PIV Study on Grid-Generated Turbulence in a Free Surface Flow

Abstract

To investigate the feature of turbulence developing behind the filter device in a current flow, the flow fields at intermediate downstream distance of an immersed grid in an open water channel are recorded using a two-dimensional (2D) Particle Image Velocimetry (PIV) system. The measurements on a series of vertical and horizontal sections are conducted to reveal the stream-wise evolution and depth diversity of grid turbulence in the free surface flow. Unlike the previous experiments by Laser Doppler Velocimetry (LDV) and Hot-Wire Anemometry (HWA), the integral scales and space-time correlations are estimated without using the Taylor hypothesis in this paper. The distributions of mean velocity, turbulence intensity and integral scale show the transition behavior of grid-generated flow from perturbations to fully merged homogenous turbulence. The distributions of velocity and turbulence intensity become more uniform with increasing distance. While the spatial divergence of integral scale becomes more pronounced as the flow structures develop downstream. The vertical distributions of flow parameters reveal the diversity of flow characteristics in the water depth direction influenced by free surface and the outer part of turbulence boundary layer (TBL) from the channel bottom. The applicability of the newly proposed two-order elliptic approximation model for the space-time correlations of the decaying grid turbulence in channel flow is verified at different positions. The calculated convection velocity for large-scale motion and sweep velocity for small-scale motion based on this model bring a new insight into the dynamic pattern of this type of flow.

Experimental study of flow and mass transport in the near-wake region of a rigid planar metal net panel

“…Grid-generated turbulence consists of a turbulence production region, immediately adjacent to the grid, followed by a decay region in which the turbulence intensity follows a power law decay (Mohamed and Larue 1990). Yao et al (2021) investigated the flow fields generated behind a fixed grid in an open channel flow using PIV, finding that the velocity and turbulence intensity tended to become more uniform with increasing downstream distance. Gan and Krogstad (2016) performed detailed 2D PIV investigations on the near wake region behind both regular and multiscale grids.…”

Experimental Study of a Fish Behavioral Barrier Based on Bubble Curtains for a River Water Intake

“…As regarding the use of PIV technique in free surface flows, literature shows there are different particular cases where this measurement method can provide valuable results. Yao et al [46] applied PIV to determine the turbulence created by a grid placed inside a free surface channel. Seol et al [47] used towed underwater PIV to determine the water vertical and horizontal velocity fields behind a floating body, in order to characterize the turbulent wake and the influence that free surface has on it.…”

Flow Field Pattern and Hydrodynamic Characteristics of a Grid Device Made with Various Grid Bar Spacings at Different Inclination Angles

“…They demonstrated that the flow velocity attenuation was mainly related to the net solidity of the plane net, with a higher velocity drop response related to a higher net solidity. Yao et al [22] analyzed the feature of turbulence developing behind the filter device in a current flow, the flow fields at an intermediate downstream distance of an immersed grid in an open water channel using a two-dimensional (2D) Particle Image Velocimetry (PIV) system. They found that the vertical distributions of flow parameters reveal the diversity of flow characteristics in the water depth direction influenced by the free surface and the outer part of the turbulence boundary layer (TBL) from the channel bottom.…”