Shaped Film Cooling Holes Research Articles

Adiabatic Effectiveness and Heat Transfer Coefficient of Shaped Film Cooling Holes on a Scaled Guide Vane Pressure Side Model

The demand of improved thermal efficiency and high power output of modern gas turbine engines leads to extremely high turbine inlet temperature and pressure ratios. Sophisticated cooling schemes including film cooling are widely used to protect the vanes and blades of the first stages from failure and to achieve high component lifetimes. In film cooling applications, injection from discrete holes is commonly used to generate a coolant film on the blade′s surface.In the present experimental study, the film cooling performance in terms of the adiabatic film cooling effectiveness and the heat transfer coefficient of two different injection configurations are investigated. Measurements have been made using a single row of fanshaped holes and a double row of cylindrical holes in staggered arrangement. A scaled test model was designed in order to simulate a realistic distribution of Reynolds number and acceleration parameter along the pressure side surface of an actual turbine guide vane. An infrared thermography measurement system is used to determine highly resolved distribution of the models surface temperature. An in-situ calibration procedure is applied using single embedded thermocouples inside the measuring plate in order to acquire accurate local temperature data.All holes are inclined 35° with respect to the model′s surface and are oriented in a streamwise direction with no compound angle applied. During the measurements, the influence of blowing ratio and mainstream turbulence level on the adiabatic film cooling effectiveness and heat transfer coefficient is investigated for both of the injection configurations.

Adiabatic Effectiveness and Heat Transfer Coefficient of Shaped Film Cooling Holes on a Scaled Guide Vane Pressure Side Model

Adiabatic Effectiveness and Heat Transfer Coefficient of Shaped Film Cooling Holes on a Scaled Guide Vane Pressure Side Model

The variation of heat transfer coefficient, adiabatic effectiveness and aerodynamic loss with film cooling hole shape.

The heat transfer coefficient and adiabatic effectiveness of cylindrical, fan shaped holes and a slot are presented for the region zero to 50 diameters downstream of the holes. Narrow-band liquid crystals were used on a heated flat plate with heated air coolant. These parameters have been measured in a steady state, low speed facility at engine representative Reynolds number based on hole diameter and pressure difference ratio (ideal momentum flux ratio). The aerodynamic loss due to each of the film cooling geometries has been measured using a traverse of the boundary layer far downstream of the film cooling holes. Compared to the cylindrical holes, the fan shaped hole case showed an improvement in the uniformity of cooling downstream of the holes and in the level of laterally averaged film cooling effectiveness. The fan effectiveness approached the slot level and both the fan and cylindrical hole cases show lower heat transfer coefficients than the slot and non film cooled cases based on the laterally averaged results. The drawback to the fan shaped hole was that the aerodynamic loss was significantly higher than both the slot and cylindrical hole values due to inefficient diffusion in the hole exit expansion.

Enhancement of Film Cooling Performance Using a Shaped Film Cooling Hole with Compound Angle Injection.

The present study is conducted to investigate the local heat/mass transfer characteristics and local film cooling effectiveness around a conical-shaped film cooling hole with compound angle orientations. The cylindrical hole and two types of shaped hole with conically-enlarged hole exits are used to investigate the effect of film cooling hole geometry. One shaped hole (shaped hole #1) expands 4° in all directions from the middle of hole to the exit. The other shaped hole (shaped hole #2) has the tilted center-line by 4° between the conical and metering holes and is enlarged by 8° to downstream side. The hole area ratios of the exit to the inlet are 2.55 and 2.48, respectively. The film cooling jet is ejected through the single hole, which is inclined at 30° to the surface based on the metering hole. The lateral injection angle is changed from 0° to 90°, and the blowing rates from 0.5 to 2.0. The naphthalene sublimation technique is used to obtain local heat/mass transfer coefficients and adiabatic/impermeable wall film cooling effectiveness around the film cooling hole. For the shaped holes, the penetration of jet is reduced, and higher and more uniform cooling performance is obtained even at relatively high blowing rates because the conically expanded hole exit reduces momentum of the coolant and promotes the lateral spreading. The better cooling performance is obtained with shaped hole #1 due to the uniform diffusion of coolant in the film cooling hole.