A Critical Examination of the Hysteresis in Wells Turbines Using Computational Fluid Dynamics and Lumped Parameter Models

2020 ◽  
Vol 142 (5) ◽  
Author(s):  
Tiziano Ghisu ◽  
Francesco Cambuli ◽  
Pierpaolo Puddu ◽  
Irene Virdis ◽  
Mario Carta ◽  
...  
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Turbine Blades ◽  
Unsteady Aerodynamics ◽  
Operating Conditions ◽  
Lumped Parameter Model ◽  
Hysteretic Behavior ◽  
Critical Examination ◽  
Wells Turbine ◽  
Lumped Parameter

Abstract The hysteretic behavior of oscillating water column (OWC)-installed Wells turbines has been known for decades. The common explanation invokes the presence of unsteady aerodynamics due to the continuously varying incidence of the flow on the turbine blades. This phenomenon is neither new nor unique to Wells turbines, as an aerodynamic hysteresis is present in rapidly oscillating airfoils and wings, as well as in different types of turbomachinery, such as wind turbines and helicopter rotors, which share significant similarities with a Wells turbine. An important difference is the non-dimensional frequency: the hysteresis appears in oscillating airfoils only at frequencies orders of magnitude larger than the ones Wells turbines operate at. This work contains a re-examination of the phenomenon, using both computational fluid dynamics (CFD) and a lumped parameter model, and shows how the aerodynamic hysteresis in Wells turbines is negligible and how the often measured differences in performance between acceleration and deceleration are caused by the capacitive behavior of the OWC system. Results have been verified with respect to both spatial and temporal discretization, for unstalled and stalled operating conditions.

A Critical Examination of the Hysteresis in Wells Turbines Using CFD and Lumped Parameter Models

2019 ◽  
Author(s):  
T. Ghisu ◽  
F. Cambuli ◽  
P. Puddu ◽  
I. Virdis ◽  
M. Carta ◽  
...  
Keyword(s):  
Turbine Blades ◽  
Unsteady Aerodynamics ◽  
Lumped Parameter Model ◽  
Hysteretic Behavior ◽  
Critical Examination ◽  
Wells Turbine ◽  
Lumped Parameter ◽  
Lumped Parameter Models ◽  
Acceleration And Deceleration ◽  
The Common

Abstract The hysteretic behavior of OWC-installed Wells turbines has been known for decades. The common explanation invokes the presence of unsteady aerodynamics due to the continuously varying incidence of the flow on the turbine blades. This phenomenon is neither new nor unique to Wells turbines, as an aerodynamic hysteresis is present in rapidly oscillating airfoils and wings, as well as in different types of turbomachinery, such as wind turbines and helicopter rotors, which share significant similarities with a Wells turbine. An important difference is the non-dimensional frequency: the hysteresis appears in oscillating airfoils only at frequencies orders of magnitude larger than the ones Wells turbines operate at. This work contains a reexamination of the phenomenon, using both CFD and a lumped parameter model, and shows how the aerodynamic hysteresis in Wells turbines is negligible, and how the often measured differences in performance between acceleration and deceleration are caused by the capacitive behavior of the OWC system.

Evaluation of Pulmonary Arterial Hypertension Using Computational Fluid Dynamics Simulation

2017 ◽  
Author(s):  
Shahab Taherian ◽  
Hamid Rahai ◽  
Jamie Shin ◽  
Jeremy Feldman ◽  
Thomas Waddington
Keyword(s):  
Fluid Dynamics ◽  
Boundary Condition ◽  
Computational Fluid Dynamics ◽  
Pulmonary Arterial Hypertension ◽  
Arterial Hypertension ◽  
In Silico ◽  
Lumped Parameter Model ◽  
Lumped Parameter ◽  
Pulmonary Arterial ◽  
Outlet Boundary Condition

In silico study of the relationships between flow conditions, arterial surface shear stress, and pressure was investigated in a patient with pulmonary arterial hypertension (PAH), using multi-detector Computed Tomography Angiography (CTA) images and Computational Fluid Dynamics (CFD). The CTA images were converted into 3D models and transferred to CFD software for simulations, allowing for patient-specific comparisons between in silico results with clinical right heart catheterization pressure data. The simulations were performed using two different methods of outlet boundary conditions: zero traction and lumped parameter model (LPM) methods. Outlet pressures were set to a constant value in zero traction method, which can produce flow characteristics solely based on the segmented distal arteries, while the lumped parameter model used a three-element Windkessel lumped model to represent the distal vasculature by accounting for resistance, compliance, and impedance of the vasculature. Considering existing limitations with both approaches, it was found that the lumped parameter Windkessel outlet boundary condition provides a better correlation with the clinical RHC pressure results than the zero traction constant pressure outlet boundary condition.

