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Numerical Investigation of Two Phase Flow in a Dual Drive Booster (DDB)
Abstract
The Dual Drive Booster (DDB) is a novel concept aimed at improving the performance of 2-shaft turbo-fan engines. The DDB concept relies on a high speed epicyclic gearbox to extract power from both the LP and HP shafts and drive the booster compressor. The DDB has also been shown to permit high power extraction from the engine without the large working line excursions which usually limit this. Efficient scavenging of the lubrication oil to prevent churning and heat generation is a requirement of such gearboxes and this paper aims to investigate performance of the oil scavenge system of a typical DDB gearbox.
Efficient scavenging of oil is essential to eradicate the risks that may arise when oil resides in the gearbox for prolonged durations. Longer residence times of oil in the gearbox can lead to rapid oil degradation. Simulations were conducted on a previously optimized geometry and the work in this paper focuses on investigating the effect of different operating conditions on scavenging performance. The effect of attitude, altitude and the inlet flow rate of oil have been simulated to understand their influence on the oil flow behaviour. Emphasis is given on the predicting potential oil churning, recirculation and pooling behaviours in the scavenge chamber that encloses the gear box.
Numerical Investigations are carried out using ANSYS Fluent. The Volume of Fluid (VOF) model is employed to model the multiphase flow arising between air and oil in the system. Validation against published experimental data for similar flow regimes and mesh independency tests were also carried out. Results indicate that the scavenging performance is not affected significantly under the various operating conditions and scenarios that were investigated. This is because the effects of the windage outweigh the effects caused by the different operating conditions that are imposed to the scavenge chamber. The windage in the system drives the oil efficiently out from the chamber with the aid of the tangential sump. Oil is distributed in an axially central section of the chamber and the total residence mass of oil is compared and is under 0.5 kg for all of the cases presented in this paper.
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The duct of a robot vacuum cleaner is the length of the flow channel between the inlet of the rolling brush blower and the outlet of the vacuum blower. To cope with the pressure drop problem of the duct flow field in a robot vacuum cleaner, a method based on Pressure Implicit with Splitting of Operators (PRISO) algorithm is introduced and the optimisation design of the duct flow field is implemented. Firstly, the duct structure in a robot vacuum cleaner is taken as a research object, with the computational fluid dynamics (CFD) theories adopted; a three‐dimensional fluid model of the duct is established by means of the FLUENT solver of the CFD software. Secondly, with the k‐ε turbulence model of three‐ dimensional incompressible fluid considered and the PRISO pressure modification algorithm employed, the flow field numerical simulations inside the duct of the robot vacuum cleaner are carried out. Then, the velocity vector plots on the arbitrary plane of the duct flow field are obtained. Finally, an investigation of the dynamic characteristics of the duct flow field is done and defects of the original duct flow field are analysed, the optimisation of the original flow field has then been conducted. Experimental results show that the duct flow field after optimisation can effectively reduce pressure drop, the feasibility as well as the correctness of the theoretical modelling and optimisation approaches are validated.
A new method for modeling surface tension effects on fluid motion has been developed. Interfaces between fluids of different properties, or "colors", are represented as transition regions of finite thickness, across which the color variable varies continuously. At each point in the transition region, a force density is defined which is proportional to the curvature of the surface of constant color at that point. It is normalized so that the conventional description of surface tension on an interface is recovered when the ratio of local transition region thickness to local radius of curvature approaches zero. The continuum method eliminates the need for interface reconstruction, simplifies the calculation of surface tension, enables accurate modeling of two- and three-dimensional fluid flows driven by surface forces, and does not impose any modeling restrictions on the number, complexity, or dynamic evolution of fluid interfaces having surface tension. Computational results for two-dimensional flows are given to illustrate the properties of the method.
This paper presents a coupled ETFM-VOF framework for the numerical simulation of multi-scale thin liquid films. A depth-averaged Eulerian thin-film model (ETFM) is used to simulate the oil flow in very thin-film regions where film thicknesses are below the grid resolution while elsewhere in the domain where grid resolution is sufficient to resolve the film, a traditional Volume-of-Fluid (VOF) approach is retained. The two approaches are coupled through momentum and mass conserving source terms and a transition criterion is introduced where the total liquid volume fraction in each cell is evaluated and either the ETFM or VOF approach used depending on the sufficiency of the local grid resolution. Using this approach, thin-film flows characterised by multiple film thickness scales may be reliably simulated at a relatively lower computational cost. The model builds upon currently available ETFM and VOF approaches to thin-film modelling and represents a novel approach to the numerical simulation of multiphase flows involving a varying range of film thickness scales in space and time. A numerical test case of the 3D rimming flow inside an idealised aero-engine bearing chamber has been used to demonstrate the approach and comparisons made against high resolution VOF solutions.
