Experimental study on unsteady aerodynamics of an oscillating three-dimensional prism in uniform and turbulent boundary layer flows using forced vibration technique

Abstract

Unsteady aerodynamic forces play a crucial role in phenomena such as vortex-induced vibration and galloping. However, the influence of turbulence on unsteady aerodynamics remains far from been fully understood. In this study, a series of forced vibration model and rigid model wind tunnel tests were conducted in both a uniform flow and three different turbulent boundary layer flows with varying turbulence conditions to investigate the unsteady aerodynamic forces of a slender three-dimensional prism. Turbulence effects on the along-wind and across-wind unsteady wind pressure, local and generalized aerodynamic force coefficients, Strouhal number, correlations and coherence functions of unsteady aerodynamic forces, and aeroelastic parameters were comparatively investigated, and the underlying mechanisms were further discussed. The results show remarkable differences in unsteady aerodynamics between the uniform and turbulent flows due to the complex coupling effects among the turbulence, vibration amplitude, and reduced wind speed. The vibration has a significant impact on the unsteady aerodynamics in the same direction. Additionally, along-wind vibration could influence across-wind unsteady aerodynamic forces, while across-wind vibration has minimal effects on along-wind aerodynamic forces. Increasing the amplitude of across-wind vibration significantly increases vertical correlation coefficients within the lock-in region but notably reduces the separation length, weakening horizontal correlation coefficients on the sideward face. Nonetheless, the unsteady aerodynamics are mainly determined by the quasi-steady states beyond the lock-in region, and the influence of vibration is generally negligible. As turbulence intensity increases, the power spectra densities of across-wind aerodynamic forces become wider, and the across-wind aerodynamic force coefficients and aeroelastic parameters exhibit more moderate variations with reduced wind speeds. Both the vertical and horizontal correlation coefficients decrease noticeably at a high level of turbulence intensity, and the end effect and the formation of nonlinear aerodynamics are also suppressed. The Strouhal number of the three-dimensional oscillating prism is little affected by turbulence. However, the lock-in region is extended in turbulent flows compared to uniform flow.