefficient and spanwise correlation of the model will both increase and approach the results of a smooth flow. Furthermore, the one-wavenumber AAF and 2D AAF increase at the high-frequency domain, and the 3D effect attenuates. This article proposes a 2D AAF model for modifying the distortion effect in wind tunnel tests.