Experimental and Numerical Investigation of the Outer Ring Cooling Concept in a Hybrid and in an All-Steel Ball Bearing Used in Aero-Engines by the Introduction of a Helical Duct

Abstract

Rolling element bearings for aero engine applications have to withstand very challenging operating conditions because of the high thermal impact due to elevated rotational speeds and loads. The high rate of heat generation in the bearing has to be sustained by the materials, and in the absence of lubrication these will fail within seconds. For this reason, aero engine bearings have to be lubricated and cooled by a continuous oil stream. When the oil has reached the outer ring it has already been heated up, thus its capability to remove extra heat from the outer ring is considerably reduced. Increasing the mass flow of oil to the bearing is not a solution since excess oil quantity would cause high parasitic losses (churning) in the bearing chamber and also increase the demands in the oil system for oil storage, scavenging, cooling, hardware weight, etc. A method has been developed for actively cooling the outer ring of the bearing. The idea behind the outer ring cooling concept was adopted from fins that are used for cooling electronic devices. A spiral groove engraved in the outer ring material of the bearing would function as a fin body with oil instead of air as the cooling medium. The method was first evaluated in an all steel ball bearing and the results were a 50% reduction in the lubricating oil flow with an additional reduction in heat generation by more than 25%. It was then applied on a Hybrid ball bearing of the same size and the former results were reconfirmed. Hybrid bearings are a combination of steel made parts, like the outer ring, the inner ring, and the cage and of ceramic rolling elements. This paper describes the work done to-date as a follow up of the work described in, and demonstrates the potential of the outer ring cooling for a bearing. Friction loss coefficient, Nusselt number, and efficiency correlations have been developed on the basis of the test results and have been compared to correlations from other authors. Computational Fluid Dynamics (CFD) analysis with ANSYS CFX has been used to verify test results and also for parametric studies.

Experimental and numerical investigations on rolling element bearing thermal behaviour

“…Numerous studies assume an oil volume fraction of a few percent at high speed. For the tested REB with a 20 L/h oil injection, Parker formula detailed in equation (14) gives an oil volume fraction respectively of 4.7% at 9700 r/min, 5.6% at 8070 r/min and 9% at 4700 r/min. On the other hand, Pouly formula in equation 15provides a higher value of 24% at 9700 r/min, 28% at 8070 r/min and 48% at 4700 r/ min.…”

“…12 A global agreement is found to emphasize the impact of lubrication design and oil flow rate on thermal management. [12][13][14] Furthermore, convective heat flux extracted from the contacts to the lubricant depends on the oil-air mist properties. Parker used an inverse method to corroborate the oil volume fraction from the measured power loss.…”

“…12 A global agreement is found to emphasize the impact of lubrication design and oil flow rate on thermal management. 12–14…”

Numerical simulation on the oil capture performance of the oil scoop in the under-race lubrication system

“…The oil phase distribution in the bearing varies with the rotating speed, oil flow rate, and oil viscosity, while the high volume fraction of oil corresponds to an optimal oil jet velocity. Flouros et al 24 carried out numerical simulation to study the temperature distribution of under-race lubricated bearings. Their research results showed that the temperature distribution in the inner ring was relatively uniform.…”