Inflow turbulence generation using an equivalent boundary layer model

Abstract

Eddy-resolved simulation of external flow usually requires inflow boundary conditions representing a turbulent boundary layer (TBL) flow, and the quality of the inflow turbulent fluctuation directly impact the accuracy and the cost of the simulation. The present study proposes a new method to generate TBL inflow turbulence, i.e., the equivalent boundary layer (EBL) model. Based on the open-channel model, EBL approximates TBL flow at a given Reynolds number by recovering the mean momentum balance with driving force. It simulates streamwise homogeneous turbulence, applying periodic boundary conditions and, thus, overcomes the complexity and artificiality incurred by the classic recycling–rescaling methods. The current paper discusses the difference between turbulent channel and boundary layer flows from the equation point of view and designs the driving force corresponding to the mean inertial force of boundary layer. Also, the total shear stress models for obtaining the driving force are validated both a priori and a posteriori. Direct numerical simulations (DNS) are carried out for EBLs at Reθ=1000,1420, and 2000 (where Reθ is the Reynolds number based on the momentum thickness), showing that the EBL model well reflects the statistical characteristics of TBL at corresponding Reynolds numbers. The application of the EBL model for the generation of inflow turbulence is also demonstrated by DNS of turbulent boundary layers with inlet Reθ=1000,1420, and 2000. The computational results agree well with generally acknowledged DNS data published in the literature, in terms of streamwise developing statistics, and profiles and energy spectra at characteristic cross sections. Judging from the mean velocity, the adjustment section is shorter than one boundary layer thickness.