Search Results (65)

This study examines the effects of jet Reynolds number (Re) and jet hole diameter (d) on flow and heat transfer in the leading-edge full-impingement cooling channel of a gas turbine nozzle guide vanes (NGV). Experiments via transient liquid crystal and numerical simulations were conducted. Results reveal that the peak Nusselt number (Nu) initially increases and then reaches a fixed value from root to tip in the spanwise direction. The area-averaged Nu presents the descending trend of the shower-head surface, pressure surface, and suction surface. In addition, the bleeding from film holes causes significant local flow acceleration and Turbulence Kinetic Energy (TKE) enhancement of 10.69%, resulting in local heat transfer elevation. The heat transfer enhancement region on both pressure and suction surfaces is inclined towards the shower-head at a 5% span region. Increasing the jet hole diameter (d) results in a decrease in both averaged Nu and TKE on the target surface. Simultaneously, the Nu gradient increases. When d = 1.6 mm, there is a recirculation zone near the hub on the suction surface and a strong crossflow near the hub on the pressure surface. The jet flow on the target surface is bending towards the shower-head. When d = 0.8 mm, the overall heat transfer is highest. However, considering heat transfer uniformity, a jet hole diameter of d = 1.2 mm offers better application. Full article

This study proposes a water-jet guidance–ultrasonic grinding hybrid process for drilling holes in ceramic matrix composites to address issues such as cracking, chipping, thermal damage, and low machining efficiency, thereby achieving high-efficiency, high-quality processing of such components. With final surface quality as the constraint, three methods—water-jet guidance, ultrasonic grinding, and the combined water-jet guidance–ultrasonic grinding—were applied to drill holes in SiC_f/SiC composite materials. The study investigated how different processes and parameters affect hole surface quality and machining efficiency. Results demonstrate that the hybrid process effectively overcomes defects inherent to single-process grinding (crazing, chipping) and laser processing (heat-affected zones, recast layers), while significantly removing surface oxides generated by water-jet-guided machining. The hole diameter deviation (<0.017 mm), hole wall surface roughness (Sa < 1.837 μm), and processing efficiency (5.25 min/hole) achieved by this composite process all outperformed those of either ultrasonic grinding or water-jet-guided processing alone. This composite process significantly enhances both processing efficiency and hole wall quality, providing a viable solution for high-quality, efficient machining of ceramic matrix composite components. Full article

This study investigated twin-propeller-induced scour on sandy seabeds with varying grain sizes (d₅₀ = 0.11, 0.5, and 0.95 mm) through a series of laboratory experiments. The effects of propeller rotation speed (rpm), offset height (y₀), propeller diameter (D_p), and sediment grain size (d₅₀) on scour development were examined. Results indicated that sediment grain size significantly influences scour patterns. A key objective was to develop predictive expressions for primary scour characteristics at equilibrium: maximum scour depth (S_max), scour hole length (L_max), and maximum scour width (B_max). Using a nonlinear regression approach, the proposed expressions demonstrated strong predictive performance. Findings show that equilibrium scour depth increases with higher Froude numbers (F₀) but decreases with larger sediment size (d₅₀) and higher propeller offset (y₀). Additionally, empirical equations were formulated to predict the temporal evolution of scour depth, achieving high correlations with experimental data (R² > 0.97). These results enhance understanding of scour induced by unconfined twin-propeller jets in harbors or navigation channels and provide valuable data for the design and protection of harbor basins. Full article

