Large eddy simulation of flow structure in the near region of a circular wall jet

Abstract

When there is a turbulent circular wall jet discharge from a nozzle into a stagnant ambient area with initial momentum, the velocity field changes greatly, especially near the wall or the interface between the jet and surrounding fluid. This accounts for the great velocity gradient produced in the entrainment between jets and any surrounding fluid and the appearance of large-scale coherent structure. This phenomenon is more distinct in the region near the jet exit. However, experimentation cannot capture this characteristic of the near region because of the restrictions inherent in experimental technology. Large eddy simulation (LES) provides the mean and turbulent velocity characteristics in the near region without disturbing the surrounding area and reproduces the coherent structure. Here, a LES study of the flow features in the near region of a circular wall jet based on the finite volume method with 8.42 million nodes is reported. The mean velocity characteristics in the near region and fully developed region simulated by LES including the decay of maximum velocity and the evolution of velocity half-width agreed well with the results of similar experiments. The mean and turbulent velocity distributions of the circular wall jet in the near region (x=0-20D) were also investigated. It was found that the distributions of normalized mean velocity in spanwise direction were similar to those in the far field (x≥20D), but not exhibited similarity in vertical direction. Moreover, the turbulent velocities in two directions were smaller than the ones in the far field. We also analyzed the probability density function (PDF) of the streamwise fluctuant velocity at several locations. Furthermore, we looked at turbulent Reynolds stresses profiles and coherent structure in the region of the jet exit vicinity and the near wall, which essentially prescribe hydrodynamic properties but are difficult to obtain from experimentation or other Reynolds average Novier-Stokes methods.