Terminal velocity and drag coefficient are the most important aerodynamic properties of agricultural products like soya in the designing of machines and processing equipment. In this study, these properties were evaluated for three soybean varieties (Sahar, Viliyams and Dpx) and five moisture content levels (4, 8, 12, 16 and 20% d.b.). First, relation of the terminal velocity and the drag coefficient with the moisture content was mathematically formulated, and then, in fluidized bed dryer was practically investigated. The results showed, with the changing of the moisture content of three varieties (Sahar, Viliyams and DPX) from 4% to 20%, the terminal velocity of three varieties increased respectively from 4.42 to 5.1, 5.12 to 5.94 and 4.71 to 5.5 (m/s) while at the same moisture content the drag coefficient decreased from 0.45 to 0.389, 0.53 to 0.452 and 0.512 to 0.444. The diagrams of the terminal velocity and the drag coefficient revealed that the terminal velocity and the drag coefficient values have a linear relationship with the moisture content, but with increasing the moisture content, terminal velocity values increased whilist drag coefficient ones decreased.

Knowledge of the aerodynamic properties of agricultural materials is needed in equipment design for operations such as pneumatic conveying in loading/unloading operations of corn silage into/from silos. While considerable information is available on seed grains, little is known about the aerodynamic behavior of corn (Zea mays L.) silage. In this research, the weighed mean terminal velocity of a sample representative of the entire bulk mass was determined using Wolf and Tatepo’s method. The terminal velocity of various particle types (leaf, stalk and corncob pieces) of chopped forage corn plants, which were kept in silo for six months, at different moisture contents (40-50, 50-60 and 60-70% w.b.) was also studied. The terminal velocity was determined by measuring the air velocity required to suspend a particle in a vertical air stream using a wind tunnel. A 3 × 3 factorial treatment arrangement with 30 replications in a completely randomized design was used to study the effect of moisture content and particle type on the terminal velocity. The mass mean terminal velocities of the corn silage at 40-50, 50-60 and 60-70% moisture contents were 7.1, 7.3 and 7.8 m/s, respectively. The results showed that only the effect of particle type on the terminal velocity of corn silage was significant. The mean values of the terminal velocity of corn leaf, stalk and cob pieces were 3.8, 6.8 and 8.8 m/s, respectively. For each particle type at a given moisture content, the terminal velocity was best described by means of the equation of velocity squared in terms of weight.

Determining the terminal velocity as one of the important aerodynamic properties of particles and grains is essential for pneumatic separation, grading, and handling. A wind tunnel system was used in the present research to measure the aerodynamic terminal velocity of pistachio nuts. Some physical properties were measured and calculated. The effects of pistachio mouth status at four levels (closed, open, and semi-open mouth, and shell) were investigated on its terminal velocity. The volume, mass and density of that were 1.33±0.37 cm3, 0.97±0.31 g and 0.72±0.18 g cm3-1, respectively. The average aerodynamic terminal velocity of pistachio was 9.43±1.38 m s-1. The aerodynamic terminal velocity of the pistachio had a direct relationship with the studied physical characteristics, except for density. The terminal velocity of open-mouth pistachio nuts (9.50±0.61 m s-1) was significantly lower than that of closed (10.12±0.51 m s-1) and semi-open mouth (10.16±0.62 m s-1) nuts, with the terminal velocity of the shells (6.51±0.65 m s-1) showing the lowest values. The results revealed that terminal velocity can be considered for pneumatic separation of shells from pistachio nuts as well as the separation of open-mouth nuts from closed-mouth ones.

The terminal velocity and coefficient of friction data are necessary for designing of handling and separating equipments. The terminal velocity data are also valuable in designing pneumatic conveying، fluidized bed dryer and cleaning equipments. In this paper، the terminal velocity and coefficient of static friction of saffron flower and its components (stigma، stamina، petal and stem) were determined as a function of moisture content. The experiments were conducted on saffron flower selected from fields of Kashmar. The data was statistically analyzed using factorial experiments with completely randomized design. The results showed that the terminal velocity of the saffron flower، stigma، stamina، petal and stem at moisture content of harvesting level to 40% (w. b.) were in the range of 1. 03 to 5. 13 m/s. With decreasing moisture content from harvesting level to 40% the terminal velocity of the flower and stem decreased significantly but the terminal velocity of the stigma، petal and stamina were not decreased significantly. The terminal velocity of the petal was the minimum value at the three moisture content levels. The coefficient of friction of saffron flower and its components on the friction surfaces were in the range of 0. 52 to 1. 1. The friction coefficients of all the components except the stem were the maximum values on polyethylene surface. The coefficients of friction were the minimum values on galvanized iron surface for all of the components. With decreasing moisture content from harvesting level to 40% (w. b.) the average values of coefficient of friction increased significantly for all of the components. The coefficient of friction of the stigma and flower were the maximum and minimum values، respectively at different levels of moisture content. Generally، at moisture content of harvesting it is possible to separate the flower، petal، stamina، stigma and stem from each others with changing air stream velocity. As well، it is possible to separate the petal from the others components at moisture levels of 70% and 40% (w. b.) using wind column device.

Hydrodynamic and mass transfer simulations of toluene rising drops have been investigated. The VOF-PLIC method with surface tension model of CSS was applied. Drops have been simulated in the three regimes of spherical, circulating, and oscillating regimes. Simulation results agreed well with existing experimental data with the average relative error of 3.63 percent. The current hydrodynamic model predicted the oscillating regime for the drop diameter of 4.4 mm and 3.5 mm drops were identified as the drops with maximum velocity. These findings agreed well with existing experimental data. In the next step of simulations, mass transfer equation was supplemented into the simulations investigating mass transfer effect on the velocity of 2 mm toluene drops. All of the properties of drops were assumed constant except surface tension coefficient. Simulation results showed that, with the assumption of concentration dependent surface tension coefficient, terminal velocity relative error was about 2 percent, while without considering of that, relative error increased to 83 percent. Streamlines, drop shapes, axial velocity, and terminal velocity were also reported.

