Contents:

  • Piotr Doerffer From the Editor   abstract | full text
  • Xiaoliang Gong and Stephan Bansmer Deformation Measurement of Flexible Birdlike Airfoil with Optical Flow   abstract | full text
  • Mirosław Kabaciński Experimental Research on Velocity Profiles in Selected Flow Systems   abstract | full text
  • Tomasz Lipecki and Paulina Jamińska Influence of Wind Structure and Aspect Ratio of Circular Cylinders on Mean Wind Pressure Coefficient   abstract | full text
  • Sławomir Pochwała, Mirosław Kabaciński and Janusz Pospolita Influence of Typical Flow Disturbing Elements on the Flow Rate in Selected Averaging Pitot Tubes   abstract | full text
  • Yaroslav Danilovych P'yanylo and Nazariy Bogda\-novych Lopuh Numerical Model of Mass Transfer in Porous Medium   abstract | full text
  • Jerzy Świrydczuk The Effect of the Turbulence Model on the Turbine Stage Flow Exit Angle Distribution   abstract | full text
  • Krzysztof Tesch Generalised Herschel Model Applied to Blood Flow Modelling   abstract | full text
  • Kamil Urbanowicz Weighting Function Approximation in Transient Pipe Flow   abstract | full text
  • Kamil Urbanowicz and Zbigniew Zarzycki Convolution Integral in Transient Pipe Flow   abstract | full text
  • Stanisław Olszewski Kepler's Orbital Motion Examined in Comparison with the Methods of Mechanics Developed by Stanescu and Tabacu   abstract | full text
  • Marcin Kujawa Torsional Buckling of Restrained Thin-Walled Bars of Open Bisymmetric Cross-section   abstract | full text
  • [advertisement] PLGrid Plus   abstract | full text

Abstracts:

hPiotr Doerffer From the Editor

 

hXiaoliang Gong and Stephan Bansmer Deformation Measurement of Flexible Birdlike Airfoil with Optical Flow

The application of the Lucas-Kanade (LK) optical flow technique has seen a huge success in a wide variety of fields. The goal of this paper is to apply the Lucas-Kanade technique in measuring the deformation of flexible birdlike airfoil due to steady aerodynamic loads at transitional low Reynolds-numbers with a single pixel resolution. A pyramidal scheme is used to implement a coarse-to-fine warping strategy to allow large displacements. A nonlinear structure tensor is employed to diffuse local data anisotropically to preserve discontinuities in the optical flow field. Median filtering is introduced after each iteration to remove outliers. The upper surface of the airfoil is sprayed with stochastic ink dot pattern for easy capture by two cameras observed from two different angles above the airfoil to create a pattern on the airfoil for the deformation measurement. Finally, a general result of wind tunnel experiments is selected, two optical flow fields are calculated on two images generated from each camera respectively, and the optical flow results are compared with the image correlation results.

 

hMirosław Kabaciński Experimental Research on Velocity Profiles in Selected Flow Systems

A problem of measuring of velocity profiles with the use of a fully automated test stand is presented in this paper. Due to the installed measurement equipment and various software alternatives it is possible to assess the inlet effect and distribution of velocities in the vicinity of averaging Pitot tubes in order to determine the phenomena occurring in their vicinity (recirculation, main stream direction) and verify the numerical models of turbulence. Due to the stream recirculation in the vicinity of the probes tested in a wind tunnel, a twoway probe was used instead of a Pitot tube. A linear module with a stepper motor formed an integral part of the measurement system whereby it was possible to determine the position of the measurement probe with a precision of 0.1mm. The measuring anemometer location, the possibility of adjusting the stream mean velocities and data acquisition were established by means of an original program. As far as the research in pipelines is concerned – the resulting characteristics allow the uncertainty of measurement to be precisely determined, which should be accounted for during the determination of air fluxes at locations which are not included in the technical documentation of a flowmeter.

 

hTomasz Lipecki and Paulina Jamińska Influence of Wind Structure and Aspect Ratio of Circular Cylinders on Mean Wind Pressure Coefficient

The paper presents analyses of the mean wind pressure coefficient distribution on the surfaces of circular cylinders. The experiment was performed in a boundary layer wind tunnel in the Wind Engineering Laboratory in Cracow, Poland. Three models were examined in the wind tunnel. The influence of the aspect ratio and wind parameters (mean wind speed profile, turbulence intensity profile, power spectral density functions) on the mean wind pressure coefficient distribution and its standard deviation was considered during the tests.

 

hSławomir Pochwała, Mirosław Kabaciński and Janusz Pospolita Influence of Typical Flow Disturbing Elements on the Flow Rate in Selected Averaging Pitot Tubes

Flowmeters with averaging Pitot tubes are becoming more and more common in the industrial practice. It is often the case in long straight sections of channels with large diameters that the conditions regarding the adequately long sections of pipelines before and behind a flowmeter cannot be fulfilled. This is associated with the occurrence of an additional measurement uncertainty with an unknown value. Most of the information regarding this issue can be found for the case of Venturi probes. The amount of data regarding the flow averaging Pitot tubes is also limited. Hence, the decision to undertake the proposed subject. The conducted research made it possible to state recommendations regarding the metrology of testing. The results indicate that it is not only the distance from the flow disturbing element that plays a role but it is also the plane in which the sensor is located that affects the uncertainty of measurements of the flow averaging Pitot tubes.

