【作者】 冯子明；

【导师】 钟兢军；

【作者基本信息】 哈尔滨工业大学 ， 动力机械及工程， 2009， 博士

【摘要】 发展超临界汽轮机组是火电行业落实“十一五”规划纲要中提出的“节能减排”国策的主要措施之一。通过采用现代设计技术,例如子午收缩以及叶片的弯扭掠等对在线运行的超临界汽轮机组进行改型设计,可以进一步提高该类机组的相对内效率,降低煤耗,减少排入大气的NOx等有害气体。同时由于超临界汽轮机组是从国外引进的设计,借助改型设计也能为我国研制具有独立知识产权的超临界汽轮机组提供技术储备。欲对国外引入的超临界汽轮机组(原型)进行改型设计,首先必须消化吸收其先进的设计理论与经验。为此,本文选择原型两典型级的具有代表性的三套叶栅,即调节级的导向叶栅以及第八压力级的静、动叶栅作为实验模型在低速风洞上进行静态吹风实验。尽管实验条件未能满足模化理论要求,但仍能相对地根据实验结果分析原型叶栅的气动性能,确认其设计思想。同时,实验数据也用于校核数值模拟软件。应用五孔球头测针详细测量了不同冲角下三套叶栅气动参数沿叶高和节距的分布。采用墨迹显示技术,显示了三套叶栅壁面(包括叶片表面和上下端壁)极限流线谱。通过对实验结果的理论分析,讨论了叶片前缘形状、载荷分布、叶片弯掠以及冲角对叶栅气动性能的影响。实验结果表明,具有子午收缩外端壁的调节级导向叶栅沿叶高形成的静压分布是均匀的,即抑制了边界层的径向流动又抵消了吸力侧出口逆压梯度段的不利影响;而其后部加载特性可以显著降低流道前部和中部的横向压力梯度,削弱了端壁横向二次流动与吸力侧壁角分离;在±10°冲角范围内,总流动损失变化不大,说明实验叶栅具有良好的冲角适应性。在第八压力级静、动叶栅的设计中,采用沿叶高改变吸力面最低压力点轴向位置的后部加载叶型和正弯叶片,显著降低了上下端壁附近叶片的气动负荷,从而减小了两端壁上的横向压力梯度,端部流动损失被降至最低。此外,叶片的正弯还分别在压力面和吸力面上形成了沿叶高的“C”型静压分布,使吸力侧壁角易堆积的边界层低能气体均匀地扩散进入主流,抑制了叶栅的壁角分离。由叶片表面流动显示可以看出,沿绝大部分叶高叶片型面边界层无径向流动,说明在这两套叶栅中径向二次流很小。为了进一步提高超临界汽轮机的气动性能,创立有自主知识产权的设计技术,本文应用经上述实验数据校核的NUMECA软件,分别对调节级导向叶栅和第八压力级静、动叶栅进行了改型设计,通过数值仿真考察了弯扭掠全三维设计技术对叶栅气动性能的影响。最后,对第八压力级进行了掠叶片的匹配设计,数值研究了掠叶片级的设计工况性能。调节级导叶改型设计的仿真结果表明,调节级导叶采用正或反弯叶片,叶栅的流动损失大致相同,但正弯叶片气动参数沿叶高的分布比反弯叶片均匀。在不对上端壁进行防磨处理的情况下,建议采用正弯叶片。与正、反弯叶片比较,具有凸型子午收缩的原型导向叶栅流动效率最高,气动参数沿叶高的分布也最均匀,在对上端壁进行防磨处理后,宜采用子午收缩调节级导叶。第八级静、动叶采用轴向掠叶片设计的仿真结果显示:与原型静、动叶栅比较,静叶栅采用后掠叶片时的流动损失稍有降低,动叶栅采用后掠叶片时总的流动损失与原型动叶栅的流动损失大致相同,因为在叶栅中部气流比端部在上游进入流道,在相同轴向位置叶栅中部气流有较大的降压比,因此沿叶高形成了两端高中间低的压力分布,即“C”型压力分布。将聚集在叶栅两端低能边界层流体扩散进主流,从而减少了低能流体在端壁壁角的堆积。而前掠静、动叶片的采用则有相反的结果,会增加总流动损失。由于气流在叶栅两端比叶展中部先进入流道,所以在相同轴向位置,形成沿叶高的中间大两端小的反“C”型压力分布,将叶片表面低能边界层流体推向两端壁角,边界层内低能流体堆积在两端,加重了叶栅吸力侧壁角分离。高压级设计工况数值仿真结果表明:叶片沿轴向掠后,叶型积迭线沿轴向倾斜对流场压力分布产生了影响。由于在不同叶高气流进入叶栅的轴向位置不同,使得后掠叶片栅沿叶高压力呈“C”型分布,前掠叶片栅压力沿叶高呈反“C”型分布。叶片沿轴向掠也改变了能量损失系数沿叶高的分布,在相同条件下对比原型叶栅级、后掠叶栅级和前掠叶栅级的总能量损失系数,原型叶栅级的最小,后掠叶栅级次之,而前掠叶栅级最大。更多还原

