A gas turbine engine includes a compressor for pressurizing ambient air which is then mixed with fuel in a combustor and ignited for generating combustion gases which flow through a turbine which extracts energy therefrom. The turbine includes stator vanes which preferentially channel the combustion gases through a row of rotor blades which in turn rotate a rotor disk for providing shaft power. Since the combustion gases are hot, the stator vanes and the rotor blades are typically internally cooled using a portion of the compressed air bled from the compressor.
More specifically, the vanes and blades typically include a hollow airfoil having an internal cooling flow channel through which is channeled the cooling air bled from the compressor for internally cooling the airfoil. Convective heat transfer cooling is typically enhanced by providing a variety of techniques, including tubulators within the airfoil which have various conventional forms. The cooling air may simply be channeled through the airfoils, or the airfoils may include trailing edge discharge apertures or film cooling holes along either the pressure or suction sides of the airfoil, or both, in accordance with conventional practice. These outlets discharge the cooling air from the airfoil directly into the combustion gases and are suitably sized to provide a minimum backflow pressure margin to prevent the combustion gases from flowing into the airfoils through these outlets.
Any compressed air which is not used for generating combustion gases, such as that used for cooling the airfoils, decreases the overall operating efficiency of the engine and, therefore, increases specific fuel consumption (SFC). Accordingly, airfoils are cooled by a myriad of different arrangements which attempt to maximize the cooling thereof while minimizing the amount of cooling air bled from the compressor. This must also be done while maintaining acceptable backflow margin and without undesirable pressure losses which decrease the efficiency thereof.
One advanced concept for cooling gas turbine engine airfoils simulates the airfoils in a laboratory environment and uses a rotating chopper to provide pulsed or intermittent flow for convection cooling. The simulation demonstrates that convective heat transfer coefficients may be increased using pulsed flow over steady flow for constant airflow; however, the mechanical assembly of moving parts used in the test are clearly impractical for use in a gas turbine engine such as one used for powering an aircraft in flight.