As result of the negative environmental impact of large hydroelectric dams and conventional diesel power plants, new renewable energy sources should be studied. Gravitational Vortex Turbines (GVTs) can provide clean energy to off-grid areas, known as Non-Interconnected Zones in Colombia, by inducing a water vortex in a turbine-generator set. The implementation of these turbines in the world has expanded due to demographic growth in remote areas, and new studies have enhanced their efficiency. However, there is not enough literature about the estimation of the incidence of their geometric and operating parameters on their performance. This paper presents a global overview of GVTs through a literature review that explores their operation as well as numerical, experimental, and analytical studies that have been conducted to improve their efficiency.
In this study, experimental/numerical investigations on the effect of axial offset of rotor offset in a final stage model of a three-stage centrifugal pump are carried out. The axial offset is intentionally given to the shaft system to both of discharge/suction side. As a result, the axial thrust is significantly affected by the axial offset in the flow rate range below 50% of the design flow rate. From the flow field computed in CFD analysis, the flow mechanism induced by the axial offset leading to the change in the axial thrust is elucidated; the interaction between the back flow form the diffuser and the impeller exiting flow is affected by the axial offset, which are responsible for the change in the angular momentum brought into side gaps and therefore in the pressure distribution inside the side gaps.
To improve the cavitation performance of a centrifugal pump, the high-pressure liquid in the front pump cavity is introduced into the cavitation area on the back of the blade by perforated holes at the front cover of the impeller. Based on the RNG k-ε turbulence model and Zwart-Gerber-be1amri cavitation model, the numerical calculation and analysis of the cavitation flow field in the model before and after perforation under different cavitation numbers is carried out by FLUENT. The results show that: The perforation at the front cover plate can effectively improve the pressure value of the cavitation area on the back of the blade. To some extent, the change of pressure gradient restrains the development of cavitation. The perforation at the front cover plate can effectively reduce the integral value of the cavitation bubble in the passage, improve the flow passage conditions in the impeller passage, and reduce the blockage degree of the cavitation to the passage. At the same time, the fluctuation range of the cavitation volume in the impeller is small in a rotation cycle after the perforation. It can be seen that the way of perforation at the front cover plate can effectively improve the cavitation performance of the centrifugal pump.
In recent years, the fog gun trucks for outdoor dust removal have been widely used and developed in China. In this paper, the spray flow field simulation of FLUENT is carried out for the spray nozzle's mass flow rate and the structure of air supply with circle radius decreasing. The analysis shows that the decreasing degree of the reducing air supply outlet produces the corresponding shear flow, which makes the air supply outlet of the fog gun obtain more energy distribution in the position of the nozzle, and it is more conducive to the divergence and uniformity of the fog droplets by sending the air generated by the nozzle to a longer distance. With the increase of nozzle mass flow rate and wind speed flow rate, it is more conducive to the air supply and divergence of droplets. The effect of adding nozzle around the ejector is better than that in the center of the ejector. A design of flat ejector with higher efficiency is proposed.
The impeller-volute interaction flow in centrifugal pump is influenced by the flow in impeller-tongue gap. In order to completely understand the mechanism of interaction between impeller-volute flow and impeller-tongue gap flow, a transient three-dimensional numerical simulation of the flow in a single stage centrifugal pump was carried out by applying sliding mesh approach and the standard k-ε turbulence model in CFD, and the derived transient flow data were time-averaged over a period of one blade passing the tongue. The analysis of the flow in the pump revealed that under off-design conditions, a reversed flow with lower pressure at small flowrates below the dutypoint or a stagnation region with higher pressure at high flowrates above the dutypoint appeared in the near tongue region in volute, which enhanced the asymmetric flow in impeller channels. It was consequently considered that the flow in impeller-tongue gap was a superposition of a drag flow by impeller and a pressure leakage flow driven by pressure difference between two sides of the tongue, and the pressure difference was zero at design condition, but increased with the deviation degree of the flow in impeller from the dutypoint. Under smaller flowrates, the gap leakage flow has direction opposite to that at higher flowrates, and affects much the volute flow. In the end, based on the analytical results, a semi-empirical model for the volute flow was deduced by one-dimensional flow continuity, and it may supply a reference for optimizing the flow in volute.