Advances in simulation of gerotor pumps: An integrated approach

2017 ◽  
Vol 231 (7) ◽  
pp. 1221-1236 ◽  
Author(s):  
Giorgio Altare ◽  
Massimo Rundo
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Integrated Approach ◽  
Element Model ◽  
Lumped Parameter Model ◽  
Lumped Parameter ◽  
Pump Flow Rate ◽  
Incomplete Filling ◽  
Pressure Ripple ◽  
Dynamics Simulations

The paper describes a multi-domain simulation of a gerotor oil pump. Three different analysis tools have been used in synergy to predict the pump flow rate, in both conditions of complete and incomplete filling, and the pressure ripple. The computational fluid dynamics software PumpLinx® has been used for the determination of the discharge coefficients, while a finite element model analysis performed with ANSYS® has allowed the evaluation of the deflection of the pump cover under the action of the delivery pressure. The data calculated with the 3D tools have been utilized as input for a lumped parameter model of the pump developed in LMS Amesim® with customized libraries. The aim of the study is to supply the guidelines for tuning the models using a reduced number of computational fluid dynamics simulations. The results collected in the experimental campaign have demonstrated that a lumped parameter approach can be suitable, if properly calibrated, to predict the pressure oscillations in conditions of defective filling. Moreover, it was found that the cover deflection has a significant importance not only on the leakages, but also on the pressure ripple.

A Computational Fluid Dynamics Comparison of Wells Turbine Blades in 2D and 3D Cascade Flow

2002 ◽  
Author(s):  
John Daly ◽  
Patrick Frawley ◽  
Ajit Thakker
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Turbine Blades ◽  
Three Dimensional ◽  
Primary Objective ◽  
Two Dimensional ◽  
Three Dimensional Model ◽  
Wells Turbine ◽  
Cascade Flow ◽  
Cascade Models

This paper deals with the application of Computational Fluid Dynamics (CFD) to the analysis of the aerodynamic characteristics of symmetrical airfoil blades in 2-Dimensional cascade flow. Theoretical two dimensional cascade analyses of Wells Turbines blade profiles have been used in the past to predict the performance of three-dimensional turbines. The use of two-dimensional cascade models is beneficial as it allows the analysis and optimisation of the blade profile with approximately one tenth the computational requirements of a three-dimensional model. The primary objective of this work was to provide further validation of the use of two dimensional cascade models by comparing the computational predictions with traditional theoretical calculation results and also with three-dimensional turbine results. A secondary objective was to use the two dimensional cascade models to better understand the blade interaction effects that occur in the Wells Turbine. The model was used to analyse and compare three different blade profiles at different cascade settings. This paper presents the results of the numerical investigation, the validation of the results and the subsequent analysis.

Applicability of an entry flow model of the brachial artery for flow models of the hemodialysis fistula

2017 ◽  
Vol 231 (8) ◽  
pp. 766-773
Author(s):  
Sulav Bastola ◽  
William D Paulson ◽  
Steven A Jones
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Arteriovenous Fistula ◽  
Brachial Artery ◽  
Poiseuille Flow ◽  
Flow Model ◽  
High Flow ◽  
Lumped Parameter Model ◽  
Flow Rates ◽  
Lumped Parameter

