Measurement of Spanwise Distribution of Turbulent Structures

On the organized motion of a turbulent plane jet

“…It should be noted that, while spectra of velocity fluctuations measured a t one point in space may fail to detect quasiperiodicity of the flow, two-point statistics, such as the coherence Coh,, between Fourier components of u obtained at two different locations in space, could be a more effective detector. I n this context, Keffer (1979) noted that, in the turbulent wake of a heated cylinder, the temperature spectrum at x/d = 40 (d is the cylinder diameter) did not exhibit a peak a t the vortex-shedding frequency, but the coherence between temperature fluctuations measured a t x/d = 6 and x/d = 40 did exhibit a significant peak a t the Strouhal frequency. Krothapalli et al (1981) presented autocorrelations and spectra of u on the centreline of a plane jet over the range 2…”

“…& Keffer (1979). The apparent conflict between this conclusion and apparent flapping led List (1982) to suggest that the evidence for either flapping or puffing, as against the independent motion of the jet boundaries, is equivocal.…”

On the origin of the organised motion in the turbulent far-wake of a cylinder

“…It is therefore not surprising that the origin of the far-wake motion is relatively closer to the cylinder than is the origin of the far-jet in relation to the jet source. Although more work is required in order to detail the precise relationship between the K~rmfin street and the secondary street [plausible suggestions have been made by Hayakawa and Hussain (1985) and Kiya and Matsumura (1988)], the present evidence suggests that the decay of the Kfirmfin street and the onset of the secondary street are connected.…”

“…The main body of available evidence (for a recent survey, see Antonia et al 1987 b) indicates the presence of three-dimensional large eddies, perhaps in the form of groups of hairpin vortices, that are arranged often (though not always) antisymmetrically about the flow centreline. There has been some speculation concerning the possible connection between the far-field organisation and the nearwake turbulent K~irm/m vortex-street whose topological features have been documented by Cantwell and Coles (1983), Hayakawa and Hussain (1985), Hussain and Hayakawa (1987) and Kiya and Matsumura (1988). Taneda (1959Taneda ( , 1983 suggested that the far-wake motion or secondary vortexstreet which appeared only after the K~rmfin street had decayed was the result of a hydrodynamic instability of the wake profile.…”