Download to read offline
Uploaded byJosep M Carbonell Oyonarte
Motoglider Cfd study
The document details a study on the aerodynamic analysis of a motoglider, focusing on airfoil performance and computational fluid dynamics (CFD) simulations. It includes an introduction, airfoil analysis, and airplane study, detailing the methodology, results, and conclusions drawn from comparing simulated and experimental data. The findings indicate an overall good match in lift coefficients, particularly in the linear region, but highlight issues with drag coefficients and the need for better turbulence modeling.
Motoglider Cfd study
- 1.
- 2. ! 1! LIST*OF*CONTENTS* 1.! INTRODUCTION*3! 2.! AIRFOIL*ANALYSIS* 4! 2.1.! Aim&of&the&analysis& 4! 2.2.! Script& 4! 2.3.! Results&and&verification& 5! 2.4.! Conclusions& 8! 3.! AIRPLANE*STUDY* 9! 3.1.! Aim&of&the&study& 9! 3.2.! Modifications&on&the&tutorial& 9! 3.3.! Geometry&and&mesh& 21! 3.4.! Results&and&Comparison& 22! 3.5.! Conclusions& 25! 4.! BIBLIOGRAPHY* 26! * LIST*OF*FIGURES* Figure!1.!Own-written!script!for!automation!process!..................................................................!4! Figure!2.!Pressure!distribution!at!3º!............................................................................................!5! Figure!3.!Velocity!distribution!at!3º!.............................................................................................!5! Figure!4.!Graph!provided!by!J.!Robertson!....................................................................................!6! Figure!5.!Cl!vs.!AoA!graph!obtained!with!CFD!analysis!.................................................................!6! Figure!6.!Cm!vs.!AoA!graph!obtained!with!CFD!analysis!..............................................................!6! Figure!7.!Cl!vs.!Cd!graph!obtained!with!CFD!analysis!...................................................................!7! Figure!8.!Cl!vs.!Cd!graph!provided!by!J.!Robertson!......................................................................!7! Figure!9.!k!definition!..................................................................................................................!10! Figure!10.!nut!definition!.............................................................................................................!11! Figure!11.!ω!definition!...............................................................................................................!12!
- 3.
- 4.
- 5. ! 4! 2.!Airfoil*analysis* 2.1.! Aim*of*the*analysis* The!process!of!the!simulation!was!based!on!the!Airfoil+study!of!Casacuberta’s!tutorial.!The! following!modifications!have!been!done:! The!study!of!the!airfoil!includes!the!process’!automation!to!simulate!a!range!of!angles!of!attack! to!save!user!time.!Acting!in!this!way,!the!user!only!has!to!introduce!the!range!that!is!expected! to!analyse.!With!an!own-written!script,!all!the!needed!folders!will!be!created.! In!addition,!the!results!obtained!will!be!also!studied!and!compared!with!the!available! experimental!data.!Because!of!the!bad!accuracy!of!the!mesh!due!to!the!low!computing!power! available,!big!differences!between!CFD!and!experimental!results!are!expected.! 2.2.!Script* Our!script,!that!can!be!seen!in!Figure!1,!was!based!on!the!one!provided!in!Casacuberta’s! tutorial.!The!script!is!defined!in!order!to!compute!all!the!processes!that!has!to!be!done! manually.!Not!only!for!one!angle!of!attack,!but!creating!also!all!the!folders!needed!to!simulate! a!range!of!angles!of!attack.!First!of!all,!the!conditions!of!the!simulation!were!changed!for!the! ones!of!the!available!experimental!data.!Moreover,!the!airfoil!is!introduced!as!a!“.dat”!file,!so! it’s!easy!to!use!this!script!for!different!airfoils.! The!range!of!AoA!is!created!using!a!while!loop!including!all!the!process,!from!the!creation!of! the!geometry!to!the!running!of!the!simulation.!With!this!process,!the!user!hasn’t!to!enter!to! each!folder!to!run!each!AoA.! Continuing!analysing!the!script,!the!existent!foilgmsh+script!is!used!to!create!the!geometry! with!different!AoA,!but!without!modifying!it,!because!it!served!perfectly!to!our!needs.!The!only! consideration!that!must!be!taken!is!that!this!script!names!the!geometry!always!clarky.dat.geo,! so!it’s!needed!to!change!this!name!every!time!to!differentiate!each!AoA.+Gmsh!Mesh! Generator!is!used,!so!after!creating!each!simulation!the!command!gmshToFoam!is!also! needed.!Continuing!analysing!the!script,!the!following!lines!have!the!function!of!proportionate! the!conditions!of!the!simulation!required.!Finally,!using!foamJob!a!log!of!the!results!of!the! simulation!is!created,!providing!the!ability!to!assess!the!state!of!it!in!every!moment.! Figure+1.+Own@written+script+for+automation+process+
- 6.
