scholarly journals Analysis and Control of Complex Flows in U-Bends Using Computational Fluid Dynamics

2014 ◽  
Author(s):  
Yiğitcan Güden ◽  
Mehmet Metin Yavuz
Keyword(s):  
Fluid Dynamic ◽  
Computation Time ◽  
Radius Of Curvature ◽  
Complex Flow ◽  
Complex Flows ◽  
Dean Number ◽  
Mean Velocity ◽  
Dean Vortices ◽  
Numerical Studies ◽  
And Control

Analysis and control of flow structure in U-bends are crucial since U-bends are used in many different engineering applications. As a flow parameter in U-bends, the ratio of inertial and centrifugal forces to viscous forces is called as Dean number. The increase of Dean number destabilizes the flow and leads to a three-dimensional flow consisting of stream wise parallel counter-rotating vortices (Dean vortices) stacked along the curved wall. Due to the curvature in U-bends, the flow development involves complex flow structures including Dean vortices and high levels of turbulence that are not seen in straight duct flows. These are quite critical in considering noise problems and structural failure of the ducts. In this work, computational fluid dynamic (CFD) models are developed using ANSYS FLUENT to simulate these complex flows patterns in square sectioned U-bend with a radius of curvature Rc/D=0.65. The predictions of mean velocity profiles on different angular positions of the U-bend are compared against the experimental results available in the literature and previous numerical studies. Performance of six different turbulence models are evaluated, namely: the standard k-ε, the k-ε Realizable, the k-ε RNG, the k-ω SST, the Reynolds Stress Model (RSM) and the Scale-Adaptive Simulation Model (SAS), to propose the best numerical approach with increasing the accuracy of the solutions while reducing the computation time. Numerical results show remarkable improvements with respect to previous numerical studies and good agreement with the available experimental data. The best turbulence model for this application is proposed considering both the computation time and the result accuracy. In addition, different flow control techniques are still under investigation to eliminate Dean vortices and to reduce turbulence levels in U-bends.

On the Unsteady Interaction Between the Leakage and the Main Passage Flow in a High Pressure Turbine Rig: CFD URANS Investigations and Comparison With the Rig Test Data

2016 ◽  
Author(s):  
Giulio Zamboni ◽  
Paolo Adami
Keyword(s):  
Test Data ◽  
Fluid Dynamic ◽  
Flow Path ◽  
Complex Flow ◽  
Complex Flows ◽  
Design Work ◽  
Flow Interactions ◽  
Present Design ◽  
Unsteady Interaction ◽  
Urans Cfd

The flow path of modern turbine stages is highly influenced by the interaction of the main passage flow with the secondary leakages used for sealing purposes. The interaction between these two flows significantly influences the topology of the overturning passage secondary flow and therefore with the performance of the turbine itself. During the aerodynamic design phase, this complex interaction is usually assessed using RANS and URANS CFD calculations. This paper reports on the use of CFD calculations to predict the complex fluid dynamic interaction between the leakage at the inner platform upstream of a single stage HPT blade and the generation of the secondary overturning passage flow within the aerofoil. Rig test data are presented for a direct comparison with the CFD considering two different rim sealing geometric configurations. The first aim of this paper is to show how the prediction of similar complex flows can be addressed to quantify the performance improvement and what results can be expected when using industrial mature simulation technology based on RANS/URANS CFD. The second objective is to support the understanding of accuracy improvements requirements and limitations still observed when comparing these flow path predictions with rig test data. This work shows that despite the ability to capture trends, the details of these complex flow interactions still represent a challenge for the state of the art RANS and URANS solvers used in the design of the gas path of the HPT turbine stages. The understanding of the accuracy in prediction capability through the comparison with rig test data is not only essential to support present design work, but also for the developments and assessment of the next generation of modelling capabilities.

