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.
CHARACTERISTICS OF UNSTEADY FLOW IN FREQUENCY DOMAIN IN A CENTRIFUGAL COMPRESSOR
Performances prediction using steady RANS solver and validation are performed on a 56 mm turbocharger compressor under three working speed-line in this paper.Unsteady flow simulation in near-surge condition at a high rotation speed is then carried out and frequency-amplitude characteristics in an impeller,vaneless diffuser and volute are studied.Results show that unsteady effect lies mainly in an impeller and is the main reason for inducing aero-acoustics in a centrifugal compressor,while in the volute,unsteady effects decrease significantly and has less contribution to acoustics level.
The Response of Axial Flow Compressors to Intake Flow Distortion
The response of a lift engine model compressor to inlet pressure distortion is studied in detail to determine the nature and extent of the critical area of spoiling. This is found to be a sector of width between 60 and 90 deg. On this basis a simple distortion index is proposed which implies that only the circumferential pressure gradients of a complex distortion pattern are significant. The “Parallel Compressor” model satisfactorily explains surge and this experience is related to different types of compressors and to complex spoiling patterns. Comments are made on the differences in behavior between compressors operating on rig test and in engines.Copyright © 1969 by ASME