Table of contents

NACA0015 is a commonly used hydrofoil for hydraulic machinery. Because the calculated flow characteristic is sensitive to the mesh density and distribution, a careful check of mesh independence should be performed before the CFD calculation. For this purpose, flow comparison was done between calculation and experimental test at the same operating condition with the Reynolds number equal to 130,000. When the span length is two times of the chord length, the ratio of lift to drag is 34.97, which is close to the test result of 36.47. The pressure coefficient and cavitation characteristic were also calculated. For example, the pressure coefficient was compared in different flow conditions with Reynolds number equal to 130,000, 200,000 and 400,000. The cavitation characteristic was calculated at different cavitation numbers, e.g. 0.5, 1.0 and 1.5. Based on these hydraulic and cavitation characteristic, a tidal turbine runner was developed by using hydrofoil NACA0015. According to our studies, the flow characteristic and cavitation index can satisfy the engineering requirements.

In this paper, the steady pressure field has been investigated numerically by computational fluid dynamics (CFD) in a nuclear reactor cooling pump. As a multiphase approach the Eulerian-Eulerian two fluid model has been applied to calculated five computational models with different kinds of blades. The analysis of inner flow field of the five model pumps shows that the pressure in the impeller increases with the increase of the gas contents and the pressure distributions are irregular at the inlet of different blades when the gas contents less than 20%. With the increase of the number of blades, the vortexes at the outlet of impeller decrease whereas the vortexes in the deep of the volute markedly increases and high velocity of the fluid huddle is generated gradually at the outlet pipes. Under the action of centrifugal force and Coriolis force, gas phase mainly concentrated at the lower velocity and lower pressure area. The radial force on the impeller gradually increases with the increase of the gas contents.

Taking the viscosity-temperature relationship of the fluid film into consideration, a 3-D numerical model was established by ANSYS software which can simulate the heat transfer between the upstream pumping mechanical seal stationary and rotational rings and the fluid film between them as well as simulate the thermal deformation, structure deformation and the coupling deformation of them. According to the calculation result, thermal deformation causes the seal face expansion and the maximum thermal deformation appears at the inside of the seal ring. Pressure results in a mechanical deformation, the maximum deformation occurs at the top of the spiral groove and the overall trend is inward the mating face, opposite to the thermal deformation. The coupling deformation indicate that the thermal deformation can be partly counteracted by pressure deformation. Using this model, the relationship between deformation and shaft speed and the sealing liquid pressure was studied. It's found that the shaft speed will both enhance the thermal and structure deformation and the fluid pressure will enhance the structure deformation but has little to do with the thermal deformation. By changing the sealing material, it's found that material with low thermal expansion coefficient and low elastic modulus will suffer less thermal-pressure deformation.

The gas-liquid two-phase flow in pelton turbines is very complicated, there are many kinds of bad-behaved flow in pelton turbines. In this paper, CFD numerical simulation for the pelton turbine was conducted using VOF two-phase model. One kind of bad-behaved flow caused by the two jets was captured, and the bad-behaved flow was analysed by torque on buckets. It can be concluded that the angle between the two jets and the value of ratio of runner diameter and jet diameter are important parameters for the bad-behaved flow. Furthermore, the reason why the efficiency of some multi-jet type turbines is very low can be well explained by the analysis of bad-behaved flow. Finally, some suggestions for improvement were also provided in present paper.

In order to get the accurate hump characteristic curve of a pump turbine in pump mode, three dimensional steady simulations were carried out using SST k-ω turbulence model with cavitation model and without cavitation model under different operation condition points with 19 mm guide vanes opening. A refinement grids were generated to adapt the turbulence model. The results obtained with cavitation model show a better agreement with experiments. The detailed analysis was undertaken to find out the relationship between the cavitation and hump region. It is concluded that the hump characteristic is related with cavitation.

As a kind of widely used device in pipe system for pressure and flow rate regulating, the valve would experience cavitation in the case when a sharp pressure drop occurs, which will induce the energy loss, noise and vibration of pipeline system, and even operational accidents. The experiment on flow resistance coefficient of a DN600 pressure-regulating valve under operation conditions from 0% to 100% openings is conducted. Based on the RNG k-e turbulence model and the Rayleigh-Plesset cavitation equation, a set of computational model is developed to simulate the turbulent flow in the valve under operational conditions from 0% to 100% openings. The computational results of flow resistance coefficient are compared to the experimental data. And the numerical simulation is employed to predict the cavitation performance of the valve at different inlet flow conditions. The transient cavitating flow is calculated to reveal the time evolution of cavitation in the valve.

