International Journal of Mechanical Engineering and Technology (IJMET) Volume 8, Issue 11, November 2017, pp. 312 318, Article ID: IJMET_08_11_034 Available online at http://www.iaeme.com/ijmet/issues.asp?jtype=ijmet&vtype=8&itype=11 ISSN Print: 0976-6340 and ISSN Online: 0976-6359 IAEME Publication Scopus Indexed CFD ANALYSIS AND COMPARISON USING ANSYS AND STAR-CCM+ OF MODEL AEROFOIL SELIG 1223 Narendiranath Babu T Associate Professor, Department of Mechanical Engineering, VIT University, Vellore, India Prateek Parmeshwar, Arth Beladiya and Akshay Bhabhra Department of Mechanical Engineering, VIT University, Vellore, India ABSTRACT Airplane structures are highly aerodynamic in nature and the science behind them generating such significant amounts of lift depends greatly on the aerofoil geometry, that is the cross-section of their wings. Aerofoils are shaped and designed in such a way that as they move through a fluid medium they generate certain aerodynamic forces which helps create a positive pressure difference producing lift. This purpose of this paper is to analyse airflow across a model aerofoil Selig 1223[4] and determine airflow patterns along with velocity and pressure profiles. The analysis is performed in ANSYS Workbench and STAR-CCM+ which are softwares used for a computational fluid dynamics (CFD). These software give an accurate visual representation of airflow solving for variables such as pressure values and velocity vectors. Parameters such as coefficients of lift and drag and their variance with respect to angle of attack are obtained using the software XFLR5 developed by MIT. Further, observing the airflow also reveals some key characteristics that might suggest some scope for design optimisation. Keywords: CFD analysis, STAR-CCM+ of model aerofoil Selig 1223 Cite this Article: Narendiranath Babu T, Prateek Parmeshwar, Arth Beladiya and Akshay Bhabhra, CFD analysis and comparison using ANSYS and STAR-CCM+ of model aerofoil Selig 1223, International Journal of Mechanical Engineering and Technology 8(11), 2017, pp. 312 318. http://www.iaeme.com/ijmet/issues.asp?jtype=ijmet&vtype=8&itype=11 1. INTRODUCTION A body is said to generate lift when the net forces acting on it have a positive resultant antiparallel to the force of gravity. A body is said to generate lift when the net forces acting on it have a positive resultant anti-parallel to the force of gravity. Airplanes have become a common sight today and although their whole design is aerodynamic it is the wing geometry that helps generate such large amounts lift in such heavy structures. Wings have an aerofoil http://www.iaeme.com/ijmet/index.asp 312 editor@iaeme.com
Narendiranath Babu T, Prateek Parmeshwar, Arth Beladiya and Akshay Bhabhra cross-section which generate certain aerodynamic forces when moving in a fluid medium. In simple terms, the aerofoil cross-section creates low pressure regions at the top side and high pressure regions below it. As such there is a net upward force created by this pressure difference and when this force created by the pressure difference exceeds the weight, that is the force of gravity, a resultant upward force comes into picture; a lift is generated [2]. This pressure difference is a consequence of velocity difference. As the aerofoil moves through a fluid, say air, the air velocity vectors flow past the wing in a direction opposite to that of the movement of the wing. These velocity vectors start to form a vortex in a counter-clockwise direction near the tail of the aerofoil. Now, since angular momentum is conserved, new vortices need to be generated that move in a clockwise direction. These vortices form around the cross-section boundary of the aerofoil. As a net effect, we have velocity vectors of airflow and vortices being added at the top of the aerofoil and the vectors of airflow and vortices being subtracted below the aerofoil. Thus, velocity is higher at top and lower at bottom. Now comes the use of Bernoulli's equation which states that the sum of pressure energy, kinetic energy and the potential energy 1.1. Remains same and thus, a decrease in kinetic energy will result in an increase in pressure energy provided the potential energy remains constant. Aerofoils have to be designed in such a way that while producing lift they also minimise drag. Drag is the aerodynamic force that opposes motion of an object as it moves through a fluid medium. This is the difference between rectangular aerofoils and tapered aerofoils. Tapered aerofoils have reduced drag due to less surface area towards the ends of wings. The accompanied reduction in lift due tapering is insignificant as the majority of the lift is produced near the fuselage due to finite wing effect. Tapering also serves in reducing the overall designing, engineering and manufacturing cost due to reduction in the materials requirement and also reduces weight. These massive wing structures need to be tested for all these aerodynamic forces such as lift, drag and other parameters such as pressure difference and airflow velocity across the aerofoil. Testing such components is not only tedious but also expensive as such large components require huge wind tunnels. As such there is a dire need of effective simulations which not only predict airflow over aerofoils accurately but also are relatively much cheap and save a lot of time. 2. CFD ANALYSIS The Navier-Stokes equations govern the motion of fluids and can be seen as Newton's second law of motion for fluids. In the case of a compressible Newtonian fluid, this yields[1] The different terms correspond to the inertial forces, pressure forces, viscous forces, and the external forces applied to the fluid. These equations are always solved together with the continuity equation: The Navier-Stokes equations represent the conservation of momentum, while the continuity equation represents the conservation of mass. These equations are at the heart of fluid flow modelling. Solving them, for a particular set of boundary conditions (such as inlets, outlets, and walls), predicts the fluid velocity and its pressure in a given geometry. Because of their complexity, these equations only admit a limited number of analytical solutions. As http://www.iaeme.com/ijmet/index.asp 313 editor@iaeme.com
