Assignment_fall2018 (1).pdf

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Assignment for AE4202 – CFD for Aerospace Engineers Introduction The assignment should be performed in groups of two students. You are free to choose your partner. Both team members should equally contribute to the work and submit a joint report. Though not recommended, you could also do the work alone and submit individual reports. The deliverable is a short report with max. 10 pages, excluding title page and list of references. The report should be submitted through the Brightspace website before November 13, 23:59 CET. If you submit the report late, one point per week of delay will be subtracted from the assignment grade, which contributes 50% to your final AE4202 grade.

AE4202 - CFD for Aerospace Engineers

Problem description

Assignment to be submitted before November 14, 23:59 CET

Consider the compressible flow of air past a RAE2822 airfoil at 2.31 degrees angle of attack. We want to reproduce a wind tunnel experiment and quantify effects of discretization and modelling errors. The Reynolds number is approximately Re = 6 · 106 based on chord length description and the Mach number is M = 0.729.

nsider the compressible flow of air past a NACA64A010 airfoil at an angle of attack ↵ = 4 . We The numerical setup consists of an airfoil placed in a channel with frictionless walls, as eproduce a wind tunnel where and theexperimental total temperature be Ttotal = 293.15K depicted in Fig. experiment, 1. The airfoil geometry values of is theknown pressureto coefficient merical setupare consists airfoil placed in a and channel with frictionless walls, in Fig. 1 providedof as an "RAE2822_TO_ICEM.dat" "RAE2822_cp_experiment.dat". Theas airdepicted is considered be = an 12 ideal gas6with dynamic viscosity given is ynolds number equals toRe · 10 andathe Mach number isbyMSutherland’s = 0.789.law. TheTheairflow is considered to in a steady state. al gas with a dynamic viscosity given by Sutherland’s law. The flow is in a steady state.

sks

Free-slip wall MM=0.729 = 0.789

Free-slip wall

Figure 1: Sketch of the geometry.

1. In ICEM, go to “File ! Geometry ! Open geometry” and select the file “naca64a010.tin” pro with this assignment. Tick on/off Surfaces and Parts in the tree to familiarise yourself with th main. Mesh the computational domain with a coarse structured grid with 15.000 to 20.000 (grid1).

2. Choose suitable boundary conditions. Impose the total pressure and temperature at the inlet an static pressure at the outlet. Use the isentropic assumption to derive the appropriate values of temperature and pressure.

Tasks 1. In ICEM, go to “File → Import Geometry → Formatted Point Data” and select the file “RAE2822_TO_ICEM.dat” provided with this assignment. Add appropriate boundaries to the geometry in order to define the computational domain. Verify that the angle of attack is 2.31 degrees and adjust if necessary. 2. Mesh the computational domain with a coarse structured multi-block grid with about 20.000 cells (grid1). Pay attention to orthogonality, smoothness and resolution of the boundary layers; aim at y+ between 20 and 200. Visualize and describe blocking and mesh in the report and discuss the mesh quality. 3. As boundary conditions, impose total temperature T0 = 291.15 K and total pressure p0 = 101325 Pa at the inflow and a static pressure of p = 71150 Pa at the outflow. This is easier if you set the CFX reference pressure to zero. Use the ‘high-resolution’ scheme for the spatial discretisation and the k-omega SST turbulence model. Choose a suitable fluid model and time-stepping scheme. Report the simulation setup and discuss the reasons for your choices. 4. Perform a steady state simulation. Plot the solver residuals to verify convergence of the simulation. Evaluate and discuss the flow conditions, i.e., Reynolds and Mach number, with respect to the target values given above. 5. Visualize the flow field: produce contour plots for the Mach number and for a second quantity of your choice. Plot the pressure coefficient along the airfoil together with the experimental reference data. Extract the lift and drag forces and summarize them in a table. Interpret your results. 6. Compute and plot the y+ value of grid1 along the airfoil. Refine the grid such that y+ < 1 for the refined grid (grid2). Visualize and describe blocking and mesh, pay attention to orthogonality and smoothness. Perform the simulation and plot the solver residuals to verify convergence of the simulation. Plot y+ for grid2 to verify that the resolution target was achieved. Critically discuss the mesh quality. 7. Perform the same post processing and visualizations as done for grid1. Include the new Cp curve in the same figure and the lift and drag forces in the same table as the results for grid 1 (same holds for point 8 and 9). Describe and evaluate the results. 8. In order to quantify the effect of numerical diffusion, repeat the simulations on both grid1 and grid2 with a first-order upwind scheme. Plot the solver residuals and verify convergence of the simulation. Repeat the same post processing and visualizations as done before. Visualize and analyse the effect on the results. 9. In order to quantify the effect of the turbulence model, repeat the simulation on the fine mesh (grid2) with a turbulence model that can better account for anisotropic turbulence. Which model did you chose and why? Plot the solver residuals and verify convergence of the simulation. Visualize and analyse the effect on the results. 10. Summarize your results, discuss them critically and suggest possible improvements.