A review on the application of hybrid RANS-LES methods in hydraulic machinery

Hydraulic machinery plays a pivotal role in various fields, and they usually operate with complex flow phenomena that may significantly affect its performance and stability. The development of computational fluid dynamics has emerged as a crucial tool for investigating high-Reynolds turbulent flow in hydraulic machinery. Compared with conventional CFD methods, i.e., RANS, and LES, hybrid RANS-LES methods (HRLMs) offer a trade-off between computational cost and simulation accuracy, and become a promising tool for exploring flow dynamics and underlying mechanisms in recent years. To promote the application of HRLMs in hydraulic machinery, this work reviews the main HRLMs applicable to hydraulic machinery, with an emphasis on their principles and inherent limitations. Furthermore, recent applications of HRLMs in pumps, turbines, and propellers are discussed. It was demonstrated that the DES-type methods are the most widely used HRLMs in hydraulic machinery, which have superior performance in predicting multi-scale vortex structures, cavitation, noise, erosion, etc. This review aspires to provide insights and guidelines for researchers interested in employing HRLMs, and endeavors to advance the understanding of complex flow mechanisms in hydraulic machinery.