Characteristics of Cooling of the Leading Edge With a Row of Dual Impinging Jets

Abstract

The leading edge of turbine blades is one of the critical areas that need to be cooled effectively because of the high local heat transfer rate of the main flow. Film cooling with different shaped holes as well as internal cooling by impinging jets has successfully been applied in modern gas turbine applications. This paper numerically studies the cooling of the leading edge with a row of dual impinging jets — two jets close to each other. Heat transfer of the dual jets is compared to that of a single jet (in a row) based on the same flow rate or jet velocity. The effect of the distance between the dual jets and the jet inclination angle is examined to seek the best geometric parameters. In addition, the curvature of the leading edge surface is considered to examine the heat transfer difference between curved and flat walls. Various jet-to-target spacing and Reynolds numbers are also studied. Results show that the dual impinging jets generally produce two high heat transfer regions in the stagnation point, and the peak value is slightly higher than the single row of jets with the same Reynolds number. When the distance between two jets is 3d, the jet flow after bouncing back from the symmetry line affects the heat transfer as a crossflow. The target surface curvature has little effect on the overall heat transfer, but the peak heat transfer coefficient is lower on the curved surface than that on the flat surface. The dual impinging jets present a higher average heat transfer around the stagnation region.

Correlation Development for Jet Impingement Heat Transfer and Force on a Moving Curved Surface

“…Ito et al (2007) observed that the Nusselt number for both flat and concave surfaces increased as the Re number increased. Li and Corder (2008) found that the secondary peak on the curved surface is seen for the small jet to plate distance (H/d), and the case with a small distance shows a higher heat transfer rate downstream. Ashok Kumar et al (2009) observed that the average heat transfer coefficient on the curved surface reduces as H/d increases beyond unity.…”

Numerical Simulation of Large Arrays of Impinging Jets on a Flat Surface

“…Kumar and Prasad (2008) found experimentally that five jet rows have the best performance compared to the single jet row and the single jet on a concave surface. Li and Corder (2008) showed that the peak value of local heat transfer for dual impinging jets is higher than a single jet. The dual impinging jets provide a higher average heat transfer around the stagnation region.…”

Combined film and impingement cooling of flat plate with reverse cooling hole

“…This effect is more significant when the material is of high thermal conductivity [4] and in case of lower jet-to-plate spacing [7]. Large number of experimental and numerical studies have been done on combined film-impingement cooling of turbine blades [6,[9][10][11], curved surfaces [12][13][14][15][16][17] and flat plates [4,5,7,8,[18][19][20][21][22].…”

“…Curvature of the plate surface can affect local flow field and cooling performance significantly. Li and Corder [12] analysed effect of plate surface curvature and its effect was found to be significant on local Nusselt number in case of dual-jet in a row as compared to single-jet in a row case although no significant effect of curvature was noticed in overall heat transfer. As far as curved surfaces are concerned, studies have found only slight increment in the overall effectiveness by the addition of impingement cooling in the combined film-impingement cooling [13].…”