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Unconventional Wind-Driven Machines
Published in Mario Alejandro Rosato, Small Wind Turbines for Electricity and Irrigation, 2018
Magnus effect is the lift force created by a fluid current on a rotating cylinder or sphere. A Flettner rotor (a.k.a. turbosail) is a cylinder rotating around its longitudinal axis (usually driven by a small motor) and a Thom rotor is a variant of the first, having discs uniformly spaced along its length. Magnus effect devices can reach extraordinarily high lift coefficients, which are proportional to their rotation speed. They feature high drag coefficients too (T. J. Craft, H. Iacovides, and B. E. Launder). We know from the theory on HAWT that the rotor’s CP is a function of the Cz/Cx quotient. Hence, it is clear that Magnus effect wind turbines present no aerodynamic advantage on conventional ones. According to Sedhagat, the CP of Magnus effect turbines can be as low as 0.1. The Japanese company Mecaro produced a 10 kW model that features a spiral fin along each cylinder, but apart from a few videos posted in YouTube, there is no technical information available about it, not even in the corporate site.
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Published in Splinter Robert, Illustrated Encyclopedia of Applied and Engineering Physics, 2017
[fluid dynamics] Lift force explained by Heinrich Gustav Magnus (1802–1870) in 1852. The lift applies to finned projectiles (wings may be a consideration, but the Magnus effect applies to vortices) as well as to other objects specifically when a form of rotation or vortex is involved (yawing or spinning projectiles), such as a ball or bullet, and also applies to a rotating fan. The lift on a ball for instance is a function of the surface area (configuration, surface roughness, and size A), geometry (e.g., golf ball), the inherent velocity (ν), the orientation of the ball, as well as the rotation and the density of the fluid medium (ρ). Magnus hypothesized that lift was derived from nonsymmetrical flow separation within the boundary layer of the projectile. The lift force, using a coefficient of lift (CL), is defined as FL = (1/2)CLρAv2. The Magnus effect is distinguishably noticeable for large objects, such as a volleyball being struck during a serve, making the ball float and suddenly visibly lift in an unpredictable trajectory (see Figure M.30).
Assessment of infection probability indices for airborne diseases in confined spaces: combination of CFD and analytical modelling
Published in Journal of Building Performance Simulation, 2023
Marzio Piller, Gabriele Bulian, Carlo Antonio Stival
In principles, particles may experience also lift-type forces (Rubinow and Keller 1961; Saffman 1965). However, in the considered scenarios, the Reynolds number for shear flow which is used to determine the shear lift force, in accordance with Saffman (1965), is significantly smaller than 1 throughout the flow domain (as reported in the Supplementary Material for the scenario 20 of the case study – see section 3), suggesting that the shear lift force can be safely neglected. Moreover, the rotation lift force associated to the Magnus effect caused by a relative rotation between the particle and the fluid (Rubinow and Keller 1961), is neglected in the present simulations due to the very small values of the rotational Reynolds number (as reported in the Supplementary Material for the scenario 20 of the case study – see section 3).
Microstructure and inertial characteristic of a magnetite Ferro fluid over a stretched sheet embedded in a porous medium with viscous dissipation using the spectral quasi-linearisation method
Published in International Journal of Ambient Energy, 2021
K. Gangadhar, P. R. Sobhana Babu, M. Venkata Subba Rao
Later on Buongiorno model (2006) and Tiwari–Das model (2007) are the two familiar mathematical techniques which are persistently utilised to contemplate the characteristics of nanofluids. The first model is concerned for seven major mechanisms of the slip between solid and fluid phases such as Brownian diffusion, inertia, thermophoresis, diffusiophoresis, Magnus effect, gravity settling and fluid drainage. Later he surmised that in the absence of turbulent effects, Brownian diffusion and thermophoresis become two vital influencing mechanisms in nanofluids. Many researchers like Buongiorno and Hu (2009), Kuznetsov and Nield (2010), Noghrehabadi, Pourrajab, and Ghalambaz (2013), Mutuku and Makinde (2014), Xua and Pop (2014), Khan and Makinde (2014) utilised Buongiorno model in their research articles.
Estimation of acoustic forces on submicron aerosol particles in a standing wave field
Published in Aerosol Science and Technology, 2018
Ramin J. Imani, Etienne Robert
In the present work, the acoustic force is estimated from the particle displacement measured in a flow-through resonator described in Section 3, using a model for the trajectories of the particles that includes contributions from primary acoustic radiation, asymmetric drift (Czyz 1990), viscosity oscillations (Mednikov 1963), and aerodynamic drag forces. In addition to these, aerosol particles experience other forces such as buoyancy, secondary radiation forces from the acoustic energy wave scattered by other suspended particles (Weiser et al. 1984) and Van der Waals forces near the boundaries of the channel walls (Qi and Brereton 1995). However, these forces are small compared to the first four (Kapishnikov et al. 2006) and are not considered in this work. The flow field in the channel can also result in net forces acting on suspended particles, for instance through the Magnus effect or Saffman lift. These were verified to be negligible in our experiments as particle trajectories remained 1D in our channel in the absence of acoustic excitation. In the following, the different elements of the model used to calculate the particle trajectories are presented.