The present experimental study was done aimed to investigate dynamic ofa single bubble rising through wall-bounded flow at high Reynoldsnumber. Thus, Rhamnolipid biosurfactant was added to stagnant fluid andbubble diameter was controlled between 2.5 and 3.5mm. The resultedReynolds number was in the range of 400 to 900 depends on biosurfactantconcentration. Rhamnolipid has a low toxicity, a high biodegradabilityand good stability at a wide range of temperatures. The results showedthat terminal velocity linearly depends on Reynolds number. Furthermore,drag coefficient is related to Eötvos number and is autonomous toReynolds number. Finally, to estimate terminal velocity and dragcoefficient, four empirical correlations were developed. Relative errors ofthe proposed correlations were less than of 3.35% and 1.97% for velocityand dimensionless velocity equations, respectively, and average errors oftwo equations proposed for drag coefficient were 4.44% and 3.26%.

This study addresses the measurement of three-dimensional (3D) bubble rising behaviour in still water with bubble equivalent diameters ranging from 2.61 mm to 5.11 mm using high-speed imaging and virtual stereo vision technology. The bubble shape, 3D trajectory/velocity, displacement angular frequency and terminal velocity of bubbles are analysed. The bubble equivalent diameter is obtained by the elliptic volume method. The bubbles are divided into small and large bubbles with a critical equivalent diameter of 4.49 mm, according to whether they are accompanied by deformation. The small bubbles (deq<4.49 mm) are spherical or ellipsoid, while the large bubbles (deq≥4.49 mm) exhibit ellipsoid, mushroom and hat shapes. The 3D trajectory is obtained by 3D reconstruction of bubble centroid coordinates. The rising trajectory of small bubbles shows 3D spiral motion, while the pitch increases gradually with the increase in the equivalent diameter. The trajectory of large bubbles is a two-dimensional (2D) zigzag. The bubble displacement curves in x- and z-directions are evaluated with third-order Fourier fitting. The results show that the bubble displacement frequency in the x and z-directions decreases with the increasing bubble diameter, and the displacement frequency in the xdirection is larger than that in the z-direction. The relative proportions of the viscous force, buoyancy, surface tension and inertial force on bubbles with different equivalent diameters are different, which leads to three trends in the vertical velocity of bubbles within the diameter range of this study. Finally, the bubble terminal velocity in still water is investigated. The terminal velocity first decreases and then increases with the increase in the equivalent diameter. The minimum value is 16.17 cm/s when the diameter of the bubble equivalent diameter is 4.49 mm. Moreover, the applicability of some classical prediction models is discussed.

In this study, the effect of variety on geometrical properties (length, width, thickness, average arithmatic and geometrical mean diameter, equivalent diameter, surface area, volume and sphericity coefficient), gravimetrical properties (true and bulk density, porosity and a thousand grain mass), frictional properties (filling and emptying angle of repose, coefficient of static friction against surfaces of aluminum, steel, galvanized iron, rubber, cement and wood) and Aerodynamical property (terminal velocity) were determined. The effect of variety was significant (P<0.01) in all Physical properties (expected true density) investigated. The most geometrical diameter belongs to Pofaki with 8.62 mm. The most coefficient of sphericity belongs to Pofaki, with 84.47% and the least coefficient one belongs to Shamshiri, with 83.34%. Most bulk density related to the Shamshiri (673 Kg/m3) and the most filling angle of repose belongs to Pofaki (32.47 degree). The highest static coefficient of friction in both varieties belongs to surface of wood (Shamshiri 0.579 and Pofaki 0.611) and the lowest coefficient of static friction for Shamshiri related to surface of aluminum (0.543) and for Pofaki related to surfaces of aluminum (0.575) and steel (0.575). Maximum terminal velocity was related to the Pofaki (11.54 m/s).

In this study، some physical properties of two wheat (Alvand cultivar) and wild oat and the effect of humidity on these properties was investigated. The effect of Grain type (wheat and oat) and humidity (9. 45، 12 and 14. 45%) on triple grain size، geometric mean diameter، sphericity index، bulk density، particle density، porosity، static coefficient of friction and terminal velocity in the factorial design was evaluated. The results showed that the Grain type and moisture levels، are significant effect on the physical properties of oat and wheat grains. There are exist significant differences between wheat and oat in terms of particle density، Bulk density and porosity. Also the moisture effect on the bulk density at 1 percent and on the particle density at 5 percent but by its effect on the percentage porosity was not significant. There was highly significant differences between the friction surfaces، Graine type and moisture levels. Between surfaces، aluminum، were Maximum and steel the lowest coefficient of friction. The coefficient of static friction and the terminal velocity increases linearly as moisture increased.

An optimal explicit guidance law that maximizes terminal velocity is developed for the reentry of a vehicle to a fixed target. The equations of motion are reduced with differential flatness approach and acceleration commands are related to the parameters of trajectory. An optimal trajectory is determined by solving a real-coded genetic algorithm. For online trajectory generation, optimal trajectory is approximated. The approximated trajectory is compared with the pure proportional navigation and genetic algorithm solutions. The near optimal terminal velocity solution compares very well with these solutions. The approach robustness is examined by Monte Carlo simulation. Other advantages such as trajectory representation with minimum parameters, applicability to any reentry vehicle configuration and any control scheme, and Time-to-Go independency make this guidance approach more favorable.