Experimental investigation of multi-scalar mixing in a turbulent coaxial jet

The present experiments focus on the (concurrent) evolution of two passive scalars (temperature and helium concentration) and velocity in a turbulent coaxial jet. The latter is based on the work of Cai et al. (J. Fluid Mech., 2011) and consists of a vertically oriented central jet of helium and air, surrounded by an annular flow of (unheated) pure air, emanating into a slow co-flow of (pure) heated air. The two scalars and velocity are measured simultaneously using a 3-wire thermal-anemometry-based probe, which is composed of two hot-wires forming an interference (or Way-Libby) probe to measure velocity and helium concentration, as well as a cold-wire for measuring temperature. The downstream and cross-stream evolutions of single and multivariable/joint statistics, including scalar fluxes, the scalar covariance, JPDFs, and the conditional scalar diffusion, will be presented and validated against previous experimental and numerical studies of coaxial jets.