The hydropower plants under Himalayan basins are mostly characterized by heavy sediment load due to geographical and metamorphic constraints. Run-off-river projects with limited size of the desilting basins allow suspended sediments to get carried into the turbine components causing wear due to sediment erosion. In the case of high head power plants consisting of Francis turbines, a large portion of the hydraulic energy is transformed into kinetic energy within the guide vanes. This causes various instabilities in the flow due to high acceleration and velocity. Some recent studies have shown that due to the combined effect of the secondary flow around the guide vanes and sediment carrying flow, the size of the clearance gap increases, which further aggravates the performance of the turbine. This study takes a reference of one of the power plants in Nepal containing high head Francis turbines. An in-depth analysis of the effect of the sediment in this power plant and sediment erosion in the turbine components has been performed. A CFD analysis of the guide vanes and runner blades corresponding to the same turbine has been conducted and the results are used to analyze the erosion pattern on the actual turbine. The detailed erosion analysis is made possible with a 3D scanner, such that the eroded regions can be captured and classified based on the flow behavior at those regions. Guide vanes and runner blades are found to be the predominant components affected by erosion. It has been seen that most of the erosion affected regions are originated from increasing clearance gaps between guide vane and facing plates caused due to continuous leakage flow within the two sides of the guide vanes.
Phenomena of surge degenerations and recoveries therefrom, which are related with so-called stall stagnation problems, are studied on the basis of numerical-experimental results by one-dimensional surge simulations on a single-stage axial flow compressor and a five-stage one. The phenomena are observed to show some different tendencies depending on the number of stages and the relative location of the compressor in the flowpath. The mass flow amplitudes, as the measure of the surge sizes, show behaviors of either continuous decrease in the amplitudes or discontinuous ones in the degeneration process. The latter is seen in the five-stage compressor and the former in the single-stage one. The difference in the tendency appears to be influenced by the levels of the compressor pressure-ratios and by the relative compressor locations also. Recoveries from seriously degenerated surge situations are observed to be achieved by opening the exit valve widely. It suggests that the stall margins available for alleviating significantly the pressure loads are indispensable in the situation. In the sense, it could be said that the stall stagnation or non-recoverable stall is the phenomenon related intimately with the surge degeneration tendency in the compressor-flowpath system characteristics, deteriorated furthermore by operational factors on-site, such as insufficient stall margins and limited flexibilities of operational procedures.
The present paper proposes and describes a through-flow analysis method of axial fan coupled with BPF and broadband noise prediction models. The flow and performance predictions of axial fan are made by streamline curvature method with empirical correlations for flow deviation and pressure losses. After the computation of streamline curvature method, the predicted flow velocity, flow angle and wake thickness distributions along fan blade span are used for calculating the acoustic pressures produced from BPF and broadband noise sources. The present method is applied to several automotive and air-conditioning fans for verifying its prediction accuracy. The fan flow, performance and noise prediction results by the present method are compared with the CFD and the measurement results. From the comparison results, the present method is shown to provide favorable prediction results within a few percent relative errors and can be used as a reliable design tool of high efficiency and low noise fan at the actual fan design practice.
In recent years, because of the energy crisis, improving the thermal efficiency of automobiles has become a very important issue. It is known that a pulsating flow generated by engine valves affects the performance and efficiency of the turbocharger adversely . However, the turbocharger characteristics under pulsating flow have not been clarified to a satisfying degree yet, and no prediction method of turbocharger performance has been established yet. In this study, an unsteady one-dimensional flow model of a turbocharger is constructed by modeling the physics of aerodynamic loss and unsteady characteristics based on experiments and 3D-CFD. Furthermore, the characteristics of the turbocharger under pulsating flow were predicted using the built one-dimensional unsteady flow model. Moreover, this one-dimensional model was implemented in GT-Power which is a one-dimensional commercial code used by many automobile companies.
For general-use turbopump inducers, high suction performance is required in a wide operating range including the cut-off point. At the low flow rates, low frequency cavitation surge is known to occur with the strong inlet backflow from the inducer. The reduced inlet blade angle would be favoured for the suppression of this inlet backflow, whereas the reduced inlet blade angle causes the deterioration of suction performance through the reduced inlet throat area. In this study, a splitter blade was adopted for the helical inducer to overcome or relieve these two conflicting problems, and the effectiveness was investigated by CFD considering cavitation. First, the favourable length and the circumferential position of short blade were investigated by 2-D cascade model. Then, the obtained suitable cascade design was applied for the 3-D helical inducer. As a result, the inlet backflow was found to be weakened at the low flow rates as expected, while keeping the good suction performance of inducer in the whole flow rate range.
