On the Aerodynamic Force of the Oscillating Airfoils

The measure of the aerodynamic force around an oscillating airfoil represents the object of many theoretical and experimental researches in the modern Aerodynamics. The classical near field methods, based on the solid surface integration of the pressure and shear stresses, and the far field methods, obtained through the integral balance of the momentum equations, are the main categories in which all the force calculation techniques are included. The far field methods offer several advantages with respect to the classical near field ones and represent a positive solution to several limitations observed in the applications. Currently, the use of far field methods in the numerical solutions is limited only to the steady flows. It does not exist a well assessed far field method for unsteady flow regimes. The present thesis concerns the development of a new measurement technique of the aerodynamic force by means of a far field approach. The method is based solely on the knowledge of the vorticity field. The role of the Lamb vector (i.e. the vortex force) in the determination of the aerodynamic force is clearly highlighted. Several numerical solutions around an airfoil in pitching conditions (from pre-stall to the dynamic stall) have been achieved in the flow transition regime. The method employed in the fluid dynamic computations is based on the Reynolds Averaged Navier Stokes (RANS) equations in an unsteady reference system. The results obtained in the thesis demonstrate the effectiveness of the present RANS method in the prediction of the dynamic stall characteristics. By means of the new far field method, the real possibility to measure the aerodynamic force also in case of unsteady flows has been demonstrated. In addition, useful qualitative and quantitative information for the aerodynamic design have been extracted through the unsteady breakdown of the force. This technique can be exploited also in the experimental applications, in which the measurement of the aerodynamic force without the knowledge of the pressure is particular critical