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Shear stress is a parameter of high significance. Through knowledge of this parameter, assessment of scour or sedimentations at different points of bed is made viable. Therefore, this paper investigated alterations in shear stress along the bend, specifically around a bridge pier, under the influence of applying submerged vanes at the upstream side of the bridge pier. With the aim of modeling submerged vanes, vanes of Plexiglas with a thickness of 20% of the pier diameter, a length of 1.5 times the pier diameter, and submergence ratio of 75% were utilized. The vanes were installed at a distance equal to 5 times the pier diameter from the pier center at a distance of 40 to 60% of the channel width from the inner bank at the upstream side of the bridge pier. Acoustic-Doppler Velocity velocimeter device was utilized for measuring three-dimensional velocity components. The experiments were conducted in a 1-meter-wide flume with a degree of curvature of 180. The results of the study suggested that upon reaching the bend apex, the maximum flow turbulence rate occurred in a transverse direction in the case of installing submerged vanes at a distance of 40% of the channel width from the inner bank towards the inner wall; while in the case of installing submerged vanes at a distance of 60% of the channel width from the inner bank, it occurred towards the outer wall, and it could be observed that the maximum longitudinal and vertical components of turbulence rate increased by 16 and 5.5% respectively upon increase in the distance of submerged vanes from the inner bank. Furthermore, the values of and turbulence shear stresses at the outer bank in the case of installing the vanes at a distance of 40% of the channel width from the inner bank were smaller than those in the case of installing the submerged vanes at a distance of 60% of the channel width from the inner bank.

A methodology for comparing the energy efficiency of different methods of regulating the total productivity of a blower station is presented. The basic principles of electrical modeling of duct networks are shown for the mathematical description of their properties and characteristics. The results of a comparison of the energy efficiency of regulating methods for a single fan and a group of five fans operating on a common line are presented. The conclusion about the high energy efficiency of the combination of start-stop control with smooth control using axial guide vanes for a blowing station of five fans is obtained.

The abrupt disconnection from the electrical grid necessitates an immediate shutdown of pump-turbines, requiring full load rejection within seconds. During this transient process, the runner undergoes rapid acceleration, inducing extreme pressure fluctuations, and impose cyclic mechanical stresses on components. There are already numerous studies on the load rejection of pump-turbines., yet experimental investigations on prototype-scale pump-turbine under realistic operational conditions remain limited. This study aims to bridge this gap by conducting comprehensive load rejection experiments on a prototype pump-turbine under different distinct scenarios: load rejection from full load and partial load conditions, respectively. High-frequency pressure sensors were deployed to monitor transient behaviors for different regions. The results demonstrate a significantly higher pressure increase when the turbine undergoes load rejection from full load compared to part load conditions. The speed of runner is 17% higher when the load is rejected from the full load. This study provides a better understanding on how the pressure fluctuations vary during the load rejection in a prototype pump-turbine and can be useful to optimizing guide vane closure laws.

Guide vanes are the most eroded component of the Francis turbine, and flow instabilities around guide vanes influence the flow field at the runner inlet. Guide vane cascade can be considered an alternative method to investigate the flow field, which maintains flow similarity with the prototype turbine. The objective of this paper is to numerically analyze the flow field around the guide vane cascade. A single guide vane cascade numerical model is developed to perform the simulation using commercial software ANSYS 2022. Two turbulence models, shear stress transport k-ω and standard k-ε, perform steady-state simulation at the best efficiency point. The pressure and velocity distribution are obtained at mid-span, and around the pressure and suction sides of the guide vane. Numerical simulation on a scaled prototype full turbine has also been performed to measure the Francis turbine’s torque and efficiency. The modified Bhilangana- III guide vane profile is installed in the B-III hydropower plant in India and taken as a reference Francis turbine. The velocity and pressure distributions obtained around guide vanes of the scaled full turbine are compared with the velocity and pressure distributions of the single guide vane cascade. A difference of 7.25 % in maximum velocity and 9.40 % in maximum pressure at the mid-span of the guide vane is found between the guide vane cascade and scaled full turbine at the best efficiency point. The overall efficiency of the scaled turbine is also measured, and a difference of 0.83 % between the numerical result and scaled hill chart at the best efficiency point was found.

Fish will die from the strike of the narrow flow passages when passage through traditional Francis turbines, in order to obtain excellent hydraulic performance as well as improve survival rate of fish, the guide vanes of fish-friendly Francis turbine model is taken as the research object. CFD method is adopted to predict the flow field characteristics of the turbine, meanwhile, the model test is carried out to validate the reliability of the numerical simulation. The results showed that, for plan A with 20 guide vanes, the internal flow of the turbine is more uniform and the pressure between the guide vanes is more symmetric in the circumferential direction, the turbine has better performance in the efficiency and operational stability.

