Abstract
When a laminar boundary layer separates because of an adverse streamwise pressure gradient, the flow is subject to increased instability with respect to small-amplitude disturbances. Laminar–turbulent transition occurs under a rapid three-dimensional (3D) development within the separated shear layer. When the following turbulent boundary layer reattaches, a laminar separation bubble is formed. To allow controlled measurements, a small-amplitude Tollmien–Schlichting wave (TS wave) was introduced into the boundary layer without (case I) and with (case II) spanwise forcing of steady 3D disturbances. Combined application of laser-Doppler anemometry (LDA) and particle image velocimetry (PIV) demonstrates the suitability of both measurement techniques to capture the development of unsteady, periodic phenomena. The transition mechanism occurring in the flow field under consideration is discussed, and results obtained by controlled measurements are compared to direct numerical simulations (DNS) and predictions from linear stability theory (LST). Flow visualizations and stereoscopic PIV measurements give better insight into the 3D breakdown of the separated shear layer.
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Abbreviations
- a :
-
amplitude
- f 0 :
-
fundamental frequency
- H 12 :
-
boundary layer shape factor, H 12=δ 1/δ 2
- h :
-
wavenumber coefficient in time
- k :
-
wavenumber coefficient in the spanwise direction
- l :
-
liter
- m :
-
meter
- Re x :
-
Reynolds number based on streamwise distance of the leading edge
- Re δ1 :
-
Reynolds number based on the displacement thickness δ 1
- s :
-
second
- t :
-
time
- u ∞ :
-
freestream velocity
- u δ :
-
velocity at the boundary layer edge
- u,v,w :
-
velocities
- u′,v′:
-
velocity fluctuations
- x :
-
streamwise coordinate
- y :
-
wall-normal coordinate
- z :
-
spanwise coordinate
- δ :
-
boundary layer thickness
- δ 1 :
-
boundary layer displacement thickness
- δ 2 :
-
boundary layer momentum thickness
- λ z :
-
spanwise wavelength
- Φ :
-
phase angle
References
Alam M, Sandham ND (2000) Direct numerical simulation of 'short' laminar separation bubbles with turbulent reattachment. J Fluid Mech 410:1–28
Boiko AV, Grek GR, Dovgal AV, Koslov VV (2002) The origin of turbulance in near-wall flows. Springer, Berlin Heidelberg New York
Briley WR (1971) A numerical study of laminar separation bubbles using the Navier–Stokes equations. J Fluid Mech 47:713–736
Fitzgerald EJ, Mueller TJ (1988) Measurements in a separation bubble on an airfoil using laser velocimetry. AIAA J 28:584–592
Gaster M (1966) The structure and behavior of laminar separation bubbles. AGARD CP 4:813–854
Klebanoff PS, Tidstrom KD, Sargent LM (1962) The three-dimensional nature of boundary layer instability. J Fluid Mech 12:1–41
Kruse M, Wagner S (1996) Measurements of laminar–turbulent transition in a flat-plate boundary layer. In: Proceedings of the 8th international symposium of laser techniques to fluid mechanics, Lisbon, 8–11 July
Kruse M (1997) Einsatz der Laser-Doppler-Anemometrie zur Untersuchung des laminar-turbulenten Grenzschichtumschlags an der ebenen Platte. Dissertation, University of Stuttgart, Germany
Lang M, Marxen O, Rist U, Wagner S (2000a) Experimental and numerical investigations on transition in a laminar separation bubble. In: Wagner S et al. (eds) Notes on numerical fluid mechanics, new results in numerical and experimental fluid mechanics. Springer, Berlin Heidelberg New York
Lang M, Marxen O, Rist U, Wagner S (2000b) LDA-Messungen zur Transition in einer laminaren Ablöseblase. In: Proceedings of 8th Fachtagung der GALA, Lasermethoden in der Strömungsmesstechnik, Freising-Weihenstephan, Germany, 12–14 Sept. Shaker, Aachen
Marxen O, Lang M, Rist U, Wagner S (2002) A combined experimental/numerical study of unsteady phenomena in a laminar separation bubble. In: Proceedings of IUTAM symposium "unsteady separated" flows, Toulouse (available on CD-ROM)
Marxen O, Rist U,Wagner S (2003) The effect of spanwise-modulated disturbances on transition in a 2-D separated boundary layer. AIAA paper no. 2003-0789
Maucher U, Rist U, Wagner S (1999) Transitional structures in a laminar separation bubble. In: Nitsche W, Heinemann R, Hilbig HJ (eds.) Notes on numerical fluid mechanics, new results in numerical and experimental fluid mechanics. Vieweg, Wiesbaden
Rist U (2002) On instability and transition in laminar separation bubbles. In: Proceedings of CEAS aerospace aerodynamics research conference, Cambridge, UK, 10–12 June 2002, (available on CD-ROM)
Rist U (1998) Zur Instabilität und Transition in laminaren Ablöseblasen. Habilitation, Universität Stuttgart, Shaker, Aachen
Rist U, Augustin K, Wagner S (2000) Numerical simulation of laminar separation-bubble control. In: Wagner S et al. (eds) Notes on numerical fluid mechanics, new results in numerical and experimental fluid mechanics. Springer, Berlin Heidelberg New York
Ronneberger O, Raffel M, Kompenhans J (1998) Advanced evaluation algorithms for standard and dual plane particle image velocimetry. In: Proceedings of 9th international symposium of laser techniques to fluid mechanics, Lisbon, 13–16 July
Spalart PR, Strelets MK (2000) Mechanisms of transition and heat transfer in a separation bubble. J Fluid Mech 403:329–349
Strunz M, Speth JF (1987) A new laminar water-tunnel to study the transition process in a Blasius boundary layer and in a separation bubble and a new tool for industrial aerodynamics and hydrodynamic research. AGARD CP 413:25-1– 25-5
Watmuff J (1999) Evolution of a wave packet into vortex loops in a laminar separation bubble. J Fluid Mech 397:119–169
Westerweel J, van Oord J (2000) Stereoscopic PIV measurements in a turbulent boundary layer. In: Stanislas M, Kompenhans J, Westerweel J (eds) Particle image velocimetry, progress toward industrial application. Kluwer, Dordrecht
Wiegand T (1997) Experimentelle Untersuchungen zum laminar-turbulenten Transitionsprozess eines Wellenzuges in einer Plattengrenzschicht. Dissertation, University of Stuttgart, Germany
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Lang, M., Rist, U. & Wagner, S. Investigations on controlled transition development in a laminar separation bubble by means of LDA and PIV . Exp Fluids 36, 43–52 (2004). https://doi.org/10.1007/s00348-003-0625-x
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DOI: https://doi.org/10.1007/s00348-003-0625-x