A Comparison of Two Load Transferring Methods in an Unsteady One-Way Fluid-Structure Interaction Analysis

Abstract

A full two-way aeroelasticity coupling analysis of rotating machinery and their main components requires considerable computational analysis and CPU time. This is why the most common methodology for this type of problem is a one-way coupling between fluid and structure. In this case, forces acting on rotor blades that result from a flow are introduced into a structural model of a blade as a local spot load in the centre of gravity or a series of local spot points deployed along the blade length. However, this method does not take into account how the forces change in a chordwise direction (along chord). An alternative way is to use the method of directly transferring the pressure field as a surface load from the CFD analysis to a structural model of a blade. In this case various interpolation methods are needed to transfer the results from the CFD mesh on to the structural mesh nodes. In this paper the authors compare how both methods of load transfer affect rotor blade stress and displacement levels during one period of rotation. Calculations were carried out for the first stage compressor blade of an aircraft engine. Ansys 12.1 was used to calculate the entire structure. Unsteady CFD calculations were carried out using Fluent for a 1.5 stage axial compressor model. For the numerical calculations a non-viscous flow was used. The unsteady forces were calculated on 10 control cross-sections of a rotor blade. The transient results obtained from the CFD calculations were transferred onto a structural rotor blade model using APDL language script. For both methods of load transference, transient displacements and transient stresses for the rotor blade were calculated. The harmonic analysis results were compared. Mesh sensivity analysis was also carried out for the structural model.