- 7.
- 8.
- 9.
- 10. ! 9! 3.!Motoglider*study* 3.1.! Aim*of*the*study* The!objectives!of!this!study!are:! •!To!compare!the!results!obtained!with!XFLR5!and!CFD! •! To!know!more!precisely!the!aerodynamics!coefficients!of!the!airplane! •! To!understand!the!behaviour!of!the!fluid!around!the!motoglider! Great!difference!between!XFLR5!and!CFD’s!results!are!expected!because,!first!of!all,!the! geometry!can’t!be!perfectly!represented!in!XFLR,!and,!furthermore!it!is!a!potential!solver.! Besides,!CFD!analysis!are!expected!to!represent!quite!rigorously!the!performance!of!the!air! around!a!shape!as!an!airplane!and!the!CL!coefficient,!but!error!in!CD!will!be!assumed.!! This!study!was!based!on!the!Very+light+aircraft+case+of!Casacuberta’s!tutorial.!Some!changes! had!to!be!done.! 3.2.! Modifications*on*the*tutorial* First!of!all,!some!dictionaries!had!to!be!modified!to!ASCII!code,!because!they!originally!were!in! binary!and!it!did!not!work!as!expected.!Of!course,!the!initial!conditions!were!substituted!for! the!motoglider’s!scope,!which!are!k,!ω!and!Cµ.+Their!values!are!defined!in!equation!3.2.1,!3.2.2! and!3.2.3.! ! = 3 2 ( & · ()* = 0.5814111111111111(3.2.1)! 2 = 34 56.*7 · !6.7 8 = 24.3324111111(3.2.2)! 34 = 0.09! = 0.052111111111111111111111(3.2.3)! Where! |U|!is!the!mean!flow!velocity! I!is!the!turbulence!intensity:!( ≈ 0.02! L!is!the!turbulent!length!scale:!8 ≈ 0.07<=3 ≈ 0.07 · 0.936 ≈ 0.0655?.!! MGC!is!the!mean!geometric!chord! All!the!previous!values!are!necessary!to!create!our!case!from!the!tutorial!case.!In!the!figures!9,! 10,!11,!12,!13,!14,!15,!16!and!17!all!the!changes!that!had!been!made!in!the!tutorial’s! dictionaries!are!shown.!As!said!before,!they!manly!represent!the!change!to!ASCII!and!the! characteristic!values!(MGC,!Aref,!…).! Firstly,!the!definition!of!k,!nut,!ω,!p!(pressure)!and!U!(mean!flow!velocity)!are!presented.! In!blue!can!be!find!the!changes!that!had!been!made!in!these!definitions.!!!
- 11.
- 12.
- 13.
- 14.
- 15.
- 16.
- 17.
- 18.
- 19.
- 20.
- 21.
- 22.
- 23.
- 24.
- 25. ! 24! ! Figure+27@+Streamlines+over+fuselage+ Combining!figure!25!and!27!can!be!viewed!that!some!boundary!layer!separation!is!present!on! the!fuselage’s!leading!edge!and!after!the!cockpit.!It!could!be!reduced!smoothing!these!points! on!the!geometry.! ! Figure+28@+Streamlines+over+the+wing+ In!figure!28!is!noted!the!downwash!produced!by!the!wing!and!the!tip!vortexes.! Finally,!the!numerical!results!and!its!comparison!with!XFLR5!data!are!presented!in!table!1.! Table+1.+Results'+comparison+ & CFD&XFLR5& Error& CL& 0.49! 0.537! 8.75%! CD& 0.02! 0.014! 42.86%! !! !
- 26.
- 27.