Cavitation in semi-open centrifugal impellers for a miniature pump

Cavitation in miniature pumps was investigated experimentally for two semi-open centrifugal impellers. Although both impellers had the same blade cross-section, one impeller had a two-dimensional blade, while the other had a leaned blade. The flows were also analyzed using a numerical model of the three-dimensional turbulent flow in the pumps near the peak efficiency point using the k-ɛ turbulence model and the VOF cavitation model. The average cavitation performance of each impeller was satisfactorily predicted by the numerical simulations. The results show that the miniature pumps have similar cavitation performances as an ordinary-size pump, with the cavitation performance of the semi-open impeller reduced by increased axial tip clearances. Also, both the hydraulic and cavitation performance of the semi-open impeller were improved by the leaned blade. The results also show that uniform flow upstream of the impeller inlet will improve the cavitation performance of a miniature pump. __________ Translated from J Tsinghua Univ (Sci & Tech), 2006, 46(8): 1451–1454 [译自: 清华大学学报(自然科学版)]     

Numerical analysis of rotating stall characteristics in vaneless diffuser with large width-radius ratio

A two-dimensional model, where the influence of wall boundary layers is neglected and inlet jetwake velocity patterns are prescribed, was applied to simulate one vaneless diffuser with a large width-radius ratio. The impact of diffuser length, impeller blade number, etc. on the rotating stall was analyzed. Computational results show that a different mechanism does exist for diffusers with large width-radius ratios. Comparison with related conclusions and references is supportive of the model. __________ Translated from Journal of Shanghai Jiao Tong University, 2007, 41(9): 1518–1521 [译自: 上海交通大学学报]     

Vibration analysis of blade-disc coupled structure of compressor

While a 3D assembly model of blade-disc structure was established, a finite element model for calculating the vibration characteristics during blade-disc coupling was built by taking into consideration the coupling action of contact stress between the blade and the disc. The vibration characteristics of the blade-disc coupling structure was calculated and analyzed using cycle analysis method with the aid of ANSYS software. The modeling experiment shows that this method is feasible for analyzing the rabbet assembly structure. __________ Translated from Journal of Aerospace Power, 2007, 22(7): 1065-1068 [译自: 航空动力学报]     

Numerical simulation of sudden-expansion two-phase flows with two-scale second-order moment particle turbulence model

A two-scale second-order moment particle turbulence model is developed, based on the concept of particle large-scale fluctuation due to turbulence and particle small-scale fluctuation due to collision. The model is employed to simulate gas-particle flows in a sudden-expansion chamber. Simulation results are compared with the experimental results and with those obtained by the single-scale second-order moment two-phase turbulence model. It is shown that the two-scale model is with higher calculating accuracy than the single-scale model. Translated from Journal of Xi’an Jiaotong University, 2006, 40(1): 97–100, 110 [译自: 西安交通大学学报]     

Numerical simulation of three-dimensional turbulent flow in multistage axial compressor blade row

Numerical simulation of three-dimensional turbulent flow in a multistage axial compressor blade row is conducted. A high resolution, third-order ENN scheme is adopted to catch the shockwave and simulate the turbulent flow correctly, while an LU-SGS implicit method is chosen to improve computation rate. A detailed and highly efficient numerical simulation system is thus constructed. The investigation is focused on the grid connecting methods between the rotor and the stator and the corresponding treatment of rotor-stator interactional surface. The final results of a three-stage axial compressor with inlet guide vanes conform well to the experimental data. __________ Translated from Chinese Journal of Applied Mechanics, 2007, 24(1): 21–25 [译自: 应用力学学报]     

New response surface model and its applications in aerodynamic optimization of axial compressor blade profile

