A Separation Criterion With Experimental Validation for Shear-Driven Films in Separated Flows

2008 ◽  
Vol 130 (5) ◽  
Author(s):  
M. A. Friedrich ◽  
H. Lan ◽  
J. L. Wegener ◽  
J. A. Drallmeier ◽  
B. F. Armaly
Keyword(s):  
Liquid Film ◽  
Gas Phase ◽  
Experimental Validation ◽  
Thin Liquid Film ◽  
Complete Separation ◽  
Separated Flows ◽  
Force Ratio ◽  
Wide Range ◽  
Inertial Surface ◽  
Film Separation

The behavior of a shear-driven thin liquid film at a sharp expanding corner is of interest in many engineering applications. However, details of the interaction between inertial, surface tension, and gravitational forces at the corner that result in partial or complete separation of the film from the surface are not clear. A criterion is proposed to predict the onset of shear-driven film separation from the surface at an expanding corner. The criterion is validated with experimental measurements of the percent of film mass separated as well as comparisons to other observations from the literature. The results show that the proposed force ratio correlates well to the onset of film separation over a wide range of experimental test conditions. The correlation suggests that the gas phase impacts the separation process only through its effect on the liquid film momentum.

scholarly journals Motion and Evaporation of Shear-Driven Liquid Films in Turbulent Gases

1991 ◽  
Author(s):  
S. Wittig ◽  
J. Himmelsbach ◽  
B. Noll ◽  
H. J. Feld ◽  
W. Samenfink
Keyword(s):  
Shear Stress ◽  
Liquid Film ◽  
Gas Phase ◽  
Film Flow ◽  
Phase Interface ◽  
Liquid Films ◽  
Numerical Code ◽  
Optical Instrument ◽  
Turbulent Characteristics ◽  
Wide Range

Detailed measurements of wavy liquid films driven by the shear stress of turbulent air flow are obtained for different air temperatures, air velocities and flow rates of the liquid. The experimental conditions are chosen from characteristic data of liquid film flow in prefilming airblast atomizers and film vaporization employing combustors. For the measurement of the local film thickness and film velocity a new optical instrument — based on the light absorption of the liquid — has been developed, which can be used at high temperatures with evaporation. The measured data of the gas phase and the liquid film are compared with the results of a numerical code using a laminar as well as a turbulent model for the film flow and a standard numerical finite volume code for the gas phase. The results utilizing the two models for the liquid film show that the film exhibits laminar rather then turbulent characteristics under a wide range of flow conditions. This is of considerable interest when heat is transferred across the film by heating or cooling of the wall. With this information the optical instrument can also be used to determine the local shear stress of the gas phase at the phase interface. Using time averaged values for the thickness, the velocity and the roughness of the film the code leads to relatively accurate predictions of the interaction of the liquid film with the gas phase.

scholarly journals Modeling of Partially Wetting Liquid Film Using an Enhanced Thin Film Model for Aero-Engine Bearing Chamber Applications

2021 ◽  
Vol 143 (4) ◽  
Author(s):  
Kuldeep Singh ◽  
Medhat Sharabi ◽  
Richard Jefferson-Loveday ◽  
Stephen Ambrose ◽  
Carol Eastwick ◽  
...  
Keyword(s):  
Thin Film ◽  
Contact Angle ◽  
Film Thickness ◽  
Liquid Film ◽  
Thin Liquid Film ◽  
Operating Conditions ◽  
Film Model ◽  
Thin Film Model ◽  
Wide Range ◽  
Aero Engine

Abstract In the case of aero-engine, thin lubricating film servers dual purpose of lubrication and cooling. Prediction of dry patches or lubricant starved region in bearing or bearing chambers are required for safe operation of these components. In this work, thin liquid film flow is numerically investigated using the framework of the Eulerian thin film model (ETFM) for conditions, which exhibit partial wetting phenomenon. This model includes a parameter that requires adjustment to account for the dynamic contact angle. Two different experimental data sets have been used for comparisons against simulations, which cover a wide range of operating conditions including varying the flowrate, inclination angle, contact angle, and liquid–gas surface tension coefficient. A new expression for the model parameter has been proposed and calibrated based on the simulated cases. This is employed to predict film thickness on a bearing chamber which is subjected to a complex multiphase flow. From this study, it is observed that the proposed approach shows good quantitative comparisons of the film thickness of flow down an inclined plate and for the representative bearing chamber. A comparison of model predictions with and without wetting and drying capabilities is also presented on the bearing chamber for shaft speed in the range of 2500 RPM to 10,000 RPM and flowrate in the range of 0.5 liter per minute (LPM) to 2.5 LPM.

Motion and Evaporation of Shear-Driven Liquid Films in Turbulent Gases

1992 ◽  
Vol 114 (2) ◽  
pp. 395-400 ◽  
Author(s):  
S. Wittig ◽  
J. Himmelsbach ◽  
B. Noll ◽  
H. J. Feld ◽  
W. Samenfink
Keyword(s):  
Shear Stress ◽  
Liquid Film ◽  
Gas Phase ◽  
Film Flow ◽  
Phase Interface ◽  
Liquid Films ◽  
Numerical Code ◽  
Optical Instrument ◽  
Turbulent Characteristics ◽  
Wide Range

Detailed measurements of wavy liquid films driven by the shear stress of turbulent air flow are obtained for different air temperatures, air velocities, and flow rates of the liquid. The experimental conditions are chosen from characteristic data of liquid film flow in prefilming airblast atomizers and film vaporization employing combustors. For the measurement of the local film thickness and film velocity a new optical instrument—based on the light absorption of the liquid—has been developed, which can be used at high temperatures with evaporation. The measured data of the gas phase and the liquid film are compared with the results of a numerical code using a laminar as well as a turbulent model for the film flow and a standard numerical finite volume code for the gas phase. The results utilizing the two models for the liquid film show that the film exhibits laminar rather than turbulent characteristics under a wide range of flow conditions. This is of considerable interest when heat is transferred across the film by heating or cooling of the wall. With this information the optical instrument can also be used to determine the local shear stress of the gas phase at the phase interface. Using time-averaged values for the thickness, the velocity, and the roughness of the film, the code leads to relatively accurate predictions of the interaction of the liquid film with the gas phase.

