Document
Computational Analysis of the External Aerodynamics of the Unpowered X - 57 Mod - III Aircraft Presented at 2019 AIAA AVIATION, June 21th 2019
Seung Y. Yoo Jared C. Duensing
NASA Armstrong Flight NASA Ames Research Center
Research Center
Acknowledgement
• NASA Armstrong Team
– Mike Frederick, Nicholas Johnson, Trong Bui, Thomas Matthews
• NASA Ames Team
– Daniel Maldonado, Jeffrey A. Housman, James C. Jensen, Cetin C. Kiris
• NASA Langley Team
– Karen A. Deere, Jeffrey K. Viken, Melissa B. Carter, Sally A. Viken
Outline
• Introduction
• Method
• Results
• Conclusion
• Questions
Introduction
• X - 57 Program • Separated into multiple phases, denoted as “MOD”, to demonstrate various technologies • Electrical power - plant • Optimized high aspect ratio wing and high lift nacelle • Tip cruise motor for reducing induced drag • Study focused on unpowered MOD - III • flow physics • differences in flow solution between CFD solvers • Purpose of the study • Aerodynamic database generation for pilot - in - the - loop simulation • Understanding of the aerodynamics of the vehicle for flight safety • Baseline performance for powered simulation
Method
• Launch Ascent Vehicle Analysis
• STAR - CCM+ (v13.04.10)
Framework – Used extensively at NASA AFRC for – Versatile NASA ARC developed airworthiness analysis framework consisting of multiple solvers – Grid – Grid • Unstructured polyhedral mesh • Overset, structured, curvilinear grids • Half - span with symmetry boundary • Full - span for all simulations condition for symmetric flow, full - span for asymmetric flow simulation – Solver • Steady state RANS structured – Solver curvilinear solver • Steady state RANS • Second - order convective flux with nd • 2 order Roe flux differencing scheme Koren limiter with algebraic multigrid solver with • Fully turbulent flow assumption, Gauss - Siedel relaxation scheme Spalart - Allmaras turbulence rotational • Fully turbulent assumption, Spalart - correction and quadratic constitutive Allmaras with rotational correction relationship
Result
• Grid Refinement Study
• Angle of attack sweep
• Sideslip angle sweep
Result – Grid Refinement Study
• Atmospheric Condition – Altitude 2500 ft, Mach 0.139, freestream velocity = 153.87 ft/s 3 2 – density 2.2078E - 3kg/m , static pressure = 1931.9 lbf/ft , static temperature 283.2K – Reynolds number 9.21E5 ° ° – Angle of attack = 10 , Sideslip angle = 20 • Aircraft configuration ° – Aileron = - 25 ° – Flap = 30 ° – Rudder = - 28 ° – Stabilator = - 15 ° – Pitch trim tab = - 18
Result – Grid Refinement Study
• STAR - CCM+ Polyhedral Grid (coarse grid shown for clarity) high lift nacelle rudder deflection pitch trim tab on stabilator stabilator flap deflection
Result – Grid Refinement Study
• LAVA structured overset curvilinear grid (coarse grid shown for clarity) pitch trim tab on stabilator flap and rudder deflection stabilator high lift nacelle
Result – Grid Refinement Study
• STAR - CCM+
– 3 resolutions: 45e6 Cells (coarse), 77e6 Cells (medium), 126e6 Cells (fine)
• LAVA
– 5 resolutions: 60.1e6 nodes (coarse), 95.2e6 nodes (medium), 248.6e6 nodes (fine), 312.6e6 nodes (very - fine), 425.7e6 nodes (extra - fine)
Result – Grid Refinement Study
STAR - CCM+ grid resolution C C C C C C D L Y l m n coarse (45e6 cells) 0.30394 1.46749 - 0.61327 0.01631 2.41895 0.12050 medium (77e6 cells) 0.30623 1.47778 - 0.61585 0.02004 2.41327 0.12257 fine (126e6 cells) 0.30797 1.47193 - 0.61886 0.01982 2.38941 0.12337 STAR - CCM+ grid resolution C error, % C error, % C error, % C error, % C error, % C error, % D L Y l m n coarse (45 mil. cell) - 1.1 - 0.3 - 0.9 - 17.7 1.2 - 2.3 medium (77 mil. cell) - 0.5 0.4 - 0.5 1.1 1.0 - 0.6 Although relative error C is large, the values are small and coarse mesh chosen to accommodate the large number of runs l for limited computing resource
Result – Grid Refinement Study
