Bearing device and rotary machine

1. A bearing device comprising:

a bearing pad having a pad surface configured to support, via an oil film, an outer circumferential surface of a rotary shaft configured to rotate around an axial line; and

a support part supporting the bearing pad so as to be swingable at a pivot position,

wherein:

a relationship of Rj<Rp<Rb is established where a radius of curvature of the rotary shaft is Rj, a radius of curvature of the pad surface is Rp, and a radius of curvature of a reference circle centered at the axial line and having a radius equal to a distance between the axial line and the pivot position on the pad surface is Rb; and

a dimension of a gap between the pad surface and the outer circumferential surface of the rotary shaft decreases as a distance increases from the pivot position in a circumferential direction.

2. The bearing device according to claim 1 , wherein the dimension of the gap between the pad surface and the outer circumferential surface of the rotary shaft is a maximum at the pivot position.

3. The bearing device according to claim 1 , further comprising a guide metal having a guide surface extending along the reference circle,

wherein a dimension of a gap between the guide metal and the outer circumferential surface of the rotary shaft is equal to the dimension of the gap between the pad surface and the outer circumferential surface of the rotary shaft at the pivot position.

4. A rotary machine comprising:

the bearing device according to claim 1 ; and

the rotary shaft,

wherein the bearing device supports the rotary shaft so as to be rotatable around the axial line.

5. A bearing device comprising:

a bearing pad having a pad surface configured to support, via an oil film, an outer circumferential surface of a rotary shaft configured to rotate around an axial line; and

a support part supporting the bearing pad so as to be swingable at a pivot position,

wherein:

a relationship of Rj<Rp<Rb is established where a radius of curvature of the rotary shaft is Rj, a radius of curvature of the pad surface is Rp, and a radius of curvature of a reference circle centered at the axial line and having a radius equal to a distance between the axial line and the pivot position on the pad surface is Rb;

the pivot position is closer to a front side in a rotation direction of the rotary shaft than a center of the pad surface in a circumferential direction; and

a relationship of Rp1<Rp2 is established where a radius of curvature of an upstream part of the pad surface closer to a rear side in the rotation direction of the rotary shaft than the pivot position is Rp1 and a radius of curvature of a downstream part of the pad surface closer to the front side in the rotation direction of the rotary shaft than the pivot position is Rp2.

6. A bearing device comprising:

two bearing pads, each having a pad surface configured to support, via an oil film, an outer circumferential surface of a rotary shaft configured to rotate around an axial line; and

two support parts supporting the two bearing pads, respectively, so as to be swingable at respective pivot positions,

wherein:

for each of the two bearing pads, a relationship of Rj<Rp<Rb is established where a radius of curvature of the rotary shaft is Rj, a radius of curvature of the pad surface is Rp, and a radius of curvature of a reference circle centered at the axial line and having a radius equal to a distance between the axial line and the pivot position on the pad surface is Rb;

the two bearing pads are at different circumferential positions; and

a relationship of RpA<RpB is established where a radius of curvature of a first of the two bearing pads having a larger load from the rotary shaft is RpA and a radius of curvature of a second of the two bearing pads having a smaller load from the rotary shaft is RpB.