Phase portrait analysis of laminar separation bubble and ground clearance interaction at critical (low) Reynolds number flow

Inspiring from nature, flying near the ground surface might increase the aerodynamic performance of Micro Aerial Vehicles (MAVs). Because of the being small in size, these birds have low flight speeds and their operating range is in the low Reynolds flow zone (Re < 2.0 x 10(5)) where a laminar separation bubble (LSB) normally appears on the suction surface of a wing. In this study, the interaction of LSB formed on a full-span wing, with the cross-section of NASA LS (1)-0417, and ground clearance is investigated at the critical Reynolds number (5 x 10(4) - 2 x 10(5)). The behavioral changes of the separation bubbles in free flow and near the ground surface have been numerically discussed in detail by different distances away from the ground (h/c) and various angle of attack (8 degrees, 12 degrees, 14 degrees, and 16 degrees). Furthermore, the patterns and behavior of multiple flows affected by the interaction of the separation bubble phenomenon with ground effect is discussed from the points of view of vortex fields, phase portrait, frequency analysis, existing stresses, and velocity profiles. The main outcomes reveal that the ground effect's general role does not work in this region of flow, and the aerodynamic performance of the full-span wing is decreased near the ground due to the bubbles. Furthermore, at 0.2 < h/c < 1, the phase portrait curves have an elliptical shape due to the bursting of the separation bubble.

Automated summary

This study investigated the interaction of LSB formed on a full-span wing with ground clearance, and found that flying near the ground surface decreases the aerodynamic performance of the full-span wing in low Reynolds flow zone. Through numerical discussions, it was also revealed that at certain distances from the ground, the phase portrait curves exhibit an elliptical shape due to the bursting of the separation bubble.