Rate of Particle Depletion via Coagulation in Isotropic Turbulence

We revisit the turbulent-coagulation fluctuation model originally proposed by Koch & Pope (2002) and extend it to regimes of elevated particle concentration and high Taylor-scale Reynolds number (Reλ). By retaining first-order fluctuations in both singlet concentration and shear rate—modeled as coupled Ornstein–Uhlenbeck processes—we derive a closed-form analytical expression for the rate ratio, incorporating the full shear–concentration correlation. Our model reduces to the Koch–Pope result in the dilute limit but reveals a power-law enhancement in collision rates at higher Reλ and particle volume fractions due to non-Gaussian concentration intermittency. These analytical predictions are validated by stochastic simulations supported by DNS, which recover the classical Koch–Pope behavior at low concentrations.