Extension of the γ-Re<sub>θt</sub> Model for Prediction of Crossflow Transition

Grabe, Cornelia; Krumbein, Andreas

doi:10.2514/6.2014-1269

Cited by 25 publications

(17 citation statements)

References 12 publications

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“…42. The now fully local γ-Re θ -CF model gives a very much more consistent prediction of the c f -distribution on the surface (wing upper side) than obtained with the former semi-local variant of the γ-Re θ -CF model [102]. In the case here, a subsonic low Reynolds number case at M = 0.26 and Re = 3.5×10 6 , the laminar regions were detected for various angles of attack by a sublimation visualization technique and numerical values for the transition points in the wing section at η = 45% are available [146].…”

Section: Fig 41 Telfona Pathfinder Configuration: Simulated Transitimentioning

confidence: 83%

“…While in [98] the concept of a 'cross flow Reynolds number' inspired by Owen and Randall [99] was investigated, in [100] a local helicity-based Reynolds number for the detection of crossflow in boundary layers was realized. Recently, further developments of the C1-FSC approach have been shown in [101][102][103][104].…”

Section: Crossflow Transition In Transport Equation Approachesmentioning

confidence: 99%

“…The second model formulation is the crossflow extension of the model developed at DLR, the γ-Re θ -CF model that additionally accounts for the effects of crossflow transition [96][97]102].…”

Section: Transition Prediction Using Transport Equation Approachesmentioning

confidence: 99%

See 2 more Smart Citations

Development and Application of Transition Prediction Techniques in an Unstructured CFD Code (Invited)

Krumbein

Krimmelbein

Grabe

et al. 2015

45th AIAA Fluid Dynamics Conference

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Section: Fig 41 Telfona Pathfinder Configuration: Simulated Transitimentioning

confidence: 83%

Section: Crossflow Transition In Transport Equation Approachesmentioning

confidence: 99%

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Development and Application of Transition Prediction Techniques in an Unstructured CFD Code (Invited)

Krumbein

Krimmelbein

Grabe

et al. 2015

45th AIAA Fluid Dynamics Conference

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“…There have been a number of notable attempts to incorporate crossflow effects into the γ-Re θt correlation based transiton model 6,7,8,9,10 and encouraging results were shown in many applications. However, all of these extensions were either based on non-local information (which violates the LCTM approach) or did not include roughness effects into the crossflow transition prediction.…”

Section: Introductionmentioning

confidence: 92%

Extending the Gamma-Rethetat Correlation based Transition Model for Crossflow Effects (Invited)

Langtry

2015

45th AIAA Fluid Dynamics Conference

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The correlation-based γ-Re θt transition model has been extended to include crossflow transition effects. This paper will detail a new empirical correlation for stationary crossflow transition based strictly on local flow quantities and the implementation into the γ-Re θt model. This new correlation for crossflow is based on the well known 45° swept NLF(2)-0415 airfoil experiment including surface roughness effects. Linear-stability predictions were also used to augment the new correlation to account for variations in the sweep angle and crossflow strength. The improved transition model has shown encouraging results for transitional flows dominated by crossflow and a number of validation test cases will be shown in this paper. Most importantly, the model maintains its compatibility and ease of implementation with modern CFD techniques such as unstructured grids and massively parallel execution. There is a strong potential that this improved transtion model will allow the 1 st order effects of transition, including crossflow, to be included in everyday industrial CFD simulations. NomenclatureAoA = Angle of attach (deg.) C f = skin friction coefficient, τ/(0.5ρU ref 2 ) dU/ds = acceleration along the streamline direction FSTI = freestream turbulence intensity (percent), 100(2k/3) 1/2 /U ref h rms = Surface roughness height (rms) k = turbulent kinetic energy Re x = Reynolds number, ρLU ref /μ Re θ = momentum thickness Reynolds number, ρθU 0 /μ Re θt = transition onset momentum thickness Reynolds number (based on freestream conditions), ρθ t U 0 /μ t  e R = local transition onset momentum thickness Reynolds number (obtained from a transport equation) R T = viscosity ratio R y = wall-distance based turbulent Reynolds number R v = vorticity Reynolds number S = absolute value of strain rate, (2S ij S ij ) 1/2 S ij = strain rate tensor, 0.5(∂u i /∂x j + ∂u j /∂x i ) Tu = turbulence intensity, 100(2k/3) 1/2 /U U = local velocity U o = local freestream velocity U ref = inlet reference velocity = unit velocity vector u' = local fluctuating streamwise velocity x/C = axial distance over axial chord 1 Senior Engineer, Flight Sciences, Boeing Commercial Airplanes -Seattle, WA, USA, and AIAA member.2 y = distance to nearest wall y + = distance in wall coordinates, ρyμ τ /μ δ = boundary layer thickness θ = momentum thickness λ θ = pressure gradient parameter, (ρθ 2 /μ)(dU/ds) μ = molecular viscosity μ t = eddy viscosity ρ = density τ = wall shear stress Ω = absolute value of vorticity, (2Ω ij Ω ij ) 1/2 Ω ij = vorticity tensor, 0.5(∂u i /∂x j -∂u j /∂x i ) = vorticity vector,  = specific turbulence dissipation rate Subscripts t = transition onset s = streamline

