| Tactical weapons usually fly in a rotation mode,producing a Magnus effect which influences flight performances such as stability of aircrafts.The missile body flying in rotation mode is generally of a body of revolution.Experimental studies show that mechanism producing the Magnus effect is very complex,comprising a lot of factors.However,the factors such as boundary layer asymmetric distortion are always neglected in previous theoretical or numerical studies,which results in great difference in results from experimental data and even the variation is different.For example,a phenomenon that negative Magnus effect happens when the body of revolution flies at small attact angle and low rotational speed is observed in the experiment but not calculated in the theoretical or numerical studies.Therefore,in order to better calculate Magnus effect of a rotating body of revolution,a numerical method to effectively simulate the asymmetric distortion of boundary layer transition is developed and the relevant flow mechanism of a rotating body of revolution is revealed through numerical simulations.A γ-Re_θtransition model proposed by Menter and Langtry has been successfully applied to simulate some subsonic flows.However,experience correlations of theγ-Re_θtransition model are developed based on experimental data of incompressible flat plates.Therefore,theγ-Re_θtransition model was modified through freestream turbulence intensity decay correction,rotation and curvature correction,crossflow transition correction and compressibility correction,according to the flow characteristic of a rotating body of revolution,to obtain aγ-Re_θ-SR-RC-CF-CC transition model capable of effectively simulating the asymmetric distortion of boundary layer transition and revealing the relevant flow mechanism of the Magnus effect of a rotating body of revolution.Firstly,a γ-Re_θ-SR transition model considering freestream turbulence intensity decay correction was developed by applying SR correction proposed by Spalart and Rumsey to theγ-Re_θtransition model.Theγ-Re_θ-SR transition model was used to simulate the flow past a two-dimensional stationary cylinder and results show:compared with theγ-Re_θtransition model,theγ-Re_θ-SR transition model predicts a more accurate boundary layer transition position of the cylinder,and theγ-Re_θ-SR transition model is able to effectively simulate flow characteristics of the cylinder,such as boundary layer transition and separation,at subcritical,critical and supercritical Reynolds numbers and reveal the flow mechanism thereof.Subsequently,a γ-Re_θ-SR-RC transition model considering both the freestream turbulence intensity decay correction and the rotation and curvature correction is developed by coupling theγ-Re_θ-RC transition model with the SST-CC turbulence model,which was verified through flow past a three-dimensional stationary cylinder.And then theγ-Re_θ-SR-RC transition model was applied to the mechanism research of a negative Magnus effect acting on a two-dimensional rotating cylinder.The results show that for a high-speed rotation or large curvature flow,theγ-Re_θ-SR-RC transition model can effectively capture the influences of rotation or curvature on the generation of turbulence kinetic energy and the flow characteristics such as boundary layer transition.The negative Magnus effect of a two-dimensional rotating cylinder was effectively simulated by a numerical simulation method for the first time.The analysis of the flow structure reveals that the influence of asymmetric distortion of boundary layer transition on boundary layer asymmetric separation is the primary factor of the negative Magnus effect.Then,crossflow transition correction to the γ-Re_θ-SR-RC transition model was carried out by a transition momentum thickness Reynolds number additional source term method to obtain aγ-Re_θ-SR-RC-CF transition model,which is applied to the mechanism research of negative Magnus effect of an ogive cylinder at a subsonic speed,a low dimensionless rotating speed and a small attack angle.The results show that when the Reynolds number is relatively high,theγ-Re_θ-SR-RC transition model fails to capture the boundary layer transition induced by crossflow instability,but theγ-Re_θ-SR-RC-CF transition model can effectively predict the crossflow transition,so that the crossflow transition correction must be considered in the research of Magnus effect of rotating body of revolution.In addition,the deflection of the flow separation area on the lee side and the low pressure area on the tail and the asymmetric distortion of boundary layer transition,caused by rotation introduce the negative Magnus effect.And finally,based on a supersonic flat plate,the compressibility correction to theγ-Re_θ-SR-RC-CF transition model is carried out by means of the correction to the empirical correlation of a transition momentum thickness Reynolds number Reθ_t so as to obtain aγ-Re_θ-SR-RC-CF-CC transition model,and theγ-Re_θ-SR-RC-CF-CC transition model is applied to the research of Magnus effect of a supersonic three-dimensional rotating sharp cone.The results show that theγ-Re_θtransition model should be corrected through comprehensively considering freestream turbulence intensity decay correction,rotation and curvature correction,crossflow transition correction and compressibility correction when used to supersonic rotating sharp cone flow. |
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