## 5 Discussion  
To evaluate the temperature and performance of the rotor, two bearings with the same geometry were used. One of them had the top foil modified and thermocouples and strain gauges were welded to it. This article focuses on the temperature distribution, without taking into account the deformation, which is the subject of study in other papers. The temperature measurement method that was used seems to be reliable. Of course, welding the measuring elements on the outside of the top foil changes its stiffness and other properties, but the foil bearing showed no disturbing signs of malfunctioning compared to the other bearing. The specially designed bump foil also helped with this. Basic dynamic parameters of the rotor journals, such as vibration trajectories and displacements of the journals in the bearings, were obtained. The vibration trajectory was filtered to 1X, which made it very easy to interpret the results. Eighteen thermocouples were welded on the surface of the top foil, which made it possible to obtain fairly good measurement resolution for the purpose of evaluating the correct operation of the foil bearing. To study the temperature distribution on the foil, either a larger number of measurement points or some approximation of the recorded data was needed. The best match across the width of the top foil was obtained using a second-order polynomial, and along the length, using a seventh-order polynomial (assuming that the temperature near the lock of the foil is the average of the points in the vicinity). Assuming that such curves and approximations describe well the temperature distribution on the top foil, an attempt was made to make the temperature distribution dependent on the rotor dynamics (that is the movement of the bearing journal). In the center of the bearing (plane of symmetry across the width of the top foil), the highest temperature value was expected, propagating to smaller values located at the edges. Such a symmetrical distribution was noticeable when the journals were close to the axis of the bearing sleeves, otherwise, the distribution across the width of the top foil became asymmetrical. This phenomenon can be effectively observed by comparing the temperature distribution and journal positions in the bearing at a given rotational speed. Thus, the symmetry of the foil temperature distribution depends strongly on the form of vibration of the entire rotor. No obvious correlation was observed between the size of the vibration trajectory and the value or temperature distribution because the flexible set of foils adapts itself to the size of the trajectory. This becomes different, however, when considering the size and shape of the trajectory. Some correlations can be observed between the shape of the vibration trajectory of the journal and the temperature distribution along the length of the top foil, and thus the gas exchange in the lubrication gap, but this is not unequivocal. Such phenomena cannot be observed on the built test rig, as it would be necessary to change the size of the trajectory and its shape under constant operating conditions in terms of journal position and rotational speed. This would require controlling the unbalance, stiffness and damping of the set of foils. In the case described herein, the vibration trajectory of the journal is associated with a given rotational speed, which causes the displacement of the high- and low-temperature areas. Another interesting finding is that when the lubricating film is lost, the rotating journal, located on the top foil, creates a space for air to enter into the lubrication gap. This is caused by the weight of the rotor, which exerts pressure on the surface of the foil, and by viscous friction, which stretches the foil in the opposite direction to the lock. In the case of the rotational speed at which there is no lubricating film, an important aspect of this phenomenon is the size and shape of the vibration trajectory, which affects the entry of air into the foil bearing.