To simulate Flow over a NACA0017 Airfoil for different angles of attack of an Airfoil for an External Flow and Compare Lift and Drag Forces.
OBJECTIVE :-
To simulate Flow over a NACA0017 Airfoil for different angles of attack of an Airfoil for an External Flow and Compare Lift and Drag Forces.
COMPUTATIONAL FLUID DYNAMICS (CFD) :-
Computational fluid dynamics (CFD) is a branch of fluid mechanics that uses numerical analysis and data structures to analyze and solve problems that involve fluid flows. Computers are used to perform the calculations required to simulate the free-stream flow of the fluid, and the interaction of the fluid (liquids and gases) with surfaces defined by boundary conditions. With high-speed supercomputers, better solutions can be achieved, and are often required to solve the largest and most complex problems. Ongoing research yields software that improves the accuracy and speed of complex simulation scenarios such as transonic or turbulent flows. Initial validation of such software is typically performed using experimental apparatus such as wind tunnels. In addition, previously performed analytical or empirical analysis of a particular problem can be used for comparison. A final validation is often performed using full-scale testing, such as flight tests.
CFD is applied to a wide range of research and engineering problems in many fields of study and industries, including aerodynamics and aerospace analysis, weather simulation, natural science and environmental engineering, industrial system design and analysis, biological engineering, fluid flows and heat transfer, and engine and combustion analysis.
Methodology:-
In all of these approaches the same basic procedure is followed.
During preprocessing
- The geometry and physical bounds of the problem can be defined using computer aided design (CAD). From there, data can be suitably processed (cleaned-up) and the fluid volume (or fluid domain) is extracted.
- The volume occupied by the fluid is divided into discrete cells (the mesh). The mesh may be uniform or non-uniform, structured or unstructured, consisting of a combination of hexahedral, tetrahedral, prismatic, pyramidal or polyhedral elements.
- The physical modeling is defined – for example, the equations of fluid motion + enthalpy + radiation + species conservation
- Boundary conditions are defined. This involves specifying the fluid behaviour and properties at all bounding surfaces of the fluid domain. For transient problems, the initial conditions are also defined.
- The simulation is started and the equations are solved iteratively as a steady-state or transient.
- Finally a postprocessor is used for the analysis and visualization of the resulting solution.
AIRFOIL :-
An airfoil (American English) or aerofoil (British English) is the cross-sectional shape of a wing, blade (of a propeller, rotor, or turbine), or sail (as seen in cross-section).
An airfoil-shaped body moving through a fluid produces an aerodynamic force. The component of this force perpendicular to the direction of motion is called lift. The component parallel to the direction of motion is called drag. Subsonic flight airfoils have a characteristic shape with a rounded leading edge, followed by a sharp trailing edge, often with a symmetric curvature of upper and lower surfaces. Foils of similar function designed with water as the working fluid are called hydrofoils.
The lift on an airfoil is primarily the result of its angle of attack. When oriented at a suitable angle, the airfoil deflects the oncoming air (for fixed-wing aircraft, a downward force), resulting in a force on the airfoil in the direction opposite to the deflection. This force is known as aerodynamic force and can be resolved into two components: lift and drag. Most foil shapes require a positive angle of attack to generate lift, but cambered airfoils can generate lift at zero angle of attack. This "turning" of the air in the vicinity of the airfoil creates curved streamlines, resulting in lower pressure on one side and higher pressure on the other. This pressure difference is accompanied by a velocity difference, via Bernoulli's principle, so the resulting flowfield about the airfoil has a higher average velocity on the upper surface than on the lower surface. The lift force can be related directly to the average top/bottom velocity difference without computing the pressure by using the concept of circulation and the Kutta–Joukowski theorem.
The various terms related to airfoils are defined below:-
- The suction surface (a.k.a. upper surface) is generally associated with higher velocity and lower static pressure.
- The pressure surface (a.k.a. lower surface) has a comparatively higher static pressure than the suction surface. The pressure gradient between these two surfaces contributes to the lift force generated for a given airfoil.
