DLR, Göttingen > 8. Nov Folie 1 > 12. STAB-Workshop > A. Krumbein Automatic Transition Prediction and Application to 3D Wing Configurations Current status of development and validation

DLR, Göttingen > 8. Nov Folie 2 > 12. STAB-Workshop > A. Krumbein Outline Introduction Transition Prescription Transition Prediction Modeling of Transitional Flow Transition Prediction Strategy Preliminary Results: ONERA M6 wing Outlook Outline

DLR, Göttingen > 8. Nov Folie 3 > 12. STAB-Workshop > A. Krumbein - prescription - prediction - transitional flow modeling - automatic, autonomous Introduction aerospace industry requirement: RANS based CFD tool with transition handling → different approaches: RANS solver + stability code + e N method RANS solver + boundary layer code + stability code + e N method RANS solver + boundary layer code + e N database method RANS solver + transition closure model or transition/turbulence model

DLR, Göttingen > 8. Nov Folie 4 > 12. STAB-Workshop > A. Krumbein - prescription - prediction - transitional flow modeling - automatic, autonomous Introduction aerospace industry requirement: RANS based CFD tool with transition handling → different approaches: RANS solver + stability code + e N method RANS solver + boundary layer code + stability code + e N method RANS solver + boundary layer code + e N database method RANS solver + transition closure model or transition/turbulence model

DLR, Göttingen > 8. Nov Folie 5 > 12. STAB-Workshop > A. Krumbein Structured approach: FLOWer + laminar BL method for swept, tapered wings + + e N database methods for TS and CF instabilities FLOWer 3D RANS, compressible, steady/unsteady structured body-fitted multi-block meshes finite volume method, cell-vertex scheme explicit Runge-Kutta time integration multi-grid acceleration mainly eddy viscosity models, Boussinesq Introduction transition prediction module

DLR, Göttingen > 8. Nov Folie 6 > 12. STAB-Workshop > A. Krumbein - automatic partitioning of flow field into laminar and turbulent regions - individual laminar zone for each element - different numerical treatment of laminar and turbulent grid points, e.g.  t = 0 in laminar zones Prescription Transition Prescription

DLR, Göttingen > 8. Nov Folie 7 > 12. STAB-Workshop > A. Krumbein - transition line on ONERA M6 wing, 4 points on upper and lower side Prescription P T upp (sec = 1) P T upp (sec = 2) P T upp (sec = 3) P T upp (sec = 4)

DLR, Göttingen > 8. Nov Folie 8 > 12. STAB-Workshop > A. Krumbein - RANS solver  shall predict transition points automatically! - stability database  shall yield accurate values of transition points! - e N database method  needs highly accurate BL data!  BL adaptation in NS grid  very time consuming, coupling with grid generator:NO!  laminar BL method  fast, cheap, easy to couple:YES! - restrictions:  linear stability theory  parallel flow assumption - independent of mesh topology, grid structure, 2D or 3D - integration paths: grid lines of the structured grid Prediction Transition Prediction

DLR, Göttingen > 8. Nov Folie 9 > 12. STAB-Workshop > A. Krumbein - algebraic models for the transition length l tr  Re l tr = 5.2 ( Re s tr ) 3/4 downstream of RANS laminar separation point  Re l tr = 2.3 ( Re   (s tr ) ) 3/2 downstream of BL laminar separation point  Re l tr = 4.6 ( Re   (s tr ) ) 3/2 downstream of TS instability - intermittency function  (s) = 1 – exp ( [ 3.36 (s - s tr )/l tr ] 2 ) s: arc length starting at the stagnation point Modeling displacement thickness Modeling of transitional flow

DLR, Göttingen > 8. Nov Folie 10 > 12. STAB-Workshop > A. Krumbein Transition prediction strategy Strategy - coupling structure

DLR, Göttingen > 8. Nov Folie 11 > 12. STAB-Workshop > A. Krumbein set s tr u and s tr l far downstream compute flowfield check for RANS laminar separation  set separation points as new s tr u,l c l  const. in cycles  call transition module  use outcome of e N -databases or BL laminar separation point as new transition point set new s tr u,l underrelaxed  s tr u,l = s tr u,l , 1.0 <  < 1.5 convergence check   s tr u,l <  noyes STOP Strategy - algorithm

DLR, Göttingen > 8. Nov Folie 12 > 12. STAB-Workshop > A. Krumbein Results -ONERA M6 wing: single-element semi-span:A = 3.8 swept:  LE = 30°  TE = 15.8° tapered: = based on ONERA D airfoil (symmetric), perpendicular to 40%-line - “designed for studies of three-dimensional flows from low to transonic speeds at high Reynolds numbers“ Preliminary Results

