Optimized design and CFD analysis of drag-reduction windshields for aviation spiral bevel gears

During high-speed rotation, the surface of aeronautic spiral bevel gears will generate significant pressure and viscous forces, which will cause a certain amount of windage power loss and reduce the efficiency of the transmission system. Based on the computational fluid dynamics, this paper analyzes the windage power loss of a single spiral bevel gear and a spiral bevel gear pair under oil injection lubrication. In addition, the shroud is used to suppress gear windage loss, and the clearance size and opening angle of the designed shroud are optimized. Finally, by comparing and analyzing the experimental results, the following conclusions were obtained: (1) For a single gear, the speed is the most important factor affecting windage loss, followed by the hand of spiral, and rotation direction; (2) For gear pairs, under oil injection lubrication, the input speed has the greatest impact on windage power loss, followed by the influence of oil injection port speed, temperature and oil injection port pressure; (3) Installing a shroud is an effective method to reduce windage power loss; (4) In the pure air phase, the smaller the clearance between the shroud and the gear surface, and the smaller the radial direction between the shroud and the shaft, the better the effect of reducing windage; (5) In the two-phase flow of oil and gas, it is necessary to design oil drainage holes on the shroud to ensure the smooth discharge of lubricating oil and improve the drag reduction effect.

With the increasing rotating speed of aviation spiral bevel gears, the load-independent windage power loss caused by hydrodynamic behavior has a greater impact on transmission efficiency. An analytical model is established to predict the windage power loss of spiral bevel gears with oil injection lubrication. The improved model regards the total windage losses as the sum of oil–gas dragging effects on the tooth flank, toe/heel, circular cone surface, circumference of the teeth, and tooth root. Then the numerical method and analytical method are combined to calculate windage losses. A multi-objective NSGA-II optimization algorithm is used to optimize the jet layout parameters. The rationality and accuracy of this model are verified by comparing the calculation results of an example with data sets of existing experimental findings and computational fluid dynamics (CFD) simulation results. The calculation results show that compared with the tooth profile assumption method in the existing literature, the improved calculation formula of windage dragging effect on tooth flank can better reflect the influence of oil injection lubrication layout parameters on windage loss and make the windage loss calculation more accurate. Finally, the influence of gear body parameters, working conditions parameters, geometric parameters, and injection lubrication layout parameters on the windage loss is examined. This research provides a theoretical basis and methodological guidance for optimization design of reducing windage power loss.

With the increasing speed of aviation spiral bevel gears, the load-independent windage power losses caused by hydrodynamic have increasingly more influence on gear transmission efficiency. Firstly, a test rig for the windage power loss of spiral bevel gear under oil-jet lubrication is established, and on this basis, a method for measuring windage torque is proposed. Next, the interactive effects of different injection lubrication parameters on the windage power loss were studied by orthogonal experiment, and the formula for calculating the windage loss was obtained by fitting the experimental data. Then, the fluid distribution, velocity field and pressure field around the gear were analysed by using a computational fluid dynamics (CFD) numerical model, and the mechanical and energy characteristics of the gear windage power loss were obtained. Finally, the dimensionless processing of the windage moment was carried out, and the variation of the dimensionless windage moment coefficient with the rotational Reynolds number is obtained. The comparison between the dimensionless windage moment coefficient of experimental data and simulation results shows that the CFD values are in good agreement with the measured data. This study provides experimental and methodological guidance for the calculation of windage power loss and windage reduction design of aviation gear pair under oil injection lubrication.

This paper proposes a method for calculating windage power losses of spiral bevel gears by dividing the losses into the sum of windage effects on tooth surface, toe/heel, conical surface, and circumferential surface, according to the gear structure. A calculation model for each component of windage losses is established based on the basic equation of fluid dynamics. Subsequently, a windage loss measurement test bench is developed, and a windage moment measurement method is proposed for experimental spiral bevel gears. The individual contributions of each windage loss component are calculated. The results of the calculations indicate that the gear speed is the primary factor that impacts windage losses, with the windage power loss being proportional to the 2.96th power of gear speed. Gear geometry parameters and the jet flow impacting the tooth surface are also significant factors, followed by the hub and spoke values in the wheel body parameters. The findings also show that an increase in lubricating oil content in oil-gas two-phase flow can significantly increase windage losses. Finally, a comparison between the dimensionless windage calculation values and the experimental measurement values demonstrates good agreement. This paper provides theoretical guidance for future research aimed at reducing windage power loss and improving the efficiency of aviation gear transmission.

