Effect of Torrential Rainfall on Aerodynamic Characteristics of MALE UAV with Two Element Airfoil Wing Using CFD Approach

Abstract

This paper presents the effect of torrential rainfall rates on the aerodynamic characteristics of a MALE UAV (Medium Altitude Long Endurance Unmanned Aerial Vehicle) with a Two-element high lift airfoil wing (TEAW) and its performance degradation like Rate of climb, Vmax using CFD software suite CFD++. The presence of droplets in the vicinity of the gap between the primary and secondary element of TEAW is also reported. Widespread rain type with torrential rainfall rates of 100 - 2000 mm/hr. and corresponding liquid water content (LWC) of 3.73 – 46.14 g/m³ at 5000 ft (1.54 km) IRA (Indian Reference Atmosphere) conditions are considered for CFD simulations. Significant reduction is seen in lift at higher angles of attack in addition to a reduction in stall angle by 2 degrees and an increase in drag due to the effect of rain. From the study it is observed that the drag value increases with LWC and lift reduction and increase in pitching moment slope with increasing LWC is minor.  The spanwise effect of rain on the TEAW with a twist is also studied. This data will be used to formulate the SOP (Standard Operating Procedure) to fly the MALE UAV in various rain conditions as required by the certification agency.