Numerical study of polymer melt flow in a three-dimensional sudden expansion: viscous dissipation effects

2014 ◽  
Vol 34 (8) ◽  
pp. 755-764
Author(s):  
Mustafa Tutar ◽  
Ali Karakus
Keyword(s):  
Viscous Dissipation ◽  
Stokes Equations ◽  
Numerical Study ◽  
Flow Behavior ◽  
Flow Analysis ◽  
Three Dimensional ◽  
Flow Characteristics ◽  
Polymer Melt ◽  
Sudden Expansion ◽  
Melt Flow

Abstract This numerical paper presents the effects of viscous dissipation on both hydrodynamic flow behavior and thermal flow characteristics of fluid included in rheological polymer flow analysis. The shear rate dependence of the viscosity is modeled using a modified form of the Cross constitutive equation, while the density changes are modeled using the modified Tait state of equation. The Navier-Stokes equations are solved in a sequential, decoupled manner with energy conservation equations using a finite volume method based fluid flow solver. Hydrodynamic and thermal boundary layer developments in an asymmetric sudden expansion for different velocity and melt flow injection temperature boundary and geometry conditions are determined under the influence of viscous dissipation effects and the results are compared with each other to measure the relative effects of viscous dissipation on the interactions of these layers for a commercial polymer melt flow, namely polypropylene (PP). The numerical results demonstrate that proposed mathematical and numerical formulations for viscosity and density variations including viscous heating terms lead to more accurate representation of the polymer melt flow and heat transfer phenomena in plane channels or mold cavity associated with a sudden expansion.

Numerical Study on Impeller Performance of Mini Hydro Turbine

2015 ◽  
Vol 772 ◽  
pp. 552-555 ◽  
Author(s):  
Kyu Han Kim ◽  
Joni Cahyono
Keyword(s):  
Stokes Equations ◽  
Numerical Study ◽  
Flow Behavior ◽  
Three Dimensional ◽  
Horizontal Axis ◽  
Navier Stokes ◽  
Navier Stokes Equations ◽  
Hydro Turbine ◽  
Pressure Distributions ◽  
Power Outputs

The aim of this paper is to numerically explore the feasibility of designing a Mini-Hydro turbine. The interest for this kind of horizontal axis turbine relies on its versatility. In the present study, the numerical solution of the discredited three-dimensional, incompressible Navier-Stokes equations over an unstructured grid is accomplished with an ANSYS program. In this study, a mini hydro turbine (3kW) has been considered for utilization of horizontal axis impeller. The turbine performance and flow behavior have been evaluated by means of numerical simulations. Moreover, the performance of the impeller varied in the pressure distribution, torque, rotational speed and power generated by the different number of blades and angles. The results trends are similar between the highest pressure distributions at the impeller also produced highest power outputs on 6 numbers of blades at impeller. The model has been validated, comparing numerical results with available experimental data.

A High-Order LES Turbulent Model to Study Unsteady Flow Characteristics in a High Pressure Turbine Cascade

2008 ◽  
Author(s):  
Tomohiko Jimbo ◽  
Debasish Biswas ◽  
Yasuyuki Yokono ◽  
Yoshiki Niizeki
Keyword(s):  
Physical Process ◽  
Pressure Loss ◽  
Flow Behavior ◽  
Flow Analysis ◽  
Three Dimensional ◽  
Flow Characteristics ◽  
Measured Data ◽  
High Order ◽  
Turbulent Model ◽  
Loss Mechanism

In this work, unsteady viscous flow analysis around turbine blade cascade using a High-Order LES turbulent model is carried out to investigate basic physical process involved in the pressure loss mechanism. This numerical analysis is assessed to the wind tunnel cascade test. Basically, all the physical phenomena occurring in nature are the effect of some cause, and the effect can somehow be measured. However, to understand the cause, detail information regarding the visualization of the phenomena, which are difficult to measure, are necessary. Therefore, in our work, firstly the computed results are compared with the measured data, which are the final outcome of the cause (of the phenomena under investigation), to verify whether our physics-based model could qualitatively predict the measured facts or not. It was found that the present model could well predict measured data. Therefore, the rest of the computed information, which were difficult to measure, were used to visualize the overall flow behavior for acquiring some knowledge of the physical process associated with the pressure loss mechanism. Our study led to an understanding that the interaction of the vortex generated on the suction and pressure surface of the blade and the secondary vortex generated on the end-wall, downstream the trailing edge resulted in the formation of a large vortex structure in this region. This unsteady three-dimensional flow characteristic is expected to play an important role in the pressure loss mechanism.

