Three-dimensional Large Eddy Simulation of the Effect of Spacing on the Flow Field Dynamic Characteristics of Three Tandem Cylinders at Subcritical Reynolds Numbers

To investigate the flow field characteristics and wake vortex shedding behind cylinders during fluid flow. This study focuses on three tandem cylinders. Large Eddy Simulation (LES) is employed to analyze the effects of varying cylinder spacing ratios ( L/D = 2 ∼ 7 ) on the lift and drag coefficients ( Clrms, Cdaxg ), the time-averaged pressure coefficient ( C p) on the cylinder surfaces, and the wake vortex shedding under subcritical Reynolds numbers ( Re = 3900, 2 × 10^4, 4 × 10^4 ). The results show that Clrms increases first and then decreases with the increase of L/D, reaching the peak at L/D = 3 (Re = 4 × 10^4, Cl_rms2 = 0.43). When Re = 2 × 10^4 ∼ 4 × 10^4, Cd_avg 1 > Cd_avg 2 > Cd_avg 3, and Cd_avg 1 remains stable at around 0.5 , while Cd_avg 2 and Cd_avg3 show a slight decreasing trend. The Cp value of the cylinder is symmetrically distributed along the flow direction, with strong negative pressure areas on both sides of the cylinder. The Cp behind the cylinder tends to -0.5. However, when Re = 3900 ∼ 4 × 10^4, the Cp of the downstream 2# and 3# cylinders at L/D = 3 is greater than 0 , and the negative pressure area disappears. St increases with the increase of L/D. When L/D = 3 ∼ 4, the increase of St is relatively large ( 27.2% ). When L/D = 7, the shedding of the tail vortex of the cylinder approaches the flow around a single cylinder (St ≈ 0.2).