On the Numerical Determination of Flow Factors

Abstract

The paper focuses on the numerical determination of Patir and Cheng’s flow factors for general roughness patterns. Improved procedures for the generation of surface roughness and flow simulation are presented. It is shown that application of these techniques resolves differences to analytical solutions of Elrod and Tripp and reduces the scatter in the results to a reasonable degree. Flow factor charts are given for the ‘standard’ Gaussian/Peklenik roughness and for sintered surfaces with high skewness.

Reduced Engine Friction and Wear

“…Surface roughness, treated as a stochastic process, is characterized by a distribution function and a correlation of amplitudes. Peeken and Knoll (1997) presented numericallyderived flow factors including surface contact effects, and showed that contact can occur when H σ (Equation 22a) is less than 4. Comparison shows that Patir and Cheng's (1979) model may over-estimate hydrodynamic action in the mixed regime, when the two surfaces are sufficiently close.…”

“…Their model used the Average Reynolds equation with flow factors that account for surface statistical parameters. Flow factors have been estimated both analytically and numerically (Tripp, 1983;Tonder, 1986;Peeken and Knoll, 1997) for different roughness orientation and contact. Predictions of frictional behavior of nominally flat surfaces under mixed lubrication compare reasonably well to corresponding experimental data (Makino et al, 1999).…”

“…Comparison shows that Patir and Cheng's (1979) model may over-estimate hydrodynamic action in the mixed regime, when the two surfaces are sufficiently close. The present model will use the flow factors, φ x and φ s , derived by Peeken and Knoll (1997).…”

A Novel Approach for Modeling Surface Effects in Hydrodynamic Lubrication

“…For the used Peklenik factors of 9 and 1/9 the lengths were chosen to be 1 node and 9 nodes. Even when other authors use longer correlation lengths [43,44], these values were chosen, based on the work of Patir and Cheng to achieve a proof of principle. As Tripp explains [42], the flow factors are not expected to be sensitive to the precise choice of correlation function, provided they refer to physically similar surface textures.…”

On the development of advanced techniques for mixed-elastohydrodynamic lubrification modelling of journal and sliding bearing systems.

“…More recently, variations in the Patir and Cheng's flow factors calculation approach have been proposed, such as: [166] who improved the flow simulation and the generation of "artificial" surface roughness; [134,143] who studied flow factors for sinusoidal surfaces that can be determined analytically near contact; [121,213] who used the Patir and Cheng approach with an asperity contact model to extend the formulation for mixed-EHD applications; and finally [102] who incorporated the inter-asperity cavitation effect in the flow factors model. Such alternative flow factors results will not be considered in the present thesis.…”