ABSTRACT
The advantages offered by eqn (24) are available also in the evaluation of the aerodynamic force and moment. Let the complex force F be defined by
F =T.), iFy (25) where F, and Fy are the x-and y-components of the aerodynamic force F. If the x-direction is aligned with the freestream velocity, then F, represents the drag and Fy represents the lift. Equation (14) is expressible as
. d F-ip z(y + us) dS +1P — L(zkrk) dt dt k (26)
where us is the tangential velocity component of the solid motion. The integral in eqn (26) can be expressed in the transformed plane as j021` fg)(y‘: + uo) dj. In actual computations, it is convenient to evaluate the integral in eqn (26) in the transformed plane. An equation similar to eqn (26) is obtainable for the moment of aerodynamic force using eqn (3). As with the boundary layer vortex strength y, the contributions to the aerodynamic force and moment are attributable to the freestream, the tangential motion of the solid surface, the normal motion of the solid surface, and the wake vortices. In applications where the transformation function fg, t) is available analytically, closed-form analytical expressions are often available for the first three contributions to the unsteady aerodynamic force F.
