scholarly journals Numerical Study and Theoretical Comparison of Outlet Hole Geometry for a Gravitational Vortex Turbine

2021 ◽  
Vol 6 (3) ◽  
pp. 491-506
Author(s):  
Alejandro Ruiz Sánchez ◽  
Jorge Andrés Sierra Del Rio ◽  
Toni Pujol
Keyword(s):  
Numerical Study ◽  
Vortex Formation ◽  
Electric Energy ◽  
Tangential Velocity ◽  
Analytical Models ◽  
Discharge Zone ◽  
Hydrokinetic Energy ◽  
Fluid Behavior ◽  
Outlet Hole ◽  
Tank Geometry

The gravitational water vortex turbine is an alternative to renewable energies, it transforms the hydrokinetic energy of the rivers into electric energy and it does not require a reservoir. According to studies carried out, the hydraulic efficiency can increase or decrease according to the turbine geometrical configuration. This paper presents a numerical (CFD) and analytical comparison between conical and cylindrical designs for the outlet. The results show a higher performance for conical geometry than the cylindrical tank. The fluid behavior in CFD and analytical studies presents a tangential velocity increase near to air core and outlet hole (similar behavior). The maximum theoretical power generated was 167 W and 150 W for conical and cylindrical design respectively. The differences between geometries of the outlet holes using CFD and analytical models were 11 and 7%, respectively. However, the closest results to the CFD model had different values of 31 and 29% for conical and cylindrical design, respectively. The furthest result regarding the CFD study was 55%. The principal difference is due to tank geometry, the change in discharge zone, as well as the ratio of diameter tank and outlet hole can increase or decrease the tangential velocity and make a stronger and more stable vortex formation. The theoretical power generated is a good parameter to select the height to place the rotor.

Vortex formation on surging aerofoils with application to reverse flow modelling

2018 ◽  
Vol 859 ◽  
pp. 59-88 ◽  
Author(s):  
Philip B. Kirk ◽  
Anya R. Jones
Keyword(s):  
Surface Pressure ◽  
Reverse Flow ◽  
Vortex Formation ◽  
Three Dimensional ◽  
Tangential Velocity ◽  
Leading Edge ◽  
Field Measurements ◽  
Reduced Frequency ◽  
Advance Ratio ◽  
Convection Speed

The leading-edge vortex (LEV) is a powerful unsteady flow structure that can result in significant unsteady loads on lifting blades and wings. Using force, surface pressure and flow field measurements, this work represents an experimental campaign to characterize LEV behaviour in sinusoidally surging flows with widely varying amplitudes and frequencies. Additional tests were conducted in reverse flow surge, with kinematics similar to the tangential velocity profile seen by a blade element in recent high-advance-ratio rotor experiments. General results demonstrate the variability of LEV convection properties with reduced frequency, which greatly affected the average lift-to-drag ratio in a cycle. Analysis of surface pressure measurements suggests that LEV convection speed is a function only of the local instantaneous flow velocity. In the rotor-comparison tests, LEVs formed in reverse flow surge were found to convect more quickly than the corresponding reverse flow LEVs that form on a high-advance-ratio rotor, demonstrating that rotary motion has a stabilizing effect on LEVs. The reverse flow surging LEVs were also found to be of comparable strength to those observed on the high-advance-ratio rotor, leading to the conclusion that a surging-wing simplification might provide a suitable basis for low-order models of much more complex three-dimensional flows.

scholarly journals A Numerical Study of Plane Ice-Sheet Flow

1986 ◽  
Vol 32 (111) ◽  
pp. 139-160 ◽  
Author(s):  
K. Hutter ◽  
S. Yakowitz ◽  
F. Szidarovszky
Keyword(s):  
Surface Temperature ◽  
Thermal State ◽  
Numerical Study ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Tangential Velocity ◽  
Rigid Base ◽  
Geothermal Heat ◽  
Functional Relations ◽  
External Forcings

