CAA is a relatively new field aiming at providing computational means for understanding the mechanisms and predicting flow generated noise. It was developed to support the constant need for noise reduction in various fields of application, notably aviation. Following the success of the earlier work on turbulence generated noise problems, such as jet noise, CAA is clearly now targeting aeroacoustic problems involving interaction with solid boundaries. To this end CAA is emerging rapidly in parallel with CFD, the impressive progress of which is part of the driving force. In fact the coupling of CFD with acoustics is one of the most challenging issues.
Recent developments in CAA are progressing along two lines: the hybrid or two stage methods and the direct solvers. Hybrid methods aim to extend the use of different types of CFD methods ranging from BEM (Boundary Element Methods) to RANS (Reynolds Averaged Navier Stokes methods) and LES (Large Eddy Simulation) in the field of acoustics. CFD will provide the unsteady flow predictions to an independent acoustic theory as for example an Euler solver or models from acoustic analogy. They are well suited for complex problems and are currently being implemented to practical problems. Direct methods on the other hand, aim to solve both the flow and the acoustics simultaneously. Unsteady flows and the sound they generate are regarded as different subjects, but parts of the same field. Starting from first principle, the solution of the compressible flow equations, will in principle provide the complete information. Contributions along this line have been reported in various contexts, starting from BEM up to advanced CFD.