CFD simulation of an UAV across a microburst

• Main Author: Vishwanathan, Gokul
• Other Authors: Chan Wai Lee
• Format: Theses and Dissertations
• Language: English
• Published: 2019
• Subjects: Engineering::Aeronautical engineering
• Online Access: http://hdl.handle.net/10356/78868
• Institution: Nanyang Technological University

Weather plays a vital role in the safe operation of aircraft and other flying vehicles. One of the least known and most significant weather phenomena is the wind shear which is defined as a small-scale meteorological phenomenon accompanied by rapidly changing winds over a small distance. One of the leading causes of wind shear includes severe weather systems like thunderstorms, downburst and many others. Of these, the straight-line winds from the outflow of localised downdrafts are believed to produce rapid changes of wind shear in small spatiotemporal scale and are called as microburst. Due to the highly restricted structure of winds and its dependence on various scales of motion, it becomes complicated for the numerical weather models to predict the evolution of such systems accurately. The primary focus of the thesis is to investigate the structure and flow-dynamics of an isolated stationary microburst using CFD simulations. The microburst-induced wind fields are modelled as a jet impingement technique on to a flat surface using both axisymmetric and planar mathematical formulation. Reynolds Averaged Navier Stokes (RANS) numerical model has been used in the present study. The simulated mean wind profile exhibits similar characteristics observed in a full-scale microburst. As per the steady state RANS model, the normalised peak radial velocity was found at a radial distance of nearly 100m above the ground. The results of the numerical simulation were compared with different laboratory experiments and other field events which match well with the numerical results with discrepancies of less than 5 % at few radial locations. In addition to this, high-resolution satellite data were also used to validate the simulation results. The numerical results compared favourably with the satellite observations suggesting the ability of CFD to aid in better understanding and modelling the flow features. The thesis also deals with the simulation on an airfoil in the turbulent wind field generated by the microburst to study its effects during take-off and landing operations. The transient loading effects on the UAV is also analysed with an increase in microburst outflow with an estimate on the peak loads and moments generated on the model.