最新刊期
卷 57 ， 期 5 ， 2023
- 摘要：The passive passing of fish through the pump station leads to a high proportion of injuries and deaths. To balance the operation efficiency and the safety of fish passing through the pump, this paper employs the computational fluid dynamics in combination with the fish damage model and the genetic algorithm to carry out multi-objective optimization research. Based on the sensitivity analysis, the significant factors affecting the performance of the tubular pump and the survival rate of fish are selected respectively. The optimal Latin hypercube sampling, Kriging model and NSGA-Ⅱ algorithm are used to construct a multi-objective optimization system. Finally, one optimization scheme with the optimal efficiency(A), one with the highest fish survival rate(C)and one that balances both(B)are obtained by assigning weight factors. The results show that the efficiency of scheme A rises by 5.2% and the fish survival rate of scheme C increases by 49.4%, compared with the initial design. The blade wrap angle, chord height and blade forward-extended angle are the key factors affecting hydraulic performance. In contrast, the blade forward-swept angle, forward-extended angle and blade thickness are the critical factors influencing the fish survival rate. Among these factors, the forward-extended angle exhibits opposite influence on the hydraulic performance and fish survival rate. In addition, the mortality by blade strike highly affects the survival rate of fish passing through the pump, while the strike probability has a small impact on this. The survival rate of fish can be improved by increasing the thickness of the blade leading edge, enlarging the blade forward-swept angle and reducing the forward-extended angle. The research results in this paper provide a reference for the ecological-protection-oriented development of large pump stations in China.关键词：bulb tubular pump;survival rate of fish;eco-friendly design;sensitivity analysis;multi-objective optimization127|10|0更新时间：2025-07-09
- 摘要：Based on previous studies, this paper proposes a novel multi-stage swirl cooling structure with different-side nozzles to further enhance the leading-edge swirl cooling and heat transfer uniformity of gas turbine blades, and tackle high pressure loss caused by flow deflection between adjacent stages of the multi-stage swirl cooling structure at the leading edge. The models of the original multi-stage swirl cooling structure on the same side and the new multi-stage swirl cooling structure on the different side are established; the flow and heat transfer characteristics of these two swirl cooling structures at multiple inlet Reynolds numbers are analyzed and compared with the three-dimensional steady numerical simulation method under constant target surface temperature. The calculation results show that the coolant is injected into the swirl chamber through tangential nozzles to form high-speed swirl flow, which significantly improves the heat transfer capacity. For single-stage swirl cooling, the circumferential velocity of coolant gradually decreases while the axial velocity increases, leading to the gradual formation of a cross flow. The cross flow impacts the downstream jet flow and weakens the downstream heat transfer. The multi-stage swirl cooling structure can inhibit the cross flow, and the average circumferential Nusselt number is increased obviously. However, the flow deflection between the adjacent stages of the original multi-stage swirl cooling structure on the same side brings high pressure loss. With the advantages of the original model, the multi-stage cooling structure on the different side reduces the pressure loss by 22%, improves the uniformity of coolant distribution, and further enhances the overall heat transfer performance of the swirl cooling structure.关键词：blade leading-edge;multistage swirl cooling;heat transfer enhancement;cross flow suppression65|23|0更新时间：2025-07-09
- 摘要：To further optimize the cooling performance at the vane leading edge of the modern advanced high-pressure turbine, this paper establishes a NASA C3X turbine vane model in which the upstream chamber is subject to the array impingement-film composite cooling. Fluid-solid conjugate heat transfer analyses are conducted to numerically investigate the flow and heat transfer characteristics of the coolant inside the vane. The effect of second-impingement structure on the composite cooling performance of the leading edge is studied with the amount of coolant mass flux in the common range. The results show that the second-impingement has little effect on convective heat transfer of the target, but can enhance the convective heat transfer intensity of the coolant in the whole flow path. The second-impingement can also balance the distribution of coolant in film holes in different regions and effectively reduce the temperature of the solid domain near film holes, especially for the leading-edge area with the showerhead. Meanwhile, under the heat conduction of the solid domain, the low temperature area near film holes will affect the region nearby, causing a reduction in overall temperature. In addition, the second-impingement significantly improves the composite cooling of the vane surface, especially the leading edge. The optimizing effect on the upstream surface generally increases first and then decreases with the increase of the mass flux of coolant, reaching a highest value of about 4.44% when M is 1.25%. The optimizing effect on the leading edge generally decreases first and then increases with the increase of the mass flux of coolant, reaching a highest value of about 9.66% when M is 1.50%, and a lowest value of about 11.70% when M is 2.25%.关键词：leading-edge;conjugate heat transfer;impingement cooling;film cooling108|23|0更新时间：2025-07-09
