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A data assimilation model for turbulent flows using continuous adjoint formulation.

He, Chuangxin and Liu, Yingzheng and Gan, Lian (2018) 'A data assimilation model for turbulent flows using continuous adjoint formulation.', Physics of fluids., 30 (10). p. 105108.

Abstract

A generalized data assimilation model for turbulent flows using the continuous adjoint formulation is proposed. Within this formulation, the Spalart–Allmaras turbulence model is modified by adding a correction function β as a spatially varying coefficient to the turbulence production term. The model-form error is thus corrected by optimizing the β distribution, using the adjoint equations and the corresponding boundary conditions, to minimize the discrepancy between the predictions and observations. In addition, a constraint is applied to drive β toward a large value to avoid the flow unsteadiness owing to the low eddy viscosity. The present adjoint-based data assimilation (ABDA) model is expected to be applicable to various flow conditions unsolvable by the simple optimization of the model constant. This model is fully equation-driven and is thus computationally cheaper than the discretized adjoint method, as well as convenient to be implemented in the existing computational fluid dynamics codes. The flow over a cylinder with synthetic observations, the free round jet, the flow over a hump, and the three-dimensional flow over a wall-mounted cube, all of which are challenging for original Reynolds-averaged Navier–Stokes simulations, are employed to successfully demonstrate the reliability and capacity of the present ABDA model. The first-order scheme applied to the adjoint equations exhibits little effects on the final assimilation results, but improves the robustness significantly, and drives β to another solution that can also minimize the cost function. The present ABDA model is efficient in the heavy assimilation work of different types of shear and separated flows.

Item Type:Article
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Status:Peer-reviewed
Publisher Web site:https://doi.org/10.1063/1.5048727
Publisher statement:© 2018 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The following article appeared in He, Chuangxin, Liu, Yingzheng & Gan, Lian (2018). A data assimilation model for turbulent flows using continuous adjoint formulation. Physics of Fluids 30(10): 105108 and may be found at https://doi.org/10.1063/1.5048727
Date accepted:06 October 2018
Date deposited:09 November 2018
Date of first online publication:25 October 2018
Date first made open access:25 October 2019

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