Investigation On Film Cooling Of Braided Composites Considering Film Hole And Braided Structure Interference

In this paper,a numerical simulation of heat transfer characteristics of 2.5 Dimensional(2.5 D)braided composites with full-size scale is first carried out.According to the geometric parameters of braided structure of 2.5 D braided composites,a full-size scale geometric model reflecting the real braiding structure of the composite material is established.In the calculation,the anisotropic thermal conductivity of each component is introduced from the yarn scale.Composite sample heating experiments are carried out to verify the reliability of this calculation method.On this basis,the influence of the anisotropic thermal conductivity at different scales and the geometric structure of the composite are studied,and the heat transfer characteristics of the 2.5 D braided composite are fully understood.The results show that the numerical calculation method that establishes full-size scale geometry model and introduces the anisotropic thermal conductivity of the composite materials from the yarn scale is relaible.The characteristics of temperature distribution of 2.5 D braided composites correspond to the characteristics of braided structure.Braiding structure has little effect on the overall heat transfer direction,but significantly affects the internal heat transfer path.Film hole will inevitably interfere with the braided structure when the 2.5D braided composites are applied in film cooling.On the basis of fully understood the relationship between braided structure and temperature distribution,the 2.5 D braided composite flat panel film cooling experiments which take the interfere between the braided structure and film holes into consideration are carried out to accumulate fundamental experimental data.The effects of blowing ratio and temperature ratio on the cooling characteristics of 2.5 D braided composites are also studied.The results show that with the increase of blowing ratio,the cooling effect is getting worse,and the coverage of the area with higher cooling efficiency in the downstream of the film hole becomes smaller and the cooling efficiency of the downstream of the film hole decreases.With the decrease of temperature ratio,the cooling efficiency of the downstream of the film hole is also decreasing.Based on the above research,the numerical calculation of conjugate heat transfer in film cooling of 2.5 D braided composites with film holes and braid interference is emphasized.The reliability of the 2.5 D braided composites flat panel film cooling confugate heat transfer numerical calculation method that establishes full-size scale geometry model and introduces the anisotropic thermal conductivity of the composite materials from the yarn scale is verified.The effects of anisotropic thermal conductivity at different scales,interference between film hole and braided structure,braided geometry of composite material and thickness of composite panel on the cooling effect of gas film are studied.The results show that the anisotropic thermal conductivity calculation method introduced from the yarn scale has smaller error and higher accuracy than the macro scale anisotropic thermal conductivity.The interference between the film hole and the composite braided structure has a significant effect on the overall cooling effect in the range of about 2 D near the film hole.The change of braiding geometry obviously changed the path of heat propagation in the solid domain,but different braid geometry had little effect on the overall effect of film cooling.Relative to changing the braiding structure of the composite material,changing the relative position of the film hole and the braided structure has a more significant effect on the cooling effect near the exit of the film hole.Under the same blowing ratio and temperature ratio conditions,with the increase of the thickness of 2.5 D braided composites,the cooling efficiency will be increased.