Comparison of Higher-Order CFD Modelling with an unsteady Panel - PowerPoint PPT Presentation

www.DLR.de • Chart 1 17th ODAS 2017 > Wilke • Pade Scheme & UPM Comparison of Higher-Order CFD Modelling with an unsteady Panel Method Gunther Wilke DLR AS-HEL June 7 th 2017 17 th ODAS Aussios, France

www.DLR.de • Chart 2 17th ODAS 2017 > Wilke • Pade Scheme & UPM Overview - Motivation - Theory - Compact Pade Scheme (and JST Scheme) - UPM - Simulation Setup - Results - CFD Grid sensitivity study - UPM Grid sensitivity study - Comparison of CFD and UPM - Summary Conclusions

www.DLR.de • Chart 3 17th ODAS 2017 > Wilke • Pade Scheme & UPM Motivation - Simulation of blade tip vortices and vortex structure - BVI noise in descent flight - interaction aerodynamics, for example tail shake - Difficulties with State of the Art Tools - CFD - 2 nd order too dissipative - plenty of grid points and still not there - Simplified Methods - accuracy - generalization/justification - Challenges with higher order schemes - stability - efficiency

www.DLR.de • Chart 4 17th ODAS 2017 > Wilke • Pade Scheme & UPM - Theory

www.DLR.de • Chart 5 17th ODAS 2017 > Wilke • Pade Scheme & UPM Howto get f ' ? Pade-Scheme - Higher order finite difference Ansatz  a f = scheme implemented by Stefan Enk ' i i in FLOWer → referred to as  f f FLOWer4 c + i + i  3 3 6h - 4 th order spatial discretization  f f with 3 rd order boundaries b +  i + i 2 2 - 4 th to 8 th order filtering 4h with down to 2 nd order boundaries  f f c  i + i 1 1 - Line implicit 2h - Grid transformation from arbitrary to Solution through Cartesian grid LU-decomposition (Thomas algorithm) - Not (yet) suitable for transonic flows

www.DLR.de • Chart 6 17th ODAS 2017 > Wilke • Pade Scheme & UPM Jameson vs Pade-Scheme Pade Finite Differences Jameson Finite Volume      d W F ˆ G    d     + + = 0 W dV + F d S + G = i   0 dt J ξ J   dt i RES = RES =     Δ t         F     1    F W S + G        Δ t J + W   + G     i V  t t   ξ t J     i Difference of Fluxes Flux Average

www.DLR.de • Chart 7 17th ODAS 2017 > Wilke • Pade Scheme & UPM UPM - Unsteady Panel Method with a free wake model - Ensures unsteady (pressure) Kutta-condition - Tip vortex roll-up model - Viscous vortex core radius model Courtesy of Yin et al. 2015

www.DLR.de • Chart 8 17th ODAS 2017 > Wilke • Pade Scheme & UPM Simulation Setup

www.DLR.de • Chart 9 17th ODAS 2017 > Wilke • Pade Scheme & UPM Numerical CFD Setup - Dual-Time Stepping with 1, 1/4, 1/8 degrees timesteps - Residual Smoothing - 2V Multigrid on JST blocks - 6 th order Pade Filter with 4 th order at the boundaries

www.DLR.de • Chart 10 17th ODAS 2017 > Wilke • Pade Scheme & UPM CFD Grid – Summary coarse medium fine blade 40k 323k 2.6 Mio fuselage 61k 490k 3.9 Mio background 1.4 Mio 11 Mio 88 Mio total 1.6 Mio 13 Mio 103 Mio fully coupled simulations with HOST

www.DLR.de • Chart 11 17th ODAS 2017 > Wilke • Pade Scheme & UPM UPM Grid - Summary coarse medium fine blade 480 1080 1920 fuselage 960 wake 10,800 28,800 86,400 total 13,680 34,080 95,040 one-way coupled simulations with HOST/METAR

www.DLR.de • Chart 12 17th ODAS 2017 > Wilke • Pade Scheme & UPM Results

www.DLR.de • Chart 13 17th ODAS 2017 > Wilke • Pade Scheme & UPM Grid Sensitivity Study (JST vs Pade) JST Hybrid-Pade

www.DLR.de • Chart 14 17th ODAS 2017 > Wilke • Pade Scheme & UPM Grid Sensitivity Study (JST vs Pade) JST Hybrid-Pade

www.DLR.de • Chart 15 17th ODAS 2017 > Wilke • Pade Scheme & UPM Grid Sensitivity Study (JST vs Pade) medium medium fine fine JST Hybrid-Pade Cost increase about 50%

www.DLR.de • Chart 16 17th ODAS 2017 > Wilke • Pade Scheme & UPM Grid Sensitivity Study (UPM) Vortex field Derivative of airloads

www.DLR.de • Chart 17 17th ODAS 2017 > Wilke • Pade Scheme & UPM Grid Sensitivity Study (UPM) experiment medium coarse fine Cost range from working day to two weeks

www.DLR.de • Chart 18 17th ODAS 2017 > Wilke • Pade Scheme & UPM Alternative Simulation Techniques Runtime factor UPM 0.3% Inviscid 63% Viscous 100% Inviscid CFD Viscous CFD UPM

www.DLR.de • Chart 19 17th ODAS 2017 > Wilke • Pade Scheme & UPM Summary & Conclusions!

www.DLR.de • Chart 20 17th ODAS 2017 > Wilke • Pade Scheme & UPM Summary & Conclusion - Established a hybrid simulation environment for helicopter rotors within FLOWer with the 4 th order compact Pade scheme - Hybrid simulation with Pade scheme significantly improved vortex conservation → better loads correlation → better acoustic correlation - Roughly 50% cost increase relative to the JST scheme - Investigated different grid sizes for UPM - reasonable results on all mesh sizes - time range from 7 hours to 2 weeks (reliable CFD ~ 4 Months) - Further investigations should examine different rotors to further validate the applied methodologies