Comparative analysis of thermal-screen efficiency behind ring belts of fan-shaped and cylindrical holes in a wide range of blowing angles and injection parameters
E.Yu. Marchukov1, A.V. Starodumov1, A.V. Shchukin2, A.V. Ilinkov2, V.V. Takmovtsev2, I.A. Popov2, A.M. Ermakov2
1Lyulka Experimental Design Bureau ODK-UMPO PJSC, Moscow, Russia
2Tupolev National Research Technical University, Kazan, Russia
Keywords: physical experiment, film cooling, thermal screen efficiency, entrance region, main mixing zone, ring of holes, cylindrical and fan-shaped holes, injection parameter, blowing angle
Abstract
Film cooling efficiency averaged over the length of a one-row ring of holes for the case of a flat surface with air blowing through fan-shaped holes was estimated experimentally and normalized by the respective efficiency for cylindrical holes in a wide range of injection parameters m (from 0.25 to 5.5) and blowing angles a (from 30° to 75°). Ranges of regime and geometric parameters of film cooling systems in which fan-shaped holes provide a higher cooling efficiency in comparison with cylindrical holes have been identified. With the case of α = 30° taken as an example, we show that very high injection parameters ( m = 4.5¸5.5) in the entrance region of the mixing zone ( x / d < 10) make the relative efficiency decrease from 1.7 to 1.05 with the increase of x / d . Simultaneously, the relative efficiency increases from 1.05 to 1.6 in the main mixing zone ( x / d > 10). Fan-shaped holes provide a higher film cooling efficiency at optimal and high values of m and α = 45° (under all other conditions being identical) in comparison with cylindrical holes both in the entrance region and in the main mixing zone. At α = 75°, the efficiency is higher than throughout the whole examined range of injection parameters and throughout the whole examined range of the normalized distance from the location of the injection place. The relative efficiency decreases from 4 to 1.5 in streamwise direction in the entrance region of the mixing zone ( x/d < 5), and it ranges between 1.5 and 2.5 in the main mixing zone ( x/d > 5) at all values of injection parameter considered in the paper.
|