AbstractThe plane steady flow of a grounded ice sheet is numerically analysed using the approximate model of Morland or Hutter. In this, the ice behaves as a non-linear viscous fluid with a strongly temperature-dependent rate factor, and ice sheets are assumed to be long and shallow. The climate is assumed to be prescribed via the accumulation/ablation distribution and the surface temperature, both of which are functions of position and unknown height. The rigid base exerts external forcings via the normal heat flow, the geothermal heat, and a given basal sliding condition connecting the tangential velocity, tangential traction, and normal traction. The functional relations are those of Morland (1984) or motivated by his work. We use equations in his notation.The governing equations and boundary conditions in dimensionless form are briefly stated and dimensionless variables are related to their physical counterparts. The thermo-mechanical parabolic boundary-value problem, found to depend on physical scales, constitutive properties, and external forcing functions, has been numerically solved. For reasons of stability, the numerical integration must proceed from the ice divide towards the margin, which requires a special analysis of the ice divide. We present this analysis and then describe the versatility and limitations of the constructed computer code.Results of extensive computations are shown. In particular, we prove that the Morland–Hutter model for ice sheets is only applicable when sliding is sufficiently large (satisfying inequality (30)). In the range of the validity of this inequality, it is then demonstrated that of all physical scaling parameters only a single π-product influences the geometry and the flow within the ice sheet. We analyse the role played by advection, diffusion, and dissipation in the temperature distribution, and discuss the significance of the rheological non-linearities. Variations of the external forcings, such as accumulation/ablation conditions, free surface temperature, and geothermal heat, demonstrate the sensitivity of the ice-sheet geometry to accumulation conditions and the robustness of the flow to variations in the thermal state. We end with a summary of results and a critical review of the model.

scholarly journals A Numerical Study of Chemical Reaction in a Nanofluid Flow Due to Rotating Disk in the Presence of Magnetic Field

2021 ◽  
Author(s):  
Muhammad Ramzan ◽  
Poom Kumam ◽  
Kottakkaran Sooppy Nisar ◽  
Ilyas Khan ◽  
Wasim Jamshed
Keyword(s):  
Differential Equation ◽  
Radial Velocity ◽  
Chemical Reaction ◽  
Axial Velocity ◽  
Numerical Study ◽  
Tangential Velocity ◽  
Rotating Disk ◽  
Partial Differential ◽  
Suction Parameter ◽  
Matlab Programming

Abstract In this paper, a numerical study of MHD steady flow due to the rotating disk with chemical reaction was explored. Effect of different parameters such as Schmidt number, chemical reaction parameter, Prandtl number, Suction parameter, heat absorption/generation parameter, Nano-particle concentration, Reynold number, Magnetic parameter, skin friction, shear stress, temperature distribution, Nusselt number, mass transfer rate, radial velocity, axial velocity, and tangential velocity was analyzed and discussed. For the simplification of non-linear partial differential equations (PDEs) into the nonlinear ordinary differential equation (ODEs), the method of Similarity transformation was employed, and the resulting partial differential equation was solved by using finite difference method through MATLAB programming. This work's remarkable finding is that with the expansion of nanoparticle concentration radial velocity, tangential velocity and temperature of the fluid was enhanced but reverse reaction for axial velocity. Furthermore, the present results are found to be in excellent agreement with previously published work.

scholarly journals Numerical Analysis of Effect of Leading-Edge Rotating Cylinder on NACA0021 Symmetric Airfoil

2019 ◽  
Vol 4 (7) ◽  
pp. 11-17
Author(s):  
Md. Abdus Salam ◽  
Vikram Deshpande ◽  
Nafiz Ahmed Khan ◽  
M. A. Taher Ali
Keyword(s):  
Free Stream ◽  
Numerical Study ◽  
Tangential Velocity ◽  
Leading Edge ◽  
Rotating Cylinder ◽  
Aerodynamic Performance ◽  
Stream Velocity ◽  
Surface Boundary ◽  
Lower Velocity ◽  
Numerical Studies

The moving surface boundary control (MSBC) has been a Centre stage study for last 2-3 decades. The preliminary aim of the study was to ascertain whether the concept can improve the airfoil characteristics. Number of experimental and numerical studies pointed out that the MSBC can superiorly enhance the airfoil performance albeit for higher velocity ratios (i.e. cylinder tangential velocity to free stream velocity). Although abundant research has been undertaken in this area on different airfoil performances but no attempt was seen to study effect of MSBC on NACA0021 airfoil for and also effects of lower velocity ratios. Thus, present paper focusses on numerical study of modified NACA 0021 airfoil with leading edge rotating cylinder for velocity ratios (i.e.) between 1 to 1.78 at different angles of attack. The numerical study indicates that the modified airfoil possess better aerodynamic performance than the base airfoil even at lower velocity ratios (i.e. for velocity ratios 0.356 and beyond). The study also focusses on reason for improvement in aerodynamic performance by close look at various parameters.

