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286 || AWSAR Awarded Popular Science Stories - 2019
acting on an airplane (see Fig. below).
For an airplane to stay afloat, the wings
must produce a lift force which is at least equal to the total weight of the vehicle. Also, for it to move forward, the engines must generate a thrust force greater than the resistive drag force exerted by the air. Larger the lift force greater is the ability of the airplane to carry more weight. Similarly, lesser the drag force more easy it is for the airplane to
slip through the air. So, we can attribute lift-to-drag ratio (L/D) to be a quantitative measure of aerodynamic efficiency. It is the aim of my doctoral research to devise a systematic design procedure that would enhance the L/D ratio of fixed wings for MAV applications.
One may ask, “We have
been designing wings for bigger
and faster flying machines such
as civil transport and military
airplanes for over a century,
so what makes this problem
still relevant and challenging in the context of designing them for smaller and slower flying machines such as a MAV?” To answer this, let us consider an airplane wing travelling through a fluid. There exists a small region of flow close to the wing surface where the effect of viscosity is more pronounced. The stability
of this region, called the boundary layer, plays a crucial role in determining whether the flow remains attached or detached to the wing surface. The detachment of flow, that is, flow separation often has an adverse effect on the aerodynamic efficiency. On this note, the flow around the wing of a civil transport airplane is known to exhibit a turbulent boundary layer that is less prone to flow separation whereas the flow over a MAV wing exhibits a laminar boundary layer that is more prone to flow separation. To add to the complexity, the laminar boundary layer, upon separation, may result in flow transition to turbulence and subsequently reattach as a turbulent boundary layer. Such a process leads to the formation of a laminar separation bubble, which modifies the effective shape of the wing surface. It is for these reasons, the knowledge gained by designing wings for larger and faster airplanes is of little significance in designing wings for
MAV applications.
Genetic algorithm leading to wing optimisation A detailed literature review revealed that the usage of optimization techniques can provide an exciting prospect in improving the aerodynamic performance of MAV wings. Optimization, in plain terms, is a process of identifying conditions that would result in high benefits- to-costs ratio in any system. A classic example would be its application in solving the well-known travelling
salesman problem (for example, Flipkart delivery process) where the aim is to identify the shortest possible route to visit all planned destinations before finally arriving at the origin of the journey. This problem, although stated in simple terms, grows in difficulty as the number of destinations ‘N’ increases. Solving this
Larger the lift force greater is the ability of the airplane to carry more weight. Similarly, lesser the drag force more easy it is for the airplane to slip through the air. So, we can attribute lift-to-drag ratio (L/D) to be a quantitative measure of aerodynamic efficiency.