Aerodynamic drag coefficients

In the development of equipment for harvesting, handling, and cleaning operations, a knowledge of the aerodynamic properties of various grains is necessary. The aerodynamic drag coefficient and the terminal velocity are the two most important aerodynamic properties. 

In order to take into account the aerodynamic forces on the liquid core, it can be assumed that the liquid core is wedge-shaped, with an aerodynamic drag coefficient of Co = 0.3, according to [2]. This assumption may have to be corrected by increasing the drag coefficient to take into account the instabilities on the liquid/gas interface that disturb the liquid surface and the gas flow around the liquid core. 

The action of an air stream on an adherent particle can also be taken into account through the aerodynamic drag coefficient ot. The conditions for particle detachment in this case are determined by the expression [272]... 

The actual detaching velocity values shown in Fig. X.l 1 for particles of different sizes are valid only for those particular conditions under which this experiment was performed a duct with a diameter of 300 mm and a length of 8 m an aerodynamic drag coefficient of 4 10 (kg sec )/m for the working section of the duct detachment of sylvite dust. 

Equations 7.26 and 7.28 contain two transport coefficients h, the heat transfer coefficient, and Cd, the aerodynamic drag coefficient. Determining the proper values of these coefficients turns out to be a significant factor in successful modeling of the process. The simulation results are sensitive to these coefficients, and their measurement is difficult. Transport coefficients can be expected to depend on the Reynolds number of the air stream adjacent to the filament. 

The aerodynamic force varies approximately as the square of the flow velocity. This fact was established in the seventeenth centui y—experimentally by Edme Marione in France and Christiaan ITuygens in Holland, and theoretically by Issac Newton. Taking advantage of this fact, dimensionless lift and drag coefficients, and Cj, respectively, are defined as... 

The force of aerodynamic drag opposing foiward motion of the vehicle depends on its drag coefficient (Cj), its frontal area (A,), the air density (p), and the velocity of the wind with respect to the vehicle. In still air, this velocity is simply the vehicle velocity (V.). If driving into a headwind of velocity V , however, the wind velocity with respect to the vehicle is the sum of these two. Multiplying the aerodynamic drag force by vehicle velocity provides the aerodynamic power requirement (PJ. 

Some paradoxes of the turbulence in canopies, or EPRs, were pointed out by Raupach and Thom in their state-of-art review of 1981, [522], The first phenomenon is the value of the drag coefficient of elements that constitute the EPR. The highly precise measurements in aerodynamic tubes brought values that depend on the obstacle shape, the flow turbulence level, and the mutual disposition of obstacles but vary near cf 0.5 for spheres and cf 1 for cylinders in the working range of the local Reynolds number 103 < Re < 105. The same coefficient determined from the field measurements in forests turned out to be several times less (in this case, the indirect calculations were performed). A similar paradox takes place for the exchange coefficients. 

They offered expressions for the drag coefficient versus the gas Reynolds number for each of the three aspect ratios (see chapter 5 for details). For e < 0.25, the ellipse becomes thin and close to a plate shape and one can assume a value of Cd 2, which is a reasonable value for a flat plate over a wide range of Reynolds numbers. So, as the element is being deformed by the aerodynamic force in our model, its instantaneous Reynolds number (based on its semi-major axis) and the corresponding drag coefficient can be calculated by interpolating between the expressions offered for drag by Mashayek et al. [6]. As shown by their study. 

The aerodynamic characteristics are determined by material, density, shape, drag coefficient, and atmospheric parameters such as temperature, pressure, and relative humidity. In addition to these parameters, the movement of a rod is strongly influenced by local winds, both horizontal and vertical components, and by wind turbulence and shear. 

The total stress normal to the surface must be balanced by atmospheric pressure plus the surface tension contribution across the curved interface. We can usually neglect surface tension effects for melts, and we can always take atmospheric pressure to be zero. The tangential stress at the surface is finite because of aerodynamic drag it is conventional to represent the stress from air drag as jPaV co, where pa is the density of the air, v is the magnitude of the relative velocity between the surface and the air, and cd is a dimensionless drag coefficient that depends on shape and on... 

Aerodynamic measures for optimizing air resistance and their reviewed potentials are described in the literature [21, p. 33], [28, p. 23], [44, p. 675]. A substitution of the main and wide-angle mirror with a camera-monitor system (CMS) is an outstanding measure. The cross-sectional area of the vehicle is reduced and the drag coefficient can be optimized. In addition, wind noise and pollution of the side windows can be significantly reduced by the elimination of the outside mirrors [27, p. 40], [33, p. 536], [44, p.720]. For concept related direct flow of the mirror areas, the proven fuel saving potential of a CMS is estimated at 2.9 % [21, p. 59]. 

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