Design And Numerical Analysis of Morphing Airfoil With Corrugated Geometry In The Application MAV’s

The main objective of the work is to enhance the aerodynamic performance during takeoff and cruise by using newly corrugated airfoil of MAV’s by Morphing it at the trailing edge. In this study, the transient nature of corrugated airfoils at low Reynolds number were assumed to be the flow is laminar, incompressible and two dimensional. The newly corrugated geometry which is parameterized from the camber line using a Radial basis function (RBF) based on interpolation method positioned at the lower surface of the airfoil i.e., NACA0015. Five morphed geometries are designed using ANSYS Space claimer. The computational domain is meshed using cartesian grid, the surface meshes with quadrilateral. Numerical simulations are performed with turbulent models i.e., k-omega, k-epsilon and Spalart allmaras. In the analysis, there is an increment of coefficient of lift and decrease in coefficient of drag by varying Reynolds number. Compared to NACA0015, corrugated NACA0015 shows good results.


I. INTRODUCTION
Micro Aerial Vehicle is a miniature of UAV's that has size restriction and maybe autonomous. The development of innovative adaptive structures on MAV's, such as "Morphing wings", can potentially reduce the complexity of the aviation structure. These are divided into Fixed wing MAVs, Rotary wing MAVs, Flapping wing MAVs. Fixed wing MAVs are aircraft models of size less than 200mm, controlled by remote. This can be as small as human palm. These MAVs have wing and propeller, helps them to fly. Rotary wing MAVs are tiny helicopters, controlled by remote. They don't have wing they use rotors. These are most commonly used MAVs. Flapping wing MAVs are most trending recent in the development of MAVs. These MAVs are most complicated then compared to other MAVs as they use the same mechanism as bird to achieve flight. As birds flap wing in different ways to achieve flight. Different birds have different ways to flap there wings, insects also have different ways to flap there wings. Now MAVs have been also designed by observing the dragonfly.
Modern craft can be as small as 5 centimetres. Most of the development of MAVs are seen for commercial, research, government and military purpose. The interest on Morphing wing has been increased due to its superior benefits. The structure that can change its geometric characteristics and also properties (stiffness and damping) according to the mission requirements or at different load conditions. [1] The main idea in positioning corrugated portion is for actuating the trailing edge. Besides, it will re-energies the flow which will helps to delay the flow from separation. The Maximum speed of a Micro Aerial vehicle would be around 10-15m/s. As we are considering a low Reynolds number. Because the boundary layer is the great deal of managing an adverse pressure without separation. The assumptions we made for this study are the flow is laminar, steady, incompressible and 2-Dimensional. MAVs have the potential to operate the missions in denser regions that near the Earth surface. Near the earth surface the airflow is turbulent. This results in turbulent intensity on the stability of the MAVs.
Most MAVs have problems during takeoff and cruise. As a result, main objective is to enhance the aerodynamics performance by using corrugated used for morphing the trailing edge. All the cases of MTE optimized airfoils have showed a significant improvement in the overall aerodynamic performance, and MTE airfoils increased the efficiency. In this paper a computational study is done in order to investigate the aerodynamic performance of newly corrugated airfoil, positioned at 25% of the chord length from the trailing edge of the airfoil by continuously morphing trailing edge wing. In order to increase the aerodynamic performance by morphing technology by placing corrugated design at the lower surface of the symmetric airfoil (i.e., NACA0015) and using by giving deflections of airfoil models (2deg, 5deg, 7deg, 9deg) at the trailing part of the airfoil. The airfoil is reconstructed from the camber line using a Radial Basis Function (RBF) based on interpolation method. Performed the study by using the concept of different turbulence models (k-omega, k-epsilon and Spalart allmaras). [2] All the three models were considered and used to analyse the newly designed aerofoil for MAVs. Compared to all the models, k-epsilon model has interpreted the good results. For MAVs, the wing must be flexible to cover a smooth configuration. Corrugated structure can undergo high aerodynamic loads and helps to morph the wing smoothly. [4]

II. AIRFOIL OPTIMIZATION
In order to model the airfoil, there is a method to be followed and to carry out the mesh deformation, calculate the aerodynamic coefficients and also attached the optimization models in the following sections.

Parameterization
To give the corrugated portion at lower portion of the NACA0015 airfoil, Radial Basis Function is used, explained as follows By using above figure, the values of Radial basis function at the predicted location can be considered, as given by Φ 1 , Φ 2 , and Φ 3 , it depends on the distance between the data location. The Predictor can be estimated by taking the weighted average w 1 Φ 1 + w 2 Φ 2 + w 3 Φ 3 + …. There are different methods in it, they are Thin-Plate spline, Spline with Tension, completely regularized spline, Multiquadric function, Inverse multiquadric function. Sometimes, they don't make greater difference.
In order to design the model, Firstly, the model dimensions are collected from NACA tools from NASA website. After, five models are modelled by giving 5 deflections(0⁰,2⁰,5⁰,7⁰,9⁰) at the trailing edge. To actuate the deflected portion a corrugated portion is positioned at 25% of chord of 150mm.

