A CFD Coupled Acoustics Approach for the Prediction of Coaxial Jet Noise
نویسندگان
چکیده
Prediction of jet noise is important for civil aircraft. Some CAA methodologies predict the full unsteady flow field of a jet in order to ascertain the far-field noise. The approach adopted here is to utilise CFD to obtain steady state information using a turbulence model and hence to provide inputs to a semi-empirical noise model, herein after referred to as the four source model. Predictions of a coaxial jet in comparison to laser measurements show that the CFD methodology can reproduce the experimental velocity field mixing and turbulence intensities. This leads to confidence that the CFD model can predict the influence of geometrical changes (such as nozzle area ratio) on the mean and turbulence field and so increase the validity of the four source model. Predictions of two geometries with differing area ratios showed that peak turbulence intensities are increased in the smaller area ratio, but this can be accounted for by the use of a ‘fully mixed’ velocity in a four source model for jet acoustics. Predictions of a three-quarter cowl geometry were used to determine the equivalent parallel coaxial jet found immediately downstream of the bullet. This was achieved by integrating the areas and mass flows in the primary and secondary streams at the nozzle exits and downstream of the bullet. It is found that a velocity ratio of 0.7 and area ratio of 2.6 at the nozzle exit planes can be considered equivalent to a velocity ratio of 0.5 and area ratio 5 in the parallel flow downstream of the bullet. Input of such information from a RANS CFD prediction may be a relatively simple method for extending the applicability of the four source model.
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تاریخ انتشار 2002