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The effect of an unsteady stator wake (simulated by wake rods mounted on a spoke-wheel wake generator) on the modeled rotor blade is studied using the pressure sensitive paint (PSP) mass-transfer analogy method. Emphasis of the current study is on the midspan region of the blade. The flow is in the low Mach number (incompressible) regime. The suction (convex) side has simple angled cylindrical film-cooling holes; the pressure (concave) side has compound angled cylindrical film-cooling holes. The blade also has radial shower-head leading edge film-cooling holes. Strouhal numbers studied range from 0 to 0.36; the exit Reynolds number based on the axial chord is 530,000. Blowing ratios range from 0.5 to 2.0 on the suction side and 0.5 to 4.0 on the pressure side. Density ratios studied range from 1.0 to 2.5, to simulate actual engine conditions. The convex suction surface experiences film-cooling jet lift-off at higher blowing ratios, resulting in low effectiveness values. The film coolant is found to reattach downstream on the concave pressure surface, increasing effectiveness at higher blowing ratios. Results show deterioration in film-cooling effectiveness due to increased local turbulence caused by the unsteady wake, especially on the suction side. Results also show a monotonic increase in film-cooling effectiveness on increasing the coolant to mainstream density ratio.

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This paper presents the swirl purge flow on a platform and a modeled land-based turbine rotor blade suction surface. Pressure-sensitive paint (PSP) mass transfer technique provides detailed film-cooling effectiveness distribution on the platform and phantom cooling effectiveness on the blade suction surface. Experiments were conducted in a low-speed wind tunnel facility with a five-blade linear cascade. The inlet Reynolds number based on the chord length is 250,000. Swirl purge flow is simulated by coolant injection through 50 inclined cylindrical holes ahead of the blade leading edge row. Coolant injections from cylindrical holes pass through nozzle endwall and a dolphin nose axisymmetric contour before reaching the platform and blade suction surface. Different “coolant injection angles” and “coolant injection velocity to cascade inlet velocity” result in various swirl ratios to simulate real engine conditions. Simulated swirl purge flow uses coolant injection angles of 30 deg, 45 deg, and 60 deg to produce swirl ratios of 0.4, 0.6, and 0.8, respectively. Traditional purge flow has a coolant injection angle of 90 deg to generate swirl ratio of 1. Coolant to mainstream mass flow rate (MFR) ratio is 0.5%, 1.0%, and 1.5% for all the swirl ratios. Coolant to mainstream density ratio maintains at 1.5 to match engine conditions. Most of the swirl purge and purge coolant approach the platform; however, a small amount of the coolant migrates to the blade suction surface. Swirl ratio of 0.4 has the highest relative motion between rotor and coolant and severely decreases film cooling and phantom cooling effectiveness. Higher MFR of 1% and 1.5% cases suffers from apparent decrement of the effectiveness while increasing relative motion.

A systematic study was performed to investigate the combined effects of film-hole geometry, blowing ratio, density ratio, and freestream turbulence intensity on a flat-plate film cooling. Detailed film-cooling effectiveness was obtained using a pressure-sensitive-paint technique. Four common geometries were used in this study: simple-angled cylindrical and fan-shaped holes, and compound-angled (β 45 deg) cylindrical and fan-shaped holes. Each plate contained one row with seven holes, and the hole diameter D and hole-length-to-diameter ratio (L∕D) are 4 mm and 7.5, respectively. The effects of the blowing ratio M, coolant-to-mainstream-density ratio DR, and freestream turbulence intensity Tu were tested within the ranges of 0.3 ∼ 2.0, 1.0 ∼ 2.0, and 0.5 ∼ 6%, correspondingly. Detailed variations of the laterally averaged effectiveness from low to high blowing ratios were obtained for three density ratios. The results indicated that effectiveness increased as increasing density ratio in general for all geometries. Fanshaped holes outweighed cylindrical ones in effectiveness at higher blowing ratios. An additional compound-angle enhanced effectiveness for cylindrical holes. For increasing turbulence intensity, effectiveness decreased for shaped holes but slightly increased for cylindrical ones. The experimental data of simple-angled fan-shaped holes were validated with empirical correlation limited to DR 1.7 ∼ 2.0, and an improved correlation was proposed to predict effectiveness at DR 1.0 ∼ 2.0. NomenclatureAR = area ratio of hole exit and inlet D = diameter of film-cooling hole, mm DR = coolant to mainstream density ratio; ρ c ∕ρ m M = blowing ratio; ρ c v c ∕ρ m v m P = pitch between adjacent holes, mm t = width of hole at trailing edge of hole breakout x = distance from trailing edge of holes, mm α = axial angle to the mainstream, deg β = compound angle to the mainstream, deg η = film-cooling effectiveness η ave = laterally averaged film-cooling effectiveness v = velocity, m∕s ξ = distance scaling parameter used in correlation ρ = density, kg∕m 3 Subscripts air = property with air injection blk = black condition c = coolant f = film fg = property with foreign gas injection m = mainstream ref = reference condition w = wall ∞ = mainstream property