Strategy for the determination of unsteady aerodynamic forces on elongated bodies in grid-generated turbulent flow

In this study, we developed a general method for estimating the unsteady aerodynamic forces on elongated bodies in grid-generated turbulent flow. The key to this method is the identification of the one-wavenumber aerodynamic transfer function (ATF) of bluff sections. Based on our previous studies, the accuracy of the strip theory in estimating the unsteady aerodynamic forces on bluff sections in isotropic homogeneous turbulence is higher than that of a thin airfoil. The thin airfoil section is therefore intended to serve as a standard configuration to calibrate the experimental parameters to satisfy the accuracy of the strip theory. This can provide a road map for the experimental determination of the unsteady aerodynamic forces on elongated bodies with different configurations in turbulent flow. To explore the deviations between the ATFs of airfoil and bluff sections, buffeting force measurement wind tunnel tests were performed on NACA 0015 airfoils and 5:1 rectangular (REC) cylinders with different length-width ratios at a 0 degrees attack angle in grid-generated turbulence. The measured one-wavenumber ATFs of the airfoil sections correspond strongly to the theoretical predictions. In addition, it was found that the one-wavenumber ATF of the REC model is larger than Sears' function at low reduced streamwise wavenumbers, which is explained by the difference between the lift generation mechanisms of the bluff and airfoil sections in grid-generated turbulence.