scholarly journals ДОСЯГНЕННЯ ЕФЕКТИВНОГО РОЗПОДІЛЕНОГО ПЛАНУВАННЯ ЗА ДОПОМОГОЮ ЧЕРГ ПОВІДОМЛЕНЬ У ХМАРІ ДЛЯ БАГАТОЗАДАЧНИХ ОБЧИСЛЕНЬ ТА ВИСОКОПРОДУКТИВНИХ ОБЧИСЛЕНЬ

2020 ◽  
Author(s):  
Старовойтенко Олексій Володимирович
Keyword(s):  
Distributed Systems ◽  
System Performance ◽  
State Of The Art ◽  
Computation Time ◽  
Cloud Services ◽  
Distributed Scheduling ◽  
Message Processing ◽  
Computational Problem ◽  
Control Units ◽  
And Control

Due to the growth of data and the number of computational tasks, it is necessary to ensure the required level of system performance. Performance can be achieved by scaling the system horizontally / vertically, but even increasing the amount of computing resources does not solve all the problems. For example, a complex computational problem should be decomposed into smaller subtasks, the computation time of which is much shorter. However, the number of such tasks may be constantly increasing, due to which the processing on the services is delayed or even certain messages will not be processed. In many cases, message processing should be coordinated, for example, message A should be processed only after messages B and C. Given the problems of processing a large number of subtasks, we aim in this work - to design a mechanism for effective distributed scheduling through message queues. As services we will choose cloud services Amazon Webservices such as Amazon EC2, SQS and DynamoDB. Our FlexQueue solution can compete with state-of-the-art systems such as Sparrow and MATRIX. Distributed systems are quite complex and require complex algorithms and control units, so the solution of this problem requires detailed research.

A Numerical Investigation of the Fluid Flow in a Chandler Loop for Thrombus Studies

2013 ◽  
Author(s):  
Hisham Touma ◽  
Iskender Sahin ◽  
Tidimogo Gaamangwe ◽  
Maud B. Gorbet ◽  
Sean D. Peterson
Keyword(s):  
Laminar Flow ◽  
Stress Field ◽  
Strain Rate ◽  
Rotation Rate ◽  
Fluid Dynamic ◽  
Working Fluid ◽  
Straight Tube ◽  
Dean Number ◽  
Chandler Loop

The Chandler loop is an artificial circulatory platform for in vitro hemodynamic experiments. In most experiments, the working fluid is subjected to a stress field via rotation of the Chandler loop, which, in turn, induces biochemical responses of the suspended cells. For very low rotation rates, the stress field can be approximated using laminar flow in a straight tube as a model. However, as the rotation rate increases, while still maintaining laminar flow, the effect of the tube curvature causes the stress field to deviate considerably from the straight tube approximation. In this manuscript, we investigate the flow and associated strain rate field of an incompressible Newtonian fluid in a Chandler loop as a function of the governing non-dimensional fluid dynamic parameters. We find that the Dean number, which is proportional to the rotation rate, is the dominant parameter in determining the fluid strain rate. We propose an empirical formula for predicting the average fluid strain rate magnitude in the working fluid that is valid over a wide parameter space to be used in lieu of the common, yet restrictive, straight tube-based prediction.

Heat Transfer for Laminar Flow in Spiral Ducts of Rectangular Cross Section

2005 ◽  
Vol 127 (3) ◽  
pp. 352-356 ◽  
Author(s):  
Michael W. Egner ◽  
Louis C. Burmeister
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Laminar Flow ◽  
Cross Section ◽  
Rectangular Cross Section ◽  
Three Dimensional ◽  
Radius Of Curvature ◽  
Dean Number ◽  
Aspect Ratios ◽  
Small Pitch

Laminar flow and heat transfer in three-dimensional spiral ducts of rectangular cross section with aspect ratios of 1, 4, and 8 were determined by making use of the FLUENT computational fluid dynamics program. The peripherally averaged Nusselt number is presented as a function of distance from the inlet and of the Dean number. Fully developed values of the Nusselt number for a constant-radius-of-curvature duct, either toroidal or helical with small pitch, can be used to predict those quantities for the spiral duct in postentry regions. These results are applicable to spiral-plate heat exchangers.

