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Researcher Gurnani, Sagarkumar Vijaykumar
Source IIT Gandhinagar
Content type Text
Educational Degree Master of Technology (M.Tech.)
Publisher IIT Gandhinagar
Date of Submission 2016-01-01
Language English
Subject Domain (in DDC) Technology ♦ Engineering & allied operations
Abstract Even though the high AR wings has aerodynamic advantage like better lift-to-drag ratio, some of the aircrafts uses low AR wings because of its low bending stress, high roll rates, less drag at high speeds, greater useful internal volume and less airfield requirement. Some of the examples of low AR aircrafts are micro aerial vehicles, paper airplanes or fighter and trainer airplanes. The fighter airplanes uses different types of aerodynamic configurations like rectangular wings or delta wings having low AR. Computational modelling of such low AR aerodynamic configurations operating at low or high speeds is the focus of this work. Hence, to compute the flow field numerically requires coupling of flight mechanics and the computational fluid dynamics. The characteristics of low aspect ratio wing like non-linear variation of lift with angle of attack, roll-stall characteristics, gust response of the square flat plate wing, shock-vortex interactions on delta wing at transonic speeds, free flight dynamics of paper airplane and the transient effects observed during oblique wing manoeuvre are studied using various computational models. The prime focus of this study is on computing the flight trajectory, Euler angles and the aerodynamic characteristics of low AR free flight gliders like paper airplanes. Paper airplanes which have captured the imagination of people for many generations typically have low aspect ratio and operate at low Reynolds Number. The aerodynamics and flight mechanics of the paper airplane is modeled using unsteady incompressible Navier-Stokes equations and six-DOF rigid body flight dynamics equations. The flight trajectory of the paper airplane considering the variation of aerodynamic characteristics during the flight is computed as a part of the overall computed solution by coupling the aerodynamics and flight mechanics. A comparative study is carried out between different dart type paper plane configurations in order to examine its effect on the range and endurance. Some of the fighter aircraft operating in transonic and supersonic regime uses delta wing type configurations. The delta wings in a transonic free stream undergoes sudden movement of the vortex breakdown location with increase in angle of incidence due to presence of shocks in the flow field. As a validation study, the aim is to the use Computational Fluid Dynamics (CFD) to examine this behavior in detail and to compare the result with available experimental data. The low AR aerodynamic concept is also applied to design a projectile that performs with high efficiency as the Mach number increases from subsonic to supersonic speed. The projectile is designed with an oblique wing concept. At low Mach number, variable geometry oblique wing would be positioned perpendicular to the incoming flow so as to provide maximum lift and as the projectile gains the speed, the wing is swept back thereby reducing the drag and decreasing fuel consumption. The time accurate CFD analysis solving the unsteady Reynolds-averaged Navier-Stokes equations for the aerodynamics coupled with standard flight mechanics form the mathematical model to obtain the optimal sweepback positions of the oblique wing and also to study the transient phenomenon occur due to the rotation of wing during the supersonic flight. An overset grid approach is used to rotate the wing from the initial perpendicular position to that of the optimum sweepback position in order to examine the maximum lift-to-drag ratio throughout its gliding phase and to achieve the maximum range for the rocket-assisted projectile.
Learning Resource Type Thesis
Organization Dept. of Mechanical Engineering