Research on active flow control to reduce aerodynamic drag of mira notchback model

Yingchao Zhang,Ruizhuo Zhou,Jinji Li,Hui Zhu,Haipeng Liu,Zhe Zhang,Chengchun Zhang 대한기계학회 2023 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.37 No.11

The lattice Boltzmann method, combined with the boundary layer model and the very large eddy simulation method, was used to simulate the MIRA notchback model to obtain an accurate unsteady flow field and a more reliable mean flow field. Based on the analysis of the tail flow state, jet holes were set up at the model tail. To analyze the effects of different jet states on the aerodynamic performance, constant jet method was used to explore the optimal values of blowing and sucking conditions, jet hole diameters and jet velocities at each position. The numerical results indicate that setting up the jet scheme can reduce the drag coefficient by inhibiting the longitudinal vortex and improving the wake structure of the model. A case of single jet placing jet holes at the bottom of the rear windshield can achieve 10 % drag reduction.

AERODYNAMIC CHARACTERISTICS OF MIRA FASTBACK MODEL IN EXPERIMENT AND CFD

Yingchao Zhang,Jintao Zhang,Kaiguang Wu,Zijie Wang,Zhe Zhang 한국자동차공학회 2019 International journal of automotive technology Vol.20 No.4

The lasting high fuel cost has recently inspired the resurgence in drag reduction research for vehicles, which calls for a thorough understanding of the vehicle wake. The acknowledged MIRA fastback vehicle model is characterized by similar real vehicle geometry, thus it is especially suitable for the above purpose. In spite of a considerable number of previous investigations, our knowledge of flow around this model remains incomplete. This paper aims to visit turbulent flow structure behind this model. An investigation has been conducted to measure the near wake flow structure of the MIRA 1/8 scale mode, using both Particle Image Velocimetry (PIV) experimental method and Computational Fluid Dynamics (CFD) simulation method. In order to capture the flow structure accurately, PIV measurement was performed in different sections along three orthogonal directions, and the CFD method acquired additional simulation results to catch the better flow status. Through the maps of the time-averaged vorticity, the instantaneous vorticity and the handled velocity vector from the PIV and CFD methods, we found out the formation mechanism of the transient flow of fastback model and summed up the schematic of flow structure. This study not only analyzed the vortex shedding characteristics of turbulent near wake, but more importantly provided insight into the complex three-dimensional features of the flow structure in the wakes of MIRA fastback model.

Insect cytokine growth-blocking peptide may regulate density-dependent phase trait of cuticular melanization in the larval armyworm, Mythimna separata

Zhang Yingchao,He Juan,Zhang Yuxia,Li Yue,Yu Yang,Jiang Xingfu,Pan Weidong 한국응용곤충학회 2020 Journal of Asia-Pacific Entomology Vol.23 No.2

Growth-blocking peptide (GBP) is a 25 amino acid insect cytokine found in lepidopteran insects that has diverse biological activities such as larval growth regulation, paralysis induction, cell proliferation and stimulation of immune cells. Density-dependent phase polyphenism is a phenomenon of phenotypic plasticity in which the expression of a variety of traits can be affected by local population density. In the present study, the armyworm Mythimna separata larvae with four rearing densities (1 larva/vial, 2 larvae/vial, 4 larvae/vial and 6 larvae/vial) were tested for cuticular melanization and body weight throughout the third-fifth instar, and the functional role of GBP in regulating the changes was investigated. The results indicated that when reared at high densities, the larvae exhibited less body weight and more degree of cuticular melanization than larvae reared at low densities. The gene expression of GBP in armyworm larvae showed an initial rise and then decline trend with increased rearing densities in the third to fifth instar. Compared with control, more degree of cuticular melanization was observed in GBP-injected larvae (500 ng/larva in volume 50 μL) than that in Ringer’s solution-injected counterparts. Furthermore, the gene expression level of dopa decarboxylase and prophenoloxidase increased significantly in GBP-injected fifth instar larvae from 6 h to 12 h after injection, suggesting the role of GBP in modulating density-dependent phase trait of armyworm cuticular melanization.

