【作者】 田勇；

【导师】 张士杰； 季路成； 肖云汉；

【作者基本信息】 中国科学院研究生院（工程热物理研究所） ， 工程热物理， 2014， 博士

【摘要】 燃气轮机中的透平叶片为了应对高温带来的叶片烧蚀风险,除了采用高温合金叶片和隔热涂层抗拒部分温升外,还必须依靠冷却技术。冷却技术的引入促使叶轮机三维粘性流动形成更复杂的流热环境。当前,对冷却透平流热环境的预测与管控已成为透平设计能力提升的重要基础。然而,面对叶片高度复杂的冷却结构导致的复杂流动与换热,全三维的精细模拟难以满足快速预测的工程需求,更难以预测变工况下引气脉动带来的非定常冷却问题。同时,作为透平流热环境组织的最关键部位之一,叶片与端壁交汇区域的流动传热出现了以叶身融合为代表的先进管控技术,但是还存在局部机理研究不足和对透平级环境和热环境下的效果与机理研究不足的问题。针对这两方面问题,本文开展了系列数值与理论研究,具体内容和结果如下：1.针对冷却透平叶片内部开展了基于流体网络法的快速模拟方法研究。发展了能考虑非定常计算、变截面元件、非理想气体工质以及压力边界、流量边界、温度边界和热流密度边界等多种边界条件的流体网络法。方法通过虚拟进出口的及时切换能实现边界流动倒灌的模拟。建立起气膜孔、冲击孔、扰流肋、扰流柱、弯曲通道以及尾缘劈缝等多种冷却结构的流体网络元件模型,使得流体网络法能应用到透平叶片冷气流动与传热的计算中。基于此方法编写计算机程序并通过算例校核初步证明了方法的可行性、快捷性和稳定性。2.研究了叶片内部流体网络与外部三维流动的耦合计算方法。通过内部冷却流体网络的计算结果给定叶片外部冷却的源项强度,通过叶片外部流场的计算结果提供叶片内部流体网络的部分边界条件,两个过程反复迭代,实现了叶片内外流场的快速耦合模拟。基于此方法编写计算机程序并以某全气膜冷却透平静叶的绝热壁模型为例开展数值研究。首先通过定常冷却计算初步证明了方法的可行性与快捷性。然后开展脉动冷气进气条件下的透平流热环境数值研究。结果发现,冷气腔进口流量的脉动会引起气膜孔下游壁温的显著变化,会在不改变冷气量周期平均值的情况下降低冷却有效度的周期平均值,脉动幅度较大时降低尤其明显；同腔各孔随时间的脉动幅度并不一定等于冷气腔进气的脉动幅度,低流量孔的脉动幅度可能更大,因而更容易出现负流量即倒灌；冷气腔进口流量脉动周期增大(即脉动速度减小)时,壁温的脉动幅度会降低,因为脉动有足够的时间传播得更远,分布更均匀；上游流量较小的气膜孔的脉动在经历下游大流量气膜孔后会因强烈掺混而迅速衰减趋于不可见,因此对大流量气膜孔下游的壁温影响非常微弱。相关结果为透平冷却裕度设计提供了参考。3.开展了叶片前缘与端壁交汇区流热环境的叶身融合管控机理研究。以某平板上孤立叶片模型为例,通过叶片／端壁融合技术设计了不同尺寸的融合面并开展数值研究。结果发现：前缘融合面通过有效削弱或消除马蹄涡实现了前缘交汇区流热环境的有效管控,一方面,马蹄涡的削弱能减小了前缘交汇区的流动分离从而改善流场的均匀性,另一方面,马蹄涡的削弱能减少自由流高温流体流入近壁从而降低壁面温度,能减小角区近壁流速从而降低壁面换热系数。前缘融合面削弱马蹄涡的具体机制是：通过展向型面间的位移生成展向压力梯度来削弱或抵消来流附面层减速引起的展向压力梯度。通过数值计算获得了融合面的尺寸设计准则：在保证融合面的展向高度足够高(大于附面层厚度)的情况下尽可能增加流向长度(至少要接近或超过展高)。最后通过理论推导发现消除马蹄涡的最佳融合面形状(中心平面内)是与来流边界层速度剖面形状一致的,其机制是,型面平移导致势流场在同一流向位置的不同展高处形成刚好与来流边界层相同的速度分布,此时的展向负压力梯度刚好可抵消来流边界层在减速过程中形成的展向压力梯度。4.开展了叶片与端壁整个交汇区(角区)流热环境的叶身融合管控机理研究。以某透平级为例,通过叶身融合技术设计了不同的融合模型,计算结果发现融合面对透平级流热环境产生了有效的管控作用。具体表现为：叶身融合技术通过端壁下沉技术准确补偿了由于融合面的引入带来的通流面积损失；侧面融合面削弱了静叶吸力面角区的分离；前缘融合面削弱了马蹄涡,抑制了前缘角区的分离；静叶的融合面降低了尾迹高度,使得动叶进口总温边界层高度也降低,在通道涡的作用下底层高总温的流体往吸力面轮毂角区堆积,而中展较低总温的流体则暴露到轮毂上,进而明显降低了轮毂绝热壁温。更多还原

