leks_01_cfd
TRANSCRIPT
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Bazat e Fluidodinamikes LlogariteseBazat e Fluidodinamikes Llogaritese
CFDCFD
CFDFDEFDA
2
0
1
Re i j
Dp u u
Dt
U
UU Altin DORRI
16/04/2010
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Fluidodinamika
• Fluidet jane shume te rendesishem per jeten• Trupi njeriut eshte rreth 65% uje• 2/3 e siperfaqes se tokes eshte mbuluar nga uji• Atmosphere eshte rreth 17 km mbi sip. e tokes
• Historia eshte modeluar permes Fluidodinamikes• Geomorphology• Migracioni njerezor dhe civilizimi• Metodat dhe teorite matematikore ne shkencat
moderne• Luftrat
• Eshte e lidhur me cdo pjese te jetes tone
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Historiku
Figura te shquara ne Fluidodinamike
Archimedes(C. 287-212
BC)
Newton(1642-1727)
Leibniz(1646-1716)
Euler(1707-1783)
Navier(1785-1836)
Stokes(1819-1903)
Reynolds(1842-1912)
Prandtl(1875-1953)
Bernoulli(1667-1748)
Taylor(1886-1975)
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Ç’ eshte Fluidodinamika?
4
Studjon LEVIZJEN e fluideveStudjon LEVIZJEN e fluideve.
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Rendesia
• Fluidet te gjithpranishem:• Moti & klima• Mjete: automobila, trena, anije, dhe
avione, etj.• Mjedis • Fiziologji dhe mjekesi• Sport & argetim• Shume shembuj te tjere!
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Moti & Klima
Tornadot
Uragane Klima Globale
Stuhi
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Mjete
Avjone
Nendetese Trena te shpejte
Anije
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Mjedisi
Ndotja e ajrit Hidraulika e lumenjve
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Fiziologji dhe Mjekesi
Pompa gjakut Paisje mjekesore te ndryshme
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Sport & Argetim
Sportet ujore
Formula 1
Gara shpejtesie ne detÇiklizem
Surf
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Komponentet e Mekanikes se Fluideve
Mekanika e Fluideve
Statika e Fluideve Dinamika e Fluideve
Laminar Turbulent
Fluidet Newtonian Fluidet Jo-Newtonian
Fluidet Ideale Fluidet Viskoze
Rrjedhjet e Komprimueshme
Rrjedhjet e Pa- Komprimueshme
CFD Zgjdhjet per Regjime te vecanta
Rheology
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Densiteti ρ
Fluidet = Lengje + Gaze
hemkomprimues variable
eshempakomprimu const
Substanca Ajer (18ºC) Uje (20ºC) Mjalte (20ºC)
Densiteti (kg/m3)
1.275 1000 1446
Viskoziteti (P) 1.82e-4 1.002e-2 190
Viscoziteti μ: rezistenca e fluideve ne levizje
)(3
Poisem
Ns
Fizika e Fluideve
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Fluidodinamika Analitike FDA
• Teoria e formulimit matematik te problemeve fizike
• Vellimi kontrollit & analiza diferenciale• Zgjidhja e sakte gjendet vetem per
raste dhe gjeometri te thjeshta• Zgjidhje perafruese per probleme
praktike• Linearizimi• Relacione empirike nga te dhenat e
eksperimenteve
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Fluidodinamika Analitike FDA
Skematike
• Shembull: rrjedhja laminare ne nje tub
Zgjidhja e sakte:2 21( ) ( )( )
4pu r R rx
Koef ferkimit:88 64
Re2 2w
dudywf
V V
Supozimi: Teresisht e zhvilluar, Perafrimi: Thjeshtezimi ekuacinit te momentit, integrimi, aplikimi kushteve kufitare per percaktimin e kostanteve te integrimit dhe perdorimi I ekuacionit te energjise per llogaritjen e humbjeve te ngarkeses
xgy
u
x
u
x
p
Dt
Du
2
2
2
2
Humbjet:1 2
1 2 f
p pz z h
2
2
32
2f
L V LVh f
D g D
UD 2000Re
00
0
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Fluidodinamika Eksperimentale (FDE)
Perkufizimi: Perdorimi i metedodologjive dhe procedurave eksperimentale per
zgjidhjen e sistemeve inxhinierike te fluideve, duke perfshire modele te plote ose ne shkalle, sisteme matjesh (instrumenta, marrje dhe reduktim te dhenash), analiza e pasigurise, analiza dimensionale dhe ngjashmerise.
