No abstract

Purpose Bearing performance characteristics, such as stiffness and load capacity, are related to the viscosity of the fluid circulating through the gap. Nanoparticle additives in lubricant are one way to enhance of the viscosity. This study aims to investigate the effect of nanoparticle additives on the thermohydrodynamic performance of journal bearing with different bearing parameters. Design/methodology/approach The temperature distribution is modeled using a three-dimensional energy equation. The velocity components are calculated on the pressure distribution governed by Dowson’s equation. Moreover, the heat transfer between the journal and lubricant is modeled with Fourier heat conduction equation. On the other hand, the viscosity equation is derived for Al2O3 nanoparticles as a function of the volume ratio and the temperature. An algorithm based on the finite difference method is developed, and a serial simulation is performed for different parameters and different volume ratio of nanoparticle. Findings With the increase in the nanoparticle volume ratio, the maximum temperature decreases for the lower clearance values, but the addition of the nanoparticle influence on the maximum temperature reverses when the clearance grows up. The nanoparticle additives increase further the maximum temperature for higher values of L/D ratios. Moreover, the effects of the nanoparticle additives on the pressure are stronger at high eccentricity ratios for all bearing parameters. Originality/value This paper provides valuable design parameters for journal bearing with lubricant containing the nanoparticle additives.

Aerostatic journal bearing applications mainly focus on high-speed precision machining, so predictable and smooth functioning of the system is crucial. Air is supplied to the bearing through a number of orifices and any unevenness in the size of these orifices will affect the performance of the system. The size difference could be due to manufacturing error and/or blockage of the orifice because of foreign materials in the air system. In this study, the performance of an aerostatic bearing with a partially blocked orifice is numerically investigated. Firstly, the airflow in the bearing clearance was modeled with Reynolds equation and this equation was numerically solved with the finite difference and differential transform hybrid method to obtain the pressure distribution. Then, the force and the stiffness are calculated from the pressure distribution for different blockage cases of the orifice and different blockage ratios. The results show that the partial blockage of the orifice significantly changes the performance of the system in a positive or a negative way according to the feeding hole position, and the blockage ratio also affects performance.

Performance parameters such as critical speed and stability are affected by various design parameters such as supply pressure, clearance between shaft and rotor (air film thickness), bearing diameter and length etc. for externally pressurized gas lubricated bearing. Literature about effects of supply pressure is generally analyzed with clearances which are lower than 100 μm. Externally pressurized gas lubricated bearings with small clearance have some practical disadvantages such as difficulties in manufacturing process and price. So, externally pressurized air bearing may become widespread with usage of higher values of clearance in the bearing. However, there is limited number of study investigating the dynamics of externally pressurized air bearing with high values of clearance. In this study the effect of supply pressure was investigated on the dynamic of an externally pressurized gas lubricated bearing with increased clearance. The flow between shaft and rotor was modeled using Reynold’s Equation which is known fluid equation of motion. And this model was solved by Alternating Direction Implicit (ADI) numerical solution method. Dynamics of the rotor was investigated for different elevated (increased) clearances.