Numerical Study of the Trajectory, Penetration, and Interaction of Single and Tandem Jets in a Crossflow Using LES

In this paper, a large eddy simulation (LES) method was used to conduct a study on single and tandem jets in a crossflow, focusing particularly on their trajectory, penetration, and interaction. The numerical model was validated with an experimental test campaign. Examination of the time-averaged flow field allowed both the velocity and the tangential angle of the jet trajectories to be examined. In addition, the penetration depth of the jet based on a scalar transport model was analyzed. The unsteady flow characteristics around the trajectories were studied using both the power spectral density (PSD) function and a spectral proper orthogonal decomposition (SPOD). The results show that the upstream jet's trajectory changes little as a function of spacing, while the downstream jet deflects as a result of the influence of the counterrotating vortex pair. In addition, the curve height of the tandem jet trajectories is significantly higher than that of the single jet. The height of the trajectory formed by the tandem jets can reach four times that of the single jet, and the penetration depth of the tandem jets can be 2.8 times that of the single jet. Meanwhile, when the spacing between the two jets is small, the coherent structures tend toward the upstream jet distribution, and the fluctuation frequency after mixing is dominated by the upstream jet. With the increase of spacing, the fluctuation frequency after mixing is greatly affected by the downstream jet, and the frequency decreases. Furthermore, when the dimensionless spacing D′ is 5.67, the frequency difference between both jets is minimal and the coherent structures are significantly reduced, indicating that flow mixing is optimal and stable.