Experimental and Theoretical Studies for Improving the Performance of a Modified Shape Savonius Wind Turbine

2020 ◽  
Vol 142 (12) ◽  
Author(s):  
W. A. El-Askary ◽  
Ahmed S. Saad ◽  
Ali M. AbdelSalam ◽  
I. M. Sakr
Keyword(s):  
Wind Velocity ◽  
Turbulence Model ◽  
Three Dimensional ◽  
Power Coefficient ◽  
Navier Stokes ◽  
Optimized Design ◽  
Percentage Increase ◽  
Aspect Ratios ◽  
Air Jet ◽  
Significant Performance

Abstract In this paper, measurements and computations are performed to study the performance of a 45-deg twisted Savonius rotor with a modified profile, at various overlap ratios (δ), aspect ratios (AR), and wind velocity (V). A free air jet test rig is used to carry out the experiments, while three-dimensional unsteady Reynolds-averaged Navier–Stokes (URANS) equations are used, in conjunction with the renormalization group (RNG) k–ɛ turbulence model, to perform the computations. The present experimental results successfully verify the simulation predictions obtained by the selected turbulence model. The RNG k–ɛ turbulence model has been chosen based on previous tests performed and published by the authors. Furthermore, both torque coefficient (CT) and power coefficient (CP) are numerically predicted at various tip speed ratios (λ) for overlap ratios (δ) ranging from 0.0 to 0.5, aspect ratios (AR) ranging from 0.75 to 3, and wind velocity values ranging from 4 to 18 m/s. Unlike the conventional rotor, the present twisted rotor with a modified profile produces significant performance improvement in the case of modified rotor without overlapping (δ = 0.0). Moreover, the peaks of CT and CP of the twisted rotor with the modified profile are enhanced with the increase in the aspect ratio. However, the percentage increase is noticed to be insignificant for AR greater than two. The maximum power coefficient (CPmax) for the twisted rotor with the modified profile and optimized design is 0.305 at a wind velocity of 6 m/s, with a performance gain of 75.3% compared to the conventional Savonius wind rotor which has CPmax=0.174.

scholarly journals Three-Dimensional Turbulent Vortex Shedding From a Surface-Mounted Square Cylinder: Predictions With Large-Eddy Simulations and URANS

2014 ◽  
Vol 136 (6) ◽  
Author(s):  
B. A. Younis ◽  
A. Abrishamchi
Keyword(s):  
Experimental Data ◽  
Turbulence Model ◽  
Stokes Equations ◽  
Three Dimensional ◽  
Large Eddy Simulations ◽  
Navier Stokes ◽  
Reynolds Stresses ◽  
Mean Flow ◽  
Navier Stokes Equations ◽  
Large Eddy

The paper reports on the prediction of the turbulent flow field around a three-dimensional, surface mounted, square-sectioned cylinder at Reynolds numbers in the range 104–105. The effects of turbulence are accounted for in two different ways: by performing large-eddy simulations (LES) with a Smagorinsky model for the subgrid-scale motions and by solving the unsteady form of the Reynolds-averaged Navier–Stokes equations (URANS) together with a turbulence model to determine the resulting Reynolds stresses. The turbulence model used is a two-equation, eddy-viscosity closure that incorporates a term designed to account for the interactions between the organized mean-flow periodicity and the random turbulent motions. Comparisons with experimental data show that the two approaches yield results that are generally comparable and in good accord with the experimental data. The main conclusion of this work is that the URANS approach, which is considerably less demanding in terms of computer resources than LES, can reliably be used for the prediction of unsteady separated flows provided that the effects of organized mean-flow unsteadiness on the turbulence are properly accounted for in the turbulence model.

