SIRM 2013 – 10th International Conference on Vibrations in Rotating Machines, Berlin, Germany, 25. – 27. February 2013 An Experimental Study on the Additional Harmonics due to Worn Journal Bearings Athanasios Chasalevris 1 , Fadi Dohnal 2,* 1 Fachgebiet Strukturdynamik, Technische Universität Darmstadt, Petersenstr. 30, 64287 Darmstadt, Germany, chasalevris@sdy.tu-darmstadt.de 2 Fachgebiet Strukturdynamik, Technische Universität Darmstadt, Petersenstr. 30, 64287, Darmstadt, Germany, dohnal@sdy.tu-darmstadt.de Abstract An experimental rotor bearing system with an elastic rotor mounted in worn journal bearings is designed and investigated. The system is operated at transient run-up and run-down conditions and the response is analyzed with emphasis on passage through the first critical speed. The wear introduces additional sub- and super-harmonics in the response signal compared to the intact system. The time histories are analyzed in the time and frequency domain by applying the short time Fourier transform in order to extract information on the influence of the wear depth on the additional super- and sub-harmonic vibration components. The defect of wear in one journal bearing is produced artificially and two cases of wear depths are investigated: a wear depth of 25% as well as 50% of radial bearing clearance. The resulting scalograms highlight that the defect of wear in a journal bearing affects the system’s response, especially during the passage through resonance, with symptoms that do not appear at other defects in journal bearings (e.g. misalignment). The chosen experimental design has the ability to excite the rotor bearing system with an electromagnetic actuator that is realized by an active magnetic bearing (AMB). This specific exciter has the ability to introduce resonance conditions in the system which is operating at a constant rotational speed and, consequently, to observe and extract the symptoms of the worn journal bearing during normal operation of the system. Nomenclature ( ) h δ θ additional fluid film thickness x axial coordinate j m journal mass 0 δ relative wear depth Ω rotating speed d m mass of disc ε eccentricity ratio EX Ω frequency of excitation m m mass of AMB journal θ circumferential coordinate r c bearing radial clearance R shaft radius s θ starting angle of the wear zone 0 d wear depth b R bearing radius f θ ending angle of the wear zone ( ) h θ fluid film thickness d R disc radius µ lubr. dynamic viscocity E Young΄s modulus S Sommerfeld number ρ material density L shaft span W load of the journal bearing 0 ϕ attitude angle d L disc width ___________________________________ * Currently at Alstom (Switzerland) Ltd, Brown Boveri Str. 7, 5401 Baden, Switzerland. 1 Paper ABS-242