Advertisement

Sādhanā

, Volume 41, Issue 9, pp 1019–1037 | Cite as

Turbulence characteristics of open channel flow over non-equilibrium 3-D mobile dunes

  • Prashanth Reddy HanmaiahgariEmail author
  • Ram Balachandar
Article
  • 152 Downloads

Abstract

This paper reports velocity measurements over mobile dunes using an acoustic Doppler velocimetry (ADV). Experiments were conducted with two different flow conditions resulting in the formation of two different size mobile dunes. Dunes height, wavelength and velocity of dunes found to be increasing with increase in average flow velocity for a constant flow depth. The quasi-stationary bed condition was assumed while measuring the velocity distribution along the depth. The effect of the non-equilibrium mobile dunes on the flow characteristics and turbulence is examined by computing turbulent intensities, turbulent kinetic energy and Reynolds shear stresses using time averaged and time–space averaged velocity measurements. The magnitudes of transverse velocities are approximately 1/10 of streamwise velocities and vertical velocities are approximately half of the transverse velocities. The considerable magnitudes of transverse velocities over mobile bedforms necessitate measurement of 3-D velocity components to analyze the flow field. Computed turbulence intensities are found to be maximum in the region consisting of the trough and the reattachment point of the dunes. It is observed that streamwise turbulence intensities near the bed are twice the transverse turbulence intensities, and transverse turbulence intensities are twice the vertical turbulence intensities. Reynolds stresses (transverse fluxes of streamwise and vertical momentum) are observed to be high on mobile bedforms which shows mobile dunes reinforce the secondary currents. Peak values of turbulent kinetic energy (TKE) and Reynolds stresses are also found in the region consisting of the trough and the reattachment point. It is visually observed in the present experiments that maximum erosion takes place at the reattachment point and eroded sediment is carried as total load and dropped on the lee slope of the subsequent downstream dune. This phenomenon is caused by flow expansion in the separation zone, and which is also the main reason for mobility of dunes and associated bedload transport. Most importantly, it is found that turbulence anisotropy increases with increase in size of mobile bedforms and anisotropy is extended up to the free surface in the flows over mobile bedforms, which proves the entire depth of flow is being disturbed by the mobile dunes.

Keywords

Mobile bedforms sediment transport turbulence bed shear stress open channel flow ADV 

