On a flow in coaxial rotating cylinders with only inner cylinder rotation, a flow transition from wavy vortex flow (WVF mode) to modulated wavy vortex flow (MWV mode) is known. WVF mode is Taylor vortex flow where an azimuthal wave mode appears. That is why the axial velocity component depends on time. MWV mode is modulated WVF mode where any new azimuthal additional wave modes appear. We measured the axial velocity component by ultrasonic Doppler method (UDM), and excitation function of various transition modes such as wavy and modulated wavy mode were obtained by analyzing temporal velocity profile with fast Fourier transfer (FFT). And we found the critical Reynolds number of transition from WVF mode to MWV mode by these excitation functions.
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