Influence of interlayer on characteristics of Kelvin-Helmholtz instability

Characteristics of the Kelvin-Helmholtz (KH) instability of the interfaces formed by two semi-infinitely distributed fluids and one interlayer were studied. It was found that the coupling effects between the interfaces should be considered if the interlayer thickness was less than 0.5 times of the disturbation wavelength. And the degenerate modes could be produced in the situation with proper parameters.