Effect of Large Amplitude Waves and Film Inertia on Mass Separation at a Sharp Corner

2018 ◽  
Vol 140 (8) ◽  
Author(s):  
Zahra Sadeghizadeh ◽  
James A. Drallmeier
Keyword(s):  
Liquid Film ◽  
Gas Phase ◽  
Large Amplitude ◽  
Thin Liquid Film ◽  
Mass Separation ◽  
Sharp Corner ◽  
Film Substrate ◽  
The Impact ◽  
Separation Results ◽  
Insight Into

The separation of a shear-driven thin liquid film from a sharp corner is studied in this paper. Partial or complete mass separation at a sharp corner is affected by two different mechanisms: liquid film inertia, which affects liquid mass separation through force imbalance at the sharp corner, and large amplitude waves (LAW) at the interface, which contributes to liquid instability at the corner. Experimental results for liquid Ref number that varies from 100 to 300 and mean film thickness from 130 to 290 μm show that both film inertia and LAW effects correlate to mass separation results. The results suggest that while both inertia of the film substrate and LAW effects enhance the mass separation, the correlations between LAW characteristics and mass separation results provide better insight into the onset of separation and the impact of the gas phase velocity on separation for the conditions studied.

Analyze of the Size of Secondary Droplets due to Film Separation at the Blade Trailing Edge

2014 ◽  
Author(s):  
Hans Josef Dohmen ◽  
Friedrich-Karl Benra ◽  
Cornelius Schepers ◽  
Sebastian Schuster
Keyword(s):  
Free Surface ◽  
Liquid Film ◽  
Thin Liquid Film ◽  
Third Party ◽  
Working Fluid ◽  
Surface Model ◽  
Trailing Edge ◽  
Secondary Droplets ◽  
Free Surface Model ◽  
Film Separation

In many turbo machinery applications the working fluid is a mixture of a gas and a liquid. In such two-phase flows the liquid phase can be assumed to be a dispersed droplet flow. As the fluid passes the blades, a part of the droplets is deposited on the blades and forms a thin liquid film. At the trailing edge the thin liquid film separates and forms secondary droplets. In this paper the ability of numerical investigations to study the size of secondary droplets is analyzed. In a first step a program solving the Thin Film Equations is used to analyze the film flow on the inlet guide vanes of an axial compressor. Secondly a CFD study with a Free Surface Model is performed to analyze the film stripping process. The ability of the Free Surface model to investigate film separation is validated against third party experimental results and the pro and contras of the Free-Surface model are presented. In the last step the stability of the formed droplets is investigated and the final droplet size is calculated.

scholarly journals The motion of curling rocks: Experimental investigation and semi-phenomenological description

2004 ◽  
Vol 82 (10) ◽  
pp. 791-809 ◽  
Author(s):  
E T Jensen ◽  
Mark RA Shegelski
Keyword(s):  
Experimental Investigation ◽  
Liquid Film ◽  
Frictional Force ◽  
Dry Friction ◽  
Thin Liquid Film ◽  
Ice Surface ◽  
Wet Friction ◽  
Wide Range ◽  
Friction Models ◽  
Rule Out

A large number of curling shots using a wide range of rotational and translational velocities on two different ice surfaces have been recorded and analyzed. The observed curling-rock trajectories are described in terms of a semi-phenomenological model. The data are found to rule out "dry-friction" models for the observed motion, and to support the idea that the curling rock rides upon a thin liquid film created at the ice surface (i.e., "wet friction"). Evidence is found to support the hypothesis that the frictional force acting upon each segment of the curling rock is directed opposite to the motion relative to this thin liquid film and not relative to the underlying fixed ice surface. PACS No.: 01.80.+b

Intrinsic Stacking Interactions of Natural and Artificial Nucleobases

2019 ◽  
Author(s):  
Drew P. Harding ◽  
Laura J. Kingsley ◽  
Glen Spraggon ◽  
Steven Wheeler
Keyword(s):  
Gas Phase ◽  
Electrostatic Interactions ◽  
Density Functional ◽  
Molecular Descriptors ◽  
Stacking Interactions ◽  
Interaction Energies ◽  
Functional Theory ◽  
Binding Partner ◽  
Heavy Atoms ◽  
Wide Range

The intrinsic (gas-phase) stacking energies of natural and artificial nucleobases were explored using density functional theory (DFT) and correlated ab initio methods. Ranking the stacking strength of natural nucleobase dimers revealed a preference in binding partner similar to that seen from experiments, namely G > C > A > T > U. Decomposition of these interaction energies using symmetry-adapted perturbation theory (SAPT) showed that these dispersion dominated interactions are modulated by electrostatics. Artificial nucleobases showed a similar stacking preference for natural nucleobases and were also modulated by electrostatic interactions. A robust predictive multivariate model was developed that quantitively predicts the maximum stacking interaction between natural and a wide range of artificial nucleobases using molecular descriptors based on computed electrostatic potentials (ESPs) and the number of heavy atoms. This model should find utility in designing artificial nucleobase analogs that exhibit stacking interactions comparable to those of natural nucleobases. Further analysis of the descriptors in this model unveil the origin of superior stacking abilities of certain nucleobases, including cytosine and guanine.

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