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POD-BASED ESTIMATION OF THE FLOW FIELD FROM FREE-SURFACE VELOCITY IN THE BACKWARD-FACING STEP

Thien Duy Nguyen
Department of Civil Engineering Ritsumeikan University 1-1-1 Noji Higashi, Kusatsu, Shiga, 525-8577, Japan; Universite Lille Nord-de-France, F-59000 Lille. UVHC TEMPO/DF2T, F-59313 Valenciennes, France

Thien X. Dinh
Department of Mechanical Engineering Ritsumeikan University 1-1-lNojihigashi, Kusatsu, Shiga, 525-8577 Japan

John Craig Wells
Department of Civil Engineering Ritsumeikan University 1-1-lNojihigashi, Kusatsu, Shiga, 525-8577 Japan

P. Mokhasi
Wolfram Research Inc, United States

D. Rempfer
Dept. of Mechanical, Materials & Aerospace Engineering, Illinois Institute of Technology, United States

Аннотация

With a view to "nowcasting" of depth-scale flow fields in rivers, estuaries, and the near-coast, this work develops empirical "measurement models" that correlate velocity at a water surface to subsurface flow fields. Free-surface flow over a backstep, as simulated by LES, is chosen as a test case. Proper Orthogonal Decomposition (POD) is first applied to both subsurface and surface velocity fields from a "training data set", whence we develop regression models between the vectors of surface and subsurface POD coefficients. These models are then applied to estimate the subsurface flow field outside the training data based on virtual "measurements" of streamwise velocity along a streamwise line at the water surface. Good predictive capability is obtained in a region some 20 step heights downstream of the step that is characterized by strong upwellings.