Unsteady RANS Simulations of Wells Turbine Under Transient Flow Conditions

2017 ◽  
Vol 140 (1) ◽  
Author(s):  
Qiuhao Hu ◽  
Ye Li
Keyword(s):  
Angular Velocity ◽  
Transient Flow ◽  
Constant Angular Velocity ◽  
Wave Frequency ◽  
Navier Stokes ◽  
Wells Turbine ◽  
Unsteady Rans ◽  
Sinusoidal Flow ◽  
Unsteady Conditions ◽  
Good Agreement

This paper presents our recent numerical simulations of a high-solidity Wells turbine under both steady and unsteady conditions by solving Reynolds-averaged Navier–Stokes (RANS) equations. For steady conditions, the equations are solved in a reference frame with the same angular velocity of the turbine. Good agreement between numerical simulation result and experimental data has been obtained in the operational region and incipient stall conditions. The exact value of stall point has been accurately predicted. Through analyzing the detailed fluid fields, we find that the stall occurs near the tip of the blade while the boundary layer keeps attached near the hub, due to the effect of radial flow. For unsteady conditions, two types of control methods are studied: constant angular velocity and constant damping moment. For the constant angular velocity, the behaviors of the turbine under both high and low sea wave frequency are calculated to compare with those obtained by quasi-steady method. The hysteresis characteristic can be observed and deeply affects the behaviors of the Wells turbine with high wave frequency. For the constant damping moment, the turbine angular velocity is time dependent. Under sinusoidal flow, the incident flow velocity in the operational region can be improved to avoid the stall.

Unsteady Rotating Flow in a Cylinder With a Free Surface

1968 ◽  
Vol 90 (4) ◽  
pp. 445-452 ◽  
Author(s):  
H. Goller ◽  
T. Ranov
Keyword(s):  
Free Surface ◽  
Angular Velocity ◽  
Stokes Equations ◽  
Constant Angular Velocity ◽  
Navier Stokes ◽  
Rotating Flow ◽  
Navier Stokes Equations ◽  
Surface Configuration ◽  
Simplifying Assumptions ◽  
Good Agreement

The investigation deals with the “spin-up” of the liquid partially filling a right circular cylinder which is impulsively accelerated from rest to a constant angular velocity. By application of certain simplifying assumptions, a simplification of the Navier-Stokes equations is obtained and numerically solved, obtaining the unsteady angular velocity distribution of the liquid and the configuration of the liquid’s free surface, as it approaches, asymptotically with time, a paraboloid. The simplifying assumptions are qualitatively verified by experiment. Measurement of the theoretically predicted free-surface configuration is obtained by an electrohydraulic servosystem designed and developed for the problem. Good agreement between experiment and theory is obtained.

Discussion: “Unsteady RANS Simulations of Wells Turbine Under Transient Flow Conditions” (Hu and Li, ASME J. Offshore Mech. Arct. Eng., 140(1), p. 011901)

2019 ◽  
Vol 141 (4) ◽  
Author(s):  
Tiziano Ghisu ◽  
Francesco Cambuli ◽  
Pierpaolo Puddu ◽  
Irene Virdis ◽  
Mario Carta
Keyword(s):  
Transient Flow ◽  
Careful Consideration ◽  
Navier Stokes ◽  
Flow Conditions ◽  
Wells Turbine ◽  
Numerical Errors ◽  
Performance Curves ◽  
Unsteady Rans ◽  
Computational Fluid Dynamics Cfd ◽  
Rans Simulations

