市街化空間の熱的環境に関する研究 : その 4. 風洞気流中における熱拡散実験

Abstract

This part is intended to investigate the structure of thermal diffusion in a wind tunnel and to compare measured temperature distribution with numerical solutions by the method which has been described previously. For this experiment, roughness elements (zh=2.8cm) were used in a wind tunnel. A part of it is heat produce area (60×60cm) which can be controlled from 0 to 2kw. Summary of results obtained may be as follows. 1. The structure of air flow when the model is not heated up. Wind profiles can be given by log-law up to 10cm in height above the model. Prandtl's mixing length is expressed as l_z=0.11Z, as Reynolds stress is approximately constant in the boundary layer. Vertical eddy diffusivities are proportional to height and horizontal eddy diffusivities decrease with increase of height. 2. Thermal diffusion experiment. Air flow over the model was observed using emitted smoke, which shows that upward wind velocity due to temperature gradient tends to increase with increase of quantity of heat from the model and decrease of wind velocity in the wind tunnel. The same result is obtained from measured temperature distributions in sectional figure. 3. Comparisons between measured and calculated temperature. The KEYPS formula which is expressed by mixing length and Richardson number (Eq.4-9) was used to estimate the eddy diffusivities in unstable conditions, in which the constantγ_z=100 was used in calculation. Calculated results were in good agreement with measured results in comparison of isotherms, where the correlation coefficients between measured and calculated temperature were from 0.95 to 0.97.