Numerical Research On The Unsteady Flow And Loss In The Transonic Compressor

To further improve the performance of the compressor in the aero-engine and other gas-turbines, it is of great importance that the mechanism of the unsteady flow in the compressor is well understood. In this thesis, efforts are devoted to developing advanced numerical methods to simulate the complex unsteady flow field in the compressor and constructing reasonal parameters to measure the loss in the compressor. Based on the achievements in these two aspects, the unsteady loss in a one-stage transonic compressor is analyzed.In the aspect of numerical method, three numerical schemes which can take multi-dimensional effects into account are developed. 1) Extension of a two-dimensional rotated Riemann solver, which has already proven its excellent robustness, to three-dimensional system. 2) A multi-dimensional upwind scheme was developed by computing the numerical fluxes at cell interfaces through solving full governing equations. This scheme can include the viscous contribution during the evaluation of the inviscid fluxes of the Navier-Stokes equations. 3)A finite volume local evolution Galerkin (FVLEG) method which is based on the bicharacteristics for linear (or linearized) hyperbolic systems were derived. The common advantages of the three schemes are simple, efficient and can be extended to unstructured grid directly. The 3D rotated Riemann solver has been already integrated into our in-house code for the compressor simulation. The numerical simulations show that the multi-dimensional scheme has better abilities to capture the discontinuities in the transonic compressor flow field.The previously developed loss audit parameters coming from the steady compressor design system do not fit the measurements of the loss generation in some local regions. The values of these parameters usually reflect the accumulating loss of a fluid element or a system. Because flows in compressor are essentially unsteady and because it is meaningful to know the influence of some design modifications on the local loss, it is therefore necessary to develop new methods to measure the loss generation in particular region of the flow field. Based on the first and second laws of thermodynamics, an expression of irreversibility for arbitrary control volume has been derived under exergy analysis framework. The intensity of the irreversibility thus computed reveals relationship between the loss generation and flow structures. Irreversibility and its intensity can provide relevant information in compressor design and optimization.