Turbulent Mixing Losses in the Passages of Centrifugal Impellers

使用与叶轮相同转速旋转的热线风速计，对有盖和无盖离心叶轮流道内的流量进行了测量。测量结果表明，在带冠叶轮内，随着流量的减小，低速区域和耗散区域从叶冠侧向吸力面附近的轮毂侧增大，雷诺法向应力值呈减小趋势。雷诺切应力定性地遵循涡粘性概念。在吸力面附近，流道方向和叶展方向的交叉处，流量对剪应力的影响较大，而其他两个交叉处的影响较小。在无冠叶轮中，t…附近出现低相对速度、高耗散和高雷诺应力由于叶片尖端泄漏和二次流的影响，中间叶片到叶片的区域更靠近机壳侧。随着流量的降低，这一区域在靠近轮毂时变大，并趋向于向吸力方向移动。在流量增大的情况下，吸力侧机壳附近的雷诺应力非常高，因为端部泄漏对那里有显著的影响。在折算流量下，由于套管附近的二次流加强，吸力上的应力也变大。然而，在三种流量下，吸力侧壳体附近的耗散明显较大，流量对耗散最大位置的影响似乎很小。湍流模型为钱学森提出的低雷诺数k-ε模型。对于雷诺平均的N-S方程、湍流能量输运方程和耗散率输运方程，我们采用欧拉显式方法。所有方程均采用Galerkin方法离散。数值计算结果与实验结果定性吻合。较少

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