Effects of Fe3O4/Water Nanofluid on the Efficiency of a Curved Pipe

2019 ◽  
Vol 11 (4) ◽  
Author(s):  
Milad Kelidari ◽  
Ali Jabari Moghadam
Keyword(s):  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Volume Concentration ◽  
Volume Fraction ◽  
Working Fluid ◽  
Radius Of Curvature ◽  
Dean Number ◽  
Curved Pipe ◽  
Overall Efficiency

Different-radius of curvature pipes are experimentally investigated using distilled water and Fe3O4–water nanofluid with two different values of the nanoparticle volume fraction as the working fluids. The mass flow rate is approximately varied from 0.2 to 0.7 kg/min (in the range of laminar flow); the wall heat flux is nearly kept constant. The experimental results reveal that utilizing the nanofluid increases the convection heat transfer coefficient and Nusselt number in comparison to water; these outcomes are also observed when the radius of curvature is decreased and/or the mass flow rate is increased (equivalently, a rise in Dean number). The resultant pressure gradient is, however, intensified by an increase in the volume concentration of nanoparticles and/or by a rise in Dean number. For any particular working fluid, there is an optimum mass flow rate, which maximizes the system efficiency. The overall efficiency can be introduced to include hydrodynamic as well as thermal characteristics of nanofluids in various geometrical conditions. For each radius of curvature, the same overall efficiency may be achieved for two magnitudes of nanofluid volume concentration.

Particle Dispersion and Deposition in a Curved Duct

2009 ◽  
Author(s):  
C. M. Winkler ◽  
S. P. Vanka
Keyword(s):  
Particle Deposition ◽  
Volume Fraction ◽  
Particle Volume Fraction ◽  
Outer Wall ◽  
Particle Dispersion ◽  
Radius Of Curvature ◽  
Dean Number ◽  
Particle Volume ◽  
Particle Tracking Method ◽  
Dean Vortex

Particle transport in ducts of square cross-section with constant streamwise curvature is studied using numerical simulations. The flow is laminar, with Reynolds numbers of Reτ = 40 and 67, based on the friction velocity and duct width. The corresponding Dean numbers for these cases are 82.45 and 184.5, respectively, where De = Rea/R, a is the duct width and R is the radius of curvature. A Lagrangian particle tracking method is used to account for the particle trajectories, with the particle volume fraction assumed to be low such that inter-particle collisions and two-way coupling effects are negligible. Four particle sizes are studied, τp+ = 0.01, 0.05, 0.1, and 1. Particle dispersion patterns are shown for each Dean number, and the steady-state particle locations are found to be reflective of the Dean vortex structure. Particle deposition on the walls is shown to be dependent upon both the Dean number and particle response time, with the four-cell Dean vortex pattern able to prevent particle deposition along the center of the outer wall.

Stereo-PIV Measurements of Turbulent Swirling Flow Inside a Pipe

2020 ◽  
Author(s):  
Ayesha Almheiri ◽  
Lyes Khezzar ◽  
Mohamed Alshehhi ◽  
Saqib Salam ◽  
Afshin Goharzadeh
Keyword(s):  
Swirling Flow ◽  
Reverse Flow ◽  
Tangential Velocity ◽  
Circular Disk ◽  
Pipe Diameter ◽  
Working Fluid ◽  
Complex Flow ◽  
Mean Velocity ◽  
Radial Profiles ◽  
The Mean