Vortex synchronization in the cylinder wake due to harmonic and non-harmonic perturbations

2016 ◽  
Vol 804 ◽  
pp. 248-277 ◽  
Author(s):  
Efstathios Konstantinidis ◽  
Demetri Bouris
Keyword(s):  
Relative Velocity ◽  
Numerical Study ◽  
Vortex Formation ◽  
Phase Portraits ◽  
Cylinder Wake ◽  
Frequency Space ◽  
Flow Past A Cylinder ◽  
Harmonic Perturbation ◽  
Perturbation Frequency ◽  
Vortex Patterns

This paper reports a numerical study of two-dimensional periodically perturbed flow past a cylinder. Both harmonic and non-harmonic perturbation waveforms of the inflow velocity are considered for a maximum instantaneous Reynolds number of 180. Phase portraits of the lift force are employed to identify the dynamical state of the cylinder wake and determine the range of kinematical parameters for which primary synchronization occurs, that is the regime where vortex formation is phase-locked to the subharmonic of the perturbation frequency. The effect of different perturbation waveforms on the synchronization range and on patterns of vortex formation is examined in detail over the normalized amplitude–frequency space. It is shown that systematic shifts of the synchronization range, towards either higher or lower frequencies, can be attained by imposing different perturbation waveforms. As a consequence, in certain regions of the parameter space it is possible to obtain multiple periodic and/or quasi-periodic wake states for waveforms of exactly the same amplitude and frequency. For the range of parameters where synchronization occurs, different vortex patterns are attained in the wake involving the shedding of solitary and binary vortices, or mixtures thereof, which can be controlled by the perturbation waveform. The phenomenology of these patterns, which result from modification of the basic Kármán mode in the unperturbed wake, is discussed and explained in terms of the generation of circulation that is induced by perturbations in the relative velocity. Vortex patterns from cylinders oscillating either in line with or transverse to a free stream are recast in the framework of the relative velocity.

Assessing the Multiple Pressure Source Hypothesis for the Sakurajima Volcano and Aira Caldera Magmatic System

2021 ◽  
Author(s):  
Robert Backhurst
Keyword(s):  
Numerical Modelling ◽  
Large Scale ◽  
Numerical Study ◽  
Deformation Source ◽  
Geodetic Data ◽  
Analytical Models ◽  
Magmatic System ◽  
Sakurajima Volcano ◽  
Subsurface Heterogeneity ◽  
Increased Risk

<p>Sakurajima, located on the southern rim of Aira caldera, is one of the most active volcanoes in Japan. From long term deformation trends, the volcano is showing an increased risk of large-scale eruption, emphasizing the need to better understand the magmatic system.</p><p>Deformation modelling, primarily using the Mogi method, has dominated the geodetic assessment history of Sakurajima. These methods, however, contain limitations, such as the assumption of a homogeneous crust, and have therefore not accurately depicted the magmatic system. Numerical modelling techniques have reduced this limitation by accounting for subsurface heterogeneity.</p><p>Analytical modelling studies have suggested multiple magmatic sources beneath Aira caldera and Sakurajima volcano, whilst the only numerical study undertaken so far indicated a single source. Here, we test the multiple deformation source hypothesis, whilst also incorporating subsurface heterogeneity and topography, using Finite Element (FE) numerical modelling, and geodetic data from Sakurajima.</p><p>Using a full 3D model geometry for Sakurajima and Aira caldera, preliminary forward modelling suggests a second deformation source produces our best fit to the measured geodetic data. Optimum results indicate a shallow prolate source 7-10 km below sea level (bsl), in addition to a deeper oblate source at ~13 km bsl. These preliminary findings produce greater shallow storage depths than the previous analytical models (3-6 km) and ties in with the trans-crustal magmatic system hypothesis.</p><p>Increasing our understanding of the Sakurajima magmatic system will enable improved interpretations of geodetic data prior to eruptions and will inform models for a range of similar volcanoes world-wide.</p>

scholarly journals VORTEX IN AXION CONDENSATE AS A DARK MATTER HALO

2010 ◽  
Vol 19 (11) ◽  
pp. 1843-1855 ◽  
Author(s):  
JAKUB MIELCZAREK ◽  
TOMASZ STACHOWIAK ◽  
MAREK SZYDŁOWSKI
Keyword(s):  
Galaxy Formation ◽  
Vortex Formation ◽  
Analytical Models ◽  
Dark Matter Halo ◽  
Low Velocity ◽  
Single Vortex ◽  
Angular Momenta ◽  
The Galaxy ◽  
De Broglie Wavelength ◽  
Present Understanding

We study the possibility of the vortex formation in axion condensates on the galactic scale. Such vortices can occur as a result of global rotation of the early universe. We study analytical models of vortices and calculate exemplary galaxy rotation curves. Depending on the setup it is possible to obtain a variety of shapes which give a good qualitative agreement with observational results. However, as we show, the extremely low velocity dispersions of the axion velocities are required to form the single vortex on the galactic scales. We find that the required velocity dispersion is of the order of σ≈10-12 ms-1. This is much smaller that predicted within the present understanding of the axion physics. The vortices in axion condensate can however be formed on the much smaller scales and give seeds to the galaxy formation and to their angular momenta. On the other hand, the vortices can be formed on the galactic scales, but only if the mass of the axion-like particles is of the order of 10-30 eV. In this case, the particle de Broglie wavelength is comparable with the galactic diameter. This condition must be fulfilled in order to keep the coherence of the quantum condensate on galactic scales.

