Li-Hao Feng

Proper orthogonal decomposition analysis of vortex dynamics of a circular cylinder under synthetic jet control

Vortex dynamics of a circular cylinder controlled by a synthetic jet positioned at the back stagnation point is experimentally investigated using particle image velocimetry (PIV) technique. The proper orthogonal decomposition (POD) method is adopted to present the variations of the POD energy, mode, coefficient, corresponding dominant frequency, and the reconstructed spanwise vorticity. It is found that the dominant dimensionless control parameters should be the synthetic jet stroke length L0/D, where D is the diameter of the experimental circular cylinder, and the equivalent momentum coefficient Cμ. For the same stroke length L0/D=3.3, the states of the wake vortex shedding are determined by the momentum coefficient. They can be categorized into three groups summarizing all the parameters tested: antisymmetric Karman vortex shedding mode (Cμ≤0.027), vortex synchronization with shedding modes varying between the symmetric and antisymmetric ones (0.061≤Cμ≤0.109), and vortex synchronization with symmetric s...

Parameter influence on the evolution of low-aspect-ratio rectangular synthetic jets

The evolution of low-aspect-ratio rectangular synthetic jets is investigated with dye and laser-induced-fluorescence (LIF) flow visualization techniques. This paper analyzes the impacts of three key parameters on the evolution of vortical structures, respectively, including orifice aspect-ratio (AR), dimensionless stroke length, and Reynolds number. Compared with circular synthetic jet, all the rectangular synthetic jets display vortex ring axis switching, and may develop into two types of stream-wise vortices I and II. The evolution of the vortex ring and the generation of stream-wise vortices are influenced by three parameters. In particular, stream-wise vortices are not detected for a low AR, stroke length or Reynolds number case.Graphical Abstract

End-Effects of a Finite Synthetic Jet on Flow Control

The end-effects of a finite synthetic jet used for controlling the flow around a two-dimensional circular cylinder are experimentally investigated in this study. The Reynolds number based on the cylinder diameter is Re = 800, and the corresponding natural vortex shedding frequency f 0 is 0.24 Hz (St = 0.21). The synthetic jet is actuated at excitation frequency f e /f 0 = 2.08, with the equivalent momentum coefficient C μ = 0.139. Six x–y planes of view from the mid-span to one of the slot ends with identical interval 5 mm are measured using two-dimensional time-resolved PIV system. It is found that the end-effects of the finite synthetic jet do not have a crucial influence on flow fields in the mid-span regions, which are independent of the slot length if it is longer than one cylinder diameter.