Vortical structure evolutions and spreading characteristics of a plane jet flow under anti-symmetric long-wave excitation

The vortical evolutions and spreading characteristics of a low-speed plane jet under anti-symmetric long-wave excitations are investigated experimentally. The perturbation is introduced with two oscillating strips located at the nozzle exit. The experiments were operated at Reynolds number of 8.2 × 103 based on the nozzle exit height. Mixing and spreading properties are influenced obviously by long-wave excitation after the end of potential core. The increments of half-width, momentum thickness, and volume flow rate depend on the excitation frequency. The results of flow visualization also reveal the dependence of excitation frequency. The power spectra of fluctuating velocities shows that the evolution of coherent structure is significantly influenced by the long-wave excitation in the downstream, but it is similar to the natural jet in the near field. The long-wave excitation at certain frequencies can promote large-scaled anti-symmetric vortical structures in the far field.