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Spatio-temporal dynamics of flow separation induced by a forward-facing step submerged in a thick turbulent boundary layer

Published online by Cambridge University Press:  14 April 2020

Xingjun Fang Open the ORCID record for Xingjun Fang [Opens in a new window]  and
Mark F. Tachie Open the ORCID record for Mark F. Tachie [Opens in a new window]
Xingjun Fang*
Affiliation:
Department of Mechanical Engineering, University of Manitoba, Winnipeg, Manitoba,R3T 5V6, Canada
Mark F. Tachie
Affiliation:
Department of Mechanical Engineering, University of Manitoba, Winnipeg, Manitoba,R3T 5V6, Canada
*
†Email address for correspondence: fangx@myumanitoba.ca
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Abstract

The effects of large-scale motion (LSM) on the spatio-temporal dynamics of separated shear layers induced by a forward-facing step submerged in a thick turbulent boundary layer (TBL) are investigated using a time-resolved particle image velocimetry. The Reynolds number based on the free-stream velocity and step height was 13 200. The oncoming TBL was developed over a cube-roughened surface and the thickness was 6.5 times the step height. The step height was chosen to coincide with the elevation where the dominant frequency of streamwise fluctuating velocity in the TBL occurred. At this elevation, the local turbulence intensity was 14.5 %. Distinct regions of elevated Reynolds stresses were observed upstream and downstream of the leading edge of the step. The unsteady dynamics of the separation bubbles upstream and downstream of the step was investigated using the reverse flow area. Both separation bubbles exhibit low-frequency flapping motion, and the dominant frequency of the downstream separation bubble is identical to the dominant frequency of the streamwise fluctuating velocity in the oncoming TBL at the step height. As the low-velocity region of LSM passes over the step, the downstream separation bubble is enlarged and subsequently undergoes a high-frequency oscillation. Turbulence motions were partitioned into low-, medium- and high-frequency regimes based on spectral analysis of the Reynolds stresses. The contributions from these partitioned turbulence motions are used to elucidate the effects of LSM on the elevated Reynolds stresses in the shear layers upstream and downstream of the step.

JFM classification

Boundary Layers: Boundary layer separation Turbulent Flows: Turbulent boundary layers
Type
JFM Papers
Information
Journal of Fluid Mechanics , Volume 892 , 10 June 2020 , A40
Copyright
© The Author(s), 2020. Published by Cambridge University Press

