Acoustic pressure fluctuations within the combustion chamber or the plenums of a liquid rocket engine (LRE) may induce temporal modulations of the injection velocities of the propellants. The dynamic response of a transcritical coaxial flame to such velocity modulations is investigated here as it is thought to be one of the mechanisms that may promote high-frequency combustion instabilities in LREs. This question is addressed through Large-Eddy Simulations (LES) of a single element LOx/GCH 4 coaxial injec-tor, the present work being focused on the case where the annular GCH 4 flow only is modulated. The simulations reveal that when this annular stream is modulated, vortices are produced and travel along the flame front, inducing local flame stretch rate disturbances. A low-order model for this process is proposed and proves to be in fairly good agreement with the results of our simulations both in terms of gain and phase.