1,720,970 research outputs found
Comparative Numerical Investigation on Flow Characteristics of Pump-Jets with Accelerating Duct and Decelerating Duct
No full textThe mutual interaction between the duct and components of pump-jet can induce significant
effects on the overall flow properties and inner flow field. In order to compare the properties of pumpjets
with accelerating and decelerating ducts and investigate the effects of duct profiles parameters of
two different ducts on the flow characteristics, a detailed numerical analysis is implemented on the flow
characteristics and interaction of the pump-jet with different duct profile parameters. Beforehand, the
comparison of experiment and simulation of propeller VP1304 and the pump-jet under mooring
conditions are adopted to validate numerical methodology. In this paper, five cambers f (f=0.5t, 0.25t, 0,
-0.25t, -0.5t) and three angles of attack α (α= 4°, 0°, -4°) of duct profile, employed to distinguish
accelerating and decelerating ducts, are considered carefully, focusing on the flow field information and
propulsion performance. The results, including the comparison of single ducts with different f and α, and
comparison of pump-jet with 2 types of ducts distinguished by different f and α, are exhibited. It shows
that the flow velocity at the outlet of the accelerating ducts is significantly higher compared to the inlet
velocity, as opposed to the phenomenon produced by decelerating ducts. Compared with the change of
α, the variation of f makes the internal evolution of the flow field more intuitive. Further results indicate
that the maximum efficiency of pump-jet drops after the modest growth as the cambers decrease, whose
location shift towards the lower advance coefficient J. The alteration of α leads to making the trend more
direct and apparent for the decelerating and accelerating ducts. It is advantageous for the high f to the
cavitation resistance of inside components, like rotor blades and stator blades. The impacts of changing
α on the distribution of pressure in pump-jets with accelerating and decelerating ducts are more
prominent than changing f. Moreover, the effects of both variations of f and α on the circumferential
distributions of the velocity components are prominent, while there are still significant differences
between these changes. Additionally, the velocity distribution at the inlet of pump-jets with decelerating
ducts is higher than that at the outlet, and the velocity distribution of pump-jets with accelerating ducts
presents the opposite pattern
The comparative transient prediction on hydrodynamic characteristics and flow field properties of pump-jets with accelerating and decelerating ducts
No full textPump-jet holds a pivotal position in various marine applications, underscoring the need for comprehending their transient behavior for the purpose of design enhancement and performance refinement. This paper employs Reynolds-averaged Navier-Stokes equations method in conjunction with Detached Eddy Simulation model. The study delves into the ramifications of accelerating and decelerating ducts, distinguished by camber f and attack angles α, on transient hydrodynamic characteristics. The hydrodynamic characteristics are investigated numerically, after the validation of the numerical methodology by comparing simulation outcomes against experimental results. Subsequently, the study delves into propulsion characteristics, followed by an exploration of time-domain and frequency-domain data transformed through fast Fourier transform to analyze thrust fluctuations and pulsating pressures. Additionally, a detailed examination of pressure distribution and velocity field is provided, aiming to dissect the mechanisms through the variations in f and alpha influence the flow field. Findings suggest that the outlet velocity of accelerating ducts significantly surpasses the inlet velocity, a behavior contrasted by decelerating ducts. Notably, the patterns of accelerating and decelerating ducts resulting from alterations in f exhibit consistent characteristics with those brought about by changes in α. However, several opposite characteristics surface in transient flow field due to the distinct modifications in the duct profile. Furthermore, by considering vorticity magnitude distribution and vortices, a comparative analysis elucidates the effects of varying f and α on rotor and stator trailing vortices. This contributes to understanding the flow instability mechanism under differing duct configurations. It is evident that changes in f and α exert significant influence on both performance and flow field
A Review on Hydrodynamic Performance and Design of Pump-Jet: Advances, Challenges and Prospects
Get PDFA pump-jet, which is generally and widely adopted on underwater vehicles for applications from deep sea exploration to mine clearing, consists of a rotor, stator, and duct, with the properties of high critical speed, high propulsion efficiency, great anti-cavitation performance, and low radiated noise. The complex interaction of the flow field between the various components and the high degree of coupling with the appendage result in the requirements of in-depth research on the hydrodynamic performance and flow field for application and design. Due to the initial application on the military field and complicated structure, there is scant literature in the evaluation of pump-jet performance and optimal design. This paper, in a comprehensive and specialized way, summarizes the pump-jet hydrodynamic performance, noise performance, and flow field characteristics involving cavitation erosion and vortices properties of tip-clearance, the interaction between the rotor and the stator and the wake field, as well as the optimal design of the pump-jet. The merits and applications range of numerical and experimental methods are overviewed as well as the design