 

hYaroslav Danilovych P'yanylo and Nazariy Bogda\-novych Lopuh Numerical Model of Mass Transfer in Porous Medium

A new numerical model of gas filtration in a porous medium is proposed and investigated. Gas filtration is modeled with a nonlinear differential equation in partial derivatives. Methods of solving the equation are discussed. A computer experiment basing on realexperiment-extracted input physical and geometrical parameters is performed and its results are analyzed. The received results agree well with the corresponding experimental data.

 

hJerzy Świrydczuk The Effect of the Turbulence Model on the Turbine Stage Flow Exit Angle Distribution

The article analyses the effect of the turbulence model on the calculated exit angles of the flow leaving the rotor of a low-pressure turbine stage. Three turbulence models were taken into account: the algebraic Baldwin-Lomax model and two advanced differential models based on the Shear Stress Transport (SST) approach proposed by Menter. The calculated results have revealed that even such extremely different turbulence models impose little difference in the resultant averaged flow exit angle distributions, especially in stages in which a regular flow pattern without flow separation andór other irregularities is observed. Larger differences can be observed in local distributions of this parameter, especially in the regions of activity of secondary vortex structures.

 

hKrzysztof Tesch Generalised Herschel Model Applied to Blood Flow Modelling

This paper introduces a new rheological model of blood as a certain generalisation of the standard Herschel-Bulkley model (Herschel W H and Bulkley R 1926 Kolloid-Zeitschrift 39 (4) 291). This model is a rheological constitutive equation and belongs to the group of the so-called generalised Newtonian fluids. Experimental data (Yeleswarapu K K et al. 1998 Mech. Res. Comm. 25 (3) 257) is compared with the results obtained from the new model, to demonstrate that it allows obtaining the best agreement together with the Luo-Kuang model (Luo X and Kuang Z B 1992 J. Biomechanics 25 (8) 929; Easthope P L and Brooks D E 1980 Biorheology 17 235). The new model may be easily implemented into commercial CFD codes, which is not that obvious for more complicated models such as differential, integral and rate type fluids (Astarita G and Marrucci G 1974 Principles of non-Newtonian Fluid Mechanics London, McGraw-Hill; Tesch K 2012 Selected Topics of Blood Flows and Microclimate Modelling in Protective Suits Gdansk, Gdansk University of Technology Press). What is more, it allows modelling of such phenomena as shear thinning, yield stress and constant viscosity values at high shear rates.

 

hKamil Urbanowicz Weighting Function Approximation in Transient Pipe Flow

A very important problem in the transient liquid pipe flow analysis is accurate and effective modeling of hydraulic resistance. The so called integral convolution of the mean local acceleration of liquid and a weighting function need to be solved in a numerical way in order to simulate unsteady resistance. A necessary condition in effective numerical calculations is that the weighting function needs to be defined as a finite sum of exponential terms. The function keeps a constant shape in a laminar flow, in a turbulent flow, its shape changes and it is dependent on the instantaneous Reynolds number. In this article an easy method is presented to determine a proper weighting function in a very straightforward manner in a quick time. A comparison of the determined functions and function prototypes in a frequency domain will be presented as well.

 

hKamil Urbanowicz and Zbigniew Zarzycki Convolution Integral in Transient Pipe Flow

This paper is devoted to the modeling of hydraulic losses during transient flow of liquids in pressure lines. Unsteady pipe wall shear stress is presented in the form of a convolution integral of liquid acceleration and a weighting function. The weighting function depends on the dimensionless time and the Reynolds number. In its first revision (Zielke W 1968 J. ASME 90 109) it had a complex and inefficient mathematical structure (featured power growth of computational time). Therefore, further work aimed at developing the so-called efficient models for correct estimation of hydraulic resistance with simultaneous linear loading of the computer's operating memory was needed. The work compared the methods of numerical solving of the convolution integral known from the literature (classic by Zielke W 1968 J. ASME 90 109 and Vardy A E and Brown J M B 2010 J. Hydraul. Eng. 136 (7) 453 and efficient by Trikha A K 1975 J. Fluids Eng. p. 97, Kagawa T et al. 1983 Trans. Jpn. Soc. Mech. Eng. 49 (447) 2638 and Schohl G A 1993 J. Fluids Eng. 115 420). The comparison highlighted the level of usefulness of the analyzed models in simulating the water hammer and revealed the demand for further research for the improvement of efficiency of the solutions.

 

hStanisław Olszewski Kepler's Orbital Motion Examined in Comparison with the Methods of Mechanics Developed by Stanescu and Tabacu

A new method developed by Stanescu and Tabacu to study the mechanics of a particle moving along a definite curve is compared with the well-known approach applied in calculating the Kepler's orbital motion. A particular effect of the rate of change of the kinetic energy of a body with respect to the change of a parameter defining the body position on the orbit is examined as an example. A comparison of the two methods shows only a slight numerical difference between the results of the Stanescu-Tabacu method and the traditional formalism. The components of the body acceleration are calculated along the orbit as an application of the new approach.

 

hMarcin Kujawa Torsional Buckling of Restrained Thin-Walled Bars of Open Bisymmetric Cross-section

The problem of torsional buckling of restrained thin-walled bars of an open constant bisymmetric cross-section was solved using the minimum total stationary elastic energy condition (J. S. Przemieniecki 1968 Theory of Matrix Structural Analysis McGraw-Hill, New York) and the Newton-Raphson method (S. C. Chapra and R. P. Canale 1998 Numerical Methods for Engineers McGraw-Hill Book Company). The consideration was restricted to the elastic structures. The example presented in the paper helps to assess the correctness of the proposed solution. This article is an addition to the author's considerations contained in M. Kujawa 2012 TASK Quart. 16 (1/2) 5.

 

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