Turbulent Mixing Losses in the Passages of Centrifugal Impellers

采用与叶轮转速相同的热线风速计，在带冠和不带冠的离心叶轮通道内进行流量测量。测量了接近零入射角时的流速，以及减小和增大流速的另外两种流速。测量结果表明，在带冠叶轮中，随着流量的减小，靠近吸力面的低速和耗散区域从叶冠侧向轮毂侧扩大，雷诺数法向应力值有减小的趋势。雷诺兹剪应力定性地遵循涡流粘度的概念。在吸力面附近，流量对通道方向和叶展方向交叉分量的剪切应力影响显著，而对其他两个交叉分量的影响较小。在无冠叶轮中，由于叶尖泄漏和二次流的双重影响，在叶尖附近出现低相对速度、高耗散和高雷诺数应力的现象。当流量减小时，该区域在靠近轮毂时增大，并趋向于向吸力方向移动。在增大流量时，由于叶尖泄漏对吸力侧机匣附近的影响较大，因此吸力侧机匣附近的雷诺数应力非常高。在减小流量时，由于套管附近的二次流加强，吸力处的应力也变大。然而，对于三种流量，吸力侧机匣附近的耗散非常高；流量对最大耗散位置的影响似乎很小。在此基础上，采用有限元法对离心叶轮流道内的流动进行了数值分析。湍流模型为Chien提出的低雷诺数k-ε模型。我们用欧拉显式方法求解了湍流能量和耗散率的Reynolds平均Navier-Stokes方程和输运方程。所有方程均采用伽辽金方法离散化。数值结果与实验结果定性一致。少

Flow measurements were made within the passages of the shrouded and unshrouded centrifugal impellers, by using a hot-wire anemometer rotated with the same speed as that of the impeller. The measurements were made for a flow rate corresponding to nearly zero incidence angle and two other flows with reduced and increased flow rates.In the shrouded impeller, the measurements show that, as the flow rate is reduced, the regions of a low velocity and a dissipation enlarge from the shroud-side to the hub-side near the suction surface and the values of Reynolds normal stresses tend to decrease. The Reynolds shear stresses qualitatively follow the eddy viscosity concept. Near the suction surface, the effects of the flow rate on the shear stresses are remarkable in the cross-component between the passagewise and blade-spanwise directions, but are little in two other cross-components.In the unshrouded impeller, a low relative velocity, a high dissipation and a high Reynolds stress appear around t … More he region of the middle blade-to-blade to the casing side due to both influences of a blade tip leakage and a secondary flow. As the flow rate is reduced, this region enlarges by nearing the hub and also tends to move toward the suction.In the increased flow rate, the Reynolds stress is remarkably high near the casing of the suction side since the tip leakage noticeably influences there. In the reduced flow rate, the stress becomes high also on the suction because of the secondary flow strengthened near the casing. For three flow rates, however, the dissipation is remarkably high near the casing of the suction side ; the influence of the flow rate on the position with the highest dissipation seems to be little.Moreover, the numerical flow analys is made in the passage of the centrifugal impeller using FEM with/without the turbulence model. The turbulence model is low Reynolds k-ε model proposed by Chien. We use the Euler explicit method for the Reynolds averaged Navier-Stokes equations and the transport equations of the turbulent energy and the dissipation rate. All equations are discretized by the Galerkin method. The numerical results qualitatively correspond with those obtained from the experiment. Less