The accurate discrimination of the aerodynamic parameters affecting the flight of sports balls is essential in the product development process. Aerodynamic studies reported to date have been limited, primarily because of the inherent difficulty of making accurate measurements on a moving or spinning ball. Manufacturers therefore generally rely on field trials to determine ball performance, but the approach is time-consuming and subject to considerable variability. The current paper describes the development of a method for mounting stationary and spinning footballs in a wind tunnel to enable accurate force data to be obtained. The technique is applied to a number of footballs with differing constructions and the results reported. Significant differences in performance are noted for both stationary and spinning balls and the importance of the ball orientation to the flow is highlighted. To put the aerodynamic data into context the results are applied in a flight model to predict the potential differences in the behaviour of each ball in the air. The aerodynamic differences are shown to have a considerable effect on the flight path and the effect of orientation is shown to be particularly significant when a ball is rotating slowly. Though the techniques reported here are applied to a football they are equally applicable to other ball types.
Much discussion surrounds the flight of a football especially that perceived as irregular and is typically done so with little understanding of the aerodynamic effects or substantive evidence of the path taken. This work establishes that for a range of FIFA approved balls there is a significant variation in aerodynamic performance.This paper describes the methods used for mounting stationary and spinning footballs in a wind tunnel enabling accurate force data to be obtained, and the analysis techniques used. The approach has been to investigate a number of scenarios: Non-spinning Reynolds Sweep, Unsteady Loads, Orientation Sensitivity (Yaw Sweep) and Spinning Reynolds Sweep. The techniques are applied to a number of footballs with differing constructions and the results reported. To put the aerodynamic data into context the results are applied in a flight model to predict the potential differences in the behaviour of each ball in the air.The paper concludes that although the drag characteristics are different for the different balls tested the simulation suggests that this has only a limited effect on the flight of the ball. It is also shown that the unsteadiness of the aerodynamic loads is unlikely to be responsible for unpredictable behaviour. However, it is also shown that there are significant differences in the lateral aerodynamic forces for a range of FIFA approved match balls, and that these aerodynamic differences have a significant effect on the flight path for both spinning and for slowly rotating balls.
Aerodynamic effects play an important part in any sport where the ball experiences significant periods of free flight. This paper investigates the aerodynamic forces generated when a football is spinning quickly to generate swerve and more slowly to generate more erratic flight. The work reports on the application of an experimental method that measures the aerodynamic loads on a non-spinning, slowly spinning and fast spinning football, using a phase-locked technique so that orientation-dependent and steady 'Magnus' forces can both be determined.The results demonstrate that the orientation-dependent aerodynamic loads, widely seen in non-spinning data in the literature, surprisingly persist up to the highest spin rates reported. When predicting ball flight, it is generally assumed that at low spin rates a quasi-static assumption is acceptable, whereby forces measured on a non-spinning ball, as a function of ball orientation, apply for the spinning case. Above an arbitrary spin rate, the quasi-static assumption is replaced with the assumption of a steady 'Magnus' force that is a function of spin rate and ball speed. Using a flight model, the quasi-static assumption is shown to be only applicable for the lowest spin rates tested and the assumption of a steady 'Magnus' force only applicable at the highest spin rates. In the intermediate spin rates (20 -40 rpm), the persistence of the orientation effects is shown to have sufficient effect on the flight to be an important additional consideration.
Various techniques to reduce the aerodynamic drag of bluff bodies through the mechanism of base pressure recovery have been investigated. These include, for example, boat-tailing, base cavities and base bleed. In this study a simple body representing a car shape is modified to include tapering of the rear upper body on both roof and sides. The effects of taper angle and taper length on drag and lift characteristics are investigated. It is shown that a significant drag reduction can be obtained with moderate taper angles. An unexpected feature is a drag rise at a particular taper length. Pressure data obtained on the rear surfaces and some wake flow visualisation using PIV are presented.
• This is an article from the journal, Proceedings of the Institution of Me- Abstract: This article considers a novel method for estimating parameters in a vehicle-handling dynamic model using a recursive filter. The well-known extended Kalman filter -which is widely used for real-time state estimation of vehicle dynamics -is used here in an unorthodox fashion; a model is prescribed for the sensors alone, and the state vector is replaced by a set of unknown model parameters. With the aid of two simple tuning parameters, the system selfregulates its estimates of parameter and sensor errors, and hence smoothly identifies optimal parameter choices. The method makes one contentious assumption that vehicle lateral velocity (or body sideslip angle) is available as a measurement, along with the more conventionally available yaw velocity state. However, the article demonstrates that by using the new generation of combined GPS/ inertial body motion measurement systems, a suitable lateral velocity signal is indeed measurable. The system identification is thus demonstrated in simulation, and also proved by successful parametrization of a model, using test vehicle data. The identifying extended Kalman filter has applications in model validation -for example, acting as a reference between vehicle behaviour and higher-order multi-body models -and it could also be operated in a real-time capacity to adapt parameters in model-based vehicle control applications.
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