Shear effect on square cylinder wake transition characteristics

Abstract

SUMMARYThe transition of square cylinder wake flow from two-dimensional (2-D) to three-dimensional (3-D) when inflow is subjected to linear shear is examined numerically. The value of the non-dimensional shear parameter (K ) considered in this study are 0.0, 0.1, and 0.2. The range of Reynolds number (Re) defined based on the centerline velocity and cylinder width is from Re = 150 to 700. The transition of the wake flow from 2-D laminar to 3-D is marked by streamwise vortical structures. Unlike in uniform flow, in shear flow the transition is characterized by single mode of spanwise wavelength. The critical Reynolds number (Re crit ), at which the transition from 2-D to 3-D occurs, is less in case of shear flow. The magnitude of the mean lift coefficient increases with increasing shear parameter on the positive side. The strength of the Karman vortices on the top side is higher and on the bottom side is lower when compared with the same in the uniform flow.

Aerodynamic performances and wake topology past a square cylinder in the interface of two different-velocity streams

“…This occurs as the flow becomes timeperiodic, but the downforce is not overcome, and average positive lift obtained, until after the flow has become three-dimensional for R > 3.1. The net downforce has also been reported for square cylinders in homogeneous upstream shear 49,71 for Re ≤ 100 and K ≤ 0.5, while for Re ≥ 150, positive lift has been observed 41,56 . Both observations are perfectly compatible with our results.…”

“…The rate of increase of C l with K sharpens as Re gets larger, while C d becomes quite independent of K for Re > 200 4,55 . C l and C d fluctuations increase both with Re and with K at low Re ≤ 150 56 and even beyond 41 , but are mostly insensitive to K at higher Re 4,5 .…”

“…Upon introducing upstream shear, there is general consensus that the stagnation point on a circular cylinder migrates towards the high-velocity side as the shear parameter K is increased, and this independently of Re [33][34][35][36][37][38][39][40][41][42] . The drift induces an acceleration of the flow along the front part on the low-velocity side, which generates a cross-stream pressure force towards it 39 .…”

“…Meanwhile, both C l and C d decrease at low Re 100 (the former pointing towards the low-velocity side) and increases instead at high Re 100 56 , a behaviour that seems to persist at much higher Re for C l but not for C d 4 , even in two-dimensional simulations for Re ≤ 1500 5 . There exist however notable two-and three-dimensional numerical studies that have reported positive growing C l for increasing K at moderate Re 41,56 . The rate of increase of C l with K sharpens as Re gets larger, while C d becomes quite independent of K for Re > 200 4,55 .…”

Structural bifurcation analysis of vortex shedding from shear flow past circular cylinder

“…This is because of the fact that the computational domain is finite, whereas the physical domain is infinite. We found that the convective boundary condition (Lankadasu and Vengadesan 2010) given in Eq. (7) is the best fit and provides the flow exit with the smooth discharge of vortices and minimizes the effect of outlet boundary on the flow near the cylinder than other boundary conditions.…”