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