Analysis of Oil Droplet Deposition Characteristics and Determination of Impact State Criterion in Aero-Engine Bearing Chamber

The research of oil/air two-phase flow and heat transfer is the fundamental work of the design of lubrication and heat transfer in aero-engine bearing chamber. The determination of impact state criterion of the moving oil droplets with the wall and the analysis of oil droplet deposition characteristics are important components. In this paper, the numerical analysis model of the impact between the moving oil droplet and the wall is established by using the finite volume method, and the simulation of oil droplet impingement on the wall is carried out. Then the effects of oil droplet diameter, impact velocity, and incident angle on the characteristic parameters of impact state are discussed. The characteristic parameters include the maximum spreading length, the maximum spreading width, and the number of splashing oil droplets. Lastly the calculation results are verified through comparing with the experimental results in the literature. The results show as follows: (1) The maximum spreading width of oil droplet firstly increases and then slows down with the incident angle and the oil droplet diameter increasing; (2) when the oil droplet diameter becomes small, the influence of the incident angle on the maximum spreading length of oil droplet is obvious and vice versa; (3) with the impact velocity and diameter of oil droplet increasing, the maximum spreading width of oil droplet increases firstly and then slows down, and the maximum spreading length increased gradually; (4) the number of splashing oil droplets increases with the incident angle and impact velocity increasing; and (5) compared with the experimental data in literature, the critical dimensionless splashing coefficient K c proposed in this paper can better distinguish the impact state of oil droplet.

West Africa Swell Spectral Shapes

Wave spectra measured at sites off West Africa are dominated by the constant presence of one or several swell wave systems. The West Africa Swell Project (WASP JIP) was carried out to propose and assess parametric models for the shapes of the swell components. Bias, variability, and dispersion of estimates are affected by the length/stationarity compromise of the record lengths and the window-tapering used to reduce their variability. In particular, shapes with sharp angles are strongly smoothed, for instance a triangular peak would appear round and reduced by 15 to 25% with rectangular or Tuckey windowing. Models that consider each wave system individually, and an arbitrary number of those, were preferred to global ones. Partitioning of directional spectra is thus a prerequisite, and needs to be tuned taking account some prior knowledge of the swell characteristics. Triangular, log-normal, Gaussian and Glenn-Jonswap shapes were considered. Sampling variability makes it difficult to distinguish between those shapes as far as swells are concerned. The models also indicate that the width of the spectrum in frequency should be inversely proportional to the peak frequency. Directional spreading width shows a similar trend. Fits to the measurements established proportionality factors for each location.