Advances in numerical boundary conditions for computational aeroacoustics

Advances in computational aeroacoustics (CAA) depend critically on the avai lability of accurate, nondispersive, least dissipative computation algorith m as well as high-quality numerical boundary treatments. This paper focuses on the recent developments of numerical boundary conditions. In a typical CAA problem, one often encounters two types of boundaries. Because a finite computation domain is used, there are external boundaries. On the external boundaries, boundary conditions simulating the solution outside the comput ation domain are to be imposed. Inside the computation domain, there may be internal boundaries. On these internal boundaries, boundary conditions sim ulating the presence of an object or surface with specific acoustic charact eristics are to be applied. Numerical boundary conditions, both external or internal, developed for simple model problems are reviewed and examined. N umerical boundary conditions for real aeroacoustic problems are also discus sed through specific examples. The paper concludes with a description of so me of the much-needed research in numerical boundary conditions for CAA.