Insights into the instability mechanisms of radially lobed nozzles

The enhanced mixing capability of radially lobed nozzles (in comparison to circular nozzles) has promoted their use in varied applications -- the precise mechanisms however are yet to be fully understood. The present study was inspired by previous experimental ((Hu et al, 2000) and numerical studies (Cooper et al, 2005) of a six -- lobed nozzle. We have also carried out some preliminary hot-wire anemometry (Amini et al, 2012) and numerical studies (Amini and Sekaran, 2015, 2016) in the past, in order to qualitatively study the flow downstream from the nozzle and obtain a three-dimensional data set from Large Eddy Simulations. The current study employs a wavelet based analysis of our experimental data in order to isolate specific instability mechanisms and identifies these modes in our well resolved numerical studies. The analysis also `follows' the formation and the transport of coherent structures (from within the nozzle to within the free jet) and confirms these mechanisms.