Wall visualization of swirling decaying flow using a dot-paint method

Abstract

This paper deals with the visualization of swirling w decaying flow in an annular cell fitted with a tangential inlet. A wall visualization method, the so-called dot-paint method,x allows the determination of the flow direction on both cylinders of the cell. This study showed the complex structure (~e of the flow field just downstream of the inlet, where 0 a recirculation zone exists, the effects of which are more sensitive on the inner cylinder. The flow structure can be q~ considered as three-dimensional in the whole entrance section. The swirl number and the entrance length were estimated v using the measured angle of the streamlines. Experimental correlations of these two parameters, taking into account the Reynolds number and the axial distance from the tangential inlet, are given. List of symbolse= R2--R, Lax Lti Lto Qv r R, R2 Re=2eU,,/v : Sn T u Qv Urn--: (rc(R~--R~) ) thickness of the annular gap (m) entrance length of axial flow on the outer cylinder (m) length of the three-dimensional flow region on the inner cylinder (m) length of the three-dimensional flow region on the outer cylinder (m) volumetric flowrate in the annular cell (m 3 s -I) radial position (m) external radius of the inner cylinder (m) internal radius of the outer cylinder (m) Reynolds number swirl number time average resulting velocity (m s-' ) time average axial velocity component (ms-') average velocity in the annulus (m s-') Correspondence to: P. Legentilhomme : time average tangential velocity component (m s -1) : axial location from the tangential inlet (m) : diameter of the tangential inlet (m) : streak angle with respect to the horizontal (degree) : angle with respect to the tangential inlet axis (degree) : kinematic viscosity of the working liquid (m E s -1)

Lagrangian trajectory model for turbulent swirling flow in an annular cell: comparison with residence time distribution measurements

“…10b: the helicoidal pitch of trajectories increases at some distance from the inlet. These results are concordant with visualization studies using a dot-paint method (Aouabed et al, 1994(Aouabed et al, , 1995. Plane projections of trajectories (Fig.…”

“…This ow, which exhibits three-dimensional motion and increasing turbulence intensities as compared to that obtained in purely axial ow, is an e cient means of enhancing heat or mass transfer phenomena (Legentilhomme & Legrand, 1990, 1991Legentilhomme, Aouabed, & Legrand, 1993). Swirl motion is created at the inlet of the device and then decays freely along the ow path, displaying very disturbed and complex ow behavior (Aouabed, Legentilhomme, Nouar, & Legrand, 1994;Aouabed, Legentilhomme, & Legrand, 1995;Legrand, Aouabed, Legentilhomme, Lef ebvre, & Huet, 1997). However, numerical simulation of this ow is di cult to achieve.…”

Numerical and experimental study of an axially induced swirling pipe flow

“…Indeed, it is well-known that swirling motion induces a very disturbed flow field which is not constant in direction due to the set-up of large eddies (Aouabed et al, 1994(Aouabed et al, , 1995de Parias Neto et al, 1998). Thus, hot wire measurements are difficult to obtain and ambiguous.…”

Swirling flow implementation in a photobioreactor for batch and continuous cultures of porphyridium cruentum

“…Figure 2 provides further indications about light chamber design and the adaptive inlet configuration. The geometrical characteristics of intermediary disks are a critical point in hydrodynamic optimization with swirling flows, as shown by Aouabed et al (1995), who used a dot-paint visualization method with tangential inlets. According to Legentilhomme and Legrand (1991), who studied various configurations of tangential inlets of circular type, swirling decaying motion can be classified in terms of inlet diameter, $ e , and annular gap width, e: (i) pure swirling flow is achieved if $ e = e, (ii) convergent swirling flow if $ e e; and (iii) divergent swirling flow if $ e < e. Mass flow conservation increases velocity in the inlet for smaller inlet diameters, resulting in more intensive swirl motion in annular space.…”