A BEM/RANS Interactive Method Applied to an Axial Tidal Turbine Farm

2020 ◽  
pp. 1-26
Author(s):  
Seungnam Kim ◽  
Yiran Su ◽  
Spyros A. Kinnas
Keyword(s):  
Computational Cost ◽  
The Body ◽  
Navier Stokes ◽  
Mass Source ◽  
Flow Solver ◽  
Interactive Method ◽  
Tidal Turbine ◽  
Coupling Approach ◽  
Rans Simulations ◽  
Wake Alignment

In this study, an interactive method coupling a boundary element method (BEM) with a viscous flow solver solving the Reynolds-averaged Navier-Stokes (RANS) equations is applied to multiturbine interaction problems. The BEM is first applied to a single turbine problem to predict its performance with/without yaw in noncavitating/ cavitating conditions. Improved wake alignment models, the full wake alignment and the unsteady wake alignment, are used to align the blade wake. The former is adequate for steady state with zero yaw, and the latter is used for unsteady predictions in the case of nonzero yaw in the incoming flow. The BEM results are compared with the experimental measurements and the results from full-blown RANS simulations for a range of tip speed ratios. The comparisons show satisfactory agreement between the numerical and experimental approaches. Afterward, the BEM/RANS coupling method is applied to multiturbine interaction problems with different layouts and different turbine-to-turbine offsets in an axial turbine farm. The method is shown to work well in this multiturbine interaction problem because of the capability of using a strictly Cartesian grid in the RANS method, which minimizes the artificial diffusion and improves the numerical accuracy of long-range flow development. Representation of a turbine by the body force/mass source fields in the BEM/RANS coupling approach reduces the number of cells required for 3D full-blown RANS simulations, and therefore reduces the computational cost in an efficient way.

scholarly journals EVALUATION OF THE APPLICABILITY OF A TURBULENT WAKE INLET BOUNDARY CONDITION

2017 ◽  
Vol 16 (2) ◽  
pp. 78
Author(s):  
P. A. Soliman ◽  
A. V. de Paula ◽  
A. P. Petry ◽  
S. V. Möller
Keyword(s):  
Stokes Equations ◽  
Transport Model ◽  
Characteristic Length ◽  
Computational Cost ◽  
The Body ◽  
Navier Stokes ◽  
Computational Time ◽  
Flow Forming ◽  
Shear Stress Transport Model ◽  
Grid Convergence Index

With the objective of reducing the computational cost of the iterative processes of aerodynamic components design, tests were carried out to study under what conditions, and with what difference, only part of the calculation domain can be solved using as input information obtained from complete simulations already solved. An experimental study of an airfoil exposed to the wake interference of an upstream airfoil at a Reynolds number of 150,000 was used to verify the solutions of the Reynolds-Averaged Navier-Stokes equations solved applying the k-ω Shear Stress Transport model for turbulence closure. A Grid Convergence Index study was performed to verify if the solution of the equations for the adopted discretization leads to results within the asymptotic range. With the physical coherence of the numerical methodology verified, comparisons between the simulations with the domain comprising the two airfoils and the domain comprising only the downstream airfoil were performed. Computational time reductions in the order of 40% are observed. The differences in the aerodynamic coefficients for the two types of simulation are presented as a function of distances non-dimensionalized by the characteristic length of the body that disturbs the flow forming the wake, showing that the difference between the two methods was inversely proportional to the distance between the two bodies. Behavior that was maintained until a point where the simulation diverges, equivalent to 25% of the characteristic length of the body that generates the wake.

A Velocity Decomposition Approach for Unsteady External Flow

2015 ◽  
Author(s):  
Yang Chen ◽  
Kevin J. Maki ◽  
William J. Rosemurgy
Keyword(s):  
Water Waves ◽  
Computational Cost ◽  
Field Method ◽  
The Body ◽  
Navier Stokes ◽  
Steady Flows ◽  
Decomposition Approach ◽  
Velocity Decomposition ◽  
Flow Domain ◽  
Benchmark Solutions

