Abstract
Minimizing energy loss and improving system load capacity and compactness are important objectives for fluid power systems. Recent studies reveal that microtextured surfaces can reduce friction in full-film lubrication, and that asymmetric textures can reduce friction and increase normal force simultaneously. As an extension of these previous discoveries, we explore how enhanced texture design can maximize these objectives together. We design surface texture using a set of distinct parameterizations, ranging from simple to complex, to improve performance beyond what is possible for previously investigated texture geometries. Here, we consider a rotational tribo-rheometer configuration with a fixed textured bottom disk and a rotating top flat disk with controlled separation gap. To model Newtonian fluid flow, the Reynolds equation is formulated in cylindrical coordinates and solved using a pseudospectral method. Model assumptions include incompressibility, steady flow, constant viscosity, and a small gap height to disk radius ratio. Multi-objective optimization problems are solved using the epsilon-constraint method along with an interior-point (IP) nonlinear programming algorithm. The trade-off between competing objectives is quantified, revealing mechanisms of performance enhancement. Various geometries are explored and optimized, including symmetric and asymmetric circular dimples, and novel arbitrary continuous texture geometries represented using two-dimensional cubic spline interpolation. Shifting from simple dimpled textures to more general texture geometries resulted in significant simultaneous improvement in both performance metrics for full-film lubrication texture design. An important qualitative result is that textures resembling a spiral blade tend to improve performance for rotating contacts.
Highlights
Friction is a significant source of energy loss in mechanical components
3.4 Two-dimensional cubic spline interpolation Here we introduce a low-dimension texture design representation that supports description of arbitrary continuous geometries
MD-16-1636 contracting channel gap height. This matches the results reported in previous experimental and theoretical studies that measurable normal forces were not detected in symmetric cylindrical surface textures [17, 21]
Summary
The influence of surface roughness within lubricated hydrodynamic contacts has been well-studied in the tribology community. Creating micro-dimples at frictional contact interfaces is known to be effective in reducing frictional losses [2,3,4]. Recent studies proposed a possibility that textured surfaces for sliding hydraulic interfaces can reduce effective friction, improve sealing, and increase the load capacity simultaneously by creating texture in favorable shapes and dimensions [5,6,7]. The roughened or dimpled surfaces in previous studies were restricted to relatively simple shapes, such as predefined shapes, randomly roughened surfaces, and macroscopic sinusoidal textures [4, 8,9,10,11,12,13,14,15,16].
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