Session: 34-12 Hydraulic turbines methods

Paper Number: 121558

121558 - Applicability of Volume of Fluid Method to Two-Phase Flow Turbomachinery Application 

Hydrodynamic bearings based on lubrication oil are commonly used in turbomachinery.  The understanding and modeling of the air-oil two-phase flows in the bearing casing, piping and drain are important during the design phase.

Given the limitations of the analytical methods and experiments, the development of robust and fast numerical methods, which can aid the engineers to assess various designs, is significant. Due to these limitations the two-phase flow simulations have become popular in the turbomachinery community.  In the past years, technical papers using the Volume of Fluid (VOF) method for such simulations, mainly for aeroengine applications, were published and the importance and engineering relevance of such approach was highlighted.  By definition, VOF method is suitable for the simulations of free surface flows of immersible phases.  In many implementations in the commercial CFD solvers, the two-phase interface is represented as a diffused interface and captured across a number of computation cells.

In this paper, the use of VOF method for the air-oil flows for turbomachinery is reviewed.  The paper first scrutinizes the use of VOF method for certain flow regimes from the perspective of the underlying VOF numerical method.  Then, based on a detailed investigation using test rig observation of a radial bearing of a turbocharger, the corresponding two-phase flow simulations using VOF are presented.  The simulations demonstrate that, provided the physical boundary conditions, e.g. realistic oil flow profile from bearing, are used; and equally important the correct use of the computation mesh and setup, accurate oil splashing and wetting pattern can be modeled. In particular, extensive grid studies show that, a sufficient fine grid is essential to correctly represent the interface; and on the other hand, identify the presence of unphysical parasite current due to numerical diffusion and interface smearing when an insufficient grid resolution is used to capture the two-phase interface.  Such misleading numerical artifact is especially inappropriate as it wrongly models the presence of the phases and their motions, and in turn leads to incorrect prediction of other flow phenomenon such as the formation of oil film, two-phase flow heat transfer and oil coking, etc.

 

Based on the knowledge gained from the radial bearing simulations, further simulations of oil drain using the VOF method are carried-out and presented to illustrate VOF applicability to different turbomachinery components.  This paper aims at illustrating the important aspects of the applications of the VOF and its engineering relevance for turbomachinery modeling and design.

Presenting Author: Christina Salpingidou Turbo Systems Switzerland Ltd

Presenting Author Biography: Christina Salpingidou has studied mechanical engineering in Aristotle University of Thessaloniki. The topic of her Ph.D was preliminary design of innovative aeroengines. She has worked for more than 3 years at MTU Aero Engines as project engineer at the preliminary design department. The last two years she works as CFD R&D engineer at Turbo Systems Switzerland Ltd (former ABB Turbocharging).

Authors:

Christina Salpingidou Turbo Systems Switzerland Ltd
Kwok Kai So Turbo Systems Switzerland Ltd