This study mainly focuses on investigating the influence of meridional contour of a steam centrifugal compressor on aerodynamic performance. An optimal design method is put forwards, in which the hub-line on the meridional plane is modified and optimized. Based on the data from numerical simulation, aerodynamic characteristics are compared in detail among a prototype and three modified impellers. It is shown that stall margin of the optimized impeller can be enlarged by approximately 50%, though at design point efficiency and pressure ratio is decreased a little bit. Under the working conditions with low flow rate, the optimized impeller exhibits the best performance compared with the prototype and two other impellers. Furthermore, numerical result is validated by the experiment and is matched the measure data very well.
For the predicting of compressor noise, Lighthill analogy method based on numerical simulation has usually been adopted. Therefore, accuracy of the numerical simulation of the flowing filed is very important to the noise estimation. In this paper, nonlinear harmonic (NLH) method, which is one of promising numerical simulation methods used for the noise prediction, is compared with dual time step (DTS) method based on the calculating of the flowing field of one and a half stage compressor. It is found that the time consumption of NLH is actually decreased by about 70% compared with DTS. All the same, pressure fluctuation in the results obtained from NLH is more obvious than that of DTS in the upstream channel and downstream channel. Meanwhile, the two series of numerical simulation results are compared respectively with experiment data measured by dynamic pressure sensors. It is observed that the results from DTS is much closer to experimental data in both time domain and frequency domain. It is believed that the overmuch fluctuation found in NLH method is mainly caused by the contradiction between actual flowing pattern and periodical assumption made by NLH method initially. In addition, the pressure distribution around rotor blade surface, which is one of important tonal noise sources, is studied in detail as well.
Summary In this paper, the pressure drop and heat transfer features of a microchannel applying micropin fins are investigated by numerical simulations and experiments. The microchannel, which is 20‐mm long, 2.7‐mm wide, and 0.3‐mm deep, is fabricated with copper and consisted of staggered diamond micropin fins. The visualization experiments, by means of the advanced technology micro‐particle image velocimetry (PIV), are conducted to discuss the mechanism of heat transfer by analysing the flow regimes. Meanwhile, 3D‐coupled numerical simulations are applied for the combination with experiments in this research. It is found that the vortex‐wake flow is stable at Reynolds number (Re) = 0 to 300, and a steady recirculating zone can be observed in the wake, where a pair of symmetrical vortices is formed. All the time, the vortex‐wake flow is unstable at Re = 300 to 650. Under this situation, it is due to the decrease of vorticity that the Nusselt number (Nu) is not significantly increased as it was expected. Thus, when Nu in the pin fin microchannel is predicted, the vorticity should be considered as well as turbulent kinetic energy (TKE). Furthermore, comparative study was carried out based on the mechanism proposed in this study among three kinds of microchannel with different fins, including staggered circular pin fins (CPF), square pin fins (SPF), and diamond pin fins (DPF).
In this paper, with the help of partial similarity principle, aerodynamic performance of a centrifugal compressor in a turbocharger unit is analyzed and improved based on a low-speed large-scaled model. In order to achieve flow similarity between the scaled compressor and the prototype, tip clearance and diffuser outlet diameter have been modified further. It is observed from the numerical results that the relative error between the scaled compressor and the prototype is less than 0.8%. It means that the flow field of the scaled compressor is similar to the prototype though the Reynolds number is neglected during the scaling process. Furthermore, the large-scaled impeller has been improved by analyzing the numerical results, and then, the improved impeller is scaled down back to the smaller one by using the partial similarity principle, which geometric dimensions have the same level as those of the prototype but performance is improved obviously. Meanwhile, the experiment results are used to validate the method.
This paper studies the influence of tip clearance on the flow characteristics related to the performance. Based on full-passage numerical simulation with experimental validation, several clearance models are established and the performance curves are obtained. It is found that there exists an optimum clearance for the stable working range. By analyzing the flow field in tip region, the role of the tip leakage flow is illustrated. In the zero-clearance model, the separation and blockage along the suction side is the main reason for rotating stall. As the tip clearance is increased to the optimum value, the separation is suppressed by the tip leakage flow. However, with the continuing increasing of the tip clearance, the scale and strength of the tip clearance vortex is increased correspondingly. When the tip clearance is larger than the optimum value, the tip clearance vortex gradually dominates the flow field in the tip region, which can increase the unsteadiness in the tip region and trigger forward spillage in stall onset.
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