Fluidelastic instability study on a rotated triangular tube array subject to two-phase cross-flow. Part II: Experimental tests and comparison with theoretical results

The extension of the existing theoretical models for fluidelastic instability to two-phase flow is investigated in this paper. Experiments were conducted on a single flexible tube in a rotated triangular tube array subjected to air-water cross-flow. The flow independent damping, added mass and critical velocity for fluidelastic instability were measured. A new formulation of the added mass as a function of the void fraction is proposed. This formulation takes into consideration the reduction of the void fraction around the tubes in a rotated triangular tube array and yields better agreement with the experimental data compared to previous formulations. The quasi-steady and unsteady models were also used to compute the critical velocity for fluidelastic instability. The results of the unsteady model were in very good agreement with the experimental data and subsequently were used to assess the validity of the quasi-steady model over a wider range of mass-damping parameter. The predictions of the quasi-steady model were found to be in good agreement with the experimental data for high void fractions. The use of the time delay parameter, experimentally determined in the first part of this paper, was found to significantly improve the results, especially for high void fractions. However, the limitation of the current setup did not allow measurements at high values of the reduced flow velocity (U/fD) for low void fractions. Nevertheless, this study confirms the validity of the measured time delay parameter and validates the quasi-steady model for the range of void fraction considered (60%-90%). (C) 2014 Elsevier Ltd. All rights reserved.