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Author:Laaksonen, Arttu
Title:Tutkimus luodin pyörimisen vaimenemisesta virtauslaskennan avulla
Study of the roll damping of a projectile using CFD methods
Publication type:Master's thesis
Publication year:2011
Pages:[12] + 72      Language:   fin
Department/School:Sovelletun mekaniikan laitos
Main subject:Lentotekniikka   (Kul-34)
Supervisor:Siikonen, Timo
Instructor:Sailaranta, Timo
OEVS:
Electronic archive copy is available via Aalto Thesis Database.
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Location:P1 Ark Aalto  3994   | Archive
Keywords:roll damping
spin damping
limited range bullet
flow simulation
luodin pyörimisen vaimeneminen
rajoitetun kantaman luoti
virtauslaskenta
Abstract (eng): The objective of this master's thesis was to study the roll damping of a projectile with different projectile geometries.
The study is carried through using computational fluid dynamics (CFD).

Bullets are usually spin-stabilized meaning that the spin of the bullet keeps the flight trajectory stable.
Spin is achieved by rifling inside the bore of a rifle.
Enhancing the damping of the roll is an effective way of limiting the range of the projectile.
This could be useful for example in training use.
Damping of the roll can be enhanced by shaping the bullet accordingly.
Earlier studies have concluded that wing-structures on both the ogive and boat tail of the bullet are efficient ways of achieving increased roll damping.

Fluent software was used for the CFD simulations.
The chosen turbulence model and grid structure were validated by simulating a bullet and comparing the results with published experimental data.
As a result of the validation process, SST k - omega was chosen for the turbulence model and wall functions were selected to be used to solve the boundary layer.

Three different modifications based on chosen bullet geometry were studied.
One of them had wings on the ogive and two had wings on the boat tail.
The base geometry itself was simulated to present comparison data.
The simulations were conducted on four supersonic Mach numbers.
The lengthened bullet with wings on boat tail achieved the highest roll damping coefficient throughout the studied region.
Shorter bullet with wings on boat tail proved unefficient at high Mach numbers.
Results of the bullet with wings on the ogive landed in between those of the other studied bullets.
Abstract (fin): Tässä diplomityössä tutkitaan luodin pyörimisen vaimentamista erilaisilla luotigeometrioilla.
Tarkastelu tehdään laskennallista virtausmekaniikkaa (CFD) käyttäen.

Luodit ovat tyypillisesti pyörimisvakavoituja, jolloin aseen piipun rihlaus asettaa luodin pyörimään ja pyöriminen pitää lennon vakaana.
Pyörimisen vaimentamisen tehostaminen on hyvä keino luodin kantaman rajaamiseksi esimerkiksi harjoituskäytössä.
Pyörimistä voidaan rajoittaa muotoilemalla luoti niin, että sen muoto tehostaa pyörimisen vaimenemista.
Maailmalla on tutkittu esimerkiksi luodin etu- ja takaosaan sijoittuvia siipiä pyörimistä vaimentavana ratkaisuna.
Tutkimusten mukaan pyörimistä hidastavaa aerodynaamista momenttia voidaan kasvattaa luodin sopivalla muotoilulla.

Virtauslaskentaan työssä käytettiin Fluent-ohjelmistoa.
Turbulenssimalli ja hilarakenne rajakerroksen ratkaisun osalta validoitiin tutkimalla luotia, jolle tunnetaan kokeellisia mittaustuloksia.
Tulosten perusteella valittiin varsinaisessa virtauslaskennassa käytettäväksi seinämäfunktioin ratkaistava rajakerros ja siihen sopiva hila sekä SST k - oomega -turbulenssimalli.

Varsinaisessa virtauslaskentaosuudessa tutkittiin kolmea saman perusgeometrian pohjalta luotua luotigeometriaa, joista yhdessä olivat siivet luodin etuosassa ja kahdessa luodin takaosassa.
Lisäksi laskettiin sileälle luodille vertailutulokset.
Tarkastelu tehtiin neljällä eri Machin luvulla ylisoonisella alueella.
Pidempi takasiipiluoti oli tehokkain vaimentamaan pyörimistä.
Lyhyempi takasiipiluoti ei toiminut suurilla Machin luvuilla tehokkaasti.
Etusiipiluodin pyörimisen vaimeneminen sijoittui kahden takasiipiluodin tulosten väliin.
ED:2011-10-17
INSSI record number: 42871
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