ERDC/CHL CHETN-IV-55
March 2003
CHL Precision Flow Table--
Description and Applications
by Steven A. Hughes
provides information about the new precision flow table experiment facility located at the U.S. Army
Engineer Research and Development Center, Coastal and Hydraulics Laboratory (CHL). The
precision flow table can examine complex steady flow problems rapidly and at low cost. This
capability is useful for understanding complicated flow problems and deciding on whether to pursue
more elaborate modeling technologies. A description of the flow table capabilities is given along
with an example application related to flow at a tidal estuary.
FLOW TABLE OVERVIEW: Coastal engineering has a rich tradition of using laboratory
facilities to reproduce at small scale, flow phenomena present at coastal projects. Common physical
modeling facilities include wave flumes, wave basins, and current flumes. These laboratory tools are
used to study complex hydrodynamic processes, to optimize engineering designs, and to provide
validation data for developing numerical modeling approaches.
Recently, CHL constructed a new precision flow table to examine flow problems related to tidal
currents interacting with inlet jetty structures. The table flow system maintains a constant flow
discharge across a horizontal portion of the table through a recirculating system regulated by valves.
Water depth is controlled by a downstream adjustable weir. Small-scale models depicting either
idealized flow boundaries or portions of actual projects are placed on the glass horizontal test section
of the flow table. Flow patterns created by the scale model solid boundaries, such as regions of flow
separation and turbulence generation, are quantified using a laser Doppler velocimeter (LDV)
located beneath the horizontal section of the table. The laser beams pass through the glass bottom
and measure two horizontal components of velocity at the vertical elevation where the laser beams
intersect. Complex flow patterns can also be visualized using traditional techniques of dye injection,
surface tracers, and bottom tracers.
APPLICATIONS: The precision flow table is particularly well suited for quick, inexpensive
studies related to quasi-steady flow interacting with solid boundaries. For example, idealized inlet
geometries can be easily constructed on the flow table using rectangular blocks or specially molded
pieces resembling rubble-mound structures. Consequences of structure modification, extension, or
realignment are easily observed and quantified without the time and expense associated with larger-
scale physical models or complex numerical hydrodynamic simulations. Tide reversal is achieved
by turning the model inlet on the table so the flow comes from the opposite direction.
Because of the small scale, numerous project options and configurations can be examined in only
one or two days with minimal preparation. This capability is ideal for brainstorming new concepts
related to channel optimization and maintenance. Those alternatives deemed worthwhile can then be
studied in more detail using sophisticated numerical codes and large-scale physical models. Thus,
the flow table can be used to winnow out proposed project alternatives early in the study which will
reduce the cost of the more detailed follow-on efforts.
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