Role Of Free-stream Turbulence on Laminar-turbulent Transition in Laminar Separation Bubbles: Laminar separation bubbles (LSBs) are encountered in many important aeronautical applications, such as wings of unmanned aerial vehicles, multi-element airfoil configurations, low-pressure turbine blades to name a few. The underlying physics are highly complex, as both unsteady separation and transition mechanisms are at work interactively. Considering technical applications, it is reasonable to assume that the most general disturbances inducing laminar-turbulent transition are due to free-stream turbulence (FST). Towards this end, a set of highly resolved Direct Numerical Simulations was carried out, where isotropic FST fluctuations are introduced to investigate the relevant physical mechanisms governing the interaction of separation and transition in LSBs. It was demonstrated that the transition process is the result of two different mechanisms: (i) strong amplification of high-frequency 2D fluctuating disturbances and (ii) low-frequency, three-dimensional modes caused by FST. Depending on the intensity of the FST, one of these mechanisms would dominate the transition process, or both mechanisms act together and contribute simultaneously. The net effect of these two events is an acceleration of transition for an increased level of FST intensity, which in turn leads to a reduction of the extent of the separation bubble in streamwise and wall-normal directions. Contributors: Shirzad Hosseinverdi & Hermann F. Fasel