【作者】 牛茂升；

【导师】 臧述升；

【作者基本信息】 上海交通大学 ， 动力机械及工程， 2010， 博士

【摘要】 燃气轮机作为能量转换和动力传递的装置,被广泛应用于国民经济中的各个领域,属能源与动力行业的关键设备,也是航空动力工程中的核心组成部件。为了进一步改善燃气轮机性能,一个很重要的方面就是必须对其内部复杂三维流动有足够的认识,以降低流动损失、提高燃气轮机整体效率水平。而动叶叶顶间隙流动是导致流道内流动损失增大、换热条件恶化、涡轮整体效率降低的重要因素之一。但由于受测量技术的限制,目前对动叶叶顶间隙流动的研究尚存在较多亟需深入研究的内容。本文利用亚音速平面叶栅试验台模拟了叶顶间隙流动,并对平面叶栅出口截面上总压、气流角以及出口速度分布进行了试验测量。同时,通过在叶片表面设置的静压孔,测量了叶片中部以及靠近叶顶截面的叶表静压分布。结合三维数值计算的方法,揭示了间隙内部流场分布、间隙进出口速度、间隙流量等试验难以测量的物理量和流动细节。本文首先深入研究了间隙高度、叶片与外壳相对转动速度以及叶栅进口冲角对间隙流动的影响情况,对间隙流动的形成机理进行了深入地分析。研究发现,间隙高度增加时,通过间隙的流量增大,间隙涡尺寸及强度都随之大幅增加,叶栅通道内气流过偏/偏转不足现象加剧,间隙流动引起的损失也基本呈线性增大;而叶片与外壳之间的相对转动会抑制并使得间隙入口速度减小,减弱通过间隙的流量,从而降低间隙流动损失;叶栅进口冲角改变时,间隙流动损失也随之变化。可以看出,在负冲角i=-8.5o时,间隙流动引起的损失减小,而在正冲角时,间隙流动损失迅速增大。在此基础上,本文对采用叶顶喷气的主动控制方法来削弱间隙流动对涡轮性能的影响进行了研究。由外部空气压缩机提供叶顶喷气所需的空气,这部分气体通过叶片空腔然后从叶顶布置的成排小孔喷出。喷气孔与叶顶表面存在一个夹角,其方向是使得喷出气体能阻碍流体进入间隙,从而降低间隙流量,削弱间隙流动。叶栅出口截面上总压测量结果表明,叶顶喷气确实能够阻碍间隙流动的形成,减小间隙流量,降低间隙流动损失,间隙流量最大下降幅度达78.25%,间隙流动损失最大可减少约21.59%。本文通过研究不同喷气参数变化对喷气效果的影响,对叶顶喷气方案的控制机理有了较为深入的理解,得出了各个参数对间隙流动控制效果的影响规律,并得到了试验条件下的最优喷气方案。文中所研究的喷气参数主要包括喷气孔在叶片厚度/弦长方向上的分布、叶顶喷气切向/流向角度等。试验结果表明,对于喷气孔在叶片厚度方向上的分布,当喷气孔布置在靠近叶片压力边位置时,能获得最佳的控制效果,间隙涡几乎消失并与叶栅尾迹融合在一起;而对于喷气孔在叶片弦长方向上的分布,前缘附近喷气孔对间隙流动的控制作用相对较小,而叶片中后部弦长位置布置喷气孔能较好的控制间隙流量、降低间隙流动损失;不同切向喷气角度对间隙流动的影响也不尽相同,当喷气孔垂直于叶顶表面时,虽然在一定程度上减弱了间隙涡,但由于上通道涡区损失增大,使得出口截面上总损失反而增大。而采用45o及60o切向喷气角度时效果相差不大,但考虑到实际加工情况,切向喷气角度可以优先考虑60o;对于喷气孔在流向方向上的角度分布,当喷气孔垂直于叶顶压力边时由于正好与间隙流动方向相反,因此能更好的抑制间隙流动,获得更佳的喷气效果。因此综合考虑叶顶喷气各个参数变化对间隙流动的影响,可以得出本文试验条件下的最佳喷气方案为:喷气孔靠近压力边喷气、喷气量为1.11%主流流量、喷气孔垂直于叶顶压力边、喷气孔分在18~72%弦长范围内、采用60o切向喷气角度。本文还通过改变叶栅进口冲角,对叶顶喷气在非设计进口条件下对间隙流动的控制效果进行了研究。试验结果可以发现,即使在较大的正/负冲角工况下,叶顶喷气仍能较好的减小通过间隙的流量、削弱间隙涡尺寸及强度,从而降低间隙流动损失。因此,上述研究结果表明叶顶喷气方案具有良好的实用性,是较好的控制间隙流动损失的措施之一。最后,采用目前常见的几个间隙流动损失模型预测了各个不同喷气工况下的间隙流动损失,其结果表明这些模型由于没有考虑叶顶喷气对间隙流动的影响,预测值与试验测量值相差较大。而Hamik & Willinger模型在Yaras & Sjolander模型的基础上,考虑了叶顶喷气对间隙流动的影响,因此采用该模型得到的间隙流动损失值与试验值吻合较好,即使在不同进口冲角工况下,Hamik & Willinger模型仍能较好的预测出此时的间隙流动损失大小。更多还原

