Hydrogen-fueled gas turbines offer the significant advantage of zero‑carbon emissions. However, the high-temperature, high-concentration water vapor environment generated by hydrogen combustion exhibits strong radiative participation. This creates a non-uniform radiative inlet condition for the downstream turbine blades. Current evaluations for film cooling effectiveness are mostly based on the uniform gas assumption or discrete hot spots. Research remains limited on non-uniform radiation effects induced by continuous curved hot spots. This study investigated the radiation effects on film cooling for hydrogen-fueled gas turbine blades using non-uniform characteristic parameters. First, a numerical method for non-gray radiation was established using the wideband k-distribution model. Second, characteristic parameters were proposed to describe the gas non-uniformities, including the temperature-weighted centroid, temperature variance, and non-gray spectral view factor. They were used to compare the relationship between non-uniform characteristics and the radiation-induced reduction in film cooling effectiveness under different non-uniformities. Results show that thin and tall high-temperature concentration phenomena should be avoided to prevent local hot spots on the film-cooled wall. A monotonic increasing relationship exists between the temperature-weighted centroid and the radiation-induced reduction in cooling effectiveness. The smaller the spectral view factor, the greater the radiation-induced reduction in cooling effectiveness. This is because the coupling effect between the spatial distribution characteristics of the high-temperature zone and the initial thermal state of film cooling. The proposed spectral view factor enables rapid comparison of the effects of different gas inlet non-uniformities on film cooling and is suitable for preliminary combustion chamber design in gas turbines.

The herringbone gear with symmetrical error will lead to the increase of eccentric load in the transmission process. According to the lumped mass method, the bending-torsion-axis coupling dynamic model of herringbone gear-bearing transmission system considering symmetrical error is established. The influence of different symmetry errors on the vibration characteristics of herringbone gears is analyzed. The results show that the symmetry error will gradually increase the difference between the dynamic load coefficients of the left and right meshing pairs. Compared with the radial displacement, the axial vibration displacement changes greatly with the increase of error. A herringbone gear-bearing transmission test bench was built to verify the correctness of the theoretical model.

Purpose Drag torque reduces the efficiency of the rotating system and affects the stability of transmission. This study aims to investigate the influence of warped friction pairs on drag torque characteristics. Design/methodology/approach Considering the geometrical characteristics and shearing mechanism of the lubricating film in the friction pair gap, the mathematical model and finite element model of the friction pair gap flow field are established for the no-load characteristics of the warped friction pair. Simulation results are used to verify the theoretical model, and the effects of warping amount and inlet flow on the no-load characteristics of the warped friction pair are studied. Findings For the warped friction pair, the drag torque exhibits an initial increase followed by a decrease as the relative speed rises, and this trend is mirrored by the ordinary friction pair; a greater oil film gradient is observed in the Type 1 friction pair when the drag torque has a descending trend; the pair exhibits a higher drag torque than the ordinary type; for the warped friction pair, with an increase in the warping amount, a decrease in the gap size and an increase in the inlet flow, the oil film volume within the gap decreases, which leads to a decrease in the theoretical flow, and an increase both in the critical relative speed for oil film contraction and the peak drag torque. Originality/value The findings of this study provide a valuable reference for subsequent research on aviation wet clutches featuring warped friction pairs.

Hydrogen-fueled engines have gained interest due to their zero-carbon emission characteristics. The high water vapor concentrations in such environments alter radiative heat transfer, challenging the accuracy of traditional heat transfer models based on hydrocarbon combustion. In addition, cold-side radiative effects on turbine blade film cooling remain underexplored. This study investigated the combined influence of gas radiation from hydrogen combustion and cold-side radiative cooling on turbine blade. By varying water vapor concentration and operating conditions, the heat transfer behavior on the cold-side was analyzed. Results show that: the film hole wall exhibits a large view factor toward the external gas environment due to the hole geometry. This allows radiative energy from the mainstream to enter this zone, where it undergoes multiple reflections and absorptions between the hole walls. The trapped energy cannot dissipate effectively outward, creating a "radiation trap" effect. A high blowing ratio and a high coolant temperature can mitigate the radiation trap effect. Under the low blowing ratio, radiative dissipation causes a cold-side temperature drop of approximately 100 K. For the film hole, under the high coolant temperature (1600 K), radiation inclusion reduces the temperature by up to 30 K. However, this cooling effect remains limited relative to the temperature rise induced by conduction. Furthermore, the methods and findings presented are applicable to nuclear reactor components, industrial furnaces, as well as to marine engines and other high-temperature energy systems.

