Mistuned forced response sensitivity of an embedded compressor rotor: Effect of sideband travelling wave excitations
This paper describes the aeromechanical aspects of forced response analysis on a 3.5 stage axial compressor. Mistuning is prominent in gas turbine engines as a result of wear and tear of blades, manufacturing variations etc. In a couple of their earlier papers the authors determined the multi-row influence on the forcing function and quantified it with a numerical value of modal force. However, one aspect, which remained unaddressed is the accuracy with, which the individual blade responses were predicted. The mistuning analysis was carried out using an in-house code and the results are validated with experimental data both in physical and travelling wave domains. The structure of the paper is as follows: The first part talks briefly about the unsteady CFD computational approach utilized to obtain the modal force values for each of the multi-row cases, which was obtained using ANSYS CFX. These modal forces were utilized to obtain the mistuned forced response predictions. The second part describes in detail the method used to quantify blade responses and goes onto account for a few discrepancies in the mistuned forced response predictions. The last part addresses the cause for these discrepancies and the authors conduct sensitivity studies to justify the anomaly. Some of the conclusions drawn from this study were 1) The max envelope of the mistuned blade response curve was well predicted by both the 3-row and the 5-row cases and the average envelope by the 4-row case 2) The response was more localized at the-11ND computationally as against experimental data,which included significant responses at other ND’s although the-11ND content dominated. 3)The discrepancy in the amplification factor prediction was mainly due to the absence of additional travelling wave excitations, which when included increased the response significantly. Irrespective of the phase addition of the sideband excitations tends to increase the response
