Pressure Turbine Research Articles

The effect of chimney entrance slope and constricted section on the performance of solar chimney power plants: A CFD approach

The depletion of hydrocarbon resources and climate change are major global issues which need to be solved urgently. Sun is a clean, inexhaustible, sustainable energy source which has the capacity to meet the future energy demands. Solar chimney power plants (SCPPs) with a simple design are competent to generate large-scale electricity. Primary components of SCPP are the chimney, turbine, and collector. In this work, impact of the chimney entrance slope and narrowed section on performance of SCPP is scrutinized. A computational fluid dynamics model (CFD) is constructed based on Manzanares plant with a chimney height (H) of 194.6 m via ANSYS FLUENT. The novel configurations are generated by changing the chimney inlet slope, θ (45°-85°) and radius of the constricted section with a fixed height (H/28). The findings demonstrate that a decrease in the slope with the constricted section improves the velocity, power and turbine pressure drop. The highest velocity of 17.9 m/s is gained for the configuration with θ = 85° compared to that of 14.3 m/s obtained for the base (θ = 45°) at 1000 W/m2. This configuration enhances power output to 60.4 kW with a rise of 31.3% in comparison to the base case at 1000 W/m2.

Effect of Evaporation and Condensation Temperature on Performance of Organic Rankine System Using R134a, R417A, R422D, R245fa

Organic Rankine Cycles (ORCs) are identified as one of the most promising technologies for generating electricity from low-grade heat sources. Unlike conventional Rankine cycles, ORCs operate at lower temperatures and pressures. This allows them to utilize organic fluids or refrigerants as the working fluid instead of water, which is better suited for high-pressure and high-temperature applications. The performance and design of an ORC system are heavily dependent on the chosen working fluid. Therefore, selecting the right working fluid is crucial for a specific application, such as solar thermal, geothermal, or waste heat recovery. This study analyzed the performance of ORCs using four different working fluids: R-134a, R-245fa, R417A, and R422D. The researchers investigated how variations in condensation and evaporation temperatures affect thermal efficiency, mass flow rate, pump power, and turbine pressure ratio. The Engineering Equation Solver (EES) program was used for analyses. The results demonstrated that condensation and evaporation temperatures significantly influence system performance. The study found that ORC systems using R417A and R422D exhibited higher efficiencies compared to the other working fluids analyzed. Additionally, these fluids required lower mass flow rates per unit of power generation compared to the other fluids.

Pressure characteristics and force analysis of pump turbine in variable-pressure outlet pump mode

A nonstationary numerical simulation was performed on the outlet pressure stabilization and periodic variable-pressure condition of a pump turbine model in the pumping condition. The objective was to dissect the flow mechanism and force characteristics of components within the outlet variable-pressure pumping condition of the pump turbine and to probe into the stability of the pump turbine under such working conditions. Additionally, the alterations in the runner state, pressure distribution, pressure pulsation, as well as the forces exerted on the runner and top cover during this process were analyzed. The results demonstrated that the internal pressure and flow pattern of the pump turbine under variable-pressure conditions fluctuated periodically in accordance with the outlet pressure. An augmented frequency of the outlet pressure variation led to an elevation in the amplitude of the internal pressure change. Nevertheless, a hysteresis difference was observed in the changes of the flow channel pressure and flow pattern. The pressure pulsation in the runner area was influenced by the runner rotation, static and dynamic interferences in the lobe-free area, and the unsteady flow induced by the alterations in the outlet pressure.

Air Excess Coefficient and Irreversibility Value Analysis of Gas Turbines

Gas turbines used in natural gas cycle power plants have been researched in terms of energy efficiency. Gas turbines used in power generation plants have a very complex structure because they contain many components. In order to determine the thermodynamic performance of this system, the efficiency of each component and the increase in entropy of each component were calculated using exergy analysis. Irreversibility was chosen as the main parameter and used for thermodynamic optimization of production. The system consists of many components. An increase in the irreversibility of a single component causes an increase in the irreversibility of other components. The effect of gas turbine pressure ratio and excess air percentage on fuel consumption, fuel exergy, combustion chamber exergy change and irreversibility change was investigated. It was observed that the increase in compressor pressure ratio increased irreversibility. Maximum irreversibility was observed in the combustion chamber. Irreversibility was compared with the excess air used in the combustion chamber. The air excess coefficient was examined as percentages of 100%, 200%, and 300%, respectively. The compression pressure ratio was examined for air excess coefficient percentage values from 3 to 40.

