Boundary-Layer Transition Prediction for Laminar Flow Control (Invited)

Crouch, J. D.

doi:10.2514/6.2015-2472

Cited by 30 publications

(16 citation statements)

References 15 publications

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“…Natural laminar flow (NLF) technology is a functional technology to reduce wall shear stress and fuel consumption of commercial aircraft (Crouch 2015;Fujino et al 2003). It is implemented on aerodynamic surfaces with zero to moderate sweep angles, where the predominant instabilities leading to transition to turbulence are Tollmien-Schlichting (T-S) waves.…”

Section: Introductionmentioning

confidence: 99%

Unit Reynolds number, Mach number and pressure gradient effects on laminar–turbulent transition in two-dimensional boundary layers

et al. 2018

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The influence of unit Reynolds number (Re 1 = 17.5 × 10 6-80 × 10 6 m −1), Mach number (M = 0.35-0.77) and incompressible shape factor (H 12 = 2.50-2.66) on laminar-turbulent boundary layer transition was systematically investigated in the Cryogenic Ludwieg-Tube Göttingen (DNW-KRG). For this investigation the existing two-dimensional wind tunnel model, PaLASTra, which offers a quasi-uniform streamwise pressure gradient, was modified to reduce the size of the flow separation region at its trailing edge. The streamwise temperature distribution and the location of laminar-turbulent transition were measured by means of temperature-sensitive paint (TSP) with a higher accuracy than attained in earlier measurements. It was found that for the modified PaLASTra model the transition Reynolds number (Re tr) exhibits a linear dependence on the pressure gradient, characterized by H 12. Due to this linear relation it was possible to quantify the so-called 'unit Reynolds number effect', which is an increase of Re tr with Re 1. By a systematic variation of M, Re 1 and H 12 in combination with a spectral analysis of freestream disturbances, a stabilizing effect of compressibility on boundary layer transition, as predicted by linear stability theory, was detected ('Mach number effect'). Furthermore, two expressions were derived which can be used to calculate the transition Reynolds number as a function of the amplitude of total pressure fluctuations, Re 1 and H 12. To determine critical N-factors, the measured transition locations were correlated with amplification rates, calculated by incompressible and compressible linear stability theory. By taking into account the spectral level of total pressure fluctuations at the frequency of the most amplified Tollmien-Schlichting wave at transition location, the scatter in the determined critical N-factors was reduced. Furthermore, the receptivity coefficients dependence on incidence angle of acoustic waves was used to correct the determined critical N-factors. Thereby, a found dependency of the determined critical N-factors on H 12 decreased, leading to an average critical N-factor of about 9.5 with a standard deviation of ≈ 0.8.

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Section: Introductionmentioning

confidence: 99%

Unit Reynolds number, Mach number and pressure gradient effects on laminar–turbulent transition in two-dimensional boundary layers

et al. 2018

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“…Re Θ = 0.404* {Re c * rle * tan (Λ)} 0.5 (1) In this equation, Re c is the Reynolds number base on local chord and Λ is the sweep of the wing leading edge. For wings with low sweep or low Reynolds number, keeping Re Θ below 100 is typically not an issue.…”

Section: A Attachment Line Contamination and Transitionmentioning

confidence: 99%

“…ATURAL laminar flow (NLF) is a technology that has been recognized for decades as having the potential to reduce aircraft drag and thus both fuel burn and emissions. Though primarily seen only on experimental and recreational aircraft in the past, it is now finding its way onto commercial aircraft for selected components with either low sweep or low Reynolds number such as nacelles, winglets and business jet wings 1,2 . The reason for its limited application thus far is that NLF, while more desirable than laminar flow control (LFC) because of its simplicity, at least historically has required a reduction in wing sweep with increasing Reynolds number to control the cross flow (CF) mode of transition.…”

Section: Introductionmentioning

confidence: 99%

Building a Practical Natural Laminar Flow Design Capability

Campbell

Lynde

2017

35th AIAA Applied Aerodynamics Conference

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A preliminary natural laminar flow (NLF) design method that has been developed and applied to supersonic and transonic wings with moderate-to-high leading-edge sweeps at flight Reynolds numbers is further extended and evaluated in this paper. The modular design approach uses a knowledge-based design module linked with different flow solvers and boundary layer stability analysis methods to provide a multifidelity capability for NLF analysis and design. An assessment of the effects of different options for stability analysis is included using pressures and geometry from an NLF wing designed for the Common Research Model (CRM). Several extensions to the design module are described, including multiple new approaches to design for controlling attachment line contamination and transition. Finally, a modification to the NLF design algorithm that allows independent control of Tollmien-Schlichting (TS) and cross flow (CF) modes is proposed. A preliminary evaluation of the TSonly option applied to the design of an NLF nacelle for the CRM is performed that includes the use of a low-fidelity stability analysis directly in the design module.

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“…Reed and Saric gave a more thorough description of these transition mechanisms in [21]. Recent practical applications of natural laminar flow can be found on the nacelles on Boeing 787 [22], the winglet on the 737max [22] and the wing on the supersonic Honda business jet [23], with zero or very small sweep angles. Qin [16] proposed to break the conventional rule of large sweep for transonic wing design by investigating the possibility of reducing wing sweep to 20° or less through careful balance of the drag-rise Mach number and skin friction drag, also considering the potential of the reduction of the wing structural weight through reduced sweep.…”

Section: Introductionmentioning

confidence: 99%

Shock Control of a Low-Sweep Transonic Laminar Flow Wing

Zhu

Qin

et al. 2019

AIAA Journal

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This paper presents a combined experimental and computational study of a low-sweep transonic natural laminar flow (NLF) wing with shock control bumps (SCBs). A transonic NLF wing with a relatively low sweep angle of 20° was chosen for this study. To avoid the complexity of the flow introduced by perforated/slotted walls commonly used for transonic wind tunnel tests for reducing the wall interference, both experimental tests and computational simulations were conducted with solid wind tunnel wall conditions. This allows for like-to-like validation of the computational simulation.Optimization of the shock control bumps was first conducted to design the wind tunnel test model with bumps. Two critical parameters of the three-dimensional SCBs for shock control, i.e. bump crest * Professor of Aerodynamics, AIAA Associate Fellow, Corresponding Author.

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Boundary-Layer Transition Prediction for Laminar Flow Control (Invited)

Cited by 30 publications

References 15 publications

Unit Reynolds number, Mach number and pressure gradient effects on laminar–turbulent transition in two-dimensional boundary layers

Unit Reynolds number, Mach number and pressure gradient effects on laminar–turbulent transition in two-dimensional boundary layers

Building a Practical Natural Laminar Flow Design Capability

Shock Control of a Low-Sweep Transonic Laminar Flow Wing

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