COBEM99

S21 Vibrações e Análise Modal

Title:

CAMPBELL S DIAGRAM FOR FLEXIBLE BLADES CRITICAL FREQUENCIES - THEORY AND EXPERIMENT

Summary :

NATURAL FREQUENCIES OF FLEXIBLE BLADES ARE CALCULATED, AMONG OTHER REASONS, TO AVOID LARGE VIBRATION AMPLITUDES AND HIGH STRESS LEVELS IN THE RANGE OF REGULAR OPERATION OF ROTATING MACHINES. CRITICAL SPEEDS ARE USUALLY DETERMINED WITH HELP OF THE CAMPBELL S DIAGRAM, IN WHICH THE BLADES NATURAL FREQUENCIES BEHAVIOUR AS FUNCTION OF THE ROTOR ANGULAR VELOCITY CAN BE ANALYSED. IN THIS WORK, THE BLADE MATHEMATICAL REPRESENTATION IS OBTAINED USING THE FINITE ELEMENT METHOD (FEM) WITH A THREE-DIMENSIONAL MODEL. AFTER ADJUSTING THE PARAMETERS OF THE FEM MODEL BY USING MEASURED NATURAL FREQUENCIES FROM BLADES IN A FREE-FREE CONFIGURATION, THE BLADES ARE DIRECTLY CLAMPED AT AN INDUSTRIAL COMPRESSOR. THE NATURAL FREQUENCIES ARE ONCE AGAIN ANALYSED IN THIS NEW BOUNDARY CONDITIONS, THEORETICALLY AS WELL AS EXPERIMENTALLY, TO ENSURE THE MODEL ACCURANCY. THESE MEASUREMENTS ALLOWS THE ESTIMATION OF BLADE ROOT STIFFNESS VALUES. AFTERWARDS, NUMERICAL SIMULATIONS ARE THEN PERFORMED TO INVESTIGATE THE INFLUENCE OF THE ANGULAR VELOCITY ON THE BLADE NATURAL FREQUENCIES USING TWO DIFFERENT CONDITIONS OF BLADE S ATTACHMENT: AN IDEAL CLAMPING AND AN ADJUSTED VALUE OF THE ROOT STIFFNESS. THE RESULTING CAMPBELL DIAGRAM PROVIDES A SIMPLE AND USEFUL APPROACH TO ESTIMATE THE ROOT STIFFNESS WHILE THE ROTOR IS OPERATING.

Author :

Santos, Ilmar Ferreira
Saracho, Cristina Minioli

Paper View :