Shear Layer Instabilities of Multiple Jets in Crossflow

The uniform density single jet in crossflow (SJICF) demonstrates absolute/global instability in the windward shear layer (SL) at low jet-to-crossflow velocity ratios (R < 3) and is convectively unstable at larger R values (Getsinger et al., 2012, 2014; Megerian et al., 2007). This work examines the change in the instability boundary of non-reacting, uniform density, multiple axially staged jets in crossflow (MJICF) as the number of jets (n = 2, 3, 4) and the spacing between the jets (L/D = {1.5, 1.6, … 2.5}) are varied. The jet dynamics and the SL transitions are studied using 40 kHz PIV (Particle Image Velocimetry) measurements of the jet center plane. The characteristic time scale of the convecting shear layer vortices and the spatial variation of the instability amplitude of the MJICF flow field are obtained using Fourier analysis and are compared to that of the SJICF operated at identical R. The complex interactions of the individual jets are also characterized using synchronization metrics.