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21/03/2014

MASTER DEGREE DISSERTATION IN MECHANICAL, AERONAUTICAL ENGINEERING. Development of an automatic shape optimization platform for a laminar profile March - September 2013. Relatori : Prof. Jan Pralits Ing. Thomas Michon. Studente : Marcello Tobia Benvenuto. 21/03/2014. 1. Introduction.

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21/03/2014

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  1. MASTER DEGREE DISSERTATION IN MECHANICAL, AERONAUTICAL ENGINEERING Development of an automatic shape optimization platform for a laminar profile March - September 2013 Relatori : Prof. Jan Pralits Ing. Thomas Michon Studente : Marcello Tobia Benvenuto 21/03/2014 1

  2. Introduction Daher Socata produces the world’s fastest single turboprop aircraft: TBM 850. As each aeronautic company, Reduce the consumption it works every day to improve the aircraft performance. Increase the max. speed Reduce the drag on the surfaces: WING Fluid mechanics 21/03/2014 2

  3. Physical phenomenon • When a body is in motion in a flow, the flow adhere to it because of the viscosity. A thinlayerarises close to the shape, calledboundary layer. 21/03/2014 3

  4. Physical phenomenon External disturbances can enter the boundary layer and generate a turbulent flow through a Transition process. Skin Friction X/C • Laminar boundary layer: Thin with regular streamlines; low skin friction. • Turbulent boundary layer: Thick with irregular fluctuations; high skin friction. The transition phenomenon is very sensitive to the shape variations 21/03/2014 4

  5. Objective Reduce the friction drag on an airfoil by keeping the flow laminar over the largest possible portion of the surface. Automatic Shape Optimization Advantages: 1) Save time during a process 2) Run multiple repetitive simulations 3) Analyze automatically the good results, finding the optimum 21/03/2014 5

  6. Contents • Optimization platform for 2D Geometry • 2D optimization High and High/Low speed - results - discussion • Creation wing - results - discussion • Conclusions • Future works 21/03/2014 6

  7. Why a 2D geometry? The wing’s behaviors are given by its profiles. Relative Thickness: 16% Chord: 1.675 m 21/03/2014 7

  8. Optimization steps and tools Create the 2D geometry Catia V 5 Create the domain and the mesh ANSYS: Design Modeler and Mesh Optimization platform Flow Solver ANSYS: Fluent Boundary layer and its stability bl3D and Nolot code Mode Frontier 21/03/2014 8

  9. Optimization steps and tools Create the 2D geometry Catia V 5 Create the domain and the mesh ANSYS: Design Modeler and Mesh Optimization platform Flow Solver ANSYS: Fluent Boundary layer and its stability bl3D and Nolot code Mode Frontier 21/03/2014 9

  10. Create the 2D geometry To limit the number of the geometric design variables Describing the shape with a small set of inputs 9 Polynomial approximations of curves CAD Software: Catia V 5 21/03/2014 10

  11. Create the 2D geometry Constraints Design Parameters • Chord = 1 meter • Radius of the circle • Position of point 2 and 9 inside square • Thickness at 25% and 75% of the chord fixed. • Tension of points 2,3,8,9 • Thickness of trailing edge 21/03/2014 11

  12. Optimization steps and tools Create the 2D geometry Catia V 5 Create the domain and the mesh ANSYS: Design Modeler and Mesh Optimization platform Flow Solver ANSYS: Fluent Boundary layer and its stability bl3D and Nolot code Mode Frontier 21/03/2014 12

  13. Create the domain and the mesh Different domains and meshes have been investigated to find the best grid in terms of time and quality • O-type domain • Radius = 90 meters Grid close to the profile: Grid Profile 21/03/2014 13

  14. Optimization steps and tools Create the 2D geometry Catia V 5 Create the domain and the mesh ANSYS: Design Modeler and Mesh Optimization platform Flow Solver ANSYS: Fluent Boundary layer and its stability bl3D and Nolot code Mode Frontier 21/03/2014 14

  15. Flow solver Numerical solution of the Navier-Stokes’s equations FLUENT Velocity and pressure distribution Pressure Coefficient distribution on the root airfoil of TBM 850. Cruise conditions. Key point for the stability analysis Cp X/C • Smoothness • Good quality 21/03/2014 15

  16. Optimization steps and tools Create the 2D geometry Catia V 5 Create the domain and the mesh ANSYS: Design Modeler and Mesh Optimization platform Flow Solver ANSYS: Fluent Boundary layer and its stability bl3D and Nolot code Mode Frontier 21/03/2014 16

  17. Boundary layer and its stability: bl3D It calculates the parameters of the boundary layer from the Cp distribution bl3D code Laminar Boundary Layer's Equations 21/03/2014 17

  18. Boundary layer and its stability: NOLOT NOLOT is based on the Linear Stability: Flow decomposed in mean flow and unsteady disturbances u = U + u' The unsteady disturbance is represented by a wave with infinitesimal amplitude Frequency Streamwise Wave number Spanmwise Wave number 21/03/2014 18

  19. Boundary layer and its stability: NOLOT Semi-empirical eN method Mack’s Law: Turbulence intensity N factor N = - 8.43 – 2.4 ln(Ti) 0.0007 < Ti < 0.0298 21/03/2014 19