Filozofia e FDE :• Vendimi per te kryer eksperimente udhehiqet nga mundesia dhe
vlefshmeria e rezultate qe priten, duke realizuar objektivat e testimit me nje pasiguri te pranueshme.
• Integrimi i Analizes Pasigurise ne gjithe fazat e testimit duhet te jete pjesa kyce per gjithe programin eksperimental• Testimi i objektit• Percaktimi i burimeve te gabimit• Vleresimi pasigurise• Dokumentimi rezultateve
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Qellimi
• Shkenca & Teknologjia: beson dhe investigon nje fenomenon/proces, provon dhe verteton nje teori (hipoteze)
• Kerkimi & Zhvillimi: dokumenton nje proces/sistem, siguron te dhena standarte (procedura standarte, vlefshmerine), kalibron instrumentat, paisjet dhe aparaturat
• Industria: optimizim dhe analizim ne projektin, jep te dhena per perdorim direkt, pergjegjesine dhe pranueshmerine e produktit
• Edukim: mesim/demonstrim
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Aplikimi i FDE
Aplikimi ne kerkim & zhvillim
Tyneli Eres Tropikale ka aftesine te krijoje Temperatura q e variojne nga 0 deri165 gradeFahrenheit dhe simulon shiun
Aplikimi ne shkence & teknologji
Figurat e shtjellave te Von Karman
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Aplikimi i FDE (2)
Shembull I aplikimit industrial
Tyneli kriogjenik i Eres ne NASA simulon Kushtet e fluturimit per nje model ne shkalle- njeInstrument kyç ne projhektimin e avjoneve.
Aplikimi ne Edukim
Laboratori I Fluidodinamikes
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57:020 Fluid Mechanics 19
Modelet reale dhe ne shkalle (3)
• Shkallet e modelit: model dhe permasa reale
• Zgjedhja e modelit ne shkalle: percaktohet permes analizes dimensionale dhe ngjashmerise fluidodinamike
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Sistemet e matjes
• Instrumentat• Shnderues elektrik per matjen e forces dhe
momentit• Mates presioni• Tubi Pitot• Anemometry me fill te nxehte• PIV, LDV
• Marres te dhenash• Portat seriale• Desktop PC’s• Skeda per marrjen e te dhenave• Software – p.sh. Labview
• Analizimi dhe reduktimi te dhenave• Interpolimi/regresi• Analiza spketrale (serite Fourier)
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Instrumentat
Qelize ngarkese
Tubi Pito
Filli nxehte 3D - PIV
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Sistemet e marrjes se te dhenave
Hardware
Software - Labview
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Analiza spektraleFFT: Konverton amplituden nga funksion te kohes ne funksion te frekuences
Qellimi: te analizoje paqartesite natyrale te shkeputjes se rrymes perreth nje seksioni terthor duke perdorur FFT.
Fast Fourier Transform
Siperfaqja e prejrjes terthore
Power spectral densityof wave elevation
Free-surface wave elevation contours
FFT of wave elevation
Time history of wave elevation
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Analiza Dimensionale• Perkufizimi: Analiza Dimensionale eshte procesi i formulimit te problemeve te
fluidodinamikes ne terma te variablave dhe parametrave jo-dimensionale
• Perse perdoret: • Reduktim I variablave ( Nqs F(A1, A2, … , An) = 0, atehere f(1, 2, … r < n) = 0, ku, F = forma e funksionit, Ai = variablat dimensionale, j = parametrat jo-dimensionale, m = numri i dimensioneve te rendesishem, n = numri i variablave dimensionale, r = n – m ). Thereby the number of experiments required to determine f vs. F is reduced.• Ndihmon ne kuptimin e fizikes se fenomenit• I dobishem ne analizim te dhenash dhe modelim• Lejon shkallezimin e dimensioneve te ndryshem fizike dhe parametrave te fluidit
Shembull
Zona e shtjellave pas nje cilindri
Rezistenca= f(V, L, r, m, c, t, e, T, etc.)