This research numerically investigates the cooling performance of Diamond-type triply periodic minimal surface (TPMS) networks as a gas turbine effusion cooling layer, augmented with various jet impingement configurations. The study analyzes the internal and external flow characteristics, pressure loss, and overall cooling effectiveness using conjugate heat transfer simulations. The Diamond design is compared to conventional film cooling and micro-hole models within a blowing ratio range of 0.5 to 2.0. The jet hole diameter and jet-to-plate distance are varied to identify an optimal double-wall cooling configuration. The results reveal that the Diamond hole mitigates the strong discharge of coolant, resulting in a more adherent cooling film, which provides excellent surface coverage. While jet impingement enhances internal heat transfer, its contribution to cooling effectiveness is minor compared to the benefit of film coverage. At an equivalent total pressure loss coefficient, the Diamond with impinging jets demonstrates 101% higher cooling effectiveness than the film hole. The thermal-mechanical analysis indicates that the Diamond model exhibits a more uniform distribution of thermal stress and displacement. The average stress is reduced by 44.7% compared to the film hole. This work confirms the TPMS-based effusion as an advanced cooling solution for next-generation gas turbines. Full article

This study deals with the effectiveness of casing-injection for a few squealer tip designs in a turbine stage to mitigate tip leakage penalties. Seventy-two Unsteady Reynolds-Averaged Navier–Stokes (URANS) simulations were conducted. Five factors were examined: number of injection holes, axial position, jet inclination, blowing ratio, and hole diameter. The ideal configuration demonstrated the highest aerodynamic loss reduction compared to the baseline flat tip by 2.66%. The optimal injection scheme was integrated with three tip-rim topologies: complete channel squealer, suction-side partial squealer, and pressure-side partial squealer. The channel squealer enhances the advantageous effects of injection; the injected jets produce a counter-rotating vortex pair that disturbs the tip leakage vortex core, while the cavity formed by the squealer rim captures low-momentum fluid, thus thermally protecting the tip surface. The injection combined with channel squealer had the highest stage isentropic efficiency and the lowest total-pressure loss, thereby validating the synergy between active jet momentum augmentation and passive geometric sealing. The best configuration shows a 2.87% total pressure loss decrement and a 4.49% total-to-total efficiency increment compared to the baseline design. The best configuration not only improved stage efficiency but also achieved a 43.9% decrease in the tip heat transfer coefficient. Full article

Nickel-based superalloys, serving as the preferred materials for hot-end structural components in aerospace engines, pose considerable challenges for the fabrication of high-quality gas film holes on their surfaces due to their inherent high hardness and strength. Water-jet-guided laser processing technology has exhibited notable potential in the realm of gas film hole fabrication; however, its engineering application is hindered by the lack of synergy between processing quality and efficiency. To tackle this issue, this study achieves efficient coupling between a 1064 nm high-power laser and a stable water jet, leveraging a multi-focal water–light coupling mode. Furthermore, an “inside-to-outside” multi-pass ring-cutting drilling strategy is introduced, and the controlled variable method is employed to investigate the influence of laser single-pulse energy, scanning speed, and pulse frequency on the surface morphology and geometric accuracy of micro-holes. Building upon this foundation, micro-holes fabricated using optimized process parameters are analyzed and validated using scanning electron microscopy and energy-dispersive spectroscopy. The findings reveal that single-pulse energy is a pivotal parameter for achieving micro-hole penetration. By moderately increasing the scanning speed and pulse frequency, melt deposition and thermal accumulation effects can be effectively mitigated, thereby enhancing the surface morphology and machining precision of micro-holes. Specifically, when the single-pulse energy is set at 0.8 mJ, the scanning speed at 25 mm/s, and the pulse frequency at 300 kHz, high-quality micro-holes with an entrance diameter of 820 μm and a taper angle of 0.32° can be fabricated in approximately 60 s. The micro-morphology and element distribution of the micro-holes affirm that water-jet-guided laser processing exhibits exceptional performance in minimizing recast layers, narrowing the heat-affected zone, and preserving the smoothness of the hole wall. Full article

