NASA ARA M100 Wingbody

Applications

  • Transonic Aerodynamics
  • External Aircraft Component Design

Models active in this Validation Case

  • Compressible flow
  • Energy models
  • Ideal gases
  • Double Precision

Objective

To profile the accuracy and performance of Envenio’s EXN/AERO manycore CFD solver on a challenging transonic aerospace test case.

Reference Case Description – ARA-M100 Wingbody

The ARA M100 wing body geometry is based on a scale wind tunnel model and is referenced by NASA as a validation case for CFD codes with compressible / transonic flow capability. The configuration of the model is similar to what is seen in civil and military transport aviation and features a finite wing, a realistic wing root and a fuselage. Dimensions are shown in Figure 1.

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Figure 1: ARA M100 general dimensions. Image source referenced in bibliography.

Mesh Description

Surface Mesh:

The surface mesh used to create the CFD grid is available on the nasa.gov site (link in bibliography). General dimensions are shown in Figure 1

Coordinates & Domain Size

X direction                                            Roll axis, positive streamwise

Y direction                                            Pitch axis, positive to starboard

Z direction                                            Yaw axis, positive to top of aircraft

 

X dimension                                          ~41m

Y dimension                                          ~21.75

Z-dimension                                          ~41m

Position of model:

Upwind face relative to inlet:                  ~20.5 m

Y position                                             Centred

Z position                                             Attached to symmetry plane

Mesh Resolution in the vicinity of the Ahmed Body:

This 3D wing/body test case is at Ma.=0.803 and chord Reynolds number Rec = 13.1 × 106. The mesh has a  distribution as follows:

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The mesh generator was instructed to use a wall function over the fuselage and direct solve-to-wall was employed on the wing. Freestream turbulence levels used as mesh generator inputs are Tu = 0.5% and µt/µ = 25.

Total Mesh Size: ~28.1 Million

Simulation Completion Criteria

The simulation should be run for at least two ‘wash throughs’ of initial conditions in order to obtain accurate surface pressure values.  For cases where far-field values are constant and equal to the initial conditions it is appropriate to use body length (i.e. wing chord) as the reference length. The number of iterations N for a washthrough is calculated using the equation below:

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where c is fuselage length, is the mean velocity magnitude and  is the time step duration. After time step N is reached, the engineer monitored the total body forces and stopped the simulation when the cumulative average force reached a statistically steady value in time.

Simulation Setup

Solver Control

Time Step                     2e-6 seconds

EXN GPU Allocation     3 Nvidia K80

EXN CPU Allocation      3 Intel Xeon 2.6GHz

 

X-axis orientation          Positive downstream

Y-axis orientation          Positive to the left of the body, looking downstream

Z-axis orientation          Positive upward, normal to ground plane

Boundary Conditions

Kinetic Energy              0.0001

K Dissipation                0.0003

Wall model                    Smooth wall

Outlet                           Zero Pressure

 

Initial Velocity               [257.1,  0,  12.9]

Angle of Attack             2.870 deg

Mach Number               0.803

Initial Kinetic Energy      0.0001

Initial K Dissipation        0.0003

Temperature                 255 Kelvin

Pressure                      315.98 kPa

Fluid Settings

Initial Velocity               [257.1,  0,  12.9]

Initial Kinetic Energy      0.0001

Initial K Dissipation        0.0003

 

Turbulence Model         Unsteady RANS, k-omega

Flow type                      Compressible

 

Precision                      Double in all mesh blocks

Constant Density          1.3864 kg/m3

Constant Viscosity        1.715 x 10-5

Other notes

Wash through time        0.0024 seconds (1200 time steps)

Total simulated time      0.013 seconds (17890 time steps, 2.5 washthroughs)

Mesh Topology             Structured multiblock, one-to-one connections at block interfaces, data written as structured arrays in CGNS format

Simulation Outcomes, Timing, and External Factors

The pressure coefficient profiles at different spanwise locations along the wing, namely at span-normalized cross section y/B = 0.123, y/B = 0.231, y/b = 0.325, y/B = 0.455, y/B = 0.633 and y/B = 0.817 are presented in Figures 2 thru 7. The pressure distribution across upper wing surface and fuselage is shown graphically in Figure 8. Table 1 shows simulation performance outcomes and Table 2 shows approximate simulation cost information.

Table 1: Simulation performance outcomes

Reporting Item EXN/Aero
Time to 1st wash-through Simulated time of 0.013 sec requires 6520 time steps.

This is equivalent to real-time ~69hrs.

Time to completion Simulated time of 0.036 sec requires 1780 time steps

This is equivalent to real time ~190 hours.

Real time per time step 38sec
CPU type Intel Xeon @ 2.6GHz
CPU cores 4
GPU type NVIDIA Tesla K80
GPU cores 3 x 2496 CUDA core per card
Available Memory 128GB system, 24GB each K80 card

Table 2: Simulation cost information, assuming an owned system and a single license of EXN/Aero, operating year-round; figures in US dollars.

Line Item Value
Capital & Operating / hour $1.52
License / hour $3.42
Compute Cost / hour $4.95
Timesteps 17,980
Timesteps / hr 94.7
MSM (timestep / $) 19.16
Total Simulation Cost $938.64

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Figure 2: Comparison of EXN/Aero simulation and experimental results at y/B=0.123

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Figure 3: Comparison of EXN/Aero simulation and experimental results at y/B=0.231

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Figure 4: Comparison of EXN/Aero simulation and experimental results at y/B=0.325

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Figure 5: Comparison of EXN/Aero simulation and experimental results at y/B=0.455

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Figure 6: Comparison of EXN/Aero simulation and experimental results at y/B=0.633

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Figure 7: Comparison of EXN/Aero simulation and experimental results at y/B=0.817

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Figure 8: Pressure coefficient contours at the cross section

The comparison of pressure coefficient profiles with the experimental profiles reveals that our model matches closely with the experiments in subsonic regions of the wing. For the two outboard wing sections (y/B  0.633) the Cp distribution is accurately represented by simulation data. For inboard sections (y/B < 0.633) the drop in Cp is delayed and smoother than the experimental data. Inset images from a Cobalt simulation using the Spalart-Almaras RANS model show an early drop in Cp on inboard sections. It is expected that mesh refinement in the vicinity of the shocks will bring EXN/Aero results more in line with experimental data sets; this work is planned as part of Enveino’s QA process and will be updated regularly on Envenio’s wiki site (accessible on envenio.ca).

Keywords

  • External Flow
  • SST-RANS
  • Compressibility
  • Energy Models
  • Double Precision
  • Integrated Boundary Values
  • External Flow
  • Lift & Drag
  • Vehicle Maneuvering
  • Transonic Flow

References

  1. Wing geometry available from https://cfl3d.larc.nasa.gov
  2. /Cfl3dv6/cfl3dv6_testcases.html
  3. ARAA-M100 Diagrams (Figure 1) http://www.memoireonline.com/05/12/5815/m_Calcul-des-performances-aerodynamiques-de-la-configuration-aile-fuselage-Ara-M100-par-maillage-hybr27.html