Search Results (212)

The blade outlet angle is a critical design parameter of vortex pump impellers, exerting a significant influence on the pump’s hydraulic performance and internal flow characteristics. In this study, numerical simulations combined with experimental validation were conducted to investigate a vortex pump, with three impellers featuring blade outlet angles of 50°, 60°, and 65° analyzed based on the SST k–ω turbulence model. To quantify irreversible energy losses, entropy production theory was adopted, while the Liutex method was utilized to characterize rigid-body vorticity. The results demonstrate that increasing the blade outlet angle leads to a reduction in head under both small-flow-rate and design-flow-rate conditions, impairs flow uniformity, strengthens vortex structures, and elevates total entropy production—with turbulent dissipation being the dominant contributor to energy losses. Additionally, larger outlet angles enhance the sensitivity of internal flow structures to off-design operating conditions. These findings offer valuable guidance for the optimization of impeller design and the development of energy-efficient vortex pumps. Full article

This study aims to evaluate the robustness of the well proved Aungier meanline model, originally developed for air and steam turbines, on Organic Rankine Cycles (ORC) turbines. More specifically, the study focuses on two pure-impulse axial turbines with partial admission and using various working fluids, including zeotropic mixtures. To this end, a three-part numerical model was developed to adapt this type of meanline model to a prediction-oriented methodology rather than a design-oriented one. Using inlet and outlet pressures, inlet temperature, and rotational speed as inputs, the model provides the resulting mass flow rate through the turbine as well as its performance characteristics. The model predictions are compared against an extensive experimental dataset comprising more than 300 operating points obtained with three pure fluids—R1233zd(E), NOVEC™ 649, and HFE7000—and three zeotropic mixtures. The model demonstrates good predictive accuracy over a wide range of operating conditions, including very low velocity ratios corresponding to severe off-design operation. Specifically, the mass flow rate is predicted with a Mean Absolute Percentage Error (MAPE) ranging from 1.23% to 3.31%, depending on the working fluid. Furthermore, over an experimental specific work range of 5 to 15 kJ/kg, the predicted numerical work exhibits a MAPE of 7.04% for 102 experimental points corresponding to the main dataset (R1233zd(E)). Finally, the total-to-total efficiency is predicted within ±4 efficiency points, showing a very good trend over a velocity ratio range from 0.06 to 0.36. Full article

Solar-aided power generation offers a pathway to reduce the carbon dioxide emissions from existing coal-fired plants. This study addresses the gap in comparing different solar integration modes by conducting a thermo-economic analysis of a 600 MW coal-fired system retrofitted with a solar tower. Four integration modes were designed and rigorously compared, encompassing series and parallel configurations at either the high-exergy reheater or the lower-exergy economizer. A detailed thermodynamic model was developed to simulate its off-design and annual performance. The results showed that integration at the primary reheater outperformed the economizer integration. Specifically, the parallel configuration at the primary reheater (Mode II) achieved the highest annual solar-to-electricity efficiency of 18.43% at a thermodynamically optimal heliostat field area of 125,025.6 m². Economic analysis revealed a trade-off, with the minimum levelized cost of energy (LCOE) of −0.00929 USD/kWh for Mode II occurring at the economically optimal area of 321,494 m² due to greater coal and emission savings. Sensitivity analysis across two other locations confirmed that the annual solar-to-electricity efficiency and LCOE are directly influenced by solar resource quality, but the thermodynamically optimal and economically optimal heliostat field area remain consistent. This work demonstrates that parallel integration with the primary reheater presents a favorable and practical configuration, balancing high solar-to-electricity conversion efficiency with favorable economics for hybrid solar–coal power plants. Full article

Systematic investigation into the structural integrity of adjustable ejectors, particularly concerning thermal–fluid–structural (TFS) coupling, is currently lacking. Utilizing the Workbench platform, this study performs unidirectional steady-state TFS coupling numerical simulation of the adjustable air ejector under off-design conditions to systematically analyze its internal flow characteristics and structural mechanical responses across various needle openings. The results show that thermal load is the dominant factor governing the ejector’s structural stress and deformation. The overall deformation is primarily characterized by axial elongation, with the maximum thermal deformation localized at the ejector’s exit section. The nozzle exit is identified as the primary structural weak point, exhibiting the highest local stress, which peaks at 196.8 MPa when the needle opening is minimized. Shock train structures extending from the nozzle’s divergent section into the mixing chamber, coupled with the axial displacement of the needle, significantly influence the ejector’s thermal deformation and thermal stress. Based on the thermally dominated stress mechanism identified, this study proposes a composite nozzle design utilizing a nickel-plated Invar alloy substrate. This material fully leverages Invar alloy’s low thermal expansion to mitigate thermal stress and deformation while the nickel plating ensures corrosion resistance, thereby significantly enhancing the nozzle’s mechanical properties and operational reliability in thermal environments. The findings of this analysis are applicable to off-design evaluations under unidirectional steady-state coupling conditions, providing a valuable reference for the structural design and strength optimization of similar ejectors operating in high-temperature, unsteady environments. Full article

