Abstract: Linear stability theory is used to study a double fluid model for a liquid jet surrounded by a coaxial gas steam.Under the different pressure gradients for liquid and gas flow,the variation of the velocity profile in the model and the thickness of the shear layer were investigated.The effects of such variation on the interfacial stability were discussed with the application of Chebyshev spectral collocation method.

Key words: free jet, velocity profile, Chebyshev collocation method, interfacial stability