Numerical simulation is carried out for gas-solid two-phase flow in a U-beam separator. In this study, the U-beam is altered with the inlet fins in order to improve the performance of the separator. The inlet fin angle of the separator are 30°, 35°, 40°, 45°, 50°, 55 ° and 60°. The governing equations are the Reynolds-Averaged Navier-Stokes equation with the standard k- model and the discrete phase model (DPM) describing the discrete two - phase flow as well as stochastic tracking model. Results show that the pressure drop deviation with fins is within 3% from those without fins. It is found that there is a maximum separation efficiency at the fin angle of 35°. Fin induces generation of a stagnation region which could collect particles and lead to change of vortical structures. The fin induced flow also causes the turbulent intensity inside the baffle to decrease to facilitate separation.

Numerical simulation is carried out for the tangential inlet cyclone separator with different dimensionless parameter (the ratio of cone-tip diameter and cylinder diameter d/D is 0.342, 0.355, 0.368, 0.382 and 0.395). Then, the stability of the vortex flow in the separator is analyzed with the energy gradient theory. The governing equation is the Reynolds-averaged Navier-Stokes equations with Reynolds Stress Model (RSM). The finite volume method is employed to simulate the flow and the velocity, pressure, separation efficiency and the turbulent intensity are obtained. Results show that the location of the maximum tangential velocity is near the axis, and the highest outer vortex tangential velocity is achieved at the dimensionless rate of 0.355. When the d/D=0.355, the tangential velocity distribution in the outer vortex is the most close to velocity distribution characteristics of free vortex. The free vortex distribution has the best stability from the energy gradient theory which may be the reason why optimal performance can be achieved at d/D=0.355. To achieve high efficiency and low pressure drop for the device studied, d/D=0.355 is the optimal dimensionless diameter ratio.

Underwater exhaust produces an intricate unsteady two-phase flow field. For exploring the methods to predict the structure of air-water flow field and revealing the interaction of gas and water, three-dimensional underwater gas jet model with the VOF multiphase flow tracking method was adopted to simulate the transient flow field of gas jet into water. The air-water two-phase flow and its acoustic characteristic of turbulent gas exhausted from underwater nozzles were experimentally investigated in the early stages. Process of bubbles formation, detachment, fragmentation and coalescence were recorded clearly. The simulated results which were compared with the prior experimental results proved that the model almost accurately catches the behaviour of underwater bubbles. A few points were set in the two phase flow field to monitor pressure fluctuation. It had shown that higher air flow rate causes intense gas-column contraction and consequent bubble fragmentation, leading to higher amplitude and frequency of pressure fluctuation.

The pressure relief valve for regulating the level of the high-pressure separator works under a pressure difference up to 15 MPa in the temperature of 415 °C. Severe cavitation erosion and particle impact lead to the valve disc's mass loss. In this paper, three-dimensional turbulent cavitating flows in the pressure relief valve are numerically simulated to reveal the mechanism of mass loss at valve disc. The RNG k- turbulence model and the mixture model with a mass transfer for cavitation are employed to simulate the cavitating flow in the pressure relief valve. The result shows that there is phase change in the pressure relief process and cavitation bubbles would be transported by high-velocity backflow to the head of valve disc. For the local pressure higher than the saturated vapor pressure, the bubbles collapse at the head of disc and cavitation erosion is formed at the head of the disc. By comparing the cases of opening of 40%, 50%, and 60%, backflow velocity and cavitation region in front of the disc decrease with the opening increase. Therefore, during the actual operation, the pressure relief valve should be kept to a relatively large opening.

In the paper, a three-dimensional model of a gravity-driven bubble rising in a narrow pipe filled with viscous liquid is built using the lattice Boltzmann method. On the Cartesian grid, the free-energy multiphase lattice Boltzmann model and the no-slip bounce-back scheme are combined together to implement the bubble interface and the solid boundary treatment, respectively. To start with, the Laplace law for bubble interface is verified with the newly built model in this paper. Then the cases where the pipe with the radius 1.2 to 2.5 times the bubble radius are carried out to investigate the effects of pipe dimension on the bubble motion, including rising velocity, deformation and jet formation. Moreover, the asymmetric characteristics of bubble biases the centre axle are explored further. The results show that the boundary condition effect consisting of the pipe dimension and the offset of bubble biasing the centre axle is of great significance to the bubble dynamics in a narrow pipe. The former factor mostly affect the velocity characteristics of the bubble, while the latter one mostly focuses on the bubble deformation and trajectory.

