Spanwise Flow Effects on Laminar Separation Bubble Formation over a Swept Wing

At low Reynolds numbers, a laminar separation bubble (LSB) forms on a wing, which degrades aerodynamic performance. This mechanism is sensitive to flow conditions, and the effect of spanwise flow on the LSB is underexplored. Prior research has shown that tip vortex-induced spanwise flow and downwash suppress the LSB near the wingtip; however, the influence of crossflow and pressure-gradient-driven spanwise flow along the wingspan remains underexplored. Following these observations, this research aims to characterize the LSB topology in the presence of spanwise flow. A swept, translating wing is mounted in a water tunnel, where the angle of attack and Reynolds number are varied. Planar particle image velocimetry is conducted over multiple spanwise planes to quantify the LSB's three-dimensional structure. On a swept wing, spanwise pressure gradients and crossflow promote the transport of spanwise vorticity and instabilities in the shear layer, which transfer fluid momentum along the span. These mechanisms are hypothesized to shrink and stabilize the LSB by redistributing and tilting vorticity. Understanding the flow mechanisms that affect the performance of low-Reynolds-number rotating wings is essential to advancing efficient and safer vehicles for urban and space exploratory rotorcraft applications.