Papers by Keyword: Coherent Structure

Abstract: Database of time series of the instantaneous three-dimensional three-component (3D-3C) velocity vector field, measured by tomographic time-resolved PIV(Tomo-PIV) in a water tunnel, was analyzed to investigate spatial topologies of coherent structures in the turbulent boundary layer (TBL). A new concept of spatial locally averaged velocity structure function of turbulence is put forward to describe the spatial dilation or compression of the multi-scale coherent structures in the TBL. According to the physical mechanism of dilation or compression of multi-scale coherent vortex structures in the turbulent flow, a new conditional sampling method was proposed as well to extract the spatial topological characteristics of physical quantities of coherent structures, such as fluctuating velocities, velocity gradients, velocity strain rates and vorticity during the bursting process in the Tomo-PIV database. Furthermore, the anti-symmetric structures are the typical spatial topologies characteristics for the velocity gradients and vorticity during coherent structures burst.

Abstract: Origins of coherent structures near wall of a turbulent boundary layer has been studied by direct numerical simulation (DNS). Forming mechanism of coherent structures agrees well with DNS results. A close relationship has been found between the evolutional characteristics and factors such as the magnitude and structural distribution of the wall local impulse, and the amount of energy and the length of loading time that the initial local impulse disturbance introduces into the wall region. Moreover, these parameters play key roles in the formation of coherent structures near wall of a turbulent boundary layer. So, the wall local impulse disturbance provides the origins for inducing the formation of coherent structures in wall region of a turbulent boundary layer.