ABSTRACT
The physical contact of the rotating rotor in operation with a stationary element involves several major physical phenomena, such as friction, impacting, modification of the system stiffness due to the physical coupling, all of them additionally affected by thermal effects
survey papers by Dimarogonas, 1969, Muszynska, 1989, Ehrich, 1990. Friction at the contacting surfaces generates tangential force pointed in a direction, which
surface properties, and is the main contributor to surface wear at the rotor/stator contact location. Due to surface wear, the rotor dynamic behavior is, therefore, transient. The rubbing-related wear opens the clearance, creating opportunity for the contact break and rub elimination. Clearance changes may, however, affect operating conditions, fluid flow, and thermal patterns of the machine. Rubbing friction may also produce material deposition, which again, would change clearance and contacting surface conditions. Friction generates an additional torque on the rotor, added to the normal operational load, thus leading to a decrease of the machine efficiency. The friction changes thermal balance, as mechanical energy converts into heat. The latter may lead to thermal problems. The frictionrelated local heating may results in a rotor bow, creating a specific form of unbalance
and 5.1.2).
