Identification of aerodynamic admittance functions in active grid generated turbulent flow

The wind loading on bridge decks depends on the turbulent wind field, but importantly also the aerodynamic characteristics of the cross-section. Aerodynamic admittance functions (AAFs) map the transfer of turbulent winds to resultant forces for a specific cross-section shape as a function of one or more frequencies and/or wavenumbers. In this study, a twin deck section model with pressure taps was tested in the wind tunnel to estimate AAFs under various turbulent flows. Homogeneous free -stream turbulence was generated by an active turbulence grid upstream of the model. Several AAF variants were estimated: 3D one-wavenumber AAFs, 3D twowavenumber AAFs, and 2D AAFs. It was observed that some of the AAFs changed slightly with the turbulence characteristics. The estimated 3D two-wavenumber AAFs are also shown to be significantly affected by the parametric coherence models used for the forces. However, an estimated 3D two-wavenumber AAF yielded an accurate lift force estimate that tended to give slightly larger forces compared to pressure tap measurements.