Junlian Yin

Hydraulic Improvement to Eliminate S-Shaped Curve in Pump Turbine

For pump turbines, an S-shaped curve can lead to failures in synchronization. To improve the hydraulic design, the component that is responsible for the formation of the S-shaped curve was identified by a hydraulic loss analysis using previous computational fluid dynamics (CFD) results, which indicates that the formation of the S-shaped curve can be ascribed to the runner. To improve the hydraulic design of the runner, a simple numerical approach for direct problem analysis was proposed, based on the bladeloading distributions of runners with and without an S-shaped curve, and directly analyzed. It was implied from the differences in the blade-loading distributions that, when the meridional passage was broadened, the formation of the S-shaped curve was suppressed. To validate this, two runners with different meridional sections were designed by means of the inverse design method. Through model tests, it was verified that the S-shaped curve was eliminated completely and the performance curve of the modified hydraulic model satisfied the requirements for safe operation in a pumped storage plant. [DOI: 10.1115/1.4023851]

Effects of water compressibility on the pressure fluctuation prediction in pump turbine

The compressible effect of water is a key factor in transient flows. However, it is always neglected in the unsteady simulations for hydraulic machinery. In light of this, the governing equation of the flow is deduced to combine the compressibility of water, and then simulations with compressible and incompressible considerations to the typical unsteady flow phenomenon (Rotor stator interaction) in a pump turbine model are carried out and compared with each other. The results show that water compressibility has great effects on the magnitude and frequency of pressure fluctuation. As the operating condition concerned, the compressibility of water will induce larger pressure fluctuation, which agrees better with measured data. Moreover, the lower frequency component of the pressure signal can only be captured with the combination of water compressibility. It can be concluded that water compressibility is a fatal factor, which cannot be neglected in the unsteady simulations for pump turbines.

Study on the effect of the impeller and diffuser blade number on reactor coolant pump performances

In this paper, CFD approach was employed to study how the blade number of impeller and diffuser influences reactor coolant pump performances. The three-dimensional pump internal flow channel was modelled by pro/E software, Reynolds-averaged Naiver-Stokes equations with the k-e turbulence model were solved by the computational fluid dynamics software CFX. By post-processing on the numerical results, the performance curves of reactor coolant pump were obtained. The results are as follows, with the blade number of the impeller increasing, the head of the pump with different diffuser universally increases in the 8Q n~1.2Q n conditions, and at different blade number of the diffuser, the head increases with the blade number of the impeller increasing. In 1.0Q n condition, when the blades number combination of impeller and diffuser chooses 4+16, 7+14 and 6+18, the head curves exist singular points. In 1.2Q n condition, the head curve still exists singular point in 6+18. With the blade number of the impeller increasing, the efficiency of the pump with different diffuser universally decreases in the 0.8Q n and 1.0Q n conditions, but in 1.2Q n condition, the efficiency of the pump with different diffuser universally increases. In 1.0Q n condition, the impellers of 4 and 5 blades are better. When the blade number combination of impeller and diffuser choose 4+11, 4+17, 4+18, 5+12, 5+17 and 5+18, the efficiencies relatively have higher values. With the blade number of the impeller increasing, the hydraulic shaft power of the pump with different diffuser universally increases in the 0.8Q n~1.2Q n conditions, and with the blade number of the diffuser increasing, the power of different impeller overall has small fluctuation, but tends to be uniform. This means the increase of the diffuser blade number has less influence on shaft power.The influence on the head and flow by the matching relationship of the blades number between impeller and diffuser is very complicated, which still need further research.This paper provides a reference for exploring the match relationship between the impeller and diffuser blade number of reactor coolant pump.

A Modified k-ε Model for Computation of Flows with Large Streamline Curvature

This paper presents an improved method for inclusion of system rotation and streamline curvature effects into existing two-equation eddy-viscosity turbulence models. A new formulation for calculation of the turbulence viscosity coefficient, which is implemented into the traditional k-ε model with a two-layer near-wall treatment in a commercial computational fluid dynamics solver, is proposed. In contrast to precious model, the modified rotation rate which appears in the formulation for turbulent viscosity coefficient is herein expressed exactly and universally. Thus, it provides an effective alternative for turbulence modeling.