- 摘要：In this paper, a dimensionless evaluation model is established based on the container size(a)and spray parameter(b)to realize the accurate and rapid evaluation of the global thermodynamic performance in the near-isothermal compressed air energy storage process with a liquid piston. Research is conducted on the variation of thermodynamic parameters during the near-isothermal compressed air energy storage process. Finally, the significant effect of liquid piston on the compressed air energy storage system is clarified. The results show that, without spraying, the air-side relative temperature changes gently when the dimensionless number of a reaches 120, which indicates that the liquid piston can realize near-isothermal compression. However, a smaller value of a can result in dramatic change of the air-side relative temperature. Under the spraying condition, the near-isothermal compression mainly occurs in the middle stage of the compression process, and the increase of the dimensionless number of b can weaken the effect of a on the air-side relative temperature. The efficiency of near-isothermal compression with a liquid piston can be higher than 95% under ideal conditions, but with a D155-30 water pump under experimental conditions, it can only be 66%.关键词：compressed air energy storage;near-isothermal compression;thermodynamic performance;dimensionless analysis85|13|0更新时间：2025-07-09
- 摘要：In order to suppress the formation and development of cavitation in the flow field around the hydrofoil, this paper establishes a new hydrofoil with its profile optimized by comparing and analyzing the performance of three classical hydrofoils, NACA0009, NACA0012 and Clark Y under different working conditions. Then, several fluid control structures are uniformly arranged on the new hydrofoil, and optimized rapidly by generalized pattern search algorithm to realize general and local control of cavitation in the flow field. The results show that the new hydrofoil has a suction surface whose bulge height is between those of the NACA0012 and Clark hydrofoils, and its maximum bulge position is backward. The new hydrofoil shows improved cavitation performance(cavitation shedding suppressed)and hydrodynamic performance(backflow development suppressed), with its lift-drag ratio up by as high as 48.8%. The multiple control structures evenly arranged on the suction surface of the new hydrofoil can continuously suppress the backflow and improve the pressure distribution. They are accurately and rapidly optimized with an optimization algorithm. As a result, the performance of the optimized hydrofoil is further improved, with the lift-drag ratio further up by 4.8%—13.6%, and the thickness and length of cavitation reduced. Therefore, optimizing the profile and adding continuous flow control structures can realize the overall and local control of the cavitation flow field, providing an effective way to improve the cavitation and hydrodynamic performance of the hydrofoil.关键词：cavitation;profile optimization;flow control structures;new hydrofoil;optimization algorithm108|90|0更新时间：2025-07-09
- 摘要：This paper aims to clarify the motion state, dispersion distribution and film spreading characteristics of the liquid injected during the compression process of the single screw compressor, and realize the rational control of liquid injection parameters. A three-dimensional space-twisted groove model of a single spiral groove is established according to the basic structure of the single screw compressor and the spatial meshing principle of multicolumn envelope meshing pair. The model is simplified according to the geometric characteristics of the spiral groove and the relative motion relationship of the meshing pair. Based on the simplified model, the water-steam two-phase flow process in the working chamber is numerically simulated during the injected liquid compression process by using computational fluid dynamics software. Then, analysis is carried out on the dispersion distribution and film forming characteristics of the injected liquid in the pressurizing channel under variable working conditions, as well as on the influence of key operating parameters such as the medium pressure and temperature, screw rotation speed, liquid injection flow rate and speed. The results show that the injected liquid converges on the wall to form a film, and the average thickness of the formed film decreases with the increase of pressure. When the temperature in the cavity rises from 80 ℃ to 200 ℃, the average thickness of the liquid film does not change much, i.e. fluctuating within 8.3%. If the rotating speed of the screw rotor is too high or the liquid spraying speed is too low, the injected liquid will be driven out of the channel by the star wheel before reaching the wall, thus reducing the cooling effect in the compression process. The average thickness of the liquid film can be effectively improved by increasing the spray liquid flow rate, which can effectively prevent leakage.关键词：single screw compressor;liquid injection;computational fluid dynamics;film forming characteristics51|5|0更新时间：2025-07-09
