Preliminary Investigation On Several Unsteady Flow Characteristics In Turbomachinery

With the world development of the technology in aeronautics, astronautics and related fields, the original research idea and design technique which were based on the assumption of steady flow mode are not qualified the higher standard of turbomachinery aerodynamic performance, thus, the research on unsteady flow became an attractive subject. However, the unsteady flow in turbomachinery is highly complicated, covering many unsteady factors. The coupling effect of multiple unsteady phenomena in turbomachinery is preliminarily investigated in this dissertation, which aims to explore the interactional mechanism and providing academic support for developing mature and effective turbomachinery unsteady design system.Separated flow is a general phenomenon in turbomachinery. This dissertation firstly focuses on the unsteady characteristic of compressor cascade separated flow under off-design condition. The separated flow under different attack angles was investigated by numerical method. The computed results show that, under larger positive attack angle large separation and vortex shedding with approximate periodic fluctuation was observed. With the increasing of the positive attack angle, the unsteady characteristic and separation phenomenon enhanced gradually. Based on this work, the effect of oscillating jet that acts on upper separated flow is investigated. By the comparison between unsteady flow with oscillating jet's disturbance and the flow without oscillating jet, an effective oscillating jet with appropriate frequency, amplitude and location is discovered, which can restrain or suspend the separated flow effectively and improve the aerodynamic performance of the cascade.Unsteady wake is also a common phenomenon in turbomachinery which has a significant impact on downstream cascade. In this study, the effect of unsteady passing wake was experimentally and computationally investigated in detail on a turbine cascade. The unsteady passing wake was generated by a row of movingcylinder as the simulation of the upstream stator wake. The results show that, as an excitation mechanism, the unsteady wake with appropriate frequency can reorganize the flow effectively while turns the random fluctuation to regular status. This was verified by experiment and computed results separately.As the connatural unsteady phenomenon in turbomachinery, the interaction between rotor and stator was one of the main focuses in turbomachinery research field. In this paper, the unsteady characteristic of rotor/stator interaction under off-design condition was investigated by numerical method of multiple computational regions dividing. The computed results show the flow field characteristic under the influence of both separation flow and rotor/stator interaction. The upstream separated flow breaks the periodic trend of rotor/stator interaction flow field, changes the attack angle of downstream inlet flow, and results the whole unsteady flow field more complicated.In this paper, we not only explore the unsteady phenomena in turbomachinery, but also evaluate the optimization methods based on the assumption of steady flow mode under unsteady flow condition. The shape of stator and rotor cascades was improved and the aerodynamic performance before and after improving was analyzed. The calculation responds good result, it shows that the stator and rotor cascades optimized by inverse problem method have better aerodynamic performance not only under the condition of steady flow, but also under the condition of unsteady flow.Further more, the effect on a transonic compressor rotor by casing treatment of circumferential groove was investigated in appendix. By numerical method, the flow field with casing treatment was compared with the flow field without casing treatment. The enlarge stability mechanism of circumferential groove was discovered and the flow detail in the blade tip was shown in this part.