Hydrogen fueled aero-engines have attracted increasing attention owing to their zero-carbon emission advantage. However, the combustion products of hydrogen contain high concentrations of water vapor, which significantly enhance gas radiation and subject the blades to higher radiative heat loads. Moreover, radiation between the impingement and film plate cannot be neglected. Existing researches have mainly focused on aviation kerosene conditions or pure film-cooling configurations, while studies on the cooling performance of film-impingement cooled turbine blade under hydrogen combustion environments remain relatively scarce. This paper studied the radiation heat transfer characteristics of film-impingement cooled turbine blade in hydrogen fueled aero-engine. Furthermore, the effects of Reynolds number, blowing ratio, the ratio of mainstream to coolant temperature, and the impingement plate surface emissivity, on both the radiation field and cooling performance were examined. It was found that the internal cavity provides an effective radiative heat transfer pathway that redirects part of the high temperature heat from the film cooled plate toward the cooler impingement plate. This radiative redistribution mitigates the adverse effects of radiation, resulting in a radiation induced reduction in cooling effectiveness that is approximately 10% lower in the film-impingement cooling configuration than in a pure film cooling structure, thereby improving the overall cooling performance of the turbine blade under hydrogen fueled conditions.

The pressure-temperature-time history is crucial for operating precision and service life of a wet clutch under high energy levels. However, there still lacks a simple and accurate model to predict the contact heat transfer at the sliding friction interface during the rotation-axial engagement process. In this paper, a transient thermal analysis of a multi-disc wet clutch is performed to capture the heat transfer behaviour of a sliding friction pair during the entire engagement cycle. The thermal conditions of the clutch are formulated by the dynamic model of a multi-body system considering the coupled effects of hydrodynamic lubrication, asperity contact, squeeze motion and sliding motion. The temperature characteristics of the clutch discs are investigated in detail by utilizing the thermal contact conductance under squeeze-sliding conditions. The peak temperatures of separator disc and friction lining are influenced by various applied pressures, material properties and load torques. As the applied pressure increases from 1.0 MPa to 1.6 MPa, the peak temperatures of the separator disc and friction lining are predicted to increase by 35.6% and 40.3%, respectively. When the load torque increases from 0 N m to 300 N m, the highest temperature of separator disc and friction lining increase by 16.3% and 15.8%, respectively. The developed thermal model could be a practicable toolkit for forecasting the temperature of a wet clutch under complex operating conditions.

PurposeDuring the clutch engagement process, spline wear reduces transmission accuracy and exerts a significant impact on the performance of the tail-push clutch system. This paper aims to conduct research on the sliding wear of engaging splines in aviation wet friction clutches and propose a method for calculating the wear amount of engaging splines as well as a method for evaluating wear failure.Design/methodology/approachConsidering the dynamic torque characteristics between the steel plate and friction plate during the engagement process of the tail-push clutch, a model is proposed to convert friction torque into dynamic torque on the spline. The spline wear depth is calculated based on the Archard wear model, and a neural network model is used to characterize the spline life.FindingsThe minimum service life of the spline occurs at Friction plate 1, which is 564.29 h. The influence of various factors on the service life of the engaging spline is analyzed, and it is found that clutch piston pressure is the most important, and the clutch driving end speed is the least important. A neural network model is used to characterize the service life of the spline, and it is evaluated that the model has a good fitting effect on the data.Originality/valueThis study provides an effective method for analyzing the wear life of the engaging spline in the helicopter tail-push clutch.

As a critical component of helicopter variable-speed transmission systems, the wet clutch directly influences transmission stability; consequently, clutch plate warping is a primary cause of operational malfunctions. This study investigates the engagement characteristics of warped friction pairs by developing an inter-plate load-carrying capacity model. This model integrates geometric, flow field, and microscopic contact characteristics, alongside the force-displacement properties of the separation spring and warped plates. Through the coupling of axial and circumferential motions, key parameters, including inter-plate bearing capacity and transmitted torque, are quantitatively determined. The results indicate that the engagement process of a warped friction pair consists exclusively of squeeze and mixed friction phases, which correspond to the non-contact, deformation, and plastic stages of the steel plate. During the squeeze phase, the piston pressure is balanced solely by the hydrodynamic pressure of the oil film, whereas in the mixed friction phase, it is supported by a combination of oil film pressure and micro-asperity contact forces. Furthermore, friction pair type 2 exhibits slightly lower torque transmission due to spline frictional resistance. Engagement tests conducted using an MM6000 tester validate the reliability of the proposed model, demonstrating engagement time errors of less than 8.5 %.

