Entrainment models for turbulent axisymmetric jets and forced plumes

Entrainment models have been used for several decades to make growth predictions for turbulent jets and plumes. Although useful, these models are based on ad-hoc assumptions, and say very little about the underlying physics. Recently, van Reeuwijk & Craske (2015) derived an energy consistent unified entrainment relation, providing contributions from mean, turbulence, buoyancy and pressure via profile coefficients. Here, we present the results of simultaneous time resolved measurement of velocity and density in an axisymmetric turbulent plume using 2D-2C particle image velocimetry (PIV) and planar laser induced fluorescence (PLIF), respectively; using refractive index matched fluids to remove uncertainties due to optical distortions. We test the existing models, and compare them to our measurements and data available in the literature. We also discuss the effects of variability in the value of entrainment coefficient and scalar to velocity spread rate. Finally, employing our experimental data we develop an entrainment model based on the relation developed by van Reeuwijk & Craske (2015), parameterizing the profile coefficients based on local Richardson number.