What question did this study set out to answer?

To understand how different upper flow velocity fluctuations influence the turbulent structure of the urban boundary layer.

March 26, 2026Open Access

Effects of Velocity Fluctuations of Upper Flow on Turbulent Structure of Urban Boundary Layer

Key Points

To understand how different upper flow velocity fluctuations influence the turbulent structure of the urban boundary layer.
Conducted experiments in a wind tunnel to simulate urban boundary layers.
Utilized different turbulence grids to generate various upper flow velocity fluctuations.
Employed hot-wires anemometer to measure streamwise and spanwise velocities.
Estimated turbulence statistics for analysis.
The integral time scale decreases with increasing z/L for different grids.
The vertical profile of Δ for the unequally spaced turbulence grid is larger than for M50 and M75 at z/L > 0.167.
The turbulent structure of the urban boundary layer is affected by the scale of upper flow velocity fluctuations.

Abstract

The effects of various velocity fluctuations of upper flow on turbulent structure of urban boundary layer were experimentally investigated. The urban boundary layer was reproduced in a wind tunnel. In order to produce various velocity fluctuations in the upper flow, three kinds of turbulence grids were set to the entrance of the test section. The streamwise and spanwise velocities were simultaneously measured by using hot-wires anemometer. Turbulence statistics were estimated. The vertical profiles of the integral time scale, , for M50 , M75 and the unequally spaced turbulence grid decrease as z/L increases. The vertical profile of Δ of the unequally spaced turbulence grid was larger than those for M50 and M75 at z/L > 0.167. It is suggested that the effects on the turbulent structure of the urban boundary layer depends on the scale of velocity fluctuations of the upper flow.

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