Estimating parameter and discretization uncertainties using a laminar–turbulent transition model

2021 ◽  
Vol 230 ◽  
pp. 105129
Author(s):  
Eduardo Tadashi Katsuno ◽  
Artur K. Lidtke ◽  
Bülent Düz ◽  
Douwe Rijpkema ◽  
João L.D. Dantas ◽  
...  
Keyword(s):  
Transition Model ◽  
Turbulent Transition ◽  
Laminar Turbulent Transition

scholarly journals Recurrent neural network for end-to-end modeling of laminar-turbulent transition

2021 ◽  
Vol 2 ◽  
Author(s):  
Muhammad I. Zafar ◽  
Meelan M. Choudhari ◽  
Pedro Paredes ◽  
Heng Xiao
Keyword(s):  
Neural Network ◽  
Recurrent Neural Network ◽  
Transition Model ◽  
Large Set ◽  
Two Dimensional ◽  
Turbulent Transition ◽  
Wide Range ◽  
Network Methods ◽  
End To End ◽  
Laminar Turbulent Transition

Abstract Accurate prediction of laminar-turbulent transition is a critical element of computational fluid dynamics simulations for aerodynamic design across multiple flow regimes. Traditional methods of transition prediction cannot be easily extended to flow configurations where the transition process depends on a large set of parameters. In comparison, neural network methods allow higher dimensional input features to be considered without compromising the efficiency and accuracy of the traditional data-driven models. Neural network methods proposed earlier follow a cumbersome methodology of predicting instability growth rates over a broad range of frequencies, which are then processed to obtain the N-factor envelope, and then, the transition location based on the correlating N-factor. This paper presents an end-to-end transition model based on a recurrent neural network, which sequentially processes the mean boundary-layer profiles along the surface of the aerodynamic body to directly predict the N-factor envelope and the transition locations over a two-dimensional airfoil. The proposed transition model has been developed and assessed using a large database of 53 airfoils over a wide range of chord Reynolds numbers and angles of attack. The large universe of airfoils encountered in various applications causes additional difficulties. As such, we provide further insights on selecting training datasets from large amounts of available data. Although the proposed model has been analyzed for two-dimensional boundary layers in this paper, it can be easily generalized to other flows due to embedded feature extraction capability of convolutional neural network in the model.

scholarly journals Laminar-turbulent transition characteristics of a 3-D wind turbine rotor blade based on experiments and computations

2020 ◽  
Vol 5 (4) ◽  
pp. 1487-1505
Author(s):  
Özge Sinem Özçakmak ◽  
Helge Aagaard Madsen ◽  
Niels Nørmark Sørensen ◽  
Jens Nørkær Sørensen
Keyword(s):  
Wind Turbine ◽  
Field Experiments ◽  
Transition Model ◽  
Bypass Transition ◽  
Cfd Simulations ◽  
Turbulent Transition ◽  
Inflow Turbulence ◽  
Blade Section ◽  
Transition Models ◽  
Laminar Turbulent Transition

Abstract. Laminar-turbulent transition behavior of a wind turbine blade section is investigated in this study by means of field experiments and 3-D computational fluid dynamics (CFD) rotor simulations. The power spectral density (PSD) integrals of the pressure fluctuations obtained from the high-frequency microphones mounted on a blade section are analyzed to detect laminar-turbulent transition locations from the experiments. The atmospheric boundary layer (ABL) velocities and the turbulence intensities (T.I.) measured from the field experiments are used to create several inflow scenarios for the CFD simulations. Results from the natural and the bypass transition models of the in-house CFD EllipSys code are compared with the experiments. It is seen that the bypass transition model results fit well with experiments at the azimuthal positions where the turbine is under wake and high turbulence, while the results from other cases show agreement with the natural transition model. Furthermore, the influence of inflow turbulence, wake of an upstream turbine, and angle of attack (AOA) on the transition behavior is investigated through the field experiments. On the pressure side of the blade section, at high AOA values and wake conditions, variation in the transition location covers up to 44 % of the chord during one revolution, while for the no-wake cases and lower AOA values, variation occurs along a region that covers only 5 % of the chord. The effect of the inflow turbulence on the effective angle of attack as well as its direct effect on transition is observed. Transition locations for the wind tunnel conditions and field experiments are compared together with 2-D and 3-D CFD simulations. In contrast to the suction side, significant difference in the transition locations is observed between wind tunnel and field experiments on the pressure side for the same airfoil geometry. It is seen that the natural and bypass transition models of EllipSys3D can be used for transition prediction of a wind turbine blade section for high-Reynolds-number flows by applying various inflow scenarios separately to cover the whole range of atmospheric occurrences.

scholarly journals Numerical modelling of turbulent transition in complex geometries

2018 ◽  
Vol 180 ◽  
pp. 02057
Author(s):  
Petr Louda ◽  
Jaromír Příhoda ◽  
Karel Kozel
Keyword(s):  
Numerical Simulation ◽  
Wind Tunnel ◽  
Numerical Modelling ◽  
Separation Bubble ◽  
Complex Geometries ◽  
Transition Model ◽  
Transonic Flows ◽  
Turbulent Transition ◽  
2D Model ◽  
Laminar Turbulent Transition

The work deals with numerical simulation of laminar-turbulent transition in transonic flows in turbine cas-cades. The 3D cascade geometry as well as 2D model cascade in a wind tunnel is simulated. The γ-ζ transition model is based on empirical criteria for start of the transition. The implementation of the model is discussed including re-formulation of the criterion for transition on separation bubble.

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