The development of fully controlled homogeneous and isotropic turbulence water tank for particle-laden flow research
Motivation And Objective
The intensity of turbulence affects many fields, such as air pollution and plastic pollution, where turbulence causes pollutants to drift around and spread globally. In addition, due to the intensification of climate change, strong typhoons will generate stronger turbulence, which will affect our survival. Of course, a coin has two sides, the study of turbulence can also be applied to the development of sustainable energy, such as wind energy. In addition, spacecraft that land on other planets are also affected by turbulence.
However, generating turbulent flow with specific properties in a laboratory setting has been a difficult task. Even if the size and energy input of the device are designed to produce the desired velocity, the inherent complexity and unpredictability of turbulence can affect experimental expectations.
Here we introduce a novel experimental facility that can generate homogeneous isotropic turbulence (HIT), which is inspired by the rotating grid concept of Friedman & Katz (2002) and Gopalan & Katz (2008), but their rotors are fixed.
Figure 1.Turbulence intensity affects many fields.
Experimental Facility
Homogeneous and Isotropic Turbulence (HIT) water tank is composed of four rotating grids, upper baffle and synchronous motors, etc. The HIT water tank in our lab is shown in Figure 2.
Figure 2-1. HIT tank with its composition and 3D model.
Figure 2-2. The front view and the top view of the HIT tank.
Figure 3. Experimental setup in our lab.
Methods
2D Particle Image Velocimetry (PIV) measurement is used to measure the turbulence characteristics including the energy dissipation rate and integral length scales. The experiment setup is including HIT tank, camera, Nd:YAG laser, pulse generator, seeding particles and light sheet optics(Figure 3).
Figure 4. PIV measurement in our laboratory. The camera captures the centre of the tank, with a field of view of 7cm x 7cm in the physical world.
Figure 5.Raw data of PIV measurement.
Preliminary Results
Figure 6 shows the uniformity of the mean velocity field measured using PIV measurement in our lab. Figure 7 shows the plastic particle (density ~1.1g/cm³) settling in quiescent flow and various level of turbulence. The results show both increase and decrease of the quiescent settling speed due to turbulence. The rich physics is worth a systematic study.
The easy-to-use lab system proves suitability for the systematic study of turbulent multiphase flow in a wide parameter space.
Figure 6. Sample mean velocity field overlays streamline in 800 rpm rotors speed with difference rotors position.
Figure 7 Sample particle trajectory.