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  • 1
    Electronic Resource
    Electronic Resource
    Computations of non-isothermal viscous and viscoelastic flows in abrupt contractions using a finite volume method (2002)
    Bradford : Emerald
    Engineering computations 19 (2002), S. 874-901 
    Details
    ISSN: 0264-4401
    Source: Emerald Fulltext Archive Database 1994-2005
    Topics: Technology
    Notes: A finite volume method is applied to numerical simulations of steady isothermal and non-isothermal flows of fluids obeying different constitutive equations: Newtonian, purely viscous with shear-thinning properties (Carreau law) and viscoelastic Upper Convected Maxwell differential model whose temperature dependence is described by a William-Landel-Ferry equation. The flow situations concern various abrupt axisymmetric contractions from 2:1 to 16:1. Such flow geometries are involved in polymer processing operations. The governing equations are discretized on a staggered grid with an upwind scheme for the convective-type terms and are solved by a decoupled algorithm, stabilized by a pseudo-transient stress term and an elastic viscous stress splitting technique. The numerical results highlight the influence of temperature on the flow situations, and also the complex behaviour of the materials under non-isothermal conditions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1108/02644400210450332
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Numerical simulation of three-dimensional duct flows of incompressible fluids by using the stream-tube method (1993)
    Springer
    Theoretical and computational fluid dynamics 4 (1993), S. 129-149 
    Details
    ISSN: 1432-2250
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract Numerical simulation of three-dimensional flows generally involves solving large-scale problems. In this paper we consider the stream-tube method in three-dimensional duct flows. The analysis uses the concept of stream tubes in a mapped computational domain of the physical domain where the streamlines are parallel and straight. The incompressibility equation is automatically verified and the primary unknowns of the problem are, in addition to the pressure, the transformation functions between the two domains. It is also shown that the flow may be computed by considering successive subdomains (the stream tubes). This results in a reduction of computing time and storage area. Incompressible viscous and elastic liquids involving memory-integral equations may be considered in the flow simulations. This part of the paper examines three-dimensional flows of Newtonian fluids. The method is applied to the flow in a duct involving a threefold rotational symmetry, where the discretized relevant equations are solved by using the Levenberg-Marquardt algorithm.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00417937
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Calculation of kinematic histories in two- and three-dimensional flows using streamline coordinate functions (1993)
    Springer
    Rheologica acta 32 (1993), S. 82-93 
    Details
    ISSN: 1435-1528
    Keywords: Stream-tube method ; rate-of-strain history ; strain history ; corotating frame ; tracking problem ; streamline ; integral constitutive equations
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Abstract In this paper, the theoretical elements of the stream-tube method are considered for the evaluation of strain-rate and strain histories required for the descriptions of memory-integral equations. One interest of the stream-tube analysis lies in the fact that the computation is performed in a transformed domain of the physical domain where the mapped streamlines are parallel and straight. Unknown mapping functions are used for analytic expressions of tensor components, for two- and three-dimensional flow situations. Calculations in three-dimensional flows for corotational models indicate that the relevant analytic expressions deduced from corotating frame determination are too complicated to be realistic for computation, but are exploitable for two-dimensional flow simulations. Strain histories are presented for two- and three-dimensional flows and may be applied to evaluation of stresses in both cases, when using codeformational constitutive equations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00396680
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  • 4
    Electronic Resource
    Electronic Resource
    Modelization of extensional experiments under constant force using memory-integral constitutive equations and stream-tube analysis (1996)
    Springer
    Rheologica acta 35 (1996), S. 337-346 
    Details
    ISSN: 1435-1528
    Keywords: Extensional flow ; polydimethylsiloxane polymer ; Wagner integral model ; rheometry ; stream-tube method
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Abstract In this paper, we propose a numerical simulation of axisymmetric extensional experiments on a viscoelastic polydimethylsiloxane (PDMS) material, using a falling-weight extensional rheometer. The polymer behaviour is represented by a K-BKZ memory-integral constitutive equation, involving a damping function of the Wagner type. Under the assumption of a homogeneous flow zone in the sample, a numerical model is set up, using the stream-tube method and approximating functions. The governing equations of the problem, associated to a limited number of unknowns, are solved by means of the Levenberg-Marquardt optimization algorithm. The numerical results are found to be consistent with the experimental data and reveal the importance of the non-homogeneous flow zone, in relation to the estimation of the extensional strain rate. The calculations involve the sensitivity of the model on the fluid parameters and those concerning the size of the initial column of fluid. The limited computing (CPU) time of the code is also to be underlined.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00403534
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  • 5
    Electronic Resource
    Electronic Resource
    Experimental and numerical study of entry flow of low-density polyethylene melts (1996)
    Springer
    Rheologica acta 35 (1996), S. 494-507 
    Details
    ISSN: 1435-1528
