This paper provides a review of several physics-based methods developed for predicting sound propagation in flows. The basic principle of physics-based methods is to incorporate some known properties of the underlying physics into the numerical model. For instance, instead of using standard polynomials or Chebyshev polynomials to interpolate the solution, physics-based methods generally use canonical solutions such as Green's functions or plane waves to construct a local description of the

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... ion. The methods described in this paper include the Green's function discretisation, the partition of unity finite element method and the wave-based discontinuous Galerkin method. The principles of these methods are described and their performance and shortcomings are discussed. A key issue that emerges in several of these methods is that the canonical solutions are only valid for uniform coefficients, while the methods are intended to be used with strongly inhomogeneous propagation media.