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An Experimental Study of Synthetic Jets From Rectangular Orifices

[+] Author Affiliations
Ivana M. Milanovic

University of Hartford, West Hartford, CT

Khairul B. M. Q. Zaman

NASA Glenn Research Center, Cleveland, OH

Paper No. HT-FED2004-56825, pp. 891-901; 11 pages
doi:10.1115/HT-FED2004-56825
From:
  • ASME 2004 Heat Transfer/Fluids Engineering Summer Conference
  • Volume 4
  • Charlotte, North Carolina, USA, July 11–15, 2004
  • Conference Sponsors: Heat Transfer Division and Fluids Engineering Division
  • ISBN: 0-7918-4693-8 | eISBN: 0-7918-3740-8
  • Copyright © 2004 by ASME

abstract

Results of an experimental investigation on isolated synthetic jets in crossflow from rectangular orifices of different aspect ratio and orientation are presented. Three aspect ratios, AR = 4, 8, and 16, with pitch α = 90°, were investigated. Additionally, the AR = 8 case was pitched at 20°. The yaw angle, β, was varied through 0°, 10°, 45° and 90°. All orifices had same exit area and the data were compared with synthetic as well as steady jet from a circular orifice of same area. Hotwire measurements were performed to obtain all three components of mean velocity and turbulent stresses. Data were acquired for momentum-flux ratio up to J = 50. Distributions of time- and phase-averaged data were obtained on the cross sectional plane at x/D = 0.5, 5 and 10, as well as on the axial plane of the symmetry. Qualitative flowfield similarity between synthetic and steady jets is observed. However, high-momentum ‘cap’ above the low-momentum ‘dome’, characteristic of steady jets, does not necessarily appear in the synthetic jet. The position and shape of the high-momentum region depend on the distance from the orifice, pitch, yaw as well as momentum-flux ratio. Consequently, the location of the minimum velocity in the ‘dome’ measured at the plane of symmetry, ymin , is adopted as a reference for penetration estimate and trajectory comparison. For AR = 16, the dome is the largest in area with maximum velocity deficit. However, the penetration is somewhat higher for AR = 4. Increase in yaw reduces the spatial extent of the dome and the penetration height but augments the velocity deficit. At low J the dome is connected to the boundary layer and traces of the cap of high momentum fluid are visible above it. Increase in J lifts the dome and reorganizes the high-momentum fluid around its perimeter, eventually bringing it underneath. Phase-averaged data document dynamic topological changes within the cycle. Phase-averaged streamwise velocity contours on the cross-sectional plane exhibit behavior commensurate with that seen in time-averaged data at various J.

Copyright © 2004 by ASME
Topics: Jets , Orifices

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