A parametric method for the axial compressor 2D blade profiles is proposed in which the blade geometries are defined with the parameters commonly used for blade definition, which ensures that the geometric significance is clear and an unreasonable blade profile is not generated. Several illustrations are presented to show the fitting precision of the method. A novel response surface model is proposed which regards the objective distribution function in the vicinity of a sample as normal school, and then generates the response surface function in the whole design space by a linear combination of distribution functions of all the samples. Based on this model, a numerical aerodynamic optimization platform for the axial compressor 2D blade profiles is developed, by which aerodynamic optimization of two compressor blade profiles are presented. __________ Translated from Acta Aeronautica et Astronautica Sinica, 2007, 28(4): 813–820 [译自: 航空学报]     

Numerical analysis of aerodynamic noise radiated from cross flow fan

The flow field in a cross flow fan was simulated by solving the 2-D unsteady Reynolds-averaged Navier-Stokes equations. The calculated pressure fluctuations of the blades, the vortex wall, and the rear wall were then used as noise sources to calculate the sound field. The Ffowcs Williams-Hawkings (FW-H) equation was employed to predict the noise field caused by these sources. The predictions show that the rear wall and the vortex wall sources contribute significantly to the total noise and that both the predicted aerodynamic performance and noise agree well with the experimental results. __________ Translated from J Tsinghua Univ (Sci & Tech), 2007, 47(2): 236–239 [译自: 清华大学学报(自然科学版)]     

Parameter for judging reactivity of coal and coke

To eliminate the judgment error of char reactivity arising from different carbon content of samples, a new parameter called specific maximum weight loss rate was introduced. It is defined as the quotient of the maximum weight loss rate in non-isothermal thermogravimetric analysis (TGA) experiment to the carbon content of the corresponding sample. The reactivity of different kinds of coal, the reactivity of the same coal type with different lithotype, and the reactivity of the char with different carbon conversion rates were checked by using the specific maximum weight loss rate, and the results were analyzed and compared with those obtained by using other criteria. The results show that the specific maximum weight loss rate can be used as a commonality parameter to evaluate and distinguish the reactivity of different coal and char. The heating rate selected in TGA experiment has no effect on the judgment. __________ Translated from Journal of Zhejiang University (Engineering Science), 2006, 40(11): 1998–2001 [译自: 浙江大学学报(工学版)]     

Reliability design method for steam turbine blades

Based on theories of probability and statistics, and taking static stresses, dynamic stresses, endurance strength, safety ratios, vibration frequencies and exciting force frequencies of blades as random variables, a reliability design method for steam turbine blades is presented. The purport and calculation method for blade reliability are expounded. The distribution parameters of random variables are determined after analysis and numerical calculation of test data. The fatigue strength and the vibration design reliability of turbine blades are determined with the aid of a probabilistic design method and by interference models for stress distribution and strength distribution. Some blade reliability design calculation formulas for a dynamic stress design method, a safety ratio design method for fatigue strength, and a vibration reliability design method for the first and second types of tuned blades and a packet of blades on a disk connected closely, are given together with some practical examples. With these methods, the design reliability of steam turbine blades can be guaranteed in the design stage. This research may provide some scientific basis for reliability design of steam turbine blades. __________ Translated from Chinese Journal of Applied Mechanics, 2007, 24(3): 331–335 [译自: 应用力学学报]     

Optimization of Venturi tube design for pipeline pulverized coal flow measurements

A Venturi flow meter was designed to accurately measure the mass flow rate of pulverized coal in power plant pipelines. Numerical simulations of the dilute turbulent gas-solid two-phase flow in a horizontal Venturi tube were used to study the effects of Venturi tube geometry on the pressure distribution in the mixture. The results show that Venturi tube geometry strongly influences the metering of the dilute gas-particle two-phase flow. The geometry can be optimized to improve the precision of the measurement and ensure stable measurements. Furthermore, the geometries of three types of Venturi tubes were optimized for an experimental study of pulverized coal mass flow rate measurements. __________ Translated from Journal of Tsinghua University (Sci & Tech), 2007, 47(5): 666–669 [译自: 清华大学学报( 自然科学版)]     

