scholarly journals Modelling of confined vortex rings

2015 ◽  
Vol 774 ◽  
pp. 267-297 ◽  
Author(s):  
Ionut Danaila ◽  
Felix Kaplanski ◽  
Sergei Sazhin
Keyword(s):  
Vortex Ring ◽  
Vortex Rings ◽  
Translational Velocity ◽  
Ring Model ◽  
Axisymmetric Vortex ◽  
Integral Characteristics ◽  
Practical Engineering ◽  
Time Variations ◽  
Physical Features ◽  
Phd Thesis

This paper is focused on the investigation of vortex rings evolving in a tube. A new theoretical model for a confined axisymmetric vortex ring is developed. The predictions of this model are shown to be in agreement with available experimental data and numerical simulations. The model combines the viscous vortex ring model, developed by Kaplanski & Rudi (Phys. Fluids, vol. 17, 2005, 087101), with Brasseur’s (PhD thesis, Stanford University) approach to deriving a wall-induced streamfunction correction. Using the power-law assumption for the time variation of the viscous length of the vortex ring, the time variations of the main integral characteristics, circulation, kinetic energy and translational velocity are obtained. Direct numerical simulation (DNS) is used to test the range of applicability of the model and to investigate new physical features of confined vortex rings recently reported in the experimental study by Stewart et al. (Exp. Fluids, vol. 53, 2012, pp. 163–171). The model is shown to lead to a very good approximation of the spatial distribution of the Stokes streamfunction, obtained by DNS. The vortex signature and the time evolution of the energy of the vortex are also accurately predicted by the model. A procedure for fitting the model with realistic vortex rings, obtained by DNS, is suggested. This opens the way to using the model for practical engineering applications.

On Approximating the Translational Velocity of Vortex Rings

2013 ◽  
Vol 135 (12) ◽  
Author(s):  
Michael Krieg ◽  
Kamran Mohseni
Keyword(s):  
Radial Velocity ◽  
Vortex Ring ◽  
Vortex Rings ◽  
Jet Flows ◽  
Volume Flux ◽  
Translational Velocity ◽  
Vortex System ◽  
Ring Configuration ◽  
Wide Range ◽  
Total Circulation

A method is presented whereby the translational velocity of a vortex ring can be approximated from the total circulation, impulse, and kinetic energy of the vortex system. Assuming a uniform vorticity density, these bulk quantities define a unique stable vortex ring configuration, and the translational velocity can be inferred from this configuration and the system scaling. Here, the accuracy of this approximation is presented for vortex rings formed from starting jets, and the translational velocity is also characterized as it relates to the driving parameters. The translational velocity is well approximated for a wide range of experimentally generated vortex rings. It is observed that starting jets with a converging radial velocity create vortex rings with a significantly higher translational velocity. The converging radial velocity was observed to increase translational velocity by as much as 30% over parallel jet flows with identical volume flux and nozzle diameter, but the exact increase is specific to the nozzle arrangement and driving conditions.

Flow Visualization for Pulsatile Vortex Ring Actuators

2008 ◽  
Author(s):  
Torin K. Clark ◽  
Michael Krieg ◽  
Kamran Mohseni
Keyword(s):  
Flow Visualization ◽  
Vortex Ring ◽  
Semimajor Axis ◽  
Time History ◽  
Vortex Rings ◽  
Translational Velocity ◽  
Vortex Ring Formation ◽  
History Of ◽  
Formation And Evolution ◽  
Visualization Techniques

Formation and evolution of vortex rings produced from pulsatile vortex ring thrusters are studied using flow visualization techniques. A vortex ring thruster consists of a cavity with an orifice at one end and an oscillating plunger at the opposite end which periodically creates a volume change in the cavity forcing a jet emission of fluid through the orifice into the surrounding reservoir. The ratio of the cylindrical jet length to its diameter, known as the stroke ratio, is a primary factor in the vortex ring formation characteristics. Flow visualization is employed in order to measure the translational velocity of the leading vortex ring for the range of stroke ratios of 2.96–5.92. The velocity time history of the vortex rings is studied with the results comparing well with theoretical approximations. Additionally vortex ring dimensions, including semimajor axis, semiminor axis, the ratio of these dimensions, and core to core radius, are considered. Also the volume of the vortex ring atmosphere is studied. The variations of these parameters with respect to stroke ratio, time, and distance from the orifice are investigated.

