Abstract
To improve the understanding of unsteady flow in modern advanced axial compressor, unsteady simulations on full-annulus multi-stage axial compressor are carried out with the harmonic balance method. Since the internal flow in turbomachinery is naturally periodic, the harmonic balance method can be used to reduce the computational cost. In order to verify the accuracy of the harmonic balance method, the numerical results are first compared with the experimental results. The results show that the internal flow field and the operating characteristics of the multi-stage axial compressor obtained by the harmonic balance method coincide with the experimental results with the relative error in the range of 3%. Through the analysis of the internal flow field of the axial compressor, it can be found that the airflow in the clearance of adjacent blade rows gradually changes from axisymmetric to non-axisymmetric and then returns to almost completely axisymmetric distribution before the downstream blade inlet, with only a slight non-axisymmetric distribution, which can be ignored. Moreover, the slight non-axisymmetric distribution will continue to accumulate with the development of the flow and, finally, form a distinct circumferential non-uniform flow field in latter stages, which may be the reason why the traditional single-passage numerical method will cause certain errors in multi-stage axial compressor simulations.
Highlights
The flow field in axial compressor is unsteady due to the blade row interaction and the flow separations.[1]
The results show that the unsteady flow in a turbomachine can be accurately simulated with a small number of modes retained in the Fourier series representation of the flow, leading to a reduction of at least one order of magnitude compared to conventional nonlinear time-resolved computational fluid dynamics (CFD) simulation methods
To accurately model the blade row interactions, a sliding plane technique is applied at the interface between the rotor and stator, which allows the wake flow of upstream blades to further develop in downstream flow field or affect the downstream flow field through the interface between rotor and stator
Summary
The flow field in axial compressor is unsteady due to the blade row interaction and the flow separations.[1]. For an unsteady time-periodic flow in axial compressors caused by the relative motion between rotor and stator, Fourier transformation is applied to transform the unsteady time-periodic flow into a coupled system of several steady-flow computations at different time stages of the period of interest This system of steady-state equations can be solved efficiently by using traditional CFD methods and, greatly reduce the computational cost. The harmonic balance method is applied to investigate the unsteady flow field in a full-annulus multi-stage axial compressor. Note that the pseudotime harmonic balance equations are similar in form to the original time-domain form of the Navier–Stokes equations so that existing well-developed steady CFD techniques may be used to efficiently solve the nonlinear harmonic balance equations, with a comparable number of iterations required. The harmonic balance method was implemented in our in-house code SPARC
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