    Keywords: Polyethylene melts ; entry flows ; pressure drops ; stream-tube methods ; Wagner integral model
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Abstract The present work deals with experimental and numerical features of entry flows of two polyethylene melts, namely a linear low-density polyethylene (LLDPE) and a low-density polyethylene (LDPE) in an axisymmetric converging geometry. The study also involves rheological characterization of the polymers and determination of flow parameters, at 160°C. For both fluids, the data are fed into a viscoelastic integral Wagner constitutive equation. The numerical flow simulations are performed by using a stream-tube mapping analysis. Consideration of a sub-domain of the total flow domain, the “peripheral stream tube”, close to the wall of the converging duct permits to relate the results of the numerical simulation to experimental flow characteristics as total and entrance pressure drops. The agreement is good for the total pressure losses, but, concerning LDPE, a lack of consistency remains for the entrance pressure drop.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00368999
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    Paper (German National Licenses)
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  • 6
    Electronic Resource
    Electronic Resource
    Numerical simulation of complex flows of non-Newtonian fluids using the stream tube method and memory integral constitutive equations (1995)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 21 (1995), S. 371-389 
    Details
    ISSN: 0271-2091
    Keywords: axisymmetric contraction ; memory integral co-deformational equations ; K-BKZ model ; streamtube method ; Levenberg-Marquardt algorithm ; singularity effects ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: In this paper a memory integral viscoelastic equation is considered for simulating complex flows of non-Newtonian fluids by stream tube analysis. A formalism is developed to take into account co-deformational memory equations in a mapped computational domain where the transformed streamlines are parallel and straight. The particle-tracking problem is avoided. Evolution in time and related kinematic quantities involved with a K-BKZ integral constitutive model are easily taken into account in evaluating the stresses. Successive subdomains, the stream tubes, may be considered for computing the main flow in abrupt axisymmetric contractions from the wall to the central flow region. The ‘peripheral stream tube’ close to the duct wall is determined by developing a non-conventional modified Hermite element. A mixed formulation is adopted and the relevant non-linear equations are solved numerically by the Levenberg-Marquardt algorithm. Although the singularity at the section of contraction is not involved explicitly, the results obtained for the peripheral stream tube clearly show the singularity effects and the extent of the recirculating zone near the salient corner. The algorithm is stable even at high flow rates and provides satisfactory solutions when compared with similar calculations in the literature.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/fld.1650210502
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  • 7
    Electronic Resource
    Electronic Resource
    THREE-DIMENSIONAL EXTRUDATE SWELL: FORMULATION WITH THE STREAM TUBE METHOD AND NUMERICAL RESULTS FOR A NEWTONIAN FLUID (1996)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 23 (1996), S. 937-952 
    Details
    ISSN: 0271-2091
    Keywords: 3D extrudate swell ; free surface flow ; stream tube method ; Levenberg-Marquardt algorithm ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Stream tube analysis, already applied to two-dimensional extrudate swell problems involving rate and integral constitutive equations for incompressible fluids, is now considered in the problem of free surface determination in a three-dimensional flow situation. The method allows computation of the unknown free surface by considering only a ‘peripheral stream tube’ limited by the wall and the jet surface and an inner stream surface. Those boundary surfaces are determined by considering the conservation equations together with boundary condition equations, solved by the Levenberg/Marquatdt optimization algorithm. The method leads to a considerable reduction in the number of degrees of freedom and the storage area. As in a previous study in the two-dimensional case, singularity problems in the vicinity of the junction points between the wall and the free surface are avoided. However, the numerical method still allows evaluati on of stress peaks due to the singularity at the exit, as may be observed for results obtained with a Newtonian fluid in a duct of square cross-section.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
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    Paper (German National Licenses)
  • 8
    Electronic Resource
    Electronic Resource
    Exit pressure effects in capillary die data (1985)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 25 (1985), S. 669-676 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The exit flow from a capillary is analyzed with the help of macroscopic mechanical energy and momentum balances. The analysis shows that primary normal stress differences cannot be determined from the exit pressures under the assumption that the flow is viscometric down to the exit. This assumption and the second one (made by Han [9]) that both slit and capillary exit pressures are the same would lead to unacceptable results. Published exit pressure data for polyethylene melts are shown to be unreliable because of large hole-pressure errors in the pressure measurements. Pressure profiles obtained with a thin tube technique for the flow of a poly(isobutylene) solution indicate that the flow does not remain fully developed near the exit. Moreover, it is shown that for this polymer solution the excess viscous dissipation at the exit contributes to approximately 90 percent of the exit pressure.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760251105
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    Paper (German National Licenses)
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