Inflow turbulence generation for large eddy simulation in non-isothermal boundary layers

Many studies have presented the importance of turbulent inflow data for large eddy simulation, and several techniques have been proposed for generating inflow fluctuations for LES in a neutral boundary layer, but few studies have considered non-isothermal cases. In this study, first wind tunnel experiments were conducted to generate both unstable and stable turbulent thermal boundary layers in a thermally stratified wind tunnel at Tokyo Polytechnic University. The decrease of turbulence due to the effect of buoyancy was clearly observed in a stable boundary layer. Then a precursor method using a long domain and a recycling procedure using a short domain to generate the turbulence statistics corresponding to the experimental data were investigated for both unstable and stable conditions. The characteristics of the generated flow (mean profiles and fluctuation profiles) by both methods agreed relatively well with those of the wind tunnel experimental data. When a recycling procedure was adopted to generate turbulence statistics in a stable boundary layer, large damping was necessary to decrease the turbulence level. For the temperature field, giving only a mean profile (no temperature fluctuation) as an inflow boundary condition of the driver region was the simplest way. Even if the inflow temperature fluctuation was not given, temperature fluctuation gradually developed in the downstream direction with velocity fluctuation in the turbulent boundary layer.