The Impact of Oil and Sealing Air Flow, Chamber Pressure, Rotor Speed, and Axial Load on the Power Consumption in an Aeroengine Bearing Chamber

2005 ◽  
Vol 127 (1) ◽  
pp. 182-186 ◽  
Author(s):  
Michael Flouros
Keyword(s):  
Power Consumption ◽  
High Speed ◽  
Air Flow ◽  
Flow Chamber ◽  
Chamber Pressure ◽  
Power Losses ◽  
Rolling Element ◽  
Oil Flow ◽  
The Impact ◽  
Circle Diameter

Trends in aircraft engines have dictated high speed rolling element bearings up to 3 million DN or more with the consequence of having high amounts of heat rejection in the bearing chambers and high oil scavenge temperatures. A parametric study on the bearing power consumption has been performed with a 124 mm pitch circle diameter (PCD) ball bearing in a bearing chamber that has been adapted from the RB199 turbofan engine DN∼2×106. The operating parameters such as oil flow, oil temperature, sealing air flow, bearing chamber pressure, and shaft speed have been varied in order to assess the impact on the power consumption. This work is the first part of a survey aiming to reduce power losses in bearing chambers. In the first part, the parameters affecting the power losses are identified and evaluated.

Reduction of Power Losses in Bearing Chambers Using Porous Screens Surrounding a Ball Bearing

2005 ◽  
Vol 128 (1) ◽  
pp. 178-182 ◽  
Author(s):  
Michael Flouros
Keyword(s):  
High Speed ◽  
Ball Bearing ◽  
Research Programme ◽  
Aircraft Engine ◽  
Chamber Pressure ◽  
Power Losses ◽  
Torque Measurements ◽  
Engine Design ◽  
Oil Flow ◽  
The Impact

Trends in aircraft engine design have caused an increase in mechanical stress requirements for rolling bearings. Consequently, a high amount of heat is rejected, which results in high oil scavenge temperatures. An RB199 turbofan bearing and its associated chamber were modified to carry out a survey aiming to reduce power losses in bearing chambers. The test bearing was a 124 mm PCD ball bearing with a split inner ring employing under-race lubrication by two individual jets. The survey was carried out in two parts. In the first part, the investigations were focused on the impact on the power losses in the bearing chamber of the operating parameters, such as oil flow, oil temperature, sealing air flow, bearing chamber pressure, and shaft speed. In the second part, the investigations focused on the reduction of the dwell time of the air and oil mixture in the bearing compartment and its impact on the power losses. In this part, porous screens were introduced around the bearing. These screens would aid the oil to flow out of the compartment and reduce droplet-droplet interactions as well as droplet-bearing chamber wall interactions. The performance of the screens was evaluated by torque measurements. A high-speed camera was used to visualize the flow in the chamber. Considerable reduction in power loss was achieved. This work is part of the European Research programme GROWTH ATOS (Advanced Transmission and Oil Systems).

Bearing Skidding Detection for High Speed and Aero Engine Applications

2021 ◽  
Author(s):  
Azzedine Dadouche ◽  
Rami Kerrouche
Keyword(s):  
High Speed ◽  
Power Losses ◽  
Severe Damage ◽  
Roller Bearings ◽  
Custom Made ◽  
Rolling Element ◽  
Aero Engine ◽  
Oil Flow ◽  
Rolling Elements ◽  
Surface Distress

Abstract Rolling-element bearings (REB) can develop severe damage due to skidding (slipping) between the rolling elements and bearing races. Skidding can be described as gross sliding between the bearing surfaces in relative motion and can result in significant surface distress such as smearing, especially at light loads and high rotational speeds. Under these conditions, skidding occurs between the rolling elements and the bearing races, leading to increased wear (higher friction coefficient), elevated bearing temperature, significant power losses and reduced service life of the bearing. The main objective of this study is to investigate the significance of various sensing technologies (induction, vibration, ultrasound, acoustic and optical) in detecting skidding in standard series roller bearings as well as custom-made roller bearings for aero engine applications. The bearings have a bore diameter of 60 mm and 90 mm, respectively. Jet and under race lubrication techniques have been used to supply oil to the bearings under test. The custom-made aero engine test bearing features special channels to allow under race lubrication of the rollers/races contacts as well as the cage land. The effect of radial load, rotational speed and oil flow on roller skidding have also been investigated and analyzed. Tests have been performed on a dedicated high speed experimental bearing facility and data was recorded using a commercially-available data acquisition system.

