A closed-loop gravity-driven water channel for density-stratified shear flows

Abstract

A closed-loop multilayer salt-stratified water channel allowing independent adjustment of velocity and density profiles has been developed for the study of stably stratified shear flows. Each of ten gravity-driven layers are adjustable for velocities from 0 to 30 cm/s and densities from 1.0 to 1.1 g/cm3. A turbulence-management section located at the inlet manifold successfully suppresses undesired turbulence due to the ten mixing layers generated at this inlet. This management section also smooths the inherent step structure of the initial velocity and density profiles. Velocity profiles can be maintained throughout an experiment, whereas density profiles change slowly in time. An inner core region of linear stable density gradient will remain stationary for a time dependent on the initial stratification, velocity profile and mixing conditions. Temperature is observed to increase at a rate near 1 °C per hour due to internal heating in the system. A description of calibration techniques and temperature-correction methods for the velocity and conductivity instrumentation is described.

Statistically steady measurements of Rayleigh-Taylor mixing in a gas channel

“…The top and bottom inlet sections of the channel are fitted with screens and flow straighteners to produce a uniform flow, assist in dissipating free stream turbulence, and minimize the boundary layer on the splitter plate and walls (Browand & Weidman 1976;Snider & Andrews 1994;Stillinger et al 1983). A 10 cm long flow straightener sits at the entrance of each channel and is made of polycarbonate honeycomb (Model # PCFR250W4.00 Plascore, Inc.), in which each honeycomb cavity is 0.635 cm in diameter.…”

Mixing efficiency in stably-stratified decaying turbulence

“…This water channel, previously described by Stillinger et al (1983a), has a test section 25 cm high, 40cm wide and 5 m long.…”

“…(1). u and w were then computed as two bidimensional least squares fits of the "linearized" voltages of both films (Stillinger et al 1983a). Such an approximation is valid in the case of small turbulence intensities.…”

Study of Air Ingress Across the Duct During the Accident Conditions

“…Dickey observed that the decay rate greatly decreased when the internal gravity waves replaced the turbulent fields [22]. Stillinger et al studied density-driven stably stratified shear flows for the velocities from steady to 30 cm/s with the density ratio from 1.0 to 1.1 g/cm 3 and found a method to maintain arbitrary velocity profiles in each layer in time [23]. Boussinesq approximation is applicable for few percent of density ratios.…”