Unsteady aerodynamic analysis of ducted fans

A steady and unsteady aerodynamic analysis of ducted fans has been developed using a frequency domain panel method based on three-dimensional linear compressible lifting surface theory. The duct is assumed to be a finite-length right-circular cylinder concentric with the rotor. Both the duct and rotor blades are modeled by simple harmonic rotating doublet sheets. The model spans a single reference passage with the influence of the rest of the configuration included by symmetry. Results for the steady state performance characteristics of a ducted rotor are compared with an Euler calculation. The effect of the duct on the unsteady aerodynamic forces induced by blade vibration is examined, and comparisons are made with two-dimensional unsteady cascade theory* Finally, it is shown that the duct has an adverse effect on the aeroelastic stability of the rotor.