To address the scientific gap concerning optimal urban wind turbine morphology, this work presents an experimental performance comparison between two small-scale wind turbine designs: a conventional three-blade horizontal-axis wind turbine (HAWT) and a duct-equipped Ayanz-inspired screw-blade turbine. Both configurations were tested in a controlled wind tunnel under steady and transient wind conditions, including synthetic gusts designed to emulate urban wind patterns. The analysis focuses on power output, aerodynamic efficiency (via the power coefficient $C_P$), dynamic responsiveness, and integration suitability. A key novelty of this study lies in the full-scale experimental comparison between a non-conventional Ayanz screw-blade turbine and a standard three-blade turbine, since experimental data contrasting these two geometries under both steady and gusty urban wind conditions are extremely scarce in the literature. Results show that while the three-blade turbine achieves a higher $C_P$ peak and greater efficiency near its optimal operating point, the Ayanz turbine exhibits a broader performance plateau and better self-starting behavior under low and fluctuating wind conditions. The Ayanz model also demonstrated smoother power build-up and higher energy capture under specific gust scenarios, especially when wind speed offsets were low. Furthermore, a methodological contribution is made by comparing the $C_P$ vs. tip speed ratio λ curves at multiple wind speeds, providing a novel framework (plateau width analysis) for realistically assessing turbine adaptability and robustness to off-design conditions. These findings provide practical insights for selecting turbine types in variable or urban wind environments and contribute to the design of robust small wind energy systems for deployments in cities. Full article

Currently, the mainstream source of electrical energy generation is fossil fuels. The unpredictable behavior of these fuels produces harmful byproducts, such as fuel gases, and leads to damage in the surrounding environment. New trends, with a focus on energy efficiency and environmental protection in the power generation sector, will alter the character of this industry. This work presents an innovative approach to addressing the challenges facing the cogeneration plant sector by integrating back-pressure turbines with the Kalina power cycle. This combination aims to produce electricity and useful thermal energy instantaneously from a single fuel source, often encountering efficiency and operational challenges. The proposed combined system enhances the advantages of both the back-pressure turbine plant and the Kalina power cycle while enhancing overall efficiency. A thermodynamic energy analysis is conducted for all components and systems under various operating conditions. The obtained results indicate that the proposed cycle possesses thermal efficiency with a range of 36–39.5% and specific fuel consumption with a range of 0.214–0.233 kg/kWh under both design and off-design conditions. Through comprehensive thermodynamic analyses, this work provides insight into the viability and advantages of integrating the back-pressure turbine with the Kalina power cycle, proposing a promising alternative for cogeneration power plants seeking enhanced performance and sustainability. Full article

In the present work, off-design operating condition is considered to be the ability of the turbine to operate down to 50% to 20% of its nominal intake air flow rate. An important consequence of these off-design points is the change in the inlet incidence angle, which varied from nominal to −20°. Tests were performed on a seven-blade rotor cascade with platform cooling through an upstream slot simulating the stator-to-rotor interface gap. To model the impact of rotation on purge flow injection, a set of fins were installed inside the slot to give the coolant flow a tangential direction. Different cascades’ off-design operating conditions were tested, covering downstream velocity values up to Ma_2is = 0.55, with two inlet turbulence intensity levels of 0.6% a and 7%. A thermal measurement campaign was conducted with the Thermochromic Liquid Crystal technique to measure the adiabatic film cooling effectiveness at various coolant-to-main-flow mass flow ratios, different incidence angles, mainstream Mach numbers, and turbulence levels. The results describe the complexity of the turbine operating under off-design operating conditions, relating the improvement in the platform thermal protection to the reduced secondary-flows activity induced by negative incidence. Full article

