Estimation of the Time Delay Associated With Damping Controlled Fluidelastic Instability in a Normal Triangular Tube Array

Abstract

Fluidelastic instability (FEI) produces large amplitude self-excited vibrations close to the natural frequency of the structure. For fluidelastic instability caused by the damping controlled mechanism, there is a time delay between tube motion and the resulting fluid forces but magnitude and physical cause of this is unclear. This study measures the time delay between tube motion and the resulting fluid forces in a normal triangular tube array with a pitch ratio of 1.32 subject to air cross-flow. The instrumented cylinder was forced to oscillate in the lift direction at three excitation frequencies for a range of flow velocities. Unsteady surface pressures were monitored with a sample frequency of 2 kHz at the mid plane of the instrumented cylinder. The instantaneous fluid forces were obtained by integrating the surface pressure data. A time delay between the tube motion and resulting fluid forces was obtained. The nondimensionalized time delay was of the same order of magnitude assumed in the semi-empirical quasi-steady model (i.e., τ2 = 0.29 d/U). Although, further work is required to provide a parameterized model of the time delay which can be embedded in a model of damping controlled fluidelastic forces, the data already provides some insight into the physical mechanism responsible.

CFD modelling of the cross-flow through normal triangular tube arrays with one tube undergoing forced vibrations or fluidelastic instability

“…A CFD methodology involving structure motion and dynamic re-meshing has been put into practice to simulate the self-excited vibrations due to This CFD methodology was evaluated by comparing predictions to ex-perimental data reported in the literature regarding i) time lag of lift coefficient under transverse forced vibrations with P/d=1.32 (Mahon and Meskell (2013)) and ii) critical velocity for 1DOF FEI with P/d=1.25 and P/d=1.375 over a range of the mass-damping parameter (Austermann and Popp (1995)).…”

“…A second series of computations were focused on the time delay of the fluid-dynamic force applied on the oscillating tube during its motion, which is key in the development of damping-controlled FEI. In particular, these computations were designed to reproduce the conditions of the experimental study by Mahon and Meskell (2013), who used a normal triangular array with P/d = 1.32 and d = 38 mm in which a single cylinder at the third row could be forced to vibrate transversely while subject to air cross-flow. They measured the time delay between lift and tube acceleration for upstream velocities from 2 to 10 m/s, which gives reduced pitch velocities from 25.4 to 127.6 and Reynolds numbers from 2.2 × 10 4 to 11.2 × 10 4 (based on pitch velocity).…”

“…First, the main calculation parameters including boundary conditions and turbulence model were selected by contrasting the predictions of pressure distribution on cylinders with the measurements conducted by Mahon and Meskell (2009) under static conditions. Then, dynamic simulations with one oscillating tube located at the third row were carried out for the sets of configurations tested by Mahon and Meskell (2013) under conditions of forced vibration and by Austermann and Popp (1995) under conditions of self-excited vibration. This methodology, which pursued the validation of the CFD model at different levels of calculation, is depicted in Fig.1.…”

A Computational Study on the Damping-Amplitude Dependence and Estimation of the Limit Cycle Oscillations for Normal Triangular Arrays with One Tube Undergoing Fluidelastic Instability

“…Numerical domain consisted in a normal triangular tube array subject to an air cross flow in which one tube is allowed to vibrate freely, geometry of the tube array is shown in Figure 1. This same geometry was previously tested by the authors and compared to experimental data at several stages (Mahon and Meskell, 2009 and 2013, [3,4], Austermann and Popp (1995) [5] and Sawadogo and Mureithi, 2013 [6]), details of the parameters, sensitivity tests and validation can be found in [2]. Figure 2 shows a detail of the deforming mesh used in this series of simulations.…”

Numerical Study of Flow-Induced Vibrations of Multiple Flexibly-Mounted Cylinders in Triangular Array

“…There are many publications about physical and numerical experiments of different aspects of flow-induced vibrations in the case with a single flexible rod or tube surrounded by the rigid array, for example, [3]- [6]. Analytical and semiexperimental models are also evolved for this simplest case (for more information see a review of Price [7]).…”