Shock wave/boundary layer interaction in a 24°turning angle of the compression ramp at Mach number 2.9 controlled by steady microjet is investigated using direct numerical simulation.Three different jet spacings ...Shock wave/boundary layer interaction in a 24°turning angle of the compression ramp at Mach number 2.9 controlled by steady microjet is investigated using direct numerical simulation.Three different jet spacings which are termed as sparse,moderate and dense are considered,and the induced vortex system and shock structures are compared.A moderate jet spacing configuration is found to generate counter-rotating vortex pairs that transport high-momentum fluid towards the vicinity of wall and strengthen the boundary layer to resist separation,reducing the separation region.The dense jet spacing configuration creates a larger momentum deficit region,reducing the friction downstream of the corner.Analysis of pressure and pressure gradient reveals that dense jet spacing configuration reduces the intensity of separation shock.The impact of varying jet spacings on the turbulent kinetic energy transport mechanism is also investigated by decomposing the budget terms in the transport equation.Furthermore,the spectral characteristics of the separation region are studied using power spectral density and dynamic mode decomposition methods,revealing that moderate jet spacing configuration suppresses low-frequency fluctuations in the separation region.展开更多
Non-equilibrium turbulence phenomena have raised great interests in recent years. Significant efforts have been devoted to non-equilibrium turbulence properties in canonical flows, e.g., grid turbulence, turbulent wak...Non-equilibrium turbulence phenomena have raised great interests in recent years. Significant efforts have been devoted to non-equilibrium turbulence properties in canonical flows, e.g., grid turbulence, turbulent wakes, and homogeneous isotropic turbulence(HIT). The non-equilibrium turbulence in non-canonical flows, however, has rarely been studied due to the complexity of the flows. In the present contribution, a directnumerical simulation(DNS) database of a turbulent flow is analyzed over a backwardfacing ramp, the flow near the boundary is demonstrated, and the non-equilibrium turbulent properties of the flow in the wake of the ramp are presented by using the characteristic parameters such as the dissipation coefficient C and the skewness of longitudinal velocity gradient Sk, but with opposite underlying turbulent energy transfer properties. The equation of Lagrangian velocity gradient correlation is examined, and the results show that non-equilibrium turbulence is the result of phase de-coherence phenomena, which is not taken into account in the modeling of non-equilibrium turbulence. These findings are expected to inspire deeper investigation of different non-equilibrium turbulence phenomena in different flow conditions and the improvement of turbulence modeling.展开更多
目的系统评价不同体位对直接喉镜气管插管效果的影响。方法采用计算机检索PubMed、Web of Science、Cochrane、Ovid、中国生物医学文献数据库、中国知网、维普及万方数据库中关于不同体位下直接喉镜气管插管的对照试验文献。经筛选文献...目的系统评价不同体位对直接喉镜气管插管效果的影响。方法采用计算机检索PubMed、Web of Science、Cochrane、Ovid、中国生物医学文献数据库、中国知网、维普及万方数据库中关于不同体位下直接喉镜气管插管的对照试验文献。经筛选文献、资料提取及评价文献质量后,采用SPSS20.0及RevMan5.3统计软件进行meta分析。结果共纳入17篇文献,13篇为随机对照试验(RCT),4篇为临床对照试验。meta分析结果显示:与简单后仰位比较,嗅物位可以提高气管插管患者的声门视野[比值比(OR)=1.35,95%置信区间(95%CI):1.11~1.63,P=0.002],提高首次插管成功率(OR=0.50,95%CI:0.37~0.66,P<0.00001),更易于插管(OR=1.58,95%CI:1.37~1.83,P<0.00001);与嗅物位比较,斜坡位的声门视野差异不明显(OR=0.87,95%CI:0.59~1.30,P=0.50),首次插管成功率无明显差异(OR=1.44,95%CI:0.76~2.75,P=0.26)。结论嗅物位能够提高声门视野,提高插管成功率,建议作为临床气管插管患者的首选体位;斜坡位在声门视野和首次插管成功率上不劣于嗅物位,未来还需要更多高质量RCT进行研究。展开更多
A direct numerical simulation of the shock/turbulent boundary layer interaction flow in a supersonic 24-degree compression ramp is conducted with the free stream Mach number 2.9.The blow-and-suction disturbance in the...A direct numerical simulation of the shock/turbulent boundary layer interaction flow in a supersonic 24-degree compression ramp is conducted with the free stream Mach number 2.9.The blow-and-suction disturbance in the upstream wall boundary is used to trigger the transition.Both the mean wall pressure and the velocity profiles agree with those of the experimental data,which validates the simulation.The turbulent kinetic energy budget in the separation region is analyzed.Results show that the turbulent production term increases fast in the separation region,while the turbulent dissipation term reaches its peak in the near-wall region.The turbulent transport term contributes to the balance of the turbulent conduction and turbulent dissipation.Based on the analysis of instantaneous pressure in the downstream region of the mean shock and that in the separation bubble,the authors suggest that the low frequency oscillation of the shock is not caused by the upstream turbulent disturbance,but rather the instability of separation bubble.展开更多
基金Supported by the National Natural Science Foundation of China(Nos.11972064,92052104)the Key Laboratory of Computational Aerodynamics,AVIC Aerodynamics Research Institute,China(No.YL2022XFX0405)the Fundamental Research Funds for the Central Universities,China.
