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Origination and evolutionof turbulent spots

Contents:

1. Incipient spot2. Turbulent spot3. Turbulent spot structure4. Turbulent spot evolution5. Interaction of turbulent spots6. Turbulent spots at low and high free stream turbulence7. Transformation of - structures into turbulent spots8. Related publications

1. Incipient spot

Smoke visualization of an incipient spot during natural transition on a flat plate at high free-stream turbulence, Tu = 1.5% (Alfredsson et al. 1996)

(see page of notes)

Turbulent spot (Alfredsson et al. 1996)

(see page of notes)

2. Turbulent spot (I)

Set-up of the turbulent spots visualization in a boundary layer (Alfredsson et al. 1996 )

(see page of notes)

2. Turbulent spot (II)

Undisturbed flat-plate boundary layer at Tu = 0.01%

(video clip by Alfredsson P.H., Bakchinov A.A., Kozlov V.V, and Matsubara M., 1996)

Uo

2. Turbulent spot (III)

Click to play

Uo

2. Turbulent spot (IV)

Turbulent spots on flat plate at Tu = 0.01%, U0 = 9.0 m/s(video clip by Alfredsson P.H., Bakchinov A.A., Kozlov V.V, and Matsubara M., 1996)

Click to play

Ensemble-averaged oscillograms across the turbulent spot in the plane of its symmetry in a flat plate boundary layer (Grek et al. 1987). Characteristic regions and fronts of the spot are marked by numbers, as in (Wygnanski et al. 1982), and letters as in (Cantwell et al. 1978): 1(A), spot leading front near wall; 2(B), leading front forward-most region; 3(C), maximum spot height; 4(F), spot trailing edge; D, region of velocity relaxation to undisturbed state

(see page of notes)

3. Turbulent spot structure

4. Turbulent spot evolution

Propagation velocity of the turbulent spot fronts in a flat-plate flow: leading front, LF(1),trailing front, TF(4). Experimental data by Grek et al. (1987) at Tu ≤ 0.04% (1),Grek et al. (1987) at Tu = 1% (2), and Wygnanski et al. (1982) (3); x0 = 300 mm,U0 = 10 m/s, for other notations see legend to the previous figure

(see page of notes)

Development and merging of two turbulent spots spacedin the spanwise direction (Grek et al. 1987)

(see page of notes)

5. Interaction of turbulent spots (I)

Development and interaction of two turbulent spots that are followingeach other (Grek et al. 1987)

(see page of notes)

5. Interaction of turbulent spots (II)

Smoke visualization of the turbulent spots in a flat plate boundary layer at low (top) and high (bottom) free-stream turbulence (Alfredsson et al. 1996)

(see page of notes)

6. Turbulent spots at low and high free stream turbulence (I)

Development characteristics of the ensemble-averaged turbulent spot at low and high free-stream turbulence: the turbulent spot structure along its centreline (a); oscillograms demonstrating propagation characteristics of the turbulent spot fronts at U0 = 10 m/s,x0 = 300 mm, Tu ≤ 0.04% (green lines), Tu = 1% (red lines) (Grek et al. 1987, 1988) (b)

(see page of notes)

6. Turbulent spots at low and high free stream turbulence (II)

7. Transformation of - structures into turbulent spots (I)

Experimental setup

(see page of notes)

Amplitude contours of the ensemble-averaged -structureat its downstream propagation in x-z plane

7. Transformation of - structures into turbulent spots (II)

U0

Hot-wire ‘visualization’ of the - structure transformation into the turbulent spot, x-z plane (video clip by Chernoray V.G., Kozlov V.V., Löfdahl L., Litvinenko Yu.A., Grek G.R., Chun H.H., 2005)

7. Transformation of - structures into turbulent spots (III)

Click to play

U0

7. Transformation of - structures into turbulent spots (IV)

Hot-wire ‘visualization’ of the - structure transformation into the turbulent spot, 3D space (video clip by Chernoray V.G., Kozlov V.V., Löfdahl L., Litvinenko Yu.A., Grek G.R., Chun H.H., 2005)

