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Integrating twisted wind profiles to Air Ventilation Assessment (AVA): The current status
A U Weerasuriya1, K T Tse1, Xuelin Zhang1
1Department of Civil and Environmental Engineering, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong.
Building and Environment
|April 15, 2020
Summary
Twisted wind flows in Hong Kong complicate Air Ventilation Assessments (AVA). This study reveals significant wind speed differences in low-density areas and assesses correction methods for AVA, finding common methods often over-predict results.
Area of Science:
- Environmental Science
- Urban Planning
- Fluid Dynamics
Background:
- Complex terrain, such as Hong Kong's, generates twisted wind flows.
- Twisted winds pose challenges for Air Ventilation Assessment (AVA) by affecting wind tunnel tests and determining wind direction probabilities.
- Existing correction methods for AVA are used in post-analysis but their accuracy is not well-established.
Purpose of the Study:
- To investigate the impact of twisted wind flows on AVA outcomes in an urban area.
- To evaluate the accuracy of three common correction methods (No-Shift, Threshold, Proportional) used in AVA post-analysis.
- To understand how building density influences the effects of twisted winds on pedestrian-level wind speeds.
Main Methods:
- Utilized a boundary layer wind tunnel to simulate urban airflow.
- Employed two distinct twisted wind profiles and compared them with conventional wind flows.
- Analyzed wind speeds at pedestrian level across areas with varying building densities.
- Assessed the performance of No-Shift, Threshold, and Proportional correction methods against twisted wind flow data.
Main Results:
- Significant discrepancies in pedestrian-level wind speeds were observed between twisted and conventional wind flows, particularly in areas with low building density.
- Wind speed differences were minimal in high-density urban areas.
- The No-Shift correction method showed frequent deviations from twisted wind flow results.
- The Threshold and Proportional methods consistently over-predicted AVA indicators.
Conclusions:
- Twisted wind flows significantly influence AVA results, especially in less built-up urban environments.
- The accuracy of common AVA correction methods is questionable, with Threshold and Proportional methods tending to overestimate ventilation indicators.
- Further research is needed to refine correction methods for twisted wind conditions in urban air quality assessments.
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