Three-dimensional distortion of free-stream turbulence with the leading-edge stagnation point of an elongated bluff body

The paper focuses on studying the unsteadiness, three-dimensionality, and distortion of free-stream turbulence approaching the stagnation point of an elongated bluff body. This aerodynamic problem is complicated because of the combination of blocking, distortion, and three-dimensional (3D) effects. Using the spectral tensor concept, a closed-form solution of the three-dimensional transfer function (3D AAF) of the fluctuating pressure at the stagnation point is proposed. The 3D AAF provides us with an appropriate way to quantitatively study these effects on the unsteady behavior of fluctuating pressures. Our experimental results indicate that the fluctuating pressure at low wavenumbers can be predicted by Bernoulli's equation. The 3D effect becomes more prominent for smaller-scale turbulence, resulting in a more correlated fluctuating pressure in a spanwise direction and a faster decay of pressure spectra at high wavenumbers. By contrast, the distortion plays a more important role in determining this rapid “roll-off” of the stagnation fluctuating pressure spectra. This tendency becomes more prominent with the increase in L_u/D, where L_u is the longitudinal turbulence scale, and D is the leading-edge body dimension. The possible physical interpretation for the unsteady behavior of fluctuating pressures at the stagnation point is discussed.