LAVA grid resolution C C C C C C D L Y l m n coarse (60.1 mil. nodes) 0.3024 1.57 - 0.6053 0.0135 2.396 0.1119 medium (95.2 mil. nodes) 0.29838 1.55 - 0.595 0.016 2.404 0.1117 fine (248.6 mil. nodes) 0.30036 1.56 - 0.5876 0.0181 2.398 0.1106 very - fine (312.6 mil. nodes) 0.30265 1.56 - 0.5844 0.0226 2.402 0.1121 extra - fine (425.7 mil nodes) 0.30237 1.56 - 0.582 0.0239 2.401 0.1126 LAVA grid resolution C error, % C error, % C error, % C error, % C error, % C error, % D L Y l m n coarse (60.1 mil. nodes) - 0.01 - 0.64 - 4.00 43.51 0.21 0.62 medium (95.2 mil. nodes) 1.32 0.51 - 2.23 33.05 - 0.12 0.80 fine (248.6 mil. nodes) 0.66 - 0.26 - 0.96 24.27 0.12 1.78 very - fine (312.6 mil. nodes) - 0.09 - 0.32 - 0.41 5.44 - 0.04 0.44
Result – Grid Refinement Study
LAVA (248.6 mil. nodes) STARCCM+ (45e6 cells) 2.5 1.5 0.5 CD CL CY Cl Cm Cn -0.5 -1
Result
• Grid Refinement Study
• Angle of attack sweep
• Sideslip angle sweep
Result – Angle of attack sweep
• 3 flap settings – 0 ° (cruise) , 10 ° (take - off), 30 ° (landing)
• Control surfaces in neutral position (no deflection)
Flap = 0 ° Flap = 10 ° Flap = 30 ° Altitude, ft 8000 2500 2500 Mach 0.233 0.149 0.139 Density, slug/ft 1.8628E - 3 2.20782E - 3 2.20782E - 3 Static pressure, lbf/ft 1571.9 1931.9 1931.9 Static temperature, K 272.3 283.2 283.2 Coefficient of viscosity, slug/ft/s 3.57532E - 7 3.68708E - 7 3.68708E - 7 Reynolds number 1.32E6 9.875E5 9.21E5
Result – Angle of attack sweep
• Lift dependency on flap deflection • lift increases with increase in flap defection angle • Angle of attack for maximum lift decreases with increase in flap deflection • Differences in solver • lift at high angle of attack • Increase in discrepancy with increase in flap deflection angle at linear region
Result – Angle of attack sweep
• Increase in solution discrepancy in lift with increase in flap deflection angle at linear region • STAR - CCM+ solution show flow separation at outboard wing that is not show in LAVA for 10 ° and 30 ° flap deflection
Result – Angle of attack sweep
• Increase in solution discrepancy in lift at high angle of attack • STAR - CCM+ solution show larger region of separated flow at higher angle of attack compared to LAVA
Result – Angle of attack sweep
• Higher pitching moment with higher flap deflection angle • Sharp increase in pitching moment for 0 ° flap angle at 20 ° angle of attack
Result – Angle of attack sweep
• Large flow separation shown on the upper surface of stabilator for 0 ° flap deflection configuration • Flow separation shown on the upper surface of stabilator on 10 ° flap deflection configuration located to inboard and trailing edge
Result
• Grid Refinement Study
• Angle of attack sweep
• Sideslip angle sweep
Result – Sideslip angle sweep
• 3 flap settings – 0 ° (cruise) , 10 ° (take - off), 30 ° (landing)
• Control surfaces in neutral position (no deflection)
Flap = 0 ° Flap = 10 ° Flap = 30 ° Altitude, ft 8000 2500 2500 Mach 0.233 0.149 0.139 Density, slug/ft 1.8628E - 3 2.20782E - 3 2.20782E - 3 Static pressure, lbf/ft 1571.9 1931.9 1931.9 Static temperature, K 272.3 283.2 283.2 Coefficient of viscosity, slug/ft/s 3.57532E - 7 3.68708E - 7 3.68708E - 7 Reynolds number 1.32E6 9.875E5 9.21E5
Result – Sideslip angle sweep
• Lift, drag, side forces all decrease with increasing sideslip angle • Drag decreasing because it is in stability axis (increases when computed in wind axis)
Result – Sideslip angle sweep
• Rolling moment - 30 ° flap produces least amount of rolling moment • Pitching moment - sharp increase in at 15 ° for all flap deflections • Yawing moment - 30 ° flap produces least amount of rolling moment
Result – Sideslip angle sweep
• Increasing separation at leading edge of right wing root with increasing flap deflection • Separated region at the leading edge of rudder
Conclusion
• Unpowered X - 57 MOD - III configuration analyzed
• Angle of attack sweep and sideslip angle sweep presented
• STAR - CCM+ and LAVA solution comparison
– flow visualization show that solution compare well at low angle of attack – Difference in predicted separation behavior at higher angle of attack