Effect of Turbulence and Offset Loading on the Performance of a Single Pad Externally Adjustable Fluid Film Bearing

2012 ◽  
Author(s):  
B. Satish Shenoy ◽  
Rammohan S. Pai B. ◽  
Raghuvir Pai B. ◽  
Shrikanth Rao D.
Keyword(s):  
Steady State ◽  
Finite Difference ◽  
Aspect Ratio ◽  
Finite Difference Method ◽  
Difference Method ◽  
Reynolds Equation ◽  
Load Capacity ◽  
Fluid Film ◽  
Wide Range ◽  
Steady State Performance

Paper deals with the effect of turbulence on steady state performance characteristics of an eccentrically loaded 120° single pad externally adjustable fluid film bearing. The bearing has an aspect ratio of one and operates over a wide range of eccentricity ratios and adjustments. Two load-offset positions (β/χ) of 0.45 and 0.55 are considered in the present analysis. Reynolds equation incorporated with the Linearized turbulence model of Ng and Pan is solved numerically using finite difference method. A comparative study predicts that, load capacity of a bearing operating with β/χ = 0.55 and Re = 16000 is superior for negative radial and tilt adjustment configuration of the pad.

Analysis of Hybrid (Hydrodynamic/Hydrostatic) Journal Bearing

2013 ◽  
Vol 650 ◽  
pp. 385-390 ◽  
Author(s):  
Vijay Kumar Dwivedi ◽  
Satish Chand ◽  
K.N. Pandey
Keyword(s):  
Finite Difference ◽  
Finite Difference Method ◽  
Difference Method ◽  
Gas Turbines ◽  
High Speed ◽  
Reynolds Equation ◽  
Journal Bearing ◽  
Load Capacity ◽  
Natural Boundary Condition ◽  
Dimensional Solution

The Hybrid (hydrodynamic/ hydrostatic) journal bearing system has found wide spread application in high speed rotating machines such as compressors, gas turbines, steam turbines, etc. The present studies include solution of Reynolds equation for hydrodynamic journal bearing with infinitely long approximation (ILA), infinitely short bearing approximation (ISA) and finite journal bearing approximation. Further Finite Journal bearing approximation considers two dimensional solution of Reynolds equation with natural boundary condition, which cannot be solved by analytical method. So, here the solutions for finite journal bearing have been done with finite difference method (a MATLAB® code is prepared for finite difference method) to get bearing performance parameters such as load capacity, Sommerfeld no., etc.

Numerical Modeling of Fluid-Induced Rotordynamic Forces in Seals With Large Aspect Ratio

2012 ◽  
Author(s):  
Alexandrina Untaroiu ◽  
Costin D. Untaroiu ◽  
Houston G. Wood ◽  
Paul E. Allaire
Keyword(s):  
Finite Difference ◽  
Aspect Ratio ◽  
Finite Difference Method ◽  
Difference Method ◽  
Dynamic Properties ◽  
Bulk Flow ◽  
Large Aspect Ratio ◽  
Flow Method ◽  
Dynamic Coefficients ◽  
Aspect Ratios

Traditional annular seal models are based on bulk flow theory. While these methods are computationally efficient and can predict dynamic properties fairly well for short seals, they lack accuracy in cases of seals with complex geometry or with large aspect ratios (above 1.0). In this paper, the linearized rotordynamic coefficients for a seal with large aspect ratio are calculated by means of a three dimensional CFD analysis performed to predict the fluid-induced forces acting on the rotor. For comparison, the dynamic coefficients were also calculated using two other codes: one developed on the bulk flow method and one based on finite difference method. These two sets of dynamic coefficients were compared with those obtained from CFD. Results show a reasonable correlation for the direct stiffness estimates, with largest value predicted by CFD. In terms of cross-coupled stiffness, which is known to be directly related to cross-coupled forces that contribute to rotor instability, the CFD predicts also the highest value; however a much larger discrepancy can be observed for this term (73% higher than value predicted by finite difference method and 79% higher than bulk flow code prediction). Similar large differences in predictions one can see in the estimates for damping and direct mass coefficients, where highest values are predicted by the bulk flow method. These large variations in damping and mass coefficients, and most importantly the large difference in the cross-coupled stiffness predictions, may be attributed to the large difference in seal geometry (i.e. the large aspect ratio AR>1.0 of this seal model vs. the short seal configuration the bulk flow code is usually calibrated for, using an empirical friction factor).

scholarly journals Flow Past A Rotating Circular Cylinder and A Rotlet Using the Finite-Difference Method

2000 ◽  
Vol 5 ◽  
pp. 85
Author(s):  
T. B. A. El Bashir
Keyword(s):  
Finite Difference ◽  
Finite Difference Method ◽  
Circular Cylinder ◽  
Difference Method ◽  
General Nature ◽  
Rotational Parameter ◽  
Rotating Circular Cylinder ◽  
Analytical Results ◽  
Wide Range ◽  
The Finite Difference Method

In this paper the flow generated by a rotlet in the presence of a circular cylinder is considered. We introduce a transformation which simplifies the equations and boundary conditions. We use the finite-difference method to obtain results in excellent agreement with all the available analytical results. Results are presented for Reynolds numbers, based on the diameter of the cylinder, in the range 0 ≤ Re ≤ 20 and the rotational parameter, α , in the range 0 ≤α ≤ 3 and strength of rotlet, β , in the range 0 ≤ β ≤ 3 . The results are found to be applicable over a wide range of values of α and β . The calculated values of the drag, lift and moment coefficients and the general nature of the streamline patterns are in good agreement with analytical results . The method is then utilized to obtain new results for which no analytical solution is possible.

Averaging effect on pitch errors in hydrostatic lead screws considering helical recess layout and nut misalignment

2017 ◽  
Vol 232 (9) ◽  
pp. 1181-1192
Author(s):  
Yongtao Zhang ◽  
Changhou Lu ◽  
Yunpeng Liu
Keyword(s):  
Finite Difference ◽  
Finite Difference Method ◽  
Difference Method ◽  
Radial Displacement ◽  
Continuity Equation ◽  
Reynolds Equation ◽  
Spatial Frequencies ◽  
The Finite Difference Method ◽  
Low Speeds ◽  
Flank Surface

The hydrostatic nut usually has different helical recess layouts and the nut misalignment (including radial displacement and tilt) may occur during movement, which will influence the averaging effect on pitch errors, i.e. the motion accuracy of the hydrostatic nut. This paper researches the averaging effect on pitch errors in capillary compensated hydrostatic lead screws, under low speeds and considering the helical recess layout and the nut misalignment. Based on the equivalent plane of the flank surface of threads, whose normal clearance is calculated by vector operations, the Reynolds equation and the flow continuity equation are solved using the finite difference method. The results show that (a) the averaging coefficient presents bulges at corresponding spatial frequencies for the hydrostatic nut with discontinuous helical recesses, (b) the positions of the first and second periodical fluctuations of the averaging coefficient are the same for the hydrostatic nut with symmetric continuous helical recesses, symmetric discontinuous helical recesses, or asymmetric continuous helical recesses, and (c) The nut misalignment has little influence on the averaging coefficient.

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