Note on the Application of the Linear Perturbation Theory to determine the Effect of Compressibility on the Wind Tunnel Constraint on a Propeller

摘要

It is shown that both in compressible and incompressible flow the pressure function behaves as a potential function, if the assumptions of the linear perturbation theory are accepted. The form of the differential equation satisfied by the pressure function in compressible flow is such that a complete correlation is readily established between the pressure field about a propeller giving a certain pressure rise in compressible flow and that about the same propeller giving the same pressure rise in incompressible flow. This fact is applied to determine the effect of compressibility on the constraint acting on a propeller in a wind tunnel. It is shown that the correction factor to the tunnel velocity to give the equivalent air velocity;corresponding to the same pressure rise across the disc and rate of rotation, is un¬affected by compressibility.