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An Experimental Study Synthetic Jets from Rectangular OrificesResults 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 a = 90deg., were investigated, Additionally, the AR = 8 case was pitched at 20 deg.. The yaw angle, , was varied through 0 deg., 10 deg., 45 deg. and 90 deg.. 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, y(submin), 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.
Document ID
20040112051
Acquisition Source
Glenn Research Center
Document Type
Preprint (Draft being sent to journal)
Authors
Milanovic, Ivana M. (Hartford Univ. CT, United States)
Zaman, Khairul B. M. Q. (NASA Glenn Research Center Cleveland, OH, United States)
Date Acquired
September 7, 2013
Publication Date
January 1, 2004
Subject Category
Aerodynamics
Report/Patent Number
HT-FED2004-56825
Meeting Information
Meeting: 2004 ASME Heat Transfer/Fluids Engineering Conference
Location: Charlotte, NC
Country: United States
Start Date: July 11, 2004
End Date: July 15, 2004
Sponsors: American Society of Mechanical Engineers
Funding Number(s)
OTHER: 22-781-30-47
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.

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