【作者】 李亮；

【导师】 王灿星；

【作者基本信息】 浙江大学 ， 流体力学， 2012， 硕士

【摘要】 旋转湍流场是工程领域中最为复杂的流场之一,它广泛的存在于各类流体机械中,如泵、风机、压缩机、水轮机等。由于旋转效应的存在,使得流场的结构发生了很大的变化。旋转湍流场的早期研究主要用实验的方法,随着计算流体力学(CFD)的发展,湍流流动数值模拟方法被大量采用。在常见的RANS方法中,基于Boussinesq线性涡粘性假设的两方程湍流模型在工程计算中应用很广泛,但是它在旋转系统的湍流模拟中存在两个明显的缺陷,即各向同性假设和模型坐标不变性。前者是基于Boussinesq假设的结果；后者则是由于对应变率张量的唯一依赖性。这些缺陷导致诸多后果,如不能准确预测管道中的二次流动(各向同性涡粘性系数)以及不能对旋转之类的非惯性效应做出正确反应(坐标无关性)。考虑到上述因素,本文基于Wallin&Johansson的显示代数雷诺应力湍流模型,通过引入扩展内禀平均旋转张量,建立了适合于旋转流动的非线性涡粘性模型。并通过对一旋转槽道流动进行数值计算来验证模型的可行性。模拟结果与实验的对比表明,该模型能够更精确地反映流动各向异性的特征,并分析了旋转对主流流动和湍流结构的影响。本文将所建立的非线性涡粘性模型应用于一多翼离心风机的流场计算中,基于数值模拟结果的性能预测和实验结果吻合良好,证实了所采用的计算模型和数值方法的可行性。通过对不同设计工况下叶轮流道内速度场和压力场的详细研究,本文发现在叶轮前盘附近区域,由于逆压梯度的作用和气流从轴向急剧转为径向,叶轮流道中存在二次涡流,并且低能量流体聚集在叶轮前盘附近；在蜗壳流道中,流体呈螺旋线运动形式向前推进；气流在靠近叶片前缘吸力面上产生边界层分离,在后缘上又重新附着在叶片表面上,形成闭式分离,并且前盘附近的分离流动现象比中间截面和后盘附近要明显得多；在小流量情况下,叶轮流道间更容易发生分离流动；另外,本文还对叶轮流道的流线进行了分析,详细揭示了叶轮流道中分离流动的变化过程。更多还原

【Abstract】 The rotating turbulent flow is one of the most complex in the engineering, which is widely used in the fluid machinery such as pump, fan, compressor and hydro-turbine. Because of the effects of rotating, the structure of the flow field has been changed. In the early, experiment method is commonly used to research the rotating turbulent flow, the numerical simulation is widely used with the development of computational fluid mechanics(CFD). Among common RANS method, two-equation turbulent models based on the Boussinesq’s hypothesis of linear eddy viscosity are widely used in the engineering, however, when used to simulate rotating turbulent flow there is two demands, that is the hypothesis of isotropy and coordinate indifference, the former is the result of Boussinesq’s hypothesis while the latter is the result of the strain rate tensor unique dependence, they causes some negative consequences, such as can’t accurately predict the second flow and represent the rotary effect in the non-inertial system.Based on the three-dimensional RANS and explicit algebraic stress models (EASM), a new method, which the extended intrinsic mean spin tensor is instead of the intrinsic mean spin tensor, is developed to simulate the turbulent flow in the span-wise rotating duct. The comparison of the simulating results with the experiment shows that the method is more suitable to solve the anisotropy flow, then the influence of rotation on mean flow and turbulent structures are analyzed.The method is also applied to simulate the internal flow of multi-blade centrifugal fan. The predicting aerodynamic performance is well accord with the experiment, it shows again that the computational model and method is reliable. The analysis of the velocity and pressure distribution in different working condition shows that the lower energy fluid is accumulated in the front plane and some second vortex appears in the impeller passage under the action of the adverse pressure gradient and the fluid turning from the axial direction to the radial direction. There is separated flow in the suction side near the leading edge of impeller, and the flow attaches near the trailing edge of impeller, which forms the closed separated flow. The phenomenon of the separated flow in the shroud is more severe than the middle plane and the hub. It is easier to generate separated flow in the impeller passage at lower flow rate. Besides. the streamline in the impeller passage is also analyzed and some flow mechanism of the separated flow in the passage is revealed.更多还原