- 摘要：In this paper, core engine components of a 10 kW free piston Stirling generator with a linear heat pipe coupled is taken as an example to illustrate the basic heat transfer and resistance characteristics of the oscillating flow heat exchanger of a thermoacoustic engine. By equating a 3D model, the Sage 1D model and CFD 2D model are adopted respectively to characterize the distribution of basic state parameters and time-averaged energy of the alternating flow heat transfer unit under rated operating conditions. The results show that the Sage 1D model is similar to the CFD 2D model in terms of the heat transfer distribution characteristics and the total amount of heat transfer calculated. The Sage 1D model can better capture the transient and time-averaged characteristics in the heat exchanger. However, the sudden cross-sectional losses at the heat exchanger interface calculated with the Sage 1D model deviate greatly from those calculated by the CFD 2D model. As a result, a local drag correction coefficient is proposed based on the resistance values calculated with the CFD 2D model, and according to the effective pressure drop and effective velocity at the abrupt cross-section. After the correction coefficient is used in the Sage model, the drag characteristics obtained using this model basically match those acquired using the CFD 2D model. The resultant heat exchanger characteristics and analysis method can be used to guide the research and engineering design of other thermoacoustic heat exchangers, exhibiting their general applicability.关键词：thermoacoustic heat engine;oscillating flow heat exchanger;heat transfer characteristics;resistance characteristics;local resistance correction49|13|0更新时间：2025-07-09
- 摘要：In this study, three-dimensional cryogenic target models are established based on the discrete ordinates radiation model and Boussinesq hypothesis to investigate the perturbations of capsule thermal distribution caused by the use of capsule supports. Variations of temperature and flow field distributions as well as the sensitivity to helium pressure in hohlraum with different capsule supports are obtained. Finally, the influence of foam material parameters of the foam shell support is investigated. The results show that the targets using tent and polar tent supports have more uniform capsule temperature distribution than those with the fill-tube support and rod support as a result of the weakened natural convection inside the hohlraum. The tent support is more effective than the polar tent support due to its better film arrangement. For the two types of non-film supports, the pure fill-tube support provides the worst temperature uniformity due to its larger fill-tube diameter when compared with the rod support. Under typical operating conditions, the capsule with tent support has the smallest maximum temperature difference of 2.45 mK; the maximum temperature differences of the capsule with the polar tent support, fill-tube support and rod support are 5.92%, 32.71% and 17.99% higher, respectively. Moreover, the temperature uniformity deteriorates with the increase of helium pressure for the four support types. The temperature uniformity of the tent support and polar tent support is less sensitive to the helium pressure change. For the foam shell support, a more uniform capsule temperature distribution can be obtained by choosing a foam shell with higher thermal conductivity and smaller thickness. The calculation results can serve as a theoretical basis to some extent for the engineering design of the capsule support.关键词：cryogenic target;capsule supports;temperature characteristic;numerical simulation49|56|0更新时间：2025-07-09
- 摘要：In this paper, a line longitudinal protection method based on improved variational mode decomposition(VMD)and abrupt energy is proposed to effectively identify faults in ring-shaped DC distribution network, improve the protection reliability, selectivity, speed and sensitivity, and ensure the stable operation of the system. To use the VMD algorithm, the number of modes that matters to the decomposition effect needs to be set first. Hence the Sparrow search algorithm(SSA)is used to find a better number of modes for the VMD algorithm so as to ensure optimal decomposition effect under this parameter. Then a protection scheme is devised according to the difference of abrupt energy at the head and tail of the line. The voltage and current fault components collected are decomposed by SSA-VMD to obtain several modal components and calculate their abrupt energy. The internal and external fault criteria are developed according to the difference of abrupt energy in the areas separated by the direct current reactor. The fault pole criteria are developed according to the difference of the abrupt energy ratio between positive and negative poles at the time of failure. A circular DC distribution network mo-del is built in PSCAD／EMTDC, and the protection method is validated by MATLAB. The results show that the proposed method works quickly(within 3 ms)and reliably for different types of faults. It can identify both internal and external faults, realize fault pole selection and protect the full length of the line. It can also well withstand transition resistance(up to 20 Ω). Under a noise level of 40 dB, it can still identify faults and resist jamming to a certain extent.关键词：DC distribution network;variational mode decomposition;sparrow search algorithm;abrupt energy;relay protection52|12|0更新时间：2025-07-09
