Football Aerodynamics

1. Football description

Two balls have been selected. One Nike ball consists of thirty-two panels of leather and Adidas fourteen panel ball is thermally bonded. These balls FIFA approved. A truncated Icosahedron Archimedean spherical shape is provided in thirty-two panel ball by stitching. The Adidas stitch-less fourteen panel ball is thermally bonded machine-pressed ball, and is more spherical as compared to a 32-panel ball. Wind tunnel testing was done on the ball and the sting on the ball had negligible aerodynamic effect.

  

 Fig. 1. Photographs of football [3]

 2. Results

a.  Flow Visualization

Smoke is used to visualise the airflow around the two balls understand the flow structure of the two balls.

Fig. 2. Flow field around a football inside a windtunnel [3]

The airflow over thirty-two panel ball became turbulent, due to the roughness and lead delayed flow separation. At 100° from horizontal direction, the airflow tends to occur. Generally, for a smooth surfaced sphere, the flow separation occurs normally to the horizontal axis. The surface is more spherical for the seamless fourteen panel ball, and it behaves similar to a smooth sphere. At an angle of 90 degrees from the horizontal axis flow separation is similar to that of a smooth sphere. Therefore, at low speeds, more aerodynamic drag can be generated in the 14-panel ball.

b. Aerodynamic Drag

From figure, we conclude that,

·       At high speeds, drag in a thirty-two panel ball is higher in comparison to a ball with fourteen panel.

·         Due to less spherical shape, the drag value for thirty-two panel ball changes more than that of a fourteen panel ball.

·        Variation in pressure that can be inflated has minimal effect on the aerodynamic properties of a football.

Fig. 3. Drag forces at different speeds for different panel balls [3]

Source: 3. “A Comparative Study of Football Aerodynamics” - Harun Chowdhury, Hazim Moria and Franz Konstantin Fuss, RMIT University, Melbourne.

Race Car Aerodynamics 

1. Introduction

Maximum speed with minimum air drag is the design parameter for racing cars. Stability was affected by lift forces were developed by cars at high speeds. So handling and stability can be improved by generating negative lift using mounted inverted wings profiles.

2. Rear wing

One third of the downforce is produced by the modern rear wings. Two sets of aerofoils are present, connected to one another by the wing endplates. The upper aerofoil provides the most downforce. To achieve the greatest possible lift coefficient multiple high aspect ratio must be present, which prevents flow separation. Circuit configuration determines the angle of attack. More down force is needed on tracks with many turns, hence angle of attack is high of the wing. Similarly, small angle of attack for long straight tracks, hence air drag is reduced and high top speed.

Figure 1: Chapparal 2E (top) and Ferrari 312 (bottom) [2]

Endplates are part of rear wing. They provide mounting for the wing and aerodynamic function. The air leakage is reduced due to three-dimensional effect around the wing tips and thus formation of trailing vortices. Reduction of up-flow from the rear wheels.

3. Front wing

The front wing of car creates about thirty-three percentage of downforce. Air first hits the front wing of the car, hence, it not only creates downforce, but also guides the streamline flow towards the rear of the car.

Figure 2: “Modern front wing configuration. Aerofoil of 2 element (1 & 2) is mounted under the nose of the car (5). Endplates (4) direct air around the wheels and curved area (4) under the nose increases wing’s efficiency.” [2]

Source: 2. “Race Car Aerodynamics” - BY Gregor Seljak.

Golf Ball Aerodynamics

Principle

Backspin leads to creation of lift force. Flight path of a golf ball is the main objective in golf ball aerodynamics, hence effect of drag cannot be ignored. The Magnus effect is the reason for generation of lift force and an example of flow around golf ball induced with a spin in shown in Fig.1.

Figure 1: Left to right flow over a golf ball with a clockwise spin at Re = 1950 [1]

Role of dimples

In a golf ball with a spin, an upward lift force is generated as the separation becomes asymmetric and wake gets deflected in the downward direction. Also, the major drag is pressure drag and not skin drag. Hence, the critical Re can be reduced with the presence of dimples in a golf ball as per analysis done and shown in figure 2. In the supercritical region, very less increase in the drag value of a golf ball can be seen. Hence, dimples are very effective in a golf ball.

Figure 2. A graphical relation between C_D, coefficient of drag and

Re, Reynolds number of a golf ball [1]

Source: 

1. R.D. Mehta, “Sports Ball Aerodynamics,” In SPORT AERODYNAMICS, Pg. 229-298. Edited By H. NØRSTRUD, Springer 2008. 

SPORTS AERODYNAMICS 

Aerodynamic properties play an important role in sports as the result in sports is mainly dependent on an athlete’s performance and his equipment. The application of aerodynamic principle in various sports do make a difference between the winners.

In sports aerodynamics, the athlete will encounter various forces and a graphical overview. If the athlete’s equipment is not optimised aerodynamically it would lead to deviation from the initial path, resulting in loss of speed or wrong trajectories or complete failure in terms of performances.

Athletes nowadays, can improve their training sessions by focusing on the output models obtained after wind tunnel testing.