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“…These are neither taken into account by the basic versions of, for example, the e N envelope method (Drela and Giles, 1987) nor the widely used transport-equation-based local correlation model γ -Re θ of Langtry and Menter (2009). Accounting for cross-flow-induced transition shall be referred to the criteriabased model of Arnal and Juillen (1987) or the recent extensions of the γ -Re θ model by Grabe and Krumbein (2014) and Langtry (2015). Measurements such as those of Zamir (1981) further suggest an earlier transition to turbulence within corner boundary layers compared to corresponding flat-plate conditions.…”

Section: Flow Solver and Numerical Settingsmentioning

confidence: 99%

Numerical analyses and optimizations on the flow in the nacelle region of a wind turbine

et al. 2018

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Abstract. The present study investigates flow dynamics in the hub region of a wind turbine focusing on the influence of nacelle geometry on the root aerodynamics by means of Reynolds averaged Navier-Stokes simulations with the code FLOWer. The turbine considered is a generic version of the Enercon E44 converter incorporating blades with flat-back-profiled root sections. First, a comparison is drawn between an isolated rotor assumption and a setup including the baseline nacelle geometry in order to elaborate the basic flow features of the blade root. It was found that the nacelle reduces the trailed circulation of the root vortices and improves aerodynamic efficiency for the inner portion of the rotor; on the other hand, it induces a complex vortex system at the juncture to the blade that causes flow separation. The origin of these effects is analyzed in detail. In a second step, the effects of basic geometric parameters describing the nacelle have been analyzed with the purpose of increasing the aerodynamic efficiency in the root region. Therefore, three modification categories have been addressed: the first alters the nacelle diameter, the second varies the blade position relative to the nacelle and the third comprises modifications in the vicinity of the blade-nacelle junction. The impact of the geometrical modifications on the local flow physics are discussed and assessed with respect to aerodynamic performance in the blade root region. It was found that increasing the nacelle diameter deteriorates the root aerodynamics, since the flow separation becomes more pronounced. Possible solutions identified to reduce the flow separation are a shift of the blade in the direction of the rotation or the installation of a fairing fillet in the junction between the blade and the nacelle.

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Extension of the γ-Re_θt Model for Prediction of Crossflow Transition

Cited by 25 publications

References 12 publications

Development and Application of Transition Prediction Techniques in an Unstructured CFD Code (Invited)

Development and Application of Transition Prediction Techniques in an Unstructured CFD Code (Invited)

Extending the Gamma-Rethetat Correlation based Transition Model for Crossflow Effects (Invited)

Numerical analyses and optimizations on the flow in the nacelle region of a wind turbine

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Extension of the γ-Reθt Model for Prediction of Crossflow Transition

Cited by 25 publications

References 12 publications

Development and Application of Transition Prediction Techniques in an Unstructured CFD Code (Invited)

Development and Application of Transition Prediction Techniques in an Unstructured CFD Code (Invited)

Extending the Gamma-Rethetat Correlation based Transition Model for Crossflow Effects (Invited)

Numerical analyses and optimizations on the flow in the nacelle region of a wind turbine

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Extension of the γ-Re_θt Model for Prediction of Crossflow Transition