Effects of different suction angles on flow structures and dissipation in the wake of a circular cylinder

Abstract

Measurements of a Particle Image Velocimetry (PIV) were carried out in a water tunnel to study the flow structures and dissipation in the cylinder wake without suction and with different suction angles (α) at Reynolds number Re = 4000 and suction flow coefficient Cμ = 2.65. The results show that suction can reduce the wake width, wake dissipation, both strength and formation length of Karman vortices at α = ±90° and α = ±112°. The first and second modes of Proper Orthogonal Decomposition (POD) dominate flow dissipation. The flow fields reconstructed by the two POD modes consist of large-scale alternate vortices (LSAV) without and with suction. The size of LSAV and dissipation strength of the two modes are reduced at α = ±90° and α = ±112°. The dominant modes of Dynamic Mode Decomposition (DMD) correspond to the main frequency and its harmonics. The reconstructed flow fields of these dominant DMD modes without suction present large-scale symmetric vortices, large-scale alternate vortices, small-scale alternate vortices and small-scale symmetric vortices. The alternate vortices replace the symmetric vortices due to suction. In addition, the dissipation of DMD modes in the main frequency band (FB2) is related to large-scale vortices' shedding, and these modes dominate flow dissipation in different cases.