【Abstract】 The supercritical turboset is being developed to save energe and reduce emission. To improve the relative inner efficiency, depress the coal cost, and reduce the harmful gas discharged into the air, several modern design technologies, such as meridian shrink shroud and bowed, swept and twisted blades, and so on, are applied to modify the on-line running supercritical turboset. In addition the re-design and modification could provide technical reserve for developing Chinese supercretical turboset with independent intellectual property rights.To re-design the introduced supercritical turboset, one has to digest and absorb its design theory and experience in the first place. Thus three representative prototype cascades, including the guide vane of the adjusted stage and the eighth stage (stator and rotor), are selected as the test model in the low speed wind tunnel. Although the test conditions don’t satisfy the requirement of modeling theory, one could analyse the aerodynamic performance of the prototype cascade and confirm its design idea according to the experiment. What’s more, the measured data can be employed to validate the CFD code.The aerodynamic parameters distributions of the three cascades along the blade hight and pitch at different incidences are detailed measured with the five-hole survey probe. And the limited streamline patterns on the endwalls of the cascades are displaced by the ink trace visualization technique. Based on the theretical analysis on the test results, the effects of the blade leading edge shape, load distribution, bowed and swept blade and incidence on the cascades aerodynamic performances are discussed in the following segment.There is an even static pressure distribution along the blade height in the adjusted stage guide vane because of the meridian-shrink shroud. Such pressure distribution could control the radial flow in the boundary layer and decrease the negative influence of the adverse pressure gradient at the suction side exit. The aft-loading characteristic of the vane largely depresses the transverse pressure gradient in the front and at the midst of the passage, and it also decreases the transverse secondary flow at the endwalls and the separation at the suction side corner. The variation of total flow loss is rather small at incidences ranged from -10°to 10°, indicating fine incidence adaptability of the test cascade. For the eighth pressure stage, the aft-loading technique and positive bowed blade profile are employed. Thus the aerodynamic loads on the upper and lower endwalls are remarkably decreased, which leads to reduced local transverse pressure gradient and the lowest flow loss on the endwalls. Due to the positive bowed vane profile, there is“C”type static pressure distributions along blade height on the vane surfaces. Such pressure distributions could decrease corner separation and result in even diffusion of the low energy gas in the corner boundary layer at the suction side into main stream. It is also shown in the test that there is no radial flow in the boundary layer on the blade surface at most of the blade hight.To improve the aerodynamic performance of the supercritical steam turbine and found the design technology with independent intellectual property rights, the modification of the adjusted stage guide vane and the eighth pressure stage are carried out. And the solver is NUMECA, which has been validated by the measured data mentioned above. The effects of bowed, twisted and swept blade on the aerodynamic performance of cascade are investigated by numerical simulations. Then the matching design of the eighth pressure stage with swept blades is carried out to study the performance of the stage with swept blades in the design operation condtions.The numerical results of the modified adjusted stage vane indicate that the positive blade leads to similar flow loss to negative blade dose, and the former one would bring more even distributions of aerodynamic parameters along the radial direction than the latter one. Without preventing abrading measure on the shroud, the positive blade is suggested to be employed. Compared with the results by positive and negative bowed blades, the prototype adjusted vane cascade, with meridian shrink shroud, is with the highest flow efficiency and the most even aerodynamic parameters distributions along the radial directions. Thus the adjusted stage vane with meridian shrink shroud is advised to be ultilized after preventing abrading measure applied to the shroud.The swept techniques, including backward swept one and forward swept one, are applied to the eighth pressure stage. For the backward swept stator and rotor, the fluid flow at radial midst enters into the passage earlier than that near the upper enwall, and greater pressure drop occurs at the passage midst, resulting in the C-type pressure distribution along the radial direction. Such pressure distribution could reduce the low energy fluid at the corner, thus there are slightly decreased and similar flow losses in the stator and rotor, respectively, compared with the prototype stage. For the forward swept stator and rotor, there are opposite effects on pressure distribution and the flow losses. A reverse-C-type pressure distribution occurs along the radial direction, and the low energy fluid flow towards the endwalls, strengthening the corner separation in the corner at the suction side. Therefore the flow loss in the stage is increased.To sum up, the pressure distribution of fluid and the energy loss coefficient could be affected by the swept blades. Since the axial positions of fluid at differet radial position differ from each other, the C-type pressure distribution occurs in the backward swept blade, but the reverse-C-type one in the forward swept blade. In addition, the total energy loss coefficient of the prototype stage is the smallest, but that of the forward swept one is the largest.更多还原