This study presents a novel method for determining the oil film thickness on face gear tooth surfaces during transmission. The method derives the film thickness from measured oil film resistance, based on a pre-calibrated relationship between resistance and thickness for point contact pairs. The procedure consists of two sequential experiments. First, the resistance across a controllable oil film is measured to establish a fitting function relating mean resistance to film thickness. Second, this function is applied to resistance measurements from operating face gear pairs to determine the minimum oil film thickness on their tooth surfaces. The method is validated against a thermal elastohydrodynamic lubrication (TEHL) model of face gears. Results confirm that under lubricated conditions, the measured resistance accurately represents that of the oil film. The calibration yields the function R '=38.72 h + 19.41 for mean resistance R ' (M Omega) and film thickness h (mu m) within the 0.1-1 mu m range, with a maximum fitting error of 2.95 %. The oil film thickness on face gear tooth surfaces is on the order of 10-1 mu m, increasing with rotational speed and decreasing with applied torque. The maximum error between the experimentally derived minimum oil film thickness and numerical simulation results is 4.7 %. This method also demonstrates potential for measuring oil film thickness on tooth surfaces of other gear types.

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.

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.

ObjectiveTo achieve rapid prediction of the root stress distribution in herringbone gears under variable operating conditions and address the high computational cost of the finite element method, a prediction model for root stress distribution based on a BP neural network was constructed.MethodsFirstly, finite element simulations were conducted on a herringbone gear pair under 20 sets of operating conditions with varying rotational speeds and load torques to obtain stress distribution data in the tooth root region. Secondly, tooth root stress tests were performed, and the simulation results were compared with the experimental data to verify the validity of the finite element model. Then, a stress subregional prediction method was adopted, in which the tooth root region was divided into three subregions, and BP neural network models were independently constructed and subsequently integrated to form a global prediction model. Finally, a set of operating conditions outside the training samples was selected, and both the finite element simulation and the proposed model were employed to obtain the root stress distribution and its maximum value, thereby validating the predictive performance.ResultsThe results indicate that the root stress distribution predicted by the model is highly consistent with that obtained from finite element simulations. The prediction error for the maximum tooth root bending stress is 4.6%, and the mean squared error of the prediction is 3.017 MPa, demonstrating the effectiveness of the proposed model. This study provides a reference for the rapid evaluation of tooth root stress in herringbone gears under variable operating conditions.

ObjectiveAiming at the limitation that single data domain models are difficult to accurately identify subtle fault features in gearbox fault diagnosis, a fault diagnosis method with multi-domain feature fusion under attention mechanism was proposed to improve diagnostic accuracy, stability and generalization ability.MethodsFirstly, dimensionless features and spectral features were extracted from the time domain and frequency domain of vibration signals. Secondly, deep time-frequency domain features were extracted by combining continuous wavelet transform with convolutional neural network (CNN). Then, an attention mechanism was introduced to dynamically weight and fuse multi-domain features, strengthening key features and weakening redundant information. Finally, a classifier was used to complete fault identification, and the effectiveness of the method was verified based on a secondary gearbox test dataset.ResultsTest results on a secondary gearbox test dataset show that the proposed method achieves a diagnostic accuracy of 99.77%, outperforming single-domain models and verifying its effectiveness and stability in identifying weak faults and adapting to multiple operating conditions.

The intermediate gearbox of high-power helicopters needs to withstand higher loads and greater heat dissipation requirements. Relying solely on the casing shell for heat dissipation can no longer meet its cooling demands, necessitating the addition of heat sinks on the casing surface to enhance heat transfer capability. This study simplifies the high-temperature surface of the intermediate gearbox casing into a flat plate of uniform thickness and investigates the influence of heat sink structure on the plate's cooling capacity through experimental and numerical simulation methods. Using CFD simulation and infrared thermography, the simulation results were compared with experimental data, revealing an average error of 1.01 %, which verifies the accuracy of the CFD simulation and confirms the V-shaped heat sink as the optimal configuration. Analysis of the effects of heat sink height, width, spacing, and width-to-spacing ratio shows that increasing height improves heat transfer performance by 12.9 %, increasing width reduces it by 12.2 %, increasing spacing improves it by 13.6 %, and increasing the width-to-spacing ratio decreases it by 27.3 %. When the optimized heat sink parameters were applied to the bottom casing of a certain high-power helicopter intermediate gearbox, temperature field simulations demonstrated that the optimized heat sinks reduced the maximum temperature at the casing bottom by 14.7K and the oil temperature by 5.8K.