Comprehensive Experimental Assessment Of Unsteady Pressure And Heat Flux In A Small-Core Turbine Over-Tip Shroud

Abstract For novel high-speed small core turbines, with tip clearance below 0.5mm, even small blade-to-blade tip clearance variation is significant. The assessment of these complex flows is pertinent to the design of the next generation of small-core turbines. This manuscript provides a thorough experimental analysis of the shroud?s unsteady heat flux and static pressure in a small-core squealer-tip blade turbine. Atomic Layer Thermopile sensors and fast response pressure transducers were used to perform high-frequency acquisition at 2MHz around the 51% axial blade chord on the shroud. Measurements were taken at engine-representative conditions at several operational conditions and tip clearances. The signals were phase-locked averaged over the revolution period and synchronized to identify individual blade and row signatures. The linear relationship between the rotational tip Reynolds and the static pressure ratio across the blade tip reveals the transition point to reverse over-tip flows. Total heat flux is decomposed into different steady and unsteady heat flux contributions. It is demonstrated that the adiabatic wall temperature governs the unsteady heat flux and contributes to one third of the total surface heat flux. A linear trend was observed between the unsteady heat flux and the tip clearance measured at the pressure and suction side rims. Similar trends were observed between the local heat flux and the pressure ratio across the tip. A comparison with CFD predictions highlights some limitations on resolving the detached and secondary flows, evidencing the necessity of complementary experimental data.

A Review of Comprehensive Guidelines for Computational Fluid Dynamics (CFD) Validation in Solar Chimney Power Plants: Methodology and Manzanares Prototype Case Study

This review provides a comprehensive examination of CFD modeling procedures for SCPP, with an emphasis on the detailed methodologies and a case study of the Manzanares prototype in Spain. The introduction delineates the historical context and physical modeling principles of solar chimneys, while highlighting their potential in industrial applications. The governing equations are meticulously discussed, covering assumptions in both 2D and 3D CFD modeling, the continuity and momentum equations, and the selection and accuracy of turbulence models, particularly the k-ε equations. The review also delves into heat transfer modeling, encompassing the energy equation and radiation modeling. Analytical evaluations of turbine pressure drop ratios and performance metrics for power generation efficiency are critically analyzed. The establishment of boundary conditions in solar chimney applications, including sky temperature assessments and distinctions between 2D and 3D boundary conditions, is extensively explored. Mesh generation techniques for both 2D and 3D CFD models are presented, supported by case studies. Parametric studies and experimental investigations are scrutinized to elucidate their impact on the performance of solar chimneys. The temperature–entropy diagram for an idealized Brayton cycle is introduced as a conceptual framework for efficiency analysis. Validation of the CFD codes, both 2D and 3D, against experimental data is performed to ensure model accuracy. The review further examines energy balance approaches in modeling solar chimneys, presenting state-of-the-art CFD results and discussing their implications in both 2D and 3D contexts. The synthesis of these findings culminates in a comprehensive conclusion, offering insights into the future directions and potential advancements in the CFD modeling of solar chimneys. This work aims to serve as a definitive reference for researchers and practitioners in the field, providing a robust foundation for the development and optimization of SCPP technology.

Analysis and Optimization of a s-CO2 Cycle Coupled to Solar, Biomass, and Geothermal Energy Technologies

This paper presents an analysis and optimization of a polygeneration power-production system that integrates a concentrating solar tower, a supercritical CO2 Brayton cycle, a double-flash geothermal Rankine cycle, and an internal combustion engine. The concentrating solar tower is analyzed under the weather conditions of the Mexicali Valley, Mexico, optimizing the incident radiation on the receiver and its size, the tower height, and the number of heliostats and their distribution. The integrated polygeneration system is studied by first and second law analyses, and its optimization is also developed. Results show that the optimal parameters for the solar field are a solar flux of 549.2 kW/m2, a height tower of 73.71 m, an external receiver of 1.86 m height with a 6.91 m diameter, and a total of 1116 heliostats of 6 m × 6 m. For the integrated polygeneration system, the optimal values of the variables considered are 1437 kPa and 351.2 kPa for the separation pressures of both flash chambers, 753 °C for the gasification temperature, 741.1 °C for the inlet temperature to the turbine, 2.5 and 1.503 for the turbine pressure ratios, 0.5964 for the air–biomass equivalence ratio, and 0.5881 for the CO2 mass flow splitting fraction. Finally, for the optimal system, the thermal efficiency is 38.8%, and the exergetic efficiency is 30.9%.