Study and practice on condition-based maintenance of induced fans in coal-fired power plants

Reducing the enormous maintenance cost is essential to enhance the competitiveness for power plants. An overall design scheme for condition-based maintenance of induced fans is proposed for large thermal power plants. The interface of the above framework is simple and convenient; the optimum maintenance strategy is given by condition monitoring and risk evaluating. The decisionsupported system was used in Guangdong Shajiao C Power Plant. The results show that it is a feasible maintenance optimization scheme for power plants. __________ Translated from J Huazhong Univ of Sci & Tech (Natural Science Edition), 2007, 35(1): 63–66 [译自: 华中科技大学学报(自然科学版)]     

Impact of dimethyl ether on engine seal materials

The resistance of many kinds of rubber materials to dimethyl ether (DME) was studied. Both the mass and volume change of rubber materials, which were put in DME and then exposed to the air for different periods of time were measured. The results show that fluorine rubber (FKM), silicone rubber (SIR), and nitrile rubber (NBR) are unsuitable as seal materials for DME engines. Common polyvinylchloride (PVC) dissolved completely in DME, which has almost no impact on vulcanizing nylon material. The constitution of ethylene propylene terpolymer rubber (EPDM) has a major impact on its resistance to DME. A kind of EPDMwith good resistance to DME was found, whose reliability was validated by 100 hours of DME engine operation. __________ Translated from Journal of Shanghai Jiaotong University, 2006, 40(8): 1257–1261 [译自: 上海交通大学学报]     

Probability strength design of steam turbine blade and sensitivity analysis with respect to random parameters based on response surface method

Many stochastic parameters have an effect on the reliability of a steam turbine blade during practical operation. To improve the reliability of blade design, it is necessary to take these stochastic parameters into account. An equal cross-section blade is investigated and a finite element model is built parametrically. Geometrical parameters, material parameters and load parameters of the blade are considered as input random variables while the maximum deflection and maximum equivalent stress are output random variables. Analysis file of the blade is compiled by deterministic finite element method and applied to be loop file to create sample points. A quadratic polynomial with cross terms is chosen to regress these samples by step-forward regression method and employed as a surrogate of numerical solver to drastically reduce the number of solvers call. Then, Monte Carlo method is used to obtain the statistical characteristics and cumulative distribution function of the maximum deflection and maximum equivalent stress of the blade. Probability sensitivity analysis, which combines the slope of the gradient and the width of the scatter range of the random input variables, is applied to evaluate how much the output parameters are influenced by the random input parameters. The scatter plots of structural responses with respect to the random input variables are illustrated to analyze how to change the input random variables to improve the reliability of the blade. The results show that combination of the finite element method, the response surface method and Monte Carlo method is an ideal way for the reliability analysis and probability strength design of the blade. __________ Translated from Proceedings of the CSEE, 2007, 27(20): 12–17 [译自: 中国电机工程学报]     

Boiling heat transfer correlations for refrigerant mixtures flowing inside micro-fin tubes

Based on experimental results of ternary non-azeotropic refrigerant mixture R417A flowing and boiling in one smooth and two internally grooved horizontal tubes with different geometrical parameters, a boiling heat transfer correlations was developed for refrigerant mixtures flowing inside micro-fin tubes by applying the enhancement factor in the present modified-Kattan model which was modified by the experimental data of R417A in a smooth tube. The comparison between the calculation and the experimental results indicates that the prediction by the present correlations is in good agreement with the experiment of refrigerant mixtures inside different microfin tubes with a standard deviation of ±30% for vapor qualities below 80%. __________ Translated from Journal of Xi’an Jiaotong University, 2007, 41(11): 1279–1283 [译自: 西安交通大学学报]     

Diagnosis method based on wavelet coefficient scale relativity correlation dimension for fault

