长通道错排射流冲击流动特性研究

【作者】 刘海涌；

【导师】 刘松龄；

【作者基本信息】 西北工业大学 ， 工程热物理， 2005， 硕士

【摘要】 错排射流冲击冷却是涡轮叶片内部的一种应用较广泛的冷却方案,它采用铸造技术将传统冷却方式应用至叶片厚度范围内,使多排冲击冷却、出流抽吸效应以及受限通道结构相综合,形成一种高效冷却方式。为了详细了解改冷却结构的强化换热机理,更有效的对其进行工程实际应用,本文采用实验研究和数值模拟相结合的方法对其流动特性进行了细致、系统的研究。 实验中,应用相似理论,在保证工况雷诺数相同的条件下将实物进行了一定比例的放大,以便更准确的对该冷却结构中通道和孔内的流场结构进行测量。实验模型为一侧错排开设有12个射流孔、居中开设一较大出流孔的矩形通道,出流孔直径为射流孔直径的4倍。通道高度可变,分别为1倍、3倍和5倍射流孔径。射流孔及出流孔均尖锐无倒角。在此几何模型下,主要研究了雷诺数Re以及通道高径比Z_r,的改变对通道、射流孔、出流孔内流场结构的影响规律,通道内流量和压力特性以及流量系数的变化规律。 在上述实验工作的基础上,本文选取了部分典型实验工况,采用实验和数值模拟相结合的方法对其进行研究,以更深入地揭示射流孔排、出流孔以及通道之间的相互作用机理。结果显示:数值模拟所得到的流动特征,如孔内、通道内的流动分布规律,都与实验数据比较一致,这表明了测量数据的准确性以及所用数值模拟方法的可靠性。 在对该错排射流受限通道结构内的流动特性进行了系统的研究之后,得出以下主要结论: 1.沿通道主流方向,通道截面内流动逐渐变得较为相似:通道内上游流场主要表现为射流间的相互作用,而在下游因射流的不断加入而形成较强的横流,射流与横流问的相互作用增强,射流受横流的推移作用在通道内发生偏移,而横流则受射流排挤在射流两侧呈绕流流动;通道内流动特性主要受通道高度比Z_r影响,随Z_r的增加流动趋于复杂,高速区分布发生明显变化,而雷诺数Re基本没有影响。 2.高度比Z_r较小(Z_r=1)时,因错排射流、端壁阻挡和逆压梯度而使通道形成的逆时针漩涡进而向孔内发展,孔内低速分离区较大,且局部区域存在回流,沿孔高度方向孔内流动难以充分发展;随着Z_r的增大,通道内形成两个角涡,发展至孔内形成孔上、下侧的两个较小漩涡,低速分离区减小,倒流区消失,孔内气流充填程度更为饱满,流动分布趋于均匀且流动可较快充分发展,高速区分布出现较大差异;雷诺数Re的变化对孔内流场的影响较小,对孔内流动充分发展程度也没有影响。西北工业大学硕士学位论文 3.沿孔内流动方向,射流孔内呈先收缩后扩张的流动形态,射流的错排布置及通道内横流对射流孔出口截面流场有直接影响;在同一高度比z,下,射流孔内流速沿通道主流方向呈增加趋势,随通道高度比z,的增加,射流间流速差别减小沿流向趋于均匀;雷诺数Re的变化对射流孔内流场的基本没有影响。 4.在小通道高度比(z,二l)时,流量及压力特性曲线和流量系数在下游位置表现出明显的加速变化趋势,随通道高度比的增加,流量特性曲线逐渐转变为近线性分布,对流量系数的影响作用减弱,雷诺数Re变化对各参数变化规律影响较小,较大雷诺数时影响程度略有提高。 5.数值模拟结果更为详细的揭示了流场结构特征,与实验测量结果符合较好,但在部分流域仍存在一定差别,说明对大范围的复杂流动的模拟计算不适宜采用单一模型,需根据不同流动部位的流动特点对计算模型进行适当调整。关键词:错排射流,冲击冷却,涡轮叶片,流场,流量系数,流阻特性,横流 数值模拟更多还原

【Abstract】 Staggered arrangement impingement cooling has been used widely in turbine machine, with individual or connected cavities cast into the modern turbine blade wall, and employs an optimize combination of impingement cooling performance, suction effects and confined passages. The detailed knowledge of the heat transfer enhancement in this configuration is required for the optimization of the cooling design. This thesis describes the experimental and numerical researches of the flow characteristics inside the staggered arrangement impingement cooling system, and numerical analysis is compared and validated with the experimental results.Experiments were conducted with large-scaled models made of Plexiglas. Twelve staggered impingement holes and a larger outlet hole on the center line in one side of the confined channel was chosen to represent part of the typical impingement cooling system. The diameter of the outlet hole is 4 times of that of the impingement hole when the orifice-to-target-wall spacing altered as 1 3 and 5 times. While flow parameters— Re and spacing Z, change, the flow fields in the cooling passage and holes will vary accordingly. The influence of altering Re and Z_r to the flow characteristics, parameters and coefficient were detailed investigated.Parts of the experimental and numerical results were presented in the thesis, which are helpful to understand intrinsic mechanisms of the heat transfer enhancement in the confined channel with staggered jet arrangement. The experimental and numerical results show consistency about the flow structures, which testify the accuracy of the experiment and the credibility of the numerical method. The major conclusions of this study are following:1. In the upstream region of the channel, jets impinge on the target wall and are affected by neighboring jets. The cross-flow formed by upstream jets grows stronger increasingly in the channel along the main flow direction. In the downstream region, it attends to deflect the jets away from theirs impinging location and leads to the similarity of flow characteristics, when it is also forced to pass round the jet. The spacing-to-diameter ratio( Z_r) of the channel plays a dominant role to the flow characteristics in the channel, when the Reynolds number shows little influence.2. A strong counter clockwise vortex forms at the end of the channel and develops into the outlet hole at the smallest value of Z_r = 1, which is caused by staggered jets arrangement, obstacle of the end wall and reverse pressure gradient. It leads to serious flow separation and local reverse flow, and prevent full developmentof the flow in the outlet hole. The counter clockwise vortex is replace by two nearly symmetric corner vortices as the spacing ratio Z_r increased to 3 and 5. Separation region decreases and reverse flow vanishes in the outlet hole, and the flow distribution becomes more uniform and fully developed. The Reynolds number has little influence to the flow characteristics and no contribution to the flow development in outlet hole.3. In the impingement holes, flows were contracted at inlet and then expanded out. The staggered arrangement of jet holes and cross-flow in the channel have important influences on the flow of impingement holes outlet. In the condition of same spacing-to-diameter ratio, the jet velocities were increased and static pressures were decreased continuously along the channel, but the variations were reduced at high Z_r.4. Mass flow flux ratio, static pressure coefficients and discharge coefficients of impingement holes changed more rapidly in the downstream region of the channel as Z_r = 1. Mass flow flux ratio variation turn to be linear and has less effect on the changing of discharge coefficient. No obvious influence of Reynolds number was a little obvious at high Reynolds number on these parameters were observed, it became slightly larger at high Reynolds number.5. The numerical results reveal the details of the flow patterns and provide good knowledge of the jet impingements in confined passage. The consis更多还原