Study on unsteady flow collaborative characteristics of semi-open impeller and diffuser in a centrifugal compressor
Centrifugal compressor, as the significant equipment in the energy field, is of very complexity in its structure. Good collaboration of individual components determines the good aerodynamic performance and running security of the compressor. Unsteady simulations were performed, based on the platform of CFX and through the UDF interface program, to evaluate the 3D collaborative aerodynamic characteristics of a semi-open impeller and diffuser in a large centrifugal compressor, and the numerical study was focused on the impeller-diffuser interaction. The result obtained from flow structures shows the development of low-velocity vortexes in the diffuser flow passage is affected by impeller-diffuser interaction. The low-velocity vortex may increase flow resistance of the flow passage, however, improving at some extent the flow condition of the neighbor one, which generates a kind of low-frequency interference. In addition, the strongest interface effect is located on the rotor blade trailing edge and the diffuser vane leading edge. Amplitude-frequency characteristics converted from the pressure pulsation on monitor points indicate that the rotor wake flow and potential repercussion of diffuser work together to generate strong vibration and excitation force. The impeller-diffuser interaction is stronger under winter operating condition than it is under design condition. Meanwhile, the impact of diffuser exerts dominating effects on the excitation force near the impeller, which should be considered when exploring the impeller damage accident causes under winter operating condition.
Experimental investigation for the effects of different unsteady source in centrifugal compressor
Experimental investigation on the unsteady flow in the vaned diffuser of a centrifugal compressor stage was performed.Detailed instantaneous flow has been measured at several different measuring positions using a hot-wire anemometer with the phase-locked ensemble-averaged technique.Different unsteady source are distinguished by circumferential-averaged technique and 'inverse spectral analysis'.The effects of different unsteady source on the flowfield and mechanism of the unsteady interaction are analyzed and explored.The results show that the repercussion effect of vaned diffuser is of the same order with the unsteadiness induced by impeller,while the repercussion effect of vaned diffuser is smaller.The repercussion effect of vaned diffuser and the unsteadiness induced by impeller decrease along the stream wise direction,and the gap between them also reduces along this direction.The unsteady effect of impeller is sensitive to the location of diffuser vane in radial gap,and it is larger near the convexity surface of the diffuser vane.The uncertain unsteady dimensionless velocity in radial gap is influenced by the repercussion effect of vaned diffuser insignificantly.
Understanding Unsteady Flow Features in Transonic Compressors
Applying computational science and engineering to the design and analysis of high-performance compressors makes it possible to understand unsteady flow effects in gas turbine engines. Simulations have produced numerical data of greatly improved geometric, physical, and numerical fidelity than previously possible, helping next-generation engines achieve unprecedented performance.