Effect of sediment erosion on pressure pulsations in a large Pelton turbine

AbstractPelton turbines functioning in sandy river environments often encounter difficulties due to the swift movement of sediment particles, leading to erosion and damage to overflow components. These challenges can result in operational instability, particularly noticeable in large turbines. Pressure pulsation is crucial for turbine stability, and alterations in overflow component profiles caused by sediment erosion can worsen pressure pulsations. This study utilizes numerical simulations to analyze turbine pressure pulsations based on surface profile changes of runner buckets after 2 and 4 years of sediment erosion in a single 500 MW large‐scale Pelton turbine. Our findings reveal that erosion leads to a gradual decrease in pressure pulsation along the bucket's splitting edge from the notch to the root. After 4 years of erosion and wear, the relative pressure pulsation amplitude in the root region increased by more than 530%. Additionally, changes occur in the thickness of the water film in the erosion area on the working surface, disrupting the flow pattern and generating more vortices. This occurrence intensifies the relative pressure pulsation amplitude and reduces bucket stability. The study findings highlight the significant impact of sediment erosion on Pelton turbine pressure pulsation, posing a considerable risk to the unit's operational stability and safety.

Thermal Power Plant Performance Analysis by Estimating Boiler Efficiency via Indirect Method: A Case Study

The performance of power plants is very critical since it is directly related with operating and electricity production costs. Among the other different type of power plants, coal-fired ones have advantages such as reliability and low cost fuel. In this paper, a coal (lignite) fired thermal power plant having capacity of 160 MW is taken into consideration and the impact of condenser pressure, moisture content of lignite, excess air coefficient, efficiency of turbine pressure and heater numbers on power plant thermal efficiency is investigated. It is aimed to determine performance losses of each equipment by means of the thermodynamics and economic analysis. In this scope, it is expected that the power plant operator will be able to evaluate the reduction potential of equipment performance losses and ensure more effective use of the power plants by correctly planning the maintenance and rehabilitation needs and times. In the calculations, the boiler efficiency was determined with EN 12952-15 standard (indirect method) since this method has higher accuracy in coal fired boilers. It is seen that the condenser pressure and excess air coefficient increments have not significant impact on power plant efficiency compared to moisture content of lignite, excess air coefficient, efficiency of turbine pressure and heater numbers. The significant effect is observed for fuel moisture content which rises from 22% to 47% and the power plant efficiency falls from 40% to 28%. The variation of the power plant thermal efficiency in case of failure of heaters is investigated and the power plant efficiency has decreased from 40.17% to 36.09% when the pre-heaters are no longer in to be in use because of any reason. In addition, revenue losses are estimated for each main equipment efficiency reduction for better use of power plant capacities and electricity lowering production costs.

Thermodynamic analysis of an advanced adiabatic compressed air energy storage system integrated with a high-temperature thermal energy storage and an Organic Rankine Cycle