A Reynolds-Averaged Navier-Stokes Solver in a Turbomachinery Design System

2007 ◽  
Author(s):  
Fahua Gu ◽  
Mark R. Anderson
Keyword(s):  
Turbulence Model ◽  
Stokes Equations ◽  
Three Dimensional ◽  
Integrated Design ◽  
Navier Stokes ◽  
Design System ◽  
Navier Stokes Equations ◽  
Wall Functions ◽  
Machine Performance ◽  
Reynolds Averaged Navier Stokes

The design of turbomachinery has been focusing on the improvement of the machine efficiency and the reduction of the design cost. This paper presents an integrated design system to create the machine geometry and to predict the machine performance at different levels of approximation, including one-dimensional design and analysis, quasi-three-dimensional-(blade-to-blade, throughflow) and full-three-dimensional-steady-state CFD analysis. One of the most important components, the Reynolds-averaged Navier-Stokes solver, is described in detail. It originated from the Dawes solver with numerous enhancements. They include the use of the low speed pre-conditioned full Navier-Stokes equations, the addition of the Spalart-Allmaras turbulence model and an improvement of wall functions related with the turbulence model. The latest upwind scheme, AUSM, has been implemented too. The Dawes code has been rewritten into a multi-block solver for O, C, and H grids. This paper provides some examples to evaluate the effect of grid topology on the machine performance prediction.

Three-Dimensional Simulation of Laminar Rectangular Impinging Jets, Flow Structure, and Heat Transfer

1999 ◽  
Vol 121 (1) ◽  
pp. 50-56 ◽  
Author(s):  
I. Sezai ◽  
A. A. Mohamad
Keyword(s):  
Heat Transfer ◽  
Three Dimensional ◽  
Streamwise Velocity ◽  
Impinging Jets ◽  
Navier Stokes ◽  
Aspect Ratios ◽  
Laminar Jets ◽  
Nusselt Number Distribution ◽  
Dimensional Simulation ◽  
Energy Equations

The flow and heat transfer characteristics of impinging laminar jets issuing from rectangular slots of different aspect ratios have been investigated numerically through the solution of three-dimensional Navier-Stokes and energy equations in steady state. The three-dimensional simulation reveals the existence of pronounced streamwise velocity off-center peaks near the impingement plate. Furthermore, the effect of these off-center velocity peaks on the Nusselt number distribution is also investigated. Interesting three-dimensional flow structures are detected which cannot be predicted by two-dimensional simulations.

Three-Dimensional Navier–Stokes Computation of Turbomachinery Flows Using an Explicit Numerical Procedure and a Coupled k–ε Turbulence Model

1992 ◽  
Vol 114 (3) ◽  
pp. 627-642 ◽  
Author(s):  
R. F. Kunz ◽  
B. Lakshminarayana
Keyword(s):  
Reynolds Number ◽  
Turbulence Model ◽  
Three Dimensional ◽  
Numerical Procedure ◽  
Secondary Flows ◽  
Quality Data ◽  
Navier Stokes ◽  
Evaluation Procedure ◽  
Pressure Probe ◽  
Time Step

An explicit, three-dimensional, coupled Navier–Stokes/k–ε technique has been developed and successfully applied to complex internal flow calculations. Several features of the procedure, which enable convergent and accurate calculation of high Reynolds number two-dimensional cascade flows, have been extended to three dimensions, including a low Reynolds number compressible form of the k–ε turbulence model, local time-step specification based on hyperbolic and parabolic stability requirements, and eigenvalue and local velocity scaling of artificial dissipation operators. A flux evaluation procedure, which eliminates the finite difference metric singularity at leading and trailing edges on H- and C-grids, is presented. The code is used to predict the pressure distribution, primary velocity, and secondary flows in an incompressible, turbulent curved duct flow for which CFD validation quality data are available. Also, a subsonic compressor rotor passage, for which detailed laser, rotating hot-wire, and five-hole pressure probe measurements have been made is computed. Detailed comparisons between predicted and measured core flow and near-wall velocity profiles, wake profiles, and spanwise mixing effects downstream of the rotor passage are presented for this case. It is found that the technique provides accurate and convergent engineering simulation of these complex turbulent flows.

