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.

With paramount electrical, optical, catalytic, and other physical and chemical properties, van der Waals heterostructures (vdWHs) have captured increasing attention. vdWHs are two-dimension (2D) heterostructures formed via van der Waals (vdW) force, paving the way for fabricating, understanding, and applications of 2D materials. vdWHs materials of large lattice constant difference can be fabricated together, forming a series of unique 2D materials that cannot form heterostructures earlier. Additionally, vdWHs provide a new platform to study the interlayer interactions between materials, unraveling new physics in the system. Notably, vdWHs embody short-range bonds weaker than covalent and ionic bonds, almost only interactions between nearest particles are considered. Owing to a clear interface, vdW interaction between two different components, devices made by vdWHs can bring amazing physicochemical properties, such as unconventional superconductivity, super capacitance in intercalation 2D structure, etc. Recently, impressive progress has been achieved in the controlled preparation of vdWHs and various applications, which will be summarized in this review. The preparation methods comprise mechanical exfoliation, liquid phase stripping, physical vapor deposition, chemical vapor deposition, and metalorganic chemical vapor deposition. The applications sections will focus on photoelectric devices, logic devices, flexible devices, and piezotronics. Finally, some perspectives in the future on the controlled preparation of vdWHs with desired properties for advanced applications will be discussed.

This paper is concerned with the study of a kind of discrete forcing immersed boundary method (IBM) by which the loosely aero-elasticity coupled method is developed to analyze turbine blade vibration. In order to reduce the spurious oscillations at steep gradients in the compressible viscous flowing field, a five orders weighted essentially nonoscillatory scheme (WENO) is introduced into the flow solver based on large eddy simulation (LES). The three-dimensional (3D) full-annulus domain of the last two stages of an industrial steam axial turbine is adopted to validate the developed method. By the method, the process of grid generation becomes very simple and the unsteady data transferring between stator and rotor is realized without the process of being averaged or weighted. Based on the analysis of some important aerodynamic parameters, it is believed that hypothesis of azimuthal periodicity is not reasonable in this case and full-annulus passages model is more feasible and suitable to the research of turbine blade vibration. Meanwhile, the blade vibration data are also discussed. It is at about 65% of rotor blade height of the last stage that an inflection point is observed and the midspan region of the blade is the vulnerable part damaged potentially by the blade vibration.

The unsteady characteristic in the tip region of an axial compressor has been numerically studied with the help of the dynamic mode decomposition analysis. The characteristics of frequency and dynamic modes are compared and discussed under different operating points and different parameters, such as tip clearance and rotating speeds. For the flowfield structures in the tip region, such as tip leakage flow, separation flow and shock wave, their relationships with the unsteadiness are studied in detail. Except for the unsteadiness caused by the interaction between rotating rotor and the stationary boundaries, it is found that the unsteadiness is attributed to the moving of the low-velocity cell. Based on the generation and the development of the low-velocity cell, the unsteady characteristics in tip region are divided into 4 types: BPF-dominated, shedding-dominated, self-induced and separation-dominated. When the tip leakage flow is weak, the unsteadiness in the tip region is only triggered by the blade sweeping. As the tip leakage flow gets stronger to a certain extent, the low-velocity cell is shed into the flow passage and mixed with the main-flow. When the main-flow is weaker under the low flowrate condition, the interaction between the low-velocity cell and the pressure side occurs and generates a new low-velocity cell near the leading-edge of the neighboring blade. The frequency of the new cell generation is actually the self-induced frequency. In the zero and small clearance model, the low-velocity is shed by the separation in the leading-edge and the casing-suction corner. By understanding these unsteady characteristics, the change tendency of the leading frequency in the rotor tip is easily explained and forecasted. Furthermore, under the transonic operation condition, the low-velocity cell is decelerated and eliminated by the shock wave in the unsteadiness of the self-induced type and the separation-dominated type, respectively. Thus, the leading frequency in the tip flow field is moderated.

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.