The geometry of the airfoil is described with a variety of terms :
- The leading edge is the point at the front of the airfoil that has maximum curvature (minimum radius).
- The trailing edge is defined similarly as the point of maximum curvature at the rear of the airfoil.
- The chord line is the straight line connecting leading and trailing edges. The chord length, or simply chord, {\displaystyle c}
, is the length of the chord line. That is the reference dimension of the airfoil section.
The shape of the airfoil is defined using the following geometrical parameters:
- The mean camber line or mean line is the locus of points midway between the upper and lower surfaces. Its shape depends on the thickness distribution along the chord.
PROCEDURE OF SIMULATION :-
- Firstly, Make MKS system and then Create Airfoil in solidworks from Insert--> Curve --> curve from XYZ coordinates and insert all the points to create spline of airfoil geometry.
- Now Extrude the Sketch to form Airfoil geometry.
- Use diiferent Angle of Attack for simulation of airfoil by using Rotate Entities to rotate thr airfoil to desired position ii.e 0,2,4,6,8,10.
- Now go to create new wizard in Flow Simulation for General settings and go with the Default settings.S
- Select the External Flow and set up time dependent Simulation with total analysis time of 5 sec and output step of 1 sec.
- Add working Fluid As Air and in velocity set the X-axis velocity 60 m/sec.
- An Computational Domain will be created and select the 2D simulation.
- Resize the Computational Domain to 5% and 10%-15% to the Chord length in both sides of the airfoil respectively.
- Now Insert the global goals
- Force(X)
- Force(Y)
- Frictional Force(X)
- Frictional Force(Y)
- And also insert the Surface Plots and Select the outer surfac of Airfoil
- Force(X)
- Force(Y)
- Insert local Mesh and select the outer surface and Refine it mesh to 3.
- Run the Simulation
- Now Create Cut Plots to plot velocity plots.
- Create Goal Plots Drag Force and Lift Force in the Airfoil.
- Repeat above Procedure for all Angles of Attacks.
RESULTS OF SIMULATION :-
CASE 1 :- ANGLE OF ATTACK =0
Slover Window
Cut plot
Drag Force = 332.8 N
Lift Force = -0.5 N (Downwards and approximatly zero)
CASE 2 :- ANGLE OF ATTACK = 2
Slover Window
Cut plot
Drag Force = 367.7 N
Lift Force = 923.5 N (Upwards)
CASE 3 :- ANGLE OF ATTACK = 4
Slover Window
Cut plot
Drag Force = 610.2 N
Lift Force = 2711.2 N (Upwards)
CASE 4 :- ANGLE OF ATTACK = 6
Slover Window
Cut plot
Drag Force = 834.8 N
Lift Force = 3584.8 N (Upwards)
CASE 5 :- ANGLE OF ATTACK = 8
Slover Window
Cut plot
Drag Force = 1098.6 N
Lift Force = 4459.5 N (Upwards)
CASE 6 :- ANGLE OF ATTACK = 10
Slover Window
Cut plot
Drag Force = 1463.1 N
Lift Force = 5382 N (Upwards)
COMPARISON OF DRAG FORCE AND LIFT FORCE :-
% COMPARISON OF DRAG FORCE AND LIFT FORCE FOR DIFFERENT ANGLES OF ATTACK
% Angle of Attack
AOA = [0 2 4 6 8 10];
% Drag Force
drag = [332.8 367.7 610.2 834.8 1098.6 1463.1];
% Lift Force
lift = [-0.5 923.5 2711.2 3584.8 4459.5 5382];
% Plotting
plot(AOA, drag,'*-')
hold on
plot(AOA, lift,'*-')
ylabel('Drag and Lift Force(N)')
xlabel('Angle of Attack')
title('Drag and Lift Force vs Angle of Attack')
legend('Drag Force','Lift Force')
grid on- From Graph it is seen that Drag Force changes Quadratically increasing with the increase in the Angle of Attack.
- And also, From Graph it is seen that Lift Force changes almost Linearly increasing with the increase in the Angle of Attack.