In recent years, the design priorities of modern marine propellers have shifted from maximizing efficiency to minimizing vibration-induced noise emissions and improving structural durability. However, an optimized design does not necessarily ensure optimal performance across the full operational range of a vessel. Due to operational constraints such as reduced docking times and regional speed regulations, propellers frequently operate off-design. This deviation from the design point leads to periodic turbulent boundary layer separation on the propeller blades, resulting in increased unsteady pressure fluctuations and, consequently, elevated hydroacoustic noise emissions. To mitigate these effects, bio-inspired modifications have been investigated as a means of improving flow characteristics and reducing pressure fluctuations. Tubercles, characteristic protrusions along the leading edge of humpback whale fins, have been shown to enhance lift characteristics beyond the stall angle by modifying the flow separation pattern. However, their influence on transient pressure fluctuations and the associated hydroacoustic behavior of marine propellers remains insufficiently explored. In this study, we apply the concept of tubercles to the blades of a hubless propeller, also referred to as a rim-drive propeller. We analyze the pressure fluctuations on the blades and in the wake by comparing conventional propeller blades with those featuring tubercles. The flow fields of both reference and tubercle-modified blades were simulated using the Stress Blended Eddy Simulation (SBES) turbulence model to highlight differences in the flow field. In both configurations, multiple helix-shaped vortex systems form in the propeller wake, but their decay characteristics vary, with the vortex structures collapsing at different distances from the propeller center. Additionally, Proper Orthogonal Decomposition (POD) analysis was employed to isolate and analyze the periodic, coherent flow structures in each case. Previous studies on the flow field of hubless propellers have demonstrated a direct correlation between transient pressure fluctuations in the flow field and the resulting noise emissions. It was demonstrated that the tubercle modification significantly reduces pressure fluctuations both on the propeller blades and in the wake flow. In the analyzed case, a reduction in pressure fluctuations by a factor of three to ten for the different BPF orders was observed within the wake flow. Full article

As an energy-saving fluid machinery component, the ejector holds significant potential for promoting energy conservation and sustainable transformation in aerospace. This review synthesizes recent progress, identifies persistent challenges, and outlines future directions for ejector technology in this field, addressing a gap in existing reviews. (1) In aero-engine systems, performance faces constraints from high-speed compression effects and flow losses. These systems require optimized design across a wide range of speeds. A mixed configuration incorporating a blade mixer achieved a 5~7% thrust increase under static conditions. (2) In high-altitude test facilities, transient start-up and flow instability under off-design conditions demand more precise models and control strategies. An alternative solution using a second throat exhaust diffuser reduced the start-up time by 50~70%. (3) In rocket-based combined cycle engines, development is limited by thermal choking, mode transition, and combustion-flow coupling issues. Optimization of the rocket layout and geometric throat increased the bypass ratio in ejector mode by 35% and improved the specific impulse by 12.5%. Future efforts should focus on constructing multi-physics coupling numerical simulation models for ejectors, analyzing unsteady flow behavior and thermal effects within ejectors, and developing performance optimization strategies based on intelligent control. These approaches are expected to enhance the engineering applicability and system efficiency of ejector technology in the aerospace field, which is increasingly focused on energy conservation and sustainable transformation. Full article

Onboard models serve as the foundation for the advanced control and fault diagnosis of aero-engines. Currently, to address the issues of high computational complexity and insufficient real-time performance in component-level aero-engine models, three improvement methods are proposed: constructing the Jacobian matrix along the reverse flow path to avoid redundant calculations; reducing the number of initial guess variables and equations in the engine co-working system through aerothermodynamic analysis, thereby achieving dimensionality reduction in the nonlinear equation sets; and leveraging the minimal variation in Jacobian inverse elements across the full flight envelope to replace them with fixed gains, thus simplifying transient performance calculations. Simulation results demonstrate that, compared to the regular Newton-Raphson method, the reverse flow method reduces the steady-state, regular transient, and small-step transient calculation time by 27.6%, 33.9%, and 30.8%, respectively, with a maximum relative error within 1.6%; the dimensionality reduction method for equations cuts the steady-state, regular transient, and small-step transient calculation time by 20.1%, 11.4%, and 11.8%, with a maximum relative error within 1.4%; and the constant Jacobian matrix inverse method reduces the calculation time by 50.9% during full flight envelope transient performance simulation, with a maximum relative error below 1.6%. All methods improve real-time performance under rated operating conditions. However, only the reverse flow method preserves both high efficiency and accuracy under off-design operating conditions. Full article

Vertical axial-flow pumps with bidirectional passages are widely used in applications requiring flow reversal. However, their unique inlet geometry often leads to asymmetric impeller inflow conditions. This study investigates the internal flow behavior and pressure pulsation characteristics of a vertical bidirectional axial-flow pump under design, critical stall, and deep stall conditions using unsteady Reynolds-averaged Navier–Stokes simulations combined with Fast Fourier Transform and wavelet analysis. Results show that the pump reaches peak efficiency at the design point, with critical and deep stall occurring at 0.6 Q_des and 0.5 Q_des, respectively. The head at the deep stall condition shows a further drop of 7.51% compared to the critical stall condition. This progressive performance degradation is attributed to vortex-induced blockage: it initiates with the intensification of the tip leakage vortex and evolves into large-scale separation vortices covering the suction surface under deep stall—a mechanism distinctly influenced by the bidirectional inlet’s stagnant water zone. Inlet asymmetry, reflected by a normalized velocity coefficient (V_n) below 0.6 in the stagnant water zone under design flow, is partially mitigated during stall due to flow confinement. Pressure pulsations at the blade leading edge are dominated by the blade passing frequency (BPF), with amplitudes under critical stall about 3.2 times those at design conditions. At the impeller outlet, critical stall produces a mixed dominant frequency (shaft frequency and BPF), whereas deep stall yields the highest pulsation amplitude (BPF ≈ 4.8 × the design value) resulting from extreme passage blockage. These findings clarify how bidirectional-inlet-induced vortices modulate stall progression and provide theoretical guidance for enhancing the operational stability of such pumps under off-design conditions. Full article

