Purpose Rainfall is one of the main atmospheric conditions that significantly affect the aerodynamic performance of the low Reynolds number flights. In this paper, the adverse effects of rain on the aerodynamic performance of a two-dimensional (2D) airfoil with a chord-based low Reynolds number of 2 × 105 and the mini-unmanned aerial vehicle (UAV) for various flight conditions, i.e. 0°–40° at Mach number 0.04 were studied numerically. The purpose of this study is to explore the aerodynamic penalties that affect the liquid water content (LWC = 5.33) of the airfoil and UAV performance in rain under different flying conditions. Design/methodology/approach The Eulerian–Lagrangian two-phase flow method is adopted to simulate the rain environment over an airfoil and mini-UAV aerodynamic performances. The Reynolds Averaged Navier–Stokes equations are considered to solve the time-averaged equations of motion for fluid flow. Findings The effect of rainfall on the airfoil and mini-UAV is studied numerically and validated experimentally. For 2D airfoil, the lift and drag coefficients for both numerical and experimental results show a very good correlation at Reynolds number 2 × 105. For three-dimensional (3D) mini-UAV, the lift and drag coefficients for both numerical and experimental results show a very good correlation at Mach number 0.04. The raindrops distribution around the airfoil, premature trailing edge separation, boundary-layer velocity profiles at five different chord positions (i.e. LE, 0.25c, 0.5c, 0.75c and 0.98c) on the upper surface of the airfoil, water film height and the location of rivulet formation on the upper surface of the airfoil are also presented. Originality/value For 2D airfoil, the recorded maximum variation of the coefficient of lift and lift-to-drag (L/D) ratio is observed to be 5.33% at an 8° and 10.53% at a 4° angle of attack (AOA) between numerical and experimental results under the influence of rainfall effect for LWC = 5.33. The L/D ratio percentage degradation is seen to be 61.9% at an AOA of 0°–2° for the rain environment. For 3D mini-UAV, the recorded maximum variation of the coefficient of lift and L/D ratio are observed to be 2.84% and 4.60% at a 30° stall AOA under the influence of rainfall effect for LWC = 5.33. The numerical results are impressively in agreement with the experimental results. UAV designers will benefit from the findings presented in this paper. This will be also helpful for training the pilots to control the airplanes in a rain environment.

Purpose The heatwave effects over an airfoil have a greater influence in the aerodynamic efficiency. The purpose of this study is to investigate the effects of heatwave upon the low Reynolds number airfoil aerodynamic performance. Design/methodology/approach In this research, the heatwave effects on micro-aerial vehicles’ wing operation are also demonstrated both numerically and experimentally, at the Chord-based Reynolds number Rec = 2 × 105, and under the influence of various environmental temperatures, i.e. 27ºC (room temperature), 40ºC and 50ºC for various flying conditions. A numerical investigation of the low Reynolds number flows with the thermal effect around the unmanned aerial vehicle is presented using the k–ɛ turbulent model. Besides that, the low Reynolds number-based wind tunnel experimental setup is developed to determine the effects of a heatwave over an airfoil. Then, the numerical simulations and wind tunnel experiments are conducted. Findings The numerical and wind tunnel’s experimental investigations have been performed on a 2D airfoil under a heatwave environment, i.e. 27ºC, 40ºC and 50ºC for different flight conditions. The numerical and experimental results revealed that the heatwave effect and aerodynamic performance are validated with experimental results. The lift and drag coefficients for both numerical and experimental results show very good correlation at Reynolds number 2 × 105. Practical implications The consequences of the increasing temperatures to varying degrees will also be experienced by all commercial aircraft. That is why some great findings are presented here, which are highly relevant for the current and future airline operations. However, sooner than later, the aviation industry should also begin to consider the rising effects of temperature on aircraft operations to develop the loss-reducing adaptable plans. Originality/value From the numerical and wind tunnel experimental results, the recorded maximum lift coefficients are observed to be 2.42, 2.39 and 2.36 for 27ºC (room temperature), 40ºC and 50ºC, respectively, at 16° angle of attack, numerically. Similarly, the recorded maximum lift coefficients are observed to be 2.410, 2.382 and 2.354 for 27ºC (room temperature), 40ºC and 50ºC, respectively, at 16° angle of attack, experimentally. The heatwave effects over an airfoil have a greater influence in the aerodynamic efficiency.

Purpose In a microburst wind, the profiles and characteristics are significantly different from those of normal boundary layer winds. The objective of this work is to study the microburst effect on the performance of aircraft for providing guidelines to frame escape strategies. Design/methodology/approach Large eddy simulation model is used to study the effect of microburst by simulating the actual physical process of microburst-generated downdraft environment over the unmanned aerial vehicle. In this work, an attempt has been made to simulate the dry microburst (microburst not accompanied by rain) numerically using the impinging jet model to explore the effect of microburst at 12° angle of attack for flight take-off condition with a Mach number 0.04. Findings The numerical results revealed the aerodynamic performance loss of an aircraft in the microburst-generated downdraft during take-off condition quantitatively. This could be a more valuable information to the aviation industry. The authors believe that the results shown in this paper will be useful for the designers of aircraft. This will also help train the pilots to control the airplanes in a microburst environment. Practical implications Severe thunderstorms are significant weather phenomena that have a significant impact on various facets of national activity, including civil and defence operations, specifically aviation, space vehicle launch and agriculture, in addition to their potential to cause damage to life and property. Originality/value The maximum percentage of pressure increases on the upper surface of the aircraft between 2 and 7 s is 99.86% under the microburst-generated downdraft condition. The flight escape maneuver could be initiated, before increasing the pressure on the upper surface of the aircraft. The aircraft flies with high airspeed through the microburst environment, where the microburst-generated downdraft is most severe.