Experimental Study of the Flow and Thermal Development of a Row of Cooling Jets Impinging on a Rotating Concave Surface

Abstract

The paper reports an experimental study of impingement cooling in a rotating passage of semi-cylindrical cross-section. Cooling fluid is injected from a row of five jet holes along the centerline of the flat surface of the passage and strikes the concave surface. The cooling passage rotates orthogonally about an axis parallel to that of the jets. Tests have been carried out, using water, both within the passage and as the jet fluid, at a fixed Reynolds number of 15,000, for clockwise and anti-clockwise rotation. Local Nusselt number measurements, using the liquid-crystal technique, show that under stationary conditions a high Nusselt number region develops around each impingement point, with secondary peaks half-way between impingement points. Rotation reduces heat transfer, leads to the disappearance of all secondary peaks and also, surprisingly, of some of the primary peaks. Flow visualization tests suggest that these changes in thermal behavior are caused because rotation increase the spreading rate of the jets. LDA and PIV measurements are also presented. They show that under stationary conditions the five jets exhibit a similar behavior, with their cores remaining intact up to the point of impingement at the top dead center. The LDA and PIV studies help explain the rather surprising thermal behavior under rotating conditions.

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“…Evidently, the central jet (Jet 3) has virtually disappeared at Ro ¼ 20.18 despite it being as strong as the others in stationary conditions. Analogous results are found for Jet 4 in clockwise rotation [33].…”

“…Moreover, the jet principally affected differs depending upon the sense of rotation: for clockwise rotation it is the central jet that is 'extinguished', while for anti-clockwise rotation, the jet next to the top is obliterated. Flow visualization and laser-Doppler velocimetry (Iacovides et al [33]) confirmed the more rapid spread of the jets and the consequent loss of these jets' identity. This is clearly brought out in Fig.…”

“…The central column in Fig. 4, from the PhD thesis of Kounadis [32] (see also Iacovides et al [33], shows the Nusselt number under non-rotating conditions, with the imprint of the five jets clearly visible. There is reasonable uniformity across the jets with the variation in peak heat-transfer coefficient varying by ,+5 per cent.…”

“…It is noted that there is also a faint peak in heat transfer mid-way between the jets associated with the collision of the radially outward flows of the adjacent Fig. 3 Test section of experimental model used in the impingement cooling study of Iacovides et al [33] jets following impact. When the assembly is rotating there is a slight general diminution in Nusselt number, much as Mattern and Hennecke had found, and a re-orientation of the major/minor axes of the (roughly) elliptic Nu contours from vertical -horizontal under stationary conditions to (in compass terminology) NE -SW for anti-clockwise rotation and NW -SE for clockwise rotation.…”

Effect of Rotation on Heat Transfer and Flow Field Inside Leading Edge Cooling Passage Using Impinging Jets

“…Iacovides et al [11] researched the impinging jet under the rotation condition with Ro = 0.18. They reported that all secondary peaks and some of the primary peaks in array jets disappear due to strong rotation effect.…”