DLR, Göttingen > 8. Nov Folie 13 > 12. STAB-Workshop > A. Krumbein Results feasibility: 1 block-grid, 384,000 points M  = 0.84, Re  = 2.0  10 6,  = - 4.0° turbulence model: Baldwin-Lomax critical N-factors: N cr TS = 4.0, N cr CF = 2.0, arbitrariliy set

DLR, Göttingen > 8. Nov Folie 14 > 12. STAB-Workshop > A. Krumbein Results Validation, 1 st test: 1 block-grid, 800,000 points M  = 0.84, Re  =  10 6,  = 3.06° → classic CFD validation test case Tu  = 0.2% → N = using Mack’s relationship WT: S2MA, Modane Center turbulence model: Baldwin-Lomax, Spalart-Allmaras with Edwards mod. (SAE), Wilcox k-  critical N-factors: N cr TS = N cr CF = transition prediction in 3 wing sections near  = z/b = 0.1, 0.5, 0.9

DLR, Göttingen > 8. Nov Folie 15 > 12. STAB-Workshop > A. Krumbein Results surface pressure and transition lines influence of TMs extremely low all transition points due to CF instabilities, except: BL,  = 0.1, lower side → lam. sep.

DLR, Göttingen > 8. Nov Folie 16 > 12. STAB-Workshop > A. Krumbein Results c p -distributions at  = 0.2, 0.44, 0.65, 0,9 almost no difference to fully turbulent re- sults accuracy of results comparable to those of others (e.g. lite- rature, TAU code)

DLR, Göttingen > 8. Nov Folie 17 > 12. STAB-Workshop > A. Krumbein Results Validation, 2 st test: 1 block-grid, 800,000 points M  = 0.262, Re  = 3.5  10 6,  = 0°, 5°, 10°, 15° Tu  = 0.2% → N = using Mack’s relationship WT: S2Ch, Chalais-Meudon transition detection in experiment: sublimation of acenaphtene turbulence model: SAE critical N-factors: N cr TS = N cr CF = transition prediction in 4 wing sections near  = 0.1, 0.44, 0.5, 0.9 upper side lower side

DLR, Göttingen > 8. Nov Folie 18 > 12. STAB-Workshop > A. Krumbein Results transition locations from experiment at  = 0.44 lower side upper side  = 0.44 upper side lower side  = 0.44 ls TS ls exp.

DLR, Göttingen > 8. Nov Folie 19 > 12. STAB-Workshop > A. Krumbein Results transition lines for  = 5° and exp. transition locations at  = 0.44 Has acenaphtene triggered transition on the lower side? Is N cr CF correct? TS CF outcome of the database methods  = 0.44 on lower side

DLR, Göttingen > 8. Nov Folie 20 > 12. STAB-Workshop > A. Krumbein Results max. N-factor curves for  = 5° at  = 0.44 on lower side from a linear stability code (from H.W. Stock using COAST (?) code): TSCF x T exp. N cr CF  3.2 In other cases, e.g. ONERA D infinite swept, N cr CF  6.0 was found.

DLR, Göttingen > 8. Nov Folie 21 > 12. STAB-Workshop > A. Krumbein Results *) G. Redecker, G. Wichmann, ‘Forward Sweep – A Favorable Concept for a Laminar Flow Wing‘, Journal of Aircraft, Vol. 28, No. 2, 1991, p What is wrong? 1. Error in coding of the 3d coupling procedure? → compute infinite swept wing flow for ONERA D airfoil using sweep angle at x T low (  = 0.44)  fails due to problems with BL code: BL code does not converge  another problem to be solved! 2. Is sweep angle correct? → account for effective sweep angle  eff =  +  = arcsin (U T /U  ) *) due to influence of changing absolute wing thickness ratio U T : velocity in the attachment line tested: 1°    6°  c p around stagnation point must be reduced to prevent BL code crash  are database results affected?  another problem to be solved!  = 4°, 5°, 6°  = 0° CF TS

DLR, Göttingen > 8. Nov Folie 22 > 12. STAB-Workshop > A. Krumbein Results What is wrong? 3. Is CF database method erroneous? → ONERA D infinite swept successfully analyzed by ISM (TU-BS) with same program for M  = 0.23, Re  = 2.4  10 6,  n = 4°,  = 60° using BL data from TAU code  Results from CF database method are almost the same as those from linear stability code COAST.  Is the functioning of the CF database method case dependent? 4. Are the grid lines of the structured grid a too bad approximation of the streamline? 5. Is the selected test case a reliable validation test case?

DLR, Göttingen > 8. Nov Folie 23 > 12. STAB-Workshop > A. Krumbein Outlook clarification/solution of the problems: convergence problems of BL code automatic determination and consideration of  eff in the iteration loop automatic reduction and adaption of c p around stagnation point guarantee that CF databse results are do not depend on manipulation of c p reproduction of the results of the ONERA D infinite swept case coupling with linear stability code LILO (G. Schrauf) empirical criteria for: - attachment line transition - bypass transition - transition in laminar separation bubbles