Forced response analysis of multi-row compressors


High cycle fatigue failure in turbomachinery is known to be attributed to two major factors, flutter and forced response. Flutter is caused by the blade vibration, which results in negative aerodynamic damping.

This research proposes an effort to investigate computationally the forced response behaviour of a 3.5 stage compressor. This will be in collaboration with Purdue university who will provide us experimental data for the same. This effort is not to just predict responses to compare with experimental data, but will investigate the physics. As an example, forced response computations include three fundamental ingredients: (1) the forcing function, (2) damping (structural and aerodynamic) and (3) mistuned response. As shown in our earlier research, if the errors in the three ingredients cancel out, you can get what appears to be excellent agreement with experimental data.

Tool Development

ANSYS CFX is a time-domain solver widely used in academia and industry. Our research has involved using this tool to conduct multi-row unsteady aerodynamic analyses and expand the knowledge of accurate prediction with affordable computation resource. The analyses have been conducted by using the state-of-the-art interface treatment between stages.

Beyond the pre-defined functionalities, this research helps integrate our understanding in aeromechanics into the usage and develop new features to fulfil the working flow of conducting forced response analysis fully within CFX. Our academic partnership with ANSYS has helped ANSYS add several modules in their software and has led to a mutual benefit for both our research and the expansion of CFX to incorporate specific modules for aeromechanical analysis. The research intends to contribute to the development of existing methods within ANSYS particularly the time transformation (TT) method which has been used to model non-uniform pitch ratio problems. This method when extended to capture multiple frequencies across multiple rows has the capability of reducing a multi stage compressor to a few rows and a few passages per row. This research seeks to determine the maximum extent to which a domain can be reduced while preserving the fidelity of the problem.

Benefits to industry

The overall benefit to industry and academia will be a significantly improved design and development system that will save time and money. This research will focus on explain the physics behind the presence of each row in the compressor and its impact on forcing. Since the research involves carrying out different multi-row simulations at various crossings and loading conditions the research will answer aeromechanical aspects of compressors including the number of rows required to predict the forcing accurately and the nature of interference physical wave reflection off a neighbouring row has on the forcing. One of the traditional methods of multi-row simulations has been to model the entire wheel .This research will provide modelling guidance for reduced passage techniques making use of state of the art interface treatment available in CFX as well as harmonic balance methods available in an in-house code MUSTANG 2.0.