Feasibility Study on Oil Droplet Flow Investigations Inside Aero Engine Bearing Chambers—PDPA Techniques in Combination With Numerical Approaches

Abstract

The present paper deals with oil droplet flow phenomena in aero engine bearing chambers. An experimental investigation of droplet sizes and velocities utilizing a Phase Doppler Particle Analyzer (PDPA) has been performed for the first time in bearing chamber atmospheres under real engine conditions. Influences of high rotational speeds are discussed for individual droplet size classes. Although this is an important contribution to a better understanding of the droplet flow impact on secondary air/oil system performance, an analysis of the droplet flow behavior requires an incorporation of numerical methods because detailed measurements as performed here suffer from both strong spatial limitations with respect to the optical accessibility in real engine applications and constraints due to the extremely time-consuming nature of an experimental flow field analysis. Therefore, further analysis is based on numerical methods. Droplets characterized within the experiments are exposed to the flow field of the gaseous phase predicted by use of our well-known CFD code EPOS. The droplet trajectories and velocities are calculated within a Lagrangian frame of reference by forward numerical integration of the particle momentum equation. This paper has been initiated rather to show a successful method of bearing chamber droplet flow analysis by a combination of droplet sizing techniques and numerical approaches than to present field values as a function of all operating parameters. However, a first insight into the complex droplet flow phenomena is given and specific problems in bearing chamber heat transfer are related to the droplet flow.

Numerical Simulation of the Oil Droplet Size Distribution Considering Coalescence and Breakup in Aero-Engine Bearing Chamber

“…In order to verify the correctness of the calculation method, the result in this paper is compared with the relevant test in literature [16]. In the literature, the Phase Doppler Particle Analyzer (PDPA) is used to sample 3000 oil droplet diameters in the aero-engine bearing chamber, and the histogram of oil diameter distribution is obtained.…”

“…Chen et al [15] analyzed the parameter relationship between the structural condition of bearing chamber and the oil droplet size distribution, clarified the oil droplet mass distribution based on the continuous oil drop size distribution, and introduced the concept of continuous oil droplet diameter into the analysis of oil droplet movement. Glahn et al [16] measure the size distribution of oil droplet using the phase Doppler particle analyzer (PDPA) technology under various operating condition in the rotating disk chamber. In conclusion, the population balance theory has been widely applied in the analysis of coalescence and breakup between bubbles and droplets.…”

Computational fluid dynamics for turbomachinery internal air systems

“…Experimental, computational and theoretical approaches have been complementary, with the potential benefits of CFD recognised at an early stage. Although early calculations showed considerable promise (see, for example, Gosman et al, 1976) production of validated methods that can be applied with confidence was not straightforward. Numerical difficulties, turbulence model limitations, lack of suitable experimental measurements, and limited understanding of the flow mechanisms involved have all hampered progress.…”

Experimental study of the pressure loss in aero-engine air-oil separators

“…Oil leaving the bearing, and sealing air entering the chamber, mix and generate a complex two-phase flow consisting of oil film formation and droplets of a large range of different diameters, down to one micrometre and below. The two-phase flow in the bearing chamber and the related heat transfer have been studied by various authors (1)(2)(3)(4)(5)(6) . Oil and air are scavenged through the scavenge port and vent port, respectively.…”