Investigation of Flow Mechanism for Solidity in Typical Modes of Variable Pitch Tandem Cascade

Due to the influence of fan geometry and aerodynamic factors, aerospace propulsion systems have difficulty operating above Mach 3.5. Even with a hybrid power system equipped with a turbofan engine, there is an issue of insufficient intermediate thrust. This is attributed to the limited acceptable inflow range of traditional fan layouts. This paper proposes a novel variable pitch tandem fan (VPTF) configuration that has the potential to overcome this limitation and further expand the operating speed range of the fan. Subsequently, based on this scheme, three-dimensional Reynolds averaged Navier-Stokes simulations were conducted for VPTF in transonic mode (Ma1 = 1.5), supersonic mode (Ma1 = 2.5), and windmilling mode (Ma1 = 4). The comprehensive impact of solidity on the performance under these three typical modes was investigated. The results show that solidity primarily affects the shock intensity within the passage, as well as the location and number of interactions with the blade surface, thus influencing the aerodynamic performance and blade loading of VPTF. It was found that when the solidity is chosen around 4.5, VPTF can achieve relatively good performance. At this solidity, it exhibits lower losses and maximum pressure ratio in the transonic mode. The supersonic and windmilling modes also exhibit lower losses.