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Design Development and CFD Simulation of a Variable Twist Wing

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Design Development and CFD Simulation of a Variable Twist Wing Imperial Journal of Interdisciplinary Research (IJIR) Vol-3, Issue-5, 2017 ISSN: 2454-1362, http://www.onlinejournal.in Design Development and CFD Simulation of a Variable Twist Wing 1 2 3 G.Sawan Kumar , Shuvendra Mohan , R.Surendra Rao 1 Space And Astronautical Engineering, University of Sapienza, Rome, Italy 2Aeronautical Engineering, Institute of Aeronautical Engineering, Dundigal, Hyderabad, India 3Mechanical Engineering Department, Kasi reddy naryan reddy college of engineering and research, Hyderabad, India Abstract: Wing twist is an aerodynamic feature these equations are difficult to solve. For a wing to added to aircraft wings to adjust lift distribution produce "lift", it must be oriented at a suitable angle along the wing. Often, the purpose of lift of attack relative to the flow of air past the wing. redistribution is to ensure that load distribution is When this occurs the wing deflects the airflow uniform from wing tip to root, it ensures that the downwards, "turning" the air as it passes the wing. effective angle of attack is always lower at the wing Since the wing exerts a force on the air to change its tip than at the root, meaning the root will stall before direction, the air must exert a force on the wing, the tip. This is desirable because the aircraft's flight equal in size but opposite in direction. This force control surfaces are often located at the wingtip, and manifests itself as differing air pressures at different the variable stall characteristics of a twisted wing points on the surface of the wing. alert the pilot to the advancing stall while still A region of lower-than-normal air pressure is allowing the control surfaces to remain effective, generated over the top surface of the wing, with a meaning the pilot can usually prevent the aircraft higher pressure existing on the bottom of the wing. from stalling fully before control is completely lost. These air pressure differences can be either measured Twist that decreases the local chord's incidence from directly using instrumentation or they can be root to tip is sometimes referred to as washout. In calculated from the airspeed distribution using this project the design is done in GAMBIT software, basic physical principles, including Bernoulli's and CFD simulation of twisted wing is done in fluent Principle which relates changes in air speed to software, the designed model is tested in software at changes in air pressure. different twist angles, and at different angles of The lower air pressure on the top of the wing attack to find the aerodynamic properties like CD, CL, generates a smaller downward force on the top of the and pressure. wing than the upward force generated by the higher air pressure on the bottom of the wing. Hence, a net Introduction upward force acts on the wing. This force is called the "lift" generated by the wing. 1.1 Introduction to wing: The different velocities of the air passing by the A wing is appendage with a surface that produces wing, the air pressure differences, the change in lift for flight or propulsion through the atmosphere, direction of the airflow, and the lift on the wing are or through another gaseous or liquid fluid. A wing is intrinsically one phenomenon. It is, therefore, an airfoil, which has a streamlined cross-sectional possible to calculate lift from any of the other three. shape producing a useful lift to drag ratio. For example, the lift can be calculated from the A wing's aerodynamic quality is expressed as pressure differences, or from different velocities of its lift-to-drag ratio. The lift a wing generates at a the air above and below the wing, or from the total given speed and angle of attack can be one to momentum change of the deflected air. There are two orders of magnitude greater than the total drag other approaches in fluid dynamics to solving these on the wing. A high lift-to-drag ratio requires a problems. All of these approaches will result in the significantly smaller thrust to propel the wings same answers if done correctly. Given a particular through the air at sufficient lift. wing and its velocity through the air, debates over which mathematical approach is the most 1.2 The aerodynamics of wing: convenient to use can be misperceived by novices as The design and analysis of the wings of aircraft is differences of opinion about the basic principles of one of the principal applications of the science flight. of aerodynamics, which is a branch of fluid mechanics. However, except for simple geometries Imperial Journal of Interdisciplinary Research (IJIR) Page 1282 Imperial Journal of Interdisciplinary Research (IJIR) Vol-3, Issue-5, 2017 ISSN: 