ABSTRACT High Reynolds number flow inside a channel of rectangular cross section is examined using Particle Image Velocimetry. One wall of the channel has been replaced with a surface of a roughness representative to that of real hydropower tunnels, i.e. a random terrain with roughness dimensions typically in the range of ≈10% - 20% of the channels hydraulic radius. The rest of the channel walls can be considered smooth. The rough surface was captured from an existing blasted rock tunnel using high resolution laser scanning and scaled to 1:10. For quantification of the size of the largest flow structures, integral length scales are derived from the auto-correlation functions of the temporally averaged velocity. Additionally, Proper Orthogonal Decomposition (POD) and higher-order statistics are applied to the instantaneous snapshots of the velocity fluctuations. The results show a high spatial heterogeneity of the velocity and other flow characteristics in vicinity of the rough surface, putting outer similarity treatment into jeopardy. Roughness effects are not confined to the vicinity of the rough surface but can be seen in the outer flow throughout the channel, indicating a different behavior than postulated by Townsend’s similarity hypothesis. The effects on the flow structures vary depending on the shape and size of the roughness elements leading to a high spatial dependence of the flow above the rough surface. Hence, any spatial averaging, e.g. assuming a characteristic sand grain roughness factor, for determining local flow parameters becomes less applicable in this case.
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Andersson, L. , Larsson, I. , Hellström, J. , Andreasson, P. , Andersson, A. and Lundström, T. (2018) Characterization of Flow Structures Induced by Highly Rough Surface Using Particle Image Velocimetry, Proper Orthogonal Decomposition and Velocity Correlations. Engineering, 10, 399-416. doi: 10.4236/eng.2018.107028.
 Bråtveit, K., Lia, L. and Olsen, N.R.B. (2012) An Efficient Method to Describe the Geometry and the Roughness of an Existing Unlined Hydro Power Tunnelin. Energy Procedia, 20, 200-206. https://doi.org/10.1016/j.egypro.2012.03.020
 Perfect, E. (1997) Fractal Models for the Fragmentation of Rocks and Soils: A Review. Engineering Geology, 48, 185-198.
 Chanson, H. (2004) The Hydraulics of Open Channel Flow: An Introduction, 2nd Edition, Elsevier, Amsterdam.
 Andersson, L.R., Larsson, I.A.S., Hellström, J.G.I., Andreasson, P. and Andersson, A.G. (2016) Experimental Study of Head Loss over Laser Scanned Rock Tunnelin. 6th International Symposium on Hydraulic Structures, Portland, 27-30 June 2016, 22-29.
 Andersson, L.R., Hellström, J.G.I., Andreasson, P. and Andersson, A.G. (2015) Numerical Simulation of Artificial and Natural Rough Surfacesin. APS 2015 Proceedings, Orlando, 20-25 June 2015.
 Bråtveit, K., Bruland, A. and Brevik, O. (2016) Rock Falls in Selected Norwegian Hydropower Tunnels Subjected to Hydropeaking. Tunnelling and Underground Space Technology, 52, 202-207. https://doi.org/10.1016/j.tust.2015.10.003
 Reinius, E. (1986) Rock Erosion. International Water Power & Dam Construction, 38, 43-48.
 Patel, S.M., Sondergeld, C.H. and Rai, C.S. (2017) Laboratory Studies of Hydraulic Fracturing by Cyclic Injection. International Journal of Rock Mechanics and Mining Sciences, 95, 8-15. https://doi.org/10.1016/j.ijrmms.2017.03.008
 Grass, A.J. (1971) Structural Features of Turbulent Flow over Smooth and Rough Boundaries. Journal of Fluid Mechanics, 50, 233-255.
 Jiménez, J. (2004) Turbulent Flows over Rough Walls. Annual Review of Fluid Mechanics, 36, 173-196. https://doi.org/10.1146/annurev.fluid.36.050802.122103
 Pope, S.B. (2001) Turbulent Flows. IOP Publishing, Bristol.
 Kruse, N., Kuhn, S. and Rudolf von Rohr, P. (2006) Wavy Wall Effects on Turbulence Production and Large-Scale Modes. Journal of Turbulence, 7, No. 31.
 Cheng, H. and Castro, I.P. (2002) Near Wall Flow over Urban-Like Roughness. Boundary-Layer Meteorology, 104, 229-259.
 Schlichting, H. and Gersten, K. (2003) Boundary-Layer Theory. 8th Edition, Springer Science, Berlin.
