The Research Of Stator Clocking Effect In Turbo Machinery Via Ring Vane Cascade

The flow in turbo machinery, which is a kind of strong 3-D unsteady flow, is of great significance to investigate and further understand this mechanism, in order to improve turbo machine's aerodynamic performance and working stabilization. A lot of experiments and numerical simulation has been carried out to investigate the clocking effect both at home and abroad. However,CFD still as a main method is used to investigate the mechanism of clocking effect as a result of the limitation of experimental measurement in high speed rotating turbo machinery. It is inappropriate to study clocking effect without considering the flow in all cascades and unequal distribution in different cascades. So in this thesis, numerical simulation will be carried out based on a ring cascade grid calculation.The unsteady flow at the mid span of a two-stage axial flow compressor was studied by means of numerical simulation based on 2-D, 3-D and ring vane cascade. However, the results from the ring cascade contain much more information of the flow, so that the interaction between blades rows can be further understood based on these results. According to different axial gaps at different clocking positions, a detailed numerical simulation has been carried out in a low speed two-stage compressor based on ring cascade. Meanwhile numerical simulation was also carried out in a 2.5 stage axial turbine in the same way, in order to investigate the mechanism of clocking effect at stages turbo machinery.By results of numerical analysis of the stator in the clocking position, we summed up the clocking effect of some basic rules: (a) uneven distribution of the upstream flow in circumferential direction of the wake produce the clocking effect and have a significant impact on the development of the downstream blade boundary layer. The change of clocking position makes disturbance into a useful superposition, which can reduce flow loss of the moving blade surface and improve the aerodynamic efficiency. (b) through the channel ring cascade calculation results, the clocking effects leading interference theory is confirmed: When the wake of upstream stator impact the blade leading edge, due to mixing of the wake with the low-energy fluid and the same boundary layer with the low-energy fluids, the mixing loss is fewer and the aerodynamic efficiency is high. on the the contrary , if mixing with mainstream with high-energy, the fluid loss becomes much larger, while the aerodynamic efficiency becomes much lower.Numerical simulation via ring cascade grid is more suitable to study the clocking effect, which can analyze all flow in all cascade without special treatment of blade'number. It can make using less computal time to study the multi-stage row and multi-cascade calculation for unsteady situation possible. It is more comprehensive and reliable to reflect the interaction of the flow channel and pressure fluctuations than single-channel calculation. So it is a useful reference for practical application.