UFORCE project

Our research aims at advancing the fundamental understanding of turbulence and wall shear stress in unsteady flows over rough as well as smooth surfaces, thereby underpinning the development of engineering models and flow control strategies.


Unsteady flow is commonplace in engineering systems as well as the natural environment, including for example, power plant startup or shutdown, the sudden closure of valves in a pipeline system, passenger trains going through a railway tunnel, the blood flow in the human body and waves over a beach.

Unsteady flow is also an intriguing topic of fundamental turbulence research since it reveals flow physics that is not always apparent in steady flows.

The research involves numerical modelling and experimental work. DNS and RANS methodologies and computer codes have been developed which are used to perform simulations generating detailed data/information on the flow behaviours.

These are complemented by experimental investigations performed in various large/sophisticated experimental facilities in several labs using LAD, PIV and hot-film anemometry. The new understanding is being implemented in the development of 1D unsteady friction models.

The flow pattern considered are accelerating, decelerating and pulsating flows. Two types of roughness as well as smooth surfaces will be studied.

Turbulence and wall shear stress in unsteady internal flows with rough surfaces (UFORCE) EPSRC, (EP/G068925/1), 2010-2013, Universities of Sheffield, Dundee and Aberdeen.

Previous projects

  • Theoretical and experimental study of the dependence of transient pipe friction on turbulence dynamics, EPSRC (EP/C015177/1), 2006-2008.
  • Unsteady friction in pipes and ducts, EC Frame 6 (C29.30/H 4957 EU Hydralab), 2007-2008.


UFORCE experimentation
UFORCE experimentation diagram


  1. He & M. Seddighi, Turbulence in transient channel flow. Journal of Fluid Mechanics, 715, pp. 60-102, 2013.
  2. S. He, C. Ariyaratne and A.E. Vardy, Wall shear stress in accelerating turbulent pipe flow, Journal of Fluid Mechanics, 685, pp. 440-460, 2011.
  3. M. Seddighi, S. He, P. Orlandi & A. Vardy, A comparative study of turbulence in a ramp-up and a ramp-down flow, Flow Turbulence and combustion, 86 (3-4), pp. 439-454, 2011.
  4. S. He, C. Ariyaratne, Wall shear stress in the early stage of unsteady turbulent pipe flow, J. Hydraul. Eng., 137 (5), pp. 606-610, 2011.
  5. C. Ariyaratne, S. He and A.E. Vardy, Wall Friction and Turbulence Dynamics in Decelerating Pipe Flows, Journal of Hydraulic Research, 48 (6), pp. 810-821, 2010.
  6. S. He and J.D. Jackson , ‘An experimental study of pulsating turbulent flow in a pipe’, European Journal of Mechanics – B/Fluids, Vol. 28, pp309-320, 2009.
  7. S. He, C. Ariyaratne and A.E. Vardy, ‘A computational study of wall friction and turbulence dynamics in accelerating pipe flows’, Computers and Fluids, Vol. 37, pp674-689, 2008.
  8. S. He and J.D. Jackson 'A study of turbulence under conditions of transient flow in a pipe’, Journal of Fluid Mechanics, vol. 408, pp1-38, 2000.
Unsteady Friction 
  1. C. Ariyaratne, S. He, A.E. Vardy. 'Wall shear stresses in decelerating pipe flows'. 33rd IAHR Congress. Water engineering for a sustainable environment, Vancouver, British Columbia, 9-14 August, 2009.
  2. A. E. Vardy, A. Bergant, S. He, C. Ariyaratne, T. Koppel, I. Annus, A. Tijsseling, D. Huo. 'Unsteady skin friction experimentation in a large diameter pipe'. 3rd IAHR meeting of the work group on cavitation and dynamic problems in hydraulic machinery and systems, Brno, Czech Republic, 14-16 October, 2009.
  3. A. Vardy, J. Brown and S. He, ‘Signs of unsteady skin friction’, presented at International Conference on pressure surges, 23-26 March 2004, Chester, UK.
  4. Vardy,AE & Brown,JMB (2010) ‘Evaluation of unsteady wall shear stress by Zielke’s method’, J Hydraulic Engineering, ASCE, Technical Note, 136(7), 453-456 [doi: 10.1061/(ASCE)HY.1943-7900.0000192 ]
  5. Vardy,AE & Brown,JMB (2010) ‘Influence of time-dependent viscosity on wall shear stresses in unsteady pipe flows’, J Hydraulics Research, 48(2), 225-237 [doi: 10.1080/00221681003726221]
  6. Vardy,AE & Brown,JMB (2011) ‘Laminar Pipe Flow with Time-dependent Viscosity’, J Hydroinformatics, 13(4), 729-740 [doi: 10.2166/hydro.2010.073]
  7. Vardy,AE (2012) ‘On asymptotic wavefronts in compressible flows’, Proc 11th int conf on Pressure Surges, Lisbon, Portugal, 24-26 Oct 2012, BHR Group, Ed: A.Anderson, 247-260 [ISBN: 978-1-85598-133-1]
  8. Shimada,M & Vardy,AE (2013) ‘Non-linear interaction of friction and interpolation errors in unsteady flow analyses’, J Hyd Engrg, ASCE, 139(4), 397-409 [DOI: 10.1061/(ASCE)HY.1943-7900.0000685]
Leak Detection - coastal
  1. Kikkert, G., O’Donoghue, T., Pokrajac, D., Dodd, N, Experimental study of bore-driven swash hydrodynamics on impermeable rough slopes, Coastal Engineerin, in press
  2. Pokrajac, D., Kikkert, G. RADINS equations for aerated shallow water flows over rough beds Journal of Hydraulic Research, in press
  3. Briganti, R., Dodd, N., Pokrajac, D., An efficient and flexible solver for the simulation of the morphodynamics of fast evolving flows on coarse sediment beaches, International Journal of Numerical Methods in Fluid, in press
  4. Steenhauer, K., Pokrajac, D., O'Donoghue, T. (2011) Simulation of bore propagation on permeable slopes using the ADER scheme, International Journal of Numerical Methods in Fluid, in press
  5. Steenhauer, K., Pokrajac, D., O'Donoghue, T., Kikkert, G. (2011) Subsurface processes generated by bore-driven swash on coarse-grained beaches, AGU Journal of Geophysical Research: Oceans, vol 116.
  6. Briganti, R., Dodd, N., Pokrajac, D., O’Donoghue, T. (2011) Non linear shallow water modelling of bore-driven swash: description of the bottom boundary layer, Coastal Engineering, 58(6): 463-477.

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