Jet electrochemical milling (JECM) offers significant advantages for fabricating fine grooves and slits in thin-walled, low-rigidity, and heat-sensitive metallic materials, such as amorphous alloys, owing to its operational flexibility, lack of material constraints, and superior surface quality. Nevertheless, conventional JECM techniques for groove machining encounter limitations including excessive overcut, restricted ability to produce microstructures with high depth-to-width ratios, and reduced machining accuracy. To address these issues, this study proposes an innovative approach termed the periodically thinning jet electrochemical milling (PT-JECM) method. This method involves initially generating a shallow microgroove through a single pass using the original nozzle diameter, followed by successive milling passes with progressively smaller nozzle diameters based on the preformed groove. Comparative analysis with traditional JECM methods reveals that this strategy significantly improves the etching factor from 1.896 to 4.318, corresponding to a 128% enhancement. Furthermore, it markedly decreases the slot width increase from 275 μm to 1 μm and improves the aspect ratio from 0.51 to 0.83, representing a 63% increase, enabling the precision machining of large aspect ratio holes and slot structures. Full article

Underwater jet scouring is an efficient, flexible underwater dredging technique, yet its complex physical mechanisms and dynamic evolution hinder dredging effectiveness evaluation. Existing studies mostly use empirical formulas and neglect the sediment properties’ influence on scour holes. This study integrates numerical simulation, theoretical derivation, and sediment characteristics to develop a universal model for efficiently predicting underwater jet scour hole morphology, overcoming existing models’ limitations of over-simplifying complex physics and insufficient experimental data alignment. Using CFD–DEM coupling to simulate scouring, it correlates key physical parameters (average/maximum shear rate, average/maximum shear velocity) with jet characteristics (nozzle diameter, velocity, distance) via theoretical derivation and simplifications, validated using multi-condition simulation data. Comparative analysis shows maximum relative errors of 13% for depth and 7% for width, confirming the engineering applicability in scour hole prediction. Full article

Hot water drilling is a drilling method that employs high-temperature and high-pressure hot water jetting to achieve ice melting drilling. Characterized by rapid drilling speed and large hole diameter, it is widely used for drilling observation holes in polar ice sheets and ice shelves. Understanding the hole-enlargement process at the bottom of hot water-drilled holes is crucial for rationally designing the structure of hot water drills. However, due to the complexity of heat transfer processes, no suitable theoretical model currently exists to accurately predict this process. To address this, this paper establishes an experimental platform for hot water drilling and conducts 24 sets of experiments under different drilling parameters using visualization techniques. The study reveals the influence mechanisms of drilling speed, hot water flow rate, hot water temperature, downhole drill shape, and nozzle structure on the hole-forming process at the borehole bottom. Experimental results indicate that the primary hole enlargement occurs near the nozzle, achieving 69–81% of the theoretical maximum borehole diameter. The thermal melting efficiency at the borehole bottom is approximately 80%, with about 20% of the input hot water energy heating the surrounding ice. Under identical hot water parameters, jet shapes and drill shapes exhibit minimal impact on borehole geometry. But the improvement of the jet speed and hot water temperature can accelerate the hole-forming process. Full article

SiC_f/SiC ceramic matrix composite (CMC), a hard and brittle material, faces significant challenges in efficient and high-quality processing of small-sized shapes. To address these challenges, the nanosecond laser was used to process micro-holes in the SiC_f/SiC CMC using a two-step drilling method, including laser pre-drilling in air and laser final-drilling with a water jet. The results of the single-parameter variation and optimized orthogonal experiments reveal that the optimal parameters for laser pre-drilling in air to process micro-holes are as follows: 1000 processing cycles, 0.7 mJ single-pulse energy, −4 mm defocus, 15 kHz pulse-repetition frequency, and 85% overlap rate. With these settings, a micro-hole with an entrance diameter of 343 μm and a taper angle of 1.19° can be processed in 100 s, demonstrating high processing efficiency. However, the entrance region exhibits spattering slags with oxidation, while the sidewall is covered by the recast layer with a wrinkled morphology and attached oxides. These effects are primarily attributed to the presence of oxygen, which enhances processing efficiency but promotes oxidation. For the laser final-drilling with a water jet, the balanced parameters for micro-hole processing are as follows: 2000 processing cycles, 0.6 mJ single-pulse energy, −4 mm defocus, 10 kHz pulse-repetition frequency, 85% overlap rate, and a 4.03 m/s water jet velocity. Using these parameters, the pre-drilled micro-hole can be finally processed in 96 s, yielding an entrance diameter of 423 μm and a taper angle of 0.36°. Due to the effective elimination of spattering slags and oxides by the water jet, the final micro-hole exhibits a clean sidewall with microgrooves, indicating high-quality micro-hole processing. The sidewall morphology could be ascribed to the different physical properties of SiC fiber and matrix, with steam explosion and cavitation erosion. This two-step laser drilling may provide new insights into the high-quality and efficient processing of SiC_f/SiC CMC with small-sized holes. Full article

