Vortex shedding induced vibration of thin strip in confined rectangular channel

To study the basic behavior of vortex shedding of spacer grids, both experiments and numerical simulations of a single flat plate with a high chord-to-thickness ratio in a confined rectangular channel were performed. Frequencies of vortex-induced vibrations were obtained through a laser Doppler vibrometer (LDV), and the upstream velocity distribution was acquired by particle image velocimetry (PIV). Two-dimensional large eddy simulations (LES) were conducted, with the PIV results being used as the inlet boundary conditions. Dynamic mode decomposition (DMD) was applied to the numerical results to identify the vortex shedding modes for a number of cases. The numerical results showed good agreement with the experiments in terms of the vortex shedding frequencies. From the simulations, three vortex shedding modes were obtained: trailing edge shedding without the leading edge-vortices coupling (Type I), weak leading edge-vortices coupled shedding (Type II), and strong leading edge-vortices coupled shedding (Type III). The leading edge vortices showed different types of characteristics, namely those that diffused before reaching the trailing edge (Type I), those that stayed close to the plate surface until they reached the trailing edge (Type II), and those that got detached from the plate surface in the transverse direction, and then moved back (Type III). The results showed that both the Reynolds number based on the plate thickness (Re-d) and dimensionless width of the channel (h/d) could affect the vortex shedding. A higher Re-d or lower h/d led to stronger leading edge vortices. Moreover, stronger leading edge vortices led to a smaller dimensionless boundary layer thickness (delta/d) at the trailing edge. Finally, the Strouhal number based on the separation distances between similarly shed rotational vortices (St(lambda)) and the thickness of the plate together with the boundary layer (St(d+2 delta)) were more robust than that based on the thickness of the plate (St(d)).