Bearing Skidding Detection for High Speed and Aero Engine Applications

2021 ◽  
Author(s):  
Azzedine Dadouche ◽  
Rami Kerrouche
Keyword(s):  
High Speed ◽  
Power Losses ◽  
Severe Damage ◽  
Roller Bearings ◽  
Custom Made ◽  
Rolling Element ◽  
Aero Engine ◽  
Oil Flow ◽  
Rolling Elements ◽  
Surface Distress

Abstract Rolling-element bearings (REB) can develop severe damage due to skidding (slipping) between the rolling elements and bearing races. Skidding can be described as gross sliding between the bearing surfaces in relative motion and can result in significant surface distress such as smearing, especially at light loads and high rotational speeds. Under these conditions, skidding occurs between the rolling elements and the bearing races, leading to increased wear (higher friction coefficient), elevated bearing temperature, significant power losses and reduced service life of the bearing. The main objective of this study is to investigate the significance of various sensing technologies (induction, vibration, ultrasound, acoustic and optical) in detecting skidding in standard series roller bearings as well as custom-made roller bearings for aero engine applications. The bearings have a bore diameter of 60 mm and 90 mm, respectively. Jet and under race lubrication techniques have been used to supply oil to the bearings under test. The custom-made aero engine test bearing features special channels to allow under race lubrication of the rollers/races contacts as well as the cage land. The effect of radial load, rotational speed and oil flow on roller skidding have also been investigated and analyzed. Tests have been performed on a dedicated high speed experimental bearing facility and data was recorded using a commercially-available data acquisition system.

Dynamic vacuum pressure tracking control with high-speed on-off valves

2018 ◽  
Vol 232 (10) ◽  
pp. 1325-1336 ◽  
Author(s):  
Gang Yang ◽  
Kai Chen ◽  
Linglong Du ◽  
Jingmin Du ◽  
Baoren Li
Keyword(s):  
Mass Flow ◽  
Pulse Width ◽  
High Speed ◽  
Pulse Width Modulation ◽  
Sliding Mode ◽  
Tracking System ◽  
Vacuum Pressure ◽  
Chamber Pressure ◽  
Asymmetric Structure ◽  
The Impact

A vacuum pressure tracking system with high-speed on-off valves is a discontinuous system due to the discrete nature of high-speed on-off valves. Chamber pressure changes in the system are determined by the mass flow rates during the processes of charging and discharging. Here, a sliding mode controller with an asymmetric compensator based on average mass flow rate is designed for accurate vacuum pressure tracking. The controller output signal is converted into the duty cycles of the high-speed on-off valves via a pulse width modulation pulsing scheme. Owing to the extreme asymmetry of the processes, an asymmetric structure comprising one high-speed on-off valve in the charging unit and three high-speed on-off valves in the discharging unit is applied to weaken the impact of asymmetry. In addition, an asymmetric compensator is also designed to modify the pulse width modulation pulsing scheme to further eliminate the asymmetry. Experimental results indicate that the proposed controller achieves better performance in pressure tracking with the asymmetric compensator overcoming process asymmetry and enhancing system robustness.

