The Dick effect is an important factor limiting the frequency stability of sequentially-operating atomic frequency standards. Here we study the impact of the Dick effect in the integrating sphere cold atom clock （IS...The Dick effect is an important factor limiting the frequency stability of sequentially-operating atomic frequency standards. Here we study the impact of the Dick effect in the integrating sphere cold atom clock （ISCAC）. To reduce the impact of the Dick effect, a 5 MHz local oscillator with ultra-low phase noise is selected and a new microwave synthesizer is built in-house. Consequently, the phase noise of microwave signal is optimized. The contribution of the Dick effect is reduced to 2.5× 10^-13τ-1/2 （3- is the integrating time）. The frequency stability of 4.6 × 10-13τ-1/2 is achieved. The development of this optimization can promote the space applications of the compact ISCA C.展开更多
In modern high-load high-pressure turbine,the secondary flow in the blade channel is very strong and occupies a large spanwise region.Although high-quality experimental data at the stage interfaces have been obtained ...In modern high-load high-pressure turbine,the secondary flow in the blade channel is very strong and occupies a large spanwise region.Although high-quality experimental data at the stage interfaces have been obtained in previous research,the influence of the clocking position on the secondary flow patterns is not fully understood.This paper investigates the clocking effect in a 1.5-stage high-pressure turbine and focuses on the variations of secondary flow patterns and their effect on the turbine performance.The detailed flow fields of various clocking positions were obtained by carrying out unsteady flow simulations using an in-house code.Among the four clocking positions in this work,the highest entropy generation was observed when the wakes from stator 1 hit the leading edges of stator 2,which is opposite to the well-known conclusion for the turbine with high-aspect-ratio blades.Detailed flow analysis showed that the wakes and the near tip secondary vortices from stator 1 showed different traces when entering the stator 2 channel and the secondary vortices clearly have a more important influence in determining the performance.The different behaviors of the secondary vortices explained the performance variations due to the clocking effect.展开更多
基金Supported by the National Natural Science Foundation of China under Grant No 11604353the Youth Innovation Promotion Association of Chinese Academy of Sciences
文摘The Dick effect is an important factor limiting the frequency stability of sequentially-operating atomic frequency standards. Here we study the impact of the Dick effect in the integrating sphere cold atom clock （ISCAC）. To reduce the impact of the Dick effect, a 5 MHz local oscillator with ultra-low phase noise is selected and a new microwave synthesizer is built in-house. Consequently, the phase noise of microwave signal is optimized. The contribution of the Dick effect is reduced to 2.5× 10^-13τ-1/2 （3- is the integrating time）. The frequency stability of 4.6 × 10-13τ-1/2 is achieved. The development of this optimization can promote the space applications of the compact ISCA C.
基金supported by the National Natural Science Foundation of China(Grant No.51876098)。
文摘In modern high-load high-pressure turbine,the secondary flow in the blade channel is very strong and occupies a large spanwise region.Although high-quality experimental data at the stage interfaces have been obtained in previous research,the influence of the clocking position on the secondary flow patterns is not fully understood.This paper investigates the clocking effect in a 1.5-stage high-pressure turbine and focuses on the variations of secondary flow patterns and their effect on the turbine performance.The detailed flow fields of various clocking positions were obtained by carrying out unsteady flow simulations using an in-house code.Among the four clocking positions in this work,the highest entropy generation was observed when the wakes from stator 1 hit the leading edges of stator 2,which is opposite to the well-known conclusion for the turbine with high-aspect-ratio blades.Detailed flow analysis showed that the wakes and the near tip secondary vortices from stator 1 showed different traces when entering the stator 2 channel and the secondary vortices clearly have a more important influence in determining the performance.The different behaviors of the secondary vortices explained the performance variations due to the clocking effect.
