Thrust Characteristics and Nozzle Role of Water Jet Propulsion

Ni, Yongyan,Liu, Weimin,Shen, Zhanhao,Pan, Xiwei Korean Society for Fluid machinery 2017 International journal of fluid machinery and syste Vol.10 No.1

Surface pressure integration and momentum method were respectively performed to evaluate the impeller thrust and the system thrust of a contra-rotating axial flow water jet propulsion, and an interesting phenomenon so-called thrust paradox was revealed. To explain the paradox, the impeller thrust and the system thrust were physically and theoretically analyzed, the results show that the impeller thrust is head involved and is determined by the hydraulic parameters upstream and downstream the impeller, while the momentum method depicted by a classic equation is valid simply under the best efficiency point. Consequently, the role of a water jet propulsion nozzle was deduced that the nozzle is mainly to limit the flow rate that crosses the impeller and to assure the system working under the best efficiency condition apart from its ability to produce momentum difference. Related mathematical formula expressed the nozzle diameter is the dominant variable used to calculate the working condition of the water jet propulsion. Therefore the nozzle diameter can be steadily estimated by the former expression. The system thrust scaling characteristics under various speeds were displayed lastly.

Numerical investigation on radial impeller induced vortex rope in draft tube under partial load conditions

Yongyan Ni,Renqing Zhu,Xiao Zhang,Zhong-yong Pan 대한기계학회 2018 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.32 No.1

The vortex rope phenomena appearing in a draft tube under partial load operations were investigated. The efforts were carried out by using a homogeneous equilibrium vapor-liquid two-phase model and a blending SST turbulence model, and the former takes account of the weak compressibility of mixed media. The vortex rope phenomena were induced by the radial impeller and three kinds of flow regimes were illustrated. Vortex rope was visible at some conditions and it displayed various patterns, while no obvious vortex rope was found under some conditions. It was found that the plant cavitation number determines that whether the vortex rope was visible or invisible. An interesting profile was that a secondary vortex filament ring entwining the vortex rope appeared clearly near the design condition. Both flow structures and pressure characteristics were studied to depict the vortex mechanism and the characteristics of the η-σ curves. Further analysis found that the shedding frequency of the vortex ring is similar with that of the precession movement.

An Outlook on Rotordynamic Pump Theory Development

Yongyan Ni,Zhongyong Pan 한국유체기계학회 2017 International journal of fluid machinery and syste Vol.10 No.2

ECHO progress was defined to depict the rotordynamic pump theory development. Experience (E) era for pumps lasted nearly one and a half hundred years before the Industrial Revolution due to the low rotation speed of motor and undeveloped manufacture ability. Classic (C) theory referring to quasi-static performance as well as the items those were not able to be steadily resolved under the level were briefly and sophisticated outlined. Since 1962, flow instabilities and the dynamic responses had come into main attention with the development of the modern technologies such as ballistic missile, rocket and space shuttle main engine, and were finally heuristically (H) elucidated by talented scholars and researchers. Recently, new applications for the pumps open (O) to the surrounding fluid and diversity of the medium such as multiphase flow need more studies and some examples were briefly introduced to display the potential problems lastly.

An Outlook on Rotordynamic Pump Theory Development

Ni, Yongyan,Pan, Zhongyong Korean Society for Fluid machinery 2017 International journal of fluid machinery and syste Vol.10 No.2

ECHO progress was defined to depict the rotordynamic pump theory development. Experience (E) era for pumps lasted nearly one and a half hundred years before the Industrial Revolution due to the low rotation speed of motor and undeveloped manufacture ability. Classic (C) theory referring to quasi-static performance as well as the items those were not able to be steadily resolved under the level were briefly and sophisticated outlined. Since 1962, flow instabilities and the dynamic responses had come into main attention with the development of the modern technologies such as ballistic missile, rocket and space shuttle main engine, and were finally heuristically (H) elucidated by talented scholars and researchers. Recently, new applications for the pumps open (O) to the surrounding fluid and diversity of the medium such as multiphase flow need more studies and some examples were briefly introduced to display the potential problems lastly.

