Numerical Study on the Periodicity of Urban Heat Dome Flow

¹ College of Civil Engineering and Architecture, Zhejiang University, Hangzhou, China
² Center for Balance Architecture, Zhejiang University, Hangzhou, China
³ International Research Center for Green Building and Low-Carbon City, International Campus, Zhejiang University, Haining, China

Corresponding author: yifanfan@zju.edu.cn

Abstract

Under calm conditions where the background synoptic wind is weak or absent, the difference between city and rural temperature allows natural convection to develop. The turbulent circulation is also referred as urban heat island circulation or urban heat dome flow. The coupling of buoyancy, inertia, and vertical stability induces a natural periodicity in the urban heat dome flow. The periodicity in urban heat dome flow is often neglected in previous urban heat dome flow research. In this article, a high-precision CFD numerical method is applied, and the city is treated as a homogeneous flat plate with a specific shape. First of all, the real atmosphere model (around 20 km in length scale) are established and validated with water tank experiments. Convergent inflows at lower level and divergent outflows at upper levels can be observed. Then, the instantaneous 3D flow field distribution is analyzed, and the periodicity of the upper outflow region (f_out) after reaching the quasi-steady state is determined. Finally, cases with different city diameters (D), regional heat flux (H₀), and ambient potential temperature gradients (∂θ/∂z) are designed and solved. A quantitative description of periodicity (f_out) and its relationship to buoyancy (B₀), inertia (U_d) and vertical stability (N) is presented.