This paper provides a resolution to the contradictory accounts of whether or not the Darrieus turbine can self-start. The paper builds on previous work proposing an analogy between the aerofoil in Darrieus motion and flapping-wing flow mechanisms. This analogy suggests that unsteadiness could be exploited to generate additional thrust and that this unsteady thrust generation is governed by rotor geometry. Rotors which do not exploit this unsteadiness will not self-start. To confirm the hypothesis, unsteady effects were measured and then incorporated into a time-stepping rotor analysis and compared to experimental data for self-starting wind turbines. When unsteady effects were included, the model was able to predict the correct starting behavior. The fundamental physics of starting were also studied and parameters that govern the generation of unsteady thrust were explored, namely, chord-to-diameter and blade aspect ratios (ARs). Further simulation showed that the Darrieus rotor is prone to be locked in a deadband where the thrust is not continuous around a blade rotation. This discrete thrust is caused by the large variation in incidence angle during startup, making the Darrieus blade ineffective during part of the rotation. The results show that unsteady thrust can be promoted through an appropriate selection of blade aspect and chord-to-diameter ratios, therefore self-starting rotors may be designed. A new definition of self-starting is also proposed.

It is well known that platoons of closely spaced passenger cars can reduce their aerodynamic drag yielding substantial savings in energy consumption and reduced emissions as a system. Most published research has focused on platoons of identical vehicles which can arguably be justified by some evidence that geometric variety has little to no effect on the overall flow characteristics in platoons of three vehicles or more. It is known that much of the aerodynamic benefit from platooning is gained by the leading two cars, so operating as vehicle pairs could potentially achieve similar environmental benefits whilst addressing many of the practical challenges associated with the safe operation of long platoons on public roads. However, it has been reported that unlike long platoons, the effect of geometry and arrangement is critical if the drag reduction of a pair is to be optimised. This paper describes a parametric study based on three geometric variants of the popular DrivAer model with different combinations and spacings. It is confirmed that vehicle geometry crucially affects the results with the best combinations matching those of long platoons and others creating a net drag increase.

A vehicle on the road encounters an unsteady flow due to turbulence in the natural wind, unsteady wakes of other vehicles and as a result of traversing through the stationary wakes of roadside obstacles. Unsteady effects occurring in the sideglass region of a vehicle are particularly relevant to wind noise. This is a region close to the driver and dominated by separated flow structures from the A-pillar and door mirrors, which are sensitive to unsteadiness in the onset flow. Since the sideglass region is of particular aeroacoustic importance, the paper seeks to determine what impact these unsteady effects have on the sources of aeroacoustic noise as measured inside the passenger compartment, in addition to the flow structures in this region. Data presented were obtained during on-road measurement campaigns using two instrumented vehicles, as well as from aeroacoustic wind tunnel tests.Conventional admittance functions relating oncoming flow yaw angle to cabin noise response are generally not suitable due to the non-linear steady state characteristics obtained in the wind tunnel, i.e. the cabin noise does not vary with yaw angle in a linear fashion under steady-state conditions. Therefore two alternative approaches were used based on instantaneous conditions to determine a quasi-steady predicted cabin noise time-history. These techniques demonstrated that the cabin noise response to oncoming flow unsteadiness remained generally quasi-steady up to fluctuation frequencies of approximately 2 to 5 Hz, where above this smaller flow scales have a progressively smaller impact on cabin noise fluctuations. Therefore, with a measurement of both the cabin noise in the steady environment of the wind tunnel and the unsteady onset flow conditions, the fluctuations (and thus the modulation) of the wind noise under these unsteady conditions is able to be predicted.