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References

Addad, Y., Laurence, D., Talotte, C. & Jacob, M. C. 2003 Large eddy simulation of forward–backward facing step for acoustic source identification. Intl J. Heat Fluid Flow 24, 562–571.CrossRefGoogle Scholar
Adrian, R. J., Meinhart, C. D. & Tomkins, C. D. 2000 Vortex organization in the outer region of the turbulent boundary layer. J. Fluid Mech. 422, 1–54.CrossRefGoogle Scholar
Adrian, R. J. & Moin, P. 1988 Stochastic estimation of organized turbulent structure: homogeneous shear flow. J. Fluid Mech. 190, 531–559.CrossRefGoogle Scholar
Awasthi, M., Devenport, W. J., Glegg, S. A. L. & Forest, J. B. 2014 Pressure fluctuations produced by forward steps immersed in a turbulent boundary layer. J. Fluid Mech. 756, 384–421.CrossRefGoogle Scholar
Blackburn, H. M., Mansour, N. N. & Cantwell, B. J. 1996 Topology of fine-scale motions in turbulent channel flow. J. Fluid Mech. 310, 269–292.CrossRefGoogle Scholar
Blackwelder, R. F. & Kaplan, R. E. 1976 On the wall structure of the turbulent boundary layer. J. Fluid Mech. 76 (1), 89–112.CrossRefGoogle Scholar
Bogard, D. G. & Tiederman, W. G. 1986 Burst detection with single-point velocity measurements. J. Fluid Mech. 162, 389–413.CrossRefGoogle Scholar
Bogard, D. G. & Tiederman, W. G. 1987 Characteristics of ejections in turbulent channel flow. J. Fluid Mech. 179, 1–19.CrossRefGoogle Scholar
Camussi, R., Felli, M., Pereira, F., Aloisio, G. & Di Marco, A. 2008 Statistical properties of wall pressure fluctuations over a forward-facing step. Phys. Fluids 20, 075113.CrossRefGoogle Scholar
Castro, I. P. 1979 Relaxing wakes behind surface-mounted obstacles in rough wall boundary layers. J. Fluid Mech. 93 (4), 631–659.CrossRefGoogle Scholar
Castro, I. P. & Robins, A. G. 1977 The flow around a surface-mounted cube in uniform and turbulent streams. J. Fluid Mech. 79, 307–335.CrossRefGoogle Scholar
Chalmers, H. A., Nyantekyi-Kwakye, B., Fang, X. & Tachie, M. F. 2019 Aspect ratio effects on turbulent flow over forward-backward-facing steps. In CSME-CFDSC Congress 2019 June 2–5, London, Ontario, Canada.Google Scholar
Christensen, K. T. & Adrian, R. J. 2001 Statistical evidence of hairpin vortex packets in wall turbulence. J. Fluid Mech. 431, 433–443.CrossRefGoogle Scholar
Cook, N. J. 1978 Wind tunnel simulation of the adiabatic atmospheric boundary layer by roughness, barrier and mixing device methods. J. Wind Engng Ind. Aerodyn. 3, 157–176.CrossRefGoogle Scholar
Elyasi, M. & Ghaemi, S. 2019 Experimental investigation of coherent structures of a three-dimensional separated turbulent boundary layer. J. Fluid Mech. 859, 1–32.CrossRefGoogle Scholar
Essel, E. E., Nematollahi, A., Thacher, E. W. & Tachie, M. F. 2015 Effects of upstream roughness and Reynolds number on separated and reattached turbulent flow. J. Turbul. 16 (9), 872–899.CrossRefGoogle Scholar
Essel, E. E. & Tachie, M. F. 2017 Upstream roughness and Reynolds number effects on turbulent flow structure over forward facing step. Intl J. Heat Fluid Flow 66, 226–242.CrossRefGoogle Scholar
Fang, X. & Tachie, M. F. 2019a Flows over surface-mounted bluff bodies with different spanwise widths submerged in a deep turbulent boundary layer. J. Fluid Mech. 877, 717–758.CrossRefGoogle Scholar
Fang, X. & Tachie, M. F. 2019b On the unsteady characteristics of turbulent separations over a forward-backward-facing step. J. Fluid Mech. 863, 994–1030.CrossRefGoogle Scholar
Fang, X. & Tachie, M. F. 2020 Tracking the flapping motion of flow separation using pointwise measurement. Phys. Fluids 32, 035106.CrossRefGoogle Scholar
Flack, K. A., Schultz, M. P. & Shapiro, T. A. 2005 Experimental support for Townsend’s Reynolds number similarity hypothesis on rough walls. Phys. Fluids 17, 035102.CrossRefGoogle Scholar
Ganapathisubramani, B., Hutchins, N., Monty, J. P., Chung, D. & Marusic, I. 2012 Amplitude and frequency modulation in wall turbulence. J. Fluid Mech. 712, 61–91.CrossRefGoogle Scholar
Graziani, A., Kerhervé, F., Martinuzzi, R. J. & Keirsbulck, L. 2018 Dynamics of the recirculating areas of a forward-facing step. Exp. Fluids 59, 154.CrossRefGoogle Scholar
Graziani, A., Lippert, M., Uystepruyst, D. & Keirsbulck, L. 2017 Scaling and flow dependencies over forward-facing steps. Intl J. Heat Fluid Flow 67, 220–229.CrossRefGoogle Scholar
Hattori, H. & Nagano, Y. 2010 Investigation of turbulent boundary layer over forward-facing step via direct numerical simulation. Intl J. Heat Fluid Flow 31 (3), 284–294.CrossRefGoogle Scholar
Hearst, R. J., Gomit, G. & Ganapathisubramani, B. 2016 Effect of turbulence on the wake of a wall-mounted cube. J. Fluid Mech. 804, 513–530.CrossRefGoogle Scholar
