Simultaneous Measurements of Mixing Fraction and Velocities of a Coaxial Jet in a Turbulent Channel Flow

Abstract

Simultaneous velocity and concentration measurements of the isothermal mixing of a confined coaxial jet in air are performed in a small scale windtunnel at ambient conditions. The Reynolds number is 26000 based on the velocity difference of streams and on the diameter of the injection port. Instantaneous concentration measurements are implemented using planar laser induced fluorescence (PLIF) of acetone seeded injected flow. Simultaneous three-component velocity measurements are performed using stereo particle image velocimetry (PIV). The contribution provides details of the PLIF-PIV measurement setup and of the methodology to obtain instantaneous measurements of the local mixing fraction and velocity. Ensemble averaged velocities, concentrations, Reynolds stresses and turbulent mass fluxes are determined at four positions downstream of the nozzle using up to 3600 PLIF-PIV recordings. The convergence of the root-mean-square of velocity and concentration measurements is assessed in exemplary regions within the shear layers of the mixing zone. The recovered profiles of ensemble averaged velocity, Reynolds stresses and turbulent mass fluxes are compared to Reynolds averaged Navier-Stokes (RANS) and scalar transport simulations. Accompanying RANS calculation of the flow exhibit a strong underestimation of mixing and diffusion rates which can be attributed to the strong anisotropic behavior of this flow.