CFD VALIDATION OF A HIGH SPEED TRANSONIC 3.5 STAGE AXIAL COMPRESSOR

摘要

CFD based optimization of transonic multi-stage compressors requires both fast and accurate numerical tools. In order to have reasonable fast analysis a low fidelity model is needed. The danger when using such a model is that if the results are not accurately predicted the optimization process can be unsuccessful in finding the true optima. There is thus a need to determine how much it is possible to simplify the CFD model without losing too much accuracy. Two different flow solvers, one in-house code and one commercial code, are here compared with experimental data obtained for a 3.5 stage compressor, named Blenda, in the recently completed European project VITAL. Both codes apply realizable k-ε turbulence modeling and mixing planes between each blade row in order to be fast enough for optimization purposes. As validation support, numerical analysis results of the well known and well documented NASA rotor 67 are also presented. Special attention is here put on the results of both low fidelity modeling without tip clearance and high fidelity modeling with tip clearance included, since this choice has a large influence on computational cost. The results show that the low fidelity model is capable of predicting the global performance parameters of rotor 67 including the shock structure. Results for the Blenda compressor indicate that the 1st and 3rd stage are well predicted by both flow solvers, whereas the 2nd stage displays significant differences, especially in local radial profiles of total temperature and total pressure levels in the hub region. The exact cause of this discrepancy is still unclear. Based on the presented results it is believed that a low fidelity model such as the one used in this study would be able to screen a design space for optimal geometries given that a safety margin is used for the predicted flow range. However, once the preliminary design has been set, a higher fidelity model would be required in order to verify the stage matching and that the overall design requirements have been fulfilled.