COMPUTATION OF UNSTEADY FLOWS AROUND OSCILLATING BLADES USING LINEAR AND NONLINEAR HARMONIC EULER METHODS

A quasi-three-dimensional time-linearized Euler method has been develo ped to compute unsteady flows around oscillating blades. In the baseli ne method, unsteady flow is decomposed into a steady flow plus a linea r harmonically varying unsteady flow. Both the steady flow equations a nd the unsteady perturbation equations are solved using a pseudo-time- marching method. Based upon this method, a novel nonlinear harmonic Eu ler method has been developed. Due to the nonlinearity of the aerodyna mic governing equations, time-averaging generates extra ''unsteady str ess'' terms. These nonlinear effects are included by a strongly couple d approach between the perturbation equations and the time-averaged eq uations, Numerical results demonstrate that nonlinear effects are very effectively modeled by the nonlinear harmonic method.