A numerical investigation to analyze effect of turbulence and ground clearance on the performance of a roof top vertical–axis wind turbine

Abstract

Recent attempts to discover energy–efficient and cost–effective power generation systems unleash tremendous capabilities of urban rooftops vertical–axis wind turbines (VAWT). Their advantages of Omni–directionality, low noise and less maintenance cost allow direct integration to urban neighborhood having unstable wind conditions. Despite continuous effort to investigate performance under a range of operating conditions, aspects such as Turbulent Intensity (TI) and ground clearance remain relatively less explored. Such effects originate either due to sharp topographical variations or placement of the turbine blades in proximity to the ground. In the present work, we perform a parametric study to quantify the performance of VAWT under various levels of TI and ground clearance. We conduct high fidelity Computational Fluid Dynamics (CFD) simulations using ANSYS Fluent and k−ε turbulence model. The H-type VAWT is employed having rated power of 1.5kW, diameter (D)of 2.5mchord length (c) of 0.2m and operates at prescribed wind speed (U0)of 12.0m/sand Tip Speed Ratio (TSR) of 1.5–4.5. We determine the performance of turbine under four levels of TI i.e., 0%, 5%, 15%25%at five ground clearance levels of 1.0c,2.5c,4.0c,7.5cand 10.0c. The results show a performance loss of 30.10%, 20.65%, 10.65% at turbine clearance heights of 1.0c,2.5c, 4.0c respectively. The height of 7.5c yield higher and more consistent performance under given operating conditions. The results for induced turbulence identify a decrease in the performance up to 45.42% corresponding to 25%TI level.