- 摘要：This paper is compiled with a view to optimize the discharge voltage form of diamond-like carbon film prepared by organic gas discharge in a hollow cathode structure, and to understand the discharge plasma composition and energy characteristics. This paper examines the characteristics of hollow cathode methane discharge plasma under different discharge voltage forms(DC voltage and repetition frequency pulse voltage)through emission spectroscopy diagnosis and numerical simulation. The results show that when the average discharge current is close, the dissociation degree of methane molecules under DC voltage is higher than that under repetition frequency pulse voltage. The dissociation of methane molecules can be promoted by increasing the DC voltage or pulse voltage amplitude, the pulse width and the pulse frequency. The proportion of single carbon ions in methane discharge plasma varies greatly under different discharge voltage forms. The discharge plasma is not fully developed and its electron energy is higher under repetition frequency pulse voltage, which is conducive to the generation of single carbon ions and makes the proportion of single carbon ions higher. The energy distribution of ions reaching the substrate under different discharge voltage forms is obtained by the deceleration electric field method. It is found that the ion energy under repetition frequency pulse voltage is higher and shows a bimodal distribution while the ion energy under DC voltage presents a unimodal distribution. The ion energy is positively correlated with the applied DC voltage or pulse voltage amplitude.关键词：diamond-like carbon film;discharge voltage form;dissociation degree of methane molecules;proportion of single carbon ions;ion energy distribution41|50|0更新时间：2025-07-09
- 摘要：Existing research suggests low accuracy of gesture recognition based on the WiFi sensing technology because of difficulties in extracting hard-to-recognize perceptual features. To solve this problem, this paper, through multidimensional reconstruction of perceptual data and two-dimensional discrete wavelet transform, proposes a high-precision gesture recognition model WiGNet based on the convolutional neural network. Firstly, based on the analysis of influence factors of channel state information, the amplitude data is extracted as the base data for gesture recognition; secondly, the perception data is reconstructed into a multidimensional matrix to fully extract the spatio-temporal characteristics of gestures; next, the two-dimensional discrete wavelet transform is applied to the reconstructed data in the temporal and spatial dimensions to reduce noise and smooth the perceptual data; finally, a neural architecture search technique is used to optimise the network depth and rationalise the number of convolutional kernels. Thus WiGNet, a gesture recognition model that can be better adapted to reconstructed data, is proposed. The experimental results show that the model significantly improves the feature identification accuracy and has a higher overall operation speed after the perception data is processed by two-dimensional discrete wavelet transform. WiGNet achieves an average recognition accuracy of 98.1% and 96.0% based on the self-built dataset and the public dataset respectively, outperforming similar models. In addition, WiGNet can not only achieve high-precision gesture recognition, but also maintain a fast computing speed and have a certain degree of robustness.关键词：channel state information;gesture recognition;two dimensional discrete wavelet transform;convolutional neural network41|19|0更新时间：2025-07-09
- 摘要：This paper proposes a stock index enhanced quantitative trading strategy based on machine learning and realizes programmed automatic trading to obtain the excess return of the benchmark stock index through short-term trading. First, the initial feature set of the stock index is generated, and the 21-dimensional features are screened by the maximum information coefficient method. Then a double-threshold unbalanced label and three prediction classification methods(T, B-B, B-T)are designed. In addition, different machine learning models are built and compared to obtain the optimal machine learning models for the long-short trading direction: LSTM-B-T model and RF-B-T model respectively. After that, a two-dimensional gamma function based on intraday rise and fall is designed. Finally, ups and downs are determined and trading signals obtained using the class probability discrimination threshold calculated by the two-dimensional gamma function and the class probability predicted by the optimal machine learning models. This strategy is applied to the backtesting and simulation trading verification of the CSI 500 ETF. The experimental results show that, compared with the random position opening strategy, the trading strategy proposed in this paper makes the transaction evaluation index improve on the whole. This strategy can obtain the ideal excess return of the benchmark index in both backtesting and three-month simulation trading verification, which are 11.24% and 11.08% respectively.关键词：stock index;exponential augmentation;quantitative trading;programmatic trading;2D gamma function;machine learning48|44|0更新时间：2025-07-09
- Technical support is provided by Beijing Founder electronics co., LTD 京ICP备09064830号-19
京公网安备11010802024621 - It is recommended to read the content of this site in Chrome&IE9+. Please switch to extreme mode in browser 360.
- Cookies We use cookies to help provide and enhance our service and tailor content. By continuing, you agree to the use of cookies.
0