Advanced adiabatic compressed air energy storage (AA-CAES) system has drawn great attention owing to its large-scale energy storage capacity, long lifespan, and environmental friendliness. However, the performance of the air turbine during the discharging process is limited by the low temperature of the compression heat. Thus, this study proposes an integrated AA-CAES system incorporating high-temperature thermal energy storage and an Organic Rankine Cycle (ORC). The high-temperature thermal energy storage is introduced to heat the discharging compressed air to enhance the air turbine performance, and the Organic Rankine Cycle is integrated to utilize the waste heat. Notably, two preheaters are deployed in a special tandem to recover the heat from the air exiting the turbine and the water exiting the hot water tank, respectively. This paper develops a thermodynamic model to simulate the proposed system, assessing the effects of heat storage temperature, ambient temperature, and inlet conditions of the air turbine on performance metrics, including exergy efficiency and exergy destruction. The simulation results indicate that, compared to thermal oil and Hitec salt, employing solar salt as the heat storage medium for the solar thermal collection and storage unit yields the best performance. The energy storage efficiency, roundtrip efficiency, exergy efficiency, exergy conversion coefficient, and energy storage density of this system are 115.6 %, 65.7 %, 78 %, 79.4 %, and 5.51 kWh/m3, respectively. Exergy analysis reveals that the exergy efficiency of interheaters (IH) is the lowest at 76.7 %, while air turbines (ATBs) exhibit the highest exergy efficiency at 91.2 %. Moreover, due to the irreversible processes of compression, expansion, and throttling, ATBS, compressors, and throttle valves collectively contribute to an exergy destruction rate as high as 79.2 %. The parameter analysis demonstrates that low ambient temperature, high inlet temperature, and high inlet pressure of the air turbine enhance energy storage performance.

Large eddy simulations of the turbine vane pressure side film cooling flows of cylindrical and fan-shaped holes with a saw-tooth plasma actuator

Large eddy simulations were conducted to study the film cooling performance of turbine pressure side with cylindrical hole, fan-shaped hole and saw tooth plasma actuator (STPA). A detailed analysis of the time-averaged film cooling flows was made. The results showed that the dual control effects of the combined design of the fan-shaped hole with the STPA reduced the exit momentum and blowing off effect of the jet flow, remaining the jet flow close to the pressure side. The combined design also effectively weakened the entrainment effects of counter rotating vortex pair (CRVP) and enlarged cooling film coverage. Therefore, the spanwise averaged cooling efficiency was improved more than 30% in comparison to the cylindrical hole, but the fan-shaped hole caused a 23.9% increase in aerodynamic loss, and the STPA had few additional aerodynamic losses. Subsequently, the instantaneous film cooling flows were analyzed, the combined design suppressed the evolution processes of the vortex rings in the near-hole region, and the coherent structures in the far downstream region were decreased in size, affecting the mixing process of coolant and gases. The CRVPs were noticeably elongated along the pressure side and moved downstream periodically over time. The present study highlighted the superiority of the combined design to improve the turbine vane cooling performance.

Investigations on rigid–flexible coupling multibody dynamics of 5 MW wind turbine

AbstractThe flexible system of wind turbines refers to the components such as blades, towers, and rotor shafts that are subjected to external forces such as wind loads, inertial forces, and gravity during operation, resulting in deformation and vibration. This paper proposes that dynamic response analysis of the flexible system, through the response data, put forward improvement measures to improve the stability. The flexible dynamic response of wind turbine was analyzed. The fluid dynamics and structural dynamics of wind turbine are analyzed by the finite element method, and the flow chart is combined to get the wind turbine velocity, pressure, shear stress, and vorticity distribution nephogram. The results provide a reference value for monitoring structural state dynamics parameters of large wind turbines. Wind power generation technology is relatively mature, and its proportion in the field of power generation is gradually increasing. Wind energy is inexhaustible and can occupy a place in the development and utilization of new energy for a long time. This study provides an important reference for determining the dynamic parameters of wind turbine operation and improves the stability and reliability of wind turbine operation. The results provide a reference value for monitoring structural state dynamics parameters of large wind turbines.

Use of zero-dimensional modelling to predict performance and assess feasibility of solid oxide fuel cell-gas turbine hybrid system

This study looks at a steady state and a dynamic model of a solid oxide fuel cell-gas turbine (SOFC-GT) system. The steady state model is used to perform a sensitivity analysis of the system’s electrical efficiency to design parameters at design point, while the dynamic model is used to predict key performance indicators across the operating range of the system. Electrical efficiency at the design point was found to be most sensitive to gas turbine pressure ratio and SOFC temperature. Power output was increased from the baseline to peak on the dynamic model and peak electrical efficiency was found to be 0.61 at 58% load.

