| Nowadays, unsteady flow and unsteady design are parts of the main focuses of turbomachinery aerodynamics research. Hence, the present dissertation attempts to discuss two important parts of unsteady design: Unsteady Flow Pattern and Edge Matching, on which preliminary investigations are performed. Because of the difficulty rising from experiment of unsteady turbomachinery flow, the author has to select CFD as a main method to conduct unsteady researches. Consequently, this dissertation begins with programming the time-accurate flow solvers and the main efforts are listed as follows:1. To be the basis of fulfilling unsteady turbomachinery design, 2D and 3D Reynolds-Averaged N-S solvers are developed with the capabilities of simulating unsteady flow of turbomachine with multiple blade rows and passages. Due to lack of data from unsteady experiment, the 2D and 3D CFD codes are validated by comparing with FLUENT and NUMECA respectively. Before putting the codes into the following researches, studies about grid and time step dependence have been conducted. Reasonable grid and time step are determined so that the numerical results can be convinced. All these indicate that the codes are reliable for unsteady flow simulation.2. Unsteady Flow Pattern is an important technique in 2D unsteady turbomachinery design.A turbine cascade is adopted as an example in unsteady flow pattern study, in which time-accurate inlet profiles are imposed to produce the cascade unsteady flowfield. The effects of unsteady flow onto cascade performance are studied and compared with those of the equivalent steady and quasi-steady cases. The main concerns focus on how the wake defect, flow angle and wake moving speed in pitchwise influence the cascade performance. Also, 'time-lag' phenomenon of cascade lift is investigated preliminarily. All these researches display some aspects of unsteady flow pattern study introductorily in future.3. As an important part of unsteady flow pattern study, 2D clocking effect is investigated ona 1.5 stage turbine cascades with stator/rotor/stator configuration. Not only the knowledge about the mechanism of clocking effect is obtained, but also the influences ofaxial gap and rotor rotating speed onto clocking effects are further demonstrated by 2D CFD simulations. Results show that the two kinds of influence both can bring some new phenomena onto clocking effect, such as the changing of potential in improving the efficiency of turbomachinery, changing of wake-transport time and so on. This study can not only advance the understanding of the mechanism of clocking effect, but also make the investigation on clocking effect more detailed, from which 3D clocking effect study and application will be benefited subsequently.4. Edge Matching is an important technique in 3D unsteady turbomachinery design which mainly aimed at the 'matching' between multiple blade rows. To be an important part of this dissertation, it is introduced comprehensively about the theory of Edge Matching, two methods of manipulating and its preliminary validation firstly. Then, as an example to testify and apply the theory, a new idea is suggested that the clocking effects can be more perfect when they are taken into account in the frame of Edge Matching theory. In order to exemplify this potential, two ways of applying edge matching are selected: one is from combinations of hub and tip section of the second stator; the other is from combinations of the two tip sections of both two stators, the intention of which is to see if the turbine aerodynamic efficiency can be further promoted over the original well clocked one. 3D numerical optimizations are conducted based on the full-optimizing method, which is the most time-consuming one in the two manipulating ways of Edge-Matching theory. Results show the importance of Edge Matching for further promoting the benefit of clocking effects. This indicates edge matching provided a new degree of design freedom for turbomachinery unsteady design. |
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