Mesh deformation
The computational domain was meshed by using Cartesian grids. To get accurate values, refinement is also given around the surface of the deflected air foil.

Flow Solver
The analysis is done by using three turbulent models.

Spalart-Allmaras model
The One-Dimensional Spalart-Allmaras is an easy model that resolves a modelled transport equation for the kinematic eddy (turbulent) viscosity. This model is generally used for wall-bounded flows and has good outputs for boundary layer subjected to ambient pressure gradients.
In Spalart allmaras, the transported variable ̃ is similar to the turbulent kinematic viscosity except in the nearwall region. [ is the production of turbulent viscosity, is the destruction of turbulent viscosity that happens in the near wall region because of the wall blocking and viscous damping, ̃ and are constants, v is the molecular kinematic viscosity and ̃ is a user-defined source term. Note: Turbulence kinetic energy is not calculated in Spalart-Allmaras model. The production term can be modelled has and k are constants, d is the distance from the wall and S is a scalar measure of the deformation tensor. The destruction term is modelled as: 3 6 /g 6 + 3 6 ] 1/6 , g = r + 2 ( 6 − ) ≡ /̃2 2 ] 1 , 2 and 3 are constants.

k-Standard Model
This model depends upon transport equations for the turbulence kinetic energy(k) and dissipation rate ( ).
The assumptions made for the flow are turbulent and effects of molecular viscosity are negligible. Therefore, this model is suitable only for turbulent models. The turbulence kinetic energy k and dissipation rate can form as follows: The effective diffusivities for the k-model are described as: Where, and are the turbulent Prandtl numbers for k and , respectively.
The result of turbulent viscosity is produced by combining k and  as follows: The production of turbulence kinetic energy maybe given by: To evaluate in a manner consistent with the Boussinesq hypothesis: = 2 . The production of  is given by: The dissipation of k is giving by: The dissipation of  is giving by: and are the dissipations of k and , and defined identically as in the standard k-model.

BOUNDARY CONDITIONS
The assumptions made for the flow are Laminar, Incompressible, steady and 2-Dimensional. The outlet domain is set be pressure-outlet and gauge pressure are zero.

III.RESULTS AND DISCUSSION
This section gives the info about the numerical simulation results for the aerodynamic performance of the Morphing trailing edge of NACA0015 at velocities 12.5m/s and 14.5m/s.

Aerodynamic performance analysis during MTE
To study the influence of Angle of attack(α) and Deflection

Flow field Analysis
As shown in fig-3 the pressure contours of 5 deflections at 12.5m/s and 14.5 m/s. The maxima and minima pressure on the airfoils is verified by the intensity of the colour. The pressure beneath the airfoil is darker, it means there is an increase of CL when the deflection is increasing. From all the pressure contours, 9 0 deflection has maximum Cp on the basis of intensity of colour beneath the airfoil. As, the increase in deflection the Cp is also getting increased, CL values are also getting increased. Angles of Attacks (AOA).  By comparing graph C L and C D versus AOA at different deflections (i.e,0 0 , 2 0 , 5 0 , 7 0 , 9 0 ) it shows as deflection is increasing, the C L is also increasing.  But, from all the results, it is observed that for take-off at θ = 50 (deflection) suitable.
As, the flow is separating at 18 0 AOA.

Observations:
 From all the results, aerodynamic efficiency has improved. The design objective is to increase the Lift-to-Drag ratio while take-off and Cruise.  For take-off 5 0 deflection is suitable. Because it delays the flow till 18 0 AOA.Morphing trailing edge concept designed and numerically analyzed in this work.  This work has been done for steady model characteristics of aerodynamics with different various conditions alpha and deflections between corrugated without morphing and with morphing.  The corrugated shape introduced to help for mechanism in future geometries. By increasing of (theta)deflection the cl and cd increases accordingly varying with angle of attack (alpha). When increasing at small alpha in different flights conditions then MTE provides to enhance the lift in a flight condition i.e., during takeoff and cruise.  The MTE concept has increased performance compare to without MTE morphing and as well as increases CL and reducing drag in different deflection of MTE, therefor at same flight conditions, the overall aerodynamic efficiency of MTE is improved than the without corrugated.  At stall point due to MTE it suppresses the flow separation and reduces the vortices, there is more advantage in large deflection conditions.  The project will be continued by fabricating the 2-dimensional models using 3d printing and testing has been done by using Low Speed Subsonic Wind-tunnel.