In 29th IAHR symposium in Kyoto 2018, Mr. Coulson gave a lecture entitled "Changes in Hydro Turbine Design - The Last 40 Years, and into The Future -" Recent runner design trends were overviewed. Future turbine techniques were also introduced.
An important flow mechanism that affects the performance and efficiency of centrifugal pumps is cavitation. In recent years, many researchers have studied the physics of cavitation in order to create appropriate detection methodologies. The aim of this paper is to review the various experimental tools that have been developed so far and enlighten the area of future research on the field of cavitation monitoring. According to the results, cavitation detection is possible, but a large number of sensors have to be used and permanent changes in the machine need to be made for increasing the results reliability. Therefore, future research steps are proposed towards the development of reliable, accurate but also easy to install and low cost experimental set ups.
To study the transient valve motions and flow pulsation of novel five-cylinder double-acting reciprocating pump, the theoretical analysis and computational fluid dynamics (CFD) method are employed to investigate the full-cycle working process of the pump. The theoretical models describing the motions and flow rates of hydraulic end are established for reciprocating pump under the actions of piston and valves. The open-close behavior of suction and discharge valves, internal turbulent flow and pulsation characteristics of the pump are studied and the effects of crank speed on those are analyzed in detail. The results show that the valves of reciprocating pump open and close quickly and non-linearly with various degrees of striking velocities and lag phenomena. Through the time and frequency domain results of flow pulsation, the single-cavity frequency is the dominant frequency. The most obvious amplitude appears for discharge flow pulsation, which gradually increases with crank speed. The results could provide useful information for the optimization of reciprocating pumping systems.
The performance of the cone meter when measuring the cryogenic fluid was investigated by numerical simulation. The results show that the discharge coefficient and pressure loss coefficient of the cone meter are almost constant when the Reynolds number in the "stable region". The cryogenic fluids, especially the liquid hydrogen, have wider stable Reynolds number ranges than the water. There is little effect of cavitation on the discharge coefficient and pressure loss coefficient at the initial stage of cavitation. Thus the effect of slight cavitation on the measurement error of the flow rate is small, whose relative error is less than ±0.5% in present cases. This study opens a new avenue for measuring the flow rate of the cryogenic fluid.
Cavitation is undesirable phenomenon and it is difficult to eliminate completely, however it is minimized to the acceptable limits. It becomes more severe under off-design conditions and lower tail race level. Shear Stress Transport (SST) turbulence model and Rayleigh-Plesset mass transfer models are used using CFX solver for performing the transient simulation and investigating the cavitation turbulent flow through Francis turbine. An attempt has been carried out to analysis of cavitating flow at low head Francis turbine under different operating conditions having varying suction heads. Experimentation has been carried out to validate the simulation results. It was found that obtained simulation results are very close agreement with experimental results. Summarizing, the performance loss and cavitation rate are found maximum under over load operating conditions. At part load operating conditions of the turbine, high amplitude of pressure at low frequency has been found which may cause fatigue damage to the turbine over time. Cavitation rate, performance loss and magnitude of pressure pulsation increase with increase of suction head.
A two-phase liquid pumping test ring is built to study the flow induced characteristics of centrifugal pump under the air-water flow working condition. Pump performances are measured under different flow rates and different inlet air void fraction (a). Pressure pulsation signal spectrums and their probability density maps are also recorded. The calculations, using URANS k-epsilon turbulence model combined with the Euler-Euler inhomogeneous two-phase model, are also performed to obtain inner flow structure inside the impeller and volute channels under different air-water conditions in order to understand the pump characteristic evolutions. The results show that the performance of centrifugal pump is more sensitive to air inlet injection at low flow rates. The maximum air void fraction of model pump could reach 10% when the pump operates at the highest efficiency point, and the performance drops sharply when the air void fraction is more than 8%. The dominant frequency of pump outlet pressure pulsation is still at the blade passing frequency even under two-phase condition. Frequency amplitude increases with the increase of a. The greater the a, the more of low frequency appears in broadband characteristics. With the increase of a, the probability density amplitude of pressure pulsation decreases gradually, and its span becomes gradually wider as well. Comparisons between numerical local results and experimental unsteady pressure can explain part of the phenomena that are found in the present paper.
