Application of the multi-fluid model to study a sea spray effect on the vertical transport of momentum in a hurricane *

Recently a significant evidence has been emerged that sea spray strongly affects the dynamics and structure of a hurricane by influencing the balance between heat influx and momentum outflux through the ocean surface. In this work we present a study of the spray effect on the air-sea exchange of momentum with recently developed Eulerian multi-fluid model. Such an approach enables us to quantify the effect of the spray on the vertical momentum transport in a marine atmospheric boundary layer (MABL) of a hurricane much more precisely compared with a more traditional mixture-type approach. Particularly it allows us to accurately describe the suppression of turbulence intensity by the spray in the air due to two different mechanisms: the turbulence attenuation, which results from the inability of spray droplets to fully follow turbulent fluctuations and the vertical transport of spray against gravity by the turbulent flow, also known as “gravity lubrication”.

The numerical and analytic results obtained for a spray laden MABL using the multi-fluid model show that the accelerating effect of the turbulence suppression dominate over decelerating effect of spray inertia increasing the wind velocity and reducing the drug coefficient. The falloff of the drag coefficient from its reference values is stronger pronounced at higher altitudes. Significant reduction of the drag coefficient occurs for spray volume fraction in the range 10^-5 - 10^-4, which  is significantly lower than that previously predicted by mixture-type models.