Increasing the efficiency of bladeless fans by applying longitudinal cylindrical grooves on the diffuser walls

The paper investigates the possibility of increasing the efficiency of bladeless fans by applying longitudinal cylindrical grooves to the inner walls of the diffuser. Bladeless fans, which are jet pump-type superchargers, show promise as propulsion systems for small aircraft with electric and gas turbine engines. The key parameter determining their efficiency is the flow entrainment ratio, which depends on the geometry and aerodynamic quality of the air passage. In this study, we perform numerical simulations to assess how the geometric parameters of the cylindrical grooves affect the fan’s aerodynamic performance. We consider the diameters of the arcs forming the grooves (3, 6, and 9 mm) and the angular step of their placement (2°, 4°, and 6°) as variable parameters. We carry out aerodynamic calculations in a threedimensional periodic setup using the ANSYS CFX software package with the k-ω SST turbulence model. Our results show that, at a fixed total pressure at the outlet of the annular gap, the primary airflow rate remains constant across all configurations. The highest efficiency occurs with a groove diameter of 6 mm and an angular pitch of 2°: in this case, the secondary airflow increases by 2 %, and thrust rises by 4 % compared to the base model without grooves. We analyze turbulent kinetic energy fields and visualize vortex structures, revealing that this configuration produces the lowest turbulence intensity and smallest vortex scales in the near-wall region, which enhances momentum transfer from the jet to the surrounding air. Grooves with a smaller diameter (3 mm) have almost no effect on performance, while larger grooves (9 mm) increase flow turbulence and reduce efficiency. Engineers can use these findings to develop highly efficient propulsion systems for unmanned aerial vehicles.