A large-eddy simulation of underexpanded supersonic swirling jets issuing into a quiescent environment was carried out for two typical swirl numbers.The corresponding nonswirling jet was also calculated for comparison and validation against the experimental data.The swirling effect on the various fundamental mechanisms that dictate the intricate flow phenomena,including flow features,shock cell structures.jet spreading characteristics and turbulence behaviors,was carefully analyzed,and it is found that the first shock cell length is reduced in the swirling jet in comparison with the nonswirling jet.A recirculation zone is formed in the high swirl number case,and the jet spreads quickly in the radial direction due to the swirling effect.Moreover,intensive turbulent fluctuations are generated along the jet shear layer and at the end of the jet potential core,which will be helpful in the mixing process.The obtained results provide a physical insight into understanding the mechanisms relevant to underexpanded supersonic swirling jets.