Citation: Patel, R.; Khan, Z.A.; Saeed, A.; Bakolas, V. CFD Investigation of Reynolds Flow around a Solid Obstacle. Lubricants 2022, 10, 150. https://doi.org/10.3390/ lubricants10070150 Received: 12 May 2022 Accepted: 30 June 2022 Published: 11 July 2022 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). lubricants Article CFD Investigation of Reynolds Flow around a Solid Obstacle Ruchita Patel 1 , Zulfiqar Ahmad Khan 1, * , Adil Saeed 1 and Vasilios Bakolas 2 1 NanoCorr, Energy & Modelling (NCEM) Research Group, Department of Design and Engineering, Bournemouth University, Poole BH12 5BB, UK; rpatel@bournemouth.ac.uk (R.P.); asaeed4@bournemouth.ac.uk (A.S.) 2 Schaeffler Technologies AG & Co. KG (Schaeffler Group), 91074 Herzogenaurach, Germany; bakolvsi@schaeffler.com * Correspondence: zkhan@bournemouth.ac.uk Abstract: The Reynolds equation defines the lubrication flow between the smooth contacting parts. However, it is questionable that the equation can accurately anticipate pressure behavior involving undeformed solid asperity interactions that can occur under severe operating conditions. Perhaps, the mathematical model is inaccurate and incomplete, or some HL (hydrodynamic lubrication) and EHL (elastohydrodynamic lubrication) assumptions are invalid in the mixed lubrication region. In addition, the asperity contact boundary conditions may not have been properly defined to address the issue. Such a situation motivated the recent study of a 3D CFD investigation of Reynolds flow around the solid obstacle modelled in between the converging wedge. The produced results have been compared to analytical and numerical results obtained by employing the Reynolds equation. The validated CFD simulation is compared with the identical wedge, with cylindrical asperity at the center. A significant increase in pressure has been predicted because of asperity contact. The current study shows that the mathematical formulation of the ML problem has shortcomings. This necessitates the development of a new model that can also include fluid flow around asperity contacts for the accurate prediction of generated pressure. Consequently, sustainable tribological solutions for extreme loading conditions can be devised to improve efficiency and component performance. Keywords: mixed lubrication (ML); computational fluid dynamics (CFD); numerical simulation 1. Introduction Any manufactured surface will be rough to some degree, which can cause friction and wear on dynamically interacting surfaces under extreme loading conditions, resulting in higher maintenance and replacement costs. The micro- and nano-features on the surface are called asperities, and their sub-interactions in lubricated contact cause intense pressure that significantly reduces the fatigue life of the lubricated components [1]. Energy efficiency is crucial for businesses and society, due to limited resources and pollution issues. Various reports state that tribological contacts consume 23% of global energy [2]. For example, a piston ring and a cylinder liner pair in an IC engine is a major source of oil consumption, and works under a mixed lubrication (ML) region. This part consumes half of the fuel energy needed to overcome the frictional losses [3]. Additionally, CO 2 emissions are proportional to energy consumption. Therefore, further developments in tribological performance will reduce the economic losses caused by friction and wear, and will have a positive impact on the environment. Proper lubrication of the contacting surfaces is important to reduce power loss, and to extend the life of all mechanical components, especially the ones working under extreme loading conditions. Tribology solutions to reduce friction and wear have come a long way for decades. In the design of lubricated engineering components, a numerical simulation of the Reynolds equation has been widely employed. Reynolds simplified the equation of hydro- dynamics to define the lubrication mechanism, and established the first partial differential Lubricants 2022, 10, 150. https://doi.org/10.3390/lubricants10070150 https://www.mdpi.com/journal/lubricants