The diffusion of conserved and reactive scalars behind line sources in homogeneous turbulence

Experimental results for the statistics of turbulent reactive plumes behind line sources are given. The results are obtained with sufficient spatial and time scale resolution and cover the near and far fields. The results for the conserved scalar, which is constructed from the two reactive scalars, are consistent with those measured in passive thermal plumes. The results for the reactive scalars show that within the experimental range, turbulent mixing is the dominant contributor to the spread rate of the plume and the contribution from chemical reaction is small. However it is found that chemical reaction has a large effect on the decay of the plume reactant concentration and this effect depends on the stoichiometric mixture fraction. The gradient model for turbulent diffusion and the conventional model for the dissipation time scale of scalar variance have been tested and it is found that they are satisfactory in the far field of the plume. However large errors can result in the near field. Also it is found that the turbulent diffusitivities derived from the conserved and reactive scalars are about the same. Various models for the mean chemical reaction rate have been checked and it is concluded that an interpolation between the frozen and equilibrium limits for the covariance of the two reactive scalars will model the mean chemical reaction rate reasonably well.