Influence of inflow thermal stratification on flow and thermal fields around a heated isolated block

• Inflow instability slightly affects mean u , increases mean w in vertical center plane • Inflow instability increases mean u and v far from the building near the ground • Inflow instability contributes to complex mean temperature change, boosting variance • Stronger inflow instability increases TKE and its three turbulent stress components • The ratio of buoyancy to shear production of TKE increases with inflow instability Thermal stratification has a strong influence on flow structures around buildings, and related studies using large-eddy simulation (LES) are widespread. However, most LES work adopts neutral conditions or simplified inflow assumptions, as thermally unstable inflow data remain limited, leaving the sensitivity of urban flow fields to inflow stability insufficiently addressed. This study employs LES with non-isothermal inflows, which were generated by precursor method, to reproduce wind-tunnel experiments and to systematically examine the effects of varying inflow thermal instability on the mean flow and turbulence statistics around an isolated building modeled as an idealized rectangular block. Results show that mean streamwise velocity on the central vertical plane changes little with increasing inflow instability, while vertical velocity responds more strongly, and turbulence intensities in all three directions increase, especially in the wake. The normalized near-ground mean temperature is not directly correlated with inflow instability. This is probably because surface heating driving buoyancy, advection of heat by inflow fluctuations, and turbulence generated by the building in the wakes interact to redistribute heat vertically and horizontally. These multiple effects decouple mean temperature from inflow conditions, whereas temperature fluctuations increase in most regions. Turbulent kinetic energy and its three component turbulent intensities all increase with inflow thermal instability. The findings, highlighting how stronger inflow thermal instability intensifies wake turbulence and near-ground temperature fluctuations, enhance the understanding of flow and thermal interactions around buildings under thermally stratified conditions, and provide valuable insights for urban ventilation assessment and thermal environment evaluation as well as environmental flow modeling.