Positive displacement hydraulic turbine (PDT) is a new class of turbine, capable of effectively generating micro and Pico hydro power for low specific speed applications. This type of turbine is not ...very popular and hence, it is interesting to research on it. With the rising concerns of environmental pollution, climate change and global warming, emphasis is laid to harness power from renewable energy sources. Micro and Pico hydro turbines are actively researched to generate clean power in addition to the existing conventional turbines. PDT was designed and developed to replace the pressure differential control valves in the hot water supply system and utilize the surplus differential head to generate power and make the system energy efficient. In the present work, experimental studies were conducted on the developed PDT at the designed rotational speed with water at 15, 50 and 110 °C and various differential heads ranging from low to high. The performance data showed the effect of fluid properties on the performance of the PDT due to the change in the temperature of the working fluid. Also, empirical co-relation was developed based on dependent variables using Buckingham π-theorem to predict the flowrate through the PDT at various heads and temperatures. This could help engineers, in future, for designing a new turbine for harnessing micro and Pico hydropower for any application.
•Performance analysis of PDT using experimental studies.•Effect of change in fluid properties at higher heads and temperatures on the performance of PDT.•Development of non-dimensional relationship between various variables using Buckingham π-theorem.•Development of empirical co-relation for flowrate prediction at all conditions.
In the low-flow rates of off-design conditions in the pump–turbines, complicated flows can develop with vortices in the flow passages, which significantly increase the vibrations and noise, resulting ...in destabilizing the pump–turbine system. Under low-flow-rate conditions, an appropriate Thoma number is the most essential requirement for stable operation in turbine mode of the pump–turbine. Thus, this study elucidated to examine the internal flow and unsteady pressure phenomena in a laboratory-scale pump–turbine model operated in turbine mode with different Thoma numbers. The experimental investigations were conducted under 70% of the flow rate at the best efficiency point with different Thoma number to observe the unsteady pressures and vortex rope behavior. Then, the numerical validations were conducted by three-dimensional unsteady-state RANS analyses in a SAS–SST model. The Thoma number did not significantly affect the performance of the pump–turbine model or the unsteady flow phenomena in the vaneless and runner regions. However, the Thoma number affected the draft tube region at low flow rate condition. At low Thoma numbers, the irregular flow phenomena along the flow direction enhanced the unsteady pressure characteristics.
•Internal flow phenomena by Thoma number of a pump-turbine model were presented.•Experimental and numerical investigations were conducted by different Thoma number.•The Thoma number effects were investigated under low-flow-rate condition.•The performance was independent of the Thoma number under low-flow-rate condition.•The Thoma number affected the draft tube region with a visible vortex rope.
In this study, numerical simulation was employed to predict the performance and internal flow characteristics of the inlet of an axial-flow pump by assigning an absolute flow angle to the inlet guide ...vane (IGV) trailing-edge flow. Further, the finite volume method based on the three-dimensional Reynolds-averaged Navier-Stokes equations was employed to discretize the governing equations. The shear stress transport model was used as the turbulence model, and an appropriate number of nodes were selected for the hexahedral grid system through a grid-dependency test. The performance curve and changes in the internal flow field were investigated based on the variation in the flow angle at the inlet of the axial-flow pump. These results can be used to establish an efficient operational plan by adjusting the IGV angle of IGV when installing a variable IGV for an axial-flow pump.
Unusual flow characteristics such as reverse flow, rotating stalls, flow recirculation, and stationary vortexes can induce high dynamic forces and torque variations on the entire system, creating a ...positive slope in the discharge-head curve. To avoid these problems, the present study investigates the hydrodynamic characteristics of a lab-scale model of a Francis type pump-turbine unit in the transition region. To verify the simulation, its results were compared with those of a laboratory-scale experiment performed over various operating ranges. The differences between the experimental and numerical speed, discharge, and torque factors were compared. The numerical analysis was well-matched the experimental tendencies in the overall operating and transition regions. The reliability of the simulations was within 4%. The unsteady RANS equations in the SAS–SST model were discretized for a detailed analysis of the pressure and internal flow characteristics. Under the runaway condition and low-discharge conditions, the frequency spectra of the pressure fluctuations were remarkable at low-frequency related to the rotating stall and blade passing frequency. These results represent a rotating stall with a frequency propagation of approximately 60% of the rotational speed of the runner. In case of the internal flow field, some blade loading distributions developed a positive shape while others developed a negative shape under the runaway condition. Although a rotating stall formed under the low-discharge condition, the form under this condition differed from that developed under runaway conditions, owing to backflow and the single stall cell.
•The unstable S-shaped characteristics in a lab-scale model were studied.•The numerical results were validated in comparison to the experimental data.•The location and rotating speed of stall under the S-curve region were observed.•The unsteady pressure characteristics were analyzed with internal flow field.
Abstract
The stall in an axial fan is directly related to detrimental phenomena such as performance degradation, vibration, noise, and flow instability at low flow rates. As a kind of passive control ...method to handle the stall, two-dimensional plates so-named anti-stall fin (ASF) were suggested by ourselves and were attached inside the casing. In this study, the ASF's effect on the internal flow pattern was visually investigated in the flow passage, and its tendency was discussed with the performance curve. Subsequently, the ASF's functional limitations for various design parameters, which the ASF can derive aerodynamically, were presented as the primary focus of this study. Each one-factor analysis was performed, and the internal flow pattern was observed in parallel at the point where the ASF lost its function. For the radial length, axial length, number of fins, and positive-tangential angle, the ASF almost retained its function up to the limitation to prevent instability but radically lost its function at a certain flow rate. For the axial gap and negative-tangential angle, the ASF gradually lost its function. Mostly, this study was based on numerical analysis, and the performance was validated through experimental tests.
