## 3 Results  
A number of tests had been carried out on the test rig described above. This article focuses mainly on the correlation between the temperature distribution on the top foil and the vibrations of the journal. For this purpose, a test was carried out by gradually reducing the rotor speed from the maximum speed to the lowest speed at which the bearings could operate, without destroying the anti-friction coating. The test consisted of: accelerating the rotor to a speed of 24,000 rpm (max. speed), running the rotor at a constant speed for about 200 s, and gradually decreasing the speed (by 2000 rpm). Each set rotational speed matched the vibration trajectories of the journal, and these affected the temperature distribution of the foil. Figure 4 shows the position characteristics of the bearing journals, which started from a value of \(-20\) um because this value was taken as the value of the radial clearance. At zero speed (0 rpm), the bearing journals were displaced from the bearing axis by this distance. The pink colour indicates the moment when the measured values were read. The course of the rotational speed is marked in black. The red (X1) and green (Y1) colours indicate the displacement of the first journal in the X and Y directions, and the navy blue (X2) and turquoise (Y2) colours indicate the displacement of the second journal. During the initial run-up period (Figure 5), up to a speed of 500 rpm, the first bearing journal changed its position by 5 um and \(-5\) um in the X and Y directions, respectively, while the second bearing journal changed its position by \(-8\) um and \(4\) um in the X and Y  
Figure 4: Rotational speed and radial displacement of the rotor versus time. Figure 3: (**a**) Thermocouple distribution on the flat surface of the top foil; (**b**) CAD model of bump foil with notches. directions, respectively. At a speed of 10,792 rpm, the displacements of the journals were as follows: X1--15 \(\upmu\)m, Y1--0 \(\upmu\)m, X2---2 \(\upmu\)m, Y2--67 \(\upmu\)m. After the maximum speed was reached, the journals reached a steady state, in relation to the value of the radial clearance, with the following values: X1--5 \(\upmu\)m, Y1--1 \(\upmu\)m, X2---2 \(\upmu\)m, Y2--22 \(\upmu\)m. As it could be observed, the second journal lifted itself higher than the first, which was held in place by the coupling. Figure 6 shows the position of the journals in both bearings, at different speeds, during a gradual run-down. The red dots indicate the positions of the journals in the bearings at a constant selected speed, and the green lines show the displacements of the journals in the bearing during the test. The word \"start\" marks the start of the test (at zero speed). The graphs have different scales to better illustrate the movement of the journals. Each of them was selected after a period of stable operation and marked on the graph shown in Figure 4. The journal of the first bearing operated close to one point from maximum speed up to about 12,000 rpm with a slight deviation in the direction perpendicular to the direction of the gravitational force (X). This region can be inscribed in a circle with a diameter of 3.5 \(\upmu\)m. As the speed decreased, the journal dropped by \(-\)15 \(\upmu\)m relative to the starting position. This kind of performance had already been observed and was largely associated with the use of a flexible coupling. The journal of the second bearing, where temperature was measured, behaved differently. With each lower set speed, it changed its position within the clearance circle until it reached a position close to the starting position. Up to a speed of 8000 rpm, it was within an area with a diameter of approximately 10 \(\upmu\)m. In both cases, the speed reduction was followed by a lowering of the journals in the direction of the gravitational force. This was caused by the loss of the gas film [19]. The graphs presented in Figures 7-16 show the vibration trajectories obtained for each set rotational speed (filtered signal according to the rotational speed--1X).