tailieunhanh - UNSTEADY AERODYNAMICS, AEROACOUSTICS AND AEROELASTICITY OF TURBOMACHINES Episode 4

Tham khảo tài liệu 'unsteady aerodynamics, aeroacoustics and aeroelasticity of turbomachines episode 4', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Comparison of Models to Predict Low Engine Order Excitation 147 Figure 1. Example of a typical turbine Campbell diagram indicating Low Engine Order resonance During the last decade intensive research and development activities have focused on the computation of wake passing frequency excitation in turbomachinery stages. The goal was to benchmark the capabilities of computational tools for further application during engine design. Furthermore the investigation of unsteady fl w physics was addressed aiming at widening the understanding of the mechanisms of aerodynamic blade vibration excitation for example in 2 . Only little work has been published on the computation and understanding of low engine order excitations. These are more difficult to predict than vane passing excitations due to the following reasons The frequency and magnitude of the low engine order excitation is not known a priori because it is caused by unknown variations in the vane geometry due to manufacturing tolerances or wear on the vanes during operation. The periodicity of the excitation is often not known a priori. The spatial periodicity of the stator exit ft w must be assumed to be over the whole circumference. 148 For a low-pressure turbine rotor 3 investigated the 2nd engine order temperature variations which emanated from the combustor. The excitation was modeled with help of measured data. A full annulus analysis was presented by 4 indicating LEO excitations due to throat width variations in the stator. 5 showed a systematic study of low engine order forced response considering the effects of throat width variation in the stator and temperature distortion. A typical sector of the stage was modeled to compute the aerodynamic excitation. In 6 linear inviscid ft w and non-linear viscous ft w models for the unsteady ft w in the ADLARF fan rotor are compared LEO boundary conditions were derived from experiments. All these investigations derived the unsteady boundary conditions either from full