Instantaneous measurements of pressure and wave flux in stratified incompressible flows are presented for the first time using combined time-resolved particle image velocimetry (PIV) and synthetic schlieren (SS). Corrections induced by variations of the refractive index in this strongly density-stratified fluid are also considered. The test case investigated here is a three-dimensional geometry consisting of a Gaussian ring-type topography forced by an oscillating tide representative of geophysical applications. Density and pressure are reconstructed from SS or PIV in combination with linear theories and combined SS-PIV. We perform a direct comparison between the experimental results and three-dimensional direct numerical simulations of the same flow conditions and control parameters. In particular, we show that the estimated velocity or density and the hence wave flux from linear theory solely based on SS or PIV can be flawed in regions of focusing internal waves. We also show that combined measurements of SS and PIV are capable of circumventing these limitations and accurately reproduce the results computed from the DNS.
NaCl identified by adding NaHSo 4 (pH reducer) for LIF RhodamineWT (pH insensitive) / Fluorescein (pH sensitive) Band-pass filter at 530 nm ( Fluorescein) Band-pass filter at 580 nm (Rhodamine)The spatio-temporal diagnosis of the density of non homogeneous salt water is a difficult task, largely because the diffusion coefficient of organic dyes is one order of magnitude lower than the that of salt. Instead of using a single dye we introduce a second dye and a blend of sodium bisulfate with sodium chloride to decrease the pH of the salt water.
Horizontal convection is flow driven by a buoyancy gradient imposed along a horizontal boundary. It is a simple model to study the influence of heating, cooling, and fresh water fluxes at the ocean surface on the meridional overturning circulation [1]. In order to investigate the flow properties and energetics of horizontal convection at high Schmidt numbers Sc = ν/κ, where in the present case ν ≈ 10 6 m 2 /s is the kinematic viscosity and κ ≈ 1.64 × 10 9 m 2 /s is the diffusion coefficient of salt in water, the flow is driven by the diffusion of salt in water across reinforced permeable FIG. 1. Side view of the tank, illuminated from the left and showing the evolution of fresh fluorescein dye water released from the right. The temporal evolution of the circulation is described by the transport of the fluorescein (green/yellow) dye, driven by a solutal horizontal density gradient, creating a turbulent plume sinking on the left of the tank (a-f). The deep circulation is shown in (g) where the flow has developed and drives a deep but weakly turbulent circulation that eventually upwells on the right of the tank.
Laboratory experimental results are presented for nonlinear Internal Solitary Waves (ISW) propagation in 'deep water' configuration with miscible fluids. The results are validated against direct numerical simulations and traveling wave exact solutions where the effect of the diffused interface is taken into account. The waves are generated by means of a dam break and their evolution is recorded with Laser Induced Fluorescence (LIF) and Particle Image Velocimetry (PIV). In particular, data collected in a frame moving with the waves are presented here for the first time.Our results are representative of geophysical applications in the deep ocean where weakly nonlinear theories fail to capture the characteristics of large amplitude ISWs from field observations.
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