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Dynamic behaviour
Published in Malcolm Millais, Building Structures, 2017
There is an empirical formula relating the Strouhal number to Reynolds number, but for a large range of Reynolds numbers the Strouhal number is about 0.2. Furthermore, this number can be used for non-cylindrical shapes.13 So, for a tall building with natural frequency fn, and using S = 0.2, the above expression can be rearranged to given the critical wind speed, Vcrit as: Vcrit=fnD0.2Hz
Viscous Flow and Boundary Layer
Published in Rose G. Davies, Aerodynamics Principles for Air Transport Pilots, 2020
Experiments (Schlichting, 1978) showed that the Strouhal number St could increase with the Reynolds number Re of the fluid flow. For a fluid flow around a cylinder, when the flow speed increases, Re increases, as does St; therefore, the frequency f of vortex shedding has to increase according to Equation (3.12). For example, power lines in wind make noise, because Karman vortex streets are formed around the power lines. The stronger the wind blows, the higher the pitch of noise that the power lines make. Shedding vortices can occur at the downstream side of a chimney, and can also occur behind the strut of fixed undercarriage when the aircraft is in flight. They also occur in boundary-layer separations.
Glossary of scientific and technical terms in bioengineering and biological engineering
Published in Megh R. Goyal, Scientific and Technical Terms in Bioengineering and Biological Engineering, 2018
Strouhal number is a dimensioless quantity describing oscillating flow mechanisms. Often, it is given as Sr = f*D/V, where Sr is the Strouhal number, f is the frequency of vortex shedding, D is the hydraulic diameter of the object in the fluid flow and V is the velocity of the fluid. The Strouhal number is a function of the Reynolds number Re. It is assumed to be equal to 0.2 in the region 200<Re<200,000.
A Computational Analysis of the Aerodynamic and Aeromechanical Behavior of a Thermo-Well for Steam Temperature Measurement in a Steam Turbine
Published in Heat Transfer Engineering, 2023
Mariusz Banaszkiewicz, Janusz Badur, Sebastian Kornet, Daniel Sławiński, Bartosz Kraszewski, Paweł Ziółkowski, Anna Rehmus-Forc, Grzegorz Bzymek
It should be added, that the Strouhal number is used in the engineering technology to analysis of e.g., flow around the vibrating body (aerofoil, rod, thermowell), flow through a blade row mounted in the rotor disk, flow around a rotating propeller or screw propeller, etc. There is broad literature discussing the problem of the formation of vortices, changes in their structure, the impact of vortex structures on objects on which they form. The research on the vorticity and the formation of structures at flow has even been carried out for hundreds of years, what is evidenced by sketches of Leonardo da Vinci [6]. Great importance in the development of knowledge of periodical phenomena had works of von Kármán about vortices generation and works of Strouhal about frequency of their formation. Detailed description of these issues can be found in the works of the pioneers [7, 8] and of contemporary authors [5, 9]. Most of the published articles related to the nonstationary structures in flow, concern the experimental work and analysis [10–13], but the importance of numerical works is growing [14–16].
Numerical investigation of mixed convection from rectangular cylinders subjected to upper cross flow
Published in Numerical Heat Transfer, Part A: Applications, 2023
Zerrin Sert, Necati Mahir, Zekeriya Altaç
In Figure 9, the effects of the aspect ratio (a = 0.5, 1, and 2), the Reynolds and Prandtl numbers on the Strouhal number are illustrated for Ri = 0 (forced convection), in Pr = 0.7 and Pr = 7 fluids. In all cases, the vortex formation behind the back of the cylinder leads to vortex shedding at different frequencies; i.e., varying Strouhal numbers. Since Ri = 0 case is the forced convection mode only, the flow characteristics of Pr = 0.7 and 7 fluids are not significantly affected by the convection heat transfer from the cylinder so the Strouhal numbers are almost identical in 100 < Re < 150 range. However, the length of the rectangular cylinder affects the location of the vortex behind the cylinder and the Strouhal number (i.e., vortex shedding frequency). For Pr = 0.7, the Strouhal number decreases with increasing aspect ratio for Re = 100 and 150. For Re = 200, the Strouhal number is minimum at the aspect ratio of 1.0 and both Prandtl numbers of 0.7 and 7. In general, the Strouhal number increases with the increasing Reynolds number. For Pr = 7 and a = 0.5 and 1, the Strouhal number increases from Re = 100 to Re = 150 but levels off between Re = 150 and 200.
Flow field and wake structure characteristics imposed by single seagrass blade surrogates
Published in Journal of Ecohydraulics, 2022
M. Taphorn, R. Villanueva, M. Paul, J. Visscher, T. Schlurmann
The result of the POD was 500 approximated flow fields. The out-of-plane velocity component (v) was used for further analysis as the generated vortices could only be characterized in this flow velocity component. For each test case, a proper location for characteristic vortices was determined at which the flow velocity is extracted for further analysis. As the formation of structure-induced vortices appeared to evolve properly in a certain distance downstream of the surrogate, the location was chosen in close vicinity to the surrogate in x-direction but depended on the specimen and its inclination. The z-coordinate was selected around ¾ of the affected flow height as the vortices were more distinct with increasing distance from the flume bottom but were influenced close to the surrogates’ tip by the flow above. The extracted time series of flow velocity (v), containing oscillations due to the vortices, was analysed by using a Fast Fourier Transformation (FFT). With this method the main frequencies of the structure-induced shed vortices were determined. Within the results, the dimensionless Strouhal number (Equation (3)) was used to assess the normalized shedding frequencies for all surrogates to compare the different geometries. The Strouhal number is defined as the vortex shedding frequency fv normalized by the cylinder diameter D and the flow velocity U (Sumer and Fredsøe 2006):