Assessment of RANS turbulence closure models for predicting airflow in neutral ABL over hilly terrain

Abstract

Implementing wind farms in heights of a hilly terrain where wind speed is expected to be large may be viewed as a means to increase wind energy production without occupying fertile lands. Micro sitting of a wind farm in these conditions can gain dramatically from CFD simulation of fluid flow in the ABL above complex topography. However, this issue still poses tough challenges regarding the turbulence model to be used and the way to operate the near wall treatment in the presence eventually of separation. In this work, prediction capacity of RANS turbulence models was studied for a typical hill under the assumption of steady state and incompressible airflow regime in neutral ABL. Two models were analyzed by using COMSOL Multiphysics software packages. These included standard , and shear-stress transport . The most up-to-date procedures dedicated to near wall treatment were applied along with refined closer coefficients adjusted for the particular case of ABL. Considering wind tunnel test data, performance of the previous models was discussed in terms of converging mesh, computational time, reattachment point position and propensity of the model to retrieve the right level of turbulence flow in conditions of neutral stratifications. Then, a numerical simulation of the turbulent airflow over two slopes shapes of the symmetry hill by the validation of the experimental data has been then carried out. Both turbulence models agree well with air-velocity tested windward of the hills H3 and H5. Therefore, it was found that the standard model performs very well at the different positions of the low slope hill, and at the summit of a steep hill, but it over-predicts wind speed close to the wall, which requires an improvement of the near-wall treatment. However, the model in neutral case of the ABL was given consistent simulation results with experimental data for prediction of the flow separation and recirculation region at the leeward side of a steep hill, whereas standard model under the neutral condition and the model by using standard coefficients were failed to predict accurately detailed characteristics of recirculation region process.

Performance Evaluation of the RANS Models in Predicting the Pollutant Concentration Field within a Compact Urban Setting: Effects of the Source Location and Turbulent Schmidt Number

“…That refers to a relatively larger scatter that is primarily due to the available deviations at the edge of the plume, where the concentrations are relatively low, and even minor differences between observed and predicted values could lead to considerably large VG values. As suggested by previous studies, the inaccurate representation of the turbulence field by two-equation viscosity models can be one of the primary sources of discrepancies found between the predictions and measurements [30,31,33]. In this regard, making a comparison between the predicted wind and turbulence flow field by all the studied closure models in this work is beneficial.…”

“…As suggested by previous studies, the inaccurate representation of the turbulence field by two-equation viscosity models can be one of the primary sources of discrepancies found between the predictions and measurements [30,31,33]. In this regard, making a comparison between the predicted wind and turbulence flow field by all the studied closure models in this work is beneficial.…”

“…Narjisse et al, evaluated the capability of the standard k − ε and Shear Stress Transport (SST) k − ω in accurately resolving the wind flow in the presence of a hilly terrain [30]. They concluded that even though standard k − ε overpredicted the wind velocity near the wall, it was still a more reasonable choice for modeling the flow for these geometries than SST k − ω which offered slightly better predictions at a much higher computational cost.…”

Computational fluid dynamics simulations of silicon μ-structure formation during excimer laser modification of silicon-nanoparticle layers

“…The direct linear solver PARDISO was used to solve a linearized version of the nonlinear system in each iteration, by applying the Newton method. The direct solver uses Gaussian elimination to solve the linearized matrix system and has been shown to be more robust than iterative solvers [15]. The chosen model settings resulted in a computation time of approx.…”

CFD modeling of the turbulent airflow over open hilly terrain: Effect of inhomogeneous ABL in neutral conditions

“…In order to attain an important potential of wind energy, it is necessary to implement the wind turbines in places where there is strong wind. For this reason, several researches have focused on the study of the airflow around hills, given the acceleration that is created on the top of the hill (Lubitz and White 2007;Narjisse and Abdellatif 2021;Yang et al 2021;Zheng and Tian 2018).…”