The work by Hu and Li (2018, “Unsteady RANS Simulations of Wells Turbine Under Transient Flow Conditions,” ASME J. Offshore Mech. Arct. Eng., 140(1), p. 011901) presents the numerical simulation of a high-solidity Wells turbine by means of a computational fluid dynamics (CFD) (Reynolds-averaged Navier–Stokes (RANS)) approach. A key aspect highlighted by the authors is the presence of a hysteretic loop in the machine's performance curves, due (according to their explanation) to the interaction of vortices shed by the blade with the blade circulation, which is responsible for the aerodynamic forces. It is our opinion that this work contains some serious errors that invalidate the results. In this brief discussion, we aim to demonstrate how the hysteresis found and discussed by the authors should not be present in the turbine analyzed in Hu and Li (2018, “Unsteady RANS Simulations of Wells Turbine Under Transient Flow Conditions,” ASME J. Offshore Mech. Arct. Eng., 140(1), p. 011901), and it is unlikely to be present in any Wells turbine. The fact that Hu and Li find hysteresis in their simulations is most likely caused by numerical errors due to an insufficient temporal discretization. This and other inaccuracies could have been avoided with a more careful consideration of the available literature.

Preliminary Results of Numerical Simulations of a Bio-Mimetic Wells Turbine

2016 ◽  
Author(s):  
Qiuhao Hu ◽  
Ye Li ◽  
Fangyi Wei
Keyword(s):  
Energy Conversion ◽  
Three Dimensional ◽  
Turbine Rotor ◽  
Navier Stokes ◽  
Maximum Efficiency ◽  
Wells Turbine ◽  
Turbulence Effects ◽  
Dimensional Simulation ◽  
Lower Torque ◽  
Good Agreement

Wells turbine is a kind of self-rectified air turbines used in an oscillatory water column (OWC) device for wave energy conversion. In this study, a steady three-dimensional simulation of a fan-shaped Wells turbine is performed on Star CCM+ commercial software by solving the Reynolds-averaged Navier-Stokes (RANS) equations. The turbulence effects are taken into account by using the Spalart-Allmaras turbulence model. Good agreement between the numerical results and the experimental results within the operation region (5< α <11 degrees) is observed. The geometry of the turbine rotor has a significant effect on the performance of energy conversion. Inspired by the aerodynamics of low Reynolds flyer, the normal fan-shaped Wells turbine is optimized by a bio-mimetic method in which the profile of a hawk moth wing of Manduca Sexta is applied on the blades. The modified turbine has a lower torque and pressure drop coefficient with higher efficiency. The maximum efficiency for the modified turbine is 0.61, compared to 0.48 for the normal fan-shaped one. By analysis of the detailed flow-field, it has also been found that only the middle parts of the blade can effectively generate the momentum. In order to acquire a higher efficiency, further optimization is carried out by refining some blade parts in the tip and the hub which cannot effectively produce power.

CFD Analysis of a 15 Stage Axial Compressor: Part II — Results

2005 ◽  
Author(s):  
T. Belamri ◽  
P. Galpin ◽  
A. Braune ◽  
C. Cornelius
Keyword(s):  
Steady State ◽  
Flow Field ◽  
Transient Flow ◽  
Axial Compressor ◽  
Navier Stokes ◽  
Cfd Analysis ◽  
Pitch Change ◽  
Leakage Flows ◽  
Transient Models ◽  
Good Agreement

The flow field of a 15 stage axial compressor is analyzed using a 3-D Navier-Stokes CFD tool. The compressor under investigation is a prototype engine, first compressor version before optimization of the Siemens V84.3A family. The paper describes steady state and transient flow simulations of the entire 15 stages compressor in one computation (not piece by piece). The simulation includes tip gaps, mass bleeds, hub leakage flows, and ranges from single passage to full 360 degrees analysis. The work is divided into two companion papers. The second paper, “CFD Analysis of a 15 Stage Axial Compressor Part II: Results” describes the application of the methods in Part I to the entire 15 stage compressor (Belamri et al, 2005). The flow in the compressor is modeled first with one blade passage per component (periodicity assumed, an interface pitch change model employed). Steady state and transient models are compared. In a second series of computations, all blade passages in 360 degrees are modeled, (no periodicity or pitch change assumptions required), for portions of the compressor. The various simulation approaches are compared to each other, and to experimental data. Good agreement between predictions and experimental results, both in the details of the flow field and the integral prediction of operating range of the compressor, were found.