Direct Power Control of PWM Rectifier With Optimal Duty Ratio Under Unbalanced Network

Yongchang Zhang,Changqi Qu,Zhengxi Li,Yingchao Zhang,Longhan Cao 전력전자학회 2015 ICPE(ISPE)논문집 Vol.2015 No.6

Direct power control (DPC) attracted wide attention due to its advantages of simple structure, quick response, strong robustness and elimination of current regulation/PWM blocks. However, conventional table-based DPC cannot work well when grid voltage is unbalanced. This paper proposes an improved DPC by using a new definition of instantaneous reactive power. As a result, the distortion in grid current is eliminated and constant active power and new reactive power are obtained. Neither complicated calculation of power compensation nor positive/negative sequence extraction of grid voltage/current is required. The corresponding switching table suitable to regulate both active power and the new reactive power is established. Furthermore, the concept of duty cycle control is introduced to further improve the steady state performance of conventional DPC. Experimental results are presented to confirm the theoretical study and the effectiveness of the proposed method.

Vibration mechanism and improved phenomenological model of the planetary gearbox with broken ring gear fault

Yingchao Luo,Lingli Cui,Jianyu Zhang,Jianfeng Ma 대한기계학회 2021 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.35 No.5

Accurate modeling of the vibration signal model of planetary gearboxes is essential for the subsequent fault diagnosis. According to the existing improved phenomenological model based on the meshing vibration, this paper conducts further investigations on the vibration mechanism of the gearbox. The time delay phenomenon of faulty ring gear tooth participating in meshing is theoretically analyzed, and the assisted phases for experimental verification are proposed and deduced. Based on the improved model, the vibration signal under the fault condition is simulated and compared with the results of traditional methods. Subsequently, the paper proposes to divide and reconstruct this signal and use the maximum correlation kurtosis deconvolution (MCKD) to enhance its impact characteristics. The results show that the phase between the fault impact and its adjacent meshing impact is consistent with the proposed assisted phase. Finally, the correctness of the vibration mechanism and the improved phenomenological model are verified experimentally.

Red Imported Fire Ant in China

Runzhi Zhang,Yingchao Li 한국응용곤충학회 2005 한국응용곤충학회 학술대회논문집 Vol.2005 No.05

Investigation of aerodynamic behaviour of a high-speed train on different railway infrastructure scenarios under crosswind

Jiqiang Niu,Yingchao Zhang,Zheng-Wei Chen,Rui Li,Huadong Yao 한국풍공학회 2022 Wind and Structures, An International Journal (WAS Vol.35 No.6

The aerodynamic behaviour of a CRH high-speed train under three infrastructure scenarios (flat ground, embankment, and viaduct) in the presence of a crosswind was simulated using a 1/8th scaled train model with three cars and the IDDES framework. The time-averaged and instantaneous flow field around the model were examined. The employed numerical algorithm was verified through a wind tunnel test, and the grid and timestep resolution analyses were conducted to ensure the reliability of the data. It was noted that the flow around the rail line was different under different infrastructure scenarios, especially in the case of the embankment, which degraded the aerodynamic performance of the train under the crosswind. The flow around the train on the flat ground and viaduct was different, although the aerodynamic performance of the train was similar in both cases. Moreover, the viaduct accidents were noted to have the most critical consequences, thereby requiring the most attention. The aerodynamic performance of the train on the windward track of the embankment under the crosswind was worse than that of the train on the leeward track. But for the other two infrastructure scenarios, the aerodynamic performance of the train on the windward track is relatively dangerous, which is mainly caused by the head car. These observations suggest that the aerodynamic behaviour of the train on an embankment under a crosswind must be carefully considered and that certain wind protection measures must be adopted around rail lines in windy areas.

