Optically observed turbulence in thrust collars at low critical Reynolds number with numerical predictions

Critical Reynolds number is a dimensionless parameter defining a transition between laminar and turbulent flow that can only be experimentally determined. As machine design pushes towards higher efficiencies, individual components such as bearings operate at higher speeds and loads. Proper modeling of bearing elements, especially at higher speeds requires accurate turbulence modeling. This paper presents the first critical Reynolds number for a Thrust Collar (TC). A high-speed camera observes the oil flow of a TC through a transparent window. The optical results show a consistent flow turbulence area in the entrance region of the flow field that increase in overall area with increasing spin speed, and decreasing axial load. The areas of turbulence correspond to a critical Reynolds number between 300 and 500. Additionally, the experimental results show that increasing the inlet velocity of the oil initially increases the turbulent area, until the speed of the oil surpasses the surface speed of the TC, at which point the turbulence disappears. Finally, the paper also presents a Computational Fluid Dynamics (CFD) turbulence model based on the k−ϵ equations. The model, aimed at characterizing the turbulence flow, correlates well to the experimental results. The CFD model predicts a slight increase in load capacity and power loss (