Aerodynamic design of a natural laminar flow nacelle and the design validation by flight testing

Riedel, H.; Horstmann, K.H.; Ronzheimer, A.; Sitzmann, Martin

doi:10.1016/s0034-1223(98)80001-8

Cited by 19 publications

(5 citation statements)

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“…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. 31,32 Contrary to the free-flight situation, the limiting N factors for wind tunnels are specific quantities depending on the flow quality of the considered facility.…”

mentioning

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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confidence: 99%

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

Stock

2006

AIAA Journal

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“…[4][5][6] In many ways, the problem of the sustainment of laminar flow over an engine nacelle is much less restrictive than the equivalent investigations on aircraft wings, as lift generation is not the primary function. Early analytical studies on the effectiveness of a natural laminar flow nacelle [7][8][9][10] indicated that a potential drag reduction of up to 2% of total aircraft drag could be achieved, without incurring a weight penalty, solely by maintaining laminar flow on an engine nacelle. This was reinforced in the NASA study by Obara 11 who indicated that the percentage drag reduction on a typical business jet configuration could be increased from 12 to 24% by extending laminar flow over all aircraft surfaces, rather than limiting efforts to the wing alone.…”

Section: A Backgroundmentioning

confidence: 99%

Influence of Surface Waviness for Laminar Flow Nacelle Applications

Medina¹,

Early²,

Riordan

2009

27th AIAA Applied Aerodynamics Conference

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Transition onset over an engine nacelle is influenced by a large number of factors (for instance, surface roughness, steps, gaps and damage), many of which can be introduced as a result of the manufacturing process. Rivetting processes can lead to the introduction of surface deviations, which can be represented as either a bump or depression wave function. Previous work on the influence of leading edge roughness has demonstrated that such surface deviations can either promote or delay transition onset. The current work at Queen's University Belfast seeks to conduct a comprehensive investigation into the consequences of a depression-type surface irregularity on the transitional characteristics exhibited by a laminar flow nacelle, with specific attention paid to both the depression amplitude and streamwise location. Intial work has indicated that careful positioning of the streamwise location of the depression relative to the leading edge is critical in the selection of appropriate manufacturing tolerances, as even milliscale depressions, which have no appreciable influence on the transitional characteristics of the boundary layer, can have a significant affect on the downstream growth of the turbulent boundary layer. There is also some evidence to suggest that small depressions placed close to the leading edge can have a stabilising effect on the laminar boundary layer, leading to a delay in the transitional Reynolds number in a manner similar to that observed for subcritical protrusions.

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“…Performance penalties from heavier nacelles with more drag may ultimately outweigh the efficiencies gained from the engine cycle and hence designers will aim for increasingly short and slim fan cowls [2] [3]. There has been a resultant effort to understand the aerodynamics of nacelles and provide improved solutions for future engines [4,5,6]. A 'slimline' nacelle is expected to be incorporated in future, large engine designs [5] however the aerodynamic performance of these designs may be a limitation, particularly at off design conditions or when installed in the pressure field around an aircraft wing [7].…”

Section: Introductionmentioning

confidence: 99%

Nacelle design for ultra-high bypass ratio engines with CFD based optimisation

Robinson

MacManus

Christie

et al. 2021

Aerospace Science and Technology

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Aerodynamic design of a natural laminar flow nacelle and the design validation by flight testing

Cited by 19 publications

References 1 publication

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

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

Influence of Surface Waviness for Laminar Flow Nacelle Applications

Nacelle design for ultra-high bypass ratio engines with CFD based optimisation

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