Wind Tunnel Studies of Natural Shock Wave — Separation Instabilities for Transonic Airfoil Tests

Dor, Juliette; Mignosi, A.; Seraudie, A.; Benoit, B.

doi:10.1007/978-3-642-83584-1_34

Cited by 11 publications

(13 citation statements)

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“…It will be shown from the experimental results that unlike the description of Dor et al [16] and similarly to the analysis of Finke [18] an unsteady phenomenon also exists in the laminar case above critical conditions, at a rather high frequency compared to turbulent buffet. The existence of this phenomenon was reported in a previous article (Brion et al [8]) and the present article provides additional details on the flow dynamics, in particular the existence of a low frequency peak similar to the turbulent buffet, which was also mentioned by Finke [18].…”

Section: Introductionmentioning

confidence: 54%

Laminar buffet and flow control

Brion

Dandois

Mayer

et al. 2019

Proceedings of the Institution of Mechanical Engineers, Part G:

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An experimental investigation of the transonic flow past the laminar OALT25 airfoil has been conducted to analyze the impact of laminar flow upon the shock wave dynamics and the existence of a laminar buffet like phenomenon. Tests have been carried out at freestream Mach numbers varying in the range of 0.7–0.8, angle of attack from 0.5° to 4°, and with two tripping configurations at the upper surface of the wing. The (airfoil) chord based Reynolds number is about three million. Results obtained from pressure taps and sensors measurements, as well as Schlieren visualizations of the flow reveal the presence of a laminar buffet phenomenon in sharp contrast with the turbulent phenomenon, as it features a freestream- and chord-based normalized frequency of about unity while turbulent buffet occurs for a frequency close to 0.07 (Jacquin et al., AIAA J 2009; 47). A low-frequency mode, at a frequency of about 0.05 is also present in the laminar situation, notably lower than the high-frequency component. The latter exhibits strong oscillations of the shock foot and vertical wavelike deformations of the shock wave and the former moves the shock back and forth over a small portion of chord, quite similar to the turbulent phenomenon. The mean flow past the laminar wing is characterized by a laminar separation bubble under the shock foot, which likely contributes much to the novel dynamics revealed by the present experiments. Two control strategies of the unsteady shock wave are implemented, one consisting of three-dimensional bumps and one consisting of steady jets blowing transversely to the freestream. It is found that bumps provide a significant reduction of the buffet intensity in the laminar situation. The jets are able to completely remove the flow unsteadiness in both laminar and turbulent conditions.

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Section: Introductionmentioning

confidence: 54%

Laminar buffet and flow control

Brion

Dandois

Mayer

et al. 2019

Proceedings of the Institution of Mechanical Engineers, Part G:

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“…Unfortunately, the 2-D transonic buffet phenomenon has received much less attention in the laminar case than in the turbulent one. Dor et al (1989) did not observe shock oscillations in buffet conditions at M = 0.75, α = 3 • , Re c = 3 × 10 6 . Just a strong increase of the pressure fluctuation level was observed without any particular frequency.…”

Section: Introductionmentioning

confidence: 69%

Large-eddy simulation of laminar transonic buffet

2018

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A large-eddy simulation of laminar transonic buffet on an airfoil at a Mach number $M=0.735$, an angle of attack $\unicode[STIX]{x1D6FC}=4^{\circ }$, a Reynolds number $Re_{c}=3\times 10^{6}$ has been carried out. The boundary layer is laminar up to the shock foot and laminar/turbulent transition occurs in the separation bubble at the shock foot. Contrary to the turbulent case for which wall pressure spectra are characterised by well-marked peaks at low frequencies ($St=f\cdot c/U_{\infty }\simeq 0.06{-}0.07$, where $St$ is the Strouhal number, $f$ the shock oscillation frequency, $c$ the chord length and $U_{\infty }$ the free-stream velocity), in the laminar case, there are also well-marked peaks but at a much higher frequency ($St=1.2$). The shock oscillation amplitude is also lower: 6 % of chord and limited to the shock foot area in the laminar case instead of 20 % with a whole shock oscillation and intermittent boundary layer separation and reattachment in the turbulent case. The analysis of the phase-averaged fields allowed linking of the frequency of the laminar transonic buffet to a separation bubble breathing phenomenon associated with a vortex shedding mechanism. These vortices are convected at $U_{c}/U_{\infty }\simeq 0.4$ (where $U_{c}$ is the convection velocity). The main finding of the present paper is that the higher frequency of the shock oscillation in the laminar regime is due to a different mechanism than in the turbulent one: laminar transonic buffet is due to a separation bubble breathing phenomenon occurring at the shock foot.

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“…Experimental studies have reported significant differences in the buffet characteristics under laminar flow conditions. For an RA16 airfoil with natural transition (Re = 3 − 6 × 10 6 ), [26] reported a strong increase of the pressure fluctuation level without any particular frequency, instead of the typical sharp spectral peak [27]. Also [28] compared laminar and turbulent buffet characteristics of an OAT15A airfoil and for the laminar case found a dominant peak at significantly higher frequencies (St ≈ 0.9) compared to the turbulent case (St ≈ 0.06).…”

Section: Introductionmentioning

confidence: 99%

Wide domain simulations of flow over an unswept laminar wing section undergoing transonic buffet

Zauner

Sandham

2020

Phys. Rev. Fluids

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Transonic buffet is an unsteady flow phenomenon that limits the safe flight envelope of modern aircraft. Scale-resolving simulations with span-periodic boundary conditions can provide detailed insight into the flow physics associated with buffet and can help to calibrate simplified models that are needed, for example, to develop more efficient wings based on laminar-flow supercritical sections. However, such simulations are often feasible only for severely restricted spanwise domains. In the current contribution, we analyse an unswept laminar-flow wing section (of Dassault Aviation's V2C profile) at a moderate Reynolds number of Re = 500,000 and a Mach number of M = 0.7 with spanwise domains equal to 5% and 100% of the airfoil chord. An implicit large-eddy simulation methodology, using a spectral error estimator to control the action of a high-order filter, is first validated against direct numerical simulations and then used for the domain width study. Quantitative differences, due to domain size, include an increase in amplitude and regularity of the buffet oscillations in the wider domain. Nevertheless, space-time analysis shows that key physical phenomena such as upstream-propagating shock waves are properly represented in the narrow domain and there is limited sensitivity to domain size of the aerodynamic coefficients. Even in the very wide domain, which is an order of magnitude wider than the largest turbulent structures measured at the trailing edge, certain features remain two-dimensional, including the shock and expansion waves that interact with the boundary layer upstream of transition. The transition mechanism is found to have subtle variations during a typical buffet cycle, with Kelvin-Helmholtz structures prominent during low-lift phases and oblique modes developing behind shock/boundarylayer interactions during high-lift phases. The availability of the wide-domain data is used for further study of the buffet mechanism, considering phase-averaged data and instantaneous flow fields to show the global structure of the buffet oscillation.

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Wind Tunnel Studies of Natural Shock Wave — Separation Instabilities for Transonic Airfoil Tests

Cited by 11 publications

References 1 publication

Laminar buffet and flow control

Laminar buffet and flow control

Large-eddy simulation of laminar transonic buffet

Wide domain simulations of flow over an unswept laminar wing section undergoing transonic buffet

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