Project (long title)Mixing and length scales in Stratified Turbulence
Campaign title (name data folder)17MILESTONE
Lead authorPierre AUGIER
Contributor Antoine Campagne, ...
Date campaign start06-06-2017
Date campaign end28-07-2017

Warning : Samuel won't be here until 12/07/2017


0 - Publications, reports from the project:

1 - Objectives

During the last decade a new theory of stratified turbulence has emerged. The project aims at testing the predictions of this theory in controlled laboratory experiments for the first time. A series of experiments of high Reynolds number and low Froude number stratified turbulence will be carried out at the Coriolis platform. Turbulence generated by an array of translating vertical cylinders in the presence of background stratification, with and without system rotation, will be studied by means of PIV. Three-dimensional velocity fields from the wake will be retrieved, from which spectra, structure functions as well as different length scales will be calculated. Mixing efficiency for different buoyancy Reynolds numbers will be estimated. The results will be compared with theoretical predictions as well as results from Direct Numerical Simulations.

2 - Experimental setup

Similar to

2.1 - Forcing

The flow is forced by an array of cylinders attached to a moving carriage.

Three different apparatus are considered:

1. As for 16MILESTONE: 6 vertical cylinders (diameter = 0.25 m, mesh = 0.75 m, solidity 0.33).

2. 4 vertical cylinders (diameter = 0.5 m, mesh of 1.5 m, solidity 0.33).

3. 3 horizontal cylinders (diameter = 5 cm, length = 4 m, z = [20, 40, 60] cm).

We did only setup 1 and 2...

We plan to study two different movements:

1. As for 16MILESTONE

2. Small-range sinusoidal oscillations (hereafter refereed as "movement 2")

We did only movement 1...

2.2 Stratification

The experiments will be performed in pure water (homogeneous) and water with density stratification (different salt concentrations). Ethanol will be introduce in order to obtain an homogeneous refractive index.

We used only moderate stratification N = 0.55 rad/s.

See page: stratification.

2.3 - Measurements

2.3.1 - PIV

For the 16MILESTONE movement, we will use one camera recording images from above for scanned PIV and one camera from the side for 2D PIV.

Horizontal camera : x between [1, 2560] and y between [400, 1761].

For the second movement (small-range sinusoidal oscillations), we will use a floating transparent plate to perform scanned stereo-PIV with 2 cameras.

The cameras and the galvanometer are controlled with scripts in the directory ~/Dev/fluidcoriolis/scripts/milestone/piv/acquisition (see the README file).

The vertical laser sheet is at 38 cm of the side wall.

2.3.2 - Salinity probes

We used 6 probes.

See measurements/probes and

3 - How to carry out an experiment

See the dedicated page howtoexp.

See also the page postproc

4 - Data and list of experiments

See the dedicated page listexp.

- We will start with the 16MILESTONE forcing with homogeneous fluid (water). Can we use small particles (30 micron) on large-scale field of view (2 m x 3 m)?

- Decay experiment with 16MILESTONE cylinders and homogeneous fluid (water).

- Control experiments as for 16MILESTONE (N = 0.55 rad/s without alcohol and 0.8 rad/s with alcohol) + very long slow experiments (2 cm/s ?).

- Decay experiments with 16MILESTONE cylinders.

- 16MILESTONE movement with large cylinders (homogeneous and 0.8 rad/s with alcohol).

- Decay experiments with large cylinders.

- Movement 2 (with scanned stereo-PIV) with large cylinders

- Movement 2 (with scanned stereo-PIV) with small cylinders

- Movement 2 (with scanned stereo-PIV) with horizontal cylinders