How to cool cities down during heat waves

The reasons for this local temperature increase are dark road and building surfaces that absorb and retain sunlight, heat generated by traffic and industry, lack of vegetation that could reduce the temperature by evaporation, and the blockage of wind by closely spaced buildings.

The urban climate group uses an atmospheric boundary layer (ABL) water tunnel to model urban heat islands and measure velocity and temperature fields. The aim is to study e.g. urban heat removal and buoyancy effects in cities at large scale.

The RSI video is in Italian. The ETHZ and Empa is in English.

The urban climate group uses an atmospheric boundary layer (ABL) water tunnel to model urban heat islands and measure velocity and temperature fields to study e.g. urban heat removal and buoyancy effects in cities at large scale. Courtesy of RSI TV and ETHZ and Empa on Youtube.

Combined PIV and LIF measurements of velocity and temperature fields

The water tunnel has a test cross section of 0.6 m x 1.0 m and the water speed can be adjusted from 0.02 m/s up to 1.5 m/s. It is equipped with a Stereo Particle Image Velocimetry (Stereo PIV) system and a 2-color Laser-Induced Fluorescence system (LIF), both from Dantec Dynamics.

Time-resolved temperature or concentration fields can be measured simultaneously together with the velocity field by combining PIV and LIF. By this, heat and concentration flows and exchange processes in the urban canopy can be quantified.

Four light sensitive sCMOS “HiSense Zyla” cameras and high speed lasers are used in combination with our powerful Dynamic Studio software to ensure reliable results.

The usage of non-toxic dyes allows to measure temperature with the LIF method at a large scale, and the precise quantitative time-resolved PIV measurements of all three velocity components reveal turbulent and coherent flow structures.

The new atmospheric boundary layer water tunnel will help to understand how to alleviate urban heat islands by improving city aeration and planting vegetation to obtain more pleasant conditions.

Dantec Dynamics is proud to support the fluid mechanics community with measurement techniques to ensure innovative research regarding climate change and heat wave mitigation.