Planar jets belong to the most researched flows. Many aspects of their instability have been wellknown for a long while. One of them is the observation that the jet is more sensitive to disturbances near the orifice exit than elsewhere. Linear stability investigations on various velocity profiles were carried out using the Orr-Sommerfeld (OS) equation to find an explanation. The velocity profiles were provided by analytical approximations and numerical computational fluid dynamics (CFD) simulations. A special method, the so-called compound matrix method (CMM) was used to solve the OS equation to provide sufficiently accurate results. The adaptation of the method for symmetric jets is derived briefly in this paper. The stability of different velocity profiles was compared based on the local spatial growth rate. The results of the comparison clearly show that velocity profiles near the orifice are more unstable than downstream ones. The local spatial growth rate of disturbance waves was higher close to the orifice. The reason for that was twofold, and these are explained in the paper.

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