Experimental investigation of the impact of tidal turbine blade design on performance in turbulent flow

The nature of tidal channel flows presents unique challenges to tidal turbine designers due to the high levels of unsteady flow from large-scale ocean turbulence. This causes fluctuating loads on the turbine blades, leading to integrity and performance issues. This paper outlines an experimental campaign performed in order to assess whether turbine blade design can be used to improve performance in unsteady flow conditions, potentially reducing the fluctuating loads, and increasing turbine lifetime as a result. Two turbines, one with low-TSR, high-solidity blades (T4) and one with high-TSR, low-solidity blades (T7), are tested in a recirculating water flume in low and high turbulence flow. It is confirmed that the two turbine designs produce the same mean power coefficient at their respective design TSRs (given similar Reynolds numbers). Relative to their performance in clean flow, the mean power coefficient of T4 increases in high-turbulence flow (I = 15%), while the mean thrust coefficient for T7 decreases. The root-mean-square fluctuations in power and thrust are similar between the two turbines. In the torque and thrust response spectra of the two turbines, a dynamic region of response to turbulence is identified. This dynamic response is found to be strongly correlated to turbine rotational frequency. In the dynamic response region, T7 is found to respond more strongly to turbulence at multiples of the blade-passing frequency compared to T4. This suggests that T7 may be more sensitive to turbulent flow than T4, but further study is needed to determine whether this results only from the higher TSR, or if the low solidity of the T7 blades also has an impact

Airport route development: a survey of current practice

To develop air services and in many cases tourism flows, airports focus their marketing effort on airlines through a process known as route development. Whilst route development is a well-known concept within the airport industry it has received limited attention in academic or industry literature. As a result little knowledge is shared about why airports use route development, what are the most common methods and what is the general level of involvement. To fill the gap, this paper investigates airport route development practice using an online survey of 124 airports worldwide. Findings show that the vast majority of airports are actively involved in route development for a range of objectives and that the process and level of involvement is extensive, although this often depends on airport size, location or ownership. Results are particularly relevant to airports that are less advanced in route development activities and also those seeking to debate route and tourism development strategies with stakeholders

The effect of 3d geometry on unsteady gust response, using a vortex lattice model

Unsteady flow response is an important consideration for a range of engineering applications, from unmanned air vehicles, where it has implications for control, to tidal turbines, where the accurate calculation of fatigue load is vital. Designers often use 2D strip-theory predictions for both steady and unsteady performance, applying Theodorsens unsteady transfer function for uniform gusts at each blade section to estimate the unsteady bending moments on the turbine blades. The purpose of this investigation is to explore the limits of the applicability of this 2D classical unsteady aerofoil theory to aerofoils with significant 3D geometry features. Using a harmonic vortex lattice model, this study shows that there are significant 3D features in the unsteady flow response, which increase with decreasing reduced frequency and with decreasing aspect ratio. The response near the blade tips is strongly 3D, and does not reach the 2D characteristic, even at high frequencies. The phase response also varies strongly along the span, leading to different blade sections responding out of phase with each other even with no spanwise gust variation. This has significant implications for bending moment calculations, with require integration of the load along the span. The observed 3D effects are shown to be caused by changes to the spanwise component of the unsteady wake, and by the presence and behaviour of a streamwise unsteady wake. The results for a model tidal turbine geometry show that the Loewy function does not capture returning wake effects adequately, but that it does model the mid-span response characteristic well at reduced frequencies over 0.8. The study concludes that using transfer functions from 2D classical aerofoil theory provides a conservative estimate of the blade loads affecting a tidal turbine, but only if no steady tip-loss corrections have been applied to the unsteady response. If tip-loss corrections are applied to the quasi-steady lift response before unsteady transfer functions are used, the resulting load amplitude will be significantly under-predicted