performance analysis of gas lubricated cylindrical journal bearing using fsi technique

PERFORMANCE ANALYSIS OF GAS LUBRICATED

CYLINDRICAL JOURNAL BEARING

USING FSI TECHNIQUE

BATCH – 2 GUIDEK.JITENDRA DR. A.GOPI CHANDG.V.SAI TEJAB.PRAVEENK.U.SHANKAR REDDY

CONTENTS Abstract Objective Bearings Lubrication Advantages Disadvantages Applications CFD & FSI techniques Combinations we analysed Results Conclusion

ABSTRACT With the development of manufacturing technology, rotating machinery becomes increasingly powerful with higher and higher rotation speed. Fluid lubricated journal bearings are widely used in large rotating machinery because of its low cost, long life, silent operation and simple application.

To choose the best suitable lubricant for different eccentricity ratio and L/D ratio combinations of journal bearings by considering the pressure, deformation and stress results obtained in analysis.

  In this thesis journal bearings for L/D ratios and different eccentricity ratios are modeled in 3D modeling software CATIA. The L/D ratio considered is 0.5,0.8 and eccentricity ratios considered are 0.2, 0.4 and 0.6. The gas lubricants considered are Air, Helium and Nitrogen.

  Journal bearing models are developed for speed of 3000 rpm to study the interaction between the fluid and structural behavior of the bearing. The speed is the input for CFD analysis and the pressure obtained from the CFD analysis is taken as input for structural analysis.

Computational fluid dynamics (CFD) and fluid structure interaction (FSI) is done in Ansys.

OBJECTIVETo choose the best suitable lubricant for

different eccentricity ratio and L/D ratio combinations of journal bearings by considering the pressure, deformation and stress results obtained in analysis.

Bearing is a machine element, which supports another moving machine element permitting the relative motion between the Contact surfaces with minimal friction.

The term "bearing" is derived from the verb "to bear" a bearing being a machine element that allows one part to bear (i.e., to support) another.

What is a Bearing:

JOURNAL BEARING

It is one, which forms the sleeve around the shaft and supports a bearing at right angles to the axis of the bearing.

The portion of the shaft resting on the sleeve is called the journal. Example of journal bearings are-__Solid bearing __Bushed bearing__Pedestal bearing.

Lubrication is the process or technique employed to reduce friction between, and wear of one or both, surfaces in close proximity and moving relative to each other, by interposing a substance called a lubricant between them.

The lubricant can be • a solid (e.g. Molybdenum disulfide MoS2) • a solid/liquid dispersion• a liquid such as oil or water• a liquid-liquid dispersion (a grease)• a Gas.

LUBRICATION

GAS LUBRICANTS USED IN BEARINGS

ADVANTAGES OF GAS LUBRICATED JOURNAL BEARINGS

• Low viscosity • Low power loss and cool operations due to low friction• High rotational speed operations• Good performance of the lubricant at extremely low and extremely high temperatures• Precise axis definition and a high accuracy over a wide

speed range• Long life due to a virtually zero wear rate • Low noise and vibration levels • Virtually no necessity for periodic maintenance • No contamination of surfaces by the lubricant.• Minimal contamination to the surrounding environment • No necessity for a fluid-recovery system; these systems

are clean • No breaking down of the film due to cavitation or

ventilation• Availability for both linear and rotary application.

• The surfaces must have an extremely fine finish• The alignment must be extremely good• Dimensions and clearances must be extremely accurate • The speed must be high • The loading must be low • Careful designing is required to avoid vibration due to compressibility of the fluid • More power is required to pressurize a compressible fluid • The design is more empirical since the flow relationships are almost impossible to solve • Required very precise machining in manufacturing • The stability characteristics are poor

DISADVANTAGES

APPLICATIONS

• Textile industries• Food processing industries• Paper industries• Used in missiles• Machine tools• Measuring and inspection instruments• Process and manufacturing equipments• Medical equipments• Coordinate measuring machines• Precision machine tools• Optical lens production equipment• Digital printers • Lithography• Diamond turning machines• Very high or low temperature manufacturing environments• Radiation manufacturing environments

CFD TECHNIQUE IN ANSYS

Computational fluid dynamics, usually abbreviated as CFD, is a branch of fluid mechanics that uses numerical analysis and algorithms to solve and analyse problems that involved fluid flows

FSI TECHNIQUE IN ANSYS

FSI is the abbreviation for Fluid Solid Interaction. In this technique the output obtained by the fluid flow

is given as input to the structural analysis of solid member in ansys.

ECCENTRICITY RATIO :

Eccentricity ratio is the ratio of eccentricity of bearing to the clearance between journal and inner diameter of bearing

Ɛ=e/ce=eccentricityc=radial clearance

L/D RATIO :

It is the ratio of length of the journal bearing to the diameter of the bearing

If L/D increases, surface area of bearing increases then pressure inside the bearing as well as stress on the bearing decreases

LUBRICANTS ANALYSED

Density

(kg/m3)

Viscosity

(Kg/m-s)

Air 1.225 1.7849e-05

Helium 0.1625 1.99e-05

Nitrogen 1.138 1.663e-05

COMBINATIONS ANALYSED

L/D=0.8

Ɛ=0.2

AIR

HELIUM

NITROGEN

Ɛ=0.4

AIR

HELIUM

NITROGEN

Ɛ=0.6

AIR

HELIUM

NITROGEN

L/D=0.5

Ɛ=0.2

AIR

HELIUM

NITROGEN

Ɛ=0.4

AIR

HELIUM

NITROGEN

Ɛ=0.6

AIR

HELIUM

NITROGEN

CATIA DESIGN

PROCEDURE

ANSYSPROCEDURE

ANALYSIS PROCESSSelect fluid flow (fluent) and static structural Fluid flow Selectgeometry>right click>import igs file>select file>ok

After importing geometry

Select mesh>right click>edit

Select part 1 >right click>supress body

Sizing >coarse >fine

coarse –fineUpdate mesh

Select mesh >right click >update>after updateSetup >right click >edit

Click ok

After clicking ok

Select model>double click >energy

click tickmark >ok

Click viscosity > laminar > ok

Select materials >air >double click

After double clicking check properties

Select >boundary conditions >zone>inlet

Go to type> select velocity inlet

Enter velocity magnitude and pressure values

Edit thermal value >ok

Sselect solution initialization

click initialize

After clicking initialization is done

Go to run calculation and edit iterations

Enter iteration value as 10Click calculate

Calculation is completed

Go to graphics and animations

Double click contours

Click tick mark on filled

After entering click tick mark> filled> click . Display

Contours of pressure is shown

Changing of exponential to float

Click apply

APPLYING FSI TECHNIQUE FROM THE SOLUTION OBTAINED BY CFD

RESULTSMATERIALS

AIR HELIUM NITROGEN

PRESSURE(MPa) 1153.36 1208.34 1053.78

DEFORMATION(m) 5.5854e-9 6.3225e-9 5.3536e-9

STRESS(MPa) 9659.5 13685 11663

RESULTS: For L/D= 0.5, Ɛ=0.2

0 0.2 0.4 0.6 0.8 10

400

800

1200

1600

2000

airheliumnitrogen

GRAPH:PR

ESSU

RE(M

Pa)

ECCENTRICITY RATIO

Eccentricity ratio vs pressure graph at L/D=0.5

CONCLUSION By considering the stress, deformation and

pressure values obtained by the analysis , we can find out best suitable lubricant for different L/D and eccentricity ratio combinations of bearings

Lubricant which produces least pressure , deformation and stress values is the best suitable one. .