Sensitivity Analysis of Geometrical Parameters to the Flow of Pre-swirl System after Turbine Blade Fracture

The pre-swirl stator-rotor system is a common and important structure in gas turbines, and its main function is to provide cold air to the turbine blades with a low relative total temperature. Under normal conditions, the boundaries of the system are symmetrical and there is sufficient margin for each blade. However, a fracture of turbine blades can upset this balance, resulting in potentially different cold-air conditions for each blade. Therefore, to ensure the safety of the other blades after a single-blade break, it is necessary to know the cold-air distribution law of the system after a blade fracture. In this paper, the effects of geometric parameters (including pre-swirl angle, α; the area ratio of nozzles and holes, ξ; gap ratio, G; and radius ratio of nozzle and hole, δ) of a pre-swirl stator-rotor system on the mass-flow-rate ratio, η; total-pressure-loss coefficient, C_p; discharge coefficient of holes, C_d; and adiabatic effectiveness, Θ_ad, are investigated by numerical simulation with a single blade fractured. The results show that most of the geometric parameter changes do not increase η_{hole_0}. Moreover, measures to increase the influence of pre-swirl nozzles can reduce the influence of blade fracture on mass flow distribution, such as larger α, smaller ξ, and smaller δ. As for C_p, C_d, and Θ_ad, they are more sensitive to changes in α and ξ. For the pre-swirl system, to avoid more serious safety problems caused by individual blade fracture, the designer should make every effort to reduce the unevenness of the cold-air distribution. Increasing the effect of the nozzle could serve the aim, but it may increase the volatility of the flow. The pre-swirl nozzle of the leaf grille type is a good option to address flow fluctuations.