Abstract
A numerical study was conducted on the influence of turbulence intensity and Reynolds number on the mean topology and transition characteristics of flow separation to provide better understanding of the unsteady jet flow of turboelectric distributed propulsion (TeDP) aircraft. By solving unsteady Reynolds averaged Navier-Stokes (URANS) equation based on C-type structural mesh and γ - Re ˜ θ t transition model, the aerodynamic characteristics of the NACA0012 airfoil at different turbulence intensities was calculated and compared with the experimental results, which verifies the reliability of the numerical method. Then, the effects of varied low Reynolds numbers and turbulence intensities on the aerodynamic performance of NACA0012 and SD7037 were investigated. The results show that higher turbulence intensity or Reynolds number leads to more stable airfoil aerodynamic performance, larger stalling angle, and earlier transition with a different mechanism. The generation and evolution of the laminar separation bubble (LSB) are closely related to Reynolds number, and it would change the effective shape of the airfoil, having a big influence on the airfoil’s aerodynamic characteristics. Compared with the symmetrical airfoil, the low-Reynolds-number airfoil can delay the occurrence of flow separation and produce more lift in the same conditions, which provides guidance for further airfoil design under TeDP jet flow.
Highlights
The research over the last several years on the fixed-wing unmanned aerial vehicles (UAVs) with turboelectric distributed propulsion (TeDP) has attracted much attention
The results reveal that the flow featuring turbulence can effectively delay the stall characteristics of an airfoil by attaching the flow over the airfoil for an ex-tended region
If the flow at the entrance is restricted by the wall and has a turbulent boundary layer, the turbulent length scale can be calculated by l = 0.4δ99%, where the δ99% is the thickness of boundary layer
Summary
The research over the last several years on the fixed-wing unmanned aerial vehicles (UAVs) with turboelectric distributed propulsion (TeDP) has attracted much attention. The TeDP system is used to provide lift when UAVs take off. Due to the driving of the distributed propulsion to the air, the flow behind the propulsion system grows extremely complex, which is accelerated, and with strong turbulence. The characteristic Reynolds number of the wing becomes ultra low because the freestream velocity is almost zero. Owing to the influence of the turbulence and low Reynolds number, the three-dimensional effect of the wing becomes more complicated, which means the wing would encounter the coupling of up and down wash flow, flow separation, laminar separation bubble, spanwise vortex and other phenomena [3,4,5,6]
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