Double wall cooling of an effusion plate with cross flow and impingement jet combination internal cooling: Comparisons of main flow contraction ratio effects

Abstract

The present study considers comparisons of hot-side effusion plate results for a mainstream flow passage with CR = 1 and for a mainstream flow passage with CR = 4. The coolant supply arrangement for both CR contraction ratio values includes simultaneous use of cross flow and an impingement jet array. For the effusion cooled/hot surface, presented are spatially-resolved distributions of surface adiabatic film cooling effectiveness, and surface heat transfer coefficients (measured using infrared thermography). These results are given for main flow Reynolds numbers Re_ms of 89,900 to 95,800. For this main flow Reynolds number range, four different combination values of crossflow Reynolds number and impingement Reynolds number are tested for each CR value, which are associated with four different values of initial blowing ratio BR. With this arrangement, crossflow Reynolds number is varied, as impingement jet Reynolds number is approximately constant. The resulting variations of surface adiabatic film cooling effectiveness and surface heat transfer coefficients are due to three competing phenomena, whose relative influences change with x/d_e location. These include increased turbulent mixing and transport result from effusion coolant jets, decreased magnitudes of local blowing ratio with streamwise location, and significant streamwise acceleration, which induces local boundary layer re-laminarization. When the CR = 4 arrangement is employed, these phenomena result in dramatic decreases of local and line-averaged heat transfer coefficients, and local and line-averaged adiabatic film effectiveness magnitudes, with streamwise development, for x/d_e > 60. Resulting values are then significantly lower than when CR = 1, provided comparisons are made at a particular streamwise location for each value of initial blowing ratio BR.

Introduction

A number of studies of cooling and thermal protection technologies, as applied to combustor liner components, have been conducted in recent years. Recent surveys of related investigations are described by Rogers et al. [1], Schulz [2], and Krewinkel [3]. Investigative approaches of effusion and film cooling performance [4], [5], [6], [7], [8], [9], [10], [11], [12], [13], [14], [15], [16], [17] include experimental [4], [5], [6], [7], [8], [9], [10], [11], [12], [13], numerical [14], and combined experimental and numerical [15], [16], [17]. Of these different investigations, only two address the influences of main flow streamwise pressure gradient [4,11]. In all cases, either surface distributions of film effectiveness values [4,5,[7], [8], [9], [10], [11], [12], [13], [14], [15], [16], [17]], or surface distributions of heat transfer coefficients [6] are provided. To supply the effusion or film coolant, some form of plenum configuration is employed [4,5,[7], [8], [9], [10], [11],14,15], or a cross flow arrangement is utilized [6,12,13,16,17]. Some investigations use normal, round hole configurations [[4], [5], [6],8,10,16], whereas inclined, compound angle, and shaped arrangements are employed in other studies [7,9,[11], [12], [13], [14], [15],17]. Hole array configurations include a single row of holes [4,[11], [12], [13]], multi-hole, full-coverage film cooling [[4], [5], [6],16,17], and effusion cooling [3,5,7–-11,14,16].

Other recent investigations supply coolant to the effusion holes using impingement jets [18], [19], [20], [21], [22], [23], [24], [25], [26], [27], [28], [29]. Most of these studies utilize normal-oriented holes with an effusion hole angle of 90° [18], [19], [20], [21], [22], [23], [24], [25], [26], [27], [28]. Relatively thin, effusion plates [[18], [19], [20], [21],[26], [27], [28]] are often used. However, effusion plate thickness is 2.0 effusion hole diameters within the investigation of Cho and Rhee [22]. Within each of these investigations, data are provided either only for the external, effusion cooled surface [18,29], or only the internal, impingement cooled surface [19,[22], [23], [24],27].

Of the studies which present numerically predicted results, LES [14,15] and RANS [[16], [17], [18], [19], [20], [21],26,27] approaches are employed. Experimental approaches include infrared thermography [[4], [5], [6], [7], [8],10,12,13], schlieren flow visualization [5], pressure sensitive paint [9,15], stereoscopic particle image velocimetry [11], liquid crystal thermography [16], temperature measurements using thermocouples [[18], [19], [20], [21],26,27], mass transfer measurements using naphthalene sublimation [22], [23], [24], and temperature sensitive paint [25].

The present study considers comparisons of hot-side effusion plate results for a mainstream flow passage with a contraction ratio CR of 1 and for a mainstream flow passage with a contraction ratio CR of 4. With the CR = 4 configuration, a substantial streamwise favorable pressure gradient is produced, which is characterized using the acceleration parameter K = (ν/V_ms²)(dV_ms/dx). The CR = 4 contraction ratio is employed because the resulting pressure gradient matches the gradient within a combustion liner application environment. The coolant supply arrangement for both CR values includes simultaneous use of cross flow and an impingement jet array. For the effusion cooled/hot surface, presented are spatially-resolved distributions of surface adiabatic film cooling effectiveness, and surface heat transfer coefficients (measured using infrared thermography). These results are given for main flow Reynolds numbers Re_ms of 89,900 to 95,800. For this main flow Reynolds number range, four different combination values of crossflow Reynolds number and impingement Reynolds number are tested for each CR value, which are associated with four different values of initial blowing ratio BR. With this arrangement, crossflow Reynolds number is varied, as impingement jet Reynolds number is approximately constant. As such, the present investigation is different from the past investigations mentioned because: (i) the effects of mainstream pressure gradient are considered for an effusion cooling arrangement with angled cooling holes, (ii) coolant is supplied to the effusion holes using a cross flow channel in combination with impingement jet array cooling, and (iii) experimental conditions, configurations, and data are different from all previous investigations. Examples of item (iii) include use of an effusion hole angle of 25°, and use of an effusion plate and an impingement plate both with a thickness of 3.0 effusion hole diameters.