When considering combustion noise in combustion chamber systems, a distinction is made between direct and indirect combustion noise. Direct combustion noise is generated in turbulent, reactive flow fields due to local fluctuations in heat release. This includes ‘turbulent’ combustion noise, in particular, which is caused by the turbulent variations in the combustion process. In contrast to direct combustion noise, indirect combustion noise (also called ‘entropy noise’) – is not produced in the combustion zone itself, but after it. Variations in the composition and temperature of the hot exhaust gases (entropy waves) generate noise in highly accelerated or delayed flow segments. In a gas turbine, for example, high levels of noise are produced in the first turbine stage immediately downstream from the combustion chamber.The numerical simulation of combustion noise requires highly sophisticated methods for numerical computation, as well as further research. Due to the enormous variations in the scale of turbulence, in the chemical reaction and in acoustics, ‘hybrid’ CFD/CAA methods and stochastic reconstruction methods are being developed at the Institute to this end.