PDF《Wind Energy》

From Dust Devil to Sustainable Swirling Wind Energy Mingxu Zhang1 , Xilian Luo1 , Tianyu Li1 , Liyuan Zhang1 , Xiangzhao Meng1 , Kiwamu Kase2 , Satoshi Wada2 , Chuck Wah Yu3 &

Zhaolin Gu1

1 School of Human Settlements and Civil Engineering, Xi'

an Jiaotong University, Xi'

an, China,

2 Photonics Control Technology Team, RIKEN Center for Advanced Photonics, The Institute of Physical and Chemical Research, Wako-shi, Saitama, Japan,

3 International Society of the Built Environment (ISBE), Milton Keynes, UK.

Dust devils are common but meteorologically unique phenomena on Earth and on Mars. The phenomenon produces a vertical vortex motion in the atmosphere boundary layer and often occurs in hot desert regions, especially in the afternoons from late spring to early summer. Dust devils usually contain abundant wind energy, for example, a maximum swirling wind velocity of up to

25 m/s, with a

15 m/s maximum vertical velocity and

5 m/s maximum near-surface horizontal velocity can be formed. The occurrences of dust devils cannot be used for energy generation because these are generally random and short-lived. Here, a concept of sustained dust-devil-like whirlwind is proposed for the energy generation. A prototype of a circular shed with pre-rotation vanes has been devised to generate the whirlwind flow by heating the air inflow into the circular shed. The pre-rotation vanes can provide the air inflow with angular momentum. The results of numerical simulations and experiment illustrate a promising potential of the circular shed for generating swirling wind energy via the collection of low-temperature solar energy. A dust devil is a small whirlwind unique weather phenomenon of a vertically oriented rotating column of air on Earth and on Mars1,2 , usually of short-lived duration, with a low pressure and warm core. The height of the dust column ranges from about several tens of metres to thousand metres2,3 . Dust devils found in nature contain an enormous amount of wind energy and can easily raise dust, sand, and debris to high altitudes3C7 . A consensus has been reached on how dust devils are formed. The ambient vertical vorticity (angular momentum) combined with a vertical motion due to heat buoyancy (solar radiation) is the main mechanism for developing the phenomenon. When a net circulation of wind flow exists around the perimeter of an area, a buoyant convection within that area can occur that would strengthen the circulation and increase the local vorticity by stretching the wind flow8C12 , as illustrated in Fig. 1a. Since both heat buoyancy and ambient vorticity tend to be unsustained in nature, the occurrences of dust devils are consequently random and short-lived. There have been wide spread use of solar heat for power generation13C15 ,among them, the utilization of a buoyancy-induced flow is an important model. Power generation using spontaneous buoyancy-induced vor- tices15 is a new method. Here, we propose the use of a circular solar-energy-collecting shed with pre-rotation vanes to produce a steady dust-devil-like wind field to generate sustainable whirlwind energy. A schematic representation of the shed is shown in Fig. 1b. A swirling air mass can flow out of the central outlet, and form a sustainable and long-lived whirlwind (swirling buoyant jet). Consequently, low-temperature solar energy is transferred into swirling wind energy. This study focuses on the inflows in the solar-energy-collecting shed and the swirling buoyant jet at the central outlet, to show the potential for swirling wind energy use. An internal mechanical model of the shed with eight vanes (Supplementary Figure 1a) was constructed for the experiment to realize the concept of dust-devil-like whirlwind depicted in Fig. 1b. The flow patterns and potential energy of the whirlwind produced by the system was investigated. The sensitivity analysis of the inlet vorticity was conducted, and the effects of temperature differences and geometrical parameters on the swirling buoyant jet were evaluated by computational fluid dynamics (CFD) numerical simulation and experimental tests. Results Velocity distribution. The inlet vorticity is a key factor in stimulating a whirlwind. Different inlet vorticities can be obtained with different air inflow incident angles through the vanes, then the effect of inlet vorticity on the buoyant jet air flow field was subsequently investigated by numerical modelling. The resultant velocity of the OPEN SUBJECT AREAS: SUSTAINABILITY FLUID DYNAMICS Received