PIVによる90°曲がり管下流の円管内乱流計測(解析・予測・制御流体計測・実験法(2),一般講演)

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We measured three-components velocity distribution in cross sections of fully developed turbulent pipe flow behind a bend by means of stereo PIV. Reynolds number 1.8x10^4 and 1.2x10^5, and ratio of inner diameter d of the pipe and radius of the centerline of the bend was 1.3. Fluctuating velocity fields was analyzed by using proper orthogonal decomposition (POD). While symmetrical counter-rotating vortices was evident in a mean velocity field in cross sections of pipe behind bend, single vortex was dominated in a velocity field reconstructed by most energetic eigenfunction mode-0. The eigenfunction with the second largest eigenvalue, mode-1, exhibited a structure such as counter-rotating vortex pair. Power spectrum of the POD coefficient of mode-1 shows a dominant peak at St=0.06, which is similar to that of the shedding frequency in the separation region of the bend. Relatively higher value of the power spectrum at the frequency lower than St=0.06 implies the dominance of the mode-1 structure on the very low frequency oscillation of the flow field.
2009-09-02