LF
L. Florentie
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Vortex generators (VGs) are awidespread means of passive flowcontrol, capable of yielding significant performance improvements to lift-generating surfaces (e.g. wind-turbine blades and airplane wings), by delaying boundary-layer separation. These small vanetype structures, which are typically arranged in arrays, trigger the formation of small vortices in the boundary layer. The flow circulation induced by these vortices causes the near-wall flow to be re-energized, thereby reducing the susceptibility of the boundary layer to separate from the surface.
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Vortex generators (VGs) are awidespread means of passive flowcontrol, capable of yielding significant performance improvements to lift-generating surfaces (e.g. wind-turbine blades and airplane wings), by delaying boundary-layer separation. These small vanetype structures, which are typically arranged in arrays, trigger the formation of small vortices in the boundary layer. The flow circulation induced by these vortices causes the near-wall flow to be re-energized, thereby reducing the susceptibility of the boundary layer to separate from the surface.
An optimization approach is presented that can be used to find the optimal source term distribution in order to represent a high-fidelity vortex-generator (VG) induced flow field on a coarse mesh. The ap- proach employs the continuous adjoint of the problem, from which an exact sensitivity is calculated and used in combination with a trust-region method to find the source term which minimizes the deviation with respect to the reference velocity field. The algorithm is applied to an incompressible flow over a rectangular VG and VG pair on a flat plate and compared to results obtained with the jBAY-model and a body-fitted mesh simulation. The results indicate that a highly accurate flow, yielding only minimal errors with respect to the shape factor, circulation and vortex core, can be obtained on coarse meshes when adding a source term to only a limited number of cells. This approach therefore demonstrates the potential of source-term models to include the effects of VGs in computations of large-scale geometries. It also allows quantification of the achievable accuracy on a particular mesh and the calculation of the source term which is optimal for a specific situation. Furthermore, the optimization approach can be used to diagnose the deficiencies of an existing source-term VG model, in this work the jBAY model.
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An optimization approach is presented that can be used to find the optimal source term distribution in order to represent a high-fidelity vortex-generator (VG) induced flow field on a coarse mesh. The ap- proach employs the continuous adjoint of the problem, from which an exact sensitivity is calculated and used in combination with a trust-region method to find the source term which minimizes the deviation with respect to the reference velocity field. The algorithm is applied to an incompressible flow over a rectangular VG and VG pair on a flat plate and compared to results obtained with the jBAY-model and a body-fitted mesh simulation. The results indicate that a highly accurate flow, yielding only minimal errors with respect to the shape factor, circulation and vortex core, can be obtained on coarse meshes when adding a source term to only a limited number of cells. This approach therefore demonstrates the potential of source-term models to include the effects of VGs in computations of large-scale geometries. It also allows quantification of the achievable accuracy on a particular mesh and the calculation of the source term which is optimal for a specific situation. Furthermore, the optimization approach can be used to diagnose the deficiencies of an existing source-term VG model, in this work the jBAY model.
Vortex generators (VGs) are a widely used means of flow control, and predictions of their influence are vital for efficient designs. However, accurate CFD simulations of their effect on the flow field by means of a body fitted mesh are computationally expensive. Therefore the BAY and jBAY models, which represent the effect of VGs on the flow using source terms in the momentum equations, are popular in industry. In this contribution we examine the ability of the BAY and jBAY model to provide accurate flow field results by looking at boundary layer properties close behind VGs. The results are compared with both body fitted mesh and other source term model RANS simulations of 3D incompressible flows, over flat plate and airfoil geometries. We show the influence of mesh resolution and domain of application on the accuracy of the models and investigate the influence of the source term on the generated flow field. Our results demonstrate the grid dependence of the models and indicate the presence of model errors. Furthermore we find that the total applied force has a larger influence on both the intensity and shape of the created vortex than the distribution of the source term over the cells.
