Analiza utjecaja tla na aerodinamičke značajke krila metodom noseće linije

master's thesis

• Title (english): Analysis of the wing aerodynamic characteristics in ground effect with application of lifting line method
• Author: Irena Peruš
• Mentor: Milan Vrdoljak (mentor)
• Mentor: Davor Horvatić (mentor)
• Committee member: Davor Horvatić (predsjednik povjerenstva)
• Committee member: Milan Vrdoljak (član povjerenstva)
• Committee member: Ana Sušac (član povjerenstva)
• Committee member: Maja Planinić (član povjerenstva)
• Committee member: Željko Skoko (član povjerenstva)
• Granter: University of Zagreb; Faculty of Science; (Department of Physics); Zagreb
• Defense date and country: 2014-07-14, Croatia
• Scientific / art field, discipline and subdiscipline: NATURAL SCIENCES; Physics

Abstract

U radu su prezentirani rezultati utjecaja tla na intenzitet cirkulacije, koeficijenta uzgona te koeficijenta induciranog otpora krila dobiveni primjenom modificirane metode noseće linije i metode zrcalne slike. Modificirana metoda noseće linije je proširenje Prandtlove metode noseće linije primjenjivo na krila složene geometrije. Takva metoda zamjenjuje trodimenzionalno krilo jednom nosećom linijom na kojoj su smješteni središnji dijelovi potkovi častih vrtloga koji zajedno čine jedan vezani vrtlog. Intenzitet cirkulacije se određuje Biot-Savartovim zakonom na način da se u kontrolne točke postavljene na tri četvrtine tetive krila primjenjuje rubni uvjet tangencijalnog optjecanja. Tako određeni intenzitet cirkulacije omogućuje izračun koeficijenta sile uzgona na mjestu noseće linije kao i inducirane brzine te s njom povezanog koeficijenta induciranog otpora. Načinjena je usporedbe ove metode sa Prandtlovom metodom, metodom vrtložne rešetke te eksperimentalnim rezultatima te se pokazalo da je metoda zadovoljavajuća. Problem utjecaja tla na aerodinamičke značajke krila rješava se uz rubni uvjet tangencijalnog strujanja uz tlo. Takav rubni uvjet omogućava da se utjecaj tla promatra kao utjecaj zrcalnog krila na realno krilo koje se nalazi na istoj udaljenosti od tla kao i realno krilo. Utjecaj tla se manifestira ponajprije preko smanjenja iznosa induciranog otpora, a potom i preko povećanja intenziteta cirkulacije oko krila te sile uzgona. Od svih geometrijskih značajki krila, dihedral, vitkost i suženje krila se pokazuju najbitnijima u analizi utjecaja tla što rezultira da se utjecaj tla ne može promatrati kao jedinstvena funkcija udaljenosti krila od tla. Radi toga je uvedena mjera utjecaja tla na koeficijent uzgona i koeficijent induciranog otpora. Ona objedinjuje sve najvažnije geometrijske značajke te bezdimenzionalnu veličinu h=b koja predstavlja mjeru udaljenosti od tla. Pomoću nje je lako, uz poznatu geometriju krila, odrediti do koje visine će postojati utjecaj tla na aerodinamičke koeficijente krila. Pokazalo se ujedno da pri takvoj analizi treba uzeti u obzir i početnu vrijednost koeficijenta uzgona pod utjecajem tla te da treba fiksirati napadni kut pri kojem se radi analiza. Tako načinjena modificirana metoda noseće linije primjenjena u analizi utjecaja tla korištena je za određivanje mjere utjecaja tla na konkretnu letjelicu složene geometrije.

Abstract (english)

This thesis are presents results of ground effect on circulation intensity, wing lift coefficient and induced-drag coefficient given by the application af a modified lifting-line method and method of mirror image. Modificated liftingline method is developed as Prandtl’s lifting-line method upgrade for wings with arbitrary geometry. Such method substitutes a 3D wing with a single lifting-line whose elements are bound parts of a horseshoe vortices which all together act as one bound vortex. Intensity of circulation is determined by Biot-Savart law applying boundary condition of tangential flow in control points allocated on a three-quarters of a local chord. That way calculated circulation intensity enables the estimation of a lift coefficient as well as the induced velocity and related induced-drag coefficient at the locus of the lifting-line. Comparison of this method with Prandtl’s and vortex lattice method along with experimental data has been made. It has been shown that modificated lifting-line method gives results in good correspondence with results of above mentioned methods and experiments. The problem of wing aerodynamic characteristics in ground effect is being solved applying the boundary condition of tangential flow at the level of ground. A boundary condition formulated as that allows us to comprehend the ground effect as influence of mirrored wing on a real wing which is placed at the same distance from the ground as a real wing. At the first place the ground effect manifests in reduction of induced drag and then in increase of circulation intensity and lift. Above all other geometric features of the wing, dihedral, aspect ratio and taper ratio are the most correlated with ground effect which points out that ground effect can’t be treat as a unique function of wing height. That leads us to introduction of a lift ground-effect influence ratio and induced-drag ground-effect influence ratio. Both of them combine the geometry of wing and dimensionless h=b ratio that represents a measure of distance between wing and ground. It becomes easy to determine the height of wing at which the ground effect becomes neglectable. It has been shown that in such analysis the starting value of a lift coefficient in ground effect at constant angle of attack should be taken in account. Modificated lifting-line method has been used for estimation of ground-effect influence ratios on a real aircraft with complex planform.

• Keywords: aerodinamičke značajke krila; metoda noseće linije
• Keywords (english): wing aerodynamic characteristics; lifting line method
• Language: croatian
• URN:NBN: urn:nbn:hr:217:120056
• Study programme: Title: Physics; specializations in: Education; Course: Education; Study programme type: university; Study level: integrated undergraduate and graduate; Academic / professional title: magistar/magistra edukacije fizike (magistar/magistra edukacije fizike)
• Type of resource: Text
• File origin: Born digital
• Access conditions: Access restricted to students and staff of home institution
• Created on: 2017-06-16 11:21:14