It has been shown recently that the near-field of subsonic turbulent jets is composed largely of wavepackets produced by the linear interaction of the perturbing velocity field with the steady base flow. However, computation of the far-field sound from such wavepacket models inevitably lead to an error of more than an order of magnitude despite a close statistical agreement near the jet axis. Recent work (Cavalieri and Agarwal, "Coherence decay and its impact on sound radiation by wavepackets", Journal of Fluid Mechanics, Vol. 748, 2014) suggests that this discrepancy may be caused by the mismatch between the perfect coherence in linear wavepacket models and the decaying coherence in experimental flow fluctuations. We investigate whether this is the case for wavepacket sound radiation in two axisym-metric turbulent jets of Mach number 0.4 and 0.6 using a Linearized Euler Equation (LEE) solver. The objective is to impose the coherence function of flow fluctuations found in experiments on near-field structures, generated using LEE with a fluctuating inflow boundary condition. This is achieved with a boundary value formulation on a cylindrical surface which encloses the jet and using the linear wave equation to project the near-field pressure on the surface to the far-field. This technique is adapted to extrapolate the two-point cross spectral density (CSD) to the far-field. The effect of multiplying the CSD on the cylindrical surface with a coherence contour envelope obtained from experiments is tested prior to projecting the results to the far-field. We observe that matching the near-field coherence profile in this manner yields far-field sound pressure levels that show good agreement with experimental results. An investigation of the CSD on the cylindrical surface reveals that the effect of the coherence envelope is to spread the hydrodynamic component of the linear wavepacket source on to acoustic wavenumbers resulting in a more efficient acoustic source. These results suggest that the decaying coherence profile observed in experiments is the missing link in relating the far-field sound to near-field fluctuations in turbulent jets. This paves the way for the development of a jet noise model which is linear in all aspects, except the coherence profile where all of the non-linearity is confined.
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