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Vortex generators (VGs) are a widely used means of flow control, and predictions of their influence are vital for efficient designs. However, accurate CFD simulations of their effect on the flow field by means of a body fitted mesh are computationally expensive. Therefore the BAY and jBAY models, which represent the effect of VGs on the flow using source terms in the momentum equations, are popular in industry. In this contribution we examine the ability of the BAY and jBAY model to provide accurate flow field results by looking at boundary layer properties close behind VGs. The results are compared with both body fitted mesh and other source term model RANS simulations of 3D incompressible flows, over flat plate and airfoil geometries. We show the influence of mesh resolution and domain of application on the accuracy of the models and investigate the influence of the source term on the generated flow field. Our results demonstrate the grid dependence of the models and indicate the presence of model errors. Furthermore we find that the total applied force has a larger influence on both the intensity and shape of the created vortex than the distribution of the source term over the cells.
Journal article
(2016)
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Daniel Baldacchino, M. M Manolesos, N.N. So rensen, Nando Timmer, N. Troldborg, S. Voutsinas, Alexander van Zuijlen, Carlos Simao Ferreira, A Gonzalez Salcedo, M. Aparicio, T. Chaviaropoulos, K. Diakakis, Liesbeth Florentie, M. Garcia, G Papadakis
Experimental results and complimentary computations for airfoils with vortex generators are compared in this paper, as part of an e_ort within the AVATAR project to develop tools for wind turbine blade control devices. Measurements from two airfoils equipped with passive vortex generators, a 30% thick DU97W300 and an 18% thick NTUA T18 have been used for benchmarking several simulation tools. These tools span low-to-high complexity, ranging from engineering-level integral boundary layer tools to fully-resolved computational uid dynamics codes. Results indicate that with appropriate calibration, engineering-type tools can capture the e_ects of vortex generators and outperform more complex tools. Fully resolved CFD comes at a much higher computational cost and does not necessarily capture the increased lift due to the VGs. However, in lieu of the limited experimental data available for calibration, high _delity tools are still required for assessing the e_ect of vortex generators on airfoil performance.
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Experimental results and complimentary computations for airfoils with vortex generators are compared in this paper, as part of an e_ort within the AVATAR project to develop tools for wind turbine blade control devices. Measurements from two airfoils equipped with passive vortex generators, a 30% thick DU97W300 and an 18% thick NTUA T18 have been used for benchmarking several simulation tools. These tools span low-to-high complexity, ranging from engineering-level integral boundary layer tools to fully-resolved computational uid dynamics codes. Results indicate that with appropriate calibration, engineering-type tools can capture the e_ects of vortex generators and outperform more complex tools. Fully resolved CFD comes at a much higher computational cost and does not necessarily capture the increased lift due to the VGs. However, in lieu of the limited experimental data available for calibration, high _delity tools are still required for assessing the e_ect of vortex generators on airfoil performance.
Computing the flow past Vortex Generators
Comparison between RANS Simulations and Experiments
Journal article
(2016)
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M. M Manolesos, NN Sorensen, N. Troldborg, Liesbeth Florentie, G Papadakis, S. Voutsinas
The flow around a wind turbine airfoil equipped with Vortex Generators (VGs) is examined. Predictions from three different Reynolds Averaged Navier Stokes (RANS) solvers with two different turbulence models and two different VG modelling approaches are compared between them and with experimental data. The best results are obtained with the more expensive fully resolved VG approach. The cost efficient BAY model can also provide acceptable results, if grid related numerical diffusion is minimized and only force coefficient polars are considered.
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The flow around a wind turbine airfoil equipped with Vortex Generators (VGs) is examined. Predictions from three different Reynolds Averaged Navier Stokes (RANS) solvers with two different turbulence models and two different VG modelling approaches are compared between them and with experimental data. The best results are obtained with the more expensive fully resolved VG approach. The cost efficient BAY model can also provide acceptable results, if grid related numerical diffusion is minimized and only force coefficient polars are considered.