Development of a Numerical Based Correlation for Performance Losses due to Surface Roughness in Axial Turbines

2014 ◽  
Vol 30 (6) ◽  
pp. 631-642 ◽  
Author(s):  
S. A. Moshizi ◽  
M. H. Nakhaei ◽  
M. J. Kermani ◽  
A. Madadi
Keyword(s):  
Turbulence Model ◽  
Three Dimensional ◽  
Turbulence Models ◽  
Navier Stokes ◽  
Streamline Curvature ◽  
Sst Turbulence Model ◽  
Stator Blade ◽  
Dimensional Models ◽  
Three Dimensional Models ◽  
Axial Turbines

AbstractIn the present work, a recently developed in-house 2D CFD code is used to study the effect of gas turbine stator blade roughness on various performance parameters of a two-dimensional blade cascade. The 2D CFD model is based on a high resolution flux difference splitting scheme of Roe (1981). The Reynolds Averaged Navier-Stokes (RANS) equations are closed using the zero-equation turbulence model of Baldwin-Lomax (1978) and two-equation Shear Stress Transport (SST) turbulence model. For the smooth blade, results are compared with experimental data to validate the model. Finally, a correlation between roughness Reynolds number and loss coefficient for both turbulence models is presented and tested for three other roughness heights. The results of 2D turbine blade cascades can be used for one-dimensional models such as mean line analysis or quasi-three-dimensional models e.g. streamline curvature method.

Formation of columnar baroclinic vortices in thermally stratified nonlinear spin-up

2012 ◽  
Vol 702 ◽  
pp. 265-285 ◽  
Author(s):  
J. R. Pacheco ◽  
R. Verzicco
Keyword(s):  
Vortex Core ◽  
Stokes Equations ◽  
Fluid Layer ◽  
Three Dimensional ◽  
Temperature Gradients ◽  
Navier Stokes ◽  
Central Vortex ◽  
Slip Boundary ◽  
Aspect Ratios ◽  
Vorticity Production

AbstractWe investigate the mechanisms that affect the formation of columnar vortices for spin-up in a cylinder where the temperatures at the horizontal walls are prescribed. Numerical results from the three-dimensional Navier–Stokes equations show that a short-lived instability, suppressed by the combined effect of rotation and stratification, generates small temperature variations in the azimuthal direction. Temperature-gradient anomalies produce vorticity, and these vortices stir the fluid at the interface of the central vortex core thus reinforcing the temperature gradients. For sufficiently strong temperature gradients, the central vortex core breaks up into several columnar vortices. It is found, in particular, that small aspect ratios (height over radius of the cylindrical fluid layer) $\Gamma = 1, 2$ tend to inhibit the instability, while larger ones, $\Gamma = 3. 3$, have the opposite effect. The main source of instability is the baroclinic vorticity production and not the presence of a solid sidewall since, counter-intuitively, the flow is more unstable for a free-slip boundary than for a no-slip one. Finally the effect of the temperature boundary conditions (isothermal versus adiabatic) on the horizontal boundaries has been investigated. The adiabatic boundaries help to preserve for longer times the sloping density interfaces that feed, with their potential energy, the baroclinic vorticity production; this results in more unstable flows.

Three-Dimensional Navier-Stokes Computation of Turbomachinery Flows Using an Explicit Numerical Procedure and a Coupled k-ε Turbulence Model

1991 ◽  
Author(s):  
R. F. Kunz ◽  
B. Lakshminarayana
Keyword(s):  
Reynolds Number ◽  
Turbulence Model ◽  
Three Dimensional ◽  
Numerical Procedure ◽  
Secondary Flows ◽  
Three Dimensions ◽  
Quality Data ◽  
Navier Stokes ◽  
Evaluation Procedure ◽  
Pressure Probe

An explicit, three-dimensional, coupled Navier-Stokes/k-ε technique has been developed and successfully applied to complex internal flow calculations. Several features of the procedure, which enable convergent and accurate calculation of high Reynolds number two-dimensional cascade flows have been extended to three-dimensions, including a low Reynolds number compressible form of the k-ε turbulence model, local timestep specification based on hyperbolic and parabolic stability requirements, and eigenvalue and local velocity scaling of artificial dissipation operators. A flux evaluation procedure which eliminates the finite difference metric singularity, at leading and trailing edges, on H- and C-grids, is presented. The code is used to predict the pressure distribution, primary velocity and secondary flows in an incompressible, turbulent curved duct flow for which CFD validation quality data is available. Also, a subsonic compressor rotor passage, for which detailed laser, rotating hot-wire and five-hole pressure probe measurements have been made is computed. Detailed comparisons between predicted and measured core flow and near wall velocity profiles, wake profiles, and spanwise mixing effects downstream of the rotor passage are presented for this case. It is found that the technique provides accurate and convergent engineering simulation of these complex turbulent flows.

