Tracking of raindrops in flow over an airfoil

The splashback that occurs when raindrops impact an airfoil results in an “ejecta fog” of small droplets near the leading edge. Acceleration of these droplets by the air flowfield is a momentum sink for the airflow and has been hypothesized to contribute to the degradation of airfoil performance in heavy rain. Presented here is a one-way coupled Lagrangian particle tracking scheme to evaluate droplet concentrations and the associated momentum sink around a NACA 64-210 airfoil section for three rainfall rates. A laminar air flowfield is determined with a standard CFD code and is used as input to the particle tracking algorithm. Raindrops are assumed to be noninteracting, nondeforming, nonevaporating, and nonspinning spheres, and are tracked through the same curvilinear grid used by the airflow code. A simple model is used to simulate impacts and the resulting splashback on the airfoil surface.