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.
Numerical Simulation of Impeller-diffuser Interaction in Centrifugal Compressor
Steady and unsteady numerical simulations of a small centrifugal compressor are presented in this paper.First,the steady and unsteady time-averaged results are compared.Then,the unsteady interaction between the impeller and diffuser is investigated by analyzing the spectrum characteristics of pressure fluctuations at the outlet of the impeller and the inlet of the radial diffuser.Finally,the unsteady influences of the impeller with and without splitters on the radial diffuser inlet are studied.Results show that the unsteady time-averaged total pressure ratio and isentropic efficiency are respectively 3.7% and 0.1% higher than those of the steady at the same mass flow;in the centrifugal compressor with splitters,pressure fluctuations at the blade passing frequency are the main fluctuations at the outlet of the impeller and the inlet of the radial diffuser.Besides,it is obvious that there are fluctuations two times the radial diffuser blade passing frequency at the outlet of the splitter and half times the impeller blade passing frequency at the inlet of the radial diffuser blades caused by the splitter.These unsteady pressure fluctuations will likely affect the fatigue strength of the centrifugal compressor.
A New Vacuum Pressure Infiltration CFRP Method and Preparation Experimental Study of Composite
In order to prepare a carbon-fiber-reinforced polymer composite (CFRP) with ideal microstructure and properties, a new vacuum pressure infiltration CFRP method is proposed based on an analysis of existing CFRP preparation process methods. Research on composite material preparation systems was carried out by using this new method principle. The system mainly includes a fiber pre-forming module, a vacuum heating infiltration module, a hot-press curing molding module, and a data acquisition control module. Under the conditions of natural curing at 0 MPa + 6 h + 25 °C, vacuum heating curing at –0.05 MPa + 30 min + 80 °C, and hot-press curing at 0.7 MPa + 5 min + 50 °C, a two-dimensional (2D) CFRP with excellent microstructure and properties was successfully prepared. Observing the microstructure of the prepared composite material, it can be found that the inside of the composite material was sufficiently and uniformly infiltrated, and common preparation defects such as holes and delamination were effectively controlled. Through the performance test, the bending strength of the material reached 790 MPa.