 Seddighi, M., He, S., Pokrajac, D., O’donoghue, T. and Vardy, A.E. (2015) Turbulence in a Transient Channel Flow with a Wall of Pyramid Roughness Journal of Fluid Mechanics, 781, 226-260.
 Krogstad, P. and Antonia, R. (1999) Surface Roughness Effects in Turbulent Boundary Layers. Experiments in Fluids, 27, 450-460.
 Patel, V. (1998) Perspective: Flow at High Reynolds Number and over Rough Surfaces—Achilles Heel of CFD. Journal of Fluids Engineering, 120, 434-444.
 Bennett, S.J. and Best, J.L. (1995) Mean Flow and Turbulence Structure over Fixed, Two-Dimensional Dunes: Implications for Sediment Transport and Bedform Stability. Sedimentology, 42, 491-513.
 Buffin-Bélanger, T., Rice, S., Reid, I. and Lancaster, J. (2006) Spatial Heterogeneity of Near-Bed Hydraulics above a Patch of River Gravel. Water Resources Research, 42, W04413. https://doi.org/10.1029/2005WR004070
 Nikora, V., McEwan, I., McLean, S., Coleman, S., Pokrajac, D. and Walters, R. (2007) Double-Averaging Concept for Rough-Bed Open-Channel and Overland Flows: Theoretical Background. Journal of Hydraulic Engineering, 133, 873-883.
 Zhao, Y., Wang, G.-C. and Lu, T.-M. (2006) Characterization of Amorphous and Crystalline Rough Surface: Principles and Applications. Academic Press, Cambridge.
 Sarkar, S. and Dey, S. (2010) Double-Averaging Turbulence Characteristics in Flows over a Gravel Bed. Journal of Hydraulic Research, 48, 801-809.
 Larsson, I.A.S., Granström, B.R., Lundström, T.S. and Marjavaara, D. (2012) PIV Analysis of Merging Flow in a Rotary Kiln. Experiments in Fluids, 53, 545-560.
 Andersson, A.G., Andreasson, P., Hellström, J.G.I. and Lundström, T.S. (2012) Modelling and Validation of Flow over a Wall with Large Surface Roughness.
 Raffel, M., Willert, C.E., Wereley, S.T. and Kompenhans, J. (2007) Particle Image Velocimetry: A Practical Guide.
 Montgomery, D.C. (2012) Design and Analysis of Experiments.
 Coleman, H.W. and Steele, W.G. (2009) Experimentation, Validation, and Uncertainty Analysis for Engineers. 3rd Edition.
 Balakumar, B.J., et al. (2009) High Resolution Experimental Measurements of Richtmyer-Meshkov Turbulence in Fluid Layers after Reshock Using Simultaneous PIV-PLIF. Proceedings of the APS Topical Group on Shock Compression of Condensed Matter, Nashville, December 2009, Volume 1195.
 (2007) LaVision Gmbh Product Manual for Davis 7.2.
 Westerweel, J. and Scarano, F. (2005) Universal Outlier Detection for PIV Data. Experiments in Fluids, 39, 1096-1100.
 Bakewell, H.P. (1967) Viscous Sublayer and Adjacent Wall Region in Turbulent Pipe Flow. The Physics of Fluids, 10, 1880.
 Erik Meyer, K., Cavar, D. and Pedersen, J.M. (2007) POD as Tool for Comparison of PIV and LES Data.
 Yue, W., Meneveau, C., Parlange, M.B., Zhu, W., Van Hout, R. and Katz, J. (2007) A Comparative Quadrant Analysis of Turbulence in a Plant Canopy. Water Resources Research, 43, W05422. https://doi.org/10.1029/2006WR005583
 Hanjalic, K. and Launder, B.E. (1972) Fully Developed Asymmetric Flow in a Plane Channel. Journal of Fluid Mechanics, 51, 301-335.
 Nakagawa, S., Na, Y. and Hanratty, T. (2003) Influence of a Wavy Boundary on Turbulence. I. Highly Rough Surface. Experiments in Fluids, 35, 422-436.
 Tennekes, H. and Lumley, J.L. (1972) A First Course in Turbulence.
 Roy, A.G., Buffin-Bélanger, T., Lamarre, H. and Kirkbride, A.D. (2004) Size, Shape and Dynamics of Large-Scale Turbulent Flow Structures in a Gravel-Bed River. Journal of Fluid Mechanics, 500, 1-27. https://doi.org/10.1017/S0022112003006396