Flight and wind-tunnel investigations on boundary-layer transition

Horstmann, K.H.; Quast, A.; Redeker, G.

doi:10.2514/3.45910

Cited by 45 publications

(16 citation statements)

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“…The highest pressure fluctuation was measured at the position x∕c 0.59, which corresponds to an envelope N factor of N ≈ 13. This high N factor value is comparable to the findings of Horstmann et al [23] and it is remarkably close to the N factors predicted by Luchini [55] using transition-triggering disturbances in the limit of thermodynamic molecular agitation.…”

Section: Time-dependence Of Transitionsupporting

confidence: 88%

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In-Flight Investigation of Transition Under Turbulent Conditions on a Laminar Wing Glove

2014

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Flight experiments carried out with a motorized glider yield insights into the aerodynamic processes acting on a laminar wing section under varying on-coming flow conditions. Measurement data are obtained on a laminar wing glove equipped with pressure transducers and wall microphones to detect transition and investigate the boundarylayer instabilities. The on-coming flow, including the instantaneous angle of attack and the turbulence characteristics, is measured with hot-wire sensors. The flight tests were carried out under calm and moderately turbulent conditions. Characteristic results for both on-coming flow conditions are presented and differences are analyzed. Selected comparisons of the experimental results with steady boundary-layer and linear stability computations are provided. The effects observed in the experiments cannot be described solely by quasi-steady theory. Unsteady changes of the pressure distribution are identified as one source for the modification of the transition development. A conclusion on the observed superimposed effect of increased levels of atmospheric small-scale turbulence on boundary-layer receptivity cannot yet be drawn from the present experiments. Nomenclature= turbulent kinetic energy density spectrum, m∕s 2 ∕m −1 E xx = one-dimensional energy density spectrum, m∕s 2 ∕m −1 F = dimensionless stream function, -k = wave number, 1∕m k x = streamwise wave number, -k z = spanwise wave number, -L I = integral length scale, m L ref = reference length, m l k = Kolmogorov length scale, m m = dimensionless pressure gradient, -N = N factor, -P = pressure, Pa P = mean pressure, Pa p 0 = pressure fluctuation, Pa q 0 = dimensionless disturbance vector, -q = dimensionless disturbance amplitude function, -Re = Reynolds number, -Tu xy = two-component turbulence intensity, -U = velocity vector U; V; W T , m∕s U = mean velocity vector U; V; W T , m∕s U e = edge velocity, m∕s U eff = effective velocity, m∕s U ref = reference velocity, m∕s U TAS = true airspeed (U ∞ ), m∕s U ∞ = freestream velocity, m∕s u 0 = fluctuation velocity vector u 0 ; v 0 ; w 0 T , m∕s x = streamwise coordinate, m y = wall-normal coordinate, m z = spanwise coordinate, m α = angle of attack, deg β = sideslip angle, deg ε = energy dissipation rate, m 2 ∕s 3 η = dimensionless Falkner-Skan variable, -θ = probe axis inclination to the flow, deg ν = kinematic viscosity, m 2 ∕s ρ = air density, kg∕m 3 Ψ = stream function, m 2 ∕s ψ = yaw angle, deg ψ = wire slant angle for θ equal to zero, deg ψ eff = effective yaw angle, deg ω = angular frequency, 1∕s

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Section: Time-dependence Of Transitionsupporting

confidence: 88%

“…Horstmann et al [23] compared low-turbulence flight and wind-tunnel investigations with linear stability computations. Carpenter et al [24,25] carried out an in-flight receptivity study for a swept wing under calm air conditions.…”

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confidence: 99%

In-Flight Investigation of Transition Under Turbulent Conditions on a Laminar Wing Glove

2014

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“…The e N method was successfully applied in European programs for the analysis of free-flight test at subsonic and transonic speeds on laminar wing gloves using as a test bed the LFU-205, 15 the Dornier Do228, 16 25 and on a nacelle. 26,27 The important outcome of that activity was the existence of free-flight limiting N factors, which were introduced as stability limits in computational methods for the design of laminar gloves for the ATTAS wing, 28 the ELFIN wing, 29 the fin on the Airbus A320, 30 and the nacelle.…”

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confidence: 99%

eN Transition Prediction in Three-Dimensional Boundary Layers on Inclined Prolate Spheroids

Stock

2006

AIAA Journal

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The capability of the e N method to predict transition in complex three-dimensional, laminar boundary layers is demonstrated. Flows around inclined prolate spheroids are ideally suited for investigation because they exhibit highly divergent and convergent three-dimensional viscous flows on curved surfaces. The inviscid flowfield is described by the potential theory and the viscous layer by a three-dimensional laminar boundary-layer method. This approach is applied in weak viscous/inviscid interaction regions only, that is, in attached laminar flow regions, and validated by comparison with measured wall pressure and skin friction in magnitude and direction. For the determination of the transition location, the laminar boundary layer is analyzed by the two N factor e N method. Excited Tollmien-Schlichting waves of constant frequencies and stationary crossflow waves of constant wavelength are computed by the local, linear stability theory. Both N factor integrations are executed along 21 streamlines, which regularly cover the surface of the prolate spheroid. First, the values of both N factors at the measured transition locations are calculated, which deliver the stability limit of the prolate spheroid in the considered wind tunnel. Second, based on the knowledge of the stability limit, the transition locations are evaluated. The prolate spheroid with an aspect ratio of 6:1 was tested in two wind tunnels at angles of attack from 0 to 30 deg and Reynolds numbers from 1.5 × × 10 6 to 43 × × 10 6 . The measured transition locations compare remarkably well with computations for all investigated flow cases. Nomenclaturea = major axis of the prolate spheroid b = minor axis of the prolate spheroid C f t = resultant skin-friction coefficient C p = pressure coefficient L = reference length, 2a N CF = value of N * CF at measured transition N TS = value of N * TS at measured transition N * CF = envelope N factors of unstable crossflow waves N * TS = envelope N factors of unstable Tollmien-Schlichting waves Re = Reynolds number based on freestream conditions and reference length, U ∞ ∞ L/µ ∞ Reδ * c = Reynolds number based on the displacement thickness of the crossflow velocity profile, U e ρ e δ * c /µ e Reδ * s = Reynolds number based on the displacement thickness of the streamwise velocity profile, U e ρ e δ * s /µ e U = velocity component in streamwise direction u = velocity component in ξ direction V = velocity component in crossflow direction v = velocity component in φ direction X, Y, Z = Cartesian coordinates, where X is in direction of the major axis of the prolate spheroid X 0 = absolute value of X coordinate of the stagnation point α = angle of attack α = angle between the velocity components u e and v e γ = local wall shear stress direction relative to a line φ = const = displacement thickness of the crossflow velocity profile, − ∞ 0 V U e dζ δ * s = displacement thickness of the streamwise velocity profile, ∞ 0 1 − U U e dζ λ = angle between the coordinates ξ and φ µ= dynamic viscosity ξ, φ, ζ = orthogonal, surface...

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“…5a). 68 As the sweep angle increases beyond a certain limit, the crossflow mechanism will prevail, with the transition front on thermograms resembling a "saw-teeth" pattern (Fig. 5b).…”

Section: Subsonic and Transonic Studiesmentioning

confidence: 97%