In the field of engineering applications, reducing frictional drag in turbulent flows is imperative to enhance energy efficiency. This study investigates the potential of grooved superhydrophobic surfaces (GSHS) in reducing drag in turbulent flows under ventilation conditions. A systematic investigation is conducted to examine the effects of effective gas film thickness (thg) and groove width (Wg) on drag reduction rate (DR) and gas film state at various Reynolds numbers (Re). The drag characteristics and reduction effects of smooth surfaces (SS), grooved surfaces (GS), superhydrophobic smooth surfaces (SHS), and GSHS are also compared. The experimental results indicate that SS and GS surfaces do not show any notable drag reduction under ventilation and may even result in a drag increase. In contrast, SHS and GSHS exhibit considerable drag reduction effects under ventilation, with the DR of GSHS increasing significantly with thg. The drag reduction effect is influenced by the interplay between thg and Wg. At varying Re, GSHS has been demonstrated to achieve substantial DR ranging from 44% to 46%. This study provides new insights into drag reduction in underwater turbulence and offers theoretical support for drag reduction techniques in engineering applications, such as underwater vehicles and pipeline flows.

CFD modelling and numerical simulation on windage power loss of aeronautic high-speed spiral bevel gears

On the estimation of the windage power losses of spiral bevel gears: An analytical model and CFD investigation

With the increasing speed of aviation gear, windage loss has been the main component of power loss. Reducing windage is of great significance to improving the transmission efficiency of aviation spiral bevel gear. Firstly, the calculation model of enclosed spiral bevel gear was established, and the basic physical mechanism of windage power loss was illustrated by numerical simulation, so as to obtain the mechanical and energy characteristics of windage loss. Then, the influence of the geometry and clearance parameters of the shroud on the windage loss was studied by orthogonal test, variance analysis and optimization design. The mechanism of the shroud to reduce the windage loss under the multi-factors was also studied, and their interaction was obtained. The results show that the tooth surface clearance, heel clearance and meshing opening are significant factors, and the most significant factor is the heel clearance. The non-significant factor is the interaction of each factor. The least significant factor is the toe clearance. In other words, the windage power loss can be reduced to the greatest extent by simultaneously reducing the meshing opening of the shroud and the clearance value between shroud and the surface of the gear. Finally, based on the mechanism of reducing windage loss of shroud, the optimization design principle affecting the structural performance of shroud is put forward, which provides theoretical guidance for the practical application of shroud in windage reduction engineering.

Secondary vortex drag reduction and heat transfer enhancement of nanofluids in hierarchical microchannels applied to thermal management of electronic components

Drag reduction through turbulent boundary layer control (TBLC) is an essential way to develop green aviation technologies. Compared with traditional approaches for drag reduction, turbulence drag reduction is a relatively new technology, particularly for skin friction drag reduction, and it is becoming a hotspot problem worldwide. This paper focuses on the research of micro fluidic-jet actuators used for outer-layer boundary layer control with high-performance computing (HPC). This study aims to reduce turbulent drag by reshaping the flow structure within the turbulent boundary layer. To ensure the calculation accuracy of the core region and reduce the consumption of computing resources, a zonal LES/RANS strategy and WMLES method are proposed to simulate the effects of fluidic-actuators for outer-layer boundary control, in which high-performance computing has to be involved. The studies are performed on the classical zero-gradient turbulent flat plate cases, in which three different control strategies named “W-control,” “V-control,” and “VW-control” are used and compared to study the effects of drag reduction under a low Reynolds number at Reτ = 470 and a higher Reynolds number at Reτ = 4700. The mechanism for drag reduction is analysed via a pre-multiplied spectral method and a parallel dynamic mode decomposition (DMD) method. The results show that the present approach can effectively simulate the outer-layer turbulent boundary control where the “V-control” with the fluidic-jet actuator array behaves well to achieve an average drag reduction (DR) rate of more than 5% for the high Reynolds number case of the flat plate boundary layer. The high Reynolds shear stress and turbulent kinetic energy distribution in the boundary layer region show an obvious uplift under the effects of actuators, which is the main mechanism for drag reduction.

In some aero-engine applications a spiral bevel gear is mounted in a bearing chamber. The windage power losses (WPL) associated with the gear make a significant contribution to the overall heat generation within the bearing chamber and a potential method of WPL reduction and lubrication/cooling oil management is to shroud the gear. At the University of Nottingham Technology Centre in Gas Turbine Transmission Systems experimental and computational techniques are being applied to enhance understanding of shroud performance and design. This paper presents results from the first stage of the investigation in which the windage losses associated with rotating an unmeshed spiral bevel gear in air have been studied. The potential to reduce gear WPL by shrouding is clearly demonstrated with the WPL for the shrouded gear reduced on average by 75% for clockwise rotation and by 70% for anticlockwise rotation. Given the physical similarity between a shrouded gear and a centrifugal fan an attempt was made to characterize the performance of the shrouded gear in a similar manner to that used for a centrifugal fan i.e. as a function of the mass flow rate of air flowing through the shroud. It is demonstrated that in many aspects the gear performance was analogous to centrifugal fan behavior. It is further demonstrated that fan design approaches could be adopted to inform the detail of the shroud design and to translate test rig performance to different operating conditions.

