A full-scale 3D Vs 2.5D Vs 2D analysis of flow pattern and forces for an industrial-scale 5MW NREL reference wind-turbine

Mandar Tabib, Adil Rasheed, M. Salman Siddiqui, Trond Kvamsdal
2017 Energy Procedia  
District heating networks are commonly addressed in the literature as one of the most effective solutions for decreasing the greenhouse gas emissions from the building sector. These systems require high investments which are returned through the heat sales. Due to the changed climate conditions and building renovation policies, heat demand in the future could decrease, prolonging the investment return period. The main scope of this paper is to assess the feasibility of using the heat demand
more » ... the heat demand -outdoor temperature function for heat demand forecast. The district of Alvalade, located in Lisbon (Portugal), was used as a case study. The district is consisted of 665 buildings that vary in both construction period and typology. Three weather scenarios (low, medium, high) and three district renovation scenarios were developed (shallow, intermediate, deep). To estimate the error, obtained heat demand values were compared with results from a dynamic heat demand model, previously developed and validated by the authors. The results showed that when only weather change is considered, the margin of error could be acceptable for some applications (the error in annual demand was lower than 20% for all weather scenarios considered). However, after introducing renovation scenarios, the error value increased up to 59.5% (depending on the weather and renovation scenarios combination considered). The value of slope coefficient increased on average within the range of 3.8% up to 8% per decade, that corresponds to the decrease in the number of heating hours of 22-139h during the heating season (depending on the combination of weather and renovation scenarios considered). On the other hand, function intercept increased for 7.8-12.7% per decade (depending on the coupled scenarios). The values suggested could be used to modify the function parameters for the scenarios considered, and improve the accuracy of heat demand estimations. Abstract NREL 5MW reference turbine, which is a popular, realistic and standardized industrial scale offshore turbine model, is used in this work for understanding the associated flow-complexities and for testing models. For such full-scale wind-turbine, the wish list is towards a accurate real-time prediction for better control and monitoring. Here, models like 2D based strip-theory [1] can help, but the extent of its applicability can be understood through a comparative performance of 2D Vs 2.5D Vs 3D CFD models. A stand-still blade condition is chosen for this study which can arise in a wind-farm when both yaw and pitch regulations are off-line. Further, even this simple stand-still condition is expected to have complex 3D effects due to blade geometry and due to the non-optimized conditions (blades twist being optimized for rotation). For such cases, the current work compares flow-profiles and forces computed by a 3D, 2.5D and 2D CFD models along the different sections of the NREL 5 MW turbine. The 2D CFD results are compared with experimentally measured drag and lift coefficient values as reported in DOWEC report [2] . The results from this study indicates that the flow close to the hub is dominated by complex 3D structures and unsteadiness while the three dimensionality and unsteadiness diminish as one moves away from the hub and towards the tip so much so that 2D simulations are sufficient for a faithful representation of the flow behavior. However, closer to the hub 2D simulations can not be utilized without adequate corrections. The work has implications for the 2D based approaches like strip-theory. Abstract NREL 5MW reference turbine, which is a popular, realistic and standardized industrial scale offshore turbine model, is used in this work for understanding the associated flow-complexities and for testing models. For such full-scale wind-turbine, the wish list is towards a accurate real-time prediction for better control and monitoring. Here, models like 2D based strip-theory [1] can help, but the extent of its applicability can be understood through a comparative performance of 2D Vs 2.5D Vs 3D CFD models. A stand-still blade condition is chosen for this study which can arise in a wind-farm when both yaw and pitch regulations are off-line. Further, even this simple stand-still condition is expected to have complex 3D effects due to blade geometry and due to the non-optimized conditions (blades twist being optimized for rotation). For such cases, the current work compares flow-profiles and forces computed by a 3D, 2.5D and 2D CFD models along the different sections of the NREL 5 MW turbine. The 2D CFD results are compared with experimentally measured drag and lift coefficient values as reported in DOWEC report [2] . The results from this study indicates that the flow close to the hub is dominated by complex 3D structures and unsteadiness while the three dimensionality and unsteadiness diminish as one moves away from the hub and towards the tip so much so that 2D simulations are sufficient for a faithful representation of the flow behavior. However, closer to the hub 2D simulations can not be utilized without adequate corrections. The work has implications for the 2D based approaches like strip-theory.
doi:10.1016/j.egypro.2017.10.372 fatcat:rz2gu3hiffebdjfm7xgra6ypna