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.

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.

scholarly journals On the Calculation of Propulsive Characteristics of a Bulk-Carrier Moving in Head Seas

2020 ◽  
Vol 8 (10) ◽  
pp. 786
Author(s):  
S. Polyzos ◽  
G. Tzabiras
Keyword(s):  
Navier Stokes ◽  
Bulk Carrier ◽  
Time Step ◽  
Towing Tank ◽  
Model Scale ◽  
Time Period ◽  
Unsteady Rans ◽  
Computational Fluid Dynamics Cfd ◽  
The Time Domain ◽  
Propeller Performance

The present work describes a simplified Computational Fluid Dynamics (CFD) approach in order to calculate the propulsive performance of a ship moving at steady forward speed in head seas. The proposed method combines experimental data concerning the added resistance at model scale with full scale Reynolds Averages Navier–Stokes (RANS) computations, using an in-house solver. In order to simulate the propeller performance, the actuator disk concept is employed. The propeller thrust is calculated in the time domain, assuming that the total resistance of the ship is the sum of the still water resistance and the added component derived by the towing tank data. The unsteady RANS equations are solved until self-propulsion is achieved at a given time step. Then, the computed values of both the flow rate through the propeller and the thrust are stored and, after the end of the examined time period, they are processed for calculating the variation of Shaft Horsepower (SHP) and RPM of the ship’s engine. The method is applied for a bulk carrier which has been tested in model scale at the towing tank of the Laboratory for Ship and Marine Hydrodynamics (LSMH) of the National Technical University of Athens (NTUA).

scholarly journals A CFD modeling procedure to assess the effect of wind in settling tanks

2018 ◽  
Vol 21 (1) ◽  
pp. 123-135 ◽  
Author(s):  
A. Gkesouli ◽  
A. Stamou
Keyword(s):  
Water Treatment ◽  
Present Model ◽  
Settling Velocity ◽  
Transient Flow ◽  
Treatment Plant ◽  
Water Treatment Plant ◽  
Cfd Modeling ◽  
Flow Conditions ◽  
Computational Fluid Dynamics Cfd ◽  
Research Questions

Abstract We propose a systematic procedure that combines computational fluid dynamics (CFD) modeling and experimental work to answer two research questions that are usually posed by researchers and managers of water treatment plants: ‘Is the effect of wind on settling tanks important?’ and ‘How can we determine this effect in our settling tanks?’ We apply this procedure in the water treatment plant of Aharnes, Athens to derive the following conclusions. (1) The effect of wind increases with increasing co-current wind velocity, increasing settling velocity and decreasing flow rate. (2) In windy steady-state flow conditions, the degree of complexity and three-dimensionality of the flow field that is observed in calm conditions is reduced and the removal efficiency decreases from 85.1 in calm conditions to 82.0%. Predicted efficiencies for constant and variable inlet solids' concentrations compare favorably with measurements. (3) In windy, transient flow conditions, field data show that the effect of wind on the tank's efficiency can be very pronounced and within the first half hour of the windy period the efficiency decreases to approximately 55%; the present model does not capture this effect, because it cannot simulate the sludge layer and the subsequent re-suspension of the settled solids.

Check Valve Behavior Under Transient Flow Conditions: A State-of-the-Art Review

1989 ◽  
Vol 111 (2) ◽  
pp. 178-183 ◽  
Author(s):  
A. R. D. Thorley
Keyword(s):  
Transient Flow ◽  
State Of The Art ◽  
Check Valve ◽  
Reliable Information ◽  
Flow Conditions ◽  
Design Engineers ◽  
Performance Curves ◽  
Valve Dynamics ◽  
Pipeline Design ◽  
Data Design

Recent advances in the understanding of check valve behavior are reviewed. It is evident that the basis now exists for providing reliable information on valve dynamics that is in a form that can be easily assimilated and used by pipeline design engineers. The use of nondimensional valve performance curves is discussed and recommended. Manufacturers are encouraged to provide these data. Design engineers are charged with the responsibility of using it and are provided with guidelines for so doing.