The orbital propellant management performance of the vane-type tank is so important for the propellant system and it determines the lifetime of the satellite. The propellant in the tank can be extruded by helium gas. To study the two phase distribution in the vane-type surface tension tank and the capability of the vane-type propellant management device (PMD), a large volume vane-type surface tension tank is analysed using 3-D unsteady numerical simulations. VOF methods are used to analyse the location of the interface of the two phase. Performances of the propellant acquisition vanes and propellant refillable reservoir in the tank are investigated. The flow conductivity of the propellant acquisition vanes and the liquid storage capacity of propellant refillable reservoir can be affected by the value of the gravity and the volume of the propellant in the tank. To avoid the large resistance causing by surface tension in an outflow of a small hole, the design of the vanes in a propellant refillable reservoir should have suitable space.

Vane type propellant management device (PMD) is one of the key components of the vane-type surface tension tank (STT), and its fluid orbital performance directly determines the STT's success or failure. In present paper, numerical analysis and microgravity experiment study on fluid orbital performance of a vane type PMD were carried out. By using two-phase flow model of volume of fluid (VOF), fluid flow characteristics in the tank with the vane type PMD were numerically calculated, and the rules of fluid transfer and distribution were gotten. A abbreviate model test system of the vane type PMD is established and microgravity drop tower tests were performed, then fluid management and transmission rules of the vane type PMD were obtained under microgravity environment. The analysis and tests results show that the vane type PMD has good and initiative fluid orbital management ability and meets the demands of fluid orbital extrusion in the vane type STT. The results offer valuable guidance for the design and optimization of the new generation of vane type PMD, and also provide a new approach for fluid management and control in space environment.

The internal flow in the rotating bucket of Pelton turbine is free water sheet flow with moving boundary. The runner operates under atmospheric and the cavitation in the bucket is still a controversial problem. While more and more field practice proved that there exists cavitation in the Pelton turbine bucket and the cavitation erosion may occur at the worst which will damage the bucket. So a well prediction about the cavitation flow on the bucket surface of Pelton turbine and the followed cavitation erosion characteristic can effectively guide the optimization of Pelton runner bucket and the stable operation of unit. This paper will investigate the appropriate numerical model and method for the unsteady 3D water-air-vapour multiphase cavitation flow which may occur on the Pelton bucket surface. The computational domain will include the nozzle pipe flow, semi-free surface jet and runner domain. Via comparing the numerical results of different turbulence, cavity and multiphase models, this paper will determine the suitable numerical model and method for the simulation of cavitation on the Pelton bucket surface. In order to investigate the conditions corresponding to the cavitation phenomena on the bucket surface, this paper will adopt the suitable model to simulate the various operational conditions of different water head and needle travel. Then, the characteristics of cavitation flow the development process of cavitation will be analysed in in great detail.

Sump model testing is mainly used to check flow conditions around the intake structure. In present paper, numerical simulation with SST turbulence model for a scaled sump model was carried out with air entrainment and two phases for prediction of locations of vortex generation. The sump model used for the CFD and experimental analysis was scaled down by a ratio of 1:10. The experiment was performed in Korea Maritime and Ocean University (KMOU) and the flow conditions around pump's intake structure were investigated. In this study, uniformity of flow distribution in the pump intake channel was examined to find out the specific causes of vortex occurrence. Furthermore, the effectiveness of an Anti Vortex Device (AVD) to suppress the vortex occurrence in a single intake pump sump model was examined. CFD and experimental analysis carried out with and without AVDs produced very similar results. Without the AVDs, the maximum swirl angle obtained for experimental and CFD analysis were 10.9 and 11.3 degree respectively. Similarly, with AVDs, the maximum swirl angle obtained for experimental and CFD analysis was 2.7 and 0.2 degree respectively. So, with reference to the ANSI/HI 98 standard that permits a maximum swirl angle of 5 degree, the use of AVDs in experimental and CFD analysis produced very desirable results which is well within the limit.

