Project Description

We are aiming at investigating the fluid-dynamics characteristics of buoyant jets and their interactions with stratified environments. Within this project we perform: 

  • High-resolution experiments using Particle Image Velocimetry (PIV) and Planar Laser Induced Fluorescence (PLIF)
  • CFD models validation and further development (RANS and LES)

Experimental Facilities

Two experimental facilities are used for this project:

  • DESTROJER facility (DEnsity Stratified Turbulent ROund free Jet ExpeRiment)
  • miniDESTROJER

The DESTROJER setup consists of a 1m x 1m x 1m cubic tank, featuring a D=12.7mm jet nozzle  diameter. The facility is made of acrylic glass to provide optical access for PIV and PLIF applications. The miniDESTROJET facility consists of a 30cm x 30cm x 30cm cubic tank instead, with a jet diameter of 2 mm. 

Both facilities are equipped with a PIV system consisting of a Phantom Miro LAB 340 high-speed camera with 2,560×1,600 pixels, achieving 800Hz as the maximum frame rate at full resolution, and a double-cavity pulsed Nd:YLF Laser system having a maximum frequency of 10,000Hz at a wavelength of 527nm. A second Phantom Miro LAB 340 camera is used for simultaneous PLIF measurements.

MiniDESTROJER (top)

 

DESTROJER (left)

Velocity field for a Turbulent jet at a Re = 5000

Near Field

Intermediate Field

Far Field

Refractive Index Matching Technique

Optical techniques such as PIV and PLIF lose applicability when the mixing fluids have different refractive index, like in the case of a flow with density gradients. In this case, raw images appear blurred (see left video below) and seed particles appear smeared in the raw images leading to unreliable measurements for both velocity and concentration fields.
We have developed a novel Refractive-Index-Matching (RIM) technique that allows to systematically identify mixing fluids for which refractive index does not change with the mixing scalar. So far, we have been successfully tested the technique with density differences up to 9%.

PIV measurements (raw data) for a buoyant jet. Bad quality images are due to non-uniform refractive index.
Density difference = 1.1%
Re = 5000
PIV measurements (raw data) with Refractive Index Matching (RIM). High quality images are obtained.
Density difference = 7.9%
Re = 5000

Measurements

Examples of measurements of buoyant jets in uniform and stratified environments are shown in the videos below.

Light jet injected into heavier fluid.

Light jet injected into heavier fluid.

Light jet into a two-layer stratified environment

Density difference = 7.9%
Re = 2100
Density difference = 7.9%
Re = 5000
Density difference = 3.16%
Re = 4000
REFERENCES
  1. S. Qin, B. Krohn, V. Petrov, A. Manera, “Velocity and Scalar Fields of a Turbulent Buoyant Jet in the Self-Similar Region”, Nuclear Technology, 1-15 (2019).
  2. B Krohn, S Qin, J Downing, V Petrov, A Manera, “An Experimental Study of Local Self-Similarity in the Mixing Transition of a Turbulent Free Jet”, Nuclear Science and Engineering 193 (1-2), pp. 171-184 (2019).
  3. S Qin, B Krohn, J Downing, V Petrov, A Manera, “High-Resolution Velocity Field Measurements of Turbulent Round Free Jets in Uniform Environments”, Nuclear Technology 205 (1-2), pp. 213-225 (2019).