Mesure de la déformée d'hélice en fonctionnement

The fan of an automotive engine cooling module provides the necessary cooling airflow through the underhood engine compartment. Its constraints very depending on the operating conditions: external temperature, underhood location, car speed, traffic... All these parameters contribute to an intermittent behavior of this fan and consequently to high mechanical stresses. Due to the plastic composite nature and size of the part, theoptical measuring techniques are the only appropriate experimental methods to characterize the behavior of the fan in operating conditions, to validate its proper design and to check the accuracy of the numerical simulations. To measure the instantanneous distortion of the fan blade, an optical sensor based on a structured light technique has been used. It provides the actual displacement along the rotational axis of the fan. The measuring equipment consists of a flash lamp which creates a network of fringes and an acquisition system connected to a CCD camera that allows to make the measurements dynamically. The calibration of the whole system is first achieved. Contour plots of the instantanneous distortion of the fan blade are then obtained. Additional measurements have been achieved with a phase-locked laser vibrometer to also provide some time variation of the local displacement as a function of the fan rotational speed. All these measurements have led to a very good correlation with the numerical structural analysis both on the maximum axial displacement (2.9 mm for the particular fan considered here) and on the shape of the distorted fan. In fact, the maximum displacements are similarly found at the trailing edge of the fan blade tip.