58988 - Numerical Investigation of Air-Oil Two-Phase Flow Pattern Transition in the Scavenge Line of an Aeroengine 

Abstract

Since most research investments in aero-engines have been targeted at the hot and cold sections, the oil system has remained an area poorly understood. Optimum sizing of the oil system can directly reduce the engine’s weight and specific fuel consumption while maximizing service life. The understanding of air/oil interaction in scavenge lines is required to influence the design of the oil systems and achieve those objectives.

The challenge is in the existence of numerous possible flow regimes and phase interactions. In scavenge lines, a complex two-phase flow results from the interaction of sealing airflow and lubrication oil [1,2]. Scavenge lines can have bends, junctions and sudden area changes which complicates their modeling by amplifying pressure gradients and turbulence generation, and also causing the flow to change morphology (annular, slug, stratified, bubbly, mist, etc.) [3].

Several multiphase flow approaches have been developed to model two-phase flow in straight scavenge lines [4,5]. However, up until now, the simulation of two-phase flow for such application remains blurry. There are still many unknowns regarding the modeling of turbulence, phase interaction and the compressibility of immiscible mixtures such as air and oil.

The present study compares the performance of two numerical models: Volume of Fluid (VOF) and Algebraic Interfacial Area Density (AIAD). AIAD is an approach implemented in the Eulerian model for modeling the air/oil flow in a suddenly expanding scavenge line against the experimental data of Ahmed et al. [6,7]. This analysis evaluates discrepancies between the two models for predicting pressure loss and void fraction. The flow regime before and after the sudden expansion is identified using iso-surfaces of the void-fraction and compared against visual data. Based on the results presented, recommendations are formulated for further work regarding the calibration of AIAD modeling parameters.

  ACKNOWLEDGEMENTS

Pratt & Whitney Canada would like to thank ANSYS Pune for their support and their notable contribution in this investigation and Mitacs for their financial support for the project IT15315.

REFERENCES

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[2] Kanarachos ST, Flouros MI. Simulation of the Air–Oil Mixture Flow in the Scavenge Pipe of an Aero Engine Using Generalized Interphase Momentum Exchange Models. WSEAS Trans. Fluid Mech. 2014; 9:144-153.

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[4] Pawloski JL, Ching CY, Shoukri M. Measurement of void fraction and pressure drop of air-oil two-phase flow in horizontal pipes. J. Eng. Gas Turbines Power. 2004;126(1):107-118.

[5] Zhang D, Goharzadeh A. Effect of sudden expansion on two-phase flow in a horizontal pipe. Fluid Dynamics. 2019; 54(1): 123-136.

[6] Ahmed WH, Ching CY, Shoukri M. Pressure recovery of two-phase flow across sudden expansions. Int. J. Multiphase Flow. 2007; 33(6): 575-594.

[7] Ahmed WH, Ching CY, Shoukri M. Development of two-phase flow downstream of a horizontal sudden expansion. Int. J. Heat Fluid Flow. 2008; 29(1):194-206.