Eighth Conference on Coastal Atmospheric and Oceanic Prediction and Processes
Eighth Symposium on the Urban Environment


LES studies on pedestrian level ventilation in Hong Kong


Carolin Weinreis, Institute of Meteorology and Climatology, Leibniz Universität, Hannover, Germany; and M. O. Letzel, S. Raasch, E. Ng, and L. Katzschner

Hong Kong is one of the most built-up and populated cities in the world. It has to handle several problems both due to their geographical location with very hot and humid summers and due to the urban heat island effect. Health and well-being of the population depends strongly on a comfortable environment. An adequate air ventilation on pedestrian level contributes to an enhancement of the urban climate but the natural wind flow is highly influenced by the building development of Hong Kong. The purpose of this project is to provide guidelines for urban designers. How can they plan future projects in Hong Kong to improve the ventilation?

This study investigates the ventilation in the densely built-up quarter Kowloon with high resolution large eddy simulations (LES). The parallelized LES model PALM was developed at the Leibniz Universität Hannover and is able to explicitly resolve all relevant energy-containing eddies. The turbulent structures between obstacles can therefore be resolved and analysed well. Simulations of two 1km x 1km quarters in Kowloon (Tsim Sha Tsui and Mong Kok) are performed to examine the wind velocity at pedestrian level and to compare the influence of the buildings on the windflow. Do high buildings have the capability to locally enhance the wind flow on pedestrian level? How can the channeling effect of street canyons improve the ventilation? What is the impact of other special obstacle structures on the wind velocitiy?

To answer these questions the model has to be set up carefully. Sensitivity studies are carried out to quantify the dependence on the model of initial and boundary conditions. An important task is the investigation of time averaging and simulation time to achieve quasi steady results with simultaneous minimization of computational costs. Similar to wind tunnel studies the dimension of a buffer around the evaluated quarters has to be figured out to obtain physically correct results. The location of measurement points has a high impact on the area-averaged ventilation. This dependence is important in case of comparsions with wind tunnel experiments.

Easterly winds are the prevalent flow for both sites but also wind from southwest is often present especially during summertime. These two conditions are simulated for Mong Kok. Tsim Sha Tsui will be analysed additionally with a new building development. One new very high building is set up in a second building dataset to gain the direct influence of that building.

Simulation results and the impacts of the building development on the ventilation will be shown and discussed.

Joint Session 17, Building—Resolving Modeling and Forecasting in Urban Areas
Wednesday, 14 January 2009, 1:30 PM-2:30 PM, Room 124A

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