A Single-Stage Centripetal Pump—Design Features and an Investigation of the Operating Characteristics

2010 ◽  
Vol 132 (2) ◽  
Author(s):  
Mihael Sekavčnik ◽  
Tine Gantar ◽  
Mitja Mori
Keyword(s):  
Single Stage ◽  
Flow Conditions ◽  
Operating Characteristics ◽  
Cfd Simulations ◽  
Pump Design ◽  
Flow Channels ◽  
Performance Curves ◽  
Computational Fluid Dynamics Cfd ◽  
Working Media ◽  
Inflow Conditions

In this paper, we present an experimental and numerical investigation of a single-stage centripetal pump (SSCP). This SSCP is designed to operate in the pump regime, while forcing the working media through impeller-stator flow channels in the radial inward direction. The measured performance curves are characterized by a hysteresis, since the throttle-closing performance curves do not correspond to the throttle-opening performance curves throughout the whole operating range. A computational fluid dynamics (CFD) model was developed to establish these throttle-closing and throttle-opening performance curves. The flow conditions obtained with the CFD simulations confirm that the hydraulic behavior of the SSCP is influenced by the partial circumferential stall that occurs in the impeller-stator flow channels. It was shown that the inflow conditions to the impeller-stator assembly considerably influence the flow rate of the stall cessation, the size of the hysteresis, and the head generated during part-load operations.

High-Fidelity Numerical Analysis of Per-Rev-Type Inlet Distortion Transfer in Multistage Fans—Part II: Entire Component Simulation and Investigation

2010 ◽  
Vol 132 (4) ◽  
Author(s):  
Jixian Yao ◽  
Steven E. Gorrell ◽  
Aspi R. Wadia
Keyword(s):  
Total Pressure ◽  
Navier Stokes ◽  
High Fidelity ◽  
Inlet Distortion ◽  
Unsteady Rans ◽  
Total Temperature ◽  
Computational Fluid Dynamics Cfd ◽  
Last Stage ◽  
Remarkable Agreement ◽  
Engine Development

Part I of this paper validated the ability of the unsteady Reynolds-Averaged Navier-Stokes (RANS) solver PTURBO to accurately simulate distortion transfer and generation through selected blade rows of two multistage fans. In this part, unsteady RANS calculations were successfully applied to predict the 1/rev inlet total pressure distortion transfer in the entirety of two differently designed multistage fans. This paper demonstrates that high-fidelity computational fluid dynamics (CFD) can be used early in the design process for verification purposes before hardware is built and can be used to reduce the number of distortion tests, hence reducing engine development cost. The unsteady RANS code PTURBO demonstrated remarkable agreement with the data, accurately capturing both the magnitude and the profile of total pressure and total temperature measurements. Detailed analysis of the flow physics identified from the CFD results has led to a thorough understanding of the total temperature distortion generation and transfer mechanism, especially for the spatial phase difference of total pressure and total temperature profiles. The analysis illustrates that the static parameters are more revealing than their stagnation counterpart and that pressure and temperature rise are more revealing while the pressure and temperature ratio could be misleading. The last stage is effectively throttled by the inlet distortion even though the overall engine throttle remains unchanged. The total temperature distortion generally grows as flow passes through the fan stages.

RANS Simulations of a Simplified Tractor/Trailer Geometry

2006 ◽  
Vol 128 (5) ◽  
pp. 1083-1089 ◽  
Author(s):  
Christopher J. Roy ◽  
Jeffrey Payne ◽  
Mary McWherter-Payne
Keyword(s):  
Vortical Structure ◽  
Three Dimensional ◽  
Navier Stokes ◽  
Base Region ◽  
Near Wake ◽  
Three Dimensional Flow ◽  
Fine Mesh ◽  
Computational Fluid Dynamics Cfd ◽  
Rans Simulations ◽  
Yaw Angle

Steady-state Reynolds-averaged Navier-Stokes (RANS) simulations are presented for the three-dimensional flow over a simplified tractor/trailer geometry at zero degrees yaw angle. The simulations are conducted using a multi-block, structured computational fluid dynamics (CFD) code. The turbulence closure model employed is the two-equation Menter k-ω model. The discretization error is estimated by employing two grid levels: a fine mesh of 20 million cells and a coarser mesh of 2.5 million cells. Simulation results are compared to experimental data obtained at the NASA-Ames 7×10ft wind tunnel. Quantities compared include vehicle drag, surface pressures, and time-averaged velocities in the trailer near wake. The results indicate that the RANS approach is able to accurately predict the surface pressure on the vehicle, with the exception of the base region. The pressure predictions in the base region are poor due to the inability of the RANS model to accurately capture the near-wake vortical structure. However, the gross pressure levels in the base region are in reasonable agreement with experiment, and thus the overall vehicle drag is well predicted.