【Abstract】 Transformation of the energy potential of fuels into useful forms of energy has been an important aspect of civilization ever since the Industrial Revolution. The invention of the gas turbine provided great impetus to the Industrial Revolution. This machine converts chemical energy of natural gas into kinetic energy. In addition to propulsion of large and medium aircrafts, gas turbine engines are also used extensively in electrical power generation and in marine applications. Thus improving the performance of the gas turbine engine has great economic and environmental value.The energy transfer in gas turbine is achieved by a change in the angular momentum of the working fluid in a rotating blade row. The flow field of a turbine blade row contains loss regions due to the creation of secondary flow within the main flow. As these regions convect into the following blade row complex interaction mechanisms occur between the loss regions of both blade rows.In order to reduce losses and improve performance of gas turbine, it is needed to understand in detail the complicated three-dimensional flow structures within the passage. However, due to the restrict of measurement technique, it is difficult to realize, especially the tip clearance flow.Tip clearance flow is created by the fluid that passes through the radial gap between the tips of the rotor blades and the stationary rotor casing. About one third of the losses of a high-pressure stage can be due to the tip clearance flow, which deteriorates the aerodynamic and thermal performance of the axial flow turbine.In this paper, detailed flow field measurements were made downstream of the cascade using a three-hole probe. Static pressure distributions were also measured on the blade surface at 50% and 97.5% span, respectively. Besides that, numerical investigations were also conducted to study phenomena which are not easily measured in the experiments, for example, tip clearance mass flow rate, detailed flow structure inside the tiny tip clearance, distributions of velocity at entrance / exit of tip clearance and so on.First of all, we investigated three of the most important factors that affected tip clearance flow, i. e., tip clearance height, endwall relative motion and incidence angle. The results indicated that losses associated with tip clearance flow rise with increases in tip clearance height, which were showed to be linearly proportional, as well as both the size and the strength of the tip clearance vortex; The relative motion between casing wall and blade rows obstrcuted tip clearance flow in axial turbines, with remarkable reduction in tip clearance mass flow; In addition, incidence angle at the cascade inlet also influenced significantly the flow structures of the tip clearance flow. At negative incidences, tip clearance loss decreases, while it increases with positive incidences.Then a novel method was investigated that aimed to reduce the rotor tip clearance flow and hence the losses associated to the interaction of the tip clearance vortex with the main passage flow. Cooling air was injected through an array of holes on the blade tip surface that were inclined in circumferential direction, such that the injected fluid could counteract the motion of the tip clearance flow. From the measurement results at the cascade exit, it could be found that tip injection could really weaken the interaction of the tip clearance flow and the main passage flow, reducing the tip clearance mass flow and its associated losses.In order to adequately understand the physics of tip injection, we investigated experimentally and numerically the influences of injection mass flow rate, chordwise/width location of injection holes and injection circumferential/streamwise angle on the tip clearance flow. It could be concluded that effects of tip injection increased with a larger injection mass flow rate. Injection location in the blade width direction played an important role in the redistribution of secondary flow within the cascade passage. With the same amout of injection holes and injection mass flow, injection located much closer to the pressure-side corner performed better in reducing tip clearance massflow and its associated losses; Considering the chordwise distribution of injection holes, holes located in the aft part of blade could obtain better performance than that in the front part when the same amount of injection holes was applied; With holes disposed to be perpendicular to the pressure side of blade, injection at a smaller circumferential angle performed better in reducing tip clearance flow.Besides that, we also analyzed the influences of tip injection on tip clearance flow at off-design conditions, to verify the effectiveness of tip injection when the approaching flow was at off-design incidences. The results indicated that even at these off-design incidences, tip injection could also act as an obstruction to the tip clearance flow and weaken the interaction between the passage flow and the tip clearance flow. It could be also found that tip injection caused the tip clearance loss to be less sensitive to the incidences. Thus, tip injection was proved to be an effective method of controlling tip clearance flow, even at off-design conditions.At the end, we predicted the losses associated with the tip clearance flow with several empirical tip clearance loss correlations. All these correlations showed great discrepancy with experiemental data. However, a modified loss model proposed by Hamik & Willinger agreed better, which was based on the loss model of Yaras & Sjolander and takes the effects of the tip injection into consideration, even at off-design conditions.更多还原