The new world energy policy is influenced by climate changes, narrow range of operation of Thermal Power Plants, potential risks of Nuclear Power Plants and limited resources of oil, gas and coal. Taking into account that renewable energy, solar and wind power particularly are very dependent on the climate, Hydro Power takes a new role in energy systems. Electricity conversion and storage in periods of lower consumption and electricity production from the stored energy in periods of higher demand or reduced production, are crucial for the maintenance of stable and efficient electrical system. This requirement has especially strengthened nowadays due to the expansion of integration of new wind and solar plants. These renewable sources are characterized with inherent intermittent production both in daily periods and periods of several days, weeks or even months. A number of technologies might be considered for the electricity conversion and storage, but the only nature and high capacity available technology is based on the pumped storage plants. This article studies the potential of the pumped storage plants as the effective and economically competitive technology for the storage of wind, solar, run-of-river and other environmentally friendly energies. Nuclear and coal fired plants can change power output to achieve demand but only at the price of extremely high maintenance cost. In addition, natural gas generators contribute to climate change and pollution only slightly less than coal. The pumped storage method is the most common storage system in the electricity sector. It is traditionally dependent on natural conditions, usually making use of rivers or lakes. However, some innovative methods such as the use of the sea as the lower reservoir, or a proposal to use a surface reservoir as the upper reservoir and an underground reservoir as the lower have emerged. Analyses indicate that there is a strong economic incentive for further investment in pumped-storage installations when other hydro storages and sites are not available.
In order to study the influence of inlet gas volume fraction (IGVF) on performance of a gas-liquid centrifugal pump, three-dimensional turbulent flow of a single-stage gas-liquid centrifugal pump has been simulated by using computational fluid dynamics (CFD). Both steady and unsteady simulations have been conducted for different inlet gas volume fraction conditions of the pump. The gas phase distribution, the internal flow field and pressure field of the pump were obtained with inhomogeneous two-fluid model. The result showed that many gas accumulation zones accompanied vortices appears in the impeller as IGVF increases, and surge would occur as IGVF reaches a certain value. The change of IGVF would change the magnitude and direction of the impeller radial force.
This paper presents detailed analyses on the steady and unsteady internal flow characteristics of a three-stage centrifugal pump under design and off-design conditions. A numerical analysis is conducted by solving three-dimensional steady and unsteady Reynolds-averaged Navier-Stokes equations with the shear stress transport (SST) turbulence model. The results of the steady and unsteady numerical analyses throughout the flow region are analyzed and compared with experimental data. A reattachment modification is used in the SST turbulence model to better capture the characteristics of flow separation due to boundary layer reattachment under the design and off-design conditions. The unsteady numerical results are in reasonable agreement with the experimental data, whereas they differ from the steady numerical results when it comes to the internal flow fields at each component stage. In particular, the time-averaged internal flow phenomena obtained from the unsteady analysis are close to the real field conditions of this pump at low flow rates. The hydraulic performances with and without the reattachment modification are similar throughout the flow region, whereas the respective flow characteristics in each impeller component are considerably different, particularly at low flow rates.
The present study investigated flow characteristics in the V-shaped region of the suction performance curve for a double-suction centrifugal pump based on the computational fluid dynamics (CFD). The V-shaped region in the time-averaged suction performance curve was simulated well. The CFD simulated the fluid oscillations due to cavitation surge and rotating cavitation well. The V-shaped region was observed in the absolute total pressure difference between the impeller inlet and outlet. The time histories showed that the cavity produced vorticity, resulting in an increase in a pressure loss, and a decrease in an impeller torque and an angular momentum flow rate. The time-averaged cavity volume, pressure loss between the impeller inlet and outlet, vorticity in the blade passage and impeller torque were examined. A Λ shape of a cavity volume curve caused a Λ shape of a vorticity curve, resulting in a Λ shape of a pressure loss curve and a V shape of an impeller torque curve. The Λ shape of the pressure loss curve and the V shape of the impeller torque curve caused the V shape of the suction performance curve.