Airworthiness regulations require that the transport airplane should be proved to ensure the survivability of the ditching for the passengers. The planned ditching of a transport airplane on the calm water is numerica...Airworthiness regulations require that the transport airplane should be proved to ensure the survivability of the ditching for the passengers. The planned ditching of a transport airplane on the calm water is numerically simulated. The effect of pitch angle on the impact characteristics is especially investigated by a subscaled model. The Reynolds-averaged Navier-Stokes （RANS） equations of unsteady compressible flow are solved and the realizable j-e equations are employed to model the turbulence. The transformation of the air-water interface is tracked by volume of fluid （VOF） model. The motion of the rigid body is modeled by dynamic mesh method. The initial ditching stage of the transport airplane is analyzed in detail. The numerical results show that as the pitching angle increases, the maximal normal force decreases and the pitching motion becomes much gentler. The aft fuselage would be sucked down by the water and lead to pitching up, whereas the low horizontal tail prevents this trend. Consequently, the transport aircraft with low horizontal tail should ditch on the water at an angle between 10 and 12 as a recommendation.展开更多
Different scaling behaviors, such as Kolmogorov (K41) scaling and Bolgiano and Obukhov (BO) scaling, have been reported in various shell models proposed for turbulent thermal convection. However, two coexistent subran...Different scaling behaviors, such as Kolmogorov (K41) scaling and Bolgiano and Obukhov (BO) scaling, have been reported in various shell models proposed for turbulent thermal convection. However, two coexistent subranges with K41 and BO scaling are not set up with Bolgiano scale interlaying between the largest scale and the dissipation scale. In this paper, we summarize fixed-point solution study of the Brandenburg model with small perturbation theory by introducing a small disturbance term as the impact of buoyancy. Three groups of fixed-point solutions with different locations of the so-called buoyancy scale, above/below which buoyancy is significant/insignifant. Both theoretical and numerical results show that a modified K41 scaling, instead of K41 and BO coexistent scaling, is set up even though buoyancy may be significant over the scaling range, which suggests that the buoyancy scale is not related exactly to the Bolgiano scale. Thus, a K41 and BO coexistent scaling behavior is not setup for the Brandenburg model.展开更多
基金co-supported by Aeronautical Science Foundation of China (No.20102351023)Research Fund for the Doctoral Program of Higher Education of China (No. 20091102120021)
文摘Airworthiness regulations require that the transport airplane should be proved to ensure the survivability of the ditching for the passengers. The planned ditching of a transport airplane on the calm water is numerically simulated. The effect of pitch angle on the impact characteristics is especially investigated by a subscaled model. The Reynolds-averaged Navier-Stokes （RANS） equations of unsteady compressible flow are solved and the realizable j-e equations are employed to model the turbulence. The transformation of the air-water interface is tracked by volume of fluid （VOF） model. The motion of the rigid body is modeled by dynamic mesh method. The initial ditching stage of the transport airplane is analyzed in detail. The numerical results show that as the pitching angle increases, the maximal normal force decreases and the pitching motion becomes much gentler. The aft fuselage would be sucked down by the water and lead to pitching up, whereas the low horizontal tail prevents this trend. Consequently, the transport aircraft with low horizontal tail should ditch on the water at an angle between 10 and 12 as a recommendation.
基金supported by the National Natural Science Foundation of China (Grant No.10902007)the Fundamental Research Funds for the Central Universitiesthe National Basic Research Program of China (Grant No.2009CB724001)
文摘Different scaling behaviors, such as Kolmogorov (K41) scaling and Bolgiano and Obukhov (BO) scaling, have been reported in various shell models proposed for turbulent thermal convection. However, two coexistent subranges with K41 and BO scaling are not set up with Bolgiano scale interlaying between the largest scale and the dissipation scale. In this paper, we summarize fixed-point solution study of the Brandenburg model with small perturbation theory by introducing a small disturbance term as the impact of buoyancy. Three groups of fixed-point solutions with different locations of the so-called buoyancy scale, above/below which buoyancy is significant/insignifant. Both theoretical and numerical results show that a modified K41 scaling, instead of K41 and BO coexistent scaling, is set up even though buoyancy may be significant over the scaling range, which suggests that the buoyancy scale is not related exactly to the Bolgiano scale. Thus, a K41 and BO coexistent scaling behavior is not setup for the Brandenburg model.
