Dezhong Wang

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]

Study on the Air Core Formation of a Gas–Liquid Separator

The gas-liquid separator is a key component in the gas removal system in thorium molten salt reactor (TMSR). In this paper, an experimental study focusing on the gas core formation in the gas-liquid separator was carried out. We observed that formation of the air core depends primarily on the back pressure in the separator. Gas core formation was visualized for a range of back pressures, swirl numbers, and Reynolds numbers. Analysis of flow patterns indicated that gas core formation may be defined as four stages: air core with suction, tadpole-shaped core, cloudy core,and rod core. When rod core is achieved, gas bubbles will be separated completely and that particular back pressure is defined as critical back pressure. The critical back pressure depends on swirl number and Reynolds number. The trends how the critical back pressures vary with the Reynolds number and the swirl number were analyzed.

Numerical approach on the performance prediction of a gas–liquid separator for TMSR

In this paper, the numerical simulation for the gas–liquid flow in a separator applied in the fission gas removal system for thorium molten salt reactor was investigated. The numerical model was established in the frame of Eulerian–Eulerian approach, in which the modeling of the forces acting on the bubbles was introduced. Based on the model, numerical simulations with three flow rates were carried out. Three key parameters (the pressure loss, the separation length, the liquid entrainment ratio) concerned with the separation performance were compared between the numerical results and the experimental data, the results indicate that the calculated results agree well with the experimental data. Hence, the numerical approach shows a promising tool for the performance prediction and the optimization of the gas–liquid separator.

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.