Development of a Turning Mid Turbine Frame With Embedded Design—Part II: Unsteady Measurements

Abstract

This paper, the second of two parts, presents a new setup for the twostage twospool facility located at the Institute for Thermal Turbomachinery and Machine Dynamics (ITTM) of Graz University of Technology. The rig was designed to reproduce the flow behavior of a transonic turbine followed by a counterrotating low pressure stage such as those in high bypass aeroengines. The meridional flow path of the machine is characterized by a diffusing Sshaped duct between the two rotors. The role of wide chord vanes placed into the mid turbine frame is to lead the flow towards the low pressure (LP) rotor with appropriate swirl. Experimental and numerical investigations performed on this setup showed that the wide chord struts induce large wakes and extended secondary flows at the LP inlet flow. Moreover, large deterministic fluctuations of pressure, which may cause noise and blade vibrations, were observed downstream of the LP rotor. In order to minimize secondary vortices and to damp the unsteady interactions, the mid turbine frame was redesigned to locate two zerolift splitters into each vane passage. While in the first part of the paper the design process of the splitters and the timeaveraged flow field were presented, in this second part the measurements performed by means of a fast response probe will support the explanation of the timeresolved field. The discussion will focus on the comparison between the baseline case (without splitters) and the embedded design.