TY - JOUR

T1 - LES case study on pedestrian level ventilation in two neighbourhoods in Hong Kong

AU - Letzel, Marcus Oliver

AU - Helmke, Carolin

AU - Ng, Edward

AU - An, Xipo

AU - Lai, Alan

AU - Raasch, Siegfried

N1 - Financial support by a Chinese University of Hong Kong Social Science Panel Direct Grant, by the German Research Foundation (DFG) under grant RA 617/15-1/ 2 and by the German National Academic Exchange Ser- vice (DAAD) is gratefully acknowledged. GIS data of Hong Kong were provided by the HKSAR Planning Department under the project ‘‘Urban Climatic Map and Standards for Wind Environment’’. The simulations worth 1.4 M€ were performed on the North German su- percomputing center HLRN (www.hlrn.de). The authors are grateful to two anonymous reviewers who provided valuable comments.

PY - 2012/12

Y1 - 2012/12

N2 - Hong Kong is one of the most densely built-up and populated cities in the world. An adequate air ventilation at pedestrian level would ease the thermal stress in its humid subtropical climate, but the high-density city severely reduces the natural ventilation. This case study investigates pedestrian level ventilation in two neighbourhoods in Kowloon, downtown Hong Kong using the parallelized large-eddy-simulation (LES) model PALM. The LES technique is chosen here for a city quarter scale pedestrian comfort study despite of its high computational cost. The aims of the paper are a) to get a comprehensive overview of pedestrian level ventilation and a better understanding of the ventilation processes in downtown Hong Kong, b) to test the LES technique on this urban scale compared to the wind tunnel and c) to investigate how numerical/physical parameters influence ventilation. This case study is restricted to neutral stratification in order to allow a direct comparison with the wind tunnel. A sensitivity study quantifies the dependence of site-averaged ventilation on numerical and physical parameters and determines an appropriate urban LES set-up for two 1 km2 neighbourhoods in Kowloon (Tsim Sha Tsui, Mong Kok) that are investigated for prevailing E and SW wind. The results reveal the critical dependence of ventilation on the urban morphology. Air paths, street orientations, ground coverage, sites fronting the water, inter connectivity of spaces, building podium size and building heights can all affect the pedestrian wind environment. Isolated tall buildings may have a pronounced impact on ventilation both locally and downstream.

AB - Hong Kong is one of the most densely built-up and populated cities in the world. An adequate air ventilation at pedestrian level would ease the thermal stress in its humid subtropical climate, but the high-density city severely reduces the natural ventilation. This case study investigates pedestrian level ventilation in two neighbourhoods in Kowloon, downtown Hong Kong using the parallelized large-eddy-simulation (LES) model PALM. The LES technique is chosen here for a city quarter scale pedestrian comfort study despite of its high computational cost. The aims of the paper are a) to get a comprehensive overview of pedestrian level ventilation and a better understanding of the ventilation processes in downtown Hong Kong, b) to test the LES technique on this urban scale compared to the wind tunnel and c) to investigate how numerical/physical parameters influence ventilation. This case study is restricted to neutral stratification in order to allow a direct comparison with the wind tunnel. A sensitivity study quantifies the dependence of site-averaged ventilation on numerical and physical parameters and determines an appropriate urban LES set-up for two 1 km2 neighbourhoods in Kowloon (Tsim Sha Tsui, Mong Kok) that are investigated for prevailing E and SW wind. The results reveal the critical dependence of ventilation on the urban morphology. Air paths, street orientations, ground coverage, sites fronting the water, inter connectivity of spaces, building podium size and building heights can all affect the pedestrian wind environment. Isolated tall buildings may have a pronounced impact on ventilation both locally and downstream.

KW - High-density city

KW - Hong Kong

KW - Pedestrian level ventilation

KW - Urban large-eddy simulation

KW - Wind environment

UR - http://www.scopus.com/inward/record.url?scp=84874612934&partnerID=8YFLogxK

U2 - 10.1127/0941-2948/2012/0356

DO - 10.1127/0941-2948/2012/0356

M3 - Article

AN - SCOPUS:84874612934

VL - 21

SP - 575

EP - 589

JO - Meteorologische Zeitschrift

JF - Meteorologische Zeitschrift

SN - 0941-2948

IS - 6

ER -