Validation of a CFD model for the evaluation of urban microclimate at high latitudes: A case study in Trondheim, Norway

The urban microclimate is a rapidly evolving field of research gaining increasing interest from public authorities and researchers. However, studies at high-latitude cities are scarce and researchers primarily focus on summerly overheating. This study focuses on the validation process of a CFD model that applies the 3D URANS approach with the realisable k-e turbulence model at a highly complex urban area in Trondheim, Norway (63.4° N) during autumn. The CFD model features a polyhedral grid of the urban environment, including geometrically explicitly modelled buildings and trees in the area of interest. Furthermore, solar radiation, longwave radiation exchange, heat transfer from the buildings, heat storage in the urban surface, and the thermal effects of evapotranspiration from trees and grass surfaces are considered. The CFD model is validated with experimental results from a network of five mobile and one reference weather stations in the study area, providing hourly-averaged measurements for wind speed, wind direction (only reference weather station) and air temperature for two 48-h periods from September 27–28 and October 19–20. The results show that the CFD model is well able to reproduce the measured conditions at the area of interest with a mean R2 of 0.60, 0.63, and 0.96 for wind speed, wind direction and air temperature, respectively, at the reference weather station. It will be used in future studies, including the analysis of the impact of urban microclimate on buildings’ energy performance, outdoor thermal and pedestrian wind comfort.publishedVersio

Validation of a CFD model for the evaluation of urban microclimate at high latitudes: A case study in Trondheim, Norway

The urban microclimate is a rapidly evolving field of research gaining increasing interest from public authorities and researchers. However, studies at high-latitude cities are scarce and researchers primarily focus on summerly overheating. This study focuses on the validation process of a CFD model that applies the 3D URANS approach with the realisable k-e turbulence model at a highly complex urban area in Trondheim, Norway (63.4° N) during autumn. The CFD model features a polyhedral grid of the urban environment, including geometrically explicitly modelled buildings and trees in the area of interest. Furthermore, solar radiation, longwave radiation exchange, heat transfer from the buildings, heat storage in the urban surface, and the thermal effects of evapotranspiration from trees and grass surfaces are considered. The CFD model is validated with experimental results from a network of five mobile and one reference weather stations in the study area, providing hourly-averaged measurements for wind speed, wind direction (only reference weather station) and air temperature for two 48-h periods from September 27–28 and October 19–20. The results show that the CFD model is well able to reproduce the measured conditions at the area of interest with a mean R2 of 0.60, 0.63, and 0.96 for wind speed, wind direction and air temperature, respectively, at the reference weather station. It will be used in future studies, including the analysis of the impact of urban microclimate on buildings’ energy performance, outdoor thermal and pedestrian wind comfort

Validation of a CFD model for the evaluation of urban microclimate at high latitudes: A case study in Trondheim, Norway

The urban microclimate is a rapidly evolving field of research gaining increasing interest from public authorities and researchers. However, studies at high-latitude cities are scarce and researchers primarily focus on summerly overheating. This study focuses on the validation process of a CFD model that applies the 3D URANS approach with the realisable k-e turbulence model at a highly complex urban area in Trondheim, Norway (63.4° N) during autumn. The CFD model features a polyhedral grid of the urban environment, including geometrically explicitly modelled buildings and trees in the area of interest. Furthermore, solar radiation, longwave radiation exchange, heat transfer from the buildings, heat storage in the urban surface, and the thermal effects of evapotranspiration from trees and grass surfaces are considered. The CFD model is validated with experimental results from a network of five mobile and one reference weather stations in the study area, providing hourly-averaged measurements for wind speed, wind direction (only reference weather station) and air temperature for two 48-h periods from September 27–28 and October 19–20. The results show that the CFD model is well able to reproduce the measured conditions at the area of interest with a mean R2 of 0.60, 0.63, and 0.96 for wind speed, wind direction and air temperature, respectively, at the reference weather station. It will be used in future studies, including the analysis of the impact of urban microclimate on buildings’ energy performance, outdoor thermal and pedestrian wind comfort

Assessing the impact of urban microclimate on building energy demand by coupling CFD and building performance simulation

To quantify the effect of different compositions of the urban surface on the urban microclimate, building energy demand, and summerly overheating of a selected 13-floor office high-rise building in Trondheim, Norway, a validated Computational Fluid Dynamics model is coupled with Building Performance Simulation. In total, four scenarios were investigated in three one-week periods in summer (15.06.20–21.06.20), autumn (16.09.20–22.09.20), and winter (21.12.20–27.12.20). The scenarios were: (1) base case or current situation; (2) no vegetation in the entire domain with no trees and grass surfaces being substituted with concrete; (3) all vegetation with all concrete, asphalt, and pavements replaced by grass; and (4) the base case situation with highly improved insulation levels of surrounding buildings. The results demonstrate clear benefits from urban greening during a one-week heat wave as the no vegetation scenario increased the cooling energy demand by 28.5%. The positive effect of evapotranspiration from grass surfaces was noticeable especially on the lowest two floors, where cooling energy demands were halved. During the simulated weeks in autumn and winter, the no vegetation scenario resulted in respectively 3.5% and 0.9% lower heating energy demands. At the investigated building, improving the insulation properties of all modeled surrounding buildings led to 0.1 °C higher average air temperatures during summer, and 0.1 °C lower during winter, while they remained unchanged in autumn. However, the energy demands were 0.8%, 0.9%, and 0.8% higher compared to the base case for summer, autumn, and winter, respectively.publishedVersio

Assessing the impact of urban microclimate on building energy demand by coupling CFD and building performance simulation

To quantify the effect of different compositions of the urban surface on the urban microclimate, building energy demand, and summerly overheating of a selected 13-floor office high-rise building in Trondheim, Norway, a validated Computational Fluid Dynamics model is coupled with Building Performance Simulation. In total, four scenarios were investigated in three one-week periods in summer (15.06.20–21.06.20), autumn (16.09.20–22.09.20), and winter (21.12.20–27.12.20). The scenarios were: (1) base case or current situation; (2) no vegetation in the entire domain with no trees and grass surfaces being substituted with concrete; (3) all vegetation with all concrete, asphalt, and pavements replaced by grass; and (4) the base case situation with highly improved insulation levels of surrounding buildings. The results demonstrate clear benefits from urban greening during a one-week heat wave as the no vegetation scenario increased the cooling energy demand by 28.5%. The positive effect of evapotranspiration from grass surfaces was noticeable especially on the lowest two floors, where cooling energy demands were halved. During the simulated weeks in autumn and winter, the no vegetation scenario resulted in respectively 3.5% and 0.9% lower heating energy demands. At the investigated building, improving the insulation properties of all modeled surrounding buildings led to 0.1 °C higher average air temperatures during summer, and 0.1 °C lower during winter, while they remained unchanged in autumn. However, the energy demands were 0.8%, 0.9%, and 0.8% higher compared to the base case for summer, autumn, and winter, respectively

CFD Simulations of Turbulent Flow in the Human Upper Airways

In this paper, investigations are conducted using Reynolds-averaged Navier-Stokes (RANS) turbulence models to investigate the importance of turbulence modelling for nasal inspiration at a constant flow rate of 250 ml/s. Four different, standard turbulence models are tested in a model geometry based on pre-operative CT images of a selected obstructive sleep-apnea syndrome (OSAS) patient. The results show only minor differences between them. Furthermore, the turbulence models do not give significantly different results than a laminar flow model. Thus, the main conclusion is that effects of turbulence are insignificant in CFD modelling of the airflow in the pre-operative model of the upper airways of the chosen patient