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1
Content available Simulation of Influence of Mechanical Elements on Karman Vortex Street Parameters
Pankanin Grzegorz
International Journal of Electronics and Telecommunications
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2019
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Vol. 65, No. 2
229--234
EN
This work presents the results of numerical modeling of Karman vortex street generation performed with ANSYS/FLUENT package application. The influence of the mechanical elements located downstream of the bluff body on the vortex frequency has been found during earlier laboratory investigations. Five various geometrical configurations have been tested. Considerable differences in pictures of distributions of pressure, horizontal and vertical velocities have appeared for various configurations. Qualitative as well as quantitative results are presented in the paper. They confirm the significant dependence of the Karman vortex street parameters on the meter configuration.
2
Numeryczna symulacja opływu generatora wirów w przepływomierzu wirowym metodą DNS
Czapla B.
Zeszyty Naukowe. Mechanika / Politechnika Opolska
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2015
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z. 105
41-44
EN
The paper presents results of numerical simulation of von Karman vortex street behind bluff body. The turbulent flow was simulated using DNS method. Von Karman vortex street is not yet fully understood, due to the unique complexity of generation of vortices. Results are significant at the designing of vortex flowmeters. Results of simulation for the bluff body located in the pipe are presented.
3
Content available remote Emission characteristics of a novel low NOx burner fueled by hydrogen-rich mixtures with methane
Dutka M., Ditaranto M., Løvås T.
Journal of Power Technologies
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2015
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Vol. 95, nr 2
105--111
EN
The use of hydrogen-rich fuels may be challenging for burner designers due to unique properties of hydrogen compared to conventional fuels such as natural gas. Burner retrofit may be required to use hydrogen-enriched fuels in combustion systems that are designed for natural gas combustion. This study aimed to experimentally investigate NOx emissions from a novel low NOx burner fueled by methane-hydrogen mixtures. The burner was tested in a cylindrical combustion chamber at atmospheric pressure. Burner thermal load of 25 kW (LHV) and air-fuel equivalence ratio of 1.15 were maintained throughout the experimental campaign. The influence of burner design parameters on NOx emissions was tested for various fuel compositions using a statistically cognizant experimental design. The study revealed that shifting the burner head upstream can deliver NOx emission reduction. In contrast, supplying fuel to the burner through secondary fuel ports increases NOx emissions, particularly when the burner head is shifted upstream. The lowest predicted NOx emissions from the burner are below 9 ppmvd at 3% of O2 and 14 ppmvd at 3% of O2 for 5% and 30% mass fraction of hydrogen in the fuel, respectively.
4
Content available Energy of intrinsic mode function for gas-liquid flow pattern identification
Sun Z., Gong H.
Metrology and Measurement Systems
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2012
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Vol. 19, nr 4
759-766
EN
Gas-liquid flows abound in a great variety of industrial processes. Correct recognition of the regimes of a gas-liquid flow is one of the most formidable challenges in multiphase flow measurement. Here we put forward a novel approach to the classification of gas-liquid flow patterns. In this method a flow-pattern map is constructed based on the average energy of intrinsic mode function and the volumetric void fraction of gas-liquid mixture. The intrinsic mode function is extracted from the pressure fluctuation across a bluff body using the empirical mode decomposition technique. Experiments adopting air and water as the working fluids are conducted in the bubble, plug, slug, and annular flow patterns at ambient temperature and atmospheric pressure. Verification tests indicate that the identification rate of the flow-pattern map developed exceeds 90%. This approach is appropriate for the gas-liquid flow pattern identification in practical applications.
5
Content available What is the role of the stagnation region in Karman vortex shedding?
Pankanin G. L.
Metrology and Measurement Systems
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2011
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Vol. 18, nr 3
361-370
EN
This paper is devoted to the problem of the appearance of a stagnation region during Karman vortex shedding. This particular phenomenon has been addressed by G. Birkhoff in his model of vortices generation. Experimental results obtained by various research methods confirm the existence of a stagnation region. The properties of this stagnation region have been described based on experimental findings involving flow visualisation and hot-wire anemometry. Special attention has been paid to the relationship between the existence of a slit in the bluff body and the size of the stagnation region. The slit takes over the role of the stagnation region as an information channel for generating vortices.