Numerical analysis of single pad of thrust bearing with the energy equation solved by the characteristic-based split method

The solution of the energy equation of thermo-elasto-hydrodynamic analysis for bearings by the finite element method usually leads to convergence difficulties due to the presence of convection terms inherited from the Navier–Stokes equations. In this work, the numerical analysis is performed with finite element method universally by adopting the characteristic-based split method to solve the energy equation. Five case studies of fixed pad thrust bearings have been set up with different geometries, loads, and lubricants. The two-dimensional film pressure is obtained by solving the Reynolds equation with pre-defined axial load on the pad. The energy equation of the lubricant film and the heat transfer equation of the bearing pad are handled by characteristic-based split method and conventional finite element method in three-dimensional space, respectively. Hot oil carry-over effect and variable lubricant viscosity are considered in the simulations. The results of the temperature distributions in the lubricant film and the bearing pad are presented. The possible usability of characteristic-based split method for future thermo-elasto-hydrodynamic analysis is discussed.

Investigation on the Backflow Induced Pre-Rotation of RCP

The pre-rotation phenomenon found at the inlet pipe of a pump under small flow rate was observed but the mechanism was not discovered. To do this, an unsteady CFD simulation with the flow rate decreasing from the best design point to a small flow rate was carried out. The numerical results show that a critical point when pre-rotation occurs exists. The flow pattern evolution on the S1 and S2 stream surface, as well as the pressure distribution at in the inlet, was analyzed. It is shown that it is the reverse flow appeared near the shroud at the leading edge which leads to the occurrence of pre-rotation. The pre-rotation only exist in the periphery of the inlet pipe and the propagation length is limited.Copyright

Numerical Analysis of Rotordynamic Coefficients of Annular Flow in Canned Motor RCP

The operating performance and safety characteristics of canned motor Reactor Coolant Pump (RCP) are vital to the nuclear reactor. The annular flow, which is between the rotor and stator, makes substantial effects on the rotordynamic characteristics of RCP. In this work, the annular flow is simulated by means of 3-dimensional CFD approaches. The annular flow field and the auxiliary impeller are modeled. The results show that the pre-swirl strength at the inlet of the annular flow is evident. Another model without the auxiliary impeller is analyzed under constant pre-swirl ratio with various axial flow rates and whirl speeds. The rotordynamic coefficients of the annular flow are obtained. The results are compared with theoretical predictions. Numerical results show that the fluid in the annular region makes remarkable effects on the rotordynamic characteristics of the canned motor RCP.Copyright

The Use of Experimental Design for the Shrink-Fit Assembly of Multi-Ring Flywheel

The flywheel of latest coolant pump provides high inertia to ensure a slow decrease in coolant flow to prevent fuel damage after the loss of power. Flywheel comprises a hub, twelve tungsten alloy blocks and a retainer ring shrink-fit assembled on the outer surface of blocks. In the structural integrity analysis, the shrinkage load due to shrink-fit and the centrifugal load due to rotation are considered, so the wall thickness of retainer ring and the magnitude of shrink-fit are key variables. In particular, these variables will change the flywheel running state. This paper considers the influence of these variables, we employ Latin hypercube design to obtain the response surface model and analyze the influence of these variables. Finally we obtain the magnitude of wall thickness of retainer ring and the range of shrink-fit.Copyright

A simple inverse design method for pump turbine

In this paper, a simple inverse design method is proposed for pump turbine. The main point of this method is that the blade loading distribution is first extracted from an existing model and then applied in the new design. As an example, the blade loading distribution of the runner designed with head 200m, was analyzed. And then, the combination of the extracted blade loading and a meridional passage suitable for 500m head is applied to design a new runner project. After CFD and model test, it is shown that the new runner performs very well in terms of efficiency and cavitation. Therefore, as an alternative, the inverse design method can be extended to other design applications.