Effect of Cross-Flow Swirl on the Trajectory of Spray in an Annular Passage

2020 ◽  
Author(s):  
Tushar Sikroria ◽  
Abhijit Kushari
Keyword(s):  
Momentum Flux ◽  
High Speed ◽  
Air Flow ◽  
Cross Flow ◽  
Flux Ratio ◽  
Liquid Jet ◽  
Swirl Number ◽  
Flow Swirl ◽  
Air Stream ◽  
The Impact

Abstract This paper presents the experimental analysis of the impact of swirl number of cross-flowing air stream on liquid jet spray trajectory at a fixed air flow velocity of 42 m/s with the corresponding Mach number of 0.12. The experiments were conducted for 4 different swirl numbers (0, 0.2, 0.42 and 0.73) using swirl vanes at air inlet having angles of 0°, 15°, 30° and 45° respectively. Liquid to air momentum flux ratio (q) was varied from 5 to 25. High speed (@ 500 fps) images of the spray were captured and those images were processed using MATLAB to obtain the path of the spray at various momentum flux ratios. The results show interesting trends for the spray trajectory and the jet spread in swirling air flow. High swirling flows not only lead to spray with lower radial penetration due to sharp bending and disintegration of liquid jet, but also result in spray with high jet spread and spray area. Based on the results, correlations for the spray path have been proposed which incorporates the effects of the swirl number of the air flow.

scholarly journals Variable rotor speed strategy for coaxial compound helicopters with lift–offset rotors

2019 ◽  
Vol 124 (1271) ◽  
pp. 96-120 ◽  
Author(s):  
Y. Yuan ◽  
D. Thomson ◽  
R. Chen
Keyword(s):  
Power Consumption ◽  
High Speed ◽  
High Performance ◽  
Normal Load ◽  
Flight Dynamics ◽  
Load Factor ◽  
Rotor Speed ◽  
Inverse Simulation ◽  
Maneuvering Flight ◽  
The Impact

ABSTRACTThe coaxial compound helicopter with lift-offset rotors has been proposed as a concept for future high-performance rotorcraft. This helicopter usually utilizes a variable-speed rotor system to improve the high-speed performance and the cruise efficiency. A flight dynamics model of this helicopter associated with rotor speed governor/engine model is used in this article to investigate the effect of the rotor speed change and to study the variable rotor speed strategy. Firstly, the power-required results at various rotor rotational speeds are calculated. This comparison indicates that choice of rotor speed can reduce the power consumption, and the rotor speed has to be reduced in high-speed flight due to the compressibility effects at the blade tip region. Furthermore, the rotor speed strategy in trim is obtained by optimizing the power required. It is demonstrated that the variable rotor speed successfully improves the performance across the flight range, but especially in the mid-speed range, where the rotor speed strategy can reduce the overall power consumption by around 15%. To investigate the impact of the rotor speed strategy on the flight dynamics properties, the trim characteristics, the bandwidth and phase delay, and eigenvalues are investigated. It is shown that the reduction of the rotor speed alters the flight dynamics characteristics as it affects the stability, damping, and control power provided by the coaxial rotor. However, the handling qualities requirements are still satisfied with different rotor speed strategies. Finally, a rotor speed strategy associated with the collective pitch is designed for maneuvering flight considering the normal load factor. Inverse simulation is used to investigate this strategy on maneuverability in the Push-up & Pull-over Mission-Task-Element (MTE). It is shown that the helicopter can achieve Level 1 ratings with this rotor speed strategy. In addition, the rotor speed strategy could further reduce the power consumption and pilot workload during the maneuver.

An Approach for Predicting the Flow Regime in an Aero Engine Bearing Chamber

2014 ◽  
Author(s):  
Wolfram Kurz ◽  
Hans-Jörg Bauer
Keyword(s):  
Flow Regime ◽  
Air Flow ◽  
Flow Regimes ◽  
Chamber Pressure ◽  
Test Rig ◽  
Oil Viscosity ◽  
Oil Film ◽  
Aero Engine ◽  
Oil Flow ◽  
Engine Bearing

