Numerical Study on Buoyancy-Driven Görtler Vortices above Horizontal Heated Flat Plate

The temperature of the solar cells on the upper surface of a solar unmanned aerial vehicle (UAV) wing is much higher than the atmospheric temperature during flight. The temperature difference will induce buoyancy-driven Görtler vortices that may influence the aerodynamic characteristics of the wing. In the present study, a hybrid RANS-LES-based approach was used to simulate the flow above a heated flat plate under different flow velocities (from 0.34 m/s to 0.63 m/s) and temperature differences (from 0 K to 60 K), and the influence of Görtler vortices on the flow was analyzed. The existence of buoyancy-driven Görtler vortices would induce velocity normal to the plate, and a negative velocity normal to the plate at the peak position would enhance the momentum exchange within the boundary layer, accelerate the transition, and increase the friction drag coefficient. The drag coefficient with a 60 K temperature difference is almost three times that with a 0 K temperature difference. With an increase in temperature difference or decrease in flow velocity, the intensity of Görtler vortices would increase. A couple of different buoyancy parameters were studied, and a combined parameter based on both the Reynolds number and Grashoff number was proposed as the index parameter of heated plate flow. The flow above a heated flat plate can be divided into three regions by the buoyancy parameter. When the buoyancy parameter is between 100 and 200, the Görtler vortices are stable, and the flow exhibits significant three-dimensional characteristics.