Exploring on Aerodynamic Characteristics of Low Reynolds Number Airfoil in Time-varying Wind Field

A solar-powered unmanned aerial vehicle generally encounters the problems that it has low Reynolds effects and is highly susceptible to gust response. Therefore, the grid velocity method was used to analyze the gust response characteristics of the airfoil FX63-137 under low Reynolds number. First, the reliability of the numerical simulation method at low Reynolds number and grid velocity method were verified with experimental data. Second, the gust response characteristics of FX63-137 airfoil under different Reynolds numbers and different angles of attack were numerically simulated. The results show that the magnitude of incremental lift coefficient in gust response decreases because laminar separation bubbles are complete as the Reynolds number decreases at a small angle of attack. They also show that laminar separation bubbles have an unloaded effect on gust response. At a high angle of attack, as the airfoil enters into stalling stage, the incremental lift coefficient begins to decline before reaching maximum gust disturbance. Because of the stalling of the airfoil, when the gust disappears, the incremental lift coefficient has a negative value. What's more, although the effective angle of attack is equal, the flow structure of the airfoil is somewhat different in upstream and downstream moments. Compared with the downstream moment, the incremental lift coefficient at the upstream moment is generally larger, and the incremental lift coefficient curve of the airfoil forms a non-closed hysteresis loop