Pelton turbines are widely used in high-head hydropower applications because of their high efficiency and reliable hydraulic performance. In this study, an existing Pelton turbine runner was used as the reference design, and an optimized runner was developed by modifying key geometric parameters, particularly the pitch circle diameter and bucket width. The reference runner had a pitch circle diameter of 312.5 mm and a bucket width of 90.3 mm, whereas the optimized runner was designed with a pitch circle diameter of 450 mm and a bucket width of 130 mm. The novelty of the work lies in the direct evaluation of a geometrically modified runner against its reference design under similar operating conditions while resolving the transient jet–bucket interaction through a VOF based numerical approach. Experimental measurements and three-dimensional simulations were used to analyze hydraulic efficiency, torque response, pressure development, and internal water-sheet behavior. The optimized runner demonstrated a marginal efficiency increase from 91.7% to 91.8%. This small difference should be interpreted cautiously, as it may lie within the range of numerical and experimental uncertainty. Accordingly, the main contribution of the study is not a significant efficiency improvement, but a clearer physical understanding of how runner geometry, jet diameter, and nozzle number jointly influence flow guidance and hydraulic loading. The results provide useful guidance for Pelton runner refinement, multi-nozzle matching, and future optimization studies involving coupled hydraulic, cavitation, and structural reliability assessments.
The inter-deck clearance height (IDH), defined as the vertical distance between decks, is a key parameter in the aerodynamic design of double-deck bridges. This parameter governs both global aerodynamic characteristics and the allocation of wind loads across different subcomponents (top/bottom decks, windward/leeward trusses) of the girder, yet its effects remain underexplored. This study examines the effects of IDH using five double-deck girders with varying IDH, combining wind tunnel tests and Computational Fluid Dynamics (CFD) simulations. Results show that the drag and lift (absolute) coefficients increase with IDH, notably at high angles of attack. For all investigated girders, roughly half of the average drag is sustained by the windward truss. Furthermore, as the IDH increases, the mean drag force borne by the leeward truss increases, whereas the share carried by the top/bottom decks decreases correspondingly; meanwhile, the primary contributor for the fluctuating drag force shifts from the leeward to the windward truss. In contrast, both the mean and fluctuating lift force are primarily carried by the decks, with the trusses having a negligible contribution, and this partitioning pattern remains unchanged regardless of IDH. Furthermore, Dynamic Mode Decomposition (DMD) reveals that increasing IDH enhances flow instability near the windward truss while suppressing vortex development in the leeward region, leading to a shorter downstream persistence of wake structures. These findings provide insights into the underlying flow mechanisms and offer guidance for the aerodynamic selection and wind-resistant design of double-deck bridges.
Ultrashort pulse laser machining is pivotal for fabricating aero-engine turbine blade film-cooling holes because of its superior performance; however, machining residues can block the laser, reduce efficiency, and promote recast layer formation, thereby deteriorating component performance. Gas-blowing aids residue removal, but traditional symmetric nozzles easily form reverse flow vortices at hole entrances in high-aspect-ratio micro-hole machining, leading to secondary residue accumulation and reduced machining efficiency. This study numerically simulates coaxial auxiliary gas-blowing flow fields of symmetric and asymmetric nozzles, investigating the effects of their structural parameters. The results show that the symmetric structure has a stable flow field but limited residue removal improvement, while the asymmetric structure achieves directional flow-field optimization. Opposite-direction angles form a "swirling jet", which suppresses reverse flow vortices, expands the high-velocity region and enhances the flow flushing capacity. Compared with the same-direction angle configuration, the opposite-direction configuration reduces stable entrance recirculation and improves axial flow penetration into the micro-hole. The optimal parameters are m = 2 mm, n = 2 mm, θ1 = 10°, and θ2 = -10°, (m is defined as the throat length, n as the divergent-section length, and θ1 and θ2 as the inclination angles of the two opposite sides of the asymmetric divergent section.) which achieves the maximum flow flushing capacity. Under this condition, the total pressure loss across the shock structure is reduced to 36.44%, indicating weaker shock-induced energy dissipation and improved momentum transport inside the micro-hole. This study provides theoretical support for the high-precision machining of high-aspect-ratio film-cooling holes.
This study investigates the aerodynamic impact of passive blade slots on the unsteady flow dynamics of a Darrieus vertical-axis wind turbine (VAWT) operating at low tip speed ratios. A two-dimensional URANS-based numerical investigation using the k–ω SST turbulence model was performed to analyze the creation of slot-induced internal jets and their interaction with the surrounding flow field. An energy-based Jet Strength Index (JSI) was introduced to quantify the momentum injection produced by the slot. The results revealed that the pressure difference between the pressure and suction sides of the blade naturally generated internal jets that injected momentum into the boundary layer and significantly modified the vortex formation. These jets developed primarily on blades 1 and 4, where they weakened the separation-induced vortices identified using the λ₂ vortex criterion and contributed to delaying the dynamic stall. The optimized slotted configuration led to a substantial aerodynamic improvement, with the torque coefficient increasing by up to 89% within the low tip-speed ratio range of λ = 1–2 for a free-stream velocity of 10 m/s. Spectral analysis of the unsteady loads indicated a rotation-driven vortex detachment characterized by a Strouhal number of St ≈ 0.07 and a reduced frequency of k ≈ 0.217 for λ = 1,25. Furthermore, near-wake analysis at λ = 2 primarily weakens separation-induced vortices and reorganizes their spatial distribution in the near wake, leading to reduced vortex strength, delayed breakdown, and more stable wake development, providing new insights into passive flow control mechanisms for enhancing VAWT performance.
Effect of gas composition on aerodynamic performance and internal flow in ethane oxidation dehydrogenation (ODH) centrifugal compressors is investigated. Although inert gases are widely used to reduce explosion risk in ODH processes, the effects of multi-component inert gases on compression thermodynamics and internal flow structures are not fully understood. The novelty of this work lies in a systematic quantification of how different inert-gas compositions change the evolution of internal flow, thereby influencing the loss mechanisms and isentropic efficiency in a high-pressure ODH environment. Three gas mixtures are evaluated: Mixture 1 (C2H6 55%, O2 15%, CO2 15%, 10%, H2 5%), Mixture 2 (C2H6 55%, O2 18%, CO2 10%, 7%, He 5%, N2 5%), and Mixture 3 (C2H6 53%, O2 18%, CO2 8%, N2 15%, 6%). Numerical simulations are conducted using a steady-state mean streamline model coupled with the SST turbulence model. The isentropic efficiency varies non-monotonically with mass flow rate, staying nearly constant from 6.5 to 7.1 kg/s and then decreasing markedly. Detailed flow analysis shows that low-density gases such as H2 and He promote leakage flow and flow separation, increasing energy dissipation; in contrast, N2 reduces separation-related losses. Compared with Mixture 1, the isentropic efficiency increases by 21.65% for Mixture 2 and further improves by 30.25% for Mixture 3 (a cumulative increase of 8.6% over Mixture 2). Overall, the results provide quantitative trends and mechanistic understanding of multi-component inert-gas effects on compressor performance, which can help researchers evaluate and design safer ODH compression systems and motivate further studies under other inert-gas combinations and operating conditions.
