Aerodynamics has played a significant role in the industry of motorsports in improving the performance and handling of the race car. Rob Smedley, the former head of vehicle performance at Williams Racing stated that - "Where teams have problems is when their development or simulation environment – so CFD [Computational Fluid Dynamics] or wind tunnel – doesn’t describe well what happens in reality (although in truth, no-one’s wind tunnel correlates absolutely 100%)". One of the reasons for this poor correlation could be arising from the fact that, in real life on track scenarios, the race cars undergo accelerating, decelerating, or cornering motion which can have a different influence on the aerodynamics of a race car which is not accounted for in the wind tunnel and simulation environment where a steady constant flow is employed. This research aims to numerically investigate the flow past the front wing of a Formula One car in ground effect subjected to accelerating and decelerating flows to understand the trends in the aerodynamic performance.

A scaling analysis is performed to determine the relevant non-dimensional numbers that influence the flow for translationally accelerating airfoils and two dimensionless numbers are arrived at, namely, the Reynolds number and the Froude number. Numerical investigations are carried out for translationally accelerating wings in ground effect to determine the influence of these dimensionless numbers on the aerodynamic forces.

Transient simulations were performed on a two-dimensional airfoil and a three-dimensional wing in ground effect subjected to translational acceleration and deceleration. The Shear Stress Transport (SST) based on k-ω was employed to model the turbulent flow. The results from the numerical investigations revealed a temporary change in the downforce and the drag force coefficients, as the airfoil (or wing) in ground effect is subjected to translational acceleration (or deceleration). In this study, the mechanisms that contribute to this temporary change in the aerodynamic force coefficients are discussed.

In professional swimming, a fraction of second can determine whether a competitor will obtain a place on the podium. Swimming techniques have been analysed for decades to increase and optimize performance in order to win medals in the biggest competitions. The arms and the hands play a major role in the forward propulsion generated by a swimmer, especially in front crawl swimming. They have been widely investigated for steady motion, from the elbow position to the hand orientation and configuration. However, it is argued that the arm velocity is continuously varying during a front crawl stroke and that this unsteadiness can enhance propulsion. For this reason, investigating the effect of unsteady motion on the propulsive forces generated by the hand is of great interest. The objective of this study is to experimentally investigate the effect of acceleration on the propulsion drag of a hand in human swimming, and how this effect evolves with finger spreading. To do so, experiments on four full-scale 3D printed hands with attached forearm and different finger spreading are performed. The experiments take place in a 2 x 2 m open glass tank filled with water. The hands, mounted on a robot arm and fully submerged, are accelerated towards a constant target velocity along a linear path. The acceleration and the velocity are varied resulting in a Reynolds number of 2 x 104 ≤ 𝑅𝑒 ≤ 6 x 104 based on the hand palm. The drag force exerting on the hand is measured as a function of time and three phases are distinguished: (i) the acceleration phase during which the drag reaches a maximum, (ii) the transition phase where the drag gradually decreases to reach a constant value during (iii) the steady phase. In parallel, two-dimensional particle image velocimetry (PIV) is performed in a plan crossing the fingers. A significant effect of acceleration was found performing experiments for four different accelerations. Higher accelerations generate stronger and more concentrated vortices behind the hand, resulting in a larger amount of circulation close to the hand. Consequently, a 25% increase is found in the drag force at the end of the acceleration when the latter is multiplied by four. No significant effect of finger spreading on the drag force during the acceleration was found. However, surprisingly, an enhancement of the drag force of 5% to 10% was measured during the transition phase and the steady phase for the closed hand compared to the hands with finger spreading. PIV showed larger amount of circulation close to the hand without finger spreading.