This paper compares experimental static pressure measurement with CFD simulation in a centrifugal compressor at 12 points through the diffuser. Three mass flow rates are selected, each for three operating speeds giving nine total operating conditions. The results show that the CFD model generally slightly underpredicts the static pressure value as compared to the experimental results. The discrepancy between experimental and numerical results ranges between -8% and +6% and is fairly consistent for a given operating condition, except for close to the blade trailing edge where the pressure variation is less regular and where the pressure is increasing most rapidly with radial position. In the consistent region, where the pressure gradient is low, the discrepancy is around two percent or less for simulations close to the design operating point. Away from the design operating point the errors increase up to approximately 5%. The simulation results were also used to investigate the effect of the position (from the blade trailing edge) of the impeller-diffuser interface (a characteristic of the frozen rotor simulation approach). Here an optimal position for the interface was found to be 2% of the blade radius. This value gave improved agreement with the experimental result in the initial region of the diffuser up to a distance of approximately 10% of the radius. At greater distances the position of the interface became less important. The results also highlighted a change in the pressure along the spanwise direction close to the tips. A dip in the pressure, which was observed in the experimental results, was only observed in the simulations close to the shroud. Close to the hub the simulation results recorded a small local peak. The simulation approach was then applied to further study the flow characteristics by examining the full-field velocity and pressure contours in the impeller and diffuser regions to identify changes due to the different operating conditions.

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This paper presents two-phase optimisation strategy for efficient planning of finishing endmilling operations when machining pocket-type features. The optimisation mechanism controls dimensional tolerances through knowledge of cutting forces and the associated cutting tool deflections. The developed model of the end milling process describes the main parameters, such as chip thickness, engagement angles, cutting forces, cutting tool deviation, and simulates the relationship between them during the cutting operation. The created strategy is feed-forward and it is focused on cutting process geometry identification and specifics of machining pocket type features. The model-based simulation covers the general case of endmilling when the chip thickness is variable along the tool path. The developed off-line optimisation methodology creates more efficient milling process with variable feed rate, compared to the same tool path cut with constant feed rate derived from the worst-case condition. Up-and down-milling were modelled and optimised, and the predicted data was evaluated experimentally.

This paper considers a 1D in‐line analytical model for centrifugal compressors with variable inlet guide vanes. A theoretical 1D model is developed to predict the effect of varying the inlet guide vane angle at different rotational speeds. An iterative algorithm is presented, which provides a fast and efficient method for evaluating the performance of the compressor under different operating conditions. The results from the analytical 1D model are presented and compared to full 3D CFD (computational fluid dynamics) simulations. The simulations validate the assumptions used in the 1D model and show good agreement between the two approaches over a range of vane angles. Qualitatively, both demonstrate the same trends as the vane angle and rotational velocities are varied. Quantitatively, the pressure ratio was found to agree within 8% and the temperature gain to within 15%. The 1D model was then modified to introduce a 5% loss in the diffuser and this was found to improve the 1D model predictions, with the pressure within 2% of the CFD value.

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