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Introduction to Computational Fluid Dynamics

Introduction to Computational Fluid Dynamics. Course Notes (CFD 4). Karthik Duraisamy Department of Aerospace Engineering University of Glasgow. Contents. Introduction (1.5) Classification of PDE, Model equations (1.5) Finite difference methods:  Spatial discretization (3)

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Introduction to Computational Fluid Dynamics

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  1. Introduction to Computational Fluid Dynamics Course Notes (CFD 4) Karthik Duraisamy Department of Aerospace Engineering University of Glasgow

  2. Contents • Introduction (1.5) • Classification of PDE, Model equations (1.5) • Finite difference methods:  Spatial discretization (3)  Temporal discretization (2)  Convergence, Consistency, Stability (2) • Grids/Boundary conditions (1) • Euler equations (1) • RANS Equations and Turbulence modeling (2) • DNS/LES (1) • Best practices in CFD (1) • Case studies/Demonstrations (3) (.) – Approximate number of lectures

  3. CASE STUDIES

  4. Best practices in CFD • Selection of Problem/model/numerical method • Feasibility study of computation • Identifying physics and required resolution in different parts of the mesh • Grid convergence • Time step convergence (unsteady) • Verification/Validation • COMMENT YOUR CODE!!! 

  5. What do you plot? • Line graphs (x vs Cp) • Contours (Velocity magnitude in a section) • Iso-surfaces (Vorticity magnitude) • Streamtraces (Streamlines) • Spectra (Energy spectra)

  6. CASE STUDY – 1

  7. Fixed wing validation • M=0.15, Re=4.5x106, α=10o, AR=0.75, rounded tip. • Extensive mean and turbulence measurements by Chow et. al. [1997] • Surface (pressure tabs) and wake measurement (pressure probes and hot wires) up to 0.68c. • Resolution good enough to compare flow viz with numerics.

  8. Surface pressure distribution y/c=0.667 y/c=0.583 φ=45o φ=90o φ

  9. Axial Velocity (x/c=-0.394) Computation Experiment

  10. Axial Velocity (x/c=-0.114) Experiment Computation

  11. Axial Velocity (x/c=0.005) Experiment Computation

  12. Axial Velocity (x/c=0.678) Computation Experiment

  13. RANS/Inviscid Comparison Swirl velocity

  14. CASE STUDY - 2

  15. Why study tip vortices?

  16. Application of Spanwise blowing • Baseline test case of Heyes et al. (Imperial college): • AR=1, NACA0012 wing section, α=7.5o, M=0.1, Re=2.2x105. • Spanwise blowing: Velocity measurements x/c=1 downstream of trailing edge. • Blowing co-efficient

  17. Validation: Baseline case, x/c=1

  18. Blowing test cases

  19. Validation: Blowing case C1, x/c=1

  20. Physics of control Axial Vorticity x/c=0.21 (from l.e.) Freestream direction

  21. Case C1: x/c=-0.95

  22. Case C1: x/c=-0.85

  23. Case C1: x/c=-0.75

  24. Case C1: x/c=-0.45

  25. Case C1: x/c=-0.25

  26. Case C1: x/c=-0.1

  27. Case C1: x/c=1.0

  28. Blowing case C1

  29. Blowing case C1

  30. Different blowing rates Core radius Peak swirl velocity Effectiveness of blowing: weak function of blowing angle

  31. CASE STUDY -3 Some thoughts from “30 years of Development and Application of CFD at Boeing” - Johnson et al., Computers and Fluids.

  32. Role of CFD • CFD has joined wind tunnel and flight testing as primary tool • Flight testing : Too expensive, but real data • Wind tunnel : Good flight envelope, accurate, but low Re, but effect of mounting, walls, not enough detail • CFD : Inexpensive, used in optimization, extrapolation of tunnel data to flight conditions and detailed understanding, but somewhat inaccurate. CFD : Very useful in design of high speed cruise configuration of full transport aircraft

  33. Well..

  34. Role of CFD

  35. Contribution of CFD in 777 design

  36. Use of CFD

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