Effect of the Austenitizing Temperature on Microstructure Evolution and Impact Toughness of a Novel Bainite Ductile Iron

Yongjin Wang,Yingchao Zhang,Renbo Song,Liang Huang,Yu Pei 대한금속·재료학회 2021 METALS AND MATERIALS International Vol.27 No.10

The effect of austenitizing temperature on microstructure evolution and impact toughness of a newly developed Fe–3.0C–2.8Si–2.0Mn–0.9V–0.2Cr bainite ductile iron was investigated in this research. The ductile iron specimens were heat treatedunder different continuous cooling process, involving austenitizing between 900 and 980 °C and followed tempering at200 °C. Optical microscopy, X-ray diffraction, scanning electron microscope and transmission electron microscope tests wereconducted to investigate the microstructure evolution. Impact toughness and Rockwell hardness were measured. The resultsshowed that the microstructure of the ductile iron mainly consisted of graphite, acicular bainite and retained austenite aftercontinuous cooling process. The austenitizing temperature could change the volume fraction and size of bainite and retainedaustenite. There existed a C-area, where retained austenite accumulated near the graphite, except for specimen austenitizedat 920 °C. The impact toughness of specimens increased first and then get worse with the increasing of austenitizing temperature. The impact toughness was related with the volume fraction of bainite and the morphology of retained austenite. The fracture mechanism of the bainite ductile iron belonged to cleavage fracture. Chunky graphite acted as the source ofmicrocrack during the impact process. The bulky retained austenite behaved as a prior path for the microcrack propagation,while the bainite and thin filmy retained austenite limited its propagation.

Fermentation characteristics, chemical composition and microbial community of tropical forage silage under different temperatures

Dongxia Li,Kuikui Ni,Yingchao Zhang,Yanli Lin,Fuyu Yang 아세아·태평양축산학회 2019 Animal Bioscience Vol.32 No.5

Objective: In tropical regions, as in temperate regions where seasonality of forage production occurs, well-preserved forage is necessary for animal production during periods of forage shortage. However, the unique climate conditions (hot and humid) and forage characteristics (high moisture content and low soluble carbohydrate) in the tropics make forage preservation more difficult. The current study used natural ensiling of tropical forage as a model to evaluate silage characteristics under different temperatures (28°C and 40°C). Methods: Four tropical forages (king grass, paspalum, white popinac, and stylo) were ensiled under different temperatures (28°C and 40°C). After ensiling for 30 and 60 days, samples were collected to examine the fermentation quality, chemical composition and microbial community. Results: High concentrations of acetic acid (ranging from 7.8 to 38.5 g/kg dry matter [DM]) were detected in silages of king grass, paspalum and stylo with relatively low DM (ranging from 23.9% to 30.8% fresh material [FM]) content, acetic acid production was promoted with increased temperature and prolonged ensiling. Small concentrations of organic acid (ranging from 0.3 to 3.1 g/kg DM) were detected in silage of white popinac with high DM content (50.8% FM). The microbial diversity analysis indicated that Cyanobacteria originally dominated the bacterial community for these four tropical forages and was replaced by Lactobacillus and Enterobacter after ensiling. Conclusion: The results suggested that forage silages under tropical climate conditions showed enhanced acetate fermentation, while high DM materials showed limited fermentation. Lactobacillus and Enterobacter were the most probable genera responsible for tropical silage fermentation.

Role of Subordinate Phases on the Dry Impact‑Abrasion Behavior of Low Chromium Cast Iron

Yu Pei,Renbo Song,Yi Li,Zhiyang Zhao,Yingchao Zhang 대한금속·재료학회 2020 METALS AND MATERIALS International Vol.26 No.12

In order to study the resistance mechanism of materials having high resistance to impact-abrasion, synergistic effect ofsubordinate phases of 2.20 wt%C–3.45 wt%Cr–3.06 wt%Mn–1.32 wt%Si–0.51 wt%Cu–0.31 wt%Ni–0.002 wt%B cast ironwas investigated under dry impact-abrasion. Subordinate phases consist of graphite, secondary precipitates and retainedaustenite. Results show that the synergistic effect of above subordinate phases can prevent matrix and carbide from peelingoff, and minimize the damage of carbide to matrix. This effect reduces the depth and width of groove from 7 to 1.2 μm andfrom 14 to 2.5 μm respectively. Above significant improvement is owing that: (1) Graphite can disperse external/internalstress, and fill carbide peeling pits. (2) Secondary precipitates, such as [Fe, Ni] and [Cr, Ni], can disperse the concentratedstress of carbide, inhibiting peeling. (3) Retained austenite can disperse the internal concentrated stress which is transferredfrom the carbide and fine precipitates to matrix.