# An experimental study on the effects of two-dimensional positive surface defects on the laminar–turbulent transition of a sucked boundary layer

- 129 Downloads

### Abstract

Laminar–turbulent transition can be effectively delayed using Laminar Flow Control (LFC) by boundary layer suction. However, major obstacles to the industrial implementation of this technique are related to practical limitations, such as proper integration of the suction system or unreliability of current design tools. The influence of surface discontinuities that can arise from installing an LFC system (and then potentially cancel or deteriorate its stabilizing effect on the boundary layer) is scarcely documented in the open literature, adding to the complexity of improving numerical models. The present investigation, therefore, focuses on experimentally characterizing the effects of surface defects on the laminar–turbulent transition of a sucked boundary layer in a two-dimensional flow, in an effort to address some of the issues mentioned above. The experimental facility and protocol for conducting this transition study are first presented, followed by a baseline characterization of the effects of wall suction alone on transition. Surface defects, in the form of cylindrical roughness elements (wires), are then introduced on the flat plate and their effects, coupled to those of wall suction, on boundary layer stability are discussed. The critical relative height (where the onset of transition coincides with the position of the surface defect) was found to be the same for cases both with and without wall suction. For the critical cases, spectral analysis of the flow immediately downstream of the defect for all suction configurations revealed a range of amplified high frequencies in addition to or in place of the natural Tollmien–Schlichting instabilities. Wall suction was, therefore, ineffective in delaying the critical relative wire height, since, in the critical cases, the transition mechanism seemed to be governed by inflection-type instabilities, rather than viscous instabilities.

### Graphical abstract

## List of symbols

## Greek symbols

- \(\alpha\)
Wave number (complex variable)

- \(\delta _1\)
Displacement thickness

- \(\delta _{99}\)
Boundary layer thickness at \(0.99 U_{\mathrm{{e}}}\)