Fluid drag greatly lowers the efficiency and increases the energy consumption of underwater vehicles and devices working in similar environments. Therefore, drag reduction has become a major topic in fluids research. Inspired by the high drag-reduction effect of shark skin, this paper experimentally and numerically investigates the drag-reduction performance of a bionic shark skin microstructure with a triangular cross section. The structural parameters are optimized through numerical simulations. The microstructure reduces the drag by reducing the velocity gradient near the wall and changes the turbulent kinetic energy distribution in the flow field near the wall. Next, samples of microstructures were prepared using the template method. Experimental rheometer tests revealed a drag reduction rate of 14.29% on the microstructure surface under the set experimental conditions. Experiments and simulations have demonstrated the high drag-reduction effect of the microstructures within a rotating flow field. The developed method and theoretical basis for numerical simulations of rotating flow fields can be utilized in pump machinery such as magnetic levitation centrifugal flow pumps.

At present, the drag reduction effect of the bionic non-smooth surface is very sensitive to the inflow angle, and the drag reduction effect can only be achieved when the inflow angle is within a certain range. In response to this problem, this article is inspired by the concave microstructure of the insect body surface of the Cybister bengalensis and proposes a cylindrical concave drag reduction technology. Firstly, a numerical model of the cylindrical concave surface drag reduction characteristics is established, and then a numerical simulation analysis is carried out using Fluent software to study the concave surface drag reduction effect and the drag reduction mechanism, and further analyze the influence of the inflow angle and turbulence energy on the cylindrical concave surface drag reduction rate. Finally, It is concluded that: (1) Under the given simulation model, the concave surface has a better drag reduction effect than the smooth surface in a larger speed range, and the maximum drag reduction rate is 6.0%. (2) The concave surface structure has a better drag reduction effect than a smooth surface. Incoming flow in all directions has the ability to reduce drag. (3) When the flow velocity of the fluid is within the range of 1-20m/s, under different inflow angle conditions, the concave structure can achieve drag reduction, and the drag reduction rate is within 10%.

In many aeroengines the accessory power offtake is achieved using a spiral bevel gear set running off one of the main shafts. The crown and bevel gears are housed in an internal gearbox and there is significant heat generation within this chamber, some of which is attributed to windage power loss (WPL) generated by the gear. Over the past few years the University of Nottingham Technology Centre (UTC) in Gas Turbine Transmissions has been researching spiral bevel gear windage power loss both computationally and experimentally using a purpose-built test rig at the UTC. In this study the test rig has been adapted such that chamber pressures up to 8 bar can be generated. Test data has been obtained that shows the effect on WPL of chamber pressure, advancing understanding of the relationship between data obtained at ambient and pressurised conditions. Three configurations have been studied: unshrouded gear, gear with 360° shroud and shrouded, crown and pinion meshing pair. Further, the effect of oil mist within the chamber on WPL has been studied. An oil mist generation system was developed for introducing a fine mist into the chamber and results are presented for varying mist flowrates. A mist measurement system was developed to sample mist mass fraction within the chamber and the data obtained is used to calculate an effective (oil/gas mixture) chamber density. Increasing chamber pressure increases Reynolds number, moving the system behavior further along the Moment coefficient-Reynolds number correlation. The Cm-Re correlation is similar in form to that for a shrouded cone, showing transitional behavior around Re = 2×106. Beyond transition Cm decreases with increasing Re. Introducing an oil spray has two effects: reduction in chamber temperature and increase in effective density of chamber fluid. Both effects can be accounted for by calculating Re and Cm based on mixture properties but it seems highly likely that the properties of the fluid under the shroud differ from those of the fluid in the external chamber.

When the hypersonic vehicle flies at high speed, there are serious problems of aerodynamic heating and drag near the nose stagnation point. Although the blunt body can reduce the heat flux near the nose, great aerodynamic drag will be produced. Similarly, the sharp edge can reduce aerodynamic drag, but the aerodynamic heating is more severe. In this paper, a new conception of cavity-channel configuration with heating and drag reduction is proposed to solve this contradiction. The aerothermal and aerodynamic performance of blunt cone applying the cavity-channel configuration is calculated and analyzed via solving N-S equation. The numerical results show that the new concept configuration can achieve the expected effect of heating and drag reduction. The higher the channel height, the better the effect of drag reduction, however, the effect of heating reduction is weakened until the heating increment appears. This paper preliminarily investigates the principle of heating and drag reduction of cavity-channel configuration and summarizes the law of applying the concept of cavity-channel to heating and drag reduction.