Research Papers: Fundamental Issues and Canonical Flows

Circulation Generation and Vortex Ring Formation by Conic Nozzles

[+] Author and Article Information
Moshe Rosenfeld

School of Mechanical Engineering, Tel Aviv University, Tel Aviv 69978, Israel

Kakani Katija, John O. Dabiri

Graduate Aeronautical Laboratories and Bioengineering, California Institute of Technology, Pasadena, CA 91125

J. Fluids Eng 131(9), 091204 (Aug 18, 2009) (8 pages) doi:10.1115/1.3203207 History: Received April 14, 2009; Revised July 08, 2009; Published August 18, 2009

Vortex rings are one of the fundamental flow structures in nature. In this paper, the generation of circulation and vortex rings by a vortex generator with a static converging conic nozzle exit is studied numerically. Conic nozzles can manipulate circulation and other flow invariants by accelerating the flow, increasing the Reynolds number, and by establishing a two-dimensional flow at the exit. The increase in the circulation efflux is accompanied by an increase in the vortex circulation. A novel normalization method is suggested to differentiate between two contributions to the circulation generation: a one-dimensional slug-type flow contribution and an inherently two-dimensional flow contribution. The one-dimensional contribution to the circulation increases with the square of the centerline exit velocity, while the two-dimensional contribution increases linearly with the decrease in the exit diameter. The two-dimensional flow contribution to the circulation production is not limited to the impulsive initiation of the flow only (as in straight tube vortex generators), but it persists during the entire ejection. The two-dimensional contribution can reach as much as 44% of the total circulation (in the case of an orifice). The present study offers evidences on the importance of the vortex generator geometry, and in particular, the exit configuration on the emerging flow, circulation generation, and vortex ring formation. It is shown that both total and vortex ring circulations can be controlled to some extent by the shape of the exit nozzle.

Copyright © 2009 by American Society of Mechanical Engineers
Your Session has timed out. Please sign back in to continue.



Grahic Jump Location
Figure 1

Sketch of the domain of computation

Grahic Jump Location
Figure 2

Comparison of the circulation evolution of the numerical (solid line) and experimental (symbols) results (De/Dp=0.6)

Grahic Jump Location
Figure 3

The evolution of the axial velocity profile at the nozzle exit (velocity program no. 1)

Grahic Jump Location
Figure 4

The scaled vorticity (contour lines between 0 to 20 with an increment of 1) for velocity program no. 2. The spatial coordinates are scaled by De.

Grahic Jump Location
Figure 5

The evolution of the total circulation, (a) normalization by piston parameters, and (b) normalization by exit parameters

Grahic Jump Location
Figure 6

The evolution of the double-star normalized circulation

Grahic Jump Location
Figure 7

The evolution of (a) the normalized circulation flux versus the formation time t∗∗, and (b) the centerline exit pressure versus te∗

Grahic Jump Location
Figure 8

The asymptotic two-dimensional contribution to the total circulation generation (%)

Grahic Jump Location
Figure 9

The evolutions of the total (lines) and vortex ring (lines with symbols) circulations

Grahic Jump Location
Figure 10

The evolutions of the total (lines) and vortex ring (lines with symbols) normalized energies

Grahic Jump Location
Figure 11

Geometry of the limiting cases (a) orifice and (b) straight tube vortex generators (De=1.5 cm, H=10 cm, Ls=45.1 cm, and L=80 cm)

Grahic Jump Location
Figure 12

The evolution of the exit centerline velocity for the cases with an equal exit diameter (De=1.5 cm)

Grahic Jump Location
Figure 13

Evolution of the (a) circulation and (b) circulation flux for the cases with an equal exit diameter (De=1.5 cm)




Some tools below are only available to our subscribers or users with an online account.

Related Content

Customize your page view by dragging and repositioning the boxes below.

Related Journal Articles
Related eBook Content
Topic Collections

Sorry! You do not have access to this content. For assistance or to subscribe, please contact us:

  • TELEPHONE: 1-800-843-2763 (Toll-free in the USA)
  • EMAIL: asmedigitalcollection@asme.org
Sign In