The Effect of Midplane Guide Vanes in a Biplane Wells Turbine

2018 ◽  
Vol 141 (5) ◽  
Author(s):  
Tapas K. Das ◽  
Abdus Samad
Keyword(s):  
Stokes Equations ◽  
Guide Vane ◽  
Flow Analysis ◽  
Leading Edge ◽  
Navier Stokes ◽  
Flow Conditions ◽  
Wells Turbine ◽  
Navier Stokes Equations ◽  
Guide Vanes ◽  
Ansys Cfx

Guide vanes (GVs) improve the performance of a turbine in terms of efficiency, torque, or operating range. In this work, a concept of different orientations of GVs in between a two-row biplane wells turbine (BWT) was introduced and analyzed for the performance improvement. The fluid flow was simulated numerically with a commercial software ANSYS CFX 16.1. The Reynolds-averaged Navier–Stokes equations with the k-ω turbulence closure model were solved for different designs and flow conditions. For the base model, the results from simulation and experiments are in close agreement. Among the designs considered, the configuration, where the blades are in one line (zero circumferential angle between blades of two plane) and the midplane guide vane has concave side to the leading edge of the blade, performed relatively better. However, the performance was still less compared to the base model. The reason behind the reduction in performance from the base model is attributed to the blockage of flow and the change of flow path occurring due to the presence of the midplane GVs. The flow analysis of different cases and the comparison with the base model are presented in the current study.

Large-Eddy simulation of rim seal ingestion

2011 ◽  
Vol 225 (12) ◽  
pp. 2881-2891 ◽  
Author(s):  
T S D O'Mahoney ◽  
N J Hills ◽  
J W Chew ◽  
T Scanlon
Keyword(s):  
Reynolds Number ◽  
Turbulence Models ◽  
Navier Stokes ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Rans Turbulence Models ◽  
Unsteady Rans ◽  
Rans Simulations ◽  
Secondary Air ◽  
The One

Unsteady flow dynamics in turbine rim seals are known to be complex and attempts accurately to predict the interaction of the mainstream flow with the secondary air system cooling flows using computational fluid dynamics (CFD) with Reynolds-averaged Navier–Stokes (RANS) turbulence models have proved difficult. In particular, published results from RANS models have over-predicted the sealing effectiveness of the rim seal, although their use in this context continues to be common. Previous studies have ascribed this discrepancy to the failure to model flow structures with a scale greater than the one which can be captured in the small-sector models typically used. This article presents results from a series of Large-Eddy Simulations (LES) of a turbine stage including a rim seal and rim cavity for, it is believed by the authors, the first time. The simulations were run at a rotational Reynolds number Reθ = 2.2 × 106 and a main annulus axial Reynolds number Rex = 1.3 × 106 and with varying levels of coolant mass flow. Comparison is made with previously published experimental data and with unsteady RANS simulations. The LES models are shown to be in closer agreement with the experimental sealing effectiveness than the unsteady RANS simulations. The result indicates that the previous failure to predict rim seal effectiveness was due to turbulence model limitations in the turbine rim seal flow. Consideration is given to the flow structure in this region.

scholarly journals Navier-Stokes Computations for Turbulent Flow Predictions in Transonic Turbine Cascade Using a Zonal Approach

1993 ◽  
Author(s):  
J. J. Yeuan ◽  
A. Hamed ◽  
W. Tabakoff
Keyword(s):  
Turbulent Flow ◽  
Viscous Flow ◽  
Turbine Blade ◽  
Turbulence Models ◽  
Navier Stokes ◽  
Turbine Cascade ◽  
Flow Conditions ◽  
Numerical Errors ◽  
Flow Through ◽  
Transonic Turbine

Numerical results are presented for viscous flow through a transonic turbine cascade using different turbulence models and H-type grids. The explicit Navier-Stokes solver used in the solution was developed with an option of conservative zonal approach for interpolation across the periodic boundaries with minimum numerical errors. This approach allows the use of a grid that is more orthogonal and less skewed which leads to higher accuracy in the prediction of turbine blade performance. The results obtained with an algebraic and two equation turbulence models, and with two types of H grids are compared at two different flow conditions.

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