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.
Full Annulus High Fidelity Fan and Compressor Simulations
Challenge Project C3L supports research efforts to design distortion tolerant fans and accurately predict the inlet conditions to the core compressor of gas turbine engines. The technical approach and computational challenges associated with the Challenge Project are presented. The simulations run have produced critical understanding that allows design and performanceprediction tools to be improved by being based more on flow physics and less on empiricism. Distortion transfer simulations of two multistage fans show the stage-bystage transfer and generation of total pressure and total temperature distortion. Fan response for each stage along the circumference showed the first stage and the middle stage performance trajectories did not follow a typical speedline pattern while the last stage performance closely resembled a typical speedline. Simulations of an Air Force Research Laboratory (AFRL) research compressor are presented to show how aerodynamic blockage varies at off design operating conditions.
Application of Time-Accurate CFD in Order to Account for Blade-Row Interactions and Distortion Transfer in the Design of High Performance Military Fans and Compressors
The application of Computational Science and Engineering to the design and analysis of high performance military fans and compressors makes it possible to explicitly account for unsteady flow effects. During this first year of Challenge Project C1I, simulations have been accomplished for three different components: an AFRL research rig, a GE VAATE core compressor, and a GE military fan. These simulations are being used to investigate how blade row interactions and distortion transfer impact fan and compressor performance. Challenges to performing such large simulations have been identified and an efficient methodology for setting-up, running, and post-processing the simulations has been developed. Simulations accomplished through this Challenge Project have produced improved geometric, physical, and numerical fidelity results than previously possible, allowing the design of next generation engines to achieve unprecedented performance.