Environmental Technology, School of Industrial Technology, Universiti Sains Malaysia, USM 11800, Pulau Pinang, Malaysia


Turbulence intensity measurements of vertical axis wind turbine (VAWT) are essential to detemineitsefficiency and performance. In this study, the eddy covariance (EC) method was used to characterise the flow and directly measure turbulence of a VAWT in a controlled indoor laboratory using an ultrasonic anemometer (at 10 Hz) at specific grid positions of upwind and downwind (in the wake) of the VAWT. In constrast to numerical simulations, this method has the potential to accurately quantify turbulence of wind turbines and thus able to describe the flow patterns around a VAWTexperimentally. Results show that at the upwind position, some of the swept area of the VAWT obstructed the flow due to the counter current flow generated by the VAWT rotors’ rotation while causing some flows to be diverted and concentrated to the concurrent flow area of the VAWT. In the wake of the VAWT, flow velocities and turbulence decreased and dispersed while at the centre line, vertical turbulence decreased towards the bottom (ground) swept area.This downward transfer of turbulence caused generally negative vertical momentum transfer. However, a slight increase of turbulence was observed at the ground surface due to flow deflection.


1.     Shafiullah,  G.M.,  A.M.T.  Oo,  A.B.M.S.  Ali,  and  P.  Wolfs, 2013.Potential challenges of integrating large-scale wind energy into the power grid - A review. Renewable & Sustainable Energy Reviews, 20: 306-321.
2.     Mertens, S., Wind Energy in Urban Area. 2002 Delft University of Technology: Holland.
3.     Balduzzi,  F.,  A.  Bianchini,  E.A.  Carnevale,  L.  Ferrari,  S, Magnani, 2012.Feasibility analysis of a  Darrieus vertical-axis wind turbine installation in the rooftop of a building. Applied Energy, 97: 921-929.
4.     Dayan,  E., 2006.Wind energy in buildings: Power generation from wind in the urban environment - where it is needed most. Refocus, 7: 33-38.
5.     H'ng, Y., Y. Yusup, H.P.S. Abdul Khalil, and T. Teng, 2014.Pilot study on indoor flows and turbulence statistics of a vertical axis wind turbine. Mechanical Engineering Research, 4: 63-78.
6.     Dabiri, J.O., 2011.Potential order-of-magnitude enhancement of wind farm power density via counter-rotating vertical-axis wind turbine arrays. Journal of Renewable and Sustainable Energy,3: 043104(1-12).
7.     Kinzel, M., Q. Mulligan, and J.O. Dabiri, 2013. Energy exchange in an array of vertical axis wind turbines. Journal of Turbulence, 14: 38-39.
8.     Cristobal,  U.R.N.,  A.  Gallegos-Munoz,  and  R.A.J.  Manuel. Numerical Analysis of a Rooftop Vertical Axis Wind Turbine. in ASME 2011 5th International Conference on Energy Sustainability, Parts A, B, and C2012. Washington, DC, USA.
9.     Ebert, P.R. and D.H. Wood, 1997.The near wake of a model horizontal-axis wind turbine - I. Experimental arrangements and initial results. Renewable Energy, 12: 225-243.
10.   Fernando, M.S.U. and V.J. Modi, 1989. A numerical-analysis of the unsteady-flow past a Savonius wind turbine. Journal of Wind Engineering and Industrial Aerodynamics, 32: 303-327.
11.   Vermeer, L.J., J.N. Sorensen, and A. Crespo, 2003. Wind turbine wake aerodynamics. Progress in Aerospace Sciences, 39: 467-510.
12.   Yang, Z.F., P. Sarkar, and H. Hu, 2012.Visualization of the tip vortices in a wind turbine wake. Journal of Visualization, 15: 39-44.
13.   Yao,   J.,   J.L.   Wang,   W.B.   Yuan,   H.M.   Wang,   L.   Cao, 2012.Analysis on the influence of turbulence model changes to aerodynamic performance of vertical axis wind turbine. International Conference on Advances in Computational Modeling and Simulation, 31: 274-281.
14.   Breton, S.P., K. Nilsson, S. Ivanell, H. Olivares-Espinosa, C. Masson, and L. Dufresne, 2012. Comparative CFD study of the effect of the presence of downstream turbines on upstream ones using  a  rotational  speed  control  system.  Science  of  Making Torque from Wind 2014. 555.
15.   Barthelmie,  R.J.,  L.  Folkerts,  G.C.  Larsen,  K.  Rados,  S.  T. Frandsenet, S. C. Pryor, B. Lange, and G. Schepers, 2006. Comparison of wake model simulations with offshore wind turbine wake profiles measured by sodar. Journal of Atmospheric and Oceanic Technology, 23: 888-901.
16.   Tabrizi, A.B., J. Whale, T. Lyons, and T. Urmee, 2015.Rooftop wind monitoring campaigns for small wind turbine applications: Effect of sampling rate and averaging period. Renewable Energy, 77: 320-330.
17.   Troldborg, N., J.N. Sorensen, and R. Mikkelsen, 2007.Actuator line simulation of wake of wind turbine operating in turbulent inflow - art. no. 012063. Science of Making Torque from Wind, 75: 12063-12063.
18.   Hunt, J.C.R. and J.F. Morrison, 2000. Eddy structure in turbulent boundary layers. European Journal of Mechanics B-Fluids, 19: 673-694.