Fluid dynamic analysis and lift enhancement of material transport and mixing around airfoil through Lagrangian coherent structures

Abstract

Flow separation around an airfoil can be effectively controlled by appropriately positioning a synthetic jet (SJ) on the airfoil surface, subsequently enhancing the airfoil's lift. This study conducts a fluid dynamics analysis of material transport and mixing related to momentum transport and mixing around an airfoil. The detailed analysis of the corresponding effects on lift improvement aids in understanding fluid dynamics through Lagrange Coherent Structures (LCSs) and their nonlinear dynamics. An additional SJ is introduced in the airfoil's rear section, combined with a high-speed, low-frequency SJ in the front section to form a combined SJ. The flow around the airfoil with this combined SJ is simulated. LCSs surrounding the SJs are identified and utilized to analyze the complex material transport and mixing processes. The impact of material transport and mixing on lift enhancement is explored through the evolution of LCSs and pressure distribution on the airfoil surface. Results demonstrate that the combined SJs further improve the airfoil's lift coefficient compared to single SJs, with the enhanced material transport and mixing of SJs playing a vital role in lift enhancement. The rear jet accumulates downstream of the rear slot, forming a tail vortex with high momentum and low pressure. The vortex generated by the front jet carries the tail vortex, continuing to move downstream when it reaches the rear slot. A pressure drop forms where the two vortices flow, enhancing the airfoil's lift. The rear jet can absorb fluid downstream and upstream of the jet slot, reducing pressure on the suction surface near the jet slot and significantly contributing to lift improvement.