DNS study of dual-plume interference in a wall-bounded turbulent flow

Turbulent mixing of dual plumes emitting simultaneously from line sources in a turbulent boundary layer has been studied using direct numerical simulation (DNS). A comparative study of three test cases has been conducted to investigate the effects of the source separation on turbulent mixing of two plumes.The dispersion and interference of dual plumes are investigated in both physical and spectral spaces, which include the analyses of turbulence statistics of the concentration field, cross-correlation between the two fluctuating plumes, pre-multiplied spectra of the velocity and concentration fields, and pre-multiplied co-spectrum of the dual plume fluctuations. As the downstream distance from the line sources increases, the plume development transitions from a turbulent convective stage to a turbulent diffusive stage. It is observed that plume released from a ground-level source reaches the turbulent diffusive stage faster than that from an elevated source. It is also observed that a smaller separation between two line sources results in a larger negative correlation coefficient between the two plumes and faster mixing of two fluctuating plumes. The pre-multiplied co-spectrum shows that even for a test case with the largest source separation, two fluctuating plumes quickly reach a complete mixing state downstream of the lines source such that they fluctuate as one single plume.