Hydrogen pipeline compression is essential for H₂ transportation, with low molecular mass limiting achievable pressure ratios. Existing meanline-based studies offer little guidance on 3D-geometry generation, while existing CFD analyses provide limited insight into secondary flows, loss mechanisms, and off-design behavior. An in-house tool combining meanline, streamline-curvature, and genetic algorithms generates CAD-ready geometries, analyzed with steady 3D CFD from surge to choke. In the absence of H₂ experimental data, validation on an air compressor showed CFD errors of 1% in pressure ratio and 2% in isentropic efficiency. Simulations of the H₂ compressor reveal that tip-leakage vortices dominate rotor-exit nonuniformity and mixing losses. Two potential stall triggers are identified: (1) incidence-induced separation at the leading-edge hub corner; (2) vaneless diffuser rotating stall, as hub separation tendencies seem connected to reduced static-pressure recovery. However, a deeper characterization would require advanced unsteady schemes. At choke onset, the incidence reaches −10°, and the relative Mach number at the leading-edge tip is 0.63, indicating a subsonic negative-incidence stall rather than sonic choking. A meanline loss breakdown analysis corroborates CFD by showing that mixing losses and skin friction prevail. Design-improvement areas have been identified to enhance the performance of hydrogen compressors for future energy systems. Full article

Air cycle systems, once largely replaced by vapour-compression technologies due to efficiency concerns, are now re-emerging as a viable and sustainable alternative for highly dynamic thermal applications and excel in ultra-low temperature. By using air as the working fluid, these systems eliminate the need for synthetic refrigerants and comply naturally with evolving environmental regulations. This study presents the conceptual design and simulation-based analysis of a novel air cycle machine developed for advanced automotive testing environments. The system is intended to replicate a wide range of climatic conditions—from deep winter to peak summer—through the use of fast-responding turbomachinery and a flexible control strategy. A central focus is placed on the radial turbine, which is designed and evaluated using a modular, open source framework that integrates geometry generation, off-design CFD simulation, and performance mapping. The study outlines a potential operating strategy based on these simulations and discusses a control architecture combining lookup tables with zone-specific PID tuning. While the results are theoretical, they demonstrate the feasibility and flexibility of the proposed approach, particularly the turbine’s role within the system. Full article

A new quasi-one-dimensional ejector model for the prediction of ejector performance is carried out, which is based on the theory of ideal gas expansion and free layer development. The model is proposed for calculation of the variable area bypass injector (VABI) and ejector nozzle in the variable cycle engine (VCE), both at the design point and off-design point. The internal structure of ejector nozzle is determined based on an analysis of the flow field of the 2D ejector nozzle Computational Fluid Dynamics (CFD) result. The flow during the expansion section is divided into three parts: primary flow, secondary flow, and mixed layer flow. Combined with the growth rate of mixing layer thickness, the calculation methods of ejector nozzle exit parameters under critical working conditions and blocking working conditions are given, and the calculated results demonstrate a strong consistency with CFD results, maintaining relative errors below 3%. This method is used to evaluate the ejector nozzle capacity quickly in the overall design stage, which provides theoretical support for the design of the main bypass system of a variable cycle engine. Full article

This work focuses on modeling the performance of the natural gas-fired Allam cycle under off-design conditions. Key thermodynamic parameters, such as turbine inlet pressure (TIP), turbine inlet temperature (TIT), and turbine outlet temperature (TOT), were evaluated at part-load and varying environmental conditions. In the former case, different control strategies were implemented in the simulation code (Thermoflex^®) to reduce the power output. In the latter case, the impact of ambient temperature (T_amb) on the minimum cycle temperature (T_min) was evaluated. The ultimate goal is to predict the thermal efficiency (η_th) and its decrease due to partial load operation and warm climate, without thermal recovery from the air separation unit (ASU). With the most efficient partial load strategy, η_th decreased from 50.4% at full load to 40.3% at about 30% load, at nominal T_min. The penalty caused by the increase in T_min due to hot weather, up to T_amb = 30 °C, was significant at loads above 60%, but limited to 0.5 percentage points (pp). Full article