Large eddy simulation of a cross-flow fan and its control using sinusoidal protrusions

The flow characteristics in a cross-flow fan is investigated using large eddy simulation with an immersed boundary method. The fan operates at the Reynolds number of Re = 5,400 based on the blade chord length and the blade tip velocity at its outer radius. Due to the rotation of cross-flow fan, an eccentric vortex locates at the lower right corner near a stabilizer, and the main flow passes by this vortex. A recirculation region at the corner of the inflow region and flow separation on blade suction surfaces are also captured in the simulation. To analyze the effects of these flow structures on the fan performance, the variation of the torque coefficient on each blade along the azimuthal direction is examined. Most of the efficiency comes from the flow in the lower left and upper right corner of the fan, but the recirculation zone narrows the inflow region, resulting in a considerable loss. The flow on the upper part also separates, providing lower efficiency and pulsations. With the protrusion installed on the leading edge of each blade, the recirculation region and the flow separation in the upper part is significantly reduced, increasing the fan efficiency.