On the Axisymmetric Vortex Flow Over a Flat Surface

1969 ◽  
Vol 36 (3) ◽  
pp. 614-619 ◽  
Author(s):  
E. W. Schwiderski
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Critical Reynolds Number ◽  
Numerical Study ◽  
Lower Boundary ◽  
Tangential Velocity ◽  
Slow Motion ◽  
Boundary Layer Separation ◽  
Local Boundary ◽  
Self Similar

The numerical study of the interaction of a potential vortex with a stationary surface recently published by Kidd and Farris [1] is extended through a transformation of the boundary-value problem to Volterra integral equations. The new calculations verified the results by Kidd and Farris and improved the bounds of the critical Reynolds number Nc, beyond which no self-similar vortex flows exist, to 5.5 < Nc < 5.6 The breakdown of the self-similar motions develops through an instability in the lower boundary layer, which is indicated by two inflection points in the tangential velocity profile. At the critical Reynolds number the lower inflection point reaches the surface and indicates the beginning of boundary-layer separation in the wake-type flow. If the Stokes linearization is applied, one arrives at a new Stokes paradox. However, this “paradox” can be resolved by correcting the free-stream pressure distortion of the Stokes approximation. The new slow-motion approximation is nonlinear and yields an integral which is also free of the Whitehead paradox. The properties of the new exact solution confirm the novel flow features previously detected in almost self-similar motions, which were constructed by adjustable local boundary-layer approximations.

scholarly journals Numerical Study of Flow Characteristics Around Confined Cylinder using OpenFOAM

2018 ◽  
Vol 7 (4.35) ◽  
pp. 617
Author(s):  
P. Mathupriya ◽  
L. Chan ◽  
H. Hasini ◽  
A. Ooi
Keyword(s):  
Reynolds Number ◽  
Vortex Shedding ◽  
Numerical Study ◽  
Vortex Formation ◽  
Plane Channel ◽  
Flow Characteristics ◽  
Strong Interactions ◽  
Two Dimensional ◽  
Computational Fluid Dynamics Cfd ◽  
Shedding Frequency

The numerical study of the flow over a two-dimensional cylinder which is symmetrically confined in a plane channel is presented to study the characteristics of vortex shedding. The numerical model has been established using direct numerical simulation (DNS) based on the open source computational fluid dynamics (CFD) code named OpenFOAM. In the present study, the flow fields have been computed at blockage ratio, β of 0.5 and at Reynolds number, Re of 200 and 300. Two-dimensional simulations investigated on the effects of Reynolds number based on the vortex formation and shedding frequency. It was observed that the presence of two distinct shedding frequencies appear at higher Reynolds number due to the confinement effects where there is strong interactions between boundary layer, shear layer and the wake of the cylinder. The range of simulations conducted here has shown to produce results consistent with that available in the open literature. Therefore, OpenFOAM is found to be able to accurately capture the complex physics of the flow.

Significant of Isothermal Flow Studies for High Swirling Flow in Unconfined Burner

2015 ◽  
Vol 789-790 ◽  
pp. 477-483
Author(s):  
A.R. Norwazan ◽  
M.N. Mohd Jaafar
Keyword(s):  
Flow Field ◽  
Combustion Chamber ◽  
Turbulent Flows ◽  
Recirculation Zone ◽  
Swirling Flow ◽  
Numerical Study ◽  
Tangential Velocity ◽  
Radial Distance ◽  
Navier Stokes ◽  
Reacting Flow

This paper is presents numerical simulation of isothermal swirling turbulent flows in a combustion chamber of an unconfined burner. Isothermal flows of with three different swirl numbers, SN of axial swirler are considered to demonstrate the effect of flow axial velocity and tangential velocity to define the center recirculation zone. The swirler is used in the burner that significantly influences the flow pattern inside the combustion chamber. The inlet velocity, U0 is 30 m/s entering into the burner through the axial swirler that represents a high Reynolds number, Re to evaluate the differences of SN. The significance of center recirculation zone investigation affected by differences Re also has been carried out in order to define a good mixing of air and fuel. A numerical study of non-reacting flow into the burner region is performed using ANSYS Fluent. The Reynolds–Averaged Navier–Stokes (RANS) realizable k-ε turbulence approach method was applied with the eddy dissipation model. An attention is focused in the flow field behind the axial swirler downstream that determined by transverse flow field at different radial distance. The results of axial and tangential velocity were normalized with the U0. The velocity profiles’ behaviour are obviously changes after existing the swirler up to x/D = 0.3 plane. However, their flow patterns are similar for all SN after x/D = 0.3 plane towards the outlet of a burner.

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