Abstract
The transition process of the boundary layer growing over a flat plate with pressure gradient simulating the suction side of a low-pressure turbine blade and elevated free-stream turbulence intensity level has been analyzed by means of PIV and hot-wire measurements. A detailed view of the instantaneous flow field in the wall-normal plane highlights the physics characterizing the complex process leading to the formation of large-scale coherent structures during breaking down of the ordered motion of the flow, thus generating randomized oscillations (i.e., turbulent spots). This analysis gives the basis for the development of a new procedure aimed at determining the intermittency function describing (statistically) the transition process. To this end, a wavelet-based method has been employed for the identification of the large-scale structures created during the transition process. Successively, a probability density function of these events has been defined so that an intermittency function is deduced. This latter strictly corresponds to the intermittency function of the transitional flow computed trough a classic procedure based on hot-wire data. The agreement between the two procedures in the intermittency shape and spot production rate proves the capability of the method in providing the statistical representation of the transition process. The main advantages of the procedure here proposed concern with its applicability to PIV data; it does not require a threshold level to discriminate first- and/or second-order time-derivative of hot-wire time traces (that makes the method not influenced by the operator); and it provides a clear evidence of the connection between the flow physics and the statistical representation of transition based on theory of turbulent spot propagation.
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References
Abu-Ghannam B, Shaw R (1980) Natural transition of boundary layers—the effects of turbulence, pressure gradient, and flow history. J Mech Eng Sci 22(5):213–228
Adrian RJ (2007) Hairpin vortex organization in wall turbulence. Phys Fluids (1994 Present) 19(4):041301
Blair M (1992) Boundary-layer transition in accelerating flows with intense freestream turbulence: part 1-disturbances upstream of transition onset. J Fluids Eng 114(3):313–321
Brandt L, Henningson DS (2002) Transition of streamwise streaks in zero-pressure-gradient boundary layers. J Fluid Mech 472:229–261
Camussi R (2002) Coherent structure identification from wavelet analysis of particle image velocimetry data. Exp Fluids 32(1):76–86
Chen KK, Thyson NA (1971) Extension of Emmons’ spot theory to flows on blunt bodies. AIAA J 9(5):821–825
Dhawan S, Narasimha R (1958) Some properties of boundary layer flow during the transition from laminar to turbulent motion. J Fluid Mech 3(04):418–436
Emmons HW (1951) The laminar–turbulent transition in a boundary layer—part 1. J Aeronaut Sci 18:490–498
Farge M (1992) Wavelet transforms and their applications to turbulence. Annu Rev Fluid Mech 24(1):395–458
Fransson JH, Matsubara M, Alfredsson PH (2005) Transition induced by free-stream turbulence. J Fluid Mech 527:1–25
Gostelow J, Blunden A, Walker G (1994) Effects of free-stream turbulence and adverse pressure gradients on boundary layer transition. J Turbomach 116(3):392–404
Hedley TB, Keffer JF (1974) Turbulent/non-turbulent decisions in an intermittent flow. J Fluid Mech 64(04):625–644
Kähler CJ, Scharnowski S, Cierpka C (2012) On the resolution limit of digital particle image velocimetry. Exp Fluids 52(6):1629–1639
Kuan C, Wang T (1990) Investigation of the intermittent behavior of transitional boundary layer using a conditional averaging technique. Exp Thermal Fluid Sci 3(2):157–173
Lengani D, Simoni D (2015) Recognition of coherent structures in the boundary layer of a low-pressure-turbine blade for different free-stream turbulence intensity levels. Int J Heat Fluid Flow 54:1–13
Lengani D, Simoni D, Ubaldi M, Zunino P (2014) POD analysis of the unsteady behavior of a laminar separation bubble. Exp Therm Fluid Sci 58:70–79
Lengani D, Simoni D, Ubaldi M, Zunino P, Bertini F (2016) Coherent structures formation during wake-boundary layer interaction on a LP turbine blade. Flow Turbul Combust. doi:10.1007/s10494-016-9741-6
Luchini P (2000) Reynolds-number-independent instability of the boundary layer over a flat surface: optimal perturbations. J Fluid Mech 404:289–309
Mandal AC, Venkatakrishnan L, Dey J (2010) A study on boundary-layer transition induced by free-stream turbulence. J Fluid Mech 660:114–146
Mans J, Kadijk E, de Lange H, van Steenhoven A (2005) Breakdown in a boundary layer exposed to free-stream turbulence. Exp Fluids 39(6):1071–1083
Matsubara M, Alfredsson PH (2001) Disturbance growth in boundary layers subjected to free-stream turbulence. J Fluid Mech 430:149–168
Mayle RE (1991) The 1991 IGTI scholar lecture: the role of laminar–turbulent transition in gas turbine engines. J Turbomach 113(4):509–536
Morkovin MV (1969) On the many faces of transition. In: Wells CS (ed) Viscous drag reduction. Springer, New York, pp 1–31
Narasimha R (1957) On the distribution of intermittency in the transition region of a boundary layer. J Aerosp Sci 24:711–712
Narasimha R, Devasia K, Gururani G, Narayanan MB (1984) Transitional intermittency in boundary layers subjected to pressure gradient. Exp Fluids 2(4):171–176
Nolan KP, Walsh EJ (2012) Particle image velocimetry measurements of a transitional boundary layer under free stream turbulence. J Fluid Mech 702:215–238
Piotrowski W, Lodefier K, Kubacki S, Elsner W, Dick E (2008) Comparison of two unsteady intermittency models for bypass transition prediction on a turbine blade profile. Flow Turbul Combust 81(3):369–394
Ramesh O, Hodson H (1999) A new intermittency model incorporating the calming effect. Rolls Royce PLC-Report-PNR
Schlatter P, Brandt L, De Lange H, Henningson DS (2008) On streak breakdown in bypass transition. Phys Fluids (1994 Present) 20(10):101505
Schröder A, Kompenhans J (2004) Investigation of a turbulent spot using multi-plane stereo particle image velocimetry. Exp Fluids 36(1):82–90
Schubauer GB, Klebanoff PS (1955) Contribution on the mechanism of boundary-layer transition, NACA TR-3489
Solomon W, Walker G, Gostelow J (1995) Transition length prediction for flows with rapidly changing pressure gradients. In: ASME 1995 international gas turbine and aeroengine congress and exposition. American Society of Mechanical Engineers, p V001T01A071
Volino R (2005) An investigation of the scales in transitional boundary layers under high free-stream turbulence conditions. Exp Fluids 38(4):516–533
Volino RJ, Schultz MP, Pratt CM (2001) Conditional sampling in a transitional boundary layer under high free-stream turbulence conditions. In: ASME turbo expo 2001: power for land, sea, and air. American Society of Mechanical Engineers, p V003T01A066
Zaki T (2013) From streaks to spots and on to turbulence: exploring the dynamics of boundary layer transition. Flow Turbul Combust 91:451–473
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The authors wish to acknowledge Prof. Ubaldi and Prof. Zunino for their precious discussions and suggestions.
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Simoni, D., Lengani, D. & Guida, R. A wavelet-based intermittency detection technique from PIV investigations in transitional boundary layers. Exp Fluids 57, 145 (2016). https://doi.org/10.1007/s00348-016-2231-8
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DOI: https://doi.org/10.1007/s00348-016-2231-8