Computational Study of Shock-Associated Noise Characteristics Using LES
Memorandum rept. Apr 2013-Mar 2014
NAVAL RESEARCH LAB WASHINGTON DC
Pagination or Media Count:
The shock-associated noise characteristics of an underexpanded jet at three jet temperatures were investigated using large-eddy simulations LES. The impact of shock cells on the flow field and near- and far-field noise characteristics were examined. The impact of shock-associated noise is confined to one and a half jet core length in the near field. The near-field shift of the shock-associated peak frequency matches well with the inverse of the shock-cell size, indicating that the variation of the shock-cell size is largely responsible for this shift. In the far field, the variation of the shock-associated peak frequency agrees well with the available empirical model over a large range of the radiation angle, but the model under-predicts the fast increase near the end of the shock-associated noise region. In addition, the distributed nature of the shock-associated noise source impacts the far-field noise characteristic if the distance is not sufficiently large. Heating decreases the shock-cell impact on the total noise, but the heating impact on the shock-associated noise level in the upstream direction is opposite to that in the downstream direction. On the other hand, heating greatly increases the mixing noise, reducing the difference between the shock-containing jets and the shock-free jets.