Extensive experimental investigation of the heat transfer characteristics of jet impingement on a variable-curvature concave surface in a wing leading edge was conducted for aircraft anti-icing applications. The experiments were carried out over a wide range of parameters: the jet Reynolds number, Re_j, from 51,021 to 85,340, the relative tube-to-surface distance, H/d, from 1.736 to 19.76, and the circumferential angle of jet holes on the piccolo tube, h, from _60_ to 60_. In addition, jet impingements with single one, two and three rows of aligned jet holes were all investigated. Experimental results revealed the effects of various parameters on the performance and characteristics of jet impingement heat transfer in the specific structure adopted here, and our insufficient understanding on the corresponding physical mechanism was presented. It was found that the jet impingement heat transfer performance was enhanced with the increase of jet Reynolds number. For single one row of jet holes, an optimal H/d of 4.5 was determined under Re_j = 51,021 and d = 2 mm, for which the jet impingement achieved the best heat transfer performance. For two and three rows of aligned jet holes, the Nux curves in the chordwise direction exhibited much different shapes due to different intensity of the interference between adjacent air jets. This work contributes to a better understanding of the jet impingement heat transfer on a concave surface in a wing leading edge, which can lead to optimal design of the aircraft anti-icing system.

Conclusions:

Extensive experimental study of the jet impingement heat transfer on a variable-curvature concave surface in a wing leading edge for aircraft wing anti-icing applications is presented. The influence of a variety of parameters that include the jet Reynolds number (Re_j), relative tube-to-surface distance (H/d), jet impingement angle (h) and the number of rows of aligned jet holes on the jet impingement heat transfer performance and characteristics were investigated, and some important conclusions can be summarized as follows:

(1) The jet Reynolds number (Re_j) has significant effect on the jet impingement heat transfer on the whole impinging surface including both the stagnation zone and the wall jet zone, and the larger the jet Reynolds number, the higher the heat transfer performance.

(2) For two rows of aligned jet holes, two peaks exist in the Nux curve in the chordwise direction due to the weak interference between each other, and the peak position does not change with the variation of jet Reynolds number; while for three rows of aligned jet holes, only one peak exists in the Nux curve in the chordwise direction due to strong interference between adjacent air jets.

(3) For single one row of jet holes, with the increase of the relative tube-to-surface distance, the jet impingement heat transfer performance firstly increases, then decreases, and there exists an optimal value to achieve the best jet impingement heat transfer performance. For the experimental conditions in this work, the optimal value of H/d was determined as 4.5 under Re_j = 51021 and d = 2 mm.

(4) Decreasing curvature radius and increasing jet impingement angle can both enhance jet impingement heat transfer performance at the stagnation point. At the same time, for oblique jet, the jet impingement heat transfer performance on the uphill side of the impinging surface is much better than that on the downhill side due to the flow confinement effect.

The results have been published on INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER  Volume: 90  Pages: 92-101

Photo of the experimental system