Generalised airforces on a cylindrical shell oscillating harmonically in a uniform flow

Abstract

The flow of air past an infinite shell is considered. In its undisturbed state the shell is a circular cylinder. A portion of the shell between two normal cross-sections is flexible, the rest of the shell being rigid and fixed. The flexible portion is closed by planes normal to the axis of the cylinder. In the absence of any oscillations of the flexible portion there is a uniform flow outside the cylinder, which has the direction of the axis of the cylinder. When the flexible portion oscillates, the uniform flow is perturbed and there is also an acoustic field generated in the space within the flexible portion with the result that there are oscillating perturbation pressures on both sides of the shell surface. A method of determining these perturbation pressures is given when the flexible portion oscillates harmonically with given frequency in a given mode. Expressions for these perturbation pressures are then used to obtain formulae for the associated generalised airforces.