In this work we address the development of the velocity decomposition algorithm, a numerical flow solution method that incorporates both velocity potential and Navier-Stokes-based solution procedures. The motivation for this is so that the field discretization required by the Navier-Stokes solver can be reduced to the region of the flow domain in which the flow is vortical. Specific advantages are that the computational cost is reduced, it is easier to discretize the flow domain, and difficult problems such as the simulation of ships maneuvering in a seaway are closer to being within reach. The target applications are broad, ranging from vortex shedding on bluff objects such as risers, to the wave induced loads on a platform in a current and irregular seas. In previous work, the algorithm has been successfully applied to address steady flows of 3-D non-lifting bodies without water waves, or 2-D bodies that can have lift and be near a water surface. In this paper, the velocity decomposition approach is extended to numerically solve for the unsteady flow of single-phase viscous flows. The velocity vector is decomposed into irrotational and vortical components. A boundary element method is used to solve for the irrotational component (designated as the viscous potential) by applying a viscous boundary condition to the body boundary. A field method is used to solve for the total velocity on a reduced domain where the flow is vortical. The new algorithm investigates two approaches to solve the unsteady problem based on different types of time-dependence exhibited by the solution. The unsteady velocity decomposition method is demonstrated on two cases, and the solutions are compared to those generated by a conventional viscous flow solver. The results by the new algorithm agree well with the benchmark solutions and exhibit a reduction in time.

A Comparison of Unsteady RANS Simulations With PIV Data in an Axial Turbomachine

2005 ◽  
Author(s):  
Daniel Brzozowski ◽  
Oguz Uzol ◽  
Yi-Chih Chow ◽  
Joseph Katz ◽  
Charles Meneveau
Keyword(s):  
Experimental Data ◽  
Transport Model ◽  
Energy Levels ◽  
Turbulence Models ◽  
Navier Stokes ◽  
Piv Measurements ◽  
Flow Solver ◽  
Reynolds Stress Transport Model ◽  
Flow Features ◽  
Rans Simulations

This paper presents a comparison of 2D unsteady Reynolds Averaged Navier-Stokes (RANS) simulations using two standard turbulence models, i.e. RNG k-ε and a Reynolds Stress Transport Model, with experimental data, obtained using two-dimensional Particle Image Velocimetry (PIV) measurements within an entire stage of an axial turbomachine. The computations are performed using the commercial flow solver FLUENT™. A sliding mesh interface between the rotor and stator domains is used. The PIV measurements are performed in a refractive-index-matched facility that provides unobstructed view, and cover the entire 2nd stage of a two-stage axial pump. The inlet velocity and turbulence boundary conditions are provided from the experimental data. Detailed side-by-side comparisons of computed and measured phase-averaged velocity as well as turbulence fields within the entire stage are presented. Quantitative comparisons between the experiments and the computations are also included in terms of line distributions within the rotor-stator gap and the stator wake regions. The results show that, although there is reasonable agreement in general between the experimental results and the computational simulations, some critical flow features are not correctly predicted. The turbulent kinetic energy levels are generally too high in the simulations, with substantial amount of unphysical turbulence generation near the blade leading edges, especially in the case of RNG k-ε model.

A Panel Method with a Full Wake Alignment Model for the Prediction of the Performance of Ducted Propellers

2015 ◽  
Vol 59 (03) ◽  
pp. 246-257 ◽  
Author(s):  
Spyros A. Kinnas ◽  
Hongyang Fan ◽  
Ye Tian
Keyword(s):  
Panel Method ◽  
Navier Stokes ◽  
Ocean Engineering ◽  
Local Flow ◽  
University Of Texas ◽  
Alignment Model ◽  
Rans Simulations ◽  
Wake Alignment ◽  
Thrust And Torque ◽  
Ducted Propellers

An improved perturbation potential-based panel method is applied to model the flow around ducted propellers. One significant development in this method is the application of full wake alignment scheme in which the trailing vortex wake sheets of the blades are aligned with the local flow velocity by also considering the effects of duct and duct wake. A process of repaneling the duct is simultaneously introduced to improve the accuracy of the method. The results from the improved wake model are compared with those from a simplified wake alignment scheme. At the same time, full-blown Reynolds-averaged Navier-Stokes (RANS) simulations are conducted via commercial solvers. The forces, i.e., thrust and torque, on the propeller predicted by this panel method under the improved wake alignment model show good agreement both with experimental measurements, a hybrid method developed by the Ocean Engineering Group of University of Texas at Austin, and the full-blown RANS simulations. Moreover, predicted pressure distribution on the blades and duct are compared among the various methods.

scholarly journals Numerical simulation and experimental validation of cavitating flow in a multi-hole diesel fuel injector

2021 ◽  
pp. 146808742199863
Author(s):  
Aishvarya Kumar ◽  
Ali Ghobadian ◽  
Jamshid Nouri
Keyword(s):  
Computational Cost ◽  
Cavitating Flow ◽  
Field Analysis ◽  
Navier Stokes ◽  
Fuel Injector ◽  
Fluid Behavior ◽  
Flow Field Analysis ◽  
Charged Couple Device ◽  
Biodiesel Fuels ◽  
High Level

This study assesses the predictive capability of the ZGB (Zwart-Gerber-Belamri) cavitation model with the RANS (Reynolds Averaged Navier-Stokes), the realizable k-epsilon turbulence model, and compressibility of gas/liquid models for cavitation simulation in a multi-hole fuel injector at different cavitation numbers (CN) for diesel and biodiesel fuels. The prediction results were assessed quantitatively by comparison of predicted velocity profiles with those of measured LDV (Laser Doppler Velocimetry) data. Subsequently, predictions were assessed qualitatively by visual comparison of the predicted void fraction with experimental CCD (Charged Couple Device) recorded images. Both comparisons showed that the model could predict fluid behavior in such a condition with a high level of confidence. Additionally, flow field analysis of numerical results showed the formation of vortices in the injector sac volume. The analysis showed two main types of vortex structures formed. The first kind appeared connecting two adjacent holes and is known as “hole-to-hole” connecting vortices. The second type structure appeared as double “counter-rotating” vortices emerging from the needle wall and entering the injector hole facing it. The use of RANS proved to save significant computational cost and time in predicting the cavitating flow with good accuracy.

Hybrid LES Approach for Practical Turbomachinery Flows—Part I: Hierarchy and Example Simulations

2011 ◽  
Vol 134 (2) ◽  
Author(s):  
Paul Tucker ◽  
Simon Eastwood ◽  
Christian Klostermeier ◽  
Richard Jefferson-Loveday ◽  
James Tyacke ◽  
...  
Keyword(s):  
Convex Surface ◽  
Computational Cost ◽  
Companion Paper ◽  
Navier Stokes ◽  
Computationally Efficient ◽  
Turbulent Structures ◽  
Hybrid Strategy ◽  
Eddy Simulation ◽  
Related Approach ◽  
Les Model

Unlike Reynolds-averaged Navier–Stokes (RANS) models that need calibration for different flow classes, LES (where larger turbulent structures are resolved by the grid and smaller modeled in a fashion reminiscent of RANS) offers the opportunity to resolve geometry dependent turbulence as found in complex internal flows—albeit at substantially higher computational cost. Based on the results for a broad range of studies involving different numerical schemes, large eddy simulation (LES) models and grid topologies, an LES hierarchy and hybrid LES related approach is proposed. With the latter, away from walls, no LES model is used, giving what can be termed numerical LES (NLES). This is relatively computationally efficient and makes use of the dissipation present in practical industrial computational fluid dynamics (CFD) programs. Near walls, RANS modeling is used to cover over numerous small structures, the LES resolution of which is generally intractable with current computational power. The linking of the RANS and NLES zones through a Hamilton–Jacobi equation is advocated. The RANS-NLES hybridization makes further sense for compressible flow solvers, where, as the Mach number tends to zero at walls, excessive dissipation can occur. The hybrid strategy is used to predict flow over a rib roughened surface and a jet impinging on a convex surface. These cases are important for blade cooling and show encouraging results. Further results are presented in a companion paper.

Simulation of the Gap Resonance Between Two Rectangular Barges in Regular Waves by a Free Surface Viscous Flow Solver

2013 ◽  
Author(s):  
B. Elie ◽  
G. Reliquet ◽  
P.-E. Guillerm ◽  
O. Thilleul ◽  
P. Ferrant ◽  
...  
Keyword(s):  
Experimental Data ◽  
Free Surface ◽  
Viscous Flow ◽  
Stokes Equations ◽  
Resonance Phenomenon ◽  
Navier Stokes ◽  
Regular Waves ◽  
Navier Stokes Equations ◽  
Flow Solver ◽  
Gap Resonance

This paper compares numerical and experimental results in the study of the resonance phenomenon which appears between two side-by-side fixed barges for different sea-states. Simulations were performed using SWENSE (Spectral Wave Explicit Navier-Stokes Equations) approach and results are compared with experimental data on two fixed barges with different headings and bilges. Numerical results, obtained using the SWENSE approach, are able to predict both the frequency and the magnitude of the RAO functions.

Simulation of laminar-turbulent transition with an explicit Navier-Stokes flow solver

1995 ◽  
Vol 11 (6) ◽  
pp. 1187-1194 ◽  
Author(s):  
Lyle D. Dailey ◽  
Ian K. Jennions ◽  
Paul D. Orkwis
Keyword(s):  
Stokes Flow ◽  
Navier Stokes ◽  
Flow Solver ◽  
Turbulent Transition ◽  
Laminar Turbulent Transition
Sign in / Sign up

Export Citation Format

Share Document