throat 55 is significantly greater than an inlet area 62 of vanes 56 causing cooling air 32 to be accelerated to a velocity substantially equal to the tangential velocity of radial impeller 52 mounted on the upstream side of high pressure turbine disk 21 radial flow inducer 48 may alternatively include a plurality of cylindrical airflow passages 100 disposed in an annular fashion about longitudinal axis 58 an illustration of one such passage being shown in fig8 the modulation of cooling flow 32 is provided by an endwall 64 and a means 66 for actuation thereof more specifically endwall 64 includes a first portion 68 substantially transverse to longitudinal axis 58 of channel 36 a second portion 70 having a circumferentially disposed array of contoured plugs 72 radially outboard of first portion 68 and adjacent to throat 55 of support member 42 and a third portion 74 connecting first portion 68 and second portion 70 adjacent to and substantially parallel with outer wall 40 referring again to fig3 endwall 64 may be moved in a direction parallel to longitudinal axis 58 as indicated by dashed lines this allows endwall 64 to cover a portion of throat 55 of channel 36 and radial flow inducer 48 wherein contoured plugs 72 fit into passageways 76 see fig4.