A reverse-flow combustor has a larger liner surface area due to airflow turning, which complicates flow and cooling control, particularly heat transfer efficiency. Effective heat management is essential for maintaining uniform temperature distribution and preventing thermal gradients. This study explores the impact of axial position and diameter of primary holes on thermal performance and flow dynamics. Results indicate that as the primary holes move toward the dome, the recirculation vortex size decreases, leading to insufficient fuel mixing, a reduction in the high-temperature area in the primary zone, and an increase in the high-temperature area of the middle zone. On the other hand, moving the primary holes downstream enhances fuel mixing, increasing high-temperature areas in the primary zone and reducing them in the middle and dilution zones, thus improving thermal boundary layers and convective heat transfer rates. When the primary hole is moved 10 mm downstream, outlet temperature improves significantly with an outlet temperature distribution factor (OTDF) of 0.21 and a radial temperature distribution factor (RTDF) of 0.16. Additionally, reducing the upper primary hole diameter strengthens jet deflection, improving fuel–gas mixing at the dome and heat transfer to the central region. With a 2.1 mm hole diameter, the temperature gradient decreases, resulting in an OTDF of 0.184 and RTDF of 0.15. Furthermore, as the momentum flux ratio increases, the jet penetration depth initially rises and then stabilizes. Momentum flux ratios between 10.6 and 15.1 significantly affect jet penetration, while further increases result in smaller fluctuations. Higher momentum flux ratios create localized high- and low-temperature zones, reducing outlet temperature distribution quality. The optimal momentum ratio for the reverse-flow combustor, ensuring effective jet penetration and better temperature distribution, is between 10.6 and 14.7, with a corresponding penetration depth of 34.3 mm to 35.1 mm. These findings offer valuable insights for improving reverse-flow combustor design and performance. Full article

This study introduces a novel application of synchrotron X-ray phase contrast imaging to investigate the internal flow dynamics and liquid jet characteristics in a direct injection gasoline nozzle. Using optimized imaging parameters, including a 19 mm insertion gap and a 0.15 ns electron pulse (16 mA), we achieved high-quality visualization of needle motion and in-nozzle flip flow. The results show that cavitation appears rapidly with increasing needle valve lift, transitioning from unstable behavior below 40 µm to stable flip flow at higher lifts. The flip flow characteristics vary between nozzle holes due to differences in inlet angles. Internal flow velocity analysis reveals significant radial and axial gradients, with initial velocity overshoot during injection start followed by stable flow. The presence of flip flow accelerates jet breakup on the flip-contact side, leading to droplet–wall interactions in the counterbore. Different nozzle geometries, particularly hole inlet angle and length-to-diameter ratio, significantly influence jet width and velocity distributions. This comprehensive approach advances our understanding of practical nozzle internal flow dynamics and provides valuable insights for optimizing fuel injection system performance in engines. Full article