Correlation dimension as a tool to describe machinery condition is introduced. Vibration signals of the fan under different working conditions are analyzed using a threshold filtering algorithm based on the region relativity of the wavelet coefficients for reducing noise. The result shows that the characteristics of the signal could be preserved completely. The correlation dimension is able to identify conditions of the fan with faults compared with the normal condition, thereby providing an effective technology for condition monitoring and fault diagnosis of mechanical equipment. __________ Translated from Journal of North China Electric Power University, 2007, 34(1): 59–62 [译自: 华北电力大学学报]     

Molecular dynamics simulation of diffusivity

Equilibrium molecular dynamics simulation was performed on water to calculate its diffusivity by adopting different potential models. The results show that the potential models have great influence on the simulated results. In addition, the diffusivities obtained by the SPCE model conform well to the experimental values. __________ Translated from Journal of Engineering Thermophysics, 2006, 27(3): 373–375 [译自: 工程热物理学报]     

Optimization for operating modes based on simulation of seasonal underground thermal energy storage

A simulation was performed, which concerned the feasibility of seasonal underground thermal energy storage (UTES) in Tianjin, China. The investigated system consisted of 8 boreholes. In summer, residual solar thermal energy was emitted into the soil surrounding the borehole heat exchangers through which the stored energy was extracted in winter with a ground coupled heat pump (GCHP) to provide a proper heating temperature. A simulation study was performed to study the influence of system operation modes on thermal recovery based on the experimental data of a GCHP system, local meteorological conditions and soil properties in Tianjin. The results indicate a thermal recovery ratio of less than 67% and different temperature distributions under three modes. Finally, an operation mode was suggested based on both lower loss and better thermal recovery in the UTES. __________ Translated from Journal of North China Electric Power University, 2007, 34(2): 74–77 [译自: 华北电力大学学报]     

Supersonic flows over cavities

The characteristics of supersonic cold flows over cavities were investigated experimentally and numerically, and the effects of cavities of different sizes on supersonic flow field were analyzed. The results indicate that the ratio of length to depth L/D within the range of 5–9 has little relevance to integral structures of cavity flow. The bevel angle of the rear wall does not alter the overall structure of the cavity flow within the range of 30°–60°, but it can exert obvious effect on the evolvement of shear layer and vortexes in cavities. __________ Translated from Journal of National University of Defense Technology, 2007, 29(3): 1–5 [译自: 国防科技大学学报]     

Study on direct measurement method of vorticity from particle images

To overcome the shortcomings of conventional methods for vorticity measurement, a new direct measurement of vorticity (DMV) method extracting vorticity from particle images was proposed. Based on the theory of fluid flow, two matched particle patterns were extracted from particle images in the DMV method. The pattern vorticity was determined from the average angular displacement of rotation between the two matched particle patterns. The method was applied on standard particle images, and was compared with the second and third order central finite difference methods. Results show that the accuracy of DMV method is independent of the spatial resolution of the sampling, and the uncertainty errors in the velocity measurement are not propagated into the vorticity. The method is applicable for measuring vorticity of a stronger rotational flow. The time interval of image sampling should be shortened to increase the measurement ranges for higher shearing distortion flows. __________ Translated from Journal of Zhejiang University (Engineering Science), 2006, 40(9): 1 644–1 647 [译自: 浙江大学学报 (工学版)]     

Assessment indices for uniform and non-uniform thermal environments

Different assessment indices for thermal environments were compared and selected for proper assessment of indoor thermal environments. 30 subjects reported their overall thermal sensation, thermal comfort, and thermal acceptability in uniform and non-uniform conditions. The results show that these three assessment indices provide equivalent evaluations in uniform environments. However, overall thermal sensation differs from the other two indices and cannot be used as a proper index for the evaluation of non-uniform environments. The relationship between the percentage and the mean vote for each index is established. __________ Translated from J Tsinghua Univ (Sci & Tech), 2006, 46(12): 1949–1952 [译自: 清华大学学报(自然科学版)]