Humble, R. A., Scarano, F. & Van Oudheusden, B. W. 2009 Unsteady aspects of an incident shock wave/turbulent boundary layer interaction. J. Fluid Mech. 635, 47–74.CrossRefGoogle Scholar
Ji, M. & Wang, M. 2010 Sound generation by turbulent boundary-layer flow over small steps. J. Fluid Mech. 654, 161–193.CrossRefGoogle Scholar
Jiménez, J. 1991 Kinematic alignment effects in turbulent flows. Phys. Fluids A 4 (4), 652–654.CrossRefGoogle Scholar
Lanzerstorfer, D. & Kuhlmann, H. C. 2012 Three-dimensional instability of the flow over a forward-facing step. J. Fluid Mech. 695, 390–404.CrossRefGoogle Scholar
Largeau, J. F. & Moriniere, V. 2007 Wall pressure fluctuations and topology in separated flows over a forward-facing step. Exp. Fluids 42, 21–40.CrossRefGoogle Scholar
Lim, H. C., Castro, I. P. & Hoxey, R. P. 2007 Bluff bodies in deep turbulent boundary layers: Reynolds-number issues. J. Fluid Mech. 571, 97–118.CrossRefGoogle Scholar
Liu, H.-Y., Bo, T.-L. & Liang, Y.-R. 2017 The variation of large-scale structure inclination angles in high Reynolds number atmospheric surface layers. Phys. Fluids 29, 035104.CrossRefGoogle Scholar
Luchik, T. S. & Tiederman, W. G. 1987 Timescale and structure of ejections and bursts in turbulent channel flows. J. Fluid Mech. 174, 529–552.CrossRefGoogle Scholar
Marino, L. & Luchini, P. 2009 Adjoint analysis of the flow over a forward-facing step. Theor. Comput. Fluid Dyn. 23, 37–54.CrossRefGoogle Scholar
Mathis, R., Hutchins, N. & Marusic, I. 2009 Large-scale amplitude modulation of the small-scale structures in turbulent boundary layers. J. Fluid Mech. 628, 311–337.CrossRefGoogle Scholar
Mohammed-Taifour, A. & Weiss, J. 2016 Unsteadiness in a large turbulent separation bubble. J. Fluid Mech. 799, 383–412.CrossRefGoogle Scholar
Moin, P. & Kim, J. 1985 The structure of the vorticity field in turbulent channel flow. Part 1. Analysis of instantaneous fields and statistical correlations. J. Fluid Mech. 155, 441–464.CrossRefGoogle Scholar
Monty, J. P., Hutchins, N., Ng, H. C. H., Marusic, I. & Chong, M. S. 2009 A comparison of turbulent pipe, channel and boundary layer flows. J. Fluid Mech. 632, 431–442.CrossRefGoogle Scholar
Moss, W. D. & Baker, S. 1980 Re-circulating flows associated with two-dimensional steps. Aeronaut. Q. 31 (3), 151–172.CrossRefGoogle Scholar
Nematollahi, A. & Tachie, M. F. 2018 Time-resolved PIV measurement of influence of upstream roughness on separated and reattached turbulent flows over a forward-facing step. AIP Adv. 8, 105110.CrossRefGoogle Scholar
Pearson, D. S., Goulart, P. J. & Ganapathisubramani, B. 2013 Turbulent separation upstream of a forward-facing step. J. Fluid Mech. 724, 284–304.CrossRefGoogle Scholar
Ren, H. & Wu, Y. 2011 Turbulent boundary layers over smooth and rough forward-facing steps. Phys. Fluids 23, 045102.CrossRefGoogle Scholar
Rosenberg, B. J., Hultmark, M., Vallikivi, M., Bailey, S. C. C. & Smits, A. J. 2013 Turbulence spectra in smooth- and rough-wall pipe flow at extreme Reynolds numbers. J. Fluid Mech. 731, 46–63.CrossRefGoogle Scholar
Sherry, M., Lo Jacono, D. & Sheridan, J. 2010 An experimental investigation of the recirculation zone formed downstream of a forward facing step. J. Wind Engng Ind. Aerodyn. 98 (12), 888–894.CrossRefGoogle Scholar
Stüer, H., Gyr, A. & Kinzelbach, W. 1999 Laminar separation on a forward facing step. Eur. J. Mech. (B/Fluids) 18, 675–692.CrossRefGoogle Scholar
Taylor, G. I. 1938 The spectrum of turbulence. Proc. R. Soc. Lond. A 164 (919), 476–490.CrossRefGoogle Scholar
Thacker, A., Aubrun, S., Leroy, A. & Devinant, P. 2013 Experimental characterization of flow unsteadiness in the centerline plane of an Ahmed body rear slant. Exp. Fluids 54, 1479.CrossRefGoogle Scholar
Vinuesa, R., Hites, M. H., Wark, C. E. & Nagib, H. M. 2015 Documentation of the role of large-scale structures in the bursting process in turbulent boundary layers. Phys. Fluids 27, 105107.CrossRefGoogle Scholar
Volina, R. J., Schultz, M. P. & Flack, K. A. 2009 Turbulence structure in a boundary layer with two-dimensional roughness. J. Fluid Mech. 635, 75–101.CrossRefGoogle Scholar
Wilhelm, D., Härtel, C. & Kleiser, L. 2003 Computational analysis of the two-dimensional-three-dimensional transition in forward-facing step flow. J. Fluid Mech. 489, 1–27.CrossRefGoogle Scholar
Wu, Y. & Christensen, K. T. 2007 Outer-layer similarity in the presence of a practical rough-wall topography. Phys. Fluids 19, 085108.CrossRefGoogle Scholar
Wu, Y. & Christensen, K. T. 2010 Spatial structure of a turbulent boundary layer with irregular surface roughness. J. Fluid Mech. 655, 380–418.CrossRefGoogle Scholar