NUMERICAL SIMULATION OF ISOTHERMAL MIXING PROCESS IN A T-SHAPED RECTANGULAR MIXER

An isothermal mixing process in a right-angled T-shaped confluence type mixer is studied to confirm the performance of turbulence model. The main-stream of air collides with the side-stream of a mixture of air and nitrogen monoxide (NO). Measurements are carried out with variations of velocity ratio, W_in/U_in (W_in is a side-stream velocity and U_in is a main-stream one) to investigate the effect of W_in/U_in on the mixing process. Mean velocity components and velocity fluctuations within the main-stream duct are measured by the two-channel counter type laser-Doppler anemometer (LDA). The distribution of NO concentration is measured through a sampling probe by a chemi-luminescence detector type NO meter. A three-dimensional flow field is calculated by a k−ε turbulence model. Inlet conditions such as velocity components and concentrations of gases are given directly by the experimental conditions.
Our results show that the pattern of velocity field is qualitatively in good agreement with experimental results even if the standard k−ε model can not predict strictly a high-degree anisotropic flow field. On the other hand, the predicted NO concentration does not agree with experimental results. The difference between the measurement and the calculation of the NO concentration is caused by the multiplicational effect of the measurement error due to the gas sampling method and the calculation error caused by the turbulence model.
The refinement on measurement method of gas concentration and computation method of turbulence models having higher performance than k−ε model to the high-degree anisotropic flow need to determine the optimal operating conditions in each tee mixer.