7/28/2019 Report tecnico di ricerca sul ciclocoptero

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Polit

Mecc

"Design of a New

ecnico di Torin

anica del volo dell'Elicottero

Relazione:

Unmanned Aerial Vehicle Cy

Marco Licheri

o

clocopter"

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Introductio

In this investigation, the re

vehicle propelled by a cyc

rotary-wing that offers g

direction of the thrust al

vehicle can be used becaus

off and landing (VTOL)

Figure 1 below shows a ty

the top and bottom positio

the blades at the left and rismall angle of attack at th

designed and developed b

and flight expetiments we

can be a viable and efficien

Fig. 1 Bl

search subject is the UAV cyclocopter, an

loidal blade system, which can be describe

od thrust levels and a superlative abilit

ost istantly by periodic pitch angle variat

e of its advantages of low-speed forward flig

nd, in particular, for its excellent hoverin

pical pitch motion of this type of rotary-wi

s produce a upward force with a large angle

ght positions produce a small amount of fose positions. In this paper, an UAV scaled

y an optimization process, and, this way, a

e conducted to demonstrate that the cycloi

t propulsion system.

de pitch angle variation during a revolution

unmanned aerial

as a horizontal

to change the

ions. This UAV

ht, vertical take-

characteristics.

g: the blades at

of attack, while

ce, because of acyclocopter was

nalytical studies

al blade system

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1. Analytical M

1.1. Aerodynamic prel

In this paper, was investig

first, it was developed

performance of the cycl

momentum theory and on

system can be rappresente

uses a multiple-streamtub

cycle of the rotor and the

flow through the rotor is

The cycloidal rotor is ideal

pressure difference exists

perpendicular to the gener

the aerodynamic model f

theories were applied to t

system. Its curious to see

as shown in Figure 2.

Fig.

As we can see, in the ups

normal direction (the inflo

maximum inflow appears a

vertical axis. On the contra

the rotor flight path is com

w, and the induced velocit

tilted slightly with respectphase angle of eccentricity

del

iminary analysis

ted the installation of a cycloidal blade on

an analytical model to examine the ch

idal blade system. This model is essen

blade element theory. It is assumed that the

by a pair of actuator disks in tandem. This

model divided into two parts: one for th

ther one for the downstream part. Its also

one-dimensional, quasi-steady incompressi

ized as an infinitesimally thin actuator cylin

between the inner and outer surfaces, and t

ted thrust vector is capable of imparting axi

r the cycloidal system, the blade element

he upstream and downstream halves of the

he typical induced inflow velocity distributi

Typical inflow distribution on the rotor

tream part of the rotor, the flow passes int

w speed is zero at azimuth angle of 0 a

t = 90) and the flow distribution is symm

ry, in the downstream part of the rotor, the t

posed of the component of the equilibrium-

vd. In the same Figure 2, we can clearly se

to the vertical axis even though, on the analis set to be zero. This way, the symmetry of

cyclocopter. At

racteristics and

tially based on

cycloidal blade

umerical model

upstream half-

ssumed that the

le and inviscid.

er over which a

he actuator disk

l momentum. In

and momentum

cycloidal blade

ons on the rotor,

the disk in the

d 180, and the

etrical about the

tal flow through

induced velocity

that the flow is

tical model, thethe flow through

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the downstream rotor is lost, phenomenon seen also on computation analysis. Anyway,

the magnitude of the induced flow velocity at the downstream rotor is smaller than of

the upstream rotor.

An other important assumption, on which the numerical theory is based, is that the

inflow velocity and the incidence angle between the inflow and the chord line areconstant along the chord of the blade.

1.2. Virtual camber effect

The peculiar aerodynamic characteristic is that these blades are subjected to a

curvilinear flow, with a behave very different from those used in a rectilinear flow. The

local inflow velocity and angle of attack of the blades are unique everywhere on the

chord, so the blades have different aerodynamics compared to that of the symmetric

blades, even though the blades are symmetrical with each other.The local pitch angles depend on the ratio of the chord to radius and the flow curvature

effects become more pronounced as this ration increases: the rotation of the rotor causes

the blade to behave like a cambered airfoil, with cospicous variations in the lift

coefficients. It was seen that the lift coefficient varied sinusoidally and the lift

coefficient curve for the blade with camber effect is shifted by approximately 0.5

compared to that without camber effect. This explain why more lift force is generated in

the downstream part than in the upstream part.

1.3 CFD Analysis

The introduction of a CFD analysis, used to determine the aerodynamics design

parameters of the cyclocopter rotor system, not only helps to predict the thrust level of

the cyclocopter rotor, but also to understand the flow conditions around the rotor and

the blades compared to the analytical and experimental methods.

1.4 CFD Model

The CFD model is based on a cycloidal blade system test apparatus, a fisical deviceintended to verify VTOL capability and hovering performance. The conditions imposed

on the boundary of the CFD model are the pressure, the no-slip wall and the symmetry

plane boundary condition. The pressure boundary is located in the edges, except the

downside edge of solution domain in order to describe an infinite space. No-slip wall

boundaries were imposed on the downside edge of the solution domain and the blades

surface to describe the ground and the surface of a blade. The symmetry plane boundary

condition is imposed for the 2-D analysis. In the CFD model of the cycloidal blade

system test apparatus, it was applied the k- low Reynolds turbolence model and

structured and unstructured meshes were used, so that the motion of the blade in

cycloidal rotor can be simulated by rotational motion of the meshes.

Finally, to compare the experimental results with the analytic results, the CFD modelwas undertaken for three different velocities. The phase angle is always set to 0.

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1.5 Results of CFD a

It was shown that the indu

normal direction through

downstream direction. Theis induced by the airflow in

velocity of the right and do

it decreases the resultant ve

180 < < 270: as predic

to tilt and an asymmetry t

outflow curvature angle. T

The comparation betwee

experimental results is in

from the experimental resu

Fig. 3 Air

2. Experimental

2.1 Experimental a

The performance of the

experimental apparatus us

system rotating about the

rotating blades system, wh

composed of six rotor blad

sinusoidal low pitch syste

by the continuos variationto obtain high efficiency in

alysis

ed airflow flows into the cycloidal blade sy

the semicircle, and then this induced airfl

curvature of the airflow of the cycloidal blside the rotor. In fact the inner airflow incre

wn side blades at angles in the range 270