The native arteriovenous fistula creates a shunt that provides the high blood flow that is needed for dialysis. Lumped parameter hemodynamic models of the arteriovenous fistula can be used to predict shear stresses and pressure losses and can be applied to help understand unsolved problems such as the high rate of arteriovenous fistula maturation failure. These models combine together flow components, such as arteries, stenosis, anastomoses, arterial compliance, and blood inertia, and each component must be modeled with an appropriate pressure–flow relationship. Poiseuille flow is generally assumed for straight vessels, but the unique high flow rates within the brachial artery of an arteriovenous fistula are expected to induce entry flow effects that are neglected in this model. To estimate the importance of these effects, brachial artery flow was modeled in a low-resistance network, such as the one that occurs when an arteriovenous fistula is constructed, through the lumped parameter model, and the predicted flow rates and pressures were compared to those predicted by computational fluid dynamics. When Poiseuille flow was assumed, the flow rate from the lumped parameter model was consistently larger than that from computational fluid dynamics, with a cycle-averaged error of 36.8%. When an entry flow model (Shah) was assumed, the lumped parameter–based flow was 6% lower than the computational fluid dynamics model at the peak of the flow waveform, and the cycle-averaged error was reduced to 7.8%. Thus, in a low-resistance (high flow) arteriovenous fistula circuit, an entry flow model can account for steeper near-wall velocity gradients. This result can provide a useful guide for designing engineering models of the arteriovenous fistula.

Computational Fluid Dynamics Thermohydrodynamic Analysis of Three-Dimensional Sector-Pad Thrust Bearings With Rectangular Dimples

2013 ◽  
Vol 136 (1) ◽  
Author(s):  
C. I. Papadopoulos ◽  
L. Kaiktsis ◽  
M. Fillon
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Carrying Capacity ◽  
Thermal Effects ◽  
Operating Conditions ◽  
Load Carrying Capacity ◽  
Performance Indices ◽  
Thrust Bearings ◽  
Load Carrying ◽  
Texture Design

The paper presents a detailed computational study of flow patterns and performance indices in a dimpled parallel thrust bearing. The bearing consists of eight pads; the stator surface of each pad is partially textured with rectangular dimples, aiming at maximizing the load carrying capacity. The bearing tribological performance is characterized by means of computational fluid dynamics (CFD) simulations, based on the numerical solution of the Navier–Stokes and energy equations for incompressible flow. Realistic boundary conditions are implemented. The effects of operating conditions and texture design are studied for the case of isothermal flow. First, for a reference texture pattern, the effects of varying operating conditions, in particular minimum film thickness (thrust load), rotational speed and feeding oil pressure are investigated. Next, the effects of varying texture geometry characteristics, in particular texture zone circumferential/radial extent, dimple depth, and texture density on the bearing performance indices (load carrying capacity, friction torque, and friction coefficient) are studied, for a representative operating point. For the reference texture design, the effects of varying operating conditions are further investigated, by also taking into account thermal effects. In particular, adiabatic conditions and conjugate heat transfer at the bearing pad are considered. The results of the present study indicate that parallel thrust bearings textured by proper rectangular dimples are characterized by substantial load carrying capacity levels. Thermal effects may significantly reduce load capacity, especially in the range of high speeds and high loads. Based on the present results, favorable texture designs can be assessed.

scholarly journals Design and Analysis of a Wind Turbine Blade with Dimples to Enhance the Efficiency through CFD with ANSYS R16.0

2018 ◽  
Vol 207 ◽  
pp. 02004
Author(s):  
M. Rajaram Narayanan ◽  
S. Nallusamy ◽  
M. Ragesh Sathiyan
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Wind Turbine ◽  
Wind Turbines ◽  
Turbine Blades ◽  
Electrical Energy ◽  
Optimum Combination ◽  
Surface Topology ◽  
Wind Turbine Blades ◽  
Lift And Drag

In the global scenario, wind turbines and their aerodynamics are always subjected to constant research for increasing their efficiency which converts the abundant wind energy into usable electrical energy. In this research, an attempt is made to increase the efficiency through the changes in surface topology of wind turbines through computational fluid dynamics. Dimples on the other hand are very efficient in reducing air drag as is it evident from the reduction of drag and increase in lift in golf balls. The predominant factors influencing the efficiency of the wind turbines are lift and drag which are to be maximized and minimized respectively. In this research, surface of turbine blades are integrated with dimples of various sizes and arrangements and are analyzed using computational fluid dynamics to obtain an optimum combination. The analysis result shows that there is an increase in power with about 15% increase in efficiency. Hence, integration of dimples on the surface of wind turbine blades has helped in increasing the overall efficiency of the wind turbine.