【Abstract】 Gas turbine blades must be cooled to prevent ablation immersed in high temperature, in addition to using super alloy and TBC(thermal barrier coating). The introduction of cooling, with the3D viscous flow field of the mainstream, leads to a much more complex aero-thermal environment. Currently, the prediction and management of the aero-thermal environment of the cooled turbine is important basis of improving design capability for cooled turbine. However, for the complex flow and heat transfer caused by the highly complex cooling configuration, full3D fine simulation is unlikely to fulfill fast prediction for engineering requirement, let alone predicting the unsteady cooling caused by pulsed bleeding air under off-design conditions; on the other hand, advanced management technology such as Blended Blade/EndWall(BBEW) was proposed for flow and heat transfer in the junction of blade and endwall which is the most important part of aero-thermal organization, but the mechanism research is not enough, and the effectiveness and mechanism in turbine stage environment and thermal environment is unclear. For these two aspects, this paper carries out numerical and theoretical research, with contents and results as follows:1. Study engineering simulation based on flow network method of internal cooling of cooled turbine. Develop the flow network method which take into account unsteadiness, variable cross-section, non-ideal gas and various kinds of boundary conditions such as pressure boundary, massflow boundary, temperature boundary and heat flux boundary. Real-time switch of virtual inlet&outlet is used to simulate backward flow of gas at the boundary. To apply the flow network method to calculation of flow and heat transfer of cooled turbine, build flow network branch models of various kinds of cooling configuration, such as film holes, impingement holes, turbulent ribs, turbulent pin-fins, bend passages, trailing edge slots and so on. A computer program is developed based on this method and checked by an example, which indicate the feasibility, quickness and stability of the method.2. Study the coupling of the internal flow network and blade external3D flow. Calculation result of internal flow network provides the source intensity of external cooling, calculation result of blade external flow provides some boundary condition of internal flow network, and by iteration of these two processes the fast method of coupling simulation of blade internal/external flow is founded. A computer programs is developed based on the method and the adiabatic wall model of a full-film cooling turbine vane is taken as example for numerical simulation. First, a calculation of steady cooling is carried out, which improves the feasibility and quickness of the method. Then begin to simulate turbine aero-thermal environment under pulsed inlet coolant. The results indicate that pulse of inlet coolant massflow will lead to a significant change of blade wall temperature downstream and reduction of period-average cooling effectiveness with the same period-average coolant massflow; the pulsing amplitude of each hole with the same cooling chamber are not all equal to that of the inlet of the cooling chamber, and those holes with lower massflow often have larger pulsing amplitude, which leads to higher tendency of negative massflow, i.e. backflow; longer pulsing period,.i.e. slower pulse, leads to smaller pulsing amplitude, for the pulse can be transported far more away and more uniform; pulse from film holes with less massflow will submerge after mixing downstream with flow from film holes with less massflow, and so it It has negligible impact on wall temperature of bladewall downstream. Results above provide references for design of turbine cooling margin.3. Study the management mechanism of the aero-thermal environment by blade/endwall blending in the junction of the leading edge of the blade and endwall. Take a wing-on-plate model as example for the research in which blending surfaces with different sizes are added to the junction, under the guidance of the Blended Blade/EndWall technology(BBEW). The results shows:leading edge blending surface succeeds in managing the aero-thermal environment in the junction of the leading edge of the blade and endwall by weakening or eliminating the horseshoe vortices(HSV), on the one hand, weakened HSV can reduce the flow separation at the leading edge junction and get more uniform flowfield, on the other hand, weakened HSV can reduce fluid in mainstream with high temperature running to the platewall which reduce the wall temperature, and can reduce the velocity near the junction which reduce the heat transfer coefficient. The mechanism of weakening HSV by leading edge blending surface goes like this:the leading edge blending surface weakens the pressure gradient from the stagnated boundary layer by negative pressure gradient generated by shift forward of blade section near the plate. The design rules of leading edge blending surface are obtained by series of numerical simulation as below: increase the streamwise length while keeping the blending surface high enough(higher then the boundary layer). At last, a theoretical derivation finds that he best shape of the blending surface in the centplane for eliminating the HSV is the same as the profile of the coming boundary layer, that the mechanism can be explained like this: the forward shift blade sections near the plate causes the same velocity profile as that of the boundary layer.4. Study the management mechanism of the aero-thermal environment by blade/endwall blending in the whole junction of the blade and endwall. Take a turbine stage as example, based on which various kinds of blending models are designed by the guidance of Blending Blade/EndWall technology(BBEW). The simulation results show that BBEW makes effective managing on the aero-thermal environment of the turbine, with details as such:BBEW compensates through-flow loss caused by introduction of the blending surface with a slight sink of the endwall. The side blending surface weakens the flow separation in the suction corner of the vane; the leading edge blending surface weakens the HSV and the flow separation at the leading edge corner; the blending surface of the vane reduce the height of the wake, which reduce the height of the boundary layer of total temperature at the inlet of the blade. Then the passage vortex moves the fluid with high total temperature at the bottom to the suction corner, while the fluid with lower total temperature expose itself to the hub wall, which reduce the adiabatic wall temperature of the hub evidently.更多还原