Experiments on an Ultrastable Gas Journal Bearing

Abstract

Approved Prepared underC o n t r a c t N o n r -3 7 3 0 ( 0 0 ) Task NR 061-131 t h e o r e t i c a l l y t h a t t h i s p o s s i b i l i t y i s p a r t i c u l a r l y advantageous f o runloaded j o u r n a l b e a r i n g s . This paper d e s c r i b e s c o r r o b o r a t i n g experiments. The experiments i n c l u d e d t h erunning of an unloaded b e a r i n g up t o speeds of 60,000 rpm and t h e c o l l e c t i o n of s t e a d y s t a t e load-displacement a t t i t u d e a n g l e d a t a a t i n t e r m e d i a t e speeds up t o and i n c l u d i n g 60,000 rpm. No s i g n of b e a r i n g w h i r l i n s t a b i l i t y w a s det e c t e d . There w a s good c o r r e l a t i o n between t h e o r e t i c a l and e x p e r i m e n t a l d a t a .Design d a t a i s i n c l u d e d as a guide f o r f u t u r e d e s i g n s .

A Review of Grooved Dynamic Gas Bearings

“…Grooved bearings have proven to be the most promising solution in terms of stability among selfacting gas bearings [59]. Malanoski experimentally showed that the herringbone-grooved journal bearings (HGJB) were less likely to suffer from the whirl instability than other types of dynamic journal bearings [60]. • Compliant-Surface GBs.…”

“…The NGT was experimentally validated first in its incompressible form by Hirs [97], who ran a floating HGJB with a load applied on the non-rotating bushing. Malanoski [60] ran a 38 mm shaft supported by shallow-grooved HGJBs without external load up to 60 kRPM with no sign of halfwhirl instability. Measurements of radial stiffness were in good agreement with the 1D centered NGT, with most of the measurement points within 10% deviation from the concentric NGT predictions.…”

“…5 associated with the classic NGT models limit its use and validity. Therefore, numerous efforts were made in order to extend its range by assessing additional effects [60,[112][113][114][115][116][117] such as the influence of (1) the local compressibility across a groove-ridge pair, (2) the end effect at the bearing edges, (3) journals operated at large eccentricities, (4) the effect of a finite number of grooves and (5) the effect of leakage flow. The investigations and the results of these additional effects are discussed in the sections below.…”

“…The introduction of infinitesimal perturbations around a static eccentricity allows to obtain linearized equations for the zeroth and the first order pressures, ultimately yielding static load capacity as well as the stiffness and damping properties. In addition, in some cases, a separation of variables (theta and z) is suggested for journal bearings operated in concentric positions, which yields only the dynamic bearing coefficients [60,98,122,123]. A comparison with the FEM analysis by Bonneau and Absi [82] suggests that the separation-of-variable approaches remain valid as long as the static eccentricity remains below 20%.…”

“…From the modeling point of view, the isothermal assumption allows not only the spatial-invariant gas viscosity but also the density to be expressed in terms of the pressure only. Castelli and Vohr [112] validated this assumption for spiral groove journal bearings by comparing their numerical results with experimental data obtained by Malanoski [60]. However, Kao [135] pointed out that the error due to such an assumption could influence the prediction of the load capacity because the heat dissipation is neglected through the surfaces.…”