PDF《Wind Energy》

12 August

2014 Accepted

14 January

2015 Published

9 February

2015 Correspondence and requests for materials should be addressed to X.L.L. ([email protected]. edu.cn) or Z.L.G. ([email protected]. edu.cn) SCIENTIFIC REPORTS |

5 :

8322 | DOI: 10.1038/srep08322

1 swirling buoyant jet (Umag) and its tangential velocity component (Ut) were selected to display the total kinetic energy and the swirling feature of the swirling buoyant jet, respectively. Umag is defined by Equation (1) as, Umag~ ???????????????????????????????? Ur

2 zUY

2 zUt

2 p ?1? where Ur is the radial velocity, UY is the vertical velocity, and Ut is the tangential velocity. The local swirling buoyant jet for one of the cases, whose condi- tions are as follows (The other simulated cases are listed in Supplementary Table 1): the solar-energy-collecting shed radius, R

5 200 m, the air inflow incident angle, a, at the inlet of the shed is 0u and the temperature difference, DT, between the heating source and ambient air is

80 K. The velocity distributions are shown in Fig. 2a and Fig. 2b. As can be seen, there is a wind region of over

3 m/s (plotted by dashed lines) occupied by the swirling buoyant jet. The cut-in velocity of a wind field for wind energy use is

3 m/s16 . Therefore, a helical wind turbine entrained in the swirling buoyant jet can potentially be developed for whirlwind energy use. Sensitivity analysis. To demonstrate the effects of DT and a on the swirling buoyant jet, a large number of simulations were carried out in this research by varying one of the parameters while keeping the other physical modelling parameters constant. Detailed results are given in Supplementary Table 2. All the resultant velocity values when using R

5 200 m for simulations exceeded

3 m/s, thus illustrating the possibility of whirlwind energy use. Therefore, a larger temperature difference would help to raise the velocity of the swirling buoyant jet, and to increase the wind energy output potential. The incident angle of the air inflow at the inlet of the solar-energy-collecting shed should be carefully chosen because of its opposite effect on the swirling velocity while positive effect on the resultant velocity (Fig. 2c). Experimental analysis. A heating shed model with R

5 2 m (Supplementary Figure 1a), was set up to test the dust-devil like swirling buoyant jet. The experiments with DT

5 50 K,

60 K, and

70 K were conducted. The swirling velocity and vertical velocity at two points were measured as marked in Supplementary Figure 1b. Measurements obtained from the experiment with DT

5 50 K were shown in Fig. 3a as an illustration. These results were plotted as a box-and-whisker diagram and then compared with the simulation values, as illustrated in Fig. 3b. The swirling velocity and vertical velocity tended to increase with the heating temperature difference and this could aid the efficacy of the swirling wind energy generation. A video of the generated swirling wind was recorded and the wind was compared with a typical dust devil found in nature (Supplementary Video 1). Similarity-theory estimation. By considering the similarity theory of fluid dynamics, the appropriate size of solar-energy-collecting shed can be obtained ........