The aerodynamic admittance of a square plate in a flow with a fully coherent fluctuation

Measurements are presented of the aerodynamic admittance of a square plate in a flow with a fully coherent fluctuation in the free‐stream velocity. The admittance relates the fluctuating force acting on the plate in the flow direction to the fluctuation in the flow velocity. It is found that, as the fluctuation frequency increases, the admittance increases from unity (its value by definition at zero frequency) in contrast to the decrease found in a turbulent flow. Furthermore, if it is assumed that the fluctuating force has two components, one involving a drag coefficient and the other a virtual mass coefficient, then the measurements show that the two coefficients are frequency dependent. Their variation with frequency is presented.