3D Effects on Fluctuating Pressure in Crossflow Rotary Device Wakes

Attempts to reduce noise pollution have historically focused on long-established technologies rather than up-and-coming ones. In underwater contexts, technologies such as sonar, drilling, and axial-flow rotary devices like propellers most often take the spotlight. Crossflow devices, including Darrius-type turbines and propulsive cyclorotors, are rising in popularity, but understanding of their acoustic behaviour lags more-established technologies. Turbomachines typically generate sound through vorticity and, where conditions are favourable for it, cavitation. High-fidelity solution of the shed vorticity in the wake of these devices is therefore a necessary precursor to physics-based acoustic models. Two-dimensional wake solutions of crossflow devices have revealed that fluctuating wake pressure is strongly influenced by blade-vortex interactions, suggesting that noise is unlikely to follow a monotonic trend with either flow speed or blade rate. In this investigation we applied LES solutions to examine the effects of three-dimensionality, with and without blade tip effects, on that two-dimensional behaviour. This work reveals the relative importance of three-dimensionality on the wake structures and fluctuating pressure behaviour of crossflow rotary devices across configurations and operating conditions, and further highlights the importance of blade-vortex interactions for acoustic prediction.