6
Numerical Studies of Bluff-Body Stabilized Lean Premixed Flame Based Combustor
Mishra D. P., Singh H. J.
Archivum Combustionis
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2010
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Vol. 30 nr 1-2
63-85
EN
The present research deals with numerical simulation of premixed flow inside the bluff body flame stabilized combustor. The effect of variation of co-flow velocity on important flow quantities such as radial velocity, static pressure, static temperature, turbulent kinetic energy, turbulence and dissipation rate have been studied thoroughly for reacting flow. Besides this, flame shape is identified with the help of temperature contours which indicates that the flame length becomes short with high co-flow velocities. It was found out that re-circulation length reduces significantly by 21.73 % as the co-flow velocity was increased. A comparison between turbulent kinetic energy for the co-flow velocity of 1.25 and 2.5 m/s shows that re-circulation zone becomes more compact and strengthened for higher co-flow velocities leading to more dissipation. Comparison between isothermal and reacting flow has been carried out for all the flow properties.
7
Content available Modelling and computation of laminar unsteady flow past oscillating and rotating circular cylinders
Baranyi L.
Journal of Theoretical and Applied Mechanics
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2000
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Vol. 38 nr 4
947-955
EN
In this paper a finite difference solution is presented for the 2D, unsteady incompressible Navier-Stokes equations for laminar flow about fixed, oscillating or rotating cylinders. Equations are transformed to a non-inertial system fixed to the cylinder. Convective terms are handled by a third order upwind difference, other space derivatives by fourth order central differences, and time derivatives by forward differences. The computed Strouhal numbers for fixed cylinders compare well with experimental results. The variation of time mean and root-mean-square values of lift and drag coefficients with rotation parameter alpha is also shown for a rotating cylinder for two different grids. Amplitude bounds of locked-in vortex shedding due to crossflow cylinder oscillation were determined for Re=180.
PL
Modelowanie i analiza nieustalonego przepływu laminarnego wokół drgających i wirujących cylindrów kołowych. W pracy przedstawiono uzyskane metodą różnic skończonych rozwiązanie równań Naviera-Stokesa opisujących dwuwymiarowy, nieściśliwy przepływ laminarny wokół cylindrów. Równania przetransformowano do inercyjnego ukłdu współrzędnych związanych z cylindrem. Człony konwekcyjne przedstawiono za pomocą różnic wstecznych trzeciego rzędu, inne pochodne przestrzenne - różnicami centralnymi czwartego rzędu, a pochodne czasowe - różnicami progresywnymi. Obliczone w ten sposób liczby Strouhala dla cylindrów utwierdzonych są zgodne z wynikami doświadczalnymi. Zmiennośc czasowych współczynników sił nośnych i oporu w zależności od parametru rotacji alfa przedstawiono również dla wirującego cylindra i dwóch siatek podziału.
8
Content available remote Numerical solution for laminar unsteady flow about fixed and oscillating cylinders
Baranyi L., Shirakashi M.
Computer Assisted Mechanics and Engineering Sciences
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1999
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Vol. 6, No. 3-4
263-277
EN
This paper presents a finite-difference solution of two-dimensional, time dependent incompressible Navier-Stokes equations for laminar flow about fixed and oscillating cylinders placed in an otherwise uniform flow. Using boundary fitted coordinates, the equations are transformed to a non-inertial reference frame fixed to the cylinder. The primitive variable formulation is used for the solution of the problem. A special transformation provides a fine grid scale near the cylinder walls and a coarse grid in the far field. Forward difference is used in time, fourth order central difference in space exept for convective terms for which a modified third-order upwind scheme is used. Velocity values are obtained explicitly , and the successive vortex shedding values were compared with experimental results for rigid cylinders and a very good agreement has been obtained. Amplitude bounds of locked-in vortex shedding due to forced crossflow oscilation of a circular cylinder are also determined for Re = 180.
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