3.5.4 Impact of wind turbine type and orientation

Urban wind energy potential: Impacts of building corner modifications

Case R4 0.20B 39% 0% 22% 59

3.5.4 Impact of wind turbine type and orientation

The wind power density is typically calculated using only the streamwise velocity component, which is the relevant velocity for the typical HAWTs [103]. Note that the results presented in Secs. 3.5.1-3.5.3 pertain to such a HAWT. However, many studies reported that VAWTs are more suitable for energy harvesting in the urban environment than HAWTs due to their omni-directionality, lower noise production, higher space efficiency and lower installation and maintenance costs [19-21, 129]. Therefore, in this study, the potential for two types of VAWTs is investigated: (i) VAWT; and (ii) H-VAWT, where the latter refers to a VAWT mounted such that its axis is horizontal. The associated wind power densities (PD) are, therefore, calculated based on the velocities for each type of turbine in Fig. 3.13 as follows: a) PDH for HAWTs: Only the streamwise velocity component (U) is used to calculate PD. b) PDVV for VAWTs: The vector sum of the streamwise and lateral velocity (V) components is used to calculate PD. c) PDVH for H-VAWTs: The vector sum of the streamwise and vertical velocity (W) components is used to calculate PD.

Figure 3.13. Three different wind turbine type/orientation for wind energy harvesting in the building passage.

Figure 3.14 presents the profiles of the dimensionless power density (a) along the passage at y/B = 0 (midplane) and z/H = 0.93, (b) just above the roof at y/B = 0.5 and z/H = 1.03 and (c) beside the buildings at y/B = 1.1 and z/H = 0.93 for the three types of wind turbines. In line with the observations discussed in Section 3.5.1, Fig. 3.14 also shows that the PD for the chamfered and the rounded corner shapes are substantially higher than those of the sharp corner along the three lines. Therefore, the discussion on the different turbine types is focused on the chamfered and the rounded corner shapes due to their comparatively high PD.

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Figure 3.14. Horizontal profiles of the dimensionless power density: (a) along the passage at y/B = 0 (midplane) and z/H = 0.93 (just below the roof); (b) just above the roof (z/H = 1.03) at y/B = 0.5 ; (c) beside the buildings at y/B = 1.1 and z/H = 0.93 for the different wind turbine types.

The findings are presented for the following three regions: - Along the passages between the buildings (Fig. 3.14a): In the upstream passage, the values of PDVH/PDref along the line are much higher than those of PDVV/PDref and PDH/PDref, which are almost comparable. This shows the potential for benefiting from the vertical component of velocity in this region. In the downstream passage, the three lines are almost overlapping, implying the dominance of the streamwise component of the velocity. The average value of

PDVH/PDref for the designs of sharp, chamfered, and rounded corners along the passage is 14%, 20%, and 16% higher than those of the PDVV/PDref and PDH/PDref. - Above the building roof (Fig. 3.14b): For the areas in the front of upstream roofs and the back

Urban wind energy potential: Impacts of building corner modifications 61

of downstream roofs, PDVH/PDref is slightly higher than PDVV/PDref and PDH/PDref. Apart from these areas, the differences between PDVH/PDref, PDVV/PDref, and PDH/PDref remain limited. The average PDVH value is higher than those of PDVV/PDref and PDH/PDref by 24%, 5%, and 6% for sharp, chamfered, and rounded corners, respectively. - Besides the buildings (Fig. 3.14c): The values of PDVV/PDref along the line beside the buildings are higher than the values of PDH/PDref and PDVH/PDref. The average PDVV/PDref values can be enhanced by 43%, 11%, and 11%, compared to the PDH/PDref and PDVH/PDref for sharp, chamfered, and rounded corners, respectively.

The analysis shows that, for wind direction 0°, i.e. parallel to the passage between the buildings, the horizontally-mounted VAWTs are the best type of turbine to maximize the wind energy harvesting along the passage between the buildings as well as above the rooftop. On the other hand, the typical (vertically-aligned) VAWTs are the best option for wind energy harvesting besides the buildings.

Figure 3.15. Contours of dimensionless power density in horizontal plane at z/H = 0.93 (just below the roof) for (a-b) sharp, (c-d) chamfered, and (e-f) rounded corner shapes at wind directions of 0° and 45°. Note that the high turbulence region (Iref > 0.16) is masked in white, signaling its unsuitability for turbine installation. The black arrow indicates the flow direction.