The horizontal oil-water separator is a device for separating water and oil through a gravity sedimentation system. In this separator, the weir is located in the apparatus between the water outlet and the oil outlet, and ultimately separates the oil from the water. Depending on the angle and height of the weir, the width of the multi-phase interface might be changed within a certain range. This study compares the separation efficiency according to the inclined angle of the weir and various inlet flow conditions through numerical analysis. The target model is a modularized FWKO (free water knock out) vessel in an oil sands plant. In the present research, the area of the oil-water interface is widened and the separation efficiency is increased for a weir leaning in the direction of the oil outlet. Furthermore, limits of separation efficiency for SOR(steam-oil ratio) value and residence time of mixture were analyzed. In conclusion, the gravitational sedimentation method can improve to about 90% without additional devices. However, the fatigue stress caused by inclining the weir have to be considered for improved stability.
The simulation of separation and settlement under two kinds of flue gas channels in the new dust removal method of shot peening is studied. By using FLUENT software and orthogonal experiment method of four factors and three levels, the influence of different velocity, pellet density, pellet size and velocity difference on the settlement rate of primary settlement channel is analyzed. The results show that the layout of flue gas channel has a significant impact on the mechanical settlement mode, which is mainly reflected in the impact of the density on the shot, and the shot density is the leading factor in several factors studied. Under the same flue structure, when the material density of the pellets is increased, the sedimentation rate of pellets can be increased, so the pellets are easier to be removed. In the process of free settlement, when the velocity of flue gas is increased, the migration path of pellets carried by flue gas increases, which is unfavorable to the removal of pellets. Therefore, the high density and inertia separation method is preferred in dust removal of shot blasting.
The discharge elbow is an important part for the axial flow pump system, and the saddle area on the performance curve is a special characteristic of the axial flow pump. In order to reveal the influence of discharge elbow on the saddle zone, the saddle zone performance of an axial flow pump with two different discharge elbows (90° and 60°) is described in this paper by simulation and test. First, the effect of discharge elbows on pump energy performance is analyzed. The results indicate that the saddle zone of model pump with different discharge elbows is always between 0.5QBEP and 0.6QBEP (QBEP represents flow rate at the best efficient point), and the head value reaches the minimum at 0.55QBEP. Then, the analysis on pressure pulsation of different models is shown. The results show that compared to 90° discharge elbow model, the peak to peak value of pressure pulsation of 60° discharge elbow model at impeller inlet and pump outlet all reduces significantly under each flow rate. When the discharge elbow is 90°, the main frequency of the pressure pulsation at impeller inlet and pump outlet is the blade passing frequency fp, and many low-frequency pulsation components appear in saddle zone. When the discharge elbow is 60°, the main frequency of pressure pulsation at pump outlet changes from the blade passing frequency fp to the axial passing frequency fn. Finally, a focus by the numerical simulation about the internal characteristics is given. It is found that a small amount of vortex occurs in these two discharge elbows at saddle zone condition while the high speed area appears in pump outlet extend. After the 90° discharge elbow is replaced by 60° discharge elbow, the streamline distribution becomes more uniform and the hydraulic loss caused by the vortex decreases.
It is requested that the hydroturbine be a small size and have high performance. Therefore, we adopted contra-rotating rotors, which can be expected to achieve radial compactification and high performance. However, a conventional contra-rotating rotor was composed of two axial flow rotors, so it had a specification suitable for high flow rate and low head. In order to achieve a small hydroturbine suitable for low flow rate and high head, we propose new type of contra-rotating rotors, which are composed of a hybrid rotor and a centrifugal rotor. In the present paper, we focus on the number of blades of the hydroturbine composed of these rotors as a first step of this research, and investigate performance by numerical analysis. As a result, it clarifies that the head of the front rotor is lowered due to the slip of the flow, and it has been confirmed that increasing the number of blades can suppress the slip of flow and improve the turbine head and the shaft power. Also, it clarifies that the shaft power of the rear rotor was almost unchanged even if the number of blades is changed, and that the meridional plane shape has a greater effect on the performance than the number of blades.