Influence of free stream effects on jet noise generation and propagation within the Goldstein acoustic analogy approach for fully turbulent jet inflow boundary conditions

Sound generation and propagation by low-Reynolds number turbulent jets from a DNS database is modelled using the Goldstein acoustic analogy method. In comparison with previous work, the DNS data feature fully resolved turbulent boundary layers at the pipe nozzle exit and include the free-stream flow to study the influence of coflow on effective noise sources. To investigate the statistics of turbulent sources, fourth-order correlation analysis is applied to the DNS data. The results are in reasonable agreement with the conventional Gaussian turbulence statistics source model. For meanflow sound propagation modelling, adjoint linearised Euler equations are solved in the frequency domain. Far-field acoustic predictions are obtained for 40 degrees and 90 degrees observer angle to the jet flow and compared with the reference far-field noise spectra obtained from the same DNS database. To investigate the validity of some commonly made approximations, the results for the locally parallel meanflow propagation model and those for the compact eddy scale approximation are also presented and compared with the reference solution.