Studies on the Pressure Buildup and Shear Flow Factors in the Cavitation Regime
Abstract
:1. Introduction
1.1. Motivation
1.2. Common Assumptions and Realization of the micro-EHD Problem
- (1)
- In macroscopically not fully filled areas the pressure corresponds to the cavitation pressure (in most cases assumed to be zero), independent of the microscopic roughness;
- (2)
- In macroscopically not fully filled areas, a shear flow factor is applied, which was determined in advance on a microscopic scale with a fully filled gap.
1.3. PFG Model and Its Application to the Calculation of Pressures and Shear Flow Factors
2. Studies with a Partially Filled Gap
2.1. Varying the Topography
2.2. Varying the Filling Level
2.3. Varying the Initial Fluid Distribution
3. Results
3.1. Shear Flow Factor
3.2. Mean Hydrodynamic Pressure
4. Summary, Discussion and Outlook
Author Contributions
Funding
Acknowledgments
Conflicts of Interest
References
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FP1: “filling level” | This procedure applies the filling level to each individual cell. Thus, no cell is initially fully filled, but each cell is partially filled with the same filling level. This procedure corresponds to a state in which initially no cell is fully filled, and no fluid pressure is present. With the movement of the topographies the fluid flows and full cells appear. |
FP 2: “bottom up” | This procedure fills the gap metaphorically from the bottom up. The fluid is distributed so that the absolute fluid volume in each cell is the same. If a cell is smaller than that volume, the cell is fully filled with its respective fluid volume. This leads to homogenous distribution of fluid in the gap and the number of initially fully filled cells is small. |
FP 3: “big to small” | This procedure fills the gap starting with the cell of greatest gap height. Subsequently, the second greatest cell is filled. This procedure continues until the available fluid volume (according to the filling level) is distributed. The cell that is filled last may only be partially filled (here cell 4). This leads to an inhomogeneous distribution with a relatively large number of fully filled cells. |
FP 4: “random cells” | This procedure fully fills random cells. A random cell is selected and fully filled until the available fluid volume is distributed (according to global filling level). The cell that is filled last may only be partially filled (here cell 24). This procedure leads to a distribution with a large number of fully filled cells. |
FP 5: “random” | This procedure chooses a random cell and attempts to fill it with a random amount of fluid. If the chosen amount fits into the cell (cell empty or only partially filled), the procedure fills it and proceeds. If the chosen amount does not fit into the remaining volume in the chosen cell, the procedure continues with a new random cell and a new random amount of fluid. The procedure continues until the complete fluid volume is distributed. Each cell can be chosen multiple times. This leads to a situation where most cells has a high filling level, but none is completely filled. |
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Müller, M.; Stahl, L.; Ostermeyer, G.-P. Studies on the Pressure Buildup and Shear Flow Factors in the Cavitation Regime. Lubricants 2020, 8, 82. https://doi.org/10.3390/lubricants8080082
Müller M, Stahl L, Ostermeyer G-P. Studies on the Pressure Buildup and Shear Flow Factors in the Cavitation Regime. Lubricants. 2020; 8(8):82. https://doi.org/10.3390/lubricants8080082
Chicago/Turabian StyleMüller, Michael, Lukas Stahl, and Georg-Peter Ostermeyer. 2020. "Studies on the Pressure Buildup and Shear Flow Factors in the Cavitation Regime" Lubricants 8, no. 8: 82. https://doi.org/10.3390/lubricants8080082