Studies on Unsteady Flow Characteristics in a High Pressure Turbine Cascade Based on a High-Order Large Eddy Simulation Turbulence Model

2012 ◽  
Vol 134 (5) ◽  
Author(s):  
Tomohiko Jimbo ◽  
Debasish Biswas ◽  
Yoshiki Niizeki
Keyword(s):  
Turbulence Model ◽  
Physical Process ◽  
Pressure Loss ◽  
Flow Behavior ◽  
Flow Analysis ◽  
Three Dimensional ◽  
Flow Characteristics ◽  
Measured Data ◽  
High Order ◽  
Loss Mechanism

In the present paper, unsteady viscous flow analysis around turbine blade cascade using a high-order LES turbulence model is carried out to investigate the basic physical process involved in the pressure loss mechanism. This numerical analysis is assessed to the wind tunnel cascade test. Basically, all the physical phenomena occurring in nature are the effect of some cause, and the effect can somehow be measured. However, to understand the cause, detail information regarding the visualization of the phenomena, which are difficult to measure, are necessary. Therefore, in the present paper, firstly the computed results are compared with the measured data, which are the final outcome of the cause (of the phenomena under investigation), to verify whether our physics-based model could qualitatively predict the measured facts or not. It was found that the present model could well predict measured data. Therefore, the rest of the computed information, which were difficult to measure, were used to visualize the overall flow behavior for acquiring some knowledge of the physical process associated with the pressure loss mechanism. The present study led to an understanding that the interaction of the vortex generated on the suction and pressure surface of the blade and the secondary vortex generated on the end wall, downstream of the trailing edge, resulted in the formation of a large vortex structure in this region. This unsteady three-dimensional flow characteristic is expected to play an important role in the pressure loss mechanism.

Numerical Study on the Flow Characteristics of the Francis Turbine With Various Blade Profiles

2013 ◽  
Author(s):  
J.-H. Jeon ◽  
S.-S. Byeon ◽  
Y.-J. Kim
Keyword(s):  
Stokes Equations ◽  
Numerical Study ◽  
Three Dimensional ◽  
Flow Characteristics ◽  
Francis Turbine ◽  
Navier Stokes ◽  
Navier Stokes Equations ◽  
Ansys Cfx ◽  
Commercial Code ◽  
Sst Turbulence Model

The Francis turbine is a kind of reaction turbines, which means that the potential energy of water converted to rotational kinetic energy. In this study, the flow characteristics have been investigated numerically in a Francis turbine on the 15 MW hydropower generation with various blade profiles (NACA 65 and NACA 16 series) and discharge angles (14°, 15°, 17°, and 18°), using the commercial code, ANSYS CFX. The k-ω SST turbulence model is employed in the Reynolds averaged Navier-Stokes equations. The computing domain includes the spiral casing, guide vanes, and draft tube, which are discretized with a full three-dimensional mesh system of unstructured tetrahedral shapes. The results showed that the change of blade profiles and discharge angles significantly influenced the performance of the Francis turbine.

A Numerical Examination of the Inkjet Refilling

2004 ◽  
Author(s):  
Kai-Shing Yang ◽  
Ing-Young Chen ◽  
Chi-Chuan Wang
Keyword(s):  
Dynamic Viscosity ◽  
Bubble Growth ◽  
Stokes Equations ◽  
Numerical Study ◽  
Three Dimensional ◽  
Flow Characteristics ◽  
Navier Stokes ◽  
Plane Boundary ◽  
Navier Stokes Equations ◽  
Numerical Examination

A numerical study is conducted to examine the flow characteristics of the inkjet print-head with special attentions on the refilling process. By solving the full set of three-dimensional transient Navier-Stokes equations and considering the process of bubble growth and collapse as a movable membrane, it is found that the double refilling channels can reduce the flow surge phenomenon considerably due to the imposed friction. However, for the additional cylinder obstacle placed at the filling channel, the flow surge phenomenon is still present. This is because of the jet-like flow along the cylinder leading to a collision and eruption of fluid angled towards the plane boundary with the presence of cylinder. The calculated results also indicated the flow surge can be moderately suppressed for fluid having larger dynamic viscosity.

Modeling and Computation of Flow in a Passage With 360-Degree Turning and Multiple Airfoils

1993 ◽  
Vol 115 (1) ◽  
pp. 103-108 ◽  
Author(s):  
W. Shyy ◽  
T. C. Vu
Keyword(s):  
Porous Medium ◽  
Global Analysis ◽  
Flow Behavior ◽  
Flow Analysis ◽  
Three Dimensional ◽  
Flow Characteristics ◽  
Hydraulic Turbine ◽  
Complex Flow ◽  
The Individual ◽  
Spiral Casing

The spiral casing of a hydraulic turbine is a complex flow device which contains a passage of 360-degree turning and multiple elements of airfoils (the so-called distributor). A three-dimensional flow analysis has been made to predict the flow behavior inside the casing and distributor. The physical model employs a two-level approach, comprising of (1) a global model that adequately accounts for the geometry of the spiral casing but smears out the details of the distributor, and represents the multiple airfoils by a porous medium treatment, and (2) a local model that performs detailed analysis of flow in the distributor region. The global analysis supplies the inlet flow condition for the individual cascade of distributor airfoils, while the distributor analysis yields the information needed for modeling the characteristics of the porous medium. Comparisons of pressure and velocity profiles between measurement and prediction have been made to assess the validity of the present approach. Flow characteristics in the spiral casing are also discussed.

scholarly journals BLOOD FLOW ANALYSIS OF POLYURETHANE HEART VALVES AT PEAK SYSTOLE