  20. Objective functions To maximize the position of transition A change of the shape of a profile can lead to different value of Cl and Cm Changes of global repartition of lift • Stability problems • Stalling problems To minimize ∆Cl = |Cl – ClTBM| To minimize ∆Cm = |Cm – CmTBM| 21/03/2014 20

  21. Optimization steps and tools Create the 2D geometry Catia V 5 Create the domain and the mesh ANSYS: Design Modeler and Mesh Optimization platform Flow Solver ANSYS: Fluent Boundary layer and its stability bl3D and Nolot code Mode Frontier 21/03/2014 21

  22. Optimization platform: Mode Frontier 21/03/2014 22

  23. Optimization platform: Mode Frontier Lift and Mom. coeff ∆Cl ∆Cm 21/03/2014 23

  24. Contents • Optimization platform for 2D Geometry • 2D optimization High and High/Low speed - results - discussion • Creation wing - results - discussion • Conclusions • Future works 21/03/2014 24

  25. Optimization 2D High speed • high speed (cruise): M=0.51; h=26000 feet; aoa=0 degrees • Strategy optimization - explore all the domain of input parameters DOE - optimize the best profiles found by DOE with genetic algorithm 21/03/2014 25

  26. Pareto front opt. 2D high speed • 399 profiles have been explored in 8 days Max ∆Cl 3% ∆Cl Max trans. 47% of the chord TBM (trans. 26% of the chord) Transition location 21/03/2014 26

  27. Best solution opt. 2D high speed BLACK = TBM RED = BEST 21/03/2014 27

  28. Robustness solution for manufacturing? 0.07% of 1765 mm = 1.19 mm c A big influence of the leading edge on the transition Solution not robust 21/03/2014 28

  29. Drag evaluation with transition model To evaluate the difference of drag, the SST-transition model is used in Fluent to study the natural transition: 21/03/2014 29

  30. Optimization 2D High/Low speed To analyze stall characteristics at low speed, the profile has been optimized also at take-off conditions - High speed (cruise): M=0.51; h=26000 feet; aoa=0 degrees - Low speed (take-off): M=0.18; h=0; aoa= > 15 degrees 21/03/2014 30

  31. Objective functions Cruise condition: • To maximize the transition location • To minimize ∆Cl and ∆Cm Take-off condition: • Maximize the max Lift coefficient 21/03/2014 31

  32. Pareto front 2D opt. High/low speed Pareto front Cl low speed Transition high speed The objective functions are in opposition one with the other The same optimization has been done for the tip profile of the wing 21/03/2014 32

  33. Discussion optimization 2D High speed • Big sensibility of the phenomenon by the shape variations • Transition moved from 26% to 47% of the chord • Viscous drag reduced of 14.26% • Improvements limited by the constraints of the shape: transition occurs close to the maximum thickness High/low speed • Each flight condition requires a different optimal shape • The presence of a new O.F. has not penalized the transition (42%) • Improvements limited by the constraints of the shape 21/03/2014 33

  34. Contents • Optimization platform for 2D Geometry • 2D optimization High and High/Low speed - results - discussion • Creation wing - results - discussion • Conclusions • Future works 21/03/2014 34

  35. Creation wing Creation of a wing with the optimal root and tip profile obtained previously Wing parameters: The same of the wing of TBM 850 - span: 12161.3 mm - dihedral: 6.5 degree 21/03/2014 35

  36. CFD Simulation 3D To compare the wing of the TBM 850 with the wing using the optimal profiles. NEW TBM Skin Friction 21/03/2014 36

  37. Results 3D New Skin Friction TBM Chord Skin friction on profile at 50% of the span 21/03/2014 37

  38. Discussion • The validation on the wing has given unexpected results in terms of drag: The effects of the flows on 2D and 3D geometry are different - trailing vortex - cross flow disturbances X - Wall shear stress 21/03/2014 38

  39. Discussion • The validation on the wing has given unexpected results in terms of drag: The effects of the flows on 2D and 3D geometry are different - trailing vortex - cross flow disturbances 21/03/2014 39

  40. Contents • Optimization platform for 2D Geometry • 2D optimization High and High/Low speed - results - discussion • Creation wing - results - discussion • Conclusions • Future works 21/03/2014 40

  41. Conclusions • I am familiar with software like Catia V 5, Fluent (2D and 3D), Fortran, Python, modeFRONTIER • I created an automatic shape optimization for 2D geometry • The strategy used, has allowed to obtain good results for 2D geometry - transition phenomenon delayed from 26% to 47% of the chord - Viscous drag reduced more than 14% 21/03/2014 41

  42. Future work and suggestions Optimization 2D: • New parameterization (CST) with other constraints can be tested • More time for the iterations can lead a better results 3D Validation: • To consider 3D effects we can run the following loop: • Study the flow around the wing • Take Cp distribution of three profiles of the wing (root, middle, tip) • Run optimization platform for the three profiles • To rebuild the wing with the three new profiles and study the flow on the wing 21/03/2014 42

  43. Thank you for your attention 21/03/2014 43

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