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ACTA AERONAUTICAET ASTRONAUTICA SINICA ›› 2022, Vol. 43 ›› Issue (7): 125512-125512.doi: 10.7527/S1000-6893.2021.25512

• Fluid Mechanics and Flight Mechanics • Previous Articles     Next Articles

Influence of “frozen viscosity assumption” on solution and gradient accuracy of adjoint system

WU Hangkong, WANG Dingxi, HUANG Xiuquan, XU Shenren   

  1. School of Power and Energy, Northwestern Polytechnical University, Xi'an 710072, China
  • Received:2021-03-17 Revised:2021-04-22 Published:2021-04-21
  • Supported by:
    National Science and Technology Major Project (2017-Ⅱ-009-0023); Innovation Foundation for Doctor Dissertation of Northwestern Polytechnical University (CX2022045)

Abstract: The introduction of the "frozen viscosity assumption" can simplify the derivation of the adjoint equation and the differentiation of flow solver subroutines, but can also lead to computational errors of sensitivities and sometimes even solution instability. To investigate the effect of laminar viscosity and eddy viscosity on computational accuracy of sensitivities, this paper presents a study on three different frozen viscosity approaches:the Frozen Laminar Viscosity approach(FLV), Frozen Eddy Viscosity approach(FEV) and Frozen Laminar and Eddy Viscosity approach(FLEV). First, the adjoint equations corresponding to full turbulence and three different frozen viscosity approaches are derived based upon the nonlinear flow equations and the objective function in an algebraic form. Then, we introduce how to use the algorithm differentiation tool to develop the discrete adjoint solver and provide the corresponding flow charts. Finally, the transonic NASA Rotor 67 is used to study the effects of different frozen viscosity approaches on solution stability, sensitivity convergence, sensitivity accuracy and asymptotic convergence rate of residual at different operating points(a peak efficiency point and a near stall point) of the adjoint solver. The results are compared with those of the linear solver and the adjoint solver with full turbulence.

Key words: adjoint solver, frozen viscosity assumption, frozon laminar viscosity approach, frozen eddy viscosity approach, frozen laminer and eddy viscosity approach, algorithm differentiationhttp

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