Marine current turbines, compared with the analogous wind turbines, have the potential to suffer cavitation. This paper focuses on the effect of cavitation on a marine current turbine and implements the two-phase flow simulations based on the Rayleigh-Plesset cavitation model. It can be found that under the influence of cavitation, the power and thrust coefficients of turbine decrease and especially near the blade tips. Due to the non-uniform hydrostatic pressure along the depth of water, the present work takes this effect into account and finds a larger cavitation area appears on the blade tips at a shallow submergence. Meanwhile the power and thrust performance of one blade change during its rotating period. In order to analyze the cavitation performance of turbine locates at a certain water depth, the variations of inflow velocity and rotor rotating speed are implemented. It indicates that, with the inflow velocity increasing, the C_P and C_T of turbine with higher rotation speed will significantly reduce due to the occurrence of cavitation, and the influence on the turbine with lower speed is small. These predicting results can provide implications for the safe and stable operation of marine current turbines.

Sliding bearings are employed to support the rotor system and limit the vibration amplitude. In high speed rotor system, cavitation often occurs in the oil film and affects the dynamic characteristics of the sliding bearing greatly. In this paper, numerical method is adopted to simulate the cavitation in the oil film with homogeneous two-phase mixture flow using Singhal-et-al cavitation model in the commercial code FLUENT-solver. Cases without cavitation model were also calculated at the same time. Many computations with different frequency ratios were conducted. Then the rotor dynamic characteristics of the sliding bearing were retrieved. The results show that the cavitation has great influences on the pressure distribution in the oil film. As the rotational speed or whirling speed of the journal increases, the cavitation will become prominent. The dynamic coefficients of the bearing such as stiffness and damping with cavitation model considered are quite different from that without cavitation. So it is worth to pay attention to and do further study about the cavitation in the sliding bearing in the high speed rotor system.

In case of hydro turbines operated at part-load condition, vortex ropes usually occur in the draft tube, and consequently generate violent pressure fluctuation. This unsteady flow phenomenon is believed harmful to hydropower stations. This paper mainly treats the internal flow simulation in the draft tube of a Francis turbine. In order to alleviate the pressure fluctuation induced by the vortex rope, air admission from the main shaft center is applied, and the water-air two phase flow in the entire flow passage of a model turbine is simulated based on a homogeneous flow assumption and SST k-ω turbulence model. It is noted that the numerical simulation reasonably predicts the pressure fluctuations in the draft tube, which agrees fairly well with experimental data. The analysis based on the vorticity transport equation shows that the vortex dilation plays a major role in the vortex evolution with air admission in the turbine draft tube, and there is large value of vortex dilation along the vortex rope. The results show that the aeration with suitable air volume fraction can depress the vortical flow, and alleviate the pressure fluctuation in the draft tube.

The impeller and casing of dredge pump are worn by sediment in the flow. However, there are few studies about abrasion of the impeller and casing for normal pump operating conditions. This paper investigated the relationship between the wear rates on the surfaces of the impeller as well as casing and the sediment concentration, with the distribution of the wear rates for normal pump operating condition analyzed. An Eulerian-Lagrangian Computational Fluid Dynamics (CFD) procedure was used to simulate steady liquid-solid two-phase flow for various operating conditions. The Finnie model was then used to predict the abrasion. The results show that, the wear rate relative value of impeller and casing surface increase as the sediment concentration increases. The wear rate relative value of impeller and casing surface is larger when the pump is in low flow rate condition, and the value of casing surface is larger than that of the impeller. The wear rate relative value of pump is low when pump is in high efficiency condition. This paper shows the abrasion characteristics on the impeller and casing with sediment flow and provides reference data for predicting the abrasion conditions in the flow passage components for a dredge pump.

In order to study characteristics of pressure fluctuation of a turbine during the starting period, a turbine with guide vanes device at no-load condition was investigated using RNG k- turbulence model. The inner flow distribution and pressure fluctuation characteristics were analyzed. Results show that the pressure fluctuations in the region between the runner and guide vanes are different around the runner inlet. The dominant frequency of pressure fluctuation in the vaneless space close to the casing outlet is the blade passing frequency, while the dominant frequency at the rest region is the twice of the blade passing frequency. The increase of amplitude of pressure fluctuation close to the casing outlet can be attribute to the large scale stall at suction side of the runner inlet.