Contents: 1. Late stage of laminar-turbulent transition on a flat plate 2. Swept-wing boundary layer 3. Test model 4. Automated measurements 5. Controlled excitation of the boundary-layer disturbances 6. Wave packet in 2D boundary layer 7. Wave packet in 3D boundary layer 8. Summary 9. Relevant publications Multimedia files – 12/13 Nonlinear wave packets in swept-wing boundary layer

1. Late stage of laminar-turbulent transition on a flat plate Flow visualization by W.S. Saric, V.V., Kozlov, V.Ya. Levchenko (1984) Direct numerical simulation (Rist et al. 1998) of laboratory experiments (Kachanov 1994) (see page of notes) K-regime of transition in a flat-plate boundary layer

2. Swept-wing boundary layer (see page of notes) External streamline (left) and the mean flow in the boundary layer (right)

3. Test model (see page of notes) General view (left) and the sketch (right) of experimental model

4. Automated measurements Traversing system (left) and the scheme (right) of automated triggered hot-wire measurements (see page of notes)

5. Controlled excitation of the boundary-layer disturbances QoQo C Z'Z' X Excitation point 0.4 C (see page of notes) Generation of the boundary layer perturbations at the model surface

0 - sweep A video clip by Chernoray V.G., Kozlov V.V., Löfdahl L., Pratt P. (2006) 6. Wave packet in 2D boundary layer (I) Click to play

Isosurfaces of the streamwise velocity component at zero sweep angle where dark and light half-tones represent positive and negative values of the disturbance amplitude, respectively (left); isolines of the mean velocity distortion for 25, 50 and 75 % of Q 0 levels and the contours of velocity fluctuations u rms with step equal to 10 % of Q 0 for the cross sections at x/c = 0.48, 0.54, 0.60, 0.66 and 0.72 (from bottom to top) (right) 0 - sweep 6. Wave packet in 2D boundary layer (II)

30 - sweep 7. Wave packet in 3D boundary layer (I) A video clip by Chernoray V.G., Kozlov V.V., Löfdahl L., Pratt P. (2006) Click to play

30 - sweep Isosurfaces of the streamwise velocity component at 30° sweep angle where dark and light half-tones represent positive and negative values of the disturbance amplitude, respectively (left); isolines of the mean velocity distortion for 25, 50 and 75 % of Q 0 levels and the contours of velocity fluctuations u rms with step equal to 10 % of Q 0 for the cross sections at x/c = 0.48, 0.54, 0.60, 0.66 and 0.72 (from bottom to top) (right) 7. Wave packet in 3D boundary layer (II)

45 - sweep 7. Wave packet in 3D boundary layer (III) A video clip by Chernoray V.G., Kozlov V.V., Löfdahl L., Pratt P. (2006) Click to play

45 - sweep Isosurfaces of the streamwise velocity component at 45° sweep angle where dark and light half-tones represent positive and negative values of the disturbance amplitude, respectively (left); isolines of the mean velocity distortion for 25, 50 and 75 % of Q 0 levels and the contours of velocity fluctuations u rms with step equal to 10 % of Q 0 for the cross sections at x/c = 0.48, 0.54, 0.60, 0.66 and 0.72 (from bottom to top) (right) 7. Wave packet in 3D boundary layer (IV)

Summary (see page of notes) Localized boundary layer distrubances at different sweep angle

Bake S., Meyer D.G.W., Rist U. (2002) Turbulence mechanism in Klebanoff transition: a quantitative comparison of experiment and direct numerical simulation. J. Fluid Mech., 459, 217 – 243. Chernoray V.G., Bakchinov A.A., Kozlov V.V., Löfdahl L. (2001) Experimental study of the K-regime of breakdown in straight and swept wing boundary layers. Phys. Fluids, 13(7), 2129 – Chernoray V.G., Dovgal A.V., Kozlov V.V., Löfdahl L. (2005) Experiments on secondary instability of streamwise vortices in a swept wing boundary layer. J. Fluid Mech., 534, 295 – 325. Chernoray V.G., Kozlov V.V., Löfdahl L., Pratt P. (2006) Hot-wire anemometry visualization of the complex turbulent flows. Thermophysics and Aeromechanics, 13(2), 229 – 237. Chernoray V., Kozlov V., Pratt P., Löfdahl, L. (2005) Hot wire visualizations of breakdown to turbulence in complex flows. In Proc. EUCASS Conf. Moscow, Russia, 2.11–2.12. Kachanov Y.S. (1994) Physical mechanisms of laminar-boundary-layer transition. Annu. Rev. Fluid Mech., 26, 411–482. Kachanov Y.S., Kozlov V.V., Levchenko V.Ya. (1978) Nonlinear development of a wave in a boundary layer. Izv. Akad. Nauk SSSR, Mekh. Zhidk. Gaza, 5, 85 – 94 (in Russian). Transl. Fluid. Dyn., 12, 383–390. Klebanoff P.S., Tidstrom K.D., Sargent L.M. (1962) The three-dimensional nature of boundary layer instability. J. Fluid Mech., 12, 1–34. Litvinenko Yu.A., Grek G.R., Kozlov V.V., Löfdahl L., Chernoray V.G. (2004) An experimental study of varicose instability of streaky structure in a boundary layer of swept wing. Thermophysics and Aeromechanics, 11(1), 1 – 11. Reed H.L., Saric W.S. (1989) Stability of three-dimensional boundary layers. Annu. Rev. Fluid Mech., 21, 235– 284. Rist U., Müller K., Wagner S. (1998) Visualisation of late-stage transitional structures in numerical data using vortex identification and feature extraction. In G.M. Carlomango and I. Grant (Eds.), Eighth Intern. Symp. on Flow Visualisation. Sorrento (Paper 109). Saric W., Kozlov V., Levchenko V. (1984) Forced and unforced subharmonic resonance in boundary layer transition. AIAA Paper 84 – Relevant publications