Abstract
Efficient numerical simulation of renewable energy wind and tidal turbines is important for the layout of devices in farms. Computational Fluid Dynamics (CFD) approaches using blade geometry resolved models are computationally expensive. Therefore, most array models use source term representations of rotors, normally actuator disk, actuator line or blade element disk. Unfortunately, these methods rarely capture enough physics to accurately predict power and at the same time correctly characterise the wake velocity field and turbulent structures.This study describes a new Generalised Actuator Disk CFD model (GAD-CFD), that achieves the required accuracy for the simulation of horizontal axis wind and tidal turbines and their wakes. This new method combines a finite volume CFD code with additional source terms representing the rotor, including: correct consideration of losses along the foil by modification of the distribution of downwash; a concise downwash distribution computation; recognition that foil cross section varies along the length; dynamically changing Reynolds numbers and the application of a tip radius correction. Also reported are foil lift and drag coefficients and their variation with thickness, surface roughness and Reynolds number, which is necessary for the proper characterisation the whole rotor.The effectiveness of this approach is investigated and validated against two experiments, and demonstrates improvements over traditional source term methods, in particular the correct CFD approach to tip losses and consequent downstream wake prediction. This study provides confidence in application to both small scale flume studies and large scale array deployments in both the marine and wind environments.
Highlights
IntroductionThe success in recent years of the renewable energy sector in demonstrating significant progress developing offshore wind and marine energy technologies are of particular interest at the current time as the availability of offshore regions for device development and deployment increase
The success in recent years of the renewable energy sector in demonstrating significant progress developing offshore wind and marine energy technologies are of particular interest at the current time as the availability of offshore regions for device development and deployment increase.While wind turbines are migrating from onshore deployments to offshore locations aiming for increased energy yield, the marine energy sector is progressing renewable energy generation technology based on the predictability of tidal flow [1]
As S809 data from JavaFoil is unavailable, a Computational fluid dynamics (CFD) simulation of the S809 foil section is conducted for the correct Reynolds numbers, the performance in the stall region is slightly inflated in the same fashion as the JavaFoil predictions discussed above, see Fig. 6
Summary
The success in recent years of the renewable energy sector in demonstrating significant progress developing offshore wind and marine energy technologies are of particular interest at the current time as the availability of offshore regions for device development and deployment increase. The growing demands of these sectors require investments in improved knowledge and technology [4,5] This can be achieved through the study of: analytical modelling, numerical modelling, practical experiment, and deployment [6e8]. Efficient CFD models of arrays typically use actuator disk, actuator line or blade element disk approaches as outlined below in the literature review. In all these methods the absence of fully resolved turbine foils in the flow regime requires assumptions regarding the flow characteristics to predict the correct turbine operating conditions.
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