The Unsteady Forces Due to Viscous Wakes in Turbomachines

The configuration of viscous wakes of cascade blades is approximated from single airfoil experiments. The unsteady force and moment on a downstream blade passing through such wakes is then calculated on the basis of the theory of isolated thin airfoils in nonuniform motion. The results indicate that the force is nearly proportional to the profile-drag coefficient of the upstream blades. For typical values of this coefficient and conventional cascade geometry the unsteady forces arising from passage through viscous wakes are of about the same size as those due to aerodynamic interference between the moving blade rows, previously estimated.