The labyrinth seal in turbomachinery is a key element that restricts leakage flow among rotor-stator clearances from high-pressure regions to low-pressure regions.The fluid-induced forces on the rotor from seals during machine operation must be accurately quantified to predict their dynamic behavior effectively.To understand the fluid-induced force characteristics of the labyrinth seal more fully,the effects of four types of pre-swirls on the leakage,flow field,and fluid-induced force of a rotary straight-through labyrinth gas seal (RSTLGS) were numerically investigated using the proposed steady computational fluid dynamics (CFD) method based on the three-dimensional models of the RSTLGS.The leakage,flow field,and fluid-induced force of the RSTLGS for six axial pre-swirl velocities,four radial preswirl angles,four circumferential positive pre-swirl angles,and four circumferential negative pre-swirl angles were computed under the same geometrical parameters and operational conditions.Mesh analysis ensures the accuracy of the present steady CFD method.The numerical results show that the four types of pre-swirls influence the leakage,flow field,and fluid-induced force of the RSTLGS.The axial pre-swirl velocity remarkably inhibits the fluid-induced force,and the circumferential positive pre-swirl angle and circumferential negative pre-swirl angle remarkably promote the fluid-induced force.The effects of the radial pre-swirl angle on the fluid-induced force are complicated,and the pressure forces and viscous forces show the maximum or minimum values at a specific radial pre-swirl angle.The pre-swirl has a negligible impact on the leakage.The four types of pre-swirls affect the leakage,flow field,and fluidinduced force of the RSTLGS to varying degrees.The pre-swirl is the influence factor affecting the leakage,flow field,and fluid-induced force of the RSTLGS.The conclusions will help to understand the fluid-induced force of labyrinth seals more fully,by providing helpful suggestions for engineering practices and a theoretical basis to analyze the fluid-structure interaction of the seal-rotor system in future research.