Flow Characteristics and Structures of Inclined Jets in a Cross-stream over a Concave Wall
Date Issued
2007
Date
2007
Author(s)
Lee, I-Chien
Abstract
This study investigates two flow fields injected into a cross-stream over a concave surface: 1) an inclined jet ejected from a forward expanded hole, and 2) five inclined jets ejected from a row of forward expanded holes. The complex flow fields between the jets and the cross-stream were measured using both digital particle image velocimetry and a flow visualization technique. This study contributes to measurements of the 3D time-averaged velocity field and to classify which flow is dominant. In a viewpoint of film cooling, the domination of jet flow or cross-stream in the flowfield will affect the cooling efficiency.or a jet ejected in a cross-stream, this study presents the flow visualization and seeded particle time-averaged concentration at four different jet-to-cross-stream velocity ratios (M) of 0.5, 1.0, 1.5, and 2.0. Measured results show that the blowing ratio has a strong effect on the flow field of a single jet flow into a cross-stream. Results from the 2D velocity measurement on the central plane of the injection hole at M =1.0 show that a strong interaction occurs between the ejected jet flow and the cross-stream at the leeward side of the ejected jet. In this region, the cross-stream is entrained into the center plane, producing an outward radial velocity to lift the ejected jet flow away from the concave wall. The lift-off velocity decay from the cross-stream along the streamwise direction causes the jet flow to reattach to the concave surface.or the five jets ejected into a cross-stream, this study presents the flow visualization, detailed time-averaged velocity fields, velocity fluctuations, and flow patterns of both the jet flow and the cross-stream at a blowing ratio of 1.0. At the center plane of the injection hole, a strong positive vertical time-averaged velocity located on the downstream provides evidence for jet flow lift-off. A counter-rotating secondary-flow vortex pair immediately forms in the jet directly above the injection hole downstream. Depending on flow characteristics, the ejected jet flow at transverse locations can be categorized into three flow zones, namely, a straight flow zone, a swirling flow zone, and a touch-down flow zone. In addition, the jet flow greatly influences the cross-stream when it passes through a row of inclined jets over a concave surface. The brief trait of the cross-stream shows that the jet flow accelerates the cross-stream at the near wall region of Z/D=0.13 in the streamwise direction when the cross-stream passes through the region between adjacent jets. The jet flow at the near wall region of Z/D=0.13 induces the cross-stream to move towards the centerline of the injection hole. Above an elevation of Z/D=0.88, the cross-stream has enough streamwise momentum flux to pass through the main jet. For a cross-stream passed through a row of inclined jets with a forward expanded hole, the streamwise velocity increased by the jet flow and the close-to-wall jet will inhibit the horseshoe vortex. Streamwise jet flow vortices induce a cross-stream occurring behind the injection hole close to the wall surface.
Subjects
Jets in a cross-stream
PIV
Flow visualization
CVP
Lift-off
3D streamline
Type
thesis
File(s)![Thumbnail Image]()
Loading...
Name
ntu-96-D89522003-1.pdf
Size
23.53 KB
Format
Adobe PDF
Checksum
(MD5):05fa62e4ecaeee3d990f6c28b23b37c7