TURBINE VANE PASSAGE EXPERIMENTS DOCUMENTING EVOLUTION OF SECONDARY FLOWS WITH CHANGES IN COMBUSTOR COOLANT INJECTION FLOWRATES

A secondary flow system with a dominant passage vortex pattern has been observed in many gas turbine vane passage studies in which there is no upstream coolant injection or only near-passage endwall coolant injection (no combustor cooling). However, it was shown in recent studies that combustor coolant introduced upstream of the vane passage changes secondary flow patterns in the passage. This results in a different secondary flow vortex system, called the ‘impingement vortex’ system. It was discussed in recent literature having combustor coolant injection. Until now, there has been no study on how increases in combustor coolant momentum effect transition from the passage vortex system to the impingement vortex system. Such a study is presented in the present paper. Velocity component measurements are taken using a five-hole probe at three axial locations in the vane passage to document secondary flow development throughout the passage. Four combustor coolant flowrate cases are considered along with a comparison case having no coolant injection. It is shown that as the combustor coolant flowrate increases, the passage vortex system weakens and, at a sufficiently high combustor coolant flowrate, the impingement vortex system appears. Knowing the detailed flow physics of this transition between the two secondary flow systems is helpful for turbine thermal designers who wish to understand how secondary flows transport coolant within the turbine vane passage.