Abstract
The shape of the blade leading edge (LE) is a design variable that cannot theoretically affect the inlet flow characteristics under the definition of the velocity triangle. However, the LE ...is the first to encounter the working fluid in terms of streamwise direction. Depending on its shape, not only the local flow characteristics but also the performance can be affected. In this study, a numerical analysis of the hydraulic and suction performance for a mixed-flow pump was performed with different shapes of the blade LE. The blade was prepared with four sets according to the ellipse ratio (ER), including a square (ER=0), round (1), elliptic (2), and parabolic (5) shape. As the shape of the blade LE was square, the flow streamline was immediately separated from the blade surface, showing a significant drop in the hydraulic performance. As the blade LE was designed in a round, elliptic, or parabolic shape instead of a square shape, the hydraulic performance did not show a noticeable difference. On the other hand, in the prediction of suction performance, the square LE obtained the best characteristics. As the LE shape gradually became a parabolic shape, the cavity blockage was reduced, and the suction performance was also improved.
Cryogenic centrifugal submersible pump is a core equipment that pressurizes and transports fluid with the centrifugal force generated from impeller’s rotation. Problems like cavitation and surging, ...attributed to the working fluid and multistage structural characteristics, negatively affect the lifespan, noise, vibration, and performance of the pump. Therefore, this study develops a pump for a general-purpose specific-speed liquified natural gas fuel-supply system. The internal flow characteristics and performance prediction were analyzed using a commercial computational fluid dynamics analysis software. The numerical analysis results demonstrated that the average head varied across all conditions, where cavitation was absent within the inducer. NPSHre was determined at a cavitation coefficient of about 1.07 and head reduction of 97 %. It was confirmed that the swirl component generated at the trailing edge had a negative effect on the impeller when the flow passed through the inducer region. Upon analyzing the existing model, we identified the problems and discussed the future research directions for improving the pump performance.
Abstract
The cryogenic centrifugal submersible pump is one of the core equipment of the technology and serves to pressurize and transport the fluid with the centrifugal force generated from the ...impeller by rotation. Due to the structural characteristics of the working fluid and multi-stage, problems such as cavitation and axial thrust negatively affect the life, noise, vibration, and performance of the pump, so it must be considered. For this reason, this research aimed to investigate a low-pressure LNG pump for an LNG fuel supply system with a general specific speed. The main components were designed based on the previous studies and CFturbo. The numerical analysis method was established and the performance prediction was conducted using commercial CFD packages. The three-dimensional Reynolds-averaged Navier-Stokes equations were discretized to analyze the internal flow field. First, the reliability of the turbulence model was proved through Hord’s experiment in the 0.357-inch ogive. Second, the steady and unsteady simulations were conducted between the single-passage and full-passage conditions in the inducer. Third, the corresponding analysis was investigated to identify problems with existing model features and find improvement directions.
Micro hydro turbines are getting renewed research interest in recovering unused energy from systems like water supply pipelines, sewage treatment and transportation plants, chemical and oil ...refineries, etc. and making them energy efficient for sustainable development. The present work dealt with this aspect wherein the unused energy of the hot water transportation pipelines, which was earlier throttled by pressure differential control valve (PDCV), was harvested and used elsewhere. A special class of multi-purpose micro hydro turbine known as the positive displacement turbine was developed for the present application which involved very low flow rates with high heads and very low specific speeds and to replace the PDCV which was frequently failing due to cavitation causing loss of energy. A framework was developed for designing such turbines and predicting their performance using CFD. The reasons for the occurrence of cavitation and flow pulsations were also examined and remedial measures were incorporated for their elimination. At the rated condition during experimental study, the base design generated 7.31 kW power with an overall efficiency of 67.7%. The socio-economic analysis was also carried out which concluded that the PDT will aid in energy conservation and reduction in CO2 emissions.
•Description of Pressure Differential Control Valve (PDCV) replacement by Positive Displacement Turbine (PDT).•Develop framework for design & performance prediction of special class of multi-purpose PDT.•Demonstrate PDT’s application in energy recovery for high head & very low flowrate conditions.•Recover unused energy from the hot water supply pipelines and make it energy efficient.•Brief description of socio-economic impact associated with the use of PDT.
Most mixed-flow pumps obtain a saddle-like Q-P curve with a backflow, owing to the increased incidence angle at low flow rates. The backflow was developed near the shroud and followed downstream ...again at its end to form a recirculating flow. The rotating stall, which could be a part of the recirculating flow, followed the impeller's rotational direction, and its properties affected the local stability. The reattaching flow became strong when the upstream flow from the blade leading edge deviated from the same circumferential degree as the dominant flow of the rotating stall heading downstream. The fluctuation in the total pressure rise decreased when the average incidence angle was smaller than that of the design flow rate. As a passive control to suppress the saddle and the above flow patterns, the impeller inlet diameter was reduced from the shroud, and the inlet blade angle was further adjusted to maintain the incidence angle. From the reduced inlet diameter, the backflow was mostly suppressed, and the saddle was improved with a wider operating range. Here, the performance near the design flow rate was almost maintained. The stability was evaluated using the fast Fourier transform, and the numerical method was validated through experimental tests.
