Surface oscillations in flow past a side cavity using stereoscopic measurement and POD

R. Tsubaki

COE program researcher, Graduate School of Science and Technology,

Kobe University, Rokkodai, Nada, Kobe, Hyogo, Japan

and

I. Fujita

Professor, Department of Architecture and Civil Engineering,

Kobe University, Rokkodai, Nada, Kobe, Hyogo, Japan

Journal of Hydroscience and Hydraulic Engineering

Vol. 24, No. 2 November, 2006, 41-51.

SYNOPSIS

When a relatively large side cavity is created in an open channel, the influence of vortices in the shear layer

and circulatory flow is exerted on the main flow, causing surface oscillations and increased water levels. The

mechanism of the oscillation is still not clearly understood because of the complexity of the phenomena. In this

research, by using a stereoscopic surface measurement system developed by the authors, time-dependent water

surface configurations are successfully measured at a sampling rate of 12 Hz, from which general features of the

surface oscillation are made clear for a wide range of Froude numbers. Then, we applied the proper orthogonal

decomposition (POD) method to measure results. We found that the surface oscillation can be clearly decomposed

into a seiche-like major mode and sub-modes with smaller wavelengths.