Flow control over a square cylinder using attached rigid and flexible splitter plate at intermediate flow regime

Abstract

A detailed flow field behind a stationary square cylinder with attached rigid and flexible splitter plates has been studied using particle image velocimetry, constant temperature anemometry, and flow visualization techniques. A wide range of lengths of the splitter plate (L/B = 0–8) are considered, and their respective wake interference is reported. The investigation is carried out at an intermediate flow regime at three Reynolds numbers 600, 1000, and 2000 (based on blocking width “B” of the cylinder). The literature seriously lacks the information on a passive flow control of bluff body wakes in this flow regime. This study shows that the wake frequency and mean drag coefficient vary nonmonotonically to splitter plate lengths. The length of the splitter plate is a critical parameter, which, apart from flow control, can also bring a significant wake transition. At L/B > 3 to L/B = 4, strong secondary vortices are shed from the trailing edge. The shedding of the secondary vortex leads to a sudden shrinkage in the recirculation bubble and an increase in the periodicity of the unsteady flow. The onset of high amplitude flapping occurs in a flexible splitter plate (L/B = 3) at Re = 2000. The vortex shedding frequency becomes higher than the first mode natural frequency of the flexible splitter plate for this length and remains in the same regime for L/B > 3. The amplitude of flapping increases up to L/B = 5 and then again recedes. The high amplitude flapping of the flexible splitter plate adversely affects the mean drag coefficient of the bluff body.

Fluid–structure–sound interaction in noise reduction of a circular cylinder with flexible splitter plate

“…Similar phenomena were also shown in Shukla et al. (2013) and Sharma & Dutta (2020).

Figure 11.Time-averaged spanwise vorticity superimposed by the time-averaged streamline, ( a ) plain cylinder, ( b ) cylinder with RSP1.0, ( c ) cylinder with FSP1.0.

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“…As a result, the energy of the dominant frequency and secondary frequency exhibits an alternate mode in the time--frequency spectrum (figure 25), whose essence is the competition in the energy assignment between the two frequencies. Similar result is also shown in the experiment of Sharma & Dutta (2020), where the FSP was used to control the flow over a square cylinder. An obvious secondary peak with a frequency of 2 times of the dominant frequency appeared in the spectrum of the flow field when a FSP with half of the side length was attached to the cylinder rear.…”

“…(2018), Qu et al. (2017) and Sharma & Dutta (2020). Furthermore, the distributions illustrate clearly that the vertical scale of fluctuation for the cylinder with FSP1.0 (figure 16 i ) is smaller than those for the other two cases (figures 16 g and 16 h ), which accords with the narrowest wake width of the cylinder with FSP1.0 shown in figure 13( b ).…”

“…(2011) to control the cylinder noise with RSP, and the experiments of Chauhan et al. (2018) and Sharma & Dutta (2020) to control the flow over a cylinder with RSP and FSP respectively, a small-scale but fairly strong trailing-edge vortex, viz. the secondary vortex named in the previous literature, occurred at the trailing edge of the splitter plate at L/D ≈ 2.…”

“…What the extension of the shear layers is accompanied by is the strength decrease of the shear layers due to diffusion (Anderson & Szewczyk 1997; Serson et al. 2014; Sharma & Dutta 2020). This strength decrease can also be perceived from figures 11.…”