The electrochemical cutting technique, utilizing electrolyte flushing through micro-hole arrays in the radial direction of a tube electrode, offers the potential for cost-effective and high-surface-integrity machining of large-thickness, straight-surface structures of difficult-to-cut materials. However, fabricating the array of jet micro-holes on the tube electrode sidewall remains a significant challenge, limiting the broader application of this technology. To enhance the efficiency and quality of machining these jet micro-holes on the tube sidewall, a helical electrode electrochemical drilling method assisted by anode vibration has been proposed. The influence of parameters, such as the rotational direction and speed of the helical electrode, as well as the vibration amplitude and frequency of the workpiece, on the machining results was investigated using fluid field simulation and machining experiments. It was found that these auxiliary movements could facilitate the renewal of electrolytes within the machining gap, thereby enhancing the efficiency and quality of electrochemical drilling. Using the optimized machining parameters, an array of 10 jet micro-holes with a diameter of 200 μm was machined on the metal tube sidewall. Electrochemical cutting with radial electrolyte flushing tests were then performed through these micro-holes. Full article

The Deep Cement Mixing Integrated Drilling, Mixing and Jetting (DMJ) technique has been developed through the installation of high-pressure spray holes at the mixing blades, with the objective of enhancing the bearing capacity of deep-mixed piles in the Yellow River floodplain. In order to enhance the bearing capacity of the foundation, variable-modulus piles and capped piles were incorporated within the DMJ piles. Engineering applications have demonstrated that DMJ piles can effectively address the issue of foundation reinforcement in the Yellow River floodplain region, minimize the wastage of cement, and reduce the environmental pollution associated with waste slurry. Nevertheless, a comprehensive study of the relevant factors is still lacking in the available literature. This study addresses this gap by conducting a numerical simulation of these two types of DMJ piles based on the preliminary field test data, with the objective of analyzing both the single-pile-bearing characteristics and the composite foundation-bearing characteristics. Furthermore, the study seeks to optimize the DMJ pile’s structure based on the simulation results. The findings demonstrate that the premature failure of a single pile during the bearing process can be averted if the modulus of the pile core reaches a minimum of 0.3 GPa or if the pile cap thickness exceeds 1 m. The utilization of large-diameter drilling, stirring and spraying piles can markedly enhance the bearing capacity of the composite foundation and mitigate the differential settlement of pile and soil. The spacing of the pile has been identified as a significant factor influencing the differential settlement of pile and soil. Consequently, this study also examines the impact of pile spacing on the differential settlement of piles and soil. Full article

Freezing damage to tunnels in cold regions has long posed a threat to the safe operation of high-speed trains and other means of transportation. Finding a reasonable and effective solution to this problem, while also considering green, low-carbon, energy-saving, and environmental protection measures, has garnered widespread attention. Herein, the concept of a novel coupled energy tunnel is proposed, which combines the technologies of an air curtain and ground source heat pump (GSHP). The aim is to effectively address the issue of freezing damage in tunnels located in cold regions, while ensuring traffic safety. First, the multifunctional experimental apparatus for testing the anti-freezing and insulation performance of a coupled energy tunnel was independently designed and developed for laboratory experiments. Second, single-factor experiments and orthogonal experiments are conducted, and the influences of five key factors (i.e., the air outlet hole diameter, air outlet hole spacing, circulating water temperature of the GSHP, wind speed at the tunnel model entrance, and airflow jet angle) on the internal temperature field of the tunnel model are discussed. Third, combined with range analysis and variance analysis, the ranking of importance for each key factor and the optimal scheme of the coupled energy tunnel are obtained as follows: wind speed at the tunnel model entrance D > circulating water temperature of GSHP C > airflow jet angle E > air outlet hole spacing B > air outlet hole diameter A, and the optimal scheme is A₂B₁C₄D₁E₂, i.e., the air outlet hole diameter is 3 mm, the air outlet hole spacing is 10 mm, the circulating water temperature of GSHP is 50 °C, the wind speed at the tunnel model entrance is 1.5 m/s and the airflow jet angle is 45°. In conclusion, the research achievements presented in this paper can offer a new perspective for the structural design of tunnels in cold regions. Additionally, they contribute to the early achievement of a carbon dioxide emissions peak and carbon neutrality, and provide some valuable and scientific references for both innovators and practitioners. Full article