Strip vibration is an important issue in the industrial steel cooling process using arrays of gas jets. Indeed, the recent growing demand for “rapid cooling” has led to a significant increase in jet velocities and some complex sheet flutter phenomena have appeared where, under certain conditions, the strip motion couples with the aerodynamic action of the jets. This aeroelastic behaviour can cause large strip oscillations and even divergence implying a strong risk of contact with the blowing boxes, which can seriously damage the strip. From observations it was assumed relevant to consider the strip as a rigid plate oscillating on its fundamental torsion mode. Hence the system is modelled as a damped oscillator with one degree of freedom in torsion and the aeroelastic forces on the plate are assumed to be a linear combination of the plate’s angular position and its time derivative. These forces can be expressed in terms of an aeroelastic stiffness coefficient and an aeroelastic damping coefficient. If one of these two coefficients becomes critical, one of two instabilities can occur: namely either divergence or flutter. A simplified half-scale model of an industrial cooling unit was built, in line with the above assumptions consisting of a rigid plate oscillating in torsion between arrays of round jets impinging on it on both sides. The measured angular position of the plate yielded the aeroelastic stiffness and damping coefficients. A parametric study led to the definition of a relevant governing reduced velocity based on the jet-to-plate distance and showed different blowing configurations where existing divergence was shifted to higher reduced velocities or even totally cancelled. Although the divergence instability of the system was well demonstrated, the role of the aeroelastic damping coefficient on the plate’s oscillations was not well identified and the industrial problem thus remains unsolved. Therefore further work is focusing on the aeroelastic behaviour of different configurations of interacting jets impinging on a rigid plate. Here the plate is forced to oscillate in torsion and is instrumented with pressure sensors (96 for an 18 cm2 jet impingement surface) to measure the unsteady jet force and provide local aeroelastic coefficients. As the plate can be translated in the three coordinate directions, surface mappings of the unsteady jet forces are obtained and analysed to give some insight into the characteristics of the aeroelastic behaviour. The integrated forces are also correlated with the earlier results.

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