Nga analiza dimensionale,
Shembuj te madhesive jodimensionale: Numri i Reynolds, Numri Froude, Numri Strouhal, Numri Euler, etj.
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Ngjashmeria FD dhe testimi modelit
• Perkufizimi: Kushtet e rrjedhjes per nje model te testuar jane teresisht te ngjashem nqs gjithe parametrat e rendesishem jodimensionale kane te njeten vlere per modelin dhe prototipin
• i modeli = i prototipi i = 1• Lejon extrapolimin nga modeli ne shkalle reale• Megjithate, ngjashmeria totale zakonishte nuk eshte e mundur. Kesisoj, shpesh eshte e nevojshme perdorimi ne shkallezim i Re ose Fr ose Ma, i.e., zgjedhja e me te rendesishem dhe adoptimi i te tjereve sa me mire te mundemi.
• Llojet e gjashmerise: • Ngjashmeria Gjeometrike: gjithe dimensionet e trupit ne tre dimensionet kane te
njejtin raport linear shkalle• Ngjashmeria Kinematike: grimcat homologe (i njeti pozicion relativ) ndodhen ne pikat
dhe kohet homologe.• Ngjashmeria Dinaike: pervec ngjashmerise kinematike, forcat e modelit dhe prototipit
duhet te kene raport konstant.
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Procesi FDE• “Procesi FDE” jane hapat per realizimin e eksperimentit dhe marrjen e te dhenave (rezultateve)
Test Set-up
Facility & conditions
Install model
Prepare measurement
systems
Data Acquisition
Data Reduction
Uncertainty Analysis
Data Analysis
Initialize data acquisition software
Run tests & acquire data
Store data
Statistical analysis
Estimate bias
limits
Compare results with benchmark data, CFD, and
/or AFD
Evaluate fluid
physics
Calibration
Prepare experimental procedures
Data reduction
equations
Estimate
precision limits
Estimate total
uncertainty
Prepare report
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FDE – “ndihmon” ne fitimin e eksperiences
Matja e densitetit dhe viskozitetit kinematik te nje fluidi Matja e prurjes, koeficentit te
ferkimit, profilit te shpejtesiseNe tubat e lemuar dhe te ashper.
Matja e shperndarjes presionit siperfaqesorKoeficentit te forces ngritese dhe rezistenceste nje profili aerodinamik
ToScanivalve
Chord-w isePressure
TapsTygonTubing
Load Cell
Load CellL
D
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Fluidodinamika Llogaritese Fluidodinamika Llogaritese CFDCFD
• CFD eshte perdorimi i metodave kompjuterike per zgjidhjen e sistemeve fluide inxhinierike, duke perfshire modelimin (matematik & fizik) dhe metodat numerike (zgidhesi, FEM, FDM, FVM, gjenerimi rrjetes, etj.).
Shkurt: Zgjidhja e ekuacioneve te N-S duke perdorur kompjuterin
• Zhvillim i teknologjive CFD qe me ardhjen e kompjuterit
ENIAC 1, 1946IBM WorkStation
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Skema e CFD
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Matematika
Navier-Stokes Equations
Mekanika e Fluidit
Fizika e Fluidit
Fluid Problem
Programi Kompjuterik
Gjuhe Programimi
Resultatet e simulimit
Kompjuter
Rjeta llogariteseGjeometri
Metoda Numerike
Discretizimi
Krahasim&Analizim
CFD
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Qellimi• Objektivi i CFD eshte te modeloje fluidin e vazhduar permes
Ekuacioneve me Diferencial te Pjeshem (PDEs), t’i diskretizoje ato ne nje problem algjebrik, ti zgjidhe, t’i provoje dhe te realizoje nje projekt baze per simulime ne vend te “krijo & testo”
• Simulimi i fenomeneve fizike te fluideve qe jane te veshtire te realizohen nga eksperimentet: shkalla e simulimeve (shkalle reale per anije, avjone), rreziqet (explozionet, rezatimet, ndotjen), fizike (parashikimi motit, shtresa kufitare planetare, evolimi yjor).
• Rezultatet e analizes CFD jane te rendesishme ne:• studimin konceptual te projekteve te reja• zhvillimin e detajuar te produktit• ekspertize• riprojektim
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Pse CFD?