References

  1. 1.
    Maji S, Hanmaiahgari P R and Subhasish Dey 2014 Experimental studies of local scour in the pressurized OCF below a wooden log across the flow. Sadhana 39(5): 1245–1257. DOI:  10.1007/s12046-014-0267-0 CrossRefGoogle Scholar
  2. 2.
    Hanmaiahgari P R, Hanif Chaudhry M and Jasim Imran 2015 Computation of gradually varied flow in compound open channel networks. Sadhana 39(6): 1523–1545. DOI:  10.1007/s12046-014-0299-5 MathSciNetzbMATHGoogle Scholar
  3. 3.
    Bennett S and Best J L 1995 Mean flow and turbulence structure over fixed, two dimensional ripples: Implications for sediment transport and bedform stability. Sedimentology 42: 491–513CrossRefGoogle Scholar
  4. 4.
    Balachandar R and Patel V C 2008 Flow over a fixed rough dune, Can. J. Civil Eng. 35: 511–520CrossRefGoogle Scholar
  5. 5.
    Bennett S J and Best J L 1996 Mean flow and turbulence structure over fixed ripples and the ripple-dune transition. In: P J Ashworth et al (Eds) Coherent flow structures in open channels. pp. 281–304, John Wiley, Hoboken, NJGoogle Scholar
  6. 6.
    Best J L 2005 The fluid dynamics of river dunes: A review and some future research directions. J. Geophys. Res. 110: 1CrossRefGoogle Scholar
  7. 7.
    Balachandar R, Hyun B-S and Patel V C 2007 Effect of depth on flow over a fixed dune. Can. J. Civil Eng. 34: 1587–1599CrossRefGoogle Scholar
  8. 8.
    Balachandar R and Bhuiyan F 2007 Higher-order moments of velocity fluctuations in an open channel flow with large bottom roughness. J. Hydraul. Eng. 133: 77–87CrossRefGoogle Scholar
  9. 9.
    Robert A and Uhlman W 2001 An experimental study of the ripple-dune transition. Earth Surf. Process. Landforms 26: 615–629CrossRefGoogle Scholar
  10. 10.
    Coleman S E, Nikora V I, McLean S R, Clunie T M, Schlicke T and Melville B W 2006 Equilibrium hydrodynamics concept for developing dunes. Phys. Fluids 18(10): 105104-1-12Google Scholar
  11. 11.
    Nikora V and Goring D 2000 Flow turbulence over fixed and weakly mobile gravel beds. J. Hydraul. Eng. 126(9): 679–690CrossRefGoogle Scholar
  12. 12.
    Bridge J S and Best J L 1988 Flow, sediment transport and bedform dynamics over the transition from dunes to upper-stage plane beds: Implications for the formation of planar lamination. Sedimentology 35: 753–763CrossRefGoogle Scholar
  13. 13.
    Schindler R J and Robert A 2005 Flow and turbulence structure across the ripple-dune transition: An experiment under mobile bed conditions. Sedimentology 52, doi: 10.1111/j.1365-3091.2005.00706x
  14. 14.
    Nikora V I and Goring D G 1998 ADV measurements of turbulence: Can we improve their interpretation. J. Hydraul. Eng. 124(6): 630–634CrossRefGoogle Scholar
  15. 15.
    Chanson H, Trevethan M and Aoki S 2008 Acoustic Doppler Velocimetry (ADV) in small estuary: Field experience and signal post-processing. Flow Meas. Instrum. 19(5): 307–313CrossRefGoogle Scholar
  16. 16.
    Goring D and Nikora V 2002 Despiking acoustic Doppler velocimeter data. J. Hydraul. Eng. 128(1): 117–126CrossRefGoogle Scholar
  17. 17.
    Wahl T L 2000 Analyzing ADV Data using WinADV. Joint Conference on Water Resources Engineering and Water Resources Planning and Management, American Society of Civil Engineers, July 30 – August 2, 2000, Minneapolis, MinnesotaGoogle Scholar
  18. 18.
    Wahl T L 2003 Discussion of despiking acoustic Doppler velocimeter data. J. Hydraul. Eng. 129(6): 484–487CrossRefGoogle Scholar
  19. 19.
    Mori N, Suzuki T and Kakuno S 2007 Noise of acoustic Doppler velocimeter data in bubbly flow. J. Eng. Mech. ASCE 133(1): 122–125CrossRefGoogle Scholar
  20. 20.
    Gyr A and Schmid A 1997 Turbulent flows over smooth erodible sand beds in flumes. J. Hydraul. Res. 35(4): 525–544CrossRefGoogle Scholar
  21. 21.
    Song T, Graf W H and Lemmin U 1994 Uniform flow in open channels with gravel bed. J. Hydraul. Res. 32(6): 861–876CrossRefGoogle Scholar
  22. 22.
    Nezu I and Nakagawa H 1993 Turbulence in open channel flows. IAHR Monograph, Balkema, RotterdamzbMATHGoogle Scholar
  23. 23.
    Krogstad P, Antonia R, and Browne L 1992 Comparison between rough-and-smooth-walled turbulent boundary layers. J. Fluid Mech. 245: 599–617.CrossRefGoogle Scholar
  24. 24.
    Holmes R R and Garcia M H 2008 Flow over bedforms in a large sand-bed river: A field investigation. J. Hydraul. Res. 46(3): 322–333CrossRefGoogle Scholar
  25. 25.
    Balachandar R and Patel V C 2002 Rough wall boundary layer on plates in open channels. J. Hydraul. Eng. ASCE 128(10): 947–951.CrossRefGoogle Scholar
  26. 26.
    Raupach M R, Antonia R A and Rajagopalan S 1991 Roughwall turbulent boundary layers. Appl. Mech. Rev. 44: 1–25CrossRefGoogle Scholar
  27. 27.
    Camenen B, Bayram A and Larson M 2006 Equivalent roughness height for plane bed under steady flow. J. Hydraul. Eng. 132(11): 1146–1158CrossRefGoogle Scholar
  28. 28.
    Sumer B M, Chua L H C, Cheng N-S and Fredsoe J 2003 Influence of turbulence on bed load sediment transport. J. Hydraul. Eng. 129(8): 585–596CrossRefGoogle Scholar

Copyright information

© Indian Academy of Sciences 2016

Authors and Affiliations

  • Prashanth Reddy Hanmaiahgari
    • 1
    Email author
  • Ram Balachandar
    • 2
  1. 1.Department of Civil EngineeringIndian Institute of Technology KharagpurKharagpurIndia
  2. 2.Department of Civil and Environmental EngineeringUniversity of WindsorWindsorCanada

Personalised recommendations