Improvements to Transonic Flowfield Calculations

Several improvements have been made to a transonic full potential flow code, to allow more accurate and flexible analysis of helicopter rotor blade flowfields. Rigid body motion about flapping, pitch, and lead-lag hinges has been incorporated into the grid, with flow velocities due to blade motion incorporated into the solution explicitly through grid velocity terms. Along with explicit handling of blade motion, inflow due to the farfield wake has been recast in terms of a velocity parallel to the shaft axis. Boundary layer effects have been incorporated into the potential flow code by using a strip-theory approach in conjunction with a 2-D boundary layer analysis in a coupled viscous-inviscid interaction. This work provides skin friction information as well as modification of the inviscid flow behavior. Also, a Newton iteration method has been developed to reduce the number of time steps required for a given analysis and to minimize errors due to approximate solution of the linear system.