| Description |
1 online resource (208 pages) |
| Series |
Forschungsberichte Aus Dem Institut Für Thermische Strömungsmaschinen Ser. ; v. 59/2015 |
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Forschungsberichte Aus Dem Institut Für Thermische Strömungsmaschinen Ser
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| Contents |
Intro; 1 Introduction; 2 State of Scientific Knowledge; 2.1 Parameter of Influence describing the Drop Impact Dynamics; 2.2 Non-Dimensional Quantities describing the Drop Impact Dynamics; 2.3 Drop-to-Film Interaction in Aero-Engine Bearing Chambers; 2.4 Phenomenological Description of the Impingement Regimes; 2.5 Transitional Regime Thresholds between Spreading and Splashing; 2.6 Secondary Droplet Generation within the Splashing Regime; 2.6.1 Crown and Cavity Evolution in the Splashing Regime; 2.6.2 Theory of Instability Driving the Break up of the Crownâ#x80;#x99;s Rim |
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2.6.3 Secondary Drop Characteristics during the Drop Impact2.7 Numerical Simulation of the Single Drop Impact onto Liquid Films; 2.8 Modelling Spray Impact; 2.9 Concretization of Objectives and Aim of Investigation; 3 Numerical Method and CFD Modelling of Single Drop Impacts; 3.1 Mathematical Method -- Volume-Of-Fluid Method; 3.2 Numerical Solution Procedure; 3.2.1 Discretization Procedure; 3.2.2 Pressure-Velocity Coupling; 3.2.3 Adaptive Mesh Refinement; 3.3 Computational Domain and Initial/Boundary Conditions; 3.3.1 2D-VOF-AMR -- Numerical Model for Crown and Cavity Expansion |
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3.3.2 3D-VOF-AMR -- Numerical Model for Splashing3.4 Concluding Discussion; 4 Experimental Validation of the VOF-AMR Method; 4.1 Experimental Method; 4.2 Results and Discussion; 4.2.1 Study of the Transitional Threshold between Spread and Splash; 4.2.2 Assessment of the 3D-VOF-AMR Method; 4.2.3 Assessment of the Axisymmetric 2D-VOF-AMR Method; 4.3 Concluding Discussion; 5 Products of Splashing Drop Impingements without Wall Effects; 5.1 Fundamental Description of a Splashing Impingement; 5.2 Analysis of the Instability driving the Disintegration of the Crown |
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5.3 Evaluation Procedure for the Following Parametric Study5.4 Effect of the Impinging Weber number; 5.5 Effect of the Froude number Fr; 5.6 Effect of the Impinging Ohnesorge Number; 5.7 Effect of the Impingement Angle a; 5.8 Concluding Discussion; 6 Products of Splashing Drop Impingements with Wall Effects; 6.1 Cavity Penetration during Deep Pool Drop Impact; 6.1.1 Fundamental Description of the Cavity Evolution; 6.1.2 Effect of the Froude Number on the Cavity Penetration; 6.1.3 Effect of the Impinging Weber number on the Cavity Penetration |
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6.1.4 Effect of the Ohnesorge Number on the Cavity Penetration6.1.5 Effect of Impingement Angle on the Cavity Penetration; 6.2 Effect of Cavity Penetration & Liquid Film Height on the Secondary Drop Generation; 6.2.1 Relation between Cavity Penetration and Lamella Expansion; 6.2.2 Effect of the Ratio H*/ Delta max, deep on Secondary Drop Generation; 7 Correlations for the Products of Splashing; 7.1 Requirements for the Drop-Film Interaction Model; 7.2 Correlations for the Maximum Cavity Penetration and the Lamella Rim Height |
| Summary |
Annotation Bearing Chambers in Aero-Engines are located near the rolling-element type of bearings which support the shafts and accomodate the resulting thrust loads. One of the main task of the bearing chambers is, beside an efficient scavenging of the lubricating oil, the cooling of the hot compartments. A very complex two-phase air-oil flow takes usually place in these bearing chambers consisting of oil droplet-laden air flows and shear-driven liquid wall films. The interaction of the droplets with the wall films is significantly influencing the wall heat transfer and the cooling performance of these systems. For this reason, a detailed characterization and modelling of the mass and momentum exchange between droplets and wall films for the unique impingement parameter range in bearing chambers is inevitable. This scientific report investigates the oil droplet impact dynamics for typical impingement regimes relevant to aero-engine bearing chambers. The application of a Direct Numerical Simulation (DNS) technique based on the Volume-of-Fluid (VOF) method and coupled with a gradient-based adaptive mesh refinement (AMR) technique allowed to characterize the drop impact dynamics during various single micro- and millimeter drop impacts onto thin and thick films. With the help of a special numerical treatment, a self-perturbing mechanism is installed that leads to the correct resolution of the crown disintegration process. The numerical methodology was thoroughly validated using the experimental results of millimeter sized drop impacts onto deep liquid pools. These results were developed with an enhanced back-illuminated high-speed imaging and Particle Tracking Velocimetry (PTV) technique. New insights into the cavity penetration, the crown's breakup dynamics and the secondary droplet characteristics following a single drop impact have been developed with the help of the isolated variation of different parameters of influence. Particularly the influence of the Froude number, the impingement angle, and the cavity-wall interaction delivered results to date not reported in scientific literature. Beside the advances in fundamental physics describing the drop impact dynamics with the help of the numerical and experimental results, a set of correlations could also be derived. From these correlations, a drop-film interaction model was formulated that is suitable for the parameter range found in bearing chambers |
| Notes |
7.3 Correlating the Secondary Drop Characteristics and Ejected Mass Fraction |
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Print version record |
| Subject |
Lubricating oils.
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lubricating oil.
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Lubricating oils
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| Form |
Electronic book
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| ISBN |
9783832594930 |
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3832594930 |
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