Numerical analysis and experimental investigation on impeller-volute match characteristics

Yongyan Ni,Xiao Wang,Zhong-yong Pan 대한기계학회 2022 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.36 No.11

Impeller-volute match is an essential issue of pump dynamic characteristics and it is very important for the understanding of the flow features in the pumps and the vibration symptom of the device. Advanced performance diagnosis and smart operation and maintenance are profoundly dependent upon the perceiving of the rotor-stator interaction. In order to describe the interaction more comprehensively, the related flows were described by both theoretical approach and numerical simulations. Both velocity distribution and area-ratio aspect were theoretically indicated and a critical condition of non-shock criterion was proposed. Numerical efforts were therefore carried out and unveiled the flow regime as well as the pressure variations. The frequency properties of the pressure variations indicated that both the shaft rotation frequency and the blade passing frequency (BPF) dominated the contents, which implicitly demonstrated the accurate simulation work. Vibration content was lastly tested to validate the numerical results and the rotor-stator interaction effects. No significant shaft rotation contents appeared in the tested vibration signals due to the precise shaft support. Other than the blade passing frequency, both sub-synchronous and super-synchronous contents of BPFs appear under nearly all conditions. It is noted that the experimental means used here are able to get sufficient information of the pump operation.

Thrust Characteristics and Nozzle Role of Water Jet Propulsion

Yongyan Ni,Weimin Liu,Zhanhao Shen,Xiwei Pan 한국유체기계학회 2017 International journal of fluid machinery and syste Vol.10 No.1

Surface pressure integration and momentum method were respectively performed to evaluate the impeller thrust and the system thrust of a contra-rotating axial flow water jet propulsion, and an interesting phenomenon so-called thrust paradox was revealed. To explain the paradox, the impeller thrust and the system thrust were physically and theoretically analyzed, the results show that the impeller thrust is head involved and is determined by the hydraulic parameters upstream and downstream the impeller, while the momentum method depicted by a classic equation is valid simply under the best efficiency point. Consequently, the role of a water jet propulsion nozzle was deduced that the nozzle is mainly to limit the flow rate that crosses the impeller and to assure the system working under the best efficiency condition apart from its ability to produce momentum difference. Related mathematical formula expressed the nozzle diameter is the dominant variable used to calculate the working condition of the water jet propulsion. Therefore the nozzle diameter can be steadily estimated by the former expression. The system thrust scaling characteristics under various speeds were displayed lastly.

Vibrio parahaemolyticus cqsA controls production of quorum sensing signal molecule 3-hydroxyundecan-4-one and regulates colony morphology

Kui Wu,Yangyun Zheng,Qingping Wu,Haiying Chen,Songzhe Fu,Biao Kan,Yongyan Long,Xiansheng Ni,Junling Tu 한국미생물학회 2019 The journal of microbiology Vol.57 No.12

In order to adapt to different environments, Vibrio parahaemolyticus employed a complicated quorum sensing system to orchestrate gene expression and diverse colony morphology patterns. In this study, the function of the putative quorum sensing signal synthase gene cqsA (VPA0711 in V. parahaemolyticus strain RIMD2210633 genome) was investigated. The cloning and expression of V. parahaemolyticus cqsA in Escherichia coli system induced the production of a new quorum sensing signal that was found in its culture supernatant. The signal was purified by high performance liquid chromatography methods and determined to be 3-hydroxyundecan- 4-one by indirect and direct mass spectra assays. The deletion of cqsA in RIMD2210633 changed V. parahaemolyticus colony morphology from the classical ‘fried-egg’ shape (thick and opaque in the center, while thin and translucent in the edge) of the wild-type colony to a ‘pancake’ shape (no significant difference between the centre and the edge) of the cqsAdeleted colony. This morphological change could be restored by complementary experiment with cqsA gene or the signal extract. In addition, the expression of opaR, a well-known quorum sensing regulatory gene, could be up-regulated by cqsA deletion. Our results suggested that V. parahaemolyticus used cqsA to produce 3-hydroxyundecan-4-one signal and thereby regulated colony morphology and other quorum sensing-associated behaviors.