Experimental investigation of flow development and gap vortex street in an eccentric annular channel. Part 1. Overview of the flow structure

Abstract

Flow visualization, laser Doppler velocimetry and planar and stereoscopic particle image velocimetry were used to investigate the isothermal velocity field along an eccentric annular channel with a diameter ratio of 0.5 and an eccentricity of 0.8 for a Reynolds number of 7300. Observation of the flow development has identified three distinct regions: the entrance region, the fluctuation-growth (FG) region and the rapid-mixing (RM) region. Weak quasi-periodic velocity fluctuations were first detected in the downstream part of the entrance region, and grew into very strong ones, reaching peak-to-peak amplitudes in the narrow gap that were nearly 60 % of the bulk velocity. Two mixing layers were identified on either side of the gap, which generated a street of counter rotating vortices and thorough large-scale mixing of the fluid in the channel.

Experimental investigation on the influence of gap vortex streets on fluid-structure interactions in hexagonal bundle geometries

“…12 can have the following interpretation. Choueiri and Tavoularis (2014) found that the lateral velocity component of the vortex street oscillated with half the rate of passage of the coherent structures in the axial direction f str /2. This was consistent with Meyer and Rehme's model (sketched in Fig.…”

“…contact between the rods would damage the fuel elements of a nuclear reactor. The experiment performed with an eccentric rod inside a circular channel (Choueiri and Tavoularis, 2014) are also included in the plot (▽ in Fig. 11).…”

“…Mahmood studied coherent structures in a square rod bundle over a range of Reynolds number (Mahmood, 2011). Later, Choueiri and Tavoularis studied the flow instability through the gap in the same geometry (Choueiri and Tavoularis, 2014;2015). They found that the velocity fluctuations along the span-wise direction in the centre of the gap, compared to those in the axial direction, were varying in time with a rate twice as slow.…”

“…Normalised structure wavelength D numbers in the legend are based on the total flow area of the test section. ∘: this work; × : data from Bertocchi et al(2018); □: data from Mahmood (2011); ⋄: data fromGuellouz and Tavoularis (2000); △: data fromDon and Tavoularis (2018); ▽: data fromChoueiri and Tavoularis (2014); * data fromLexmond et al (2005).…”

Numerical simulation of turbulent flow in a channel containing a small slot

“…The authors also concluded that the flow is quite similar to a spatial mixing layer formed between the slower fluid (inside the gap) and the faster fluid from main channel. One year later Choueiri and Tavoularis (2014) attributed the "gap vortex street" formation in an eccentric annular channel to the instability of two mixing layers on both sides the gap.…”