| Summary: | 碩士 === 國立臺灣大學 === 機械工程學研究所 === 88 === The phenomenon of mixed convection flow with periodic oscillation in the vertical channel is numerically investigated in the present study. It is assumed that both velocity and temperature fields are fully developed .In the stability analysis ,the infinitesimal disturbances are imposed on the fully developed laminar base flow ,and then the growth rate of the disturbances is calculated after one period of oscillation . If the growth rate decays (σ < 0),the flow is stable and keeps laminar ; if the growth rate grows up (σ > 0),the flow is unstable and may become transient to turbulent.
The results compared with those of Chen and Chung about non-oscillatory mixed convection channel flow in 1998 show that the flow studied is generally stabler. The flow is slightly more unstable only with low oscillation frequency . In other words, the imposed oscillation stabilizes the flow . The results also indicate that the least stable mode of the disturbances is two-dimensional for low flow oscillation frequency and three-dimensional for higher flow oscillation frequency . Those results are in contrast with the current knowledge on the plane channel flow where the instability was found to start with two-dimensional disturbance in the consecutive transition stages to turbulence .
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