Abstract
A multigrid method is applied to a fourth-order accurate (spatially and temporally) ® nite difference Runge± Kutta time-marching scheme. This is used to solve the nonlinearEuler equations for the ef® cient prediction of noise radiation from turbofan engine inlets. This noise prediction approach computes a steady-state solution ® rst, and thena source is turnedonand theunsteadysolution is computed.Thishas the advantageofusingthe samenumerical scheme to evaluate the residuals of the governing equations in both the steady and unsteady calculations, which means that the steady-state solution is smoothand nonumerical errors contaminate the acoustic solution.The highresolution steady-state ow® elds are calculated ef® ciently using a full approximation storage multigrid method. This makes it to possible to attain steady-state solutions on extremely ® ne meshes designed for high-frequency turbofan noise problems. It is also shown that acoustic results for a JT15D inlet are accurately represented by the present approach.
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