Air bypass system for rotor shaft cooling

A gas turbine comprising:

• a compressor section;
• a combustion section downstream of the compressor section;
• and
• a turbine section downstream of the combustion section, the turbine section comprising:
• a nozzle comprising an inner band, and outer band, and an airfoil extending between the inner band and the outer band, the airfoil defining an internal passage;
• a diaphragm comprising an inner wall radially spaced from the inner band, a first rail extending radially between the inner wall and the inner band, and a second rail opposite the first rail and extending radially between the inner wall and the inner band;
• wherein the inner wall, the first rail, and the second rail collectively define a diaphragm cavity radially inward of the inner band, and wherein the first rail defines a first rail aperture;
• a manifold positioned in the diaphragm cavity, the manifold comprising a first wall extending from the first rail to the second rail and in contact with the inner wall of the diaphragm, a second wall extending from the first rail to the second rail and in contact with the inner wall of the diaphragm, and a third wall coupled to the first wall and the second wall and extending from the first rail to the second rail, wherein the first wall defines a first wall aperture;
• and wherein the manifold and the diaphragm collectively define a manifold chamber in fluid communication with the first rail aperture;
• and
• a tube extending through the internal passage defined by the airfoil, through the first wall aperture, and into the diaphragm cavity, the tube being in fluid communication with the manifold chamber;
• wherein compressed air flows through the tube into the manifold chamber exits the manifold chamber through the first rail aperture.