Experimental investigation on the surface wave characteristics of conical liquid film

The disintegration of the liquid sheet is due to the growth of the unstable surface wave. Research on the surface wave characteristics mainly uses the linear stability analysis, and the surface wave characteristics, for example the frequency and wave length of the surface wave, have not been analyzed well experimentally. In the present study, the proper orthogonal decomposition is adopted to analyze the instantaneous spray images and the extracted surface waves on the interface of the gas and liquid. The wavelength and frequency of the surface wave are obtained, and the influence of the injector mass flow rate is investigated. The results show that the spray pattern moves from onion stage to tulip stage and fully developed wavy cone stage with the increase of liquid mass flow rate. In the tulip stage, the wave frequency decreases slightly and then increases with the increase of liquid mass flow rate. On the contrary, the wavelength increases gradually with the increase of liquid mass flow rate and then decreases slightly. This variation trend is caused by the competition effect of the film thickness and the axial film velocity. The decrease of film thickness decreases the wave frequency and increases the wavelength, while the increase of the axial film velocity increases the wave frequency and decreases the wavelength. In the fully developed wavy cone stage, the wave frequency increases gradually with the increase of liquid mass flow rate. And the bandwidth of the surface wave frequency increases gradually, which means that the leading role of the dominant surface wave is weakened and the conical film is dominated by surface waves with multiple frequencies. The wavelength decreases with the increase of liquid mass flow rate because of the significant increased axial film velocity.