The classical Reynolds theory reveals that a converging gap is the first necessary condition to generate a hydrodynamic pressure in a viscous fluid film confined between two solid surfaces with a relative sliding/rolling motion. For hundreds of years, the classical lubrication mechanics has been based on the frame of the Reynolds theory with no slip assumption. Recent studies show that a large boundary slip occurs on an ultrahydrophobic surface, which results in a very small friction drag. Unfortunately, such a slip surface also produces a small hydrodynamic pressure in a fluid film between two solid surfaces. This paper studies the lubrication behavior of infinite width slider bearings involving a mixed slip surface (MSS). The results of the study indicate that any geometrical wedges (gaps), i.e., a convergent wedge, a parallel gap, and even a divergent wedge, can generate hydrodynamic pressure in an infinite slider bearing with a mixed slip surface. It is found that with an MSS, the maximum fluid load support capacity occurs at a slightly divergent wedge (roughly parallel sliding gap) for an infinite width slider bearing, but not at a converging gap as what the classical Reynolds theory predicts. Surface optimization of a parallel sliding gap with a slip surface can double the hydrodynamic load support and reduce the friction drag by half of what the Reynolds theory predicts for an optimal wedge of a traditional slider bearing.

No abstract

Active flow control should be adopted at more than one critical position in highly loaded aspirated compressors due to the severe flow separation and obvious three-dimensional characteristics of the flow field. A deep insight into the mechanism of the simplified compound boundary layer suction in a highly loaded compressor cascade was experimentally and numerically revealed in this paper. Locations of the two suction slots in the studied compound suction schemes were determined through previous experimental investigations on the single-slot suction schemes. Base on the one-side suction manner and the shared suction recycle system, the suction flow distribution over the suction surface slot (SS4) presented to be C-type along the spanwise both in single-slot cases and the compound suction schemes. On the other hand, the flow distribution over the endwall slot (EW1) was no longer that even along the axial direction after it cooperates with the SS4 slot, especially under the small total suction flow rate. The studied compound suction scheme owns obvious advantages in improving aerodynamic performance of the compressor cascade, when the total suction flow rate is big enough for both slots. About one-sixth loss reduction was achieved in the compound suction scheme with 1.5% suction flow rate. Therefore, the simplification of suction equipment via sharing one set of suction system and employing one-side suction manner is proved to be feasible and as effective in the studied multi-slot suction schemes.

No abstract

No abstract