E ffects of heavy rainfall on aerodynamic efficiency have been one of the causes of many aircraft accidents for both transport and light general aviation airplanes. Meteorologists and aviation communities have been interested in rainfall associated with thunder storms for many years to standardize rainfall measurements and to express these in terms of quantifiable parameters such as liquid water content (LWC) and rainfall rates. In one of the earliest works in this area, Rhode1 indicated that the aerodynamic drag increased to result in an 18% reduction in the true airspeed of the DC-3 aircraft flying in heavy rain with a LWC of 50 g/m3. Experimental work reported by Hanes2 also pointed out that the heavy rainfall rate of 1500 mm/h may cause
The essential components and details of the flow model to capture the impact of rainfall on aerodynamic surfaces such as an isolated wing and the aircraft model will be outlined. Computed results will be discussed and directions for future work outlined. The approach used in this study is to model the effect of rainfall droplets on the aerodynamic configurations and based on the droplet–aerodynamic surface interaction predict the behavior of the characteristics of the aerodynamic configurations. Both liquid films as well as droplet impingement studies are taken into account. A Lagrangian formulation is used to track the dispersed phase in the continuous flow field. The effects of mass, momentum and energy transfer due to the dispersed phase were accounted in the Eulerian equations by adding the source term. It is important to create the coupling of mass, momentum and energy between the continuous and dispersed phases. In order to achieve this, a two way momentum coupling is used by assuming rain drops to be
The wall-film model, the liquid drop impinges upon a boundary surface of the wall and forms a thin film detail of which can is shown in Figure 3(a). The wall film model can be divided into four major parts i.e. interactions of the particles during the initial impact with a wall boundary, subsequent tracking on surfaces, calculation of film variables and coupling to the gas phase. To model the film near the wall thin film equations are solved which is nothing but continuity, momentum and energy equation for the thin film thickness. The basic mechanisms for the wall-film model are shown schematically in Figure 3(b). The main assumptions used for the wall-water film model that the temperature changes slowly in the film particles and never exceeds the boiling temperature of the liquid and that the particles in the thin film are in direct contact with the wall surface and heat transfer is by conduction from the wall to the water film, the thickness is bounded not to exceed 1 mm. These assumptions facilitate an analytical integration of the thin film equations.The wall interaction regimes are calculated using the Bai-Gosman21 impingement model for a drop-wall interaction based on local information. According to the model the four regimes (splash, spread, rebound and stick) depend on the wall temperature and impact energy of the particles. Below the boiling temperature of