Turbulent Mixing Losses in the Passages of Centrifugal Impellers

用热线风速仪以与叶轮相同的转速旋转，对带罩和不带罩的离心叶轮通道内的流量进行了测量。测量结果表明，在带冠叶轮中，随着流量的减小，吸力面附近的低速区和耗散区从叶侧向轮毂侧扩大，雷诺法向应力值趋于减小。雷诺剪应力定性地遵循涡动粘性概念。在吸力面附近，流量对叶展方向和叶向之间的切应力影响显著，而对叶展方向和叶向之间的切应力影响不大;在无冠叶轮中，在叶展方向附近出现低的相对速度、高的耗散和高的雷诺应力，而在叶展方向附近出现低的相对速度、高的耗散和高的雷诺应力。 关于我们 由于叶尖泄漏和二次流的影响，中间叶片到叶片的区域向机匣侧移动。当流量减小时，该区域在靠近轮毂处扩大，并趋向于向吸力侧移动。在流量增大时，由于叶尖泄漏的显著影响，靠近吸力侧机匣处的雷诺应力非常高。在降低的流量下，吸力面上的应力也变得很高，因为二次流在壳体附近得到加强。在三种流量下，吸力面的机匣附近的耗散都很大，而流量对耗散最大位置的影响不大。此外，本文还对离心叶轮流道进行了有无湍流模型的有限元数值分析。湍流模型采用Chien提出的低雷诺数k-ε模型。采用Euler显式方法求解雷诺平均Navier-Stokes方程、湍流能量输运方程和耗散率输运方程。所有方程均采用Galerkin法离散。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