In this study, the design of the BWT mast that can work optimally in areas with low wind speeds (1 m/s to 5 m/s) was determined by doing a comparison between the Initial Design (ID) simulation results with Modified Design 1 (MD1) and Modified Design. Design 2 (MD2), to get a model that has an optimal tendency to oscillate with a predetermined wind speed. The oscillation tendency will be discussed based on the comparison of several parameters as follows: fluid motion analysis parameters based on animation are used to determine the minimum speed for the BWT model to oscillate; frequency parameters to get the value of the oscillation frequency of each BWT model; as well as the comparison of the lift constant ratio (CL) with the drag constant (CD) parameters to show the magnitude of the coefficient of oscillatory displacement at BWT.
Based on the results of the CFD simulation, which is presented in Figs. 3, 4, and 5 performed on each model shape with variations in speed, the shape of the airflow stability after passing through the mast can be obtained. The stability of the air after passing through the object that has been obtained can show the stability of BWT oscillations when applied. It can be seen in the Initial Design (ID) animation showing the stability of the air flow after passing through the object when the wind speed is 1 m/s to 5 m/s as shown in Table 1. Furthermore, Modified Design 1 (MD1) shows the stability of the air flow after passing through the object when the wind speed is 1 m/s to 5 m/s. While the Modified Design 2 (MD2) shows the stability of the air flow after passing through the object when the wind speed is 1 m/s to 5 m/s. This shows that the ID model will start to oscillate at a wind speed of 3 m/s, while the MD1 and MD2 models will start to oscillate at a wind speed of 1 m/s. So, it can be seen that the BWT with the MD1 and MD2 models can already oscillate in an area with a wind speed of 1 m/s.
In addition, this is supported by the Coefficient Force graph from the simulation results that have been carried out with 3 Bladeless Wind Turbine (BWT) mechanical models, which show the frequency, lift coefficient (CL), and drag coefficient (CD) in each model in the Table 1.
Table 1
Simulation results, oscillation frequency, lift coefficient, drag coefficient, and drift coefficient, on the bladeless wind turbine model
V (m/s) | Frequency (Hz) | Lift Coefficient | Drag Coefficient | Drift Coefficient (CL/CD) |
ID | MD1 | MD2 | ID | MD1 | MD2 | ID | MD1 | MD2 | ID | MD1 | MD2 |
1 | 2,00 | 5,00 | 6,75 | 140,00 | 18,00 | 6,00 | 198,30 | 19,20 | 4,00 | 0,71 | 0,94 | 1,50 |
2 | 5,00 | 9,00 | 14,00 | 124,16 | 18,50 | 7,50 | 149,16 | 16,00 | 4,00 | 0,83 | 1,16 | 1,88 |
3 | 7,50 | 13,50 | 20,00 | 123,75 | 15,04 | 10,00 | 128,75 | 16,00 | 4,00 | 0,96 | 0,94 | 2,50 |
4 | 10,00 | 17,50 | 25,00 | 99,00 | 15,59 | 11,20 | 117,70 | 16,90 | 4,00 | 0,84 | 0,92 | 2,80 |
5 | 9,30 | 17,00 | 28,00 | 95,70 | 10,77 | 12,00 | 78,50 | 11,68 | 4,00 | 1,22 | 0,92 | 3,00 |
*ID: Initial design; MD1: Modified design 1; MD2: Modified design 2 |
Furthermore, the frequency data for each model is processed and produces a frequency graph for each model, which can be seen in Fig. 6.
Based on Fig. 6, the MD2 model has a higher frequency value than the other 2 models, which is 8 Hz, followed by the MD1 model of 5 Hz and ID of 2 Hz at a wind speed of 1 m/s. In addition, the frequency value of each model at a wind speed of 5 m/s also shows that the MD2 model has the highest value of 28 Hz, followed by MD1 of 17 Hz and ID of 9.3 Hz. This shows that the MD2 model can oscillate well at wind speeds in the range of 1 m/s to 5 m/s compared to other models. In addition, a graph of the lift coefficient ratio (CL) with the drag coefficient (CD) is also obtained which is presented in Fig. 7.
In Fig. 7, the ratio of the lift coefficient (CL) to the drag coefficient (CD) which produces the coefficient of oscillatory displacement force in the MD2 model has the largest CL/CD coefficient ratio compared to other models at each tested wind speed. So, it shows that the MD2 model has better sensitivity to wind motion than the ID and MD1 models at the same wind speed.