A Continuous Time Domain Direct Identification Method for Unsteady Fluid Dynamic Model in Incompressible Flow

Abstract

To identify the unsteady fluid dynamic model for a solid moving in the fluid, a new identification method that operates in the continuous time domain is proposed. It is illustrated that this new identification method is more accurate and appropriate for identifying unsteady fluid dynamic model in incompressible flow in comparison with the classical frequency domain or discrete domain method. This new method is applied to identify the unsteady fluid dynamic models of a NACA0012 airfoil and the effect of the fluid viscosity on the model parameter is analyzed. The result shows that the added mass in viscous flow is dependent on the input signal frequency and is exactly the added mass in inviscid flow when the frequency approaches infinity. Based on this discovery, the long controversy on the relationship of added mass between viscous and inviscid flow is solved. Then, the enlightenment of this discovery on the identification of both linear and nonlinear unsteady aerodynamic model in incompressible flow is illustrated. At last, the advantage of the new acquired unsteady fluid dynamic model is discussed in comparison with the classical quasi-steady aerodynamic model.