air bled from the discharge of compressor 20 which is routed to and through the turbine in a manner well known in the art the compressor discharge has been the logical choice for the coolant flow since the pressure of the compressor discharge airflow referred to hereinafter as the 34 cooling air 34 is high enough to drive the cooling air through the tortuous path associated with the turbine structure however because the cooling air has had work performed on it by the compressor its temperature level has been increased and as compressor compression ratios are increased and as aircraft velocities increase a corresponding rise in the temperature of the cooling air is experienced as a result an increasingly higher percentage of cooling flow is required to cool the turbine to acceptable temperature levels as mentioned earlier this cooling air must bypass the combustor and perhaps one or more turbine stages before being returned to the propulsive cycle thus giving rise to a performance penalty in proportion to the amount of cooling air used it thus becomes advantageous to reduce the amount of cooling air required referring now to fig3 there is depicted in graphical form the change in turbine relative cooling flow rates and specific fuel consumption as a function of the change in cooling air temperature for a typical gas turbofan engine of the variety depicted in fig1 as an illustration an estimate of the cooling airflow and specific fuel consumption reductions that can be realized by cooling the turbine blade cooling air of a two stage core engine turbine of current design is shown in fig3 it may be observed from the figure that in this.