The Coefficient of Discharge of 30° Inclined Film Cooling Holes With Rounded Entries or Exits

Abstract

The coefficients of discharge of 30° inclined holes having a length to diameter ratio of 6, and rounded entries or exits have been measured for a range of crossflow conditions. The rounding radius varied from 0 to 1 hole diameters, and the crossflow Mach numbers from 0 to 0.5. Rounding the hole inlet was found to be beneficial, with increases of up to 15% being obtained at high coolant (inlet) side crossflow Mach numbers. Rounding the exit produced no significant benefit. The crossflow effects have been correlated using inlet and outlet additive loss coefficients. These reflect the changes in pressure drop across the hole necessary to maintain the hole mass flow rate when crossflows are applied. The correlated data have been incorporated in a computer program which gives good predictions of discharge coefficient in the presence of either a coolant crossflow or a mainstream crossflow or both.

Engine Representative Discharge Coefficients Measured in an Annular Nozzle Guide Vane Cascade

“…It is well known that, for sharp edged holes, losses within the hole are dominated by inlet separation for small lid ratios, but that frictional losses increase steadily with increasing lid ratio (Andrews and Mkpadi, 1983). The values without crossflow closely agree with those predicted by Lichtarowicz et al (1965), who concluded that for lid ratios in the range 2-10, the Cd for choked flow would be given by :…”

“…that commonly highlighted in the literature), in that the discharge coefficient with crossfiow is lower than the non-crossflow case for all pressure ratios. The data shows good agreement with an extrapolated version of sharp-edged hole data given by Hay et al (1994a;Ild = 6.0,9 = 30°, a In contrast, the data presented in Figure 8 (Row 3; lid = 7.5, e = 28 0 and a = 7°) illustrates the case where, at the same pressure ratio, the with-crossflow data is initially lower than the noncrossflow data, but becomes higher than the non-crossflow case as the pressure ratio increases, and then tends to the same value at the critical pressure ratio (PR = 1.89), where the flow chokes. This is termed the 'crossover' phenomenon by the authors.…”

“…The second method involves modifying a basic hole Cd for the effects of geometric variations and the presence of crossflows. This technique has been found to accurately model individual effects -as demonstrated by Lichtarowicz et al (1965), Rogers and Hersh (1975), Tillman and len (1984), Tay Chu et al (1985), Hay et al (1987), McGreehan and Schotsch (1988) and Hay et al (1994a) although it is, not surprisingly, less successful under more complex conditions. The final method is by directly measuring the Cd of a hole having the correct geometry under the design flow conditions.…”

Discharge Coefficient Measurements for Flow Through Compound-Angle Conical Holes with Cross-Flow

“…They concluded that inlet radiusing and chamfering increases the discharge coefficient substantially. Hay et al (1994) measured 146 M. E. TASLIM AND S. UGARTE the discharge coefficients for 30 • inclined cylindrical holes with rounded inlet and exit and a range of cross-flows on both sides of the holes. A major conclusion of this study was that while inlet radiusing was beneficial, rounding of the exit did not produce any significant benefit.…”

Discharge Coefficient Measurements for Flow Through Compound‐Angle Conical Holes with Cross‐Flow

“…They concluded that inlet radiusing and chamfering increases the discharge coefficient substantially. Hay et al (1994) measured 146 M. E. TASLIM AND S. UGARTE the discharge coefficients for 30…”