It has become a general trend for new energy to be connected to the power grid, and the tasks of peak and frequency regulation undertaken by hydropower units are tough. Inevitably, the Francis turbine operates under a transient process, which brings serious pressure fluctuations and instability problems. In the present study, a three-dimensional simulation of Francis turbines with the water pipeline system during the load rejection process is carried out. Results indicated that when a straight line is used to close guide vanes, the Francis turbine generates significant rotational speed, which poses a threat to system safety and stability. Based on this, the sinusoidal closing law proposed in the present study can effectively reduce the maximum rotational speed by 2.6%. After the end of load rejection, the difference in rotational speed between the two closing laws is 5.15%.

Various countermeasures including geometry optimization have been proposed and proved to have a huge impact on flow filed within the draft tube in order to mitigate the vortex rope and the induced pressure fluctuations for Francis turbine under part load operation. However, the effect of these approaches on the hydro-dynamics in upstream region still remains unclear, which is of great significance for the overall performance of the unit. This study aims to explore the influences of modified draft tube with inclined conical diffuser on the pressure fluctuations in whole flow passage. The results reveal that Generation-1 and Generation-2 draft tubes are effective in alleviating pressure fluctuations resided in the draft tube, but the former one would trigger a low-frequency pressure fluctuation with higher amplitude in the runner zone. In addition, the modified draft tube has a very limited effect on the high-frequency pressure fluctuations in the guide vane and vaneless areas. To eliminate the adverse effect of inclined conical diffuser, a design with a transitional section is put forward to smoothly connect the runner zone and inclined conical diffuser. This further developed Generation-2 draft tube presents a reasonably good performance in terms of improving flow stabilities, i.e. alleviating the pressure fluctuations not only in draft tube but also in upstream region such as runner zone. This study provides reference for obtaining a better mitigating effect on pressure fluctuations in the whole turbine flow passage.

Fan systems used to transport fluids are widely used and have become a major consumer of electrical energy worldwide. A significant part of the available energy of transported air in HVAC systems has usually been lost (in the form of dynamic pressure) at the system outlet. It is well-known that using outlet diffusers leads to this energy loss be reduced. In some cases, it is necessary to use shortened wide-angle diffusers, which have a higher coefficient of minor energy loss (local resistance). In the present work, a numerical study of the possibilities of increasing the energy efficiency of wide-angle plane diffusers, using splitter vanes, is accomplished. Diffusers with expansion angles of 30, 45 and 60 deg studied. The results obtained indicate the impact of the number of splitter vanes on the minor energy (local resistance) loss coefficient of the studied diffusers.

Hydroelectric power plants with the aim of being used to generate electrical energy are mostly operated in areas with sedimentation content which can cause wear and tear on the components of the hydropower plant. This activity is emphasized to determine the effect of quartz sand on the rate of abrasion on the guide vanes of the Francis type water turbine. This activity was carried out using a water turbine guide blade abrasion test tool with a guide blade test object made of SUS 304 stainless steel material. The results are presented quantitatively and qualitatively, the greater the concentration and diameter of the quartz sand particles, the water pressure and the angle given at the same time, the greater the rate of abrasion that occurs in the francis type water turbine guide vane. The highest abrasion rate was 5.10 (g/cm 2 x hour) in the angle variation test with a constant Q and a water: sand ratio of 70%: 30%.

Generally, industrial gas turbines (IGT) face transient behavior during start-up, load change, shutdown and variations in ambient conditions. These transient conditions shift engine thermal equilibrium from one steady state to another steady state. In turn, various aero-thermal and mechanical stresses are developed that are adverse for engine’s reliability, availability, and overall health. The transient behavior needs to be accurately predicted since it is highly related to low cycle fatigue and early failures, especially in the hot regions of the gas turbine. In the present paper, several critical aspects related to transient behavior and its modeling are reviewed and studied from the point of view of identifying potential research gaps within the context of fault detection and diagnostics (FDD) under dynamic conditions. Among the considered topics are, (i) general transient regimes and pertinent model formulation techniques, (ii) control mechanism for part-load operation, (iii) developing a database of variable geometry inlet guide vanes (VIGVs) and variable bleed valves (VBVs) schedules along with selection framework, and (iv) data compilation of shaft’s polar moment of inertia for different types of engine’s configurations. This comprehensive literature document, considering all the aspects of transient behavior and its associated modeling techniques will serve as an anchor point for the future researchers, gas turbine operators and design engineers for effective prognostics, FDD and predictive condition monitoring for variable geometry IGT.