Generation and characteristics of vortex rings free of piston vortex and stopping vortex effects

2016 ◽  
Vol 811 ◽  
pp. 138-167 ◽  
Author(s):  
Debopam Das ◽  
M. Bansal ◽  
A. Manghnani
Keyword(s):  
Vortex Ring ◽  
Early Stage ◽  
Bubble Diameter ◽  
Velocity Variation ◽  
Vortex Rings ◽  
Translational Velocity ◽  
Core Diameter ◽  
Stage Of Development ◽  
Theoretical Predictions ◽  
Ring Diameter

This paper presents a novel method for generating vortex rings that circumvents some of the drawbacks associated with existing methods in producing them. The predominant effects that occur in previously used methods are due to the presence of some of the other vortices such as the stopping vortex, piston vortex, image vortex and orifice lip generated vortices in the early stage of development. These disturbances influence the geometric, kinematic and dynamic characteristics of a vortex ring and lead to mismatches with classical theoretical predictions. It is shown in the present study that the disturbance free vortex rings produced follow the classical theory. Flow visualization and particle image velocimetry experiments are carried out in the Reynolds number (defined as the ratio of circulation ($\unicode[STIX]{x1D6E4}$) and kinematic viscosity ($\unicode[STIX]{x1D708}$)) range, $2270<Re_{\unicode[STIX]{x1D6E4}}<6790$, to find the translational velocity, total and core circulation, core diameter, ring diameter and bubble diameter. In reference to the earlier studies, significant differences are noted in the variations of the vortex ring diameter and core diameter. A model for the core diameter during the formation stage is proposed. The translational velocity variation with time shows that the second-order accurate formula derived using Hamilton’s equation by Fraenkel (J. Fluid Mech., vol. 51, 1972, pp. 119–135) predicts it best.

Investigations Of Pressure Pulsations In A Model Of Draft Tube Of Hydraulic Turbine Caused By Vortex Rings

2016 ◽  
Vol 11 (4) ◽  
pp. 25-32
Author(s):  
Sergey Skripkin ◽  
Mikhail Tsoy ◽  
Sergey Shtork ◽  
Pavel Kuibin
Keyword(s):  
Vortex Ring ◽  
High Speed ◽  
Draft Tube ◽  
Hydraulic Turbine ◽  
Vortex Rings ◽  
Experimental Investigations ◽  
Visualization Technique ◽  
Vortex Rope ◽  
Hydro Turbine ◽  
Hydraulic Turbines

Current work is devoted to experimental investigations of behavior of precessing vortex rope in a draft tube model of hydraulic turbine. We used combination of stationary and freely rotating swirlers as a hydro turbine model. Such construction provides velocity distribution on the draft tube inlet close to distribution in natural hydraulic turbines operated at non-optimal conditions. The phenomenon of precessing vortex rope reconnection with further formation of vortex ring was founded in this experimental research using high-speed visualization technique. Synchronization of highspeed visualization and pressure measurements allowed us to relate pressure shock on the draft tube wall with vortex ring moving along wall.

scholarly journals Experimental Research on the Transverse Effective Bending Rigidity of Shield Tunnels

2019 ◽  
Vol 2019 ◽  
pp. 1-17 ◽  
Author(s):  
Gang Zheng ◽  
Yawei Lei ◽  
Tao Cui ◽  
Xuesong Cheng ◽  
Yu Diao ◽  
...  
Keyword(s):  
Sandy Soil ◽  
Bending Rigidity ◽  
Concentrated Force ◽  
Concentrated Load ◽  
Ring Model ◽  
Loading Patterns ◽  
Steel Tank ◽  
Practical Engineering ◽  
Tunnel Diameter ◽  
Load Tests

