The rotor-stator cavity represents a critical component in engine secondary air systems. Due to its large-volume characteristics, the parameter response and flow evolution during engine transient processes exhibit distinctive features that differ from steady-state conditions. Therefore, this study investigates the transient flow evolution in rotor-stator cavities subjected to impulsive changes in rotation rate through theoretical analysis and direct numerical simulation. We examine three distinct conditions: infinite cavities and enclosed cavities under both laminar and turbulent conditions, exploring their transient processes during transient from one stable condition to another. In infinite cavities with initial steady state, the transient process experiences rapid momentum and mass exchange between rotor and stator boundary layers. Compared to start-from-rest scenarios, the transient duration is significantly reduced. For enclosed laminar cavities, the impulsive change generates disturbances at the shroud that excite circular waves propagating radially inward before restabilizing while maintaining laminar conditions. Due to the presence of the shroud and hub in enclosed cavity, the transient process captures circular waves that cannot be observed in infinite cavities, while the presence of the shroud accelerates the transition process. In turbulent enclosed cavities, we observe that following an impulsive increase in rotation rate, the rotor boundary layer adjusts rapidly while the stator side experiences delayed adaptation with small-scale vortex breakdown initiating at high radial positions. After the transient phase ends, the rotor boundary layer maintains laminar characteristics while turbulence intensity increases on the stator side. Although the rotor boundary layer maintains laminar conditions in both laminar and turbulent cavities, these states differ significantly. Under turbulent conditions, disturbances from the turbulent stator penetrate the core region, generating perturbations on the disk. These transient phenomena, distinctly different from steady-state behavior, may significantly impact engine efficiency and operational safety in practical applications. This work provides fundamental insights into impulsive rotation changes in rotor-stator systems, establishing a foundation for future investigations of more complex transient conditions.

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• Boundary layer receptivity, stability & separation
• Boundary layers
• Flow instability
• Rotating turbulence
• Structure & turbulence of boundary layers