Flow measurements behind attached ring-type turbulence promoters

Abstract

The flow field behind attached ring-type turbulence promoters of various sizes in a smooth pipe has been investigated by measuring the mean velocity and turbulence intensity profiles for downstream distances up to 100 promoter heights at a Reynolds number of 20 500 (based on pipe diameter and average velocity). Measurements have been limited to distances downstream of the flow reattachment region. The results indicate that for the smallest tested promoter with nondimensional height h+=12.5, the disturbance introduced does not have much influence in the core region and the flow behind the promoter reorganizes and recovers very quickly (within a streamwise distance equivalent to 20–30 promoter heights). On the other hand, for the largest promoter tested (h+=100), the flow in the core is significantly perturbed and the return of the flow to a self-preserving state has not been achieved, even at a downstream distance of 100 promoter heights. Furthermore,the mean velocity profile in the core region of the pipe with the largest promoter is much more uniform than the corresponding smooth pipe profile, indicating enhanced mixing. The longitudinal turbulence energy spectra in the sublayer, buffer layer, and logarithmic layer suggest that the sublayer structures are maintained and/or enhanced by large wallward motions originated in the core. These results are fairly consistent with the vortex model of Kobashi and Ichijo [Exp. Fluids 4, 49 (1986)].

Aerodynamically Generated Acoustic Resonance in a Pipe With Annular Flow Restrictors

“…It is postulated that signi"cant interaction between the two obstacles can exist only if the #ow reaching the downstream one has not recovered fully its equilibrium condition. For the case of developed turbulent #ow, the typical length of the separated region behind a very thin obstacle is 8}12 times its height h, while recovery may well require an additional length of 10}15h (Bullock et al 1990;Scho"eld & Logan 1990;Liou et al 1990). These lengths can be compared to the experimental bounds obtained for l R /h and l K /h and shown in Table 1.…”