CFD analysis and comparison using ANSYS and STAR-CCM+ of model aerofoil Selig 1223 these equations are difficult to solve using analytical methods, we employ numerical techniques such as finite difference and finite volume methods that convert these complex partial differential equations into simple algebraic equations that are easy to solve and hence compute. But of course, we cannot solve these equations for the geometry as a whole as different variables have different values at different points. This is where meshing comes into picture. Meshing involves dividing the geometry into grids and small finite volume. The sizes of these grids are such that the solutions to the Navier-Stokes equations can be reasonably approximated in the volume. The differential equations are solved using numerical methods in these small nodes and a general picture of the simulation is developed. Naturally, the finer the mesh size and the smaller the volume of the grid, the more accurate solution gets. CFD analysis is reaching an optimal mesh count as even though finer mesh will result in accurate solutions they will cost significant computation time. 2.1. Methodology for modelling Analysis of the aerofoil Selig 1223 first required its designing and construction [3]. Aerofoils are smooth and curved structures and as such their construction in any CAD software requires the use of coordinates which the software then extrapolates to form a wing cross-section. The coordinates for the aerofoil taken from aerofoil database were imported into SolidWorks, a CAD software, following which a curve through the points was plotted giving the aerofoil cross-section. The cross-section was then extruded to give the resulting wing geometry. Now airflow across this generated CAD had to be simulated and compared in ANSYS and STAR- CCM+. The lift and drag values for the aerofoil were obtained using another software called XFLR5. Figure 1 Aerofoil Cross-section The basic flow chart for the modelling consisted of the following a) Flow chart (b) CAD Figure 2 Modelling of CAD http://www.iaeme.com/ijmet/index.asp 314 editor@iaeme.com
Narendiranath Babu T, Prateek Parmeshwar, Arth Beladiya and Akshay Bhabhra 2.2. Airflow Analysis The CFD analysis in ANSYS and STAR-CCM+ was performed. The analysis using these softwares simulated the presence of out aerofoil in a wind tunnel. As such a control volume had to be setup that simulated wind flow towards the aerofoil accurately. The control volume was setup and contained air-flow at the speed of 20m/s. The size of the control volume gave an accurate simulation of the atmosphere and the size was so selected such that no need of extra unnecessary meshing was required. The control volume setup was followed by meshing. In STAR-CCM+ the meshing consisted of standard mesh in standard plane areas and the boundary regions were meshed using finer mesh structures to get an accurate result of the simulation. After setting up the meshing and subjecting the geometry to the various boundary and physics conditions such as the properties of the air the given aerofoil was set for simulation of air-flow. (a) Domain Figure 3 Control Volume STAR-CCM+ (b) Boundary Condition (a) Mesh Figure 4 STAR-CCM+ (b) Closer look at mesh (a) Mesh (b) Closer look at mesh Figure 5 STAR-CCM+ http://www.iaeme.com/ijmet/index.asp 315 editor@iaeme.com
CFD analysis and comparison using ANSYS and STAR-CCM+ of model aerofoil Selig 1223 3. RESULTS AND CONCLUSION Analysis with STAR-CCM+ with an inlet velocity of 20m/s revealed velocity flow vectors across the aerofoil and pressure difference across and near the regions of aerofoils. As is evident from the pressure values that a significant positive lift will be generated due to the airflow across the aerofoil. It is key to note the airflow near the tail of the aerofoil. We observe some amount of recirculation of airflow. Recirculation results in excess of air mass and thus, consequently results in larger pressure values effectively reducing the lift. This provides scope for the design optimisation of Selig 1223 in order to generate lesser amounts of airflow recirculation as well as wake regions. (a) Velocity plot (b) Closer look at plot Figure 6 STAR-CCM+ (a) Pressure Plot (b) Closer look at plot Figure 7 STAR-CCM+ (a) Airflow approaching (b) Airflow over aerofoil Figure 8 STAR-CCM+ http://www.iaeme.com/ijmet/index.asp 316 editor@iaeme.com
Narendiranath Babu T, Prateek Parmeshwar, Arth Beladiya and Akshay Bhabhra (a) Fully developed flow (b) Airflow separation Figure 9 STAR-CCM+ Figure 10 ANSYS results Figure 11 XFLR5 Results Figure 12 XFLR5 Results http://www.iaeme.com/ijmet/index.asp 317 editor@iaeme.com
CFD analysis and comparison using ANSYS and STAR-CCM+ of model aerofoil Selig 1223 REFERENCES [1] Abdulnaser Sayma Computational Fluid Dynamics. [2] Karna S. Patel, Saumil B. Patel, Utsav B. Patel, Prof. Ankit P. Ahuja CFD Analysis of an Aerofoil. UVPCE, Ganpat University [3] Shreyas Krishnamurthy, Suraj Jayashankar, Sharath V Rao, RochenKrishna, Shankargoud Nyaman-navar CFD Analysis of an RC Aircraft Wing. [4] Airfoil Database: http://m-selig.ae.illinois.edu/ads/coord_database.html [5] National Aeronautics and Space Administration https://www.grc.nasa.gov/www/k- 12/airplane/liftco.html [6] MD Khaleel, Marampalli Shilpa and L.Farooq Modeling and CFD Analysis on one Stage of Turbine of Gas Turbine Engine. International Journal of Civil Engineering and Technology, 8(5), 2017, pp. 638 645. [7] Abdul Razzaque Ansari and Prashant Kumar Rana, CFD Analysis of Aerodynamic Design of Maruti Alto Car. International Journal of Mechanical Engineering and Technology, 8(3), 2017, pp. 388 399. http://www.iaeme.com/ijmet/index.asp 318 editor@iaeme.com