Wyniki wyszukiwania - BazTech

1

Hydrodynamic effects produced by oscillating foil in fluid

Kudela H., Kozłowski T.

Journal of Energy Science

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2010

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Vol. 1, nr 1

69-80

EN

In the paper we presented the numerical results related to the unsteady effects produced by the oscillating foil in fluids. The paper was inspired by the studies over insects and birds fly. It was shown that by choosing of the frequency and amplitude of oscillations it can be generated the different kind of the vortex Karman street and this way control the drag, lift and thrust force exerted on the object. For numerical study vortex-in-cell method was used. We establish numerically relationship between Strouhal number amplitude of oscillations and vortices topology behind the oscillating foil by constructing the phase space diagram. The computational result are in consistent with the existent experimental data.

2

Investigation of unsteady vorticity layer eruption induced by vortex patch using vortex particles method

Kudela H., Malecha Z. M.

Journal of Theoretical and Applied Mechanics

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2007

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Vol. 45 nr 4

785-800

EN

The study of eruption of the vortex boundary layer phenomenon due to motion of the patch of vorticity above the wall is presented here. The vortex particle method is chosen to investigate the phenomenon. It shows the eruptive character of the vortex induced boundary layer. Such visualization is possible through the use of the vortex particle method. Description of the numerical method is given. The obtained numerical results are confronted with the numerical and analytical data of other researchers, conforming to a great extent wit h the conclusions.

PL

W pracy przedstawiono wyniki badań numerycznych zjawiska erupcji warstwy wirowej wywołanej przejściem skoncentrowanej struktury wirowej w pobliżu ściany. Do badań wybrano metodę cząstek wirowych. Pokazano erupcyjny charakter warstwy przyściennej indukowanej przez łatę wirową. Przedstawiono dokładny opis prezentowanej metody numerycznej. Omówiono mechanizm formowania się osobliwości w warstwie przyściennej. Wyniki numeryczne skonfrontowano z wynikami badań analityczno-numerycznymi innych badaczy. Przedstawione wyniki numeryczne dobrze potwierdziły hipotezy dotyczące natury erupcji warstwy. Zweryfikowały tym samym niezwykłą przydatność do badania tego typu zjawisk metody cząstek wirowych.

3

Prediction of unsteady VAWT aerodynamics by lifting line theory

Dumitrescu H., Cardos V.

International Journal of Applied Mechanics and Engineering

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2004

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Vol. 9, no 4

675-686

EN

Based on the lifting line theory and a free vortex wake model, a method including dynamic stall effects is presented for predicting the performance of a three-dimensional vertical-axis wind turbine. A vortex model is used in which the wake is composed of trailing streamwise and shedding spanwise vortices, whose strengths are equal to the change in the bound vortex strength as dictated by Helmholtz and Kelvin's theorems. Performance parameters are calculated by applying the Biot-Savart law along with the Kutta-Joukowski theorem and a semi-empirical dynamic stall model. Predictions are shown to compare favorably with the existing experimental data. The method can predict local and global performances more accurately than the previous momentum models.

4

Method of calculation of normal force on propeller at angle of attack by simplifed vortex method.

Strzelczyk P.

Archive of Mechanical Engineering

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2004

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Vol. LI, nr 4

515-531

EN

In the paper, the author presents a certain approach to the calculation of performance of the propeller exposed to inclined inflow conditions. The method presented in the paper employs the results of vortex of propeller for avaraged velocity field as well as momentum and angular momentum theorem for the propeller wake. The blade element in the model is regarded as a source of tangential and axial force. Thanks to the approximation of lift force coefficient vs. angle of attack by sine curve one can get a quadric equation for local, axial velocity component. The approach allows us to avoid an interative solution for the induced velocities. The tangential induced velocity may be calculated from the relations obtained from vortex theory of propeller. A profile drag is incorporated to the calculation when the value of inflow angle is known. The presented method was compared with available data for propeller operating at angle of attack and in the axial inflow. The comparison showed good agreement with experimental data for the trust and power coefficients for a wide range of advance ratios and blade settings, and angles of attack ranging from 0-15 degrees.

PL

W pracy przedstawiono praktyczną metodę wyznaczania charakterystyk aerodynamicznych śmigieł w warunkach napływu skośnego. Zastosowana metoda łączy wyniki uproszczonej metody wirowej z zasadą zachowania pędu i momentu pędu dla przepływu ośrodka idealnego. Dzięki przybliżeniu współczynnika siły nośnej sinusoidą uzyskano zamkniętą postać wzorów na prędkości indukowane. Wyniki obliczeń uzyskane na podstawie przedstawionego w pracy modelu matematycznego zostały porównane z dostępnymi danymi doświadczalnymi. Porównanie to pokazało bardzo dobrą zgodność obliczeniowych charakterystyk ciągu, mocy i siły normalnej z wynikami pomiarów w przypadku kątów natarcia śmigła w przedziale 0-15 stopni i dla szerokiego zakresu kątów nastawienia łopat. Dzięki swej prostocie opisywania metoda może być z powodzeniem stosowana w praktycznych obliczeniach charakterystyk aerodynamicznych śmigieł.

5

A two-dimensional vortex model for vertical axis wind turbines

Dumitrescu H., Cardos V.

International Journal of Applied Mechanics and Engineering

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2002

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Vol. 7, no 4

1173-1187

EN

The present paper compares the aerodynamic loads predicted by a vortex model with wind tunnel measurements for a straight-bladed Darrieus rotor. A computation unsteady discrete-vortex method, based on lifting line theory and a free vortex wake model, is used. Thus the wake is composed of shedding spanwise discrete vortices, whose strengths are equal to the change in the bound vortex strength as dictated by Kelvin's theorem and performance parameters are calculated by application of the Biot-Savart law along with the Kutta-Joukovski theorem. The popular Beddoes-Leishman dynamic-stall model is incorporated in the method and a better approach is obtained. The transient normal and tangential-force coefficients predicted with dynamic-stall effects are compared with wind tunnel data for one and two NACA 0018 straight-bladed rotors. The results are given for a rotor with a large solidity (chord-to-radius of 0.20) at two tip-speed ratios ('lambda' = 1.5 and 3.0) and at a low Reynolds number of 3.8*104. The comparisons between experimental data and theoretical results show the predictions by the marching-vortex method to be more accurate than those estimated by a code based on streamtube theory.