Flying Aspects and Distance of Ellipsoidal Seeds
1975 Volume 37 Issue 1 Pages 26-33
Details
1975 Volume 37 Issue 1 Pages 26-33
Ellipsoidal or spindle-like seeds, such as the ones of grass or grain, flying in the air after being launched out at the high speed of 10-40m/s from a spinner of a centrifugal distibutor, differ in distribution from what happens in the case of spheres.
It is observed in the former that some fall down near at our feet and some considerably far from us.
The purpose of this paper is to report the flying distance and the width of distribution of those particles, which were observed by the high speed camera that caught their flying aspects, and in the experiment by means of wind-tunnel that indicated how different were those coefficients of air-resistance by direction.
1. The particles which are launched from the blade are not provided with any force of rotating motion. However, their rotation movment sometimes occurs through the balance of air-resistance on their flight.
2. The general flight of seed particles is 30°-70° in the positive or negative angle against the horizontal. However, they cannot keep flying long in the same condition. They change their flying conditions, from one stable condition to another.
3. When the particles whose shape is almost spheroidal, start flying at a slow speed, they are subject to the law of free falling. However, the particles in other case are not subject to the law. Since their lift becomes positive or negative in accordance with their flying orientation, the velocity of their falling is so much indefinite.
4. The surface coefficients of air resistance in the three directions of X, Y and Z are Cx≥Cy≥zC in all studied ellipsoidal seed particles within Re>103. One relative formula will be found by arranging the results of those seed particles on the basis of the sphericity φ.
5. The lift of an oat seed will come to zero, when its attack angle α comes to the approximate-10° and is prone to increase more rapidly in positive of α than in negative. Its maximum value will come at α≈50. The lift for the Sphericity φ will come to its maximum at φ≈0, 3 and will be decreased rectilinearly when φ is coming near 1.
6. If the weight and initial velocity and length of the three axes of the particles which are launched should predict their flying distance and the width of their distribution, it will be very convenient to us.
The average of flying distance where the density becomes thickest is follows:
l≈1/2K1[ln(2K3Vx02/g+1)+ln(1.5K1Vx0/g+K3Vx02)1/2+1)]
The width of distribution in X-direction will be able to be known by the following semi-experimental formula:
Dx≈1/K1[ln(2K3Vx02/g+1)-ln(1.5K1Vx0/(g+K3Vx02)1/2+1)]+3.5×10-3γ
In this case, it should be taken Into consideration that their distributing width will be increased through the vector of Y-direction by ther jumping on the spinner.
K1=SγlCx/2w
K3=SγlCl/2w
vx0=Initial velocity for x-direction [m/s]
g=Acceleration of gravity [m/s2]
S=surface area of particle [m2]
w=Weight of particle [kg]
γl=Specific weight of eir [kg/m3]
γ=Specific weight of particle [kg/m3]