文摘Shock wave/boundary layer interaction in a 24°turning angle of the compression ramp at Mach number 2.9 controlled by steady microjet is investigated using direct numerical simulation.Three different jet spacings which are termed as sparse,moderate and dense are considered,and the induced vortex system and shock structures are compared.A moderate jet spacing configuration is found to generate counter-rotating vortex pairs that transport high-momentum fluid towards the vicinity of wall and strengthen the boundary layer to resist separation,reducing the separation region.The dense jet spacing configuration creates a larger momentum deficit region,reducing the friction downstream of the corner.Analysis of pressure and pressure gradient reveals that dense jet spacing configuration reduces the intensity of separation shock.The impact of varying jet spacings on the turbulent kinetic energy transport mechanism is also investigated by decomposing the budget terms in the transport equation.Furthermore,the spectral characteristics of the separation region are studied using power spectral density and dynamic mode decomposition methods,revealing that moderate jet spacing configuration suppresses low-frequency fluctuations in the separation region.
基金Project supported by the National Natural Science Foundation of China(Nos.11572025,11772032,and 51420105008)the National Basic Research Program of China(No.2014CB046405)the U.K.Engineering and Physical Sciences Research Council(EPSRC)(Nos.EP/K024574/1 and EP/L000261/1)
文摘Non-equilibrium turbulence phenomena have raised great interests in recent years. Significant efforts have been devoted to non-equilibrium turbulence properties in canonical flows, e.g., grid turbulence, turbulent wakes, and homogeneous isotropic turbulence(HIT). The non-equilibrium turbulence in non-canonical flows, however, has rarely been studied due to the complexity of the flows. In the present contribution, a directnumerical simulation(DNS) database of a turbulent flow is analyzed over a backwardfacing ramp, the flow near the boundary is demonstrated, and the non-equilibrium turbulent properties of the flow in the wake of the ramp are presented by using the characteristic parameters such as the dissipation coefficient C and the skewness of longitudinal velocity gradient Sk, but with opposite underlying turbulent energy transfer properties. The equation of Lagrangian velocity gradient correlation is examined, and the results show that non-equilibrium turbulence is the result of phase de-coherence phenomena, which is not taken into account in the modeling of non-equilibrium turbulence. These findings are expected to inspire deeper investigation of different non-equilibrium turbulence phenomena in different flow conditions and the improvement of turbulence modeling.
文摘目的系统评价不同体位对直接喉镜气管插管效果的影响。方法采用计算机检索PubMed、Web of Science、Cochrane、Ovid、中国生物医学文献数据库、中国知网、维普及万方数据库中关于不同体位下直接喉镜气管插管的对照试验文献。经筛选文献、资料提取及评价文献质量后,采用SPSS20.0及RevMan5.3统计软件进行meta分析。结果共纳入17篇文献,13篇为随机对照试验(RCT),4篇为临床对照试验。meta分析结果显示:与简单后仰位比较,嗅物位可以提高气管插管患者的声门视野[比值比(OR)=1.35,95%置信区间(95%CI):1.11~1.63,P=0.002],提高首次插管成功率(OR=0.50,95%CI:0.37~0.66,P<0.00001),更易于插管(OR=1.58,95%CI:1.37~1.83,P<0.00001);与嗅物位比较,斜坡位的声门视野差异不明显(OR=0.87,95%CI:0.59~1.30,P=0.50),首次插管成功率无明显差异(OR=1.44,95%CI:0.76~2.75,P=0.26)。结论嗅物位能够提高声门视野,提高插管成功率,建议作为临床气管插管患者的首选体位;斜坡位在声门视野和首次插管成功率上不劣于嗅物位,未来还需要更多高质量RCT进行研究。
基金supported by the National Natural Science Foundation of China (Grant Nos 110632050 and 10872205)the National Basic Research Program of China (Grant No 2009CB724100)Projects of CAS INFO-115-B01
文摘A direct numerical simulation of the shock/turbulent boundary layer interaction flow in a supersonic 24-degree compression ramp is conducted with the free stream Mach number 2.9.The blow-and-suction disturbance in the upstream wall boundary is used to trigger the transition.Both the mean wall pressure and the velocity profiles agree with those of the experimental data,which validates the simulation.The turbulent kinetic energy budget in the separation region is analyzed.Results show that the turbulent production term increases fast in the separation region,while the turbulent dissipation term reaches its peak in the near-wall region.The turbulent transport term contributes to the balance of the turbulent conduction and turbulent dissipation.Based on the analysis of instantaneous pressure in the downstream region of the mean shock and that in the separation bubble,the authors suggest that the low frequency oscillation of the shock is not caused by the upstream turbulent disturbance,but rather the instability of separation bubble.