The uniform rigidity ring model is commonly used to design the segmented structures of shield tunnels. However, model tests have been primarily used to study the transverse effective rigidity ratio η with a concentrated force, which is notably different from realistic loading patterns. To obtain more reasonable η values, in this study, tests were performed with a concentrated load on an experimental bench and with a realistic loading pattern in sandy soil in a rigid steel tank. Three types of segmental ring models were designed and tested: straight-jointed, stagger-jointed, and uniform rings. The test results indicated that the η values of the stagger-jointed assembly mode were clearly larger than those of the straight-jointed assembly mode under both loading patterns. η increased as the load increased under the realistic loading conditions, whereas η decreased as the load increased under the concentrated load. More importantly, the η values derived from the realistic load tests were considerably larger than those derived from the concentrated load tests for both assembly modes (i.e., 0.423–0.672 and 0.587–0.761 for the straight-jointed and stagger-jointed assembly modes, respectively), and the former should be recommended for practical engineering applications. Furthermore, formulas relating η to the ratio of the cover depth to the tunnel diameter were proposed for sandy soil.

Laminar to Turbulent Buoyant Vortex Ring Regime in Terms of Reynolds Number, Bond Number, and Weber Number

2018 ◽  
Vol 140 (5) ◽  
Author(s):  
Xueying Yan ◽  
Rupp Carriveau ◽  
David S. K. Ting
Keyword(s):  
Reynolds Number ◽  
Vortex Ring ◽  
Weber Number ◽  
High Speed ◽  
Reynolds Numbers ◽  
Bond Number ◽  
Vortex Rings ◽  
Transition Regime ◽  
Turbulent Vortex ◽  
Buoyant Vortex Rings

When buoyant vortex rings form, azimuthal disturbances occur on their surface. When the magnitude of the disturbance is sufficiently high, the ring will become turbulent. This paper establishes conditions for categorization of a buoyant vortex ring as laminar, transitional, or turbulent. The transition regime of enclosed-air buoyant vortex rings rising in still water was examined experimentally via two high-speed cameras. Sequences of the recorded pictures were analyzed using matlab. Key observations were summarized as follows: for Reynolds number lower than 14,000, Bond number below 30, and Weber number below 50, the vortex ring could not be produced. A transition regime was observed for Reynolds numbers between 40,000 and 70,000, Bond numbers between 120 and 280, and Weber number between 400 and 800. Below this range, only laminar vortex rings were observed, and above, only turbulent vortex rings.

Vortex ring-like structures in gasoline fuel sprays under cold-start conditions

2009 ◽  
Vol 10 (4) ◽  
pp. 195-214 ◽  
Author(s):  
S Begg ◽  
F Kaplanski ◽  
S Sazhin ◽  
M Hindle ◽  
M Heikal
Keyword(s):  
Vortex Ring ◽  
High Speed ◽  
Phenomenological Study ◽  
Theoretical Models ◽  
High Speed Photography ◽  
Fuel Injector ◽  
Fuel Injectors ◽  
Fuel Sprays ◽  
Phase Doppler Anemometry ◽  
Ring Model

A phenomenological study of vortex ring-like structures in gasoline fuel sprays is presented for two types of production fuel injectors: a low-pressure, port fuel injector (PFI) and a high-pressure atomizer that injects fuel directly into an engine combustion chamber (G-DI). High-speed photography and phase Doppler anemometry (PDA) were used to study the fuel sprays. In general, each spray was seen to comprise three distinct periods: an initial, unsteady phase; a quasi-steady injection phase; and an exponential trailing phase. For both injectors, vortex ring-like structures could be clearly traced in the tail of the sprays. The location of the region of maximal vorticity of the droplet and gas mixture was used to calculate the temporal evolution of the radial and axial components of the translational velocity of the vortex ring-like structures. The radial components of this velocity remained close to zero in both cases. The experimental results were used to evaluate the robustness of previously developed models of laminar and turbulent vortex rings. The normalized time, , and normalized axial velocity, , were introduced, where tinit is the time of initial observation of vortex ring-like structures. The time dependence of on was approximated as and for the PFI and G-DI sprays respectively. The G-DI spray compared favourably with the analytical vortex ring model, predicting , in the limit of long times, where α = 3/2 in the laminar case and α = 3/4 when the effects of turbulence are taken into account. The results for the PFI spray do not seem to be compatible with the predictions of the available theoretical models.

Navier-Stokes simulations of axisymmetric vortex rings

1988 ◽  
Author(s):  
S. STANAWAY ◽  
B. CANTWELL ◽  
P. SPALART
Keyword(s):  
Navier Stokes ◽  
Vortex Rings ◽  
Axisymmetric Vortex
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