A Simple Model for the Average Local Entrainment Rate

A new expression for the mean local entrainment rate in a turbulent intermittent flow is obtained. This expression is used to obtain a simple model for the entrainment rate assuming that an indicator function can be defined for the flow, that the interface defined by the indicator function is homogeneous in two directions, and that the turbulent Reynolds number is very large. A particularly simple form is obtained if the intermittency is in a scalar imbedded in a turbulence field and the correlation coefficient for the indicator function is self_similar. The final expression compares favorably with the limited existing data and with other model expressions. Recommendations for experimental verification are presented.