Author(s): Hitoshi Miyamoto; Tohru Kanda; Nobuyuki Hyodo
Linked Author(s): Hitoshi MIYAMOTO
Keywords: Proper orthogonal decomposition; Particle image velocimetry; Recirculating flow; Coherent structure; Turbulent mixing layer; Concave bed
Abstract: Turbulent behaviors in an open-channel flow over a concave bed are investigated using proper orthogonal decomposition (POD). Examined here is the Reynolds number dependence of turbulent structures in the flow. Spatiotemporal data of the velocity fields are experimentally measured by particle image velocimetry (PIV). At first, flow characteristics obtained from the PIV measurement, such as instantaneous and mean velocities, turbulent intensity and Reynolds stress, are discussed with respect to the different Reynolds numbers. As the Reynolds number becomes larger, a recirculating flow in the concave gradually grows to a large spatial scale. Distributions of the Reynolds stress and the turbulent intensity closely relate to the scale of the recirculating flow and their peaks mostly appear along a mixing shear layer between the main-channel and the concave. Then, principal components of the velocity fluctuations are extracted by employing the POD. From distributions of the POD eigenvectors, first several modes of the principal components relate to the effect of the recirculating flow and a few modes in succession indicate the effect of coherent structures along the mixing layer. A cumulative contribution of the POD modes to the total velocity fluctuation energy shows that the velocity fluctuation due to the recirculating flow is most dominant when the major axis of the recirculating flow is consistent with the diagonal line of the concave. The result suggests that the POD is effectively available for quantitatively detecting the dominant factors of the velocity fluctuations in this flow.
Year: 2001