The linearized incompressible Navier-Stokes equations in cylindrical coordinates are solved rnby a Chebyshev spectral collocation method, in order to study the temporal instabilities of viscous rnswirling jets near a nozzle exit. To investigate the roles of centrifugal instability on the linear growth rnrate of the flows, the azimuthal velocity of the basic flow is either centrifugally stable or unstable. Rernsults show that the swirl enhances the maximum linear growth rates of disturbances under certain parnrameters, and that the increases of the growth rates for the centrifugally unstable velocity profile are rnmore evident. For the centrifugally stable one, swirl slighfly decreases the growth rate of the axisymrnmetric mode, and obviously increases the growth rates of negative helical modes. For a fixed swirl ratio rnq, there exists a critical wave number ncr ＜ 0, the growth rate will increase with azimuthal wave numrnber decreasing when n ＞ ncr and decrease when n ＜ ncr. For a fixed negative azimuthal wave number,rnthere also exists a critical qcr, the growth rate will increase with azimuthal wave number when q ＜ qcr rnand vice versa. For the centrifugally unstable one, two peaks are found in the dispersion relation rncurve, which implies that the dominant mode switches from the Kelvin-Helmholtz unstable wave at low rnaxial wave numbers to the centrifugally unstable one at high axial wave numbers. The influences of rnsome parameters, such as momentum thickness of shear layer, size of vortex core, and Reynolds numrnbers are also outlined in the present study. The obtained results suggest that centrifugal instability does rnplay an active role in the enhancement of mixing in swirling flows.%用Chebyshev谱配置法求解柱坐标下线化不可压缩Navier-Stokes方程，分析喷管rn出口附近粘性旋拧射流的线性稳定性.为了研究离心不稳定对线性增长率的影响，本rn研究中基本流的周向速度可以是离心稳定的，也可以是离心不稳定的.结果表明在一rn定参数下旋拧能增强扰动的线性增长率，且对于离心不稳定的剖面增长率升高更大.rn对于离心稳定的速度型，有旋拧时轴对称模态的增长率轻微下降，而负周向波数扰动rn的增长率明显上升；对于离心不稳定的速度型，可以观察到优势模态由低波数时的rnKelvin-Helmholtz(K-H)不稳定波转换到高波数时的离心不稳定波.
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