• Lejon studimin e fenomenit te rrjedhjes• Me i lire se eksperimentet• Jo i merzitshem dhe lejon perseritjen• Me i shpejte se eksperimentet per te kryer
studime parametrike• “E bukur” !!!! (shumengjyreshe)• “Kënaqesi”??
- s’eshte e “vertete” ??
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CFD eshte “kenaqesi” ??
Sepse na ndihmon te njohim …
• Kompjuterin kur ai nuk llogarit• Analizen numerike
kur kjo deshton• Fiziken
kur ajo nuk duket realiste
N.q.s. i pelqeni keto, atehere CFD is 4U
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Pse CFD? (vazhdim)
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Simulimi (CFD)Simulimi (CFD) EksperimentiEksperimenti
Kostua I lire I shtrenjte
Koha Shkurter Gjate
Shkalla Çdo shkalle Mesme/Vogla
Informacioni Gjithe zona Pikat e matjes
Perseritja Gjithnje Disa here
Siguria SigurtNdonjehere I
pasigurt
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Ku perdoret CFD?
• Ku perdoret CFd?• Aerospace• Automobilize
m• Biomjekesi• Procese kimike• HVAC• Hidraulike• Marine• Nafte & Gas• Gjenerim Fuqie• Sporte
F18 Store Separation
Aerospace
Automobilizem
Biomjekesi
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57:020 Fluid Mechanics 35
Polymerization reactor vessel - prediction of flow separation and residence time
effects.
Streamlines for workstation ventilation
HVAC
Procese kimike
Hidraulike
Ku perdoret CFD?
• Ku perdoret CFd?• Aerospace• Automobilizem• Biomjekesi
• Procese kimike
• HVAC• Hidraulike• Marine• Nafte & Gas• Gjenerim Fuqie• Sporte
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57:020 Fluid Mechanics 36
Flow of lubricating mud over drill bit
Flow around cooling towers
Marine
Nafte & Gas
Sporte
Impiante fuqie
Ku perdoret CFD?
• Ku perdoret CFd?• Aerospace• Automobilizem• Biomjekesi• Procese kimike• HVAC• Hidraulike• Marine• Nafte & Gas• Gjenerim Fuqie• Sporte
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Modelimi
• Formulimi matematik i problemeve fizike per sistemet inxhinierike te fluideve
• Ekuacionet themelore: Ekuacionet e Navier-Stokes (momentit), ekuacioni vazhdueshmerise, ekuacioni Poisson per presionin, ekuacioni energjise, ekuacioni gjendjes per gazin ideal, djegia (ekuacionet per reaksionet kimike), rrjedhja shume-fazore (p.sh. ekuacioni Rayleigh), dhe modelet e turbulences (RANS, LES, DES).
• Kordinatat: Karteziane, cilindrike dhe sferike rezultojne ne forma te ndryshme per ekuacionet themelore
• Kushtet Fillestare IC (supozimi fillestar per zgjidhjen) dhe Kushtet Kufitare BC (mos-rreshqitje, siperfaqe lire, gradienti zero, simetria, shpejtesi/presion, hyrje/dalje)
• Kushtet e rrjedhjes: perafrimet gjeometrike, zona, numri Reynolds and numri Mach, etj.
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Modelimi (shembuj)
Animimi siperfaqes se lire per anijen ne valete rregullta
Zhvillimi flakes ne siperfaqe te lire (Bell et al., 2001)
Evolimi shtreses perzier ne 2D ngarkuar me grimca dhe numer te Stokes 0.3 respektivisht shkalles kohore te stjelles(C.Narayanan)
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57:020 Fluid Mechanics 39
Modelimi (shembuj, vazhdim)
3D vortex shedding behind a circular cylinder (Re=100,DNS,J.Dijkstra)
DES, Re=105, Iso-surface of Q criterion (0.4) for turbulent flow around NACA12 with angle of attack 60 degrees
LES of a turbulent jet. Back wall shows a slice of the dissipation rate and the bottom wall shows a carpet plot of the mixture fraction in a slice through the jet centerline, Re=21,000 (D. Glaze).
