Application-Specific Parallel Linear Solver for Nonlinear Harmonics Method with Implicit Time Integration

The present paper covers specific parallel implementation details of the nonlinear harmonics (NLH) method within an implicit time integration framework. The NLH method plays an important role in industrial turbomachinery applications as it accounts for unsteady effects in modelling of compressors and turbines on a base of low-cost stationary approaches: the flow is modelled using the Reynolds-Averaged Navier–Stokes approach, the mixing plane method is used for the rotorstator interface, and only one periodic sector of a blade passage per row is considered. The main focus is on the adaptation of the linear solver used in the Newtonian process of the implicit scheme. The goal of this work is to significantly reduce memory consumption and improve performance. This goal is achieved by using a specialized block sparse matrix storage format, adapted linear solver preconditioners with approximate inverse diagonal blocks, and a combination of single- and double-precision real number formats.