Abstract Stereo-PIV is used to map turbulent strongly swirling flow inside a pipe connected to a closed recirculating system with a transparent test section of 0.6 m in length and a pipe diameter of 0.041 m. The Perspex pipe was immersed inside a water trough to reduce the effects of refraction. The working fluid was water and the Reynolds number based on the bulk average velocity inside the pipe and pipe diameter was equal to 14,450. The turbulent flow proceeds in the downstream direction and interacts with a circular disk. The measurements include instantaneous velocity vector fields and radial profiles of the mean axial, radial and tangential components of the velocity in the regions between the swirler exit and circular disk and around this later. The results for mean axial velocity show a symmetric behavior with a minimum reverse flow velocity along the centerline. As the flow developed along the pipe’s length, the intensity of the reversed flow was reduced and the intensity of the swirl decays. The mean tangential velocity exhibits a Rankine-vortex distribution and reached its maximum around half of the pipe’s radius. As the flow approaches the disk, the flow reaches stagnation and a complex flow pattern of vortices is formed. The PIV results are contrasted with LDV measurements of mean axial and tangential velocity. Good agreement is shown over the mean velocity profiles.

Ultrasound Vector Flow Imaging – could be a new tool in evaluation of arteriovenous fistulas for hemodialysis?

2017 ◽  
Vol 18 (4) ◽  
pp. 284-289 ◽  
Author(s):  
Ilaria Fiorina ◽  
Maria Vittoria Raciti ◽  
Alfredo Goddi ◽  
Vito Cantisani ◽  
Chandra Bortolotto ◽  
...  
Keyword(s):  
Venous Aneurysm ◽  
Flow Imaging ◽  
Angular Deviation ◽  
Complex Flow ◽  
Mean Velocity ◽  
Ultrasound Technique ◽  
Arteriovenous Fistulas ◽  
The Mean ◽  
Vessel Walls ◽  
Ultrasound Scanner

Introduction We report the use of a new ultrasound technique to evaluate the axial and lateral components of a complex flow in the arteriovenous fistula (AVF). Vector Flow Imaging (VFI) allows to identify different components of the flow in every direction, even orthogonal to the flow streamline, represented by many single vectors. VFI could help to identify flow alterations in AVF, probably responsible for its malfunction. Methods From February to June 2016, 14 consecutive patients with upper-limb AVF were examined with a Resona 7 (Mindray, Shenzhen, China) ultrasound scanner equipped with VFI. An analysis of mean velocity, angular direction and mean number of vectors impacting the vessel wall was carried out. We also identified main flow patterns present in the arterial side, into the venous aneurysm and in correspondence of significant stenosis. Results A disturbed flow with the presence of vectors directed against the vessel walls was found in 9/14 patients (64.28%): in correspondence of the iuxta-anastomotic venous side (4/9; 44.4%), into the venous aneurysmal tracts (3/9; 33.3%) and in concomitance of stenosis (2/9; 22.2%). The mean velocity of the vectors was around 20-25 cm/s, except in presence of stenosis, where the velocities were much higher (45-50 cm/s). The vectors directed against the vessel walls presented high angle attack (from 45° to 90°, with a median angular deviation 65°). Conclusions VFI was confirmed to be an innovative and intuitive imaging technology to study the flow complexity in the arteriovenous fistulas.

An Explicit Non-Real Time Data Reduction Method of Triple Sensors Hot-Wire Anemometer in Three-Dimensional Flow

1988 ◽  
Vol 110 (2) ◽  
pp. 110-119 ◽  
Author(s):  
Y. T. Chew ◽  
R. L. Simpson
Keyword(s):  
Real Time ◽  
Three Dimensional ◽  
Computation Time ◽  
Reynolds Stresses ◽  
Hot Wire ◽  
Time Data ◽  
Three Dimensional Flow ◽  
Mean Velocity ◽  
Dimensional Flow ◽  
The Mean

An explicit non-real time method of reducing triple sensor hot-wire anenometer data to obtain the three mean velocity components and six Reynolds stresses, as well as their turbulence spectra in three-dimensional flow is proposed. Equations which relate explicitly the mean velocity components and Reynolds stresses in laboratory coordinates to the mean and mean square sensors output voltages in three stages are derived. The method was verified satisfactorily by comparison with single sensor hot-wire anemometer measurements in a zero pressure gradient incompressible turbulent boundary layer flow. It is simple and requires much lesser computation time when compared to other implicit non-real time method.

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