Dual-Loop μ-Synthesis Direct Thrust Control for Turbofan Engines

As the power unit of an aircraft, the engine’s primary task is to provide the demanded thrust, making research on direct thrust control crucial. However, being a complicated multivariable system, effective multivariable direct thrust control methods are currently lacking. The main content of this paper is threefold. First, it presents a dual-loop multivariable μ-synthesis direct thrust control scheme for mixed-exhaust low-bypass turbofan engines, which is a typical rotationally symmetric machine. The scheme adjusts fuel flow for thrust control and nozzle area to control the turbine pressure ratio, ensuring thrust tracking while maintaining the engine’s key parameters within safe limits. Second, a fast, accurate thrust estimation algorithm based on aerodynamic thermodynamics and component characteristics is introduced. At last, considering the model uncertainties between off-design and design points, a weight function frequency shaping μ-synthesis control design method is proposed to address internal loop coupling and external disturbance suppression. Nonlinear simulations within the flight envelope show that μ-synthesis direct thrust control achieves robust servo tracking and disturbance rejection, with a maximum steady-state thrust error of no more than 0.1%, and the key parameters are not over their safety boundaries.

Sustainable freshwater/energy supply through geothermal-centered layout tailored with humidification-dehumidification desalination unit; Optimized by regression machine learning techniques

The application of regression machine learning techniques is crucial for the analysis and optimization of energy systems based on geothermal energy to produce freshwater, power, and heating. This study applied regression machine learning techniques to investigate and optimize a geothermal tri-generation energy system that combines double-flash geothermal energy, humidification-dehumidification desalination, and transcritical carbon dioxide Rankine cycle. The goal was to produce freshwater, power, and heating. The algorithms performed remarkably well, with R-squared values surpassing 96 %. It is worth mentioning that for specific parameters like freshwater production, heating capacity, and efficiency, the R-squared values exceeded an impressive 99 %. The optimum conditions include maintaining a Rankine pressure ratio of 3, a mass flow rate of 30 kg/s, a geothermal temperature of 220 °C, and a turbine pressure ratio of 2.2. By following these ideal parameters, it is possible to achieve the highest level of system performance. This will lead to the production of 7.88 kg/s of freshwater, the generation of 1283 kW of power, a heating capacity of 30.8 kg/s, and an impressive system efficiency of 24.98 %. The findings reveal that the integration of regression machine learning algorithms in geothermal energy systems for freshwater, power, and heating production holds great promise for a sustainable and efficient future.

Numerical Investigation of Performance and Flow Characteristics of Francis Turbine in Part Load Condition

Abstract Due to the complexity of the flow phenomena inside Francis turbines, it is very time-consuming and expensive to determine their performance and flow characteristics under different operating conditions through model tests and field measurements. The use of computational fluid dynamics (CFD) to improve turbine design and performance is a more cost-effective alternative to traditional methods of forecasting flow characteristics in different flow domains across the whole turbine channel. The performance and flow characteristics of the turbine under various part load working circumstances are studied by numerical simulations employing the shear stress transfer SST (k − ω) turbulence model. Four different operating conditions from 50%,70%,80% and 100% of the maximum and minimum power were analyzed, and the flow characteristics across the entire turbine channel were investigated in detail. The study results shows the calculated efficiencies of four operating condition have good agreement with measured ones, and the efficiency differences between numerical simulation and measurement are below 0.44%. Visualization of velocity and pressure in the whole Francis turbine shows that output torque, output power, and performance are in good agreement with experiment results. This study’s findings can be utilized to improve the design, efficiency, and hydraulic stability of Francis turbines.

Modeling and optimization of hybrid geothermal-solar energy plant using coupled artificial neural network and genetic algorithm

Avoiding solar thermal energy storage reduces efficiency in hybrid solar-geothermal energy systems, making them impractical. To address this challenge, a synergistic approach involves the integration of these resources in the construction of hybrid power plants. An experiment is conducted with five independent variables: evaporator temperature, separator pressure, inlet pressure of turbine 2, effectiveness of vapor generator 1, and desalination mass ratio. Unlike most energy systems that rely on a single optimization pattern, this study utilizes response surface methodology (RSM) to design and gather data through simulation. Additionally, an artificial neural network (ANN) is employed alongside RSM to establish mappings from independent variables to response variables, including thermal efficiency and levelized cost of product. The selection of objective functions derived from ANN is predicated on their commendable performance, denoted by an R-squared value of 1. Furthermore, a cost function is formulated with the dual aims of maximizing thermal efficiency and minimizing the levelized cost of product. This function is subsequently optimized through the application of genetic algorithms (GAs). The findings elucidate that specific parameter values—namely, a desalination mass ratio of 2.43, separator pressure of 455.77 kPa, effectiveness of vapor generator 1 of 0.82, inlet pressure of turbine 2 of 12000 kPa, and evaporator temperature of −11.51 ℃—conducive to the optimal condition are identified, yielding a thermal efficiency of 30.47% and a levelized cost of product of 13.04 $/GJ. This endeavor is anticipated to furnish an algorithmic framework not only for modeling hybrid plants but also for optimizing electrical power generation processes.

