67 research outputs found
A Study of Aerodynamic Drag of Contemporary Footballs
No full textAbstractMost modern footballs possess varied surface characteristics which can affect the flight trajectory of the football. Although the aerodynamic behavior of other sports balls have been studied well, little information is available about the aerodynamic behavior of newly introduced footballs with varied seam configurations and number of panels. Therefore, the primary objective of this study is to understand the surface characteristics mainly the seam depth and seam height and their effects on aerodynamic of a range of new generation balls. Four new generation footballs: Kapanya, Cafusa, Tango and Brazuca were selected for this study. Seam length and depth of seam for each ball were measured using 3D scanning technology and also manual measurement. Additionally, the aerodynamic drag forces were measured using wind tunnel over a range of wind speeds for two positions of each ball. It was found that the seam length and depth of seam have influence on the aerodynamic drag of these modern footballs. Results also indicate that the sideway variation of aerodynamic drag is minimal for the Brazuca ball. As a result, this ball may have better stability in flight. The lowest aerodynamic drag was found for the Cafusa ball at high speeds which indicates that this ball is suitable for long distance pass. However, it has highest sideway drag variation that may cause instability in flight
A Study of Dimple Characteristics on Golf Ball Drag
No full textAbstractDimples on the golf ball have significant effect on its aerodynamic properties as well as the flight trajectory. The aerodynamic of golf ball is still not fully understood in spite of a significant number of published data in the open literature. Most studies were conducted using the wind tunnel testing and Computational Fluid Dynamics (CFD) simulation. This paper examines the aerodynamic effect of dimple depth on golf balls. 3D printing technology was used to manufacture 11 balls with varied dimple depth. RMIT Aero Wind Tunnel was used to measure the drag forces over a range of wind speeds. It was found that the drag coefficient of golf ball varied significantly due to varied dimple geometry. The results indicate that the increase of the dimple depth ratio or surface roughness of the golf ball can shift the transition to a lower Reynolds number and increase the drag coefficient in transcritical regime. The results also established a positive linear correlation between relative roughness and drag coefficient
Aerodynamic Body Position of the Brakeman of a 2-man Bobsleigh
No full textAbstractThis paper examines the aerodynamic behaviour of a standard 2-man bobsleigh including the crews. The body position of the brakeman was studied over a range of angles from 25 to 90 degrees relative to the wind direction. Wind tunnel experiments were undertaken on a 50% scale model of 2-man bobsleigh and the crews. Aerodynamic drag forces were measured over a range of wind speeds (40 to 120km/h) in the wind tunnel environment. Additionally, wool tufts and smoke were used to visualise the airflow characteristics around the bobsleigh and crews. The results show that the body inclination angle of the brakeman has significant effect on the overall aerodynamics of bobsleighing and the most aerodynamic body position of the brakeman was found at 55 degree with the minimal drag. The results also indicate that this particular body position of the brakeman can reduce the drag over 10% compared to his body position at 90 degree. However, the brakeman's body position over 35 degree indicates an increase of drag
Development of Flexible Thermoelectric Cells and Performance Investigation of Thermoelectric Materials for Power Generation
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An Experimental Study of a Cyclonic Vertical Axis Wind Turbine for Domestic Scale Power Generation
No full textAbstractThe primary objective of this paper is to investigate a cyclonic domestic scale vertical axis wind turbine with semicircular shaped blades under a range of wind speeds. A 16-bladed rotor was initially designed and itstorques and angular speeds were measured over a range of wind speeds using a wind tunnel. Additionally, a cowling device was developed to enhance the turbine efficiency by directing the air flow from the rear blades into the atmosphere. Another 8-bladed rotor was also manufactured to investigate the effect of blade number on the maximum power generation. The aerodynamic performance of the cowling device wasalso investigated. Maximum power curves as a function of wind speeds were established for each configuration. The results indicated that the 16-bladed wind turbine can be used for domestic scale wind power generation. The results show that the cowling device has positive effect to increase the rotor speed to a significant amount. With the use of the cowling device, the average rotor speed increased by about 26% for the 16-bladed rotor compared to the baseline configuration. A significant increase (about 40%) of rotor speed was also found for the 8-bladed rotor with the cowling device. The results also indicated that the cowling device can be used to increase the power output of this cyclonic type vertical axis wind turbine especially with a reduce number of blades
Theoretical and Experimental Study to Determine the Solar Concentration Limit with Passive Cooling of Solar Cells
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Bio-Inspired Design: Aerodynamics of Boxfish
No full textAbstractThis paper investigates the aerodynamic behavior of a boxfish using both experimental and computational methods. A scaled up model boxfish was manufactured and tested in RMIT Industrial Wind Tunnel under a range of Reynolds numbers and yaw angles. The drag, lift and side forces and their corresponding moments were measured simultaneously. A CAD model of the boxfish was used in CFX FLUENT Computational Fluid Dynamics (CFD) modeling. The CFD modeling data were validated using the experimental findings. The results indicate that the drag coefficient of a boxfish is around 0.10 which is significantly lower than current drag coefficient of a passenger car. Hence, a boxfish shape can be adapted for achieving low drag and energy efficient motor vehicle design
Adjacent Wake Effect of a Vertical Axis Wind Turbine
No full textAbstractThe main objective of this study is to understand the effect of turbine placement and surrounding structures. Using Urban Green Energy's UGE-4K vertical axis wind turbine and the ANSYS computational fluid dynamics package (CFX), a dynamic fluid analysis was undertaken looking at the wake of the turbine through a variety of different inlet speeds and rotational frequencies to determine suitable flow recovery for optimal placement of subsequent turbines. The results showed that the wake interference is minimal at around 5 times the diameter of the turbine downstream. Results also show that flow recovery was a lot slower to the right of the turbine especially along a line 15° from the centre of the turbine to the right as this is coincident with the vortices generated from the turbines rotation
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