Click to play

8. Related publications (I)

Alfredsson P.H., Bakchinov A.A., Kozlov V.V., Matsubara M. (1996) Laminar–turbulent transition at a high level of a free stream turbulence. In P.W. Duck and P.Hall (Eds.), Nonlinear Instability and Transition in Three- Dimensional Boundary Layers (423–436). Dordrecht: Kluwer.Amini J., Lespinard G. (1982) Experimental study of an "incipient spot" in a transitional boundary layer. Phys. Fluids, 25, 1743-1750.Barrow J., Barnes F.H., Ross M.A.S. (1984) The structure of a turbulent spot in Blasius flow. J. Fluid Mech., 149, 319-337.Breuer K.S., Landahl M.T. (1990) The evolution of a localized disturbance in a laminar boundary layer. Part 2. Strong disturbances J. Fluid Mech., 220, 595-621.Cantwell D., Coles D., Dimotakis P. (1978) Structure and entrainment in the plane of symmetry of a turbulent spot. J. Fluid Mech., 87, 641-671.Chernoray V.G., Grek G.R., Kozlov V.V., Litvinenko Yu.A. (2010) Spatial hot-wire visualization of the -structure transformation into the turbulent spot on the smooth flat plate surface and riblet effect on this process. J. Visualization, 13(2), 151-158.Elder J.W. (1960) An experimental investigation on turbulent spot and breakdown to turbulence. J. Fluid Mech., 9., 235-246. Emmons H.W. (1951) The laminar-turbulent transition in a boundary layer. Part 1. J. Aeronaut. Sci.,18(7), 490-498.Grek G.R., Kozlov V.V., Ramazanov M.P. (1987) Laminar–turbulent transition at high free stream turbulence. Preprint ITAM 8–87.

Grek G.R., Kozlov V.V., Ramazanov M.P. (1990) Investigation of boundary-layer stability in a pressure gradient flow at high free-stream turbulence. Fluid Dynamics, 2, 52-58.Litvinenko Yu.A., Chernoray V.G., Kozlov V.V., Loefdahl L., Grek G.R., Chun H.H. (2006) The Influence of Riblets on the Development of a L-Structure and Its Transformation into a Turbulent Spot. Doklady Physics, 51(3), 144–147.

8. Related publications (II)

Litvinenko Yu.A., Chernoray V.G., Kozlov V.V., Loefdahl L., Grek G.R. (2007) Control of L-structure transformation into the turbulent spot by means of riblets. In Proc. Intern. Conf. on the Methods of Aerophys. Research (pt.1,152-156). Novosibirsk.Matsubara M., Kozlov V., Alfredsson P.H., Bakchinov A.A., Westin, K.J.A. (1996) On flat plate boundary layer perturbations at high free stream turbulence level. In Proc. Eighth Internat. Conf. on Methods of Aerophysical Research (pt.1, 174–179). Novosibirsk.Narasimha R., Subramanian C., Badri Narayanan M.A. (1982) Turbulent spot growth in favourable pressure gradients. Rep. 82 FM 12, Bangalore, India.Schubauer G.B., Klebanoff P.S. (1956) Contributions on the mechanics of boundary layer transition. NACA Rep. - No. 1289.Vasudevan K.P., Dey J., Prabhu A. (2001) Spots propagation characteristics in laterally strained boundary layers. Exp Fluids 30(5), 488–491.Wygnanski I., Sokolov M., Friedman D. (1976) On a turbulent spot in a laminar boun-dary layer. J. Fluid Mech., 78, 785-819.Wygnanski I., Haritonidis J.H., Kaplan R.E. (1979) On a Tollmien-Schlichting wave packet produced by a turbulent spot. J. Fluid Mech., 92, 505-528.Wygnanski I., Haritonidis J.H., Zilberman H. (1982) On the spreading of a turbulent spot in the absence of a pressure gradient. J. Fluid Mech., 123, 69-90.