Film cooling characteristics of rows of round holes at various streamwise angles in a crossflow: Part I. Effectiveness

Abstract

Film cooling effectiveness were studied experimentally on rows of cylindrical holes with streamwise angles of 30°, 60°a nd 90°, in a flat plate test facility with a zero pressure gradient. Detailed effectiveness and heat transfer results for a single cylindrical hole at the same inclinations have been presented in Yuen and Martinez-Botas [C.H.N. Yuen, R.F. Martinez-Botas, Film cooling characteristics of a single hole at various streamwise angles: Part I. Effectiveness, Int. J. Heat Mass Transfer 46 (2003) 221-235; C.H.N. Yuen, R.F. Martinez-Botas, Film cooling characteristics of a single hole at various streamwise angles: Part II. Heat transfer coefficient, Int. J. Heat Mass Transfer 46 (2003) 237-249] with the same test facility and measurement technique. This present investigation commenced with a single row of holes with two pitch-to-diameter ratios (p/D) of 3 and 6. It then presents and discusses the effects of introducing inline and staggered rows for each streamwise angle and pitch-to-diameter ratio. The row spacing in the inline and staggered rows is 12.5 diameters in the streamwise direction. The short but engine representative hole length (L/D = 4) is constant for all geometries. The blowing ratio ranges from 0.33 to 2, and the freestream Reynolds number based on the freestream velocity and hole diameter (Re D ) was 8563. Both local values and laterally averaged ones are presented, the latter refers to the averaged value across the central hole. The current results are compared with the experimental results obtained by other researchers, the effects of the additional inline and staggered rows, and of the variations in injection angle, pitch-to-diameter ratio are described.The objectives of the present study are to provide a consistent set of measurements in terms of effectiveness and heat transfer coefficients presented in the companion paper [C.H.N. Yuen, R.F. Martinez-Botas, Film cooling characteristics of rows of round holes at various streamwise angles: Part II. Heat transfer coefficient, Int. J. Heat Mass Transfer, in press], obtained systematically with the same test facility, and to deliver a better understanding of film cooling performance. The present results also serve as a database with 105 test cases, in addition to the 21 cases presented in [C.H.N. Yuen, R.F. Martinez-Botas, Film cooling characteristics of a single hole at various streamwise angles: Part I. Effectiveness, Int. J. Heat Mass Transfer 46 (2003) 221-235], for future numerical modelling.

Film cooling characteristics of rows of round holes at various streamwise angles in a crossflow: Part II. Heat transfer coefficients

“…The effects of the hole length have been studied by Burd and Simon [13,14], Brundage et al [15] and Walters and Leylek [16], and some of the findings have been reported in [1][2][3]17], and are summarised here. In general, short holes are subject to skewed jet velocity profiles with a maximum value greater than that of a turbulent jet for the same mass flow in the downstream half of the hole, with low blowing ratios.…”

“…11 shows the distribution of h/h 0 with two inline rows of 30°holes, a pitch-to-diameter ratio of 3 and a row spacing-to-diameter ratio of 12.5. The large h/h 0 values at a blowing ratio of 2 and x/D greater than 11 may reflect the large increase in effectiveness observed in [3] and relate to jet reattachment. The two inline rows of 30°holes with a pitch-to-diameter ratio of 3 gave smaller h/h 0 values than the corresponding single row in Fig.…”

“…It comprised of a colour JVC CCD camera, two light sources, and a 24-bit frame grabber installed in a computer. The temperature and hue calibration for the liquid crystals, the image capture procedures and the data reduction method used are also the same as those employed in the previous studies [1][2][3].…”

“…in the absence of film cooling 2 coolant or secondary injection aw adiabatic wall w wall Overbar laterally-averaged measurements of temperature such as these reported in this paper benefits from knowledge of local velocities and wall pressures reviewed in Yuen and MartinezBotas [1,3], and will not be repeated here.…”

Experimental study of full coverage film cooling optimization

“…Generally, these studies focused on the effects of geometric factors and aerothermic factors on the performance of film cooling. Geometric factors involve injection angle [5], arrangement of holes (inline or staggered) [6], hole exit shape [2], inter-holes distance and inter-rows distance [7]. Aerothermic factors consist of blowing ratio [8], turbulence level Tu [9], temperature ratio T j /T∞ [8], density ratio ρ j /ρ∞ [10].…”