Stokes-Dependent Droplet Collection Efficiency on a NACA 0012 Airfoil: Insights from Droplet-Informed Simulations

We conducted three-dimensional, Euler-Lagrange simulations of a droplet-laden airflow impinging on a NACA 0012 airfoil under various operating conditions, where a Langevin model was used to include the effect of free-stream turbulence on droplet trajectory. We considered free-stream velocities in the range of 60≤U≤240 m/s, chord lengths in the range of 0.5≤c≤2 m, and droplet diameters in the range 1≤d_p≤160 microns. To minimize the computational cost of collecting statistically significant data, we employ statistical overloading of droplets, allowing us to simulate millions of impinging droplets in a short time span. We monitored the droplet collection efficiency〈β〉as well as droplet impingement velocity〈V_imp〉and angle 〈Θ〉. Our findings indicate that droplet collection efficiency, which quantifies the likelihood of droplet impingement on the airfoil surface, increases with droplet size and free-stream velocity but decreases with airfoil size. However, we demonstrate that the Stokes number, which integrates these parameters, primarily dictates droplet impingement behavior. Furthermore, we observe droplet behavior becoming Stokes number independent at very small and very large values of the Stokes number.