Purpose Frictional heat generated by high-speed friction of aerospace mechanical seals induces temperature rise of the sealing rings and end face thermal deformation, and even leads to seal failure. This paper aims to conduct research on the thermal characteristics of mechanical seals and obtains the variation laws of the temperature field and thermal deformation characteristics of mechanical seals.Design/methodology/approach The frictional heat sources on the sealing surface are calculated, the boundary conditions of mechanical seals are determined, and the thermo-mechanical coupling model is established. Based on the MM6000 testing machine, temperature rise verification tests for mechanical seals are carried out to verify the accuracy of the simulation model.Findings Thermal warpage deformation occurs on the sealing surface of the rotating ring, and the maximum deformation of the mechanical seals is located at the outer diameter of the rotating ring's sealing surface. Meanwhile, the actual contact area and high-temperature zone on the sealing surface gradually move from the radial outer side to the inner side with operating time. The maximum error between the simulation and experimental values is 15.5%, which verifies the accuracy of the simulation model in this paper.Originality/value A thermo-mechanical coupling model for analyzing the thermal characteristics of mechanical seals is established, which provides a reference for the study of the thermal characteristics of mechanical seals.Peer review The peer review history for this article is available at:

PurposeThe symmetry error affects the load-sharing performance of herringbone gear transmission systems. This paper aims to investigate the influence of symmetry error on the load-sharing characteristics of herringbone gear systems.Design/methodology/approachBased on the lumped mass method, the time-varying meshing stiffness and symmetry error are introduced to establish a dynamic model of herringbone gear bending-torsion-shaft coupling, and the load-sharing performance test is carried out on the herringbone gear test bench to verify the correctness of the theoretical analysis.FindingsThe greater the symmetry error, the larger the load distribution coefficient, the more obvious the eccentric load of the system. And the error of the experimental results and theoretical results is 15.01%, the larger the load, the better the load-sharing performance, which verifies the consistency between the test results and the theoretical analysis.Originality/valueThe research results provide reference value for the load-sharing characteristics of herringbone gears with symmetry error.Peer reviewThe peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-03-2025-0125/

Purpose The symmetry error generated in the machining process of herringbone gears will destroy the stability of the transmission system. The purpose of this paper is to establish a symmetry error measurement model of herringbone gear based on spiral measurement method, and to evaluate the transmission accuracy of herringbone gear based on the measured symmetry error. Design/methodology/approach A symmetry error measurement model of herringbone gear based on spiral measurement method is proposed. The measurement method is verified by three coordinate measuring instrument. The transmission error analysis model of herringbone gear is established. The influence of speed and load on it is analyzed. Findings At the same speed, when the load increases from 100 N·m to 500 N·m, the transmission error increases and the transmission accuracy of the system decreases. Under the same load, the speed is increased from 100 rpm to 500 rpm, which has little effect on the transmission error. Originality/value The measurement method and analysis model used in this paper provide reference value and significance for the measurement and analysis of symmetry error. Peer review The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-09-2024-0350/

The wet friction clutch in aviation, serving as a central hub in the helicopter transmission system, involves a friction pair composed of mating steel plates and friction discs. Under high power and high-speed operating conditions, these components rub against each other, generating a significant amount of heat, which leads to a high propensity for warping deformation and thermal failure of the friction pair. Based on the principles of heat generation and heat transfer, the thermal flux density and heat source distribution coefficient of the friction pair were calculated. The convective heat transfer calculation methods for rectangular oil grooves and concentric circular grooves, as well as the friction pair’s annular surface and contact surface, were derived. A thermo-mechanical coupled model for the wet friction clutch with multiple friction pairs was established in ABAQUS, revealing the distribution and temporal variation of the temperature and stress fields during engagement. Transient temperature measurement experiments were conducted on the MM6000 test rig to validate the model, and the results obtained, including the trend of temperature rise and peak temperature during engagement, were found to be consistent with the ABAQUS simulation calculations. The maximum temperature difference between the simulation temperature and the test temperature is 7.86 °C, and the maximum temperature difference percentage is 4.37

Turbine blades in hydrogen combustion environments endure elevated thermal loads due to increased gas temperatures (>2000 K) and water vapor (H2O) concentrations (>25 % vol.), significantly enhancing radiative heat flux. Combustor outlet temperature non-uniformity further induces spatially varying radiation distributions, critically impacting blade thermal profiles. This study examines coupled radiation-convection heat transfer in film-cooled blades under inlet strip conditions (both temperature and water vapor concentration), introducing the Inlet Steam Distribution Index (ISDI) to quantitatively evaluate the combined effects of thermo-species non-uniformity on cooling performance. Results show that the coupled radiation and non-uniform water vapor distribution induce a thermal "self-balancing" effect through radiation heat flux redistribution, reducing local temperature gradients and promoting more uniform cooling effectiveness. The coupled water vapor-temperature strips predominantly govern cooling effectiveness distributions through radiation flux patterns, with maximum thermal impact occurring in high-temperature/high-radiation regions. Three distinct regimes emerge: the centered strip produces low wall temperatures bilaterally, the dual-side strips yield high bilateral temperatures, and the unilateral strip creates localized heating in corresponding regions. The ISDI effectively characterizes water vapor non-uniformity effects, demonstrating consistent rankings (dual-side > unilateral > uniform > centered) for both cooling efficiency and ISDI values regardless of radiation consideration. This study can provide radiative heat transfer principles for decarbonized propulsion design under extreme H2O conditions.