Three-dimensional natural convection in a box: a numerical study

1977 ◽  
Vol 83 (1) ◽  
pp. 1-31 ◽  
Author(s):  
G. D. Mallinson ◽  
G. De Vahl Davis
Keyword(s):  
Natural Convection ◽  
Stokes Equations ◽  
Numerical Study ◽  
Three Dimensional ◽  
Three Dimensions ◽  
Navier Stokes ◽  
Navier Stokes Equations ◽  
Aspect Ratios ◽  
Inertial Interaction ◽  
Longitudinal Temperature

The solution of the steady-state Navier–Stokes equations in three dimensions has been obtained by a numerical method for the problem of natural convection in a rectangular cavity as a result of differential side heating. In the past, this problem has generally been treated as though it were two-dimensional. The solutions explore the three-dimensional motion generated by the presence of no-slip adiabatic end walls. For Ra = 104, the three-dimensional motion is shown to be the result of the inertial interaction of the rotating flow with the stationary walls together with a contribution arising from buoyancy forces generated by longitudinal temperature gradients. The inertial effect is inversely dependent on the Prandtl number, whereas the thermal effect is nearly constant. For higher values of Ra, multiple longitudinal flows develop which are a delicate function of Ra, Pr and the cavity aspect ratios.

AERODYNAMIC PERFORMANCE OF AN AXIAL COMPRESSOR WITH A CASING GROOVE COMBINED WITH INJECTION

2013 ◽  
Vol 37 (3) ◽  
pp. 283-292 ◽  
Author(s):  
Dae-Woong Kim ◽  
Jin-Hyuk Kim ◽  
Kwang-Yong Kim
Keyword(s):  
Turbulence Model ◽  
Parametric Study ◽  
Stokes Equations ◽  
Three Dimensional ◽  
Axial Compressor ◽  
Aerodynamic Performance ◽  
Navier Stokes ◽  
Navier Stokes Equations ◽  
Stall Margin ◽  
Transonic Axial Compressor

Aerodynamic performance of a transonic axial compressor with a casing groove combined with injection has been investigated in this work. Three-dimensional Reynolds-averaged Navier–Stokes equations with k-ε turbulence model are discretized by finite volume approximations and solved on hexahedral grids for the flow analyses. For parametric study, the front and rear lengths and height of the casing groove are selected as the geometric parameters and are changed with constant injection to investigate their effects on the stall margin and peak adiabatic efficiency. As a result of the parametric study, the maximum stall margin and peak adiabatic efficiency are found to be obtained in the axial compressor having 70% height of the reference groove. The results show that the application of the casing groove combined with injection to an axial compressor is effective for the simultaneous improvement of both the stall margin and peak adiabatic efficiency of the compressor.

Three Dimensional Numerical Simulation of Vortex Structures in Barak River

2015 ◽  
Vol 772 ◽  
pp. 120-124
Author(s):  
S. Kiran ◽  
Upendra Kumar ◽  
Amit Kumar Dey
Keyword(s):  
Turbulence Model ◽  
Three Dimensional ◽  
Free Water ◽  
Velocity Profiles ◽  
Navier Stokes ◽  
Navier Stokes Equation ◽  
Secondary Current ◽  
Secondary Currents ◽  
Outer Bank ◽  
Barak River

Natural channel have complex three dimensional flow structures particularly at the outer bank cell due to the combined effects of secondary currents and higher velocity profiles. In this paper Computational fluid dynamics is used to study the meandering bend of the Barak River. Numerical modeling is done using Reynolds averaged continuity and Navier Stokes equation. These equations are solved by finite volume method. Appropriate representation of counter-rotating secondary flow in the channel bend requires both the suitable treatment of the free water surface and a turbulence model that can resolve the anisotropy of turbulence. Hence the volume of fluid method (VOF) was used to model the free surface and reynolds stress turbulence model (RSM) has been used to close the RANS equations. Higher velocity profiles were prominent at the outer bank. Skew induced stream wise vorticity was observed close to the outer bank which confirms the existence of corner induced secondary current. The vortices formed were found to be of Prandtl’s first kind.

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