Abstract
This study investigates the impact of building aspect ratio (building-height-to-street-canyon-width-ratio), wind speed and surface and air-temperature difference (Δθs−a) on the heating environment within street canyon. The Reynolds-averaged Navier-Stokes (RANS) and energy transport equations were solved with Renormalization group (RNG) theory version of k-\({\varepsilon}\) turbulence model. The validation process demonstrated that the model could be trusted for simulating air-temperature and velocity trends. The temperature and velocity patterns were discussed in idealized street canyons of different aspect ratios (0.5–2.0) with varying ambient wind speeds (0.5–1.5 m/s) and Δθs−a (2–8 K). Results show that air-temperatures are directly proportional to bulk Richardson number (R b ) for all but ground heating situation. Conversely, air-temperatures increase significantly across the street canyon with a decrease in ambient wind speed; however, the impact of Δθs−a was negligible. Clearly, ambient wind speed decreases significantly as it passes over higher AR street canyons. Notably, air-temperatures were the highest when the windward wall was heated and the least during ground heating. Conversely, air-temperatures were lower along the windward side but higher within the street canyon when the windward wall was heated.
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Abbreviations
- AR:
-
Aspect ratio
- H:
-
Street canyon height (m)
- W:
-
Street canyon width (m)
- X/W:
-
Spatial co-ordinate in X-direction non-dimensionalised by street canyon width
- \({\overline{{u}}_i }\) :
-
Mean streamwise (u) and vertical (υ) velocity components (ms−1)
- u a :
-
Horizontal inflow wind speed (ms−1)
- \({\varepsilon}\) :
-
Dissipation rate of turbulent kinetic energy (m2s−3)
- θ g :
-
Ground level temperature (K)
- μ eff :
-
Effective turbulent viscosity
- G b :
-
Turbulence kinetic energy production due to buoyancy (kgm−1s−3)
- Pr t :
-
Turbulent Prandtl number
- υ :
-
Kinematic viscosity (μ eff /ρ) (m2s−1)
- \({\overline{{u}'_i {u}'_j}}\) :
-
Reynolds stresses (m2s−2)
- Re y :
-
Wall distance based Reynolds number
- g :
-
Acceleration due to gravity (ms−2)
- p :
-
Pressure (Pascal)
- u i :
-
Velocity components (u,v) in the x and z directions (ms−1)
- Z/H:
-
Spatial coordinate in Z direction non-dimensionalized by street canyon height
- Re H :
-
Reynolds number (based on street canyon height) = uaH/ ν
- R b :
-
\({{\rm Bulk \, Richardson \, number} = \frac{gH(\theta_a -\theta_g )}{\theta_a u_a ^{2}}}\)
- k :
-
Turbulent kinetic energy (m2s−2)
- θ a :
-
Ambient air-temperature (K)
- μ t :
-
Turbulent viscosity
- G k :
-
Turbulence kinetic energy production due to mean velocity gradient (kgm−1 s −3)
- β :
-
Thermal expansion coefficient (K)
- S ij :
-
Mean rate of strain tensor (1/s)
- \({\alpha_{k}, \alpha_{\varepsilon}}\) :
-
Inverse Prandtl number for k and \({\varepsilon}\)
- Δθ s−a :
-
Difference between the surface and ambient air-temperature (K)
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Acknowledgements
The authors are grateful to the University Research Committee, University of Hong Kong, for providing necessary funding for this work. The first author is also thankful to the Department of Mechanical Engineering, Mehran University of Engineering and Technology (MUET), Jamshoro, Pakistan for providing necessary facilities to carry out this work.
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Open Access This is an open access article distributed under the terms of the Creative Commons Attribution Noncommercial License (https://creativecommons.org/licenses/by-nc/2.0), which permits any noncommercial use, distribution, and reproduction in any medium, provided the original author(s) and source are credited.
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Memon, R.A., Leung, D.Y.C. On the heating environment in street canyon. Environ Fluid Mech 11, 465–480 (2011). https://doi.org/10.1007/s10652-010-9202-z
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DOI: https://doi.org/10.1007/s10652-010-9202-z