Purpose Thermal failure and incomplete separation often occur in aviation wet friction clutches. The purpose of this study is to improve the performance and reliability of the clutch, considering the influence of lubricating oil, in this paper, the finite element method is used to simulate the friction pair of clutch with separation spring. Design/methodology/approach Considering the influence of lubricating oil, based on computational fluid dynamics principle and applying multiple reference frame method, simulation is carried out in FLUENT software to study the distribution of flow field and temperature field of clutch friction pair and separation spring under the condition of maximum relative speed of 3000 r/min. Findings The middle friction pair has more oil distribution, while the two sides have less oil distribution, and the highest oil volume exceeds that of the lowest by a factor of 3.49. Under the influence of lubricating oil distribution and component heat conduction, the temperature of the separation spring on both sides is higher than that of the separation spring in the middle. The axial temperature distribution law of the friction pair is the same as that of the separation spring, and the difference of the highest temperature between the friction pair is 136.41°C. Social implications The heat generation of the clutch is studied to improve the performance of the clutch and ensure the safety of the helicopter. Originality/value By analyzing the temperature and flow field of a wet friction clutch with a separation spring, engineers can help provide the service life and reliability of the clutch friction pair.

In wet friction clutches, the friction pair is separated by adding separating springs to reduce the drag torque, but the increase of the separating spring will inevitably have a certain impact on the engagement characteristics of the friction clutch. In view of this characteristic, considering the structural parameters of the separating spring, the inter-disc bearing capacity and transmission torque model of the wet multi-plate friction clutch during the engagement process are established, and the variable-order numerical differentiation method is used to solve the problem to explore the influence of the wave number, thickness and width of the separating spring on the characteristics of the rotational speed, inter-sheet bearing capacity, transmission torque and oil film thickness of the wet multi-plate friction clutch engagement process. The results show that the wave number of the separating spring has a significant influence on the mating characteristics of other parameters, so the wave number should be appropriately reduced to reduce the clutch engagement time under the condition of ensuring that the separating spring has sufficient strength.

The motion state of the friction plate in a wet friction clutch is investigated by analyzing the causes of friction coefficient formation. This study establishes static and dynamic friction coefficient models for the friction plate based on a fractal model. The fractal dimension and scaling coefficient are studied to understand the fractal characteristics and variation patterns of the surface morphology of friction pairs during engagement. The MM6000 friction and wear testing machine is utilized for experiments, measuring surface morphology changes due to wear and changes in the engagement motion state of the friction plate. The theoretical content is compared and analyzed to verify the accuracy of the friction coefficient prediction model for the friction pair. Experiments are conducted on paper-based friction materials under different bonding pressures, and the relationship between bonding times and surface morphology changes is established. A comparative experiment between the joint motion state and dynamic simulation is performed, concluding that the micro convex contact model has certain accuracy in predicting the contact state of friction plates under various working conditions.

The vibration response of the multi-piece wet friction clutch of the coaxial twin-rotor helicopter tail rotor drive system has a certain influence on the stability of the entire tail drive system. According to the concentrated mass method, the multi-degree-of-freedom vibration differential equation of the multi-piece wet friction clutch model is established, as well as considering the unbalanced position of the clutch rotor in the rotational motion, the steel plates and friction plates are equivalent to spline pairs, the vibration displacement generated by the dynamic bonding process in the radial direction is analyzed, comparative analysis is carried out through experiments and theoretical simulations. The results show that both the equivalent dual steel plate and the equivalent friction plate will produce vibration displacement in the Y direction in the steady state, which is consistent with the assumption of clutch rotor imbalance.

There is no lubrication in the contact area, which leads to a significant influence of the thermal characteristics on the friction dynamics and life of the helicopter intermediate reducer because the helicopter experiences severe loss of lubrication. In this study, for evaluating the non-linear friction dynamics and transient thermal network models of the intermediate gearbox, a multi-time scale coupling method was proposed to establish a proportional allocation method between the oil film region and the rough peak contact region of the tooth surface by considering the effect of temperature and to study the adsorption film under the condition of severe lubrication loss. The coupled thermal and kinetic characteristics of the severe lubrication loss condition were obtained by calculating the friction coefficients in the lubricated and dry-friction regions. The results showed that the friction coefficient of the bevel gear tooth surface fluctuated between 0.1 and 0.6, and the degree of the gear axis trajectory shift was more evident owing to the increase in the friction force excitation caused by the increase in the friction coefficient.