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.

Purpose During the manufacturing process of spiral bevel gears, certain surface roughness is inevitably generated on tooth surfaces. In elastohydrodynamic lubrication (EHL), surface roughness directly influences film thickness distribution, thereby altering pressure distribution. The objective of this study is to investigate the effects of surface roughness characteristics on the lubrication performance of spiral bevel gears. Design/methodology/approach A mixed EHL model was established for spiral bevel gears through two-dimensional digital filtering numerical simulation of rough surfaces and experimental measurement of surface topography. This model enables systematic investigation of oil film pressure, film thickness and temperature distribution characteristics on gear tooth surfaces with varying surface roughness parameters. Findings Surface roughness significantly affects the lubrication performance of spiral bevel gear tooth surfaces. Larger root mean square (RMS) values of rough surfaces lead to increased oil film pressure and temperature, while reducing the minimum film thickness at the necking location. When surface texture orientation conflicts with lubricant flow direction, substantial impacts on lubrication characteristics are observed. Ground surfaces exhibit film thickness characteristics closest to numerically simulated rough surfaces, whereas milled surfaces demonstrate smaller minimum film thicknesses. Originality/value Developing a mixed EHL model for spiral bevel gears that integrates numerically simulated roughness and measured real topography data. Peer review The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-04-2025-0162/

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 %.

PurposeUnder actual operating conditions, particularly in harsh environments where lubricant may transition from a fully flooded to a starved state, and considering that machined surfaces inherently exhibit roughness leading to asperity dry contact, heavy loads and plastic deformation, the study aims to accurately capture the real meshing state of spiral bevel gears with surface roughness and improve fatigue life prediction by accounting for the combined effects of surface topography and material elastoplasticity.Design/methodology/approachAn elastoplastic hydrodynamic lubrication (PEHL) contact model for gear pairs is established. This model integrates the influences of surface roughness and material elastoplasticity to simulate the lubrication behavior of spiral bevel gears under real operating conditions.FindingsResults indicate that the proposed PEHL model for spiral bevel gears better reflects their actual service conditions compared to existing elastohydrodynamic lubrication (EHL) models. This improvement enhances the accuracy of fatigue life predictions based on lubrication contact analysis.Originality/valueDeveloping an PEHL contact model that explicitly considers the combined effects of surface topography (roughness) and material elastoplasticity, tailored to the actual operating conditions of spiral bevel gears. This model fills a gap in existing EHL-based approaches by more realistically capturing the complex interactions between surface characteristics and material behavior.

This paper proposes a new transverse-torsional coupled planetary gear transmission model with a self-adjustment backlash control model, which offers an effective approach to reducing vibration and controlling system stability. The nonlinear governing equation is derived, and the system dynamics behaviors and double-parameter stability region are explored. Several valuable conclusions can be drawn. First, bifurcation diagrams under different parameters are obtained. Colorful bifurcation characteristics are observed, and different parameters cause remarkable differences in the system dynamic response. Second, different initial values can lead to dramatically different motion states, and the change in system input parameters can significantly affect the attractor's structure. Third, solution domain structures under different parameter combinations are obtained and comprehensively analyzed. A flame-shaped structure is observed and evolves with the change of parameters. Fourth, double-parameter stable regions are presented and carefully analyzed, providing an effective visual tool to study system stability and the variation trend caused by parameter changes. The research on bifurcation characteristics, initial attractor, solution domain structure, and double-parameter stability significantly reveals the colorful nonlinear behaviors of the planetary gear system. The study in this paper could be utilized as the optimization method for the design of gear transmission system and a guide for field problems.