The paper discusses an approach to predict the two-phase flow regime in an aero engine bearing chamber. In general, one of two distinct flow regimes can occur in a bearing chamber. At lower shaft speeds, the oil flow is only partially affected by the air flow, which is driven by the rotating shaft. At higher shaft speeds, however, the rotating air flow forces the oil film at the chamber walls to rotate, too. Thus, the two flow regimes correspond to two very different oil film distributions inside a bearing chamber presumably with significant consequences for the internal wall heat transfer. In order to determine the driving parameters for the flow regimes and the change between them, experiments were carried out with a bearing chamber test rig. With this test rig all relevant operating parameters as well as the geometry of the bearing chamber could be varied independently. The analysis of the experimental data allowed defining a general parameter which takes into account the chamber pressure, shaft speed, oil viscosity and chamber length. The influence of the oil flow rate and the overall dimensions are assessed qualitatively.

A Model for Oil Flow and Fluid Temperature Inlet Mixing in Hydrodynamic Journal Bearings

2018 ◽  
Vol 141 (2) ◽  
Author(s):  
Thomas Hagemann ◽  
Hubert Schwarze
Keyword(s):  
Boundary Conditions ◽  
High Speed ◽  
Hydrodynamic Lubrication ◽  
Three Dimensional ◽  
Journal Bearings ◽  
Conductive Heat ◽  
Fluid Temperature ◽  
Inlet Region ◽  
Oil Flow ◽  
The Impact

The quality of predictions for the operating behavior of high-speed journal bearings strongly depends on realistic boundary conditions within the inlet region supplying a mixture of hot oil from the upstream pad and fresh lubricant from the inlet device to the downstream located pad. Therefore, an appropriate modeling of fundamental phenomena within the inlet region is essential for a reliable simulation of fluid and heat flow in the entire bearing. A theoretical model including hydraulic, mechanical, and energetic effects and the procedure of its numerical implementation in typical bearing codes for thermo-hydrodynamic lubrication is described and validated. Convective and conductive heat transfer as well as dissipation due to internal friction in the lubricant is considered for the space between pads or the pocket where the inlet is located. In contrast to most other models, the region between the physical inlet and the lubricant film is part of the solution domain and not only represented by boundary conditions. The model provides flow rate and temperature boundary conditions for extended Reynolds equation and a three-dimensional (3D) energy equation of film and inlet region, respectively. The impact of backflow from the inlet region to the outer supply channel possibly occurring in sealed pockets is taken into account. Moreover, the model considers the influence of turbulent flow in the inlet region.

Experiments on a Large Flexure Pivot Journal Bearing: Summary of Test Results and Comparison With Predictions

2020 ◽  
Vol 142 (3) ◽  
Author(s):  
Giuseppe Vannini ◽  
Filippo Cangioli ◽  
Enrico Ciulli ◽  
Matteo Nuti ◽  
Paola Forte ◽  
...  
Keyword(s):  
High Speed ◽  
Maximum Load ◽  
Numerical Code ◽  
Test Facility ◽  
Temperature Management ◽  
Unit Load ◽  
Rolling Element ◽  
Oil Flow ◽  
Static And Dynamic Loads ◽  
The University

Abstract Flexure pivot® journal bearings (FPJBs) have typically been used in small high-speed applications such as integrally geared compressors and multistage high-speed compressors, where the temperature management and the rotordynamic stability of the machine are the main targets. Nevertheless, the need for high-speed applications may also be applicable to large compressors and for this reason a large 280 mm diameter four-pad FPJB with L/D = 0.7 has been designed, built, and tested by the Authors. The test facility is a novel rig, setup at the University of Pisa, that includes a floating test bearing and a rigid rotor supported by two stiff rolling element bearings. Both static and dynamic loads are applied through hydraulic actuators, capable of 270 kN static and 40 kN overall dynamic load. The instrumentation can measure all the relevant test boundary conditions as well as the static and dynamic quantities that characterize the bearing performance. This paper presents the results from a test campaign conceived to explore not only the design conditions (7000 rpm rotational speed and 0.75 MPa unit load) but also the sensitivity to the unit load (from 0.2 MPa minimum load up to 2.2 MPa maximum load) as well as the oil flow. The results are discussed and compared with predictions from an existing numerical code.

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