scholarly journals Three-Dimensional Aerodynamic Analysis of a Darrieus Wind Turbine Blade Using Computational Fluid Dynamics and Lifting Line Theory

2017 ◽  
Author(s):  
Francesco Balduzzi ◽  
Alessandro Bianchini ◽  
Giovanni Ferrara ◽  
David Marten ◽  
George Pechlivanoglou ◽  
...  
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
High Performance ◽  
Three Dimensional ◽  
Unsteady Aerodynamics ◽  
Cost Effective ◽  
Navier Stokes ◽  
Line Theory ◽  
Wake Model ◽  
Lifting Line

Due to the rapid progress in high-performance computing and the availability of increasingly large computational resources, Navier-Stokes computational fluid dynamics (CFD) now offers a cost-effective, versatile and accurate means to improve the understanding of the unsteady aerodynamics of Darrieus wind turbines and deliver more efficient designs. In particular, the possibility of determining a fully resolved flow field past the blades by means of CFD offers the opportunity to both further understand the physics underlying the turbine fluid dynamics and to use this knowledge to validate lower-order models, which can have a wider diffusion in the wind energy sector, particularly for industrial use, in the light of their lower computational burden. In this context, highly spatially and temporally refined time-dependent three-dimensional Navier-Stokes simulations were carried out using more than 16,000 processor cores per simulation on an IBM BG/Q cluster in order to investigate thoroughly the three-dimensional unsteady aerodynamics of a single blade in Darrieus-like motion. Particular attention was payed to tip losses, dynamic stall, and blade/wake interaction. CFD results are compared with those obtained with an open-source code based on the Lifting Line Free Vortex Wake Model (LLFVW). At present, this approach is the most refined method among the “lower-fidelity” models and, as the wake is explicitly resolved in contrast to BEM-based methods, LLFVW analyses provide three-dimensional flow solutions. Extended comparisons between the two approaches are presented and a critical analysis is carried out to identify the benefits and drawbacks of the two approaches.

scholarly journals Three-Dimensional Aerodynamic Analysis of a Darrieus Wind Turbine Blade Using Computational Fluid Dynamics and Lifting Line Theory

2017 ◽  
Vol 140 (2) ◽  
Author(s):  
Francesco Balduzzi ◽  
David Marten ◽  
Alessandro Bianchini ◽  
Jernej Drofelnik ◽  
Lorenzo Ferrari ◽  
...  
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
High Performance ◽  
Three Dimensional ◽  
Unsteady Aerodynamics ◽  
Cost Effective ◽  
Navier Stokes ◽  
Line Theory ◽  
Wake Model ◽  
Lifting Line

Due to the rapid progress in high-performance computing and the availability of increasingly large computational resources, Navier–Stokes (NS) computational fluid dynamics (CFD) now offers a cost-effective, versatile, and accurate means to improve the understanding of the unsteady aerodynamics of Darrieus wind turbines and deliver more efficient designs. In particular, the possibility of determining a fully resolved flow field past the blades by means of CFD offers the opportunity to both further understand the physics underlying the turbine fluid dynamics and to use this knowledge to validate lower-order models, which can have a wider diffusion in the wind energy sector, particularly for industrial use, in the light of their lower computational burden. In this context, highly spatially and temporally refined time-dependent three-dimensional (3D) NS simulations were carried out using more than 16,000 processor cores per simulation on an IBM BG/Q cluster in order to investigate thoroughly the 3D unsteady aerodynamics of a single blade in Darrieus-like motion. Particular attention was paid to tip losses, dynamic stall, and blade/wake interaction. CFD results are compared with those obtained with an open-source code based on the lifting line free vortex wake model (LLFVW). At present, this approach is the most refined method among the “lower-fidelity” models, and as the wake is explicitly resolved in contrast to blade element momentum (BEM)-based methods, LLFVW analyses provide 3D flow solutions. Extended comparisons between the two approaches are presented and a critical analysis is carried out to identify the benefits and drawbacks of the two approaches.

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