【作者】 刘海涌；

【导师】 刘松龄；

【作者基本信息】 西北工业大学 ， 航空宇航推进理论与工程， 2007， 博士

【摘要】 随着铸造技术的发展，在涡轮叶片内部已经可以铸造出更微小的冷却通道，并且可以在微小通道中使用冲击冷却。冲击冷却有着较高的换热效率，可以大幅提高壁面的局部换热系数，射流冲击还可以在冷气通道内形成强烈的旋涡，从而使整个通道内的换热效果得到进一步的改善。本文以涡轮叶片内部梯形受限冷气通道为对象，综合考虑了射流／旋流／溢流的复合作用，在放大模型上详细研究了通道、出流孔内的流动特性以及靶面、出流侧壁面上的换热特性，并获得了各孔排的流量系数。在实验研究基础上，本文还进行了相应的数值模拟研究，以深入了解该冷却结构的强化换热机理。实验模型分为流动实验模型和换热实验模型两种。实验模型通道截面为梯形，在梯形一侧侧壁上开有两排错排分布的射流孔，气流由射流孔进入通道。另一侧壁上有一排出流孔。在通道底部的靶面上，有3排复合倾斜的气膜孔。同时在通道一侧的端壁上开设有一个直径很大的端头出流孔。换热模型与流动模型的通道截面形状及几何尺寸相同，但通道长度约为流动模型的60％，并且靶面上没有气膜孔。在两个实验模型中，射流角度均包含35°和45°两种情况。在上述模型中，主要研究了射流入射角度、出流比以及射流雷诺数的变化对通道和侧壁出流孔内的流动特性和靶面、出流侧壁面上换热特性的影响规律。其中流动实验模型的雷诺数范围为15000～30000，端头出流比为0.25和0.5；换热实验模型的雷诺数范围为10000～40000，端头出流比范围为0～0.5。经实验和数值模拟，得出以下主要结论：1．梯形通道内形成了很强的旋流流动，小射流对靶面具有较好的冲击作用，而大射流则对通道内的旋流起到了很好的促进作用，大、小射流间存在较强的相互作用；侧壁出流孔内的流动充满度较低，这预示了较低的流量系数；2．通道端头出流在通道内形成的横流对该冷却结构的流动特性及换热特性有着重要影响。在通道下游，横流加速了大射流与通道旋流的融合，削弱了小射流对靶面的冲击作用，提高了通道截面内的流动充满度；对于侧壁出流孔，横流使其入流条件恶化，增加了入口流动损失，使孔内出现回流现象，孔流量系数迅速减少；较强的横流严重削弱了靶面冲击换热核心区的换热能力，在部分工况下甚至使冲击换热核心区消失，而对于出流侧壁面的换热性能，横流的影响相对较小。3．射流入射角度对通道内的流动结构和靶面上的局部Nu数影响较大。较小的射流入射角度容易促进通道内旋流的形成与发展，对提高通道内的流动充满度有积极作用，可以改善侧壁出流孔的入流条件，但会减弱射流对横流作用的抵抗能力；较大的射流入射角度会提高靶面的换热能力，但使出流侧壁面的换热能力略有下降。4．射流雷诺Re的变化对通道和侧壁出流孔内的流动结构没有明显影响，但对靶面和出流侧壁面上的换热特性有着显著影响。Re的增加将大幅提高换热面上的换热能力，但随着Re的不断增加，换热面上换热强度的提高程度将逐渐减小。5．气膜孔出流量和出流位置的改变对通道和侧壁出流孔内的流场影响很小，但会影响到气膜孔流量系数的分布；通道端头出流的增加使侧壁出流孔和射流孔的流量系数减小；射流入射角的变化只对部分孔的流量系数数值略有影响，但不会影响其分布规律。6．在本文研究的冷却结构中，旋流的强化换热能力接近甚至超过了冲击冷却的强化作用；与光滑管流条件下的通道壁面换热相比，本结构中靶面和出流侧壁面上的换热能力是相同通道雷诺数条件下光滑管流换热能力的2～3倍。7．利用数值模拟方法可以对流动和换热问题进行预测，在本文所采用的湍流模型及壁面函数处理方法下，有关流动特性的计算结果与相应实验结果符合的较好；而对于换热特性，计算结果和实验结果在局部区域仍存在一定差异。更多还原

【Abstract】 High turbine inlet temperature in modern gas turbine engines requires propercooling techniques to protect it from overheat. Among all of the heat transferenhancement techniques, jet impingement has the most significant potential toincrease the local heat-transfer coefficient. Recent development in casting technologyhas allowed very intricate internal passage to be manufactured. This has opened upthe possibility of casting small diameter different geometry impingement passage intoturbine blades. The jet air, after impingement, is constrained to flow along the channelformed between the orifice plate and the inner surface of the airfoil envelope, releasesfrom the film cooling holes or enters other chamber. Strong swirl can be induced inthe passage by the jets. It is expected that the cooling effect in such passage would beincreased by an optimize combination of impingement cooling, swirl cooling and filmcooling. In order to gain greater in-sight into the flow structure of confined passage,get detail knowledge of heat transfer characteristic on the passage inner surface,experimental and numerical investigations of aerodynamic aspects and heat transfercharacteristic were carried out in large scaled test models.Two test models with trapezoid cross section were built up in the experiment, onefor flow field measurements and the other for the heat transfer measurements. On oneside of the passage, the air entered in from a row of 40 staggered arrangementimpingement holes. A row of 25 exit holes was opened on the opposite side to theimpingement orifice plate. There were three rows of film cooling holes withcompound angle on the bottom wall of the passage, each row contained 15 holes. Aneven larger outlet hole could be found in one end wall of the passage. The geometryof heat transfer measurements model was same as that of the flow field measurementsone, but the length of the passage was shortened about 40 percent and the film coolingholes were canceled. In both flow field measurements model and heat transfermeasurements models, the impingement angle of 35°and 45°were considered. Therange of Re number for flow field measurements was 15000 to 30000, while theoutflow flux ratio of the outlet hole varied as 0.25 and 0.5. For the heat transfermeasurements model, the range of Re number and the outflow flux ratio of the outlethole were 10000 to 40000 and 0 to 0.5 respectively.Parts of the experimental and numerical results were presented in the thesis. The influences of impingement angle, outflow flux ratio and Re number on both flowfields and heat transfer were detailed investigated. The major conclusions of this studyare shown as following:1. A strong swirl was found in the trapeziform passage. The smaller jets impingedeffectively on the bottom wall, while the larger jets mostly devoted into the swirl.Strong interaction effect existed between the smaller and larger jets.2. Crossflow was formed in the passage by the out flow at the end of the passage.In the downstream region, the jets were deflected by the crossflow, and the intensityof swirl was augmented. The increasing of crossflow intensity leaded to reverse flowin the exit hole, and the Nu numbers on bottom wall were reduced rapidly when thatof the exit side wall affected slightly.3. Smaller impingement angle could increase the swirl intensity and decrease theflow loss of the exit hole, when larger impingement angle increased the resistanceability of the jets on the crossflow effect and enhanced local Nu number on the bottomwall.4. Re number had no obvious effect on the flow structure of the passage and exithole, but played primary role on the Nu number of bottom wall and side wall. Theheat transfer was augmented distinctly with Re number increasing.5. The location and mass flux of film cooling holes had little effect on the flowstructure, but would affect the discharge coefficient of film cooling hole. Thedischarge coefficients of the impingement holes and exit holes decreased with theincreasing of crossflow intensity.6. In the studied cooling configuration, the level of heat transfer enhancement byswirl flow could approach, and even exceed the level of impingement cooling.Compared with the smooth pipe flow, the Nu number were augmented about 200 to300 percent on the bottom wall and side wall.7. The numerical results reveal the details of the flow patterns in the passage. Theconsistency of the numerical simulation and experiments are well in most of themeasured domains. Yet some differences still appear in some zones, which could beameliorated by the improved turbulence model and wall function.更多还原