- \(\omega\)
Angular frequency

- \(\theta\)
Momentum thickness

## Roman symbols

- Cp
Pressure coefficient

*d*Suction hole diameter

*H*Shape factor

*h*Wire diameter

- LST
Linear stability theory

- PSD
Power spectral density

*p*Porosity

*Re*Reynolds number

*U*Streamwise (

*x*) component of velocity- \(u'\)
Streamwise (

*x*) component of velocity fluctuation*x*Streamwise coordinate

*y*Normal coordinate to the flat plate wall

*z*Spanwise coordinate

## Subscripts and superscripts

- \(\infty\)
Freestream

*e*Boundary layer edge

- SD
Surface defect

- xT
Transition location

## Notes

## References

- Al-Maaitah A, Nayfeh A, Ragab S (1989) Effect of wall suction on the stability of compressible subsonic flows over smooth two-dimensional backward-facing steps. In 2nd Shear Flow Conference, AIAA-89-0983Google Scholar
- Arnal D, Archambaud J (2008) Laminar-turbulent transition control: Nlf, lfc, hlfc. Advances in Laminar-Turbulent Transition Modeling, RTO-EN-AVT-151Google Scholar
- Beguet S, Perraud J, Forte M, Brazier J-P (2016) Modeling of transverse gaps effects on boundary-layer transition. Journal of Aircraft 54(2):794–801CrossRefGoogle Scholar
- Braslow A (1999) A history of suction-type laminar flow control with emphasis on flight research. Monographs in Aerospace History, (13)Google Scholar
- Bulgubure C, Arnal D (1992) Dassault Falcon 50 laminar flow flight demonstrator. In DGLR/AAAF/RAeS 1st European Forum on Laminar FlowGoogle Scholar
- Burden HW (1969) The effect of wall porosity on the stability of parallel flows over compliant boundaries. Technical report, Naval Ship Research and Development Center, Washington D.CGoogle Scholar
- Carpenter P, Porter L (2001) Effects of passive porous walls on boundary-layer instability. AIAA Journal 39(4):597–604CrossRefGoogle Scholar
- Choudhari M (1994) Effect of nonzero surface admittance on receptivity and stability of compressible boundary layerGoogle Scholar
- Costantini M, Risius S, Klein C (2015) Experimental investigation of the effect of forward-facing steps on boundary layer transition. Procedia IUTAM 14:152–162CrossRefGoogle Scholar
- Dovgal A, Kozlov V, Michalke A (1994) Laminar boundary layer separation: instability and associated phenomena. Progress in Aerospace Sciences 30(1):61–94CrossRefGoogle Scholar
- Feindt E (1956) Investigation on the dependence of laminar-turbulent transition on surface roughness and pressure gradient. Schiffbautechnischen Geselschaft Jahrbach, 50Google Scholar
- Fransson JH (2004) Leading edge design process using a commercial flow solver. Experiments in fluids 37(6):929–932CrossRefGoogle Scholar
- Gregory N (1962) On critical suction conditions for laminar boundary-layer control by suction in perforation. Technical report, Aeronautical Research Council Report No. 24Google Scholar
- Head M (1955) The boundary layer with distributed suction. British A.R.C. Reports & Memoranda, (2783)Google Scholar
- Heinrich R, Choudhari M, Kerschen E (1988) A comparison of boundary layer receptivity mechanisms. In 1st National Fluid Dynamics Conference, page 3758Google Scholar
- Hunt L, Downs R, Kuester M, White E, Saric W (2010) Flow quality measurements in the Klebanoff-Saric wind tunnel. In 27th AIAA Aerodynamic Measurement Technology and Ground Testing Conference, AIAA2010-4538Google Scholar
- Joslin R (1998) Overview of laminar flow control. Technical report, NASA/TP-1998-208705Google Scholar
- Juillen J, Casalis G, Arnal D (1995) Aspiration discontinue : résultats expérimentaux et comparaisons aux résultats de calculs de stabilité. Technical report, CERT DERAT 107/5018.93Google Scholar
- Klebanoff P, Tidstrom K (1972) Mechanism by which a two-dimensional roughness element induces boundary-layer transition. The Physics of Fluids 15(7):1173–1188CrossRefGoogle Scholar
- Mack L (1977) Transition and laminar instability. JPL Publication 77-15Google Scholar
- MacManus D, Eaton J (1996) Predictions and observations of the flow field induced by laminar flow control microperforations. Experimental thermal and fluid Science 13(4):395–407CrossRefGoogle Scholar
- Maddalon D (1991) Hybrid Laminar Flow Control flight research. Research and Technology, NASA, TM 4331:47Google Scholar
- Marec J-P (2001) Drag reduction: a major task for research. In Aerodynamic Drag Reduction Technologies, pages 17–27. SpringerGoogle Scholar
- Methel J, Vermeersch O, Forte M, Casalis G (2018) Experimental characterization of the laminar-turbulent transition of a sucked boundary layer due to surface defects in a two-dimensional incompressible flow. 2018 Flow Control Conference, AIAA AVIATION Forum, AIAA2018-3214Google Scholar
- Morkovin M, Reshotko E, Herbert T (1994) Transition in open flow systems-a reassessment. Bull. Am. Phys. Soc. 39:1882Google Scholar
- Nenni J, Gluyas G (1966) Aerodynamic design and analysis of an LFC surface. Astronautics & Aeronautics 4(7):52Google Scholar
- Perraud J, Séraudie A, Reneaux J, Arnal D, Tran D (2005) Effect of 2d and 3d imperfections on laminar-turbulent transition. In CEAS Katnet Conference on Key Aerodynamic TechnologiesGoogle Scholar
- Rayleigh J (1880) On the stability, or instability, of certain fluid motions. Proc. London Math. Soc. 9:57–70MathSciNetzbMATHGoogle Scholar
- Reed H, Nayfeh A (1986) Numerical-perturbation technique for stability of flat-plate boundary layers with suction. AIAA journal 24(2):208–214MathSciNetCrossRefGoogle Scholar
- Reed H, Saric W, Arnal D (1996) Linear stability theory applied to boundary layers. Annual Review of Fluid Mechanics 28(1):389–428MathSciNetCrossRefGoogle Scholar
- Reneaux J, Blanchard A (1992) The design and testing of an airfoil with hybrid laminar flow control. In DGLR/AAAF/RAeS 1st European Forum on Laminar FlowGoogle Scholar
- Reynolds G, Saric W (1986) Experiments on the stability of the flat-plate boundary layer with suction. AIAA journal 24(2):202–207CrossRefGoogle Scholar
- Saric W (2008) Experiments in 2-D boundary layers: stability and receptivity. Advances in Laminar-Turbulent Transition Modelling, NATO Educational Notes, pages 8–1Google Scholar
- Saric WS, Carpenter AL, Reed HL (2011) Passive control of transition in three-dimensional boundary layers, with emphasis on discrete roughness elements. Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 369(1940):1352–1364CrossRefGoogle Scholar
- Schrauf G, Bieler H, Thiede P (1992) Transition prediction-the deutsche airbus viewGoogle Scholar
- Tani I (1961) Effect of two-dimensional and isolated roughness on laminar flow. In Boundary layer and flow control, pages 637–656. ElsevierGoogle Scholar
- Tilton N, Cortelezzi L (2015) Stability of boundary layers over porous walls with suction. AIAA Journal 53(10):2856–2868CrossRefGoogle Scholar
- Titchener N, Colliss S, Babinsky H (2015) On the calculation of boundary-layer parameters from discrete data. Experiments in Fluids 56(8):159CrossRefGoogle Scholar
- Wang Y, Gaster M (2005) Effect of surface steps on boundary layer transition. Experiments in Fluids 39(4):679–686CrossRefGoogle Scholar
- Watanabe T, Kobayashi R (1991) Effect of a single roughness element on boundary layer transition over a wedge. Experimental Thermal and Fluid Science 4(5):558–566CrossRefGoogle Scholar
- Wörner A, Rist U, Wagner S (2003) Humps/steps influence on stability characteristics of two-dimensional laminar boundary layer. AIAA Journal 41:192–197CrossRefGoogle Scholar