Dynamic stability of micropolar lubricated hydrodynamic offset-halves journal bearings

Abstract

<jats:p> The plain circular journal bearings are not found to be stable by researchers when used in high speed rotating machineries. Hence, extensive research in the study of stability characteristics of non-circular bearings or lobed bearings assumed importance, of late. Present article deals with the stability analysis of non-circular offset bearing by taking selected set of input and output parameters. Modified Reynolds equation for micropolar lubricated rigid journal bearing system is solved using finite element method. Two kinds of input parameters namely, offset factors (0.2, 0.4) and aspect ratios (1.6, 2.0) have been selected for the study. The important output characteristics such as load, critical mass, whirl frequency ratio, and threshold speed are computed and plotted for various set of values of input parameters. The results obtained indicate that micropolar lubricated circular offset bearing is highly stable for higher offset factor and higher aspect ratio. </jats:p>

Static and dynamic performances of an offset bearing under a micropolar lubricant

“…It means if the center of the upper half of the journal is displaced toward the right with some offset (offset = 0.4) let the fluid film compresses and produces sufficient hydrodynamic pressure to support the higher values of load. From the above discussion and previous work, 25 it is crystal clear that a higher offset with higher eccentricity promotes an increase in load capacity. Therefore, the authors decided to choose a higher offset, that is ( δ = 0.4), in the preceding section.…”

“…The geometric, operating, and lubricant parameters used as input for evaluating the output performance of an offset bearing are given in Table 1. Based on the results reported by Chetti 18 and Sharma and Krishna, 25 a micropolar parameter, l m , is chosen in the range of 1–50.…”

“…The same trend is observed in the case of results reported by Chetti. 18 Further to strengthen the validation of the program, dynamic performance is compared with the published result, 25 with the help of results from Figure 3. In both cases, slight variations in presented and published results may be due to differences in mesh sizes taken.…”

“…It is also noted that normal∂ w ¯ / normal∂ x is of small order, therefore normal∂ w / normal∂ x and its second derivative can also be neglected as compared to ∂ 2 w ¯ / normal∂ y 2. Thus, on simplifications, the following set of equations is obtained: The boundary conditions at bearing and journal surfaces are as follows: By integrating equations (4a)–(4d) with suitable boundary conditions (5a) and (5b), the velocity components obtained are as follows: where Now, substituting equations (6a)–(6d) into equation (1) and integrating across the film, the modified Reynolds equation for micropolar fluids in a non-dimensional form is obtained as follows 25 : where the common non-dimensional terms can be expressed as follows: There are two important non-dimensional parameters, which distinguish the micropolar lubrication from Newtonian lubrication. The first parameter is characteristic length ( l m ), which characterizes the interacti...…”

“…However, very few studies such as Sharma and Krishna 25 concerning investigation of the stability of offset bearings with the micropolar lubrication are scanned during the reviewing of the literature. Very recently, Sharma and Krishna 25 presented the static and dynamic characteristics of offset-halves bearings. They found that a higher offset promotes the stability of bearings.…”