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Ligjet e ruajtjes
in outMinm outm
outin mmdt
dM
outin mm
0dt
dMMasesMomentitEnergjise
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Ekuacioni I-re i N-S
41
Ruajtja e mases Ekuacioni vazhdueshmerise
0
i
i
x
U
Dt
D Komprimueshem
0, Dt
Dconst
0
i
i
x
UPakomprimueshem
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Ekuacioni II-te i N-S
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Ruajtja e Momentit (Ligji II Njutonit F=ma)Ekuacioni Momentit
V
j
IV
i
ij
III
j
II
i
ji
I
j gxx
P
x
UU
t
U
k
kij
j
i
i
jij x
U
x
U
x
U
3
2
I : Ndryshimi lokal me kohen
II : Termi konektin i momentit
III: Forcat siperfaqesore
IV: Termi difuziv momentit (shkembimet ne nivel molekular) forcat e viskozitetit
V: Forcat e mases
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Ekuacioni III-te i N-S
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Ruajtja Energjise (Ligji I-re TD)Ekuacioni Energjise
V
i
jij
IV
i
III
i
i
II
ii
I
x
U
x
T
x
UP
x
TUc
t
Tc
2
2
I : Ndryshimi lokal i energjise me kohen (termi lokal)II: Termi konvektivIII: Puna e presionitIV: Fluksi nxehtesise (termi difuziv)V: Transmetimi pakthyeshem i energjise mekanike ne nxehtesi
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Diskretizimi Numerik
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Metodat e diskretizimit Diferencat e Fundme FDM
Te thjeshta per aplikime, per rrjeta te thjeshat dhe te strukturuara Elementet e Fundem FEM
Cdo lloj gjeometrie Volumet e Fundme FVM
Ruajtjen, cdo lloj gjeometrie
Ekuacionet Analitike Ekuacionet e DiskretizuarDiskretizimi
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Rrjetat llogaritese
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Rrjeta te strukturuara
- Cdo nyje ka te njetin numer elemetesh perreth saj
– vetem per gjeometri te thjeshta Rrjeta te pastrukturuara
- Per cdo lloj gjeometrie
– strukture e shrregullt te dhenash Rrjete e strukturuar me blloqe
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Kushtet Kufitare BC
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Kushte Kufitare tipikeMos-rreshqitje (Muret), Aksialsimetrik, Hyrj, Dalje, Periodike
Inlet ,u=c,v=0
o
No-slip walls: u=0,v=0
v=0, dp/dr=0,du/dr=0
Outlet, du/dx=0 dv/dy=0,dp/dx=0
r
xAxialsimetrik Kushte periodike ne
drejtimin gjatesor te nje profili aerodinamik
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Skema e Modelimit ne CFD
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Procesi CFD
Modeli Viskozitetit
Kushtet Kufitare
Kushtet Fillestare
Kufiri Konvergjences
Konture
Saktesia(single/double)
Skema Numerike
Vektore
Vija rrymeVerifikimi
Gjeometri
Zgjedhja e Gjeometrise
Parametrat Gjeometrike
Fizika Rjjeta Zgjdhja Post-Processing
KomprimushemON/OFF
Parametrat e Rrjedhjes
Pastrukturuar(automatic/
manual)
Stacionare/Jostacionare
Forces Report(lift/drag, shear stress, etc)
XY Plot
Forma dhe Permasat e
Zones
Trasmetim Nxehtesie ON/OFF
Strukturuar(automatic/
manual)
Tentativat/hapat
Vertetimi
Rezultatet
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Gjeometria
• Zgjedhja e kordinatave te duhura• Percaktimi i permasave dhe formes se zones• Ndonje thjeshtezim i nevojshem? • Cfare lloj formash duhen zgjedhur per krijimin
e nje gjeometrie te mire? (vija, rrathe, ovale, etj.)
• Per softet komerciale gjeometria krijohet permes softit, (edhe vecmas nga vete softi, si Gambit, si FlowLab ose se bashku)
• Per softe kerkimi, perdoren softe komerciale (p.sh. Gridgen).
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Fizika
• Kushtet e rrjedhjes dhe parametrat e fluidit 1. Kushtet e rrjedhjes: viskoz, joviskoze, laminar
ose turbulent, etj. 2. Parametrat e Fluidit: densiteti, viskoziteti,
dhe percjellshmeria termike, etj.