A novel pathway for achieving efficient integration of SOFC/SOEC and addressing photovoltaic duck curve challenge

This study presents a novel method that directly integrates SOFC oxy-fuel combustion and SOEC co-electrolysis to tackle the challenges of high-energy consumption of SOFC/SOEC integration and photovoltaic duck curve. To explore the viability of this method, a biomass-solar complementary scenario is pioneered and its performance is assessed from thermodynamic and economic standpoints. The results show that the studied scenario achieves CHP and exergy efficiencies of 50.67% and 43.68% with the corresponding total product cost rate (Ċtot) of 45.44 $/h and the levelized cost of products (cp) of 14.61 $/GJ under the design conditions. The system annually produces 17485 tons of freshwater and 1432 tons of oxygen. Exergy analysis identifies the afterburner (AB-II) and supercritical CO2 recompression power cycle (SCRPC) as the primary contributors to exergy destruction with 381.74 kW and 343.62 kW, which alone account for over half of the total irreversibility. Increasing the isentropic efficiency of gas turbine (ηGT) and SOFC operating pressure (Pop) improves the overall thermodynamic performance, but enhancing SOFC current density and gasification temperature has adverse effects. Across varying Pop andηGT, there exist optimal Ċtot (44.83 $/h) and cp (14.47 $/GJ), which are obtained at ηGT of 80% and Pop of 600 kPa, as well as at ηGT of 87.14% and Pop of 800 kPa, respectively. This research can provide a reference for the development of cyclic energy storage technologies and the low-carbon transition in the energy fields.

Performance evaluation of multicombustor engine for Mach3+-Level propulsion system

Turbine-based combined cycles are widely considered as a propulsion system for hypersonic vehicles. The inadequate performance of turbine-based engines has resulted in thrust traps, thereby limiting the development of turbine-based combined cycles. To satisfy the performance requirements over a wide speed range, a novel Mach 3+-level multicombustor engine is proposed, and its performance potential is investigated, where an intermediate bypass burner reheats the core airflow to generate more cycle work and the second bypass duct heated by a bypass afterburner provides the main source of the engine thrust at high Mach numbers. Results show that the multicombustor engine extends the flight envelope from Mach 2.5 to 3.5 and increases the thrust by 32% compared with the conventional engine. The application of an intermediate bypass burner reduces the turbine pressure ratio by 43%, thereby reducing the number of turbine stages. The concept of a multicombustor engine is promising for designing the power systems of hypersonic vehicles.

Presenting new artificial intelligence techniques for finding optimum performance of solar chimney power plant

The various applications of solar energy have progressed significantly over recent decades. In this paper, finding the optimum performance criteria of a SCPP is studied. The mathematical modelling of 1-D flow is written and the optimum performance is determined for each group of geometric and environmental variables including the angle of collector roof (β), chimney divergence (α) and ambient wind velocity (Va ). In addition, different artificial intelligence techniques including regression tree, genetic programming and a novel method named trended regression tree are applied to find optimum performance conditions at any arbitrary group of α, β and Va . Results indicate that maximum power output (Pt ) and associated mass flow rate ( m ˙ ) increase with increasing chimney divergent angle and wind velocity at a constant collector roof angle. Comparing the obtained results of artificial intelligence techniques shows that trended regression tree method predicts the optimum conditions of SCPP better than other methods. Genetic programming is used to present fitted algebraic functions on Pt and m ˙ and the ratio of turbine pressure drop to pressure potential (PR). Results demonstrate the algebraic relation of PR estimates the PR accurately at each group of variables.