method. It also concludes the main challenges faced in practical applications and proposes a vision for future research. It was found that the compact structure and complex internal and external flow field make the pump-jet significantly different, also leading to higher performance. As the focus of cavitation research, vortices interact with the complex structure of the pump-jet, leading to instabilities of the flow field, such as vibration, radiated noise, and cavitation erosion. The effective approaches are adopted to reduce radiated pump-jet with minimal influence on the hydrodynamic performance, such as eliminating the tip clearance and installing the sawtooth duct. Advanced optimal technology can achieve high performance, cavitation performance, and acoustic performance, possessing good prospects. Further developments in investigation and the application of pump-jets in the multidisciplinary integration of fluid dynamics, acoustics, materials, chemistry, and bionics should be the main focus in future research
Effect of Tip Clearance on the Internal Flow and Hydraulic Performance of a Three-Bladed Inducer
Get PDFThe influence of the tip clearance on the internal flow and hydraulic performances of a 3-bladed inducer, designed at ALTA, Pisa, Italy, are investigated both experimentally and numerically. Two inducer configurations with different blade tip clearances, one about equal to the nominal value and the other 2.5 times larger, are considered to analyze tip leakage effects. The 3D numerical model developed in ANSYS CFX to simulate the flow through the inducer with 2 different clearances under different operating conditions is illustrated. The internal flow fields and hydraulic performance predicted by the CFD model under different operating conditions are compared with the corresponding experimental data obtained from the inducer tests. As expected, both experimental and numerical results indicate that higher pressure rise and hydraulic efficiency are obtained from the inducer configuration with the nominal tip clearance
Experimental and numerical study on hydraulic performances of a turbopump with and without an inducer
Get PDFThe hydraulic performance of a centrifugal turbopump with and without a 3-bladed axial inducer has been studied both experimentally and numerically. A 3D numerical model has been used to simulate the flow through from the inlet to the outlet ducts of the turbopump with and without an inducer using the ANSYS CFX code. The sensitivity of the numerical results has been analyzed with reference to the adopted turbulent flow models, to the length of the input and output ducts included in the simulations, to the reference positions used for the evaluation of the total pressure rise and to the temperature of the operating fluid. The measured and predicted hydraulic performances of the turbopump with and without the inducer have been compared under different operating conditions. As expected, the predicted hydraulic performance of the turbopump is significantly influenced by the lengths of the inlet and outlet ducts, the turbulence models and, at low flow rates, the reference positions of the total pressure rise measurements. The pressure rise coefficients obtained from the simulations using an inlet duct with length of 3 rTi and 10 rTi were significantly lower than the experimental results, while at low flow rates those referring to the inlet duct with length greater than 10 rTi were significantly higher than those obtained for the shorter inlet duct. With reference to the effect of the pressure measurement locations, the difference between the numerical results of the pressure rise coefficient and the experimental values was much higher when the data were obtained at the locations where the transducers was mounted in the experimental tests at lower flow rates. Moreover, the hydraulic performance of the turbopump at lower flow rates can be significantly influenced by the use of the upstream inducer, with a pressure drop of 20% in particular at 60% of the design flow rate
Geometry Effects on Flow Instabilities of Different Three-Bladed Inducers
No full textThe paper presents the results of an activity carried out on a three-bladed inducer and compares the experimental data from other similar inducers. All the inducers considered in the present study have been designed by means of the simplified analytical model recently developed by some of the authors. The main effects of different geometrical solutions on hydraulic performance and flow instabilities of the pumps under noncavitating and cavitating conditions are presented in the paper
Study on Hydraulic Performances of a 3-Bladed Inducer Based on Different Numerical and Experimental Methods
Get PDFThe hydraulic performances of a 3-bladed inducer, designed at Alta, Pisa, Italy, are investigated both experimentally and numerically. The 3D numerical model developed in ANSYS CFX to simulate the flow through the inducer and different lengths of its inlet/outlet ducts is illustrated. The influence of the inlet/outlet boundary conditions, of the turbulence models, and of the location of inlet/outlet different pressure taps on the evaluation of the hydraulic performance of the inducer is analyzed. As expected, the predicted hydraulic performance of the inducer is significantly affected by the lengths of the inlet/outlet duct portions included in the computations, as well as by the turbulent flow model and the locations of the inlet/outlet pressure taps. It is slightly affected by the computational boundary conditions and better agreement with the test data obtained when adopting the k - ω turbulence model. From the point of the pressure tap locations, the pressure rise coefficient is much higher when the inlet/outlet static pressure taps were chosen in the same locations used in the experiments
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
- …