3. Kushtet dhe parametrat jane ne forme dimensionale ne softet komerciale CFD dhe ne forme jodimensionale per softet e kerkimore.
• Zgjedhja e Modelit: zakonisht fiksohet nga kodi dheka opsione per t’u zgjedhur nga perdoruesi
• Kushtet Kufitare dhe Fillestare: nuk fiksohen nga kodi, perdoruesi duhet ti fiksoje per secilin rast aplikimi.
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Rrjeta
• Rrjeta duhet te jete e mire krijuar per te zgjidhur tiparet me te rendesishme te rrymes qe varen nga parametrat e kushteve te levizjes (p.sh., Re), si dhe imtesimi rrjetes afer shtreses kufitare ne mure
• Rrjeta mund te gjenerohet ose nga kode komerciale (Gridgen, Gambit, etj.) ose kode kerkimore.
• Rrjeta se bashku me kushtet kufitare duhet eksportuar nga kodi qe e kakrijuar ne nje format te caktuar qe mund te jihet nga kodi CFD komercial ose kerkimor
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Zgjidhja
• Vendosja e parametrave te duhur numerike• Zgjdhja e zgjidhesit te duhur• Procedura e zgjidhjes (p.sh. Rrjedhje pakomprimueshme)
Zgjidhaj e ekuacionit te momentit, ekuacionit te presionit te Poisson dhe marrja e fushes se rrjedhjes per madhesite ne shqyrtim si: shpejtesi, intensiteti turbulences, presionit dhe madheisve integrale (forca ngirtese, rezistenca etj)
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Rezultatet
• Raporton historikun e rezultateve te ruajtura ne kohe te shpejtesise, presionit, temperatures, etj.
• Raporton rezultatet per madhesite integrale, si renia totale presionit, koeficenti ferkimit (rrjedhja ne tuba), koeficentin e forces ngitese dhe rezistences (rrjedhja ne nje profil aerodinamik), etj.
• Plotime XY qe paraqesin shperndarjen e shpejtesise/presionit, koeficentit ferkimit (rrjedhja ne tuba), koeficentin e forces ngitese dhe rezistences (rrjedhja ne nje profil aerodinamik), etj.
• Te dhena nga FDA ose FDE mund te importohen dhe vendosen ne krye te XY plots per krahasim dhe vleresim
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Post-processing
• Analizim dhe vizualizim• Llogaritja e variablave qe rrjedhin
Shtjellshmeria Sforcimi preres ne mure
• Llogaritja e parametrave integrale: forca, momente
• Vizualizimi (zakonishte me softe komerciale)Konture te thjeshta 2DPlotimi 3D i kontureve te
isosiperfaqevePlotimi vektoreve dhe vijave te rrymesAnimime
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Shembull i procedures CFD (Gjeometria)
• Simulimi rrjedhjes turbulente (Re=143K) perreth Clarky airfoil me kend te rrymes 6 grade.
• Aplikohet per zonen forma “C”• Rezja Rc e zones dhe gjatesia pas saj Lo duhen
specifikuar qe permasat e zones te mos influencojne ne rezultatet e simulimit
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Shembull i procedures CFD (Fizika)S’ka transmetim nxehtesie
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Shembull i procedures CFD (Rrjeta)
Rrjea duhet e imet prane profilit per te zgjidhur shtresen kufitare
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Shembull i procedures CFD (Zgjidhja)
Residuals vs. iteration
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Shembull i procedures CFD (Raportimi)
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Shembull i procedures CFD (Post-processing)
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Softe komerciale• Software CFD 1. FLUENT: http://www.fluent.com 2. FLOWLAB:
http://www.flowlab.fluent.com 3. CFDRC: http://www.cfdrc.com 4. STAR-CD: http://www.cd-adapco.com 5. CFX/AEA:
http://www.software.aeat.com/cfx
• Software per gjenerim Rrjete 1. Gridgen: http://www.pointwise.com 2. GridPro: http://www.gridpro.com
• Software per Visualizim 1. Tecplot: http://www.amtec.com 2. Fieldview: http://www.ilight.com
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FALEMINDERIT PER VEMENDJEN!
MIREPRESIM PYETJE
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