This study investigates the evolution of axial loads in the secondary air system following shaft failure in aeroengines. It addresses a significant gap in the existing literature regarding the effects of inertial forces within the cavity, as well as the unclear mechanisms by which the geometric parameters of the flow path influence these forces. A combined approach of three-dimensional simulation and experimental validation is utilized to propose a method for analyzing the evolution of axial loads during the fast transient response process, based on changes in the Cavity Inertial Force Dominant Zone (CIDZ). The research examines both single cavities and cavity–tube combination flow paths to explore the impact of inertial forces on the axial load response process and, subsequently, the influence of flow path geometric parameters on this response. The results demonstrate that inertial forces within the cavity and the geometric parameters of the flow path significantly affect the axial load response process by influencing the intensity, phase, and minor oscillation amplitude of the axial load response at various end faces within the cavity. The variation in a single geometric parameter in this study resulted in a maximum impact exceeding 500% on the differences in axial loads at different end faces within the cavity. The study offers theoretical support for the load response analysis of the secondary air system in the context of shaft failure, serving as a foundation for safety design related to this failure mode.

Experimental investigations and datasets in the open literature remain scarce for the fast transient response of air systems induced by sudden internal structural failures, hindering rigorous experimental validation of the governing trends associated with multiple influencing factors. To address this gap, we establish a fast transient air-system test platform and develop a step boundary simulation device based on mechanical energy storage, enabling rapid and repeatable boundary transients. The experiments demonstrate that the minimum boundary-change time is less than 6 ms, satisfying the simulation requirement for boundary transients associated with typical sudden structural failures (≤10 ms). Guided by a dimensionless analysis, we conduct fast transient cavity-venting experiments under varying outlet areas, cavity geometric parameters, and initial pressure ratios, thereby obtaining the transient response data of the cavity pressure. In parallel, we simulate the test process using a three-dimensional numerical approach validated against the experiments; by combining experimental and numerical results, we systematically analyze the effects of key factors on the fast transient response during cavity venting and elucidate the underlying mechanisms. This paper provides experimentally validated data and a reliable experimental methodology for studying fast transient response processes in air systems, and it supports the passive safety design of aero-engines.

Existing low-dimensional cavity element models developed under the lumped-parameter assumption, which neglect cavity geometric parameters and inertial effects within the cavity, cannot meet the simulation requirements of aircraft-engine secondary air systems (SAS) during the fast transient response processes. To address this gap, this study proposes a modular modeling methodology for a fast transient cavity low-dimensional model. The cavity is partitioned into modules according to the internal flow features during the fast transient response, and the partition ratios are determined by evaluating how different geometric parameters affect these flow characteristics. Using this method, low-dimensional models are constructed for single-port cavities and dual-port cavities under various geometric parameters, and the fast transient depressurization response is investigated. In parallel, corresponding three-dimensional models are established using a validated simulation approach, and three-dimensional computations are performed. Comparison between the low-dimensional and three-dimensional results confirms that the proposed method effectively reproduces the key flow phenomena in the cavity during the fast transient events with credible predictive accuracy. This work optimizes existing low-dimensional simulation algorithms for air systems and provides technical support for studying fast transient responses in aircraft-engine SAS.