Copyright © 2016 by ASME Country-Specific Mortality and Growth Failure in Infancy and Yound Children and Association With Material Stature
Use interactive graphics and maps to view and sort country-specific infant and early dhildhood mortality and growth failure data and their association with maternal
The presented work aims to identify a Volume of Fluid (VOF) CFD approach for the transient simulation of air/oil flows inside an aero-engine bearing chamber. Typically VOF requires relatively fine grids and consequently small time-steps to sufficiently resolve the formation of oil films and their interaction with air flows. The need to achieve a stationary-state which requires flow times on the order of seconds makes the compromise between simulation accuracy and simulation times a challenging choice when using the VOF method. In this work, the use of the Compressive Interface Reconstruction scheme with bounded second order implicit time discretization has enabled a significant speed-up of the simulation times against the previously adopted explicit Geometric-Reconstruction scheme. The results are evaluated against experimental data available in the literature.
This paper presents results of the threedimensional numerical modelling of the air/oil twophase flow inside an aero engine bearing chamber. Simulations with different shaft speeds and chamber geometries were carried out and compared to experimental data in order to evaluate the potential and accuracy of the Volume-of-Fluid method for the modelling of complex multiphase flows.
For different bearing chamber scavenge offtake geometries and shaft speeds, the resulting scavenge characteristics, film thicknesses and flow pattern were analysed. Especially for the prediction of the scavenge characteristics, good agreement of numerical and experimental results was obtained. However, the accurate prediction of oil distribution and film thicknesses showed to be sensitive to the mesh resolution. Nevertheless, even with a coarse mesh, correct tendencies were observed.
With the application of a local Adaptive Mesh Refinement algorithm, the prediction of the oil film formation was improved. An additional influence of the surface-capturing scheme within the Volume-of-Fluid method on the solution accuracy has been identified.
In this paper, we present results for the application of an Eulerian-Lagrangian technique to the transient simulation of an oil film formation on the walls of an aeroengine bearing chamber. The flow of oil in an aeroengine bearing chamber consists of high speed oil droplets interacting with the bearing structures and flowing oil film. The situation in the chamber is highly rotational and consisting of sheared flow of air over oil. The bearing chamber may also be located in the vicinity of the combustion chamber. The oil provides lubrication and cooling of the hot structures. Modelling the flow in the bearing chamber is therefore complex. The Volume of Fluid (VoF) technique offers a potential platform to model droplet-film interaction; however, it requires fine mesh details to capture the flow to the droplet level. Such detailed resolution would not be practical for the complete chamber geometry because of the prohibitively expensive computational overhead requirements. A Lagrangian formulation is therefore proposed to represent the droplets as source terms in the Navier-Stokes equation while the film is represented using VoF. This effectively reduces the need to resolve the droplets explicitly. The predicted film formation pattern compares with experimental results.
Copyright © 2014 by Rolls-Royce plc Country-Specific Mortality and Growth Failure in Infancy and Yound Children and Association With Material Stature
Use interactive graphics and maps to view and sort country-specific infant and early dhildhood mortality and growth failure data and their association with maternal
Several methods have been previously used to approximate free boundaries in finite-difference numerical simulations. A simple, but powerful, method is described that is based on the concept of a fractional volume of fluid (VOF). This method is shown to be more flexible and efficient than other methods for treating complicated free boundary configurations. To illustrate the method, a description is given for an incompressible hydrodynamics code, SOLA-VOF, that uses the VOF technique to track free fluid surfaces.
Aircraft Engine; Ceramics; Coal, Biomass and Alternative Fuels; Education; Electric Power; Manufacturing Materials and Metallurgy
- B Chandra
- K Simmons
- S Pickering
- M Tittel
Chandra, B., Simmons, K., Pickering, S., and Tittel, M.,
2010, "Factors Affecting Oil Removal From an
Aeroengine Bearing Chamber," Volume 1: Aircraft
Engine; Ceramics; Coal, Biomass and Alternative
Fuels; Education; Electric Power; Manufacturing
Materials and Metallurgy, pp. 219-228.
Study of Gas/Liquid Behavior Within an Aeroengine Bearing Chamber
- B Chandra
- K Simmons
- S Pickering
- S H Collicott
- N Wiedemann
Chandra, B., Simmons, K., Pickering, S., Collicott, S.
H., and Wiedemann, N., 2013, "Study of Gas/Liquid
Behavior Within an Aeroengine Bearing Chamber," J.
Eng. Gas Turbines Power, 135(5), p. 51201.