| Summary: | A two-dimensional numerical study was conducted for flow past a square rod in the presence of two control rods. One is placed vertically in the upstream direction and the second one is placed horizontally in the downstream direction of the square rod. The influence of gap spacing was studied by taking <i>g</i><sub>1</sub> = 1−5 and <i>g</i><sub>2</sub> = 0.5−5 (where g<sub>1</sub> is the gap between the upstream control rod and the main rod, and g<sub>2</sub> is the space between the main rod and the downstream control rod) at <i>Re</i> = 160. The simulation results were obtained in the form of vorticity contour, drag and lift coefficients, Strouhal number, and force statistics. Under the effect of gap spacing, three different flow modes were found and named according to their behavior. It was found that the mean drag coefficient showed decreasing behavior by increasing the value of g<sub>2</sub> continually at a fixed value of g<sub>1</sub>. The largest value of <inline-formula> <math display="inline"> <semantics> <mrow> <mi>C</mi> <mi>d</mi> <mi>m</mi> <mi>e</mi> <mi>a</mi> <mi>n</mi> </mrow> </semantics> </math> </inline-formula> was found at (<i>g</i><sub>1</sub>, <i>g</i><sub>2</sub>) = (1, 1) and the greatest percentage reduction in <inline-formula> <math display="inline"> <semantics> <mrow> <mi>C</mi> <mi>d</mi> <mi>m</mi> <mi>e</mi> <mi>a</mi> <mi>n</mi> </mrow> </semantics> </math> </inline-formula> was obtained at (<i>g</i><sub>1</sub>, <i>g</i><sub>2</sub>) = (1, 3), which is 139.72%. The effect of thrust was also noticed for all selected values of g<sub>1</sub> and g<sub>2</sub>. Furthermore, it was noticed that the Strouhal number and the root mean square values of the drag and lift coefficients smaller values than the single rod values, except for the C<i>lrms</i> value of (<i>g</i><sub>1</sub>, <i>g</i><sub>2</sub>) = (1, 3) and (1, 4).
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