Simulation of Unsteady Flow Around a Cylinder

2015 ◽  
Vol 3 (2) ◽  
pp. 28-49
Author(s):  
Ridha Alwan Ahmed
Keyword(s):  
Stokes Equations ◽  
Lift Coefficient ◽  
Reynolds Numbers ◽  
Mean Value ◽  
Navier Stokes ◽  
Cylinder Surface ◽  
Navier Stokes Equations ◽  
Flow Around A Cylinder ◽  
Numerical Grid ◽  
Good Agreement

       In this paper, the phenomena of vortex shedding from the circular cylinder surface has been studied at several Reynolds Numbers (40≤Re≤ 300).The 2D, unsteady, incompressible, Laminar flow, continuity and Navier Stokes equations have been solved numerically by using CFD Package FLUENT. In this package PISO algorithm is used in the pressure-velocity coupling.        The numerical grid is generated by using Gambit program. The velocity and pressure fields are obtained upstream and downstream of the cylinder at each time and it is also calculated the mean value of drag coefficient and value of lift coefficient .The results showed that the flow is strongly unsteady and unsymmetrical at Re>60. The results have been compared with the available experiments and a good agreement has been found between them

Numerical Modeling of Evolution of Boundary Between Incompressible Gas and Liquid in Two-Dimensional Region

2006 ◽  
Vol 4 ◽  
pp. 224-236
Author(s):  
A.S. Topolnikov
Keyword(s):  
Numerical Modeling ◽  
Interphase Boundary ◽  
Incompressible Liquid ◽  
Stokes Equations ◽  
Numerical Code ◽  
Navier Stokes ◽  
Two Phase ◽  
Navier Stokes Equations ◽  
Incompressible Media ◽  
Good Agreement

The paper is devoted to numerical modeling of Navier–Stokes equations for incompressible media in the case, when there exist gas and liquid inside the rectangular calculation region, which are separated by interphase boundary. The set of equations for incompressible liquid accounting for viscous, gravitational and surface (capillary) forces is solved by finite-difference scheme on the spaced grid, for description of interphase boundary the ideology of Level Set Method is used. By developed numerical code the set of hydrodynamic problems is solved, which describe the motion of two-phase incompressible media with interphase boundary. As a result of numerical simulation the solutions are obtained, which are in good agreement with existing analytical and experimental solutions.

Mathematical modeling of Couette flow in anomalous thermoviscous liquid

2011 ◽  
Vol 8 (1) ◽  
pp. 143-152
Author(s):  
S.F. Khizbullina
Keyword(s):  
Mathematical Modeling ◽  
Angular Velocity ◽  
Numerical Experiment ◽  
Temperature Dependence ◽  
Steady Flow ◽  
Couette Flow ◽  
Outer Cylinder ◽  
Flow Regimes ◽  
Constant Angular Velocity ◽  
Coaxial Cylinders

The steady flow of anomalous thermoviscous liquid between the coaxial cylinders is considered. The inner cylinder rotates at a constant angular velocity while the outer cylinder is at rest. On the basis of numerical experiment various flow regimes depending on the parameter of viscosity temperature dependence are found.

On the Flow Fields of Inertial Impactors

1974 ◽  
Vol 96 (4) ◽  
pp. 394-400 ◽  
Author(s):  
V. A. Marple ◽  
B. Y. H. Liu ◽  
K. T. Whitby
Keyword(s):  
Flow Field ◽  
Stokes Equations ◽  
Relaxation Method ◽  
Water Model ◽  
Navier Stokes ◽  
Visualization Technique ◽  
Navier Stokes Equations ◽  
Theoretical Results ◽  
Plate Distance ◽  
Good Agreement

The flow field in an inertial impactor was studied experimentally with a water model by means of a flow visualization technique. The influence of such parameters as Reynolds number and jet-to-plate distance on the flow field was determined. The Navier-Stokes equations describing the laminar flow field in the impactor were solved numerically by means of a finite difference relaxation method. The theoretical results were found to be in good agreement with the empirical observations made with the water model.