2454-1362, http://www.onlinejournal.in 1.3 Design parameters of wing: Fig. 1. Full length wing with design parameters. S =span AR =aspect ratio (b2/s) sweep thickness 2. Figure Wing Section(washout) Λ =tapper ratio (Ctip/Croot) Θ= wing twist angle. In wing twist there are two kinds, geometric twist and aerodynamic twist. Aerodynamic twist is defined 1. Figure Full length wing with design as "the angle between the zero-lift angle of an airfoil parameters. and the zero-lift angle of the root airfoil." In essence, this means that the airfoil of the wing would actually change shape as it moved farther away from the 1.4 Twist: fuselage. Typically the zero-lift line is rotated downward toward the wing tips, similar to geometric The wing twist distribution is perhaps the least twist. Twist is applied to wings so that the outboard controversial design parameter to be selected. The section of the wing does not stall first. When an twist must be chosen so that the cruise drag is not aircraft is pitching nose up and increasing its angle of excessive. Extra washout helps the stalling attack, the airflow over the wing eventually reaches a characteristics and improves the induced drag at point where it becomes turbulent, causing a loss in higher C 's for wings with additional load L lift. By twisting the outboard portion of the wing distributions too highly weighted at the tips. Twist down, the stall is delayed in that area, simply also changes the structural weight by modifying the because the angle of attack is lower in that region. moment distribution over the wing. Twist on swept- Wing twist is an aerodynamic feature added to back wings also produces a positive pitching moment aircraft wings to adjust lift distribution along the which has a small effect on trimmed drag. The wing. selection of wing twist is therefore accomplished by Often, the purpose of lift redistribution is to ensure examining the trades between cruise drag, drag in that the wing tip is the last part of the wing surface to second segment climb, and the wing structural stall, for example when executing a roll or steep weight. The selected washout is then just a bit higher climb, it involves twisting the wingtip a small to improve stall. amount downwards in relation to the rest of the wing. This ensures that the effective angle of attack is 1.5 Introduction to twist wing always lower at the wingtip than at the root, meaning A technical definition of geometric twist the root will stall before the tip. This is desirable would go something like this: "an actual change in because the aircraft's flight control surfaces are often the airfoil angle of incidence, usually measured with located at the wingtip, and the variable stall respect to the root airfoil." In other words, if you characteristics of a twisted wing alert the pilot to the were to look at a wing from the side, the airfoil advancing stall while still allowing the control (cross section) of the wing would rotate as you surfaces to remain effective, meaning the pilot can moved away from the aircraft fuselage. In most usually prevent the aircraft from stalling fully before aircraft, the airfoil twists down as we move along the control is completely lost. wing further from the fuselage. This is referred to as Twist that decreases the local chord's incidence from "washout. root to tip is sometimes referred to as washout. Twist that increases the local incidence from root to tip is less common and is called wash-in. The X-29 had strong wash-in to compensate for the additional root- first stalling promoted by the forward sweep. Wing twist can also rarely refer to the deflection of the wing when it is made of insufficiently stiff materials, actuation of the flaps can, instead of deflecting air as intended, cause the wing itself to be deflected and is related to compressibility effects, Imperial Journal of Interdisciplinary Research (IJIR) Page 1283 Imperial Journal of Interdisciplinary Research (IJIR) Vol-3, Issue-5, 2017 ISSN: 2454-1362, http://www.onlinejournal.in this problem has mostly been eradicated however, inexpensive but sufficiently accurate to provide some with modern high-strength alloys and composites. guidance for advanced design studies or to be incorporated in a multidisciplinary optimization. The Literature Survey boundary layer analysis consists of a quasi-3D finite difference method, based on inputs from a 3D Euler 2.1 Wing design: analysis. A parametric fit of integral boundary layer The wing may be considered as the most properties to the amplification rate predicted by important component of an aircraft, since a fixed- linear stability analysis, leads to a simplified method wing aircraft is not able to fly without it, the wing for predicting TS transition and the onset of geometry and its features are influencing all other instability of stationary cross flow modes.
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