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1

Strouhal number effects on dynamic boundary layer evolution over a wedge surface from initial flow to steady flow: analytical approach

Bachiri Mohamed, Bouabdallah Ahcen

International Journal of Applied Mechanics and Engineering

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2022

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Vol. 27, no. 4

26--39

EN

The present work studies the effects of the physical parameter characterizing the laminar flow regime, namely the Strouhal number, on the evolution of the unsteady dynamic boundary-layer developed along a wedge surface. Similarity method is used to transform unsteady momentum equation to dimensionless form. Using superposition method between diffusion and convective flows solutions, an ad hoc velocity profile formula is proposed. The obtained results confirm perfectly the numerical data given by Blasius, Falkner-Skan and Williams-Rhyne for all Strouhal numbers. A new accurate analytical function of the local skin friction is established for all time values and for different wedge surface directions. In order to give further clarification on the flows evolutions from diffusion flow to convective flow, in the whole space domain, new skin friction coefficient curves are plotted for all Strouhal numbers and for different wedge surface directions.

2

Visualization of flow past square cylinders with corner modification

Virkam C. K., Ravindra H. V., Krishne Gowda Y. T.

Journal of Mechanical and Energy Engineering

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2020

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Vol. 4, No 3

285--293

EN

This article presents the results for flow past a square cylinder and two square cylinders of same and different size with corner modifications by varying the spacing ratio. Here, experimental work is conducted in a recirculatory channel filled with water. A set of aluminum discs made to rotate to create the flow in the test section. Motor is used to vary the speed of water. Fine aluminum powder is used as a tracer medium. It is observed that vortex shedding frequency decreases by placing second cylinder in the downstream of the first cylinder. For a similar size cylinders, the width of the eddy in the middle of the cylinders increases with increase in spacing ratio. With the increase of spacing ratio to 6, the flow past each cylinder behaves like single square cylinder. If upstream square cylinder size is smaller than the downstream square cylinder, the eddy size is reduced in between the cylinder compared to the downstream of the second cylinder. If upstream square cylinder size is bigger than the downstream square cylinder, the eddy size is larger in between the cylinder compared to the downstream of the second cylinder.

3

On a Robust Descriptor of the Flue Organ Pipe Transient

Hruška Viktor, Dlask Pavel

Archives of Acoustics

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2020

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Vol. 45, No. 3

377--384

EN

The initial transient of an organ pipe is known to be of great influence to the perceived sound quality. At the same time, the unsteady process of the tone onset is essentially nonlinear and lacks exact repeatability, so the search for a robust descriptor is in place. Initial transients were recorded using an adjustable flue organ pipe. The blowing pressure and cut-up height were varied. Prony’s method was employed to analyze the results. Utilizing the Principal Component Analysis (PCA) on the standardized exponential model coefficients, it was shown that the transients are well described by just one scalar parameter. Its value is predominantly dependent on the number of important Prony’s components taking part in the transient process (i.e., the overall complexity of the transient signal). A strong correlation was found between the PCA component and the Strouhal number inverse.

4

Badania modelowe liczby strouhala oblodzonego cięgna mostu podwieszonego przy umiarkowanej turbulencji napływającego powietrza

Tatara M.

Zeszyty Naukowe. Mechanika / Politechnika Opolska

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2017

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z. 108

131--134

EN

The paper presents the investigation of the Strouhal number for stationary iced cable model of cable-supported bridges using wind tunnel tests. The investigations were performed in a Climatic Wind Tunnel Laboratory of the Czech Academy of Sciences in Telč, the iced cable model was made by using 3D printing method.

5

Investigations of Strouhal numbers of iced cable models of cable-supported bridges with respect to angle of wind attack

Górski P., Tatara M., Pospišil S., Kuznetsov S., Marušić A.

Czasopismo Techniczne. Budownictwo

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2015

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Y. 112, iss. 2-B

417--432

EN

The influence of the ice accretion, angle of attack and Reynolds number on the flow field around iced cables of cablesupported bridges is not clearly understood. The Strouhal number is one of the most important parameters which is necessary for an analysis of the vortex excitation response of slender structures. This paper presents the method and results of wind tunnel investigations of the Strouhal number of stationary iced cable models of cable-supported bridges. The investigations were conducted in a climatic wind tunnel laboratory of the Czech Academy of Sciences in Telč. The methodology leading to the experimental icing of the inclined cable model in the climatic section of the laboratory was prepared. The shape of the ice on the cable was registered by photogrammetry and numerical evaluation. For the aerodynamic investigations, the iced cable model in a smaller scale was reproduced using a 3D printing procedure. The Strouhal number was determined within the range of the Reynolds number between 2.4·104 and 16.4·104, based on the dominant vortex shedding frequency measured in the flow behind the model. The model was orientated at three principal angles of wind attack for each of the Reynolds number values. In order to recognize the tunnel blockage effect, the Strouhal number of a smooth circular cylinder was tested. Strong agreement with the generally reported value in the subcritical Reynolds number range for a circular cylinder was obtained.

