Application Of Scale-Adaptive Turbulence Method To The Flow Around Slender Body Of Revolution

The large separation flows remains being highly concerned in the field of aerospace and weapon et al.,and in the numerical research of which,the development of turbulence model has been the bottleneck factor.In recent years,benefiting from the resoluton of turbulence spectrum and grid independency,the Scale-Adaptive Simulation(SAS)approach as a typical RANS/LES method,has received wide interest.Thus,SAS method is one of the major focuses and new SAS formulations are proposed in current study.By using the new SAS approach and numerically simulating the flows around slender bodies of revolution at high angle of attack,the flow unsteadiness and the Lee-side vortex oscillation were further researched in this practical complex engineering.The main contents of this study are indicated as follows:To avoid the issue of energy anomaly near the stagnation point in bluff body flows,a new reformulated production limiter considering the efforts of strain rate tensor and rotation tensor is proposed for the SAS method.Meanwhile,two other limiters only considering strain or vorticity are also conducted for compartion.By comparing the energy generation and turbulent viscosity level in different regions,the concrete mechanism and capabilities of different limiters in adjusting the turbulent energy are carefully tested through the typical test cases,and the adjusting capability of the recommended production limiter in bluff body flows is validated.By theoretically researching the von Karman scale and the grid scale,as well as the physical mechanism of SAS method and DES method,the correspondence between the two scales was analysed based on the equilibrium and the relations with the boundary layer thickness.A new ISAS(Improved SAS)method with the Scale-Adaptive concept and DES formulation was proposed by introducing the von Karman scale into the DES scale equation.The physical of ISAS model was obtained by analysising the adjust process of Lvk scale.Under different grid test cases,the comparison between ISAS,DES and SAS shows that the new ISAS method gives consideration to both computational efficiency and accuracy,and has the ability of grid sensiticity as well as turbulence spectrum formulation,which indicates the appropriate use of ISAS in the large separated flows.To choose the available grid generation method for the flow around slender bodies of revolution,different grid topologies were compared and the result shows the Fan topology has a higher precision.And then,The new ISAS model was employed to calculate the slender flow under different coditons.According to the steady and unsteady results,the effectiveness of the new ISAS method in the simulation of slender flow has been confirmed.The unsteady axial evolution can be divided into random high-frequency oscillation region,preriodic low-frequency oscillation region and the von Karman region,through the analysis of the forebody frequency spectra associated with the vortex oscillation features.The unsteady characteristics of slender flows along with the angle of attack shows that as the angle increasing,the section frequency becomes larger and the low frequency region moves closer to the nose apex as well as the von Karman region.Based on the representation and induction relationship of the instantaneous lee-side vortices,the detailed processes of the low-frequency vortex oscillation are achieved:the vortex oscillation always begins with the breaking of the remaining vortex,which is the triggering factor of the unsteady features in the slender flow.Based on the idea of "vortex dividing and divided",the influence of the vortex oscillation to the axial evolution and the aerodynamic characteristics of slender flow are also gained:as the incidence increasing,the unsteady axial evolution becomes faster and the section force becomes smaller because of the vortex oscillation.The correlations between the unsteady aerodynamic data and the vortex oscillation are obtained according to the force distribution front and behind the vortex breaking.the unsteady lee-side vortices oscillation law along the incidences is summarized:as the angle of the attack increasing,the vortex breaking loction moves closer to the nose apex,the vortex breaking becomes more obvious and the vortex oscillation amplitude becomes larger.Finally,the correlations between the low-frequency vortex oscillation and the tip perturbation are studied by changing the perturbation circumferential location,The relation between the vortices rising order,the location of the vortex breaking,and the location of the tip perturbation is obtained.The numerical result shows that the low-frequency oscillation of vortex is related to the perturbation sensitivity.