連続点煙源からのトレーサガス拡散の数値計算 : 第2報,不安定温度境界層内の濃度分布

抄録

The numerical simulation results of tracer gas diffusion from a continuous point source in an unstable boundary layer were obtained and compared with wind tunnel experiment results. The flow fields were predicted by the k-ε model. The obtained turbulent kinetic energy showed good agreement with that from wind tunnel experiments when the buoyancy term of the dissipation equation was eliminated and the wall functions including universal functions were used. Then the predicted turbulent kinetic energy was divided into directional turbulence intensities using algebraic equations and an eddy viscosity concept. Using estimated turbulence intensities, tracer gas diffusion was simulated by a Lagrangian particle dispersion model. Predicted mean concentration profiles showed good agreement when turbulence intensities were obtained from algebraic equations. The Lagrangian time scale T_L was estimated from the flow calculation results, T_L=(k/ε)/C_1ψ, and compared with analytically obtained profiles. The model constant C_1ψ=2, the same value as in the neutral boundary layer, was obtained for the simulation of the tracer gas diffusion in an unstable boundary layer.