PL

Wpływ oblodzenia, kąta natarcia wiatru i liczby Reynoldsa na zjawisko opływu powietrza wokół oblodzonych cięgien mostów podwieszonych nie został dotychczas dobrze poznany. Liczba Strouhala jest jednym z ważniejszych parametrów, którego znajomość jest niezbędna na etapie analizy odpowiedzi smukłych konstrukcji na wzbudzenie wirowe. W artykule przedstawiono sposób i wyniki badań liczby Strouhala nieruchomych modeli oblodzonych cięgien mostów podwieszonych. Badania wykonano w tunelu aerodynamicznym z komorą klimatyczną Laboratorium Czeskiej Akademii Nauk w Telč. W komorze klimatycznej wykonano doświadczalne oblodzenie modelu cięgna o osi nachylonej pod kątem 30° do płaszczyzny poziomej. Kształt oblodzonej powierzchni zarejestrowano metodą fotogrametrii cyfrowej. Do badań w tunelu aerodynamicznym wykonano nowy model sekcyjny oblodzonego cięgna metodą druku 3D. Liczbę Strouhala wyznaczono w zakresie wartości liczby Reynoldsa od 2,4·104 do 16,4·104 na podstawie pomiaru częstości odrywania się wirów w śladzie aerodynamicznym za modelem. Badania wykonano przy trzech podstawowych kierunkach napływającego powietrza. W celu określenia wpływu zjawiska blokowania tunelu na wyniki pomiarów wykonano badanie liczby Strouhala gładkiego walca kołowego. Otrzymane wartości były zgodne z wartościami podanymi w literaturze przedmiotu w zakresie podkrytycznym liczby Reynoldsa.

6

Wyznaczanie liczby strouhala dla opływu palisady płynem lepkim metodą dopasowywania kroku czasowego

Niedźwiedzka A., Sobieski W.

Mechanik

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2014

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R. 87, nr 7CD

485—494

PL

W artykule przedstawiono rozważania dotyczące opływu liniowej palisady profili kołowych powietrzem przy zmiennej prędkości przepływu. Pokazano prostą i praktyczną metodę określania liczby Strouhala, bez konieczności wykonywania kosztownych eksperymentów. Po wyznaczeniu liczby Strouhala dla jednej prędkości, można ją następnie wykorzystać w kolejnych symulacjach, z innymi prędkościami przepływu, o ile geometria układu nie ulegnie zmianie. Zaproponowane podejście ma charakter uniwersalny i może być stosowane w dowolnych opływach zarówno palisad, jak i profili pojedynczych. Model symulacyjny wykonano Metodą Objętości Skończonych w środowisku obliczeniowym ANSYS. Celem badań było sprawdzenie skuteczności i czasochłonności metody.

EN

This article presents considerations for linear flow around a stockade of circular profiles with variable flow rates. Shown a simple and practical method for determining of the Strouhal number, without the need for costly experiments. After determining of the Strouhal number for single-speed, it can then be used in subsequent simulations, with the other flow rates, as long as the geometry of the system is not changed. The proposed approach is universal and can be used both in any flow around stockades and individual profiles. The simulation model was performed by Finite Volume Method in the ANSYS computing environment. The aim of the study was to examine the effectiveness and time-consuming of this method.

7

Badania modelowe liczby Strouhala oblodzonego cięgna mostu podwieszonego

Górski P., Pospišil S, Kuznetsov S, Tatara M., Marušić A

Budownictwo i Architektura

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2014

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Vol. 13, nr 2

201--208

PL

W artykule przedstawiono sposób i wyniki badań liczby Strouhala nieruchomego modelu oblodzonego cięgna mostu podwieszonego. Badania wykonano w tunelu aerodynamicznym z komorą klimatyczną Laboratorium Czeskiej Akademii Nauk w Telc. W komorze klimatycznej wykonano doświadczalne oblodzenie modelu cięgna o osi nachylonej pod kątem 300 do płaszczyzny poziomej. Kształt oblodzonej powierzchni zarejestrowano metodą fotogrametrii cyfrowej. Do badań w tunelu aerodynamicznym wykonano nowy model sekcyjny oblodzonego cięgna metodą druku 3D. Liczbę Strouhala wyznaczono w zakresie wartości liczby Reynoldsa od 28 do 122 na podstawie pomiaru częstości odrywania się wirów w śladzie aerodynamicznym za modelem.

EN

The paper presents the method and results of wind tunnel investigations of Strouhal number of stationary iced cable model of cable-stayed bridge. The investigations were performed in a Climatic Wind Tunnel Laboratory of the Czech Academy of Sciences in Telc. The experimental icing of the inclined cable model in the climatic chamber of the laboratory was made. The shape of the iced model was registered by a numerical photogrammetry method. For the aerodynamic tunnel investigations, the new iced cable model was made by using 3D printing method. The Strouhal number was determined within the range of the Reynolds number between 28·103 and 122·103, on the basis of the dominant vortex shedding frequency measured in the flow behind the model.

8

Design and performance of the converging-diverging vortex flowmeter

Sun Z.

Metrology and Measurement Systems

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2011

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Vol. 18, nr 1

129-136

EN

The converging-diverging structure is introduced to extend the lower limit of measurement of vortex flowmeters. As a compact device, the converging-diverging vortex flowmeter is proposed and designed, and its performance is studied experimentally. It is found that, first of all, an up to 51% extension of the lower measurement limit can be realized through the converging-diverging structure, compared with conventional vortex flowmeters; second, the converging-diverging vortex flowmeter with a trapezoidal bluff body has a larger Strouhal number and smaller pressure loss. The results suggest that the converging-diverging vortex flowmeter provides an alternative device especially suitable for the measurement of low-velocity fluids.