The equivalent curvature radius and entrainment velocity are essential parameters for lubricating modified face gear pairs and require further investigation. An analytical model for the equivalent curvature radius and entrainment velocity of an orthogonal face gear pair with tooth profile and axial modifications on the spur gear is proposed in this paper. Quadratic parabolas are used to modify the tooth tip and root of the spur gear while retaining the involute profile in the middle; the axial modification also employs quadratic parabolas. Using the coordinate system of the shaper cutter, the tooth surface equations of the modified orthogonal face gear pair are established. Applying the theory of differential geometry, the equivalent curvature radius of point contact is derived. Considering the relative motion of the gear pair, the entrainment velocity is obtained. The equivalent curvature radius and entrainment velocity with and without modifications are compared, and the effects of modification parameters on them are analyzed. The results indicate that in the modified region, the equivalent curvature radius is smaller than that of the unmodified tooth surface, exhibiting a gradual decrease with a discontinuity at the junction point; here, the entrainment velocity vx is discontinuous at the connection, while vy decreases gradually. Additionally, the optimal modification parameters ensuring continuity of both the equivalent curvature radius and entrainment velocity are determined as ∆1 = 0.06 mm, L1 = 2.44 mm, and am = 0.0003.

As turbine inlet temperatures in aero-engines rise, thermal radiation effects on turbine blades cooling become increasingly critical. Complex geometric structures, including concave and convex surfaces, can modify heat transfer and radiation transfer paths compared to the mainly used film-cooled plate model. This study employs a wideband model for H2O/CO2 absorption coefficients with high volume fractions under high-temperature, high-pressure conditions. The discrete ordinates and turbulence coupled models are employed to investigate the convection-radiation heat transfer laws of three characteristic surface curvatures: concave, convex, and flat. The results show that along the flow direction, the spanwise-averaged cooling effectiveness decreases by approximately 0.04-0.1 (concave), 0.06-0.11 (flat), and 0.07-0.12 (convex) under gas and walls radiation. The radiation-induced reduction in cooling effectiveness diminishes downstream, reaching its minimum near the outlet and maximum adjacent to the film hole. Additionally, radiation decreases the average heat transfer coefficient (h(f) /h(0)) by about 0.1 and expands the downstream regions with h(f) /h(0) < 1, as it diminishes mixing-induced heat flux between coolant and mainstream. Regarding the net heat flux reduction (NHFR) performance, radiation remains detrimental. Along the flow direction, the radiation-induced NHFR reduction diminishes progressively downstream. The radiation reduces spanwise-averaged NHFR by 0.05-0.12 (concave), 0.1-0.15 (flat), and 0.1-0.16 (convex).

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/

This paper proposed a single-pair gear system model with transverse-torsional coupling and backlash adjustment mechanism. This model can provide a brand-new way to control the system's motion state and improve its stability. Systematically, the system's nonlinear dynamics, initial attractors, solution domain structure, and stability region analysis under different parameters were obtained and investigated. Based on this model and related analysis, several conclusions can be summarized. First, the bifurcation diagrams were obtained, and the critical switching points and the routes from 1T-periodic motion to chaos motion were systematically analyzed. This is valuable for static system parameter control. Second, the initial motion attractors under different parameters were investigated. This reveals the nonlinear behaviors and dynamic distribution of solutions during field adjustment. Furthermore, the solution domain structures under different parameter combinations were studied. This offers a visualized method to assist in the gear system's design and an effective tool to ensure motion stability. Finally, a double-parameter stability analysis was conducted based on different parameter combinations. Once unstable motion is generated, this can be used to provide the nearest or fastest route to 1T-periodic motion. The study of nonlinear behaviors and stability has significantly expanded the understanding of the gear system and can be used as guidance for parameter control in practical applications.