Structural characteristics of a heated jet in cross-flow emanating from a raised, circular stack

The structural characteristics of a jet heated to 425 K and emitted from a raised, circular stack into a 300 K cross-flow were studied via cross-plane stereo particle-image velocimetry measurements at multiple streamwise locations downstream of the stack exit. Similar measurements of an unheated jet at equivalent Reynolds number and similar blowing ratio provided a baseline of comparison for the heated case. Instantaneous velocity fields for the heated and unheated jets were marked by intense, small-scale vortices and only a weak indication of a counter-rotating vortex pair (CVP). Upon filtering by proper orthogonal decomposition (POD) to recover only the large-scale flow features, the imprint of the CVP was clearly discerned in the instantaneous fields. The CVP of the heated jet was stronger as well as larger and advected further into the cross-flow compared to that of the unheated jet. While this large-scale reconstruction by POD embodied 35 % of the turbulent kinetic energy, it was found that these large-scale motions captured a vast majority of the Reynolds shear stress, indicating a predominance of the CVP in this regard.