Rotation invariant constitutive relation for Reynolds stress structure parameter

A new Reynolds stress constitutive formula is constructed using the first- order statistics of turbulent fluctuations instead of the mean strain rate. It includes zero empirical coefficients. The formula is validated with the direct numerical simulation （DNS） data of turbulent channel flow at Reτ=180. The Reynolds stresses given by the proposed formula agree very well with the DNS results. The good agreement persists even after the multi-angle rotation of the coordinate system, indicating the rotation in- variance of the formula. The autocorrelation of the fluctuating velocity rather than the mean strain rate is close to the essence of the Reynolds stress.

Numerical study of a trapezoidal bypass dual throat nozzle

Bypass Dual Throat Nozzle(BDTN)is a novel type of fluidic thrust vectoring nozzle.To improve the infrared stealth performance of BDTN,a nozzle based on BDTN is proposed and numerically simulated.Each cross-section along the x-axis of the novel nozzle becomes a trapezoid,which is named“BDTN-TRA.”The main numerical simulation results show that BDTN-TRA can produce a thrust vectoring angle when the upper or lower bypass valve is open.The angle difference between the two conditions mentioned above is usually approximately 1°-2°.Even if the two bypasses are closed,BDTN-TRA can produce a small thrust vectoring angle at around 3°-5°.When the sidewall angle increases from 60°to 90°,the thrust coefficient and thrust vectoring angle under each work condition usually decrease.A larger aspect ratio indicates better performance.As the aspect ratio increases over 7.2,the performance of BDTN-TRA is quite close to that of BDTN with rectangular cross-sections at the same aspect ratio.These features will benefit the control and trimming for future aircraft design,especially for the flying wing layout aircraft.Last but not least,BDTN-TRA has a more extraordinary mixing performance compared with BDTN.The distributions of static temperature and axial velocity along the x-axis of BDTN-TRA with sidewall angle of 60°decrease faster than those of BDTN.When the total temperature of the inlet equals 1600 K,the static temperature difference between BDTN-TRA with sidewall angles of 60°and 90°is over 360 K at twice the length of the nozzle downstream of the nozzle exit,which is the reflection for excellent infrared stealth for the fighter.

5-Formylcytosine and 5-Carboxylcytosine Significantly Reduce the Catalytic Activity of Hhal DNA Methyltransferase

DNA methylation is an essential epigenetic modification, and found to be dynamically changed due to the ob- servation of active DNA demethylation. During active demethylation, 5-methylcytosine （5mC） was oxidized step- wise by ten-eleven translocation （TET） enzymes into 5-hydroxymethylcytosine （5hmc）, 5-formylcytosine （5fC）, and 5-carboxylcytosine （5caC）. Then, the subsequent excision of 5fC and 5caC combined with base excision repair further restored cytosine, which completes the demethylation process. Here, we report that 5-formylcytosine and 5-carboxylcytosine significantly reduce the activity of HhaI DNA methyltransferase to methylate target cytosines when present on the hemi-modified sequence of the complementary DNA. This finding demonstrates that 5fC and 5caC function as more than intermediates for active DNA demethylation.

Extension of the KDO turbulence/transition model to account for roughness

Wall roughness significantly influences both laminar-turbulent transition process and fully developed turbulence.A wall roughness extension for the KDO turbulence/transition model is developed.The roughness effect is introduced via the modification of the k andνt boundary conditions.The wall is considered to be lifted to a higher position.The difference between the original position and the higher position,named as equivalent roughness height,is linked to the actual roughness height.The ratio between the two heights is determined by reasoning.With such a roughness extension,the predictions of the KDO RANS model agree well with the measurements of turbulent boundary layer with a sand grain surface,while the KDO transition model yields accurate cross-flow transition predictions of flow past a 6:1 spheroid.