Mechanism and Flow Control on the Mismatching of Impeller and Vaned Diffuser Caused by Inlet Prewhirl for Centrifugal Compressors

2016 ◽  
Author(s):  
Qiangqiang Huang ◽  
Xinqian Zheng ◽  
Aolin Wang
Keyword(s):  
Flow Control ◽  
Control Method ◽  
Three Dimensional ◽  
Navier Stokes ◽  
Vaned Diffuser ◽  
Inlet Distortion ◽  
Computational Fluid Dynamics Cfd ◽  
Stagger Angle ◽  
Good Agreement ◽  
Matching Relation

Air often flows into compressors with inlet prewhirl, because it will obtain a circumferential component of velocity via inlet distortion or swirl generators such as inlet guide vanes. A lot of research has shown that inlet prewhirl does influence the characteristics of components, but the change of the matching relation between the components caused by inlet prewhirl is still unclear. This paper investigates the influence of inlet prewhirl on the matching of the impeller and the diffuser and proposes a flow control method to cure mismatching. The approach combines steady three-dimensional Reynolds-averaged Navier-Stokes (RANS) simulations with theoretical analysis and modeling. The result shows that a compressor whose impeller and diffuser match well at zero prewhirl will go to mismatching at non-zero prewhirl. The diffuser throat gets too large to match the impeller at positive prewhirl and gets too small for matching at negative prewhirl. The choking mass flow of the impeller is more sensitive to inlet prewhirl than that of the diffuser, which is the main reason for the mismatching. To cure the mismatching via adjusting the diffuser vanes stagger angle, a one-dimensional method based on incidence matching has been proposed to yield a control schedule for adjusting the diffuser. The optimal stagger angle predicted by analytical method has good agreement with that predicted by computational fluid dynamics (CFD). The compressor is able to operate efficiently in a much broader flow range with the control schedule. The flow range, where the efficiency is above 80%, of the datum compressor and the compressor only employing inlet prewhirl and no control are just 25.3% and 31.8%, respectively. For the compressor following the control schedule, the flow range is improved up to 46.5%. This paper also provides the perspective of components matching to think about inlet distortion.

Low-Pressure Compressor Near-Stall Predictions Using Unsteady CFD Methods

2021 ◽  
Author(s):  
David Vanpouille ◽  
Dimitrios Papadogiannis ◽  
Stéphane Hiernaux
Keyword(s):  
Low Pressure ◽  
Navier Stokes ◽  
Phase Lag ◽  
Sliding Mesh ◽  
Tip Leakage ◽  
Eddy Simulation ◽  
Surge Margin ◽  
Large Eddy ◽  
Unsteady Rans ◽  
Pressure Compressor

Abstract Surge margin is critical for the safety of aeronautical compressors, hence predicting it early in the design process using CFD is mandatory. However, close to surge, steady-state Reynolds Averaged Navier-Stokes (RANS) simulations are proven inadequate. Unsteady techniques such as Unsteady RANS (URANS) and Large Eddy Simulation (LES) can provide more reliable predictions. Nevertheless, the accuracy of such methods are dependent on the method used to handle the rotor/stator interfaces. The most precise method, the sliding mesh, requires simulating the full annulus or a periodic sector, which can be very costly. Other techniques to reduce the domain exist, such as the phase-lagged approach or geometric blade scaling, but introduce restrictive assumptions on the flow at near-stall conditions. The objective of this paper is to investigate the near-stall flow of a low-pressure compressor using unsteady methods of varying fidelity: URANS with the phase lag assumption, URANS on a periodic sector and a high-fidelity LES on a smaller periodic sector achieved using geometric blade scaling. Results are compared to experimental measurements. An overall good agreement is found. Results show that the tip leakage vortex is not the origin of the stall on the studied configuration and a hub corner separation is initiated. LES further validates the (U)RANS flow predictions and brings additional insight on unsteady flow separations.

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