Vane Clocking Effects on the Resonant Response of an Embedded Rotor

Abstract

st torsion mode resonant response of IBR-2 generated by the wakes from the upstream stators is quantified non-intrusively utilizing an Agilis NSMS for six vane clocking configurations at the design and high loading conditions. The forcing function to IBR-2 consists of the Stator1 wakes and the potential fields from Stators-1 and Stator-2, and their aerodynamic interactions. Thus, the IBR-2 resonant response experiments involve classic vane clocking, with the IGV, Stator-1 and Stator-2 each having identical vane counts. I. Introduction IGH Cycle Fatigue (HCF) and resonant response of turbomachine blading resulting from flow-induced vibrations continues to be a significant problem throughout the gas turbine industry. Design resonant response analyses consider a tuned blade row, i.e. a rotor with all blades having the same structural properties and thus, identical natural frequencies. In fact, there are small blade-to-blade structural property variations, termed mistuning, which are known to lead to significant increases in blade resonant response amplitude as compared to that of the tuned blade row, with mistuning often cited as an HCF source. Turbomachinery rotors have typically been bladed-disks, with individual blades inserted into a slotted disk and retained by means of a dove-tail or fir-tree attachment. Advances in manufacturing techniques have resulted in bladed-disks with increased uniformity, i.e. small mistuning. Unfortunately, smaller mistuning does not translate into lower amplitude blade vibrations. In addition, new manufacturing techniques have enabled integrally bladed rotors (IBRs) wherein the blades and disk are machined from a single piece of material. However, as compared to bladed-disks, IBRs have both much smaller mistuning and mechanical damping. As compared to bladed-disks, IBRs exacerbate the potential for large amplitude resonant response and HCF because of reduced mechanical damping and mistuning. The implementation of IBRs into engine designs also affects the development of acceptable rotors. When bladed-disks are found to have unacceptably high vibration amplitudes and vibratory stress during development or in the field, a traditional approach is to incorporate friction dampers. However, resonant response problems in IBRs may not be able to be solved with friction dampers because they cannot be easily implemented. Hence, new solutions are required to address IBR resonant response problems. In this regard, vane clocking is a potential technique for the control of the resonant response of embedded rotors. A particular embedded rotor is subjected to the periodic passing of the wakes from the upstream airfoil row and the potential disturbances from both the upstream and the downstream airfoils rows, i.e. an embedded rotor is subjected to three forcing functions, Figure 1. With airfoil rows having similar vane counts, the stationary vane rows can be indexed relative to one another to affect the airfoil row unsteady aerodynamic interactions. This circumferential indexing of vanes in adjacent rows with similar vane counts is termed vane clocking. Experimental research has shown that vane clocking can be an effective tool to increase turbine performance 1-4 , increase compressor