**2. Low Reynolds number aerodynamics**

The aerodynamic performances of airfoils in low Reynolds number flows considerably relate to a major range of engineering applications. The low Reynolds number flows are described that the viscous forces within fluid gain dominant characterization compared with inertial forces. Hereby, boundary layer physics such as laminar boundary layer separation, reattachment, and transition phenomena can frequently occur at low Reynolds number flows, affecting the performance of airfoils with the important changes of lift and drag forces.