2006 ◽  
Vol 18 (01) ◽  
pp. 13-18
Author(s):  
CHEUNG-HWA HSU
Keyword(s):  
Blood Flow ◽  
Heart Valves ◽  
Stokes Equations ◽  
Flow Analysis ◽  
Anticoagulation Therapy ◽  
Three Dimensional ◽  
Flow Characteristics ◽  
Maximum Flow ◽  
Navier Stokes ◽  
Hemodynamic Characteristics

Polyurethane (PU) heart valves provide central flow at peak systole and the associated hemodynamic characteristics are superior to that of mechanical valves with almost no anticoagulation therapy for patients. Durability performances, on the other hand, are also superior to those of biological valves. This paper analyzes blood flow characteristics of the PU heart valves at fully open position with computational fluid dynamics. These data provide information for the improvement of leaflets and leaflet support geometry to minimize the scale of recirculation zone of the flow field. To simulate the hemodynamic characteristics of the blood flow, CFX-4.3 software with the finite volume method is utilized to analyze the three-dimensional Reynolds-averaged Navier-Stokes equations. By modifying the geometry of leaflets along with the supports, the scale of vortex flow and blood velocity are reduced obviously. Maximum flow velocity reduces 33% compared to that of original model at peak systole.

Navier-Stokes Flow Analysis for Hydraulic Turbine Draft Tubes

1990 ◽  
Vol 112 (2) ◽  
pp. 199-204 ◽  
Author(s):  
T. C. Vu ◽  
W. Shyy
Keyword(s):  
Stokes Flow ◽  
Stokes Equations ◽  
Flow Behavior ◽  
Flow Analysis ◽  
Three Dimensional ◽  
Hydraulic Turbine ◽  
Navier Stokes ◽  
Numerical Result ◽  
Wide Range ◽  
Draft Tubes

Three-dimensional turbulent viscous flow analyses for hydraulic turbine elbow draft tubes are performed by solving Reynolds averaged Navier-Stokes equations closed with a two-equation turbulence model. The predicted pressure recovery factor and flow behavior in the draft tube with a wide range of swirling flows at the inlet agree well with experimental data. During the validation of the Navier-Stokes flow analysis, particular attention was paid to the effect of grid size on the accuracy of the numerical result and the importance of accurately specifying the inlet flow condition.

A numerical study of inkjet refilling

2004 ◽  
Vol 218 (12) ◽  
pp. 1481-1497
Author(s):  
K-S Yang ◽  
I-Y Chen ◽  
C-C Wang
Keyword(s):  
Fluid Flow ◽  
Bubble Growth ◽  
Stokes Equations ◽  
Numerical Study ◽  
Three Dimensional ◽  
Flow Characteristics ◽  
Navier Stokes ◽  
Channel Design ◽  
Navier Stokes Equations ◽  
Inkjet Printer

A numerical study is conducted to examine the flow characteristics of the inkjet printer head with special attention made to the refilling process. By solving the full set of three-dimensional transient Navier-Stokes equations and considering the process of bubble growth and collapse as a movable membrane, the fluid flow inside the channel and the ejected droplet from the nozzle can be modelled. The calculated results indicate that the single refilling channel design provides the fastest refilling rate but also reveals pronounced flow surge/overshot phenomena. By using a double refilling channel design, the flow surge/overshot phenomenon can be reduced considerably owing to the imposed friction. Moreover, the flooding phenomenon is much less pronounced. However, placing an additional cylinder obstacle in the single filling channel will not reduce the flow surge/overshot phenomenon.

Flow Behavior Around Stayvanes and Guidevanes of a Francis Turbine

1996 ◽  
Vol 118 (1) ◽  
pp. 110-115 ◽  
Author(s):  
Toshiaki Suzuki ◽  
Tomotatsu Nagafuji ◽  
Hiroshi Komiya ◽  
Takako Shimada ◽  
Toshio Kobayashi ◽  
...  
Keyword(s):  
Viscous Flow ◽  
Flow Behavior ◽  
Flow Analysis ◽  
Three Dimensional ◽  
Flow Characteristics ◽  
Francis Turbine ◽  
Good Prediction ◽  
Three Dimensional Flow ◽  
Dimensional Flow ◽  
Pressure Distributions

The three-dimensional computation of steady and incompressible internal flows is of interest in numerical simulations of turbomachinery, and such simulations are currently under investigation, from inviscid to viscous flow analyses. First, surface pressure distributions have been measured for the stayvanes and the guidevanes of a Francis turbine. They are presented to verify the numerical results. Second, both inviscid and viscous three-dimensional flow analyses have been made, so as to predict the flow behavior in the same domain. Comparison of the measured pressure distributions to the predicted pressure distributions has been made to study the usefulness of the present simulations. It can be pointed out that a global analysis which includes a runner flow passage, except runner blades, is necessary to predict the three-dimensional flow characteristics and that inviscid flow analysis has the capability of good prediction for flow without separation. Viscous flow analysis gives similar results, though it is necessary to investigate further the improvement of prediction accuracy. Flow characteristics around the stayvanes and the guidevanes are also discussed.

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