On Turbulence Measurements In Hydraulic Jumps With Adv Techniques

ROMAGNOLI, M.; LOPARDO, R.; GARCÍA, C.M.

Lake Placid, New York, USA.

Conferencia; Hydraulic Measurements and Experimental Methods Conference; 2007

Environmental and Water Resources Institute of ASCE (EWRI) y International Association of Hydraulic Engineering and Research (IAHR)

A hydraulic jump is a rapidly varied transition from supercritical to subcritical flow andit is characterized by the presence of high flow turbulence levels and air entrainment.Hydraulic jumps has been studied by many researchers in the past, but most of theworks have focused on an integral analysis and little is known about internal flow andturbulence structures due to the adverse experimental conditions for water velocitymeasurements within the hydraulic jump. This work explores issues on turbulencemeasurements in hydraulic jumps using acoustic Doppler velocimeters (ADV)techniques. Previous studies showed that ADVs are capable of reporting accurate meanvalues of water velocity in three directions, even in low flow velocities. In addition,ADVs have proved to yield a good description of turbulence when certain conditionsare satisfied. These restrictions are related to the instrument configuration (samplingfrequency and noise energy level) and flow conditions (convective velocity andturbulence scales in the flow). This work explores and analyzes these restrictions as wellas other issues on turbulence measurements using ADVs in hydraulic jumps. A microacoustic Doppler velocimeter (micro ADV, SonTek) has used in this work to recordtime signals of flow velocities in a free hydraulic jumps generated downstream avertical sluice gate in a horizontal rectangular flume. Measurements have beenperformed using ADVs in different locations within the hydraulic jump for differentflow conditions represented by different Froude numbers. It was found that in theregions of high flow turbulence levels and air entrainment, the computed powerspectrums of the velocity signals showed a flat plateau which is characteristic ofDoppler noise. Furthermore, the restrictions previously mentioned to yield a gooddescription of the flow turbulence were not always satisfied. This suggests that thecapability of the acoustic Doppler velocimeter to resolve flow turbulence in theseregions is questionable. However, the ADV performance significantly improved in thetransition region between the end of the hydraulic jump and the flow conditionsdownstream, where both the air concentration and the turbulence intensity decrease.