ISBN 978-93-5156-328-0 International Conference of Advance Research and Innovation (ICARI-2014)

155 ICARI

Analysis of Drag and Lift Force Acting On the Flat Plate Ankit Chauhan, Raj kumar Singh Department of Mechanical Engineering, Delhi Technological University, New Delhi, India

Abstract

Analysis of the drag and lift forces acting on the surface of a flat plate was done as flat plate is most fundamental of all the design configurations. The analysis was done under various conditions of the fluid flow viz. laminar and turbulent and the plate configuration was changed from horizontal to gradually inclined positions. When the top surface of the flat plate is considered, air velocity was found to increase on moving along the plate’s length. Different results of drag and lift forces were obtained, when analyzing the flow on flat plate at different angles.

1. Introduction Aerodynamics is the study of motion of air when

it flows around a solid object. Automotive aerodynamics is the study of the aerodynamics of road vehicles. The main concerns of automotive aerodynamics are reducing drag, reducing wind noise, minimizing noise emission, and preventing undesired lift forces and other causes of aerodynamic instability at high speeds. As the petroleum reserve is decreasing at a rapid rate and is estimated to be over in about 40 to 50 years, the main concern of all automotive engineers these days is the efficiency of the vehicle. Efficiency of the vehicle can be effectively increased by improving its shape. Even the stability of vehicle at high speed mainly depends on the shape of the vehicle.

DRAG FORCE: It is the force that acts in the opposite direction to the motion of the vehicle or in the direction of flow of air around the moving vehicle. It provides resistance to the motion of the vehicle and more power and hence more fuel is needed to overcome this force. Fd=(cd*ρ*v2*A)/2 Fd is the drag force, which is by definition the force component in the direction of the flow velocity,

ρ is the mass density of the fluid,

v is the speed of the object relative to the fluid and A is the reference area Larger the drag force on the vehicle, larger will be its Corresponding Author, E-mail address: All rights reserved: http://www.ijari.org

fuel consumption. Drag force can be reduced to some extent by optimizing the basic shape of the vehicle. Flat plate was chosen for the analysis of lift and drag force because flat plate is most fundamental of all the design considerations. By this analysis, we can optimize the angle for windshield, bonnet etc. Small change in angle of the wind shield or bonnet can effectively increase the vehicle’s stability at higher speeds and can decrease its fuel consumption. We analyzed the drag and lift force acting on the flat plate at different angles and finally a graph was plotted showing the variation in drag and lift force with change in angle of inclination of the flat plate.

2. Computational Fluid Dynamics Computational fluid dynamics or CFD is the

branch of fluid mechanics, which uses numerical methods to analyze and solve the problem which involves fluid flow. Using the CFD (computational fluid dynamics) modeling, instead of wind tunnel have many advantages like, it saves our time and provides the same results at lesser expense. Wind tunnel needs much space to perform the experiments but same results can be obtained by using CFD, which does require only a computer.

All CFD problems are generally based upon the Navier-Stokes equations. The general form the equation is

Where v is the flow velocity, ρ is the fluid

density, p is the pressure, is the stress tensor, and f

Article Info

Article history: Received 2 January 2014 Received in revised form 10 January 2014 Accepted 20 January 2014 Available online 1 February 2014 Keywords CFD Modeling, Drag and Lift Force, Aerodynamics, Flat plate

ISBN 978-93-5156-328-0 International Conference of Advance Research and Innovation (ICARI-2014)

156 ICARI

represents body forces (per unit volume) acting on the fluid and ∇ is the del operator. The left side of the equation describes acceleration, and may be composed of time dependent or convective effects (also the effects of non-inertial coordinates if present). The right side of the equation is in effect a summation of body forces and divergence of stress (pressure and shear stress).

3. Computational Model The two dimensional model of the plate was

drawn for simplicity and the grid points were clustered along the wall where the velocity gradients were large. Firstly, the flow over a flat plate aligned parallel to free stream flow was modeled. Because of the symmetry only one half of the geometry of the plate was generated. The length of the flat plate was taken as 0.5 m and height of the computational domain was taken as 0.40 m. To ensure that uniform free stream flow exist, inlet was located far enough upstream of the plate. Further grid points were made clustered near the wall where velocity gradients were large. The grids used were generated with FLUENT’S grid generation package GAMBIT. Due to simplicity of the domain and to keep the skewness as low as possible a structured quad grid with over 900 cells on which flow variables(velocity, pressure, etc.) were calculated throughout the computational domain was generated. After the generation of grid appropriate boundary conditions to determine the type of the flow modeled were set. Because of the no slip condition, the flat plate was assigned the boundary condition of wall. The leftmost edge of the computational domain was assigned the velocity inlet while the rightmost edge was assigned the pressure outlet boundary condition. The symmetry boundary condition was specified to the leading edge of the domain to force the flow field variables to be mirror imaged across a symmetry plane. Thereafter a mesh was generated as shown in the figure 2.2. Similarly, the mesh was generated for flat plate at an angle 20 degree, 40

degree and 60 degree.

Fig: 1. Structured mesh of a flat plate

4. Simulation 4.1 Processing

All the processing i.e., the analysis of the fluid flow in the computational domain was done using the software FLUENT 6.3. The grid was imported from GAMBIT and checked for correctness. The fluid was specified as air along with its properties. Numerical parameters and solution algorithms were selected and starting values for all the flow field variables was specified. Beginning with the initial guesses, discretized forms of the continuity equation and the Navier – Stokes equation were solved iteratively by the software at the center of each cell. More than 2000 iterations were carried out to bring about the convergence of the solution. The convergence is

obtained when the residuals which are a measure of how much the solution deviates from exact are zero or very low. After the convergence of the solution the forces acting on the plate were calculated by specifying the velocity of the incoming fluid and the dimensions of the plate. The flow was subsequently changed to turbulent and corresponding results were obtained.

5. Analysis 5.1 Post processing

Fig: 2. Contours of static pressure (pascal)

ISBN 978-93-5156-328-0 International Conference of Advance Research and Innovation (ICARI-2014)

157 ICARI

Fig: 3. Contours of velocity magnitude (m/s)

The post processing of the solution obtained was also done using FLUENT version 6.3. In post processing stage various flow field variables such as velocity and pressure were plotted and analyzed graphically.

Similarly, the processing was done for flat plate inclined at 20degrees and 40 degrees and results are shown as follows.

Fig: 4. Contours of static pressure (pascal)- Flat plate inclined at 20 degree(left) and 40 degree(right)

Fig: 5. Contours of velocity magnitude of flat plate inclined at 20 degree (left) and 40 degree (right)

ISBN 978-93-5156-328-0 International Conference of Advance Research and Innovation (ICARI-2014)

158 ICARI

6. Results

Following results were obtained from the FLUENT 1. Flat Plate parallel to flow stream.

Table: 1. Results for plate parallel to flow direction

Drag Force, Fd

Lift Force, Fl

Coefficient of drag, Cd

Coefficient of lift, Cl

Laminar flow

0.0005N

0 0.43 0

2. Plate inclined at 200 to horizontal

Table: 2. Results for plate inclined at 200 to horizontal

Drag Force, Fd

Lift Force, Fl

Coefficient of drag, Cd

Coefficient of lift, Cl

Laminar flow

0.65N 50.63N

0.0013 0.048

3. Plate inclined at 400 to horizontal

Table: 3. Results for plate inclined at 400 to horizontal

Drag Force, Fd

Lift Force, Fl

Coefficient of drag, Cd

Coefficient of lift, Cl

Laminar flow

0.07N 284N 0.0006 1.288

4. Plate inclined at 600 to horizontal Table: 4. Results for plate inclined at 600 to horizontal

Drag Force, Fd

Lift Force, Fl

Coefficient of drag, Cd

Coefficient of lift, Cl

Laminar flow

0.33N

705N 0.0012235385

2.558653

7. Conclusion After analyzing all the results obtained from

fluent, it was concluded that angle of inclination of the flat plate have significant effect on the drag force acting on the flat plate. It was seen that drag force changes prominently as we increase the angle of inclination of the flat plate with the horizontal. It was also observed that static pressure acting on the flat plate changes its value along its length i.e. it is not constant for overall length of the flat plate. Pressure is maximum at the leading edge of the flat plate and decreases gradually along the length of the flat plate. An opposite pattern was observed in case of velocity of air along the flat plate. Velocity has minimum value at the leading edge of the plate and increases along the length of the flat plate and reaches its maximum value at the trailing edge of the flat plate.

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