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This study investigates the particle dispersion characteristics in the turbulent wake of a simplified vehicle model (Ahmed body) for two values of the rear slant angle ϕ (25° and 40°) to study the effect of flow separation. In the experiments (Reynolds number Rel=1.90 ×105), smoke particles were released from a source and visualized with a laser sheet. Concentration fields were analyzed to calculate the vertical (Sy) and lateral (Sz) smoke spread. The findings indicate that the flow topology and concentration fields in the wake are highly dependent on ϕ. In the ϕ=40° case, separation on the rear slant disrupts the trailing vortices originating on the rear slant edges and significantly alters the wake topology. The growth of vertical smoke spread saturates after the recirculation region. The uniform mixing and absence of trailing vortices concentrate the smoke particles in the model midplane. In the ϕ=25° case, the signatures of trailing vortices were observed in the concentration fields behind the model. The vertical smoke spread is less, and the lateral smoke spread is more compared to the ϕ=40° case. The growth of the smoke spread (Sy, Sz) driven by the trailing vortices persists for a long distance, even after the recirculation region. The disruption of trailing vortices brought about by the flow separation appears to be an important effect driving the vertical smoke spread in the wake. The connection between the turbulent velocity structures and concentration structures will need to be explored with combined velocity and concentration measurements in the wake.
This study investigates the particle dispersion characteristics in the turbulent wake of a simplified vehicle model (Ahmed body) for two values of the rear slant angle ϕ (25° and 40°) to study the effect of flow separation. In the experiments (Reynolds number Rel=1.90 ×105), smoke particles were released from a source and visualized with a laser sheet. Concentration fields were analyzed to calculate the vertical (Sy) and lateral (Sz) smoke spread. The findings indicate that the flow topology and concentration fields in the wake are highly dependent on ϕ. In the ϕ=40° case, separation on the rear slant disrupts the trailing vortices originating on the rear slant edges and significantly alters the wake topology. The growth of vertical smoke spread saturates after the recirculation region. The uniform mixing and absence of trailing vortices concentrate the smoke particles in the model midplane. In the ϕ=25° case, the signatures of trailing vortices were observed in the concentration fields behind the model. The vertical smoke spread is less, and the lateral smoke spread is more compared to the ϕ=40° case. The growth of the smoke spread (Sy, Sz) driven by the trailing vortices persists for a long distance, even after the recirculation region. The disruption of trailing vortices brought about by the flow separation appears to be an important effect driving the vertical smoke spread in the wake. The connection between the turbulent velocity structures and concentration structures will need to be explored with combined velocity and concentration measurements in the wake.
The study of the movement of pollutants through ducts facilitates the assessment and control of ambient air quality problems (AQ). Among other things, understanding the deposition and distribution of particulate matter in elbows is important for practical engineering applications. In this study, the turbulent flow field and particle deposition in a 90° bend is investigated using RANS simulation. The RNG k-ε turbulence model was employed to calculate the airflow flow field and the discrete phase model (DPM) was used to simulate the particle phase motion. Where for the discrete phase, the Discrete Random Wander (DRW) model was considered and the deposition of particles with sizes of 1, 3, 5, 10, 20, and 40 μm in the flow field was investigated separately. Grid-independent validation of the models used in the simulations was performed. The effects of inlet velocity, particle size, and direction of gravity on the flow field and particle deposition in the elbow were considered. The results show that the flow field in the bend is strongly influenced by the above parameters. Among them, the turbulent disturbance in the bend section is the most intense, with high turbulent energy value, and it is also the region with the largest energy loss. The inlet velocity is negatively correlated with the deposition rate, and the particle size is positively correlated with the deposition rate.
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