【作者】 孔满昭；

【导师】 刘松龄；

【作者基本信息】 西北工业大学 ， 热能工程， 2005， 硕士

【摘要】 在高性能发动机中,为了有效地保护其热端部件(例如涡轮叶片)并延长其寿命,必须采用先进的冷却技术。在所有提高传热的技术中,冲击冷却对于提高当地的传热系数具有最大的潜力,其冲击所形成的高速气流,极大的改善了当地的换热状况,特别适用于局部高温的地区。本文主要通过实验和数值模拟的方法对在受限通道射流冲击结构的流场特征进行了详细的研究。 两个实验模型为几何参数不一样的矩形通道,在通道的顶部开有3个错位排列的冲击射流孔和一个出流孔,孔的进出口都不带倒角的。用五孔探针对射流孔、通道和出流孔的流场进行详细测量;测量了射流沿通道的沿程压力分布;得到出流孔的流量系数。实验中主要研究了不同的射流孔雷诺数Re(以第一个射流孔的定义的雷诺数)、不同通道高度比(通道高度与射流孔径的比值)、不同的射流孔间距的改变对流场和流量系数的影响规律。同时用FLUENT6.0软件对本实验模型进行了数值模拟,以便更好的了解流场的细节和更好的理解其作用机理。结果表明,实验数据与数值模拟的结果相一致。 在对该射流冲击冷却结构的流动特性进行了系统的研究之后,得出以下主要结论: 1.射流孔的流场结构较为简单,主要受到通道横流的影响稍向流动的方向偏转。由于通道的质量流量相对较弱,横流对射流孔内流场的影响不明显。 2.射流和通道横流的相互作用使得通道的流动结构很复杂;由射流产生的漩涡,将通道气流推向通道的顶端与两侧;在通道中由于射流对横流的阻挡作用,气流绕过射流向下游流动;通道的高速区不仅仅是射流直接冲击的目标靶面,同时在通道两侧和顶部都存在着高速区。 3.出流孔内的流场结构主要由通道的流动特性所决定;由于在出流孔入口的通道末端气流的不均匀性,使得在出流孔内形成了漩涡结构,涡的强度随着通道高度的增加而变得更强;不同的通道高度,漩涡的方向是不一样的;出流孔存在着漩涡结构和低速分离区,使得孔的流量系数较低。西北工业大学硕士学位论文4.通道高度比的改变明显的改变的该冲击模型的流场结构;而雷诺数的改变, 在本实验的范围内对流场结构没有明显的影响。5.数值计算所得到的流场结构与实验测量所得到的结果相一致。关键词冲击冷却,流场特征,漩涡,流量系数,流阻特性,数值模拟。更多还原

【Abstract】 In order to protect the high temperature components (turbine blades for example) and prolong the life of high performance aero-engines advanced cooling technologies must be applied. Among all of the cooling technologies, the impingement cooling is the most potential one to enhance local heat transfer coefficient. The impingement of the jet forms high speed airflows on the cooled surface. These airflows can be used to improve local heat-transfer conditions significantly especially in the area with very high heat flux and temperature. This thesis describes the experimental and numerical researches of the flow characteristics of the impingement cooling in confined passages.The experimental models are two rectangular channels with different geometry parameters. There are three stagger impinging holes and a outlet-hole on the top wall of the channels. Flow fields in the jet holes, passage and exit hole were measured with five hole probes. Pressure distributions along the channel were measured on the side wall and exit of the jet holes. Discharge coefficients of the jet hole and exit hole were obtained. The effects of the variations of Reynolds number (based on the diameter the jet velocity in the most upstream jet hole), height/jet hole diameter ratio, space between the jet holes on the flow fields and discharge coefficients were studied. Numerical simulations were carried out with FLUENT 6.0. It provided the details of the investigated flow fields and better understanding of the mechanisms in the formation of them. The consistency of the experimental data and numerical results are fairly good.The major conclusions drawn from this study are following:1. Flow characteristics of the impingement holes are comparatively simple. The impinging airflow was pushed downstream slightly by the effect of the cross-flow in the passage. The effect of the cross flow was not significant due to mass flow rate in the passage was relatively small.2. The interaction of the jets and with the cross-flow leads to the formation of the complicated flow pattern in the passage. Many vortices induced by the jets are observed. The vortices push the impinging flows moving upward and laterally. Theblockage effect of the jets forces the flow moving around the jets in the passage. High velocity flows not only exist on the target wall but also on the side and top walls of the passage.3. Flow pattern in the exit hole is mainly controlled by the flow pattern in the passage. Vortex is formed in the exit hole due to the non-uniform flow field at its inlet the strength of the vortex is increased with reducing passage height. Variation of the rotating direction dependent on height of the passage is measured. Vortex and large sized separation zones lead to highly non-uniform flow fields in the exit hole and very low values of discharge coefficients.4. Channel height/jet hole diameter ratio plays the most important role in the flow